SEARCH

SEARCH BY CITATION

Keywords:

  • macrophage;
  • nitric oxide;
  • nutrition;
  • tuberculosis;
  • vitamin D

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Immunological ‘checkpoints’ of Mtb infection
  5. Innate immune mechanisms during TB infection
  6. Targeting host immunity for prevention and cure of TB
  7. Nutritional supplementation in the treatment of TB
  8. The clinical relevance of vitamin D in TB
  9. The role of NO in resistance against and control of TB
  10. Interventions targeting cell-mediated immunity in TB patients co-infected with HIV and helminths
  11. Therapeutic implications of effector mechanisms against Mtb induced by cytotoxic T lymphocytes
  12. Cytokines as adjuvant immunotherapy in the treatment of active TB
  13. Concluding remarks
  14. Conflict of interest statement
  15. Acknowledgements
  16. References

Achieving global control of tuberculosis (TB) is a great challenge considering the current increase in multidrug resistance and mortality rate. Considerable efforts are therefore being made to develop new effective vaccines, more effective and rapid diagnostic tools as well as new drugs. Shortening the duration of TB treatment with revised regimens and modes of delivery of existing drugs, as well as development of new antimicrobial agents and optimization of the host response with adjuvant immunotherapy could have a profound impact on TB cure rates. Recent data show that chronic worm infection and deficiencies in micronutrients such as vitamin D and arginine are potential areas of intervention to optimize host immunity. Nutritional supplementation to enhance nitric oxide production and vitamin D-mediated effector functions as well as the treatment of worm infection to reduce immunosuppressive effects of regulatory T (Treg) lymphocytes may be more suitable and accessible strategies for highly endemic areas than adjuvant cytokine therapy. In this review, we focus mainly on immune control of human TB, and discuss how current treatment strategies, including immunotherapy and nutritional supplementation, could be optimized to enhance the host response leading to more effective treatment.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Immunological ‘checkpoints’ of Mtb infection
  5. Innate immune mechanisms during TB infection
  6. Targeting host immunity for prevention and cure of TB
  7. Nutritional supplementation in the treatment of TB
  8. The clinical relevance of vitamin D in TB
  9. The role of NO in resistance against and control of TB
  10. Interventions targeting cell-mediated immunity in TB patients co-infected with HIV and helminths
  11. Therapeutic implications of effector mechanisms against Mtb induced by cytotoxic T lymphocytes
  12. Cytokines as adjuvant immunotherapy in the treatment of active TB
  13. Concluding remarks
  14. Conflict of interest statement
  15. Acknowledgements
  16. References

In the Western world, tuberculosis (TB) was long considered a disease of the past, controlled by effective public health systems that compensated for the relative shortcomings of the available intervention strategies. However, due to the lack of effective vaccines, early biomarkers, rapid diagnostic tools and novel therapeutic agents, the incidence rate is still high, with 1.4 million deaths due to TB in 2010, mostly in resource-poor areas [1]. Of particular concern in sub-Saharan Africa is the high proportion of TB patients co-infected with the human immunodeficiency virus (HIV), further increasing morbidity and mortality. In most individuals, infection with the causative agent Mycobacterium tuberculosis (Mtb) remains latent without symptoms or transmission to others, but in approximately 5%–10% the infection progresses to active disease, killing many of those who are not diagnosed and effectively treated [2]. TB has become the focus of attention in many parts of the world because of an alarming proportion of cases caused by drug-resistant bacteria. Nearly 50% of culture-positive patients in areas such as Belarus carry multidrug-resistant (MDR) TB, which is defined as resistance to the two most important antimycobacterial drugs isoniazid (INH) and rifampicin [3]. Shortening the duration of TB treatment to increase compliance, development of new antimicrobial agents and treatment strategies to optimize the host response could all have a profound impact on the TB cure rate and the control of the infection, in particular as drug resistance is rapidly increasing. Considerable effort is now being made to develop new vaccines, but how bacteria surviving inside phagocytic cells can delay initiation of an effective immune response and how they can be detected and eliminated more efficiently remain to be determined.

Mycobacterium tuberculosis is the most successful human pathogen known, as indicated by its ability to infect up to one-third of the global population. The spread of the disease has not been limited despite the use of the Bacillus Calmette-Guérin (BCG) vaccine for more than 90 years. Mtb has achieved such success through evolving multiple mechanisms to avoid destruction and adapt to the host. Recent advances in understanding of the delicate balance between the host and Mtb have been reviewed extensively [4-7]. Despite increased knowledge of host defence mechanisms against Mtb, the optimal innate or cell-mediated immune (CMI) response to achieve immunity is unknown [5, 8]. It is evident that human TB is not as homogenous from the host response perspective as it is under strict experimental conditions using laboratory strains of Mtb [9-12]. Animal models are essential for understanding host immunity, especially in the early stages of innate response [13]. However, it is relatively difficult to translate preclinical laboratory findings into novel treatment and diagnostic strategies.

From the clinical perspective, the importance of the CMI response is confirmed by several important observations. First, in HIV-infected patients, there is 10% yearly risk of developing TB compared with a 5% lifetime risk in immunocompetent individuals [14]. Secondly, during treatment with tumour necrosis factor (TNF)-α inhibitors or other immunosuppressive drugs such as corticosteroids, there is an increased risk of developing active TB amongst latently infected individuals [14-17]. Moreover, individuals with decreased expression of T helper (Th)1-related cytokines, due to mutations in the genes of the interleukin (IL)-12/IL-23/interferon (IFN)-γ pathway are susceptible to mycobacterial infections [18-20]. Thus, the CMI response against TB plays a fundamental protective role against the development and outcome of active disease.

The most important areas to consider to achieve global TB control are: (i) improvement of vaccine efficacy; (ii) development of more effective and rapid diagnostic tools; (iii) establishment of shorter treatment regimens; and (iv) development of strategies for identifying patient groups at risk of developing active disease. Shortening the duration of TB treatment through revised regimens and/or modes of delivery of existing drugs, development of new antimicrobial agents and optimizing the host response via adjuvant immunotherapy could greatly improve TB cure rates. Of note, adjuvant cytokine immunotherapy is unlikely to be accessible for the majority of patients in highly endemic resource-poor areas. The priorities in such areas should be eliminating poverty, optimizing immunity by nutritional supplementation and treating HIV. In this review, we will mainly focus on the immune control of human TB, and discuss how the current treatment strategies could be optimized through the understanding of innate and adaptive immunity during TB infection.

Immunological ‘checkpoints’ of Mtb infection

  1. Top of page
  2. Abstract
  3. Introduction
  4. Immunological ‘checkpoints’ of Mtb infection
  5. Innate immune mechanisms during TB infection
  6. Targeting host immunity for prevention and cure of TB
  7. Nutritional supplementation in the treatment of TB
  8. The clinical relevance of vitamin D in TB
  9. The role of NO in resistance against and control of TB
  10. Interventions targeting cell-mediated immunity in TB patients co-infected with HIV and helminths
  11. Therapeutic implications of effector mechanisms against Mtb induced by cytotoxic T lymphocytes
  12. Cytokines as adjuvant immunotherapy in the treatment of active TB
  13. Concluding remarks
  14. Conflict of interest statement
  15. Acknowledgements
  16. References

The heterogeneity of human susceptibility to TB can be demonstrated by the Lübeck disaster in 1929 [21, 22] when 251 infants were accidentally challenged with an oral dose of virulent Mtb instead of the attenuated strain used in the BCG vaccine; 72 children died within 1 year, 135 developed TB but recovered and 44 became tuberculin-positive but remained well. The heterogeneity of human susceptibility to TB is also evident from studies of close (living in close household contacts) contacts of TB cases. Even after prolonged exposure, only 5%–10% of close contacts of patients with smear-positive TB develop active disease [23]. It has been estimated that up to 50% develop latent TB as indicated by a positive tuberculin skin test [23]. However, a fraction of exposed individuals do not show any signs of induction of systemic immunity to TB, indicating sufficient protection by innate immune mechanisms [13]. This fact has long been disregarded, but knowledge of innate immune functions emerging during the last decade may explain how the host can clear or control TB infection without involvement of the adaptive immune response.

Much of the present understanding of host immunity is based on studies using inbred mouse strains. It is clear that there will be little variation in the observed immune response of the infected animals in such studies, with an initial increase in bacterial load in the tissues until the onset of adaptive immunity [24]. However, recent studies in outbred monkeys [25] and rabbits [26] have shown that the heterogeneity of human TB may be better demonstrated using these models. In a study in macaques, it was shown that within the same TB-infected animal, a spectrum of different lesions is present, although with less advanced lesions in tissues from animals with latent TB [27].

On the basis of recent observations, we hypothesize that Mtb has to pass immunity ‘checkpoints’ to establish infection (Fig. 1) [27]. The time it takes for the bacterium to pass the checkpoints, if it does, varies greatly between individuals ranging from a few weeks in patients with an impaired immune response, such as those infected with HIV, to decades in initially resistant hosts.

image

Figure 1. The ‘checkpoint’ model of host immunity against TB. (1) Eradication of the initial infection by an efficient innate immunity. (2) Innate immunity may not be sufficient to control further dissemination of Mtb to distant foci. (3) Adaptive immunity could control the infection which is maintained in a latent phase. (4) Adaptive immunity may clear the infection in some individuals. (5) Inadequate control of replication, and therefore Mtb may be detected in cultures in the absence of clinical symptoms. (6) Uncontrolled Mtb replication leads to symptomatic TB. (7) TB mortality is high without treatment, in particular amongst patients co-infected with HIV. (8) The bacillary load rapidly decreases during antimycobacterial treatment. (9) In a minority of treated patients, viable bacilli persist and cause relapse. To prevent progression to active TB, there are potential critical time-points for intervention (I1–I4). (I1). Innate immune mechanisms could be enhanced by nutritional supplementation (vitamin D or arginine). (I2) Eradication or control of the infection could be achieved by inhibiting factors that inhibit the Th1 pathway, for example by treating HIV and chronic helminth infections. Strengthening Th1 responses could be achieved by adjuvant cytokine therapy or nutritional intervention. (I3) In the presence of active disease, antimycobacterial chemotherapy is superior to interventions targeting immunity. Antibiotic therapy could be optimized by measuring drug levels and minimal inhibitory concentrations of Mtb according to the concepts of therapeutic drug monitoring. In patients with extensive inflammation and tissue damage, anti-inflammatory drugs could be of benefit. (I4) Bacterial load rapidly decreases during the first weeks of antimycobacterial treatment. At this stage adjuvant cytokine therapy and nutritional interventions could optimize a Th1-directed response and immune control could be regained.

Download figure to PowerPoint

To pass the first checkpoint, Mtb must avoid being killed by the infected phagocytes, including neutrophils, macrophages and dendritic cells (DCs), of which macrophages are the primary target cells. It is likely that the interaction between these cells plays a key function in the early clearance of Mtb. However, Mtb has developed strategies to counteract innate immune mechanisms such as phagosomal maturation [28, 29] and intracellular killing. Apoptosis is also inhibited [30] and partly replaced by host detrimental necrosis [31, 32]. Failure of macrophages to eradicate the initial infection allows progression towards the next checkpoint and the spread of infection to distal sites [33]. Such failure may be due to deficient phagolysosomal fusion or autophagy [34], impaired production of antimycobacterial peptides such as LL-37 or α-defensins [35] and other antimycobacterial compounds such as nitric oxide (NO). Of note, Mtb can be present in apparently normal lung tissue, indicating that the bacterium is able to coexist with its host without causing tissue damage and inflammation [36]. The mechanisms by which macrophages are able to maintain a persister state of Mtb need further investigation, albeit acidification of phagosomes and phagolysosomal protease activity have been determined to play a role [29]; NO, which is produced by human macrophages at sites of Mtb infection, is also thought to be important [37]. There is evidence that Mtb, if exposed to suboptimal doses of NO, can respond to this stressor by switching to an NO-tolerant phenotype [38].

The second checkpoint is passed when innate immunity fails to control the infection, allowing Mtb to start replicating to an extent that adaptive immunity is utilized. Enhanced inflammation caused by necrosis of infected host cells harbouring replicating bacteria is probably needed for the induction of antigen presentation to induce both cytotoxic T cell activity and an effective Th1 response to enhance macrophage activity via production of IFN-γ [39]. Depending on host immunity and bacterial factors, the infection may progress to active disease. However, latent TB is observed in individuals who can control the infection by an effective adaptive immune response. It is also possible at this stage that the infection may be completely cleared. This is clinically important, as traditional tests for latent TB such as interferon IFN-γ assays measure the CMI response to Mtb, but do not determine whether the bacteria are still viable [2].

Progression to active disease occurs, due to insufficient immune control, when the third and final checkpoint is reached. Excessive inflammation contributes to the pathology; there is evidence that Mtb takes advantage of immune activation leading to necrosis [31], which is a prerequisite for the bacterium to spread to other individuals. Draining of the bacilli-containing necrotic cores of caseating granulomas or cavities into the bronchial tree is the major route by which Mtb is transmitted. A recent study of antigen variability in Mtb showed that in contrast to many other pathogenic microorganisms, which rely on antigen variability to evade specific immunity, Mtb has highly conserved antigen epitopes. This finding implies that at a certain stage of infection, Mtb manipulates the host immune response to take advantage of T cell-mediated immunity [40]. Necrosis that is thus generated through host immunity is the platform from which Mtb can spread in the human population.

Details of the immune mechanisms that can be targeted to optimize host immune responses, according to the checkpoint model, will be discussed below. Through interventions targeting the immune system, Mtb could thus be prevented from passing checkpoint 3, allowing more efficient clearance of infection.

Innate immune mechanisms during TB infection

  1. Top of page
  2. Abstract
  3. Introduction
  4. Immunological ‘checkpoints’ of Mtb infection
  5. Innate immune mechanisms during TB infection
  6. Targeting host immunity for prevention and cure of TB
  7. Nutritional supplementation in the treatment of TB
  8. The clinical relevance of vitamin D in TB
  9. The role of NO in resistance against and control of TB
  10. Interventions targeting cell-mediated immunity in TB patients co-infected with HIV and helminths
  11. Therapeutic implications of effector mechanisms against Mtb induced by cytotoxic T lymphocytes
  12. Cytokines as adjuvant immunotherapy in the treatment of active TB
  13. Concluding remarks
  14. Conflict of interest statement
  15. Acknowledgements
  16. References

The fact that many individuals heavily exposed to Mtb do not develop infection despite not being immunized [23] suggests that several inherent and innate immune mechanisms are active before checkpoint 2. Alveolar macrophages represent the primary niche for replication of the bacillus, and macrophage functions such as phagosomal acidification [29] and autophagy [41] are important mechanisms by which these cells can control Mtb. The innate immune response to Mtb is triggered by several pattern recognition receptors, primarily Toll-like receptors (TLRs) 2 and 9 [7]. Also, cytosolic innate receptor complexes, such as NOD2 and NALP3, recognize Mtb molecules and may affect phagosomal maturation and autophagy [7, 34]. A proinflammatory cytokine and chemokine response is mounted [7], recruiting neutrophils, DCs and macrophages to the site of infection. Recruited neutrophils may have several important functions during the early phases of infection. Initially, they may be beneficial to the host through phagocytosing and killing virulent Mtb via Nadph Oxidase 2 (Nox2)-generated reactive oxygen species (ROS) and other antimicrobial molecules (defensins, LL-37) [35], but also offer a niche that favours bacterial survival and growth. During this process neutrophils become apoptotic. Because apoptotic cells are cleared from the tissue by macrophages, Mtb-containing apoptotic neutrophils can be transferred to the macrophages and mount a proinflammatory response [42, 43]. This can also occur in DCs, where apoptotic neutrophils can facilitate DC maturation and augment subsequent Th cell activation [44]. A well-recognized virulence-associated attribute of Mtb is its ability to impair apoptosis in macrophages [45, 46], as well as in neutrophils, thereby delaying the adaptive immune response [47] and forming an intracellular environment to survive and proliferate.

Although the early innate immune reaction can be seen as an infectious stage dominated by bacterial proliferation and spreading, it can also lead to a proper adaptive immune response in individuals in whom innate immunity is not limiting the infection (e.g. after checkpoint 1 in the model shown in Fig. 1). It has recently been suggested that neutrophils can form a link between innate and adaptive immune activation during the early phase of TB infection, by enhancing both a proinflammatory macrophage response and DC maturation [42].

Targeting host immunity for prevention and cure of TB

  1. Top of page
  2. Abstract
  3. Introduction
  4. Immunological ‘checkpoints’ of Mtb infection
  5. Innate immune mechanisms during TB infection
  6. Targeting host immunity for prevention and cure of TB
  7. Nutritional supplementation in the treatment of TB
  8. The clinical relevance of vitamin D in TB
  9. The role of NO in resistance against and control of TB
  10. Interventions targeting cell-mediated immunity in TB patients co-infected with HIV and helminths
  11. Therapeutic implications of effector mechanisms against Mtb induced by cytotoxic T lymphocytes
  12. Cytokines as adjuvant immunotherapy in the treatment of active TB
  13. Concluding remarks
  14. Conflict of interest statement
  15. Acknowledgements
  16. References

The rationale for treatment strategies that aim to strengthening the host immune response during TB is to reduce the risk of disease progression upon exposure and to optimize the treatment of active TB by stimulating the host immune response (Fig. 1). The timing for such interventions is important and should be considered carefully in relation to the immunological life cycle of Mtb. In terms of our model, this means the infection will be stopped at checkpoint 1 and extensive tissue damage prevented (Fig. 1). Interventions based on enhancing host immunity may cover both prevention and active disease such as HIV and chronic worm infection as well as optimizing nutritional status in the case of vitamin D and arginine supplementation. Such strategies can be cost-effective in reducing the risk of developing TB and preventing development of severe active disease in malnourished and HIV-infected individuals.

Nutritional supplementation in the treatment of TB

  1. Top of page
  2. Abstract
  3. Introduction
  4. Immunological ‘checkpoints’ of Mtb infection
  5. Innate immune mechanisms during TB infection
  6. Targeting host immunity for prevention and cure of TB
  7. Nutritional supplementation in the treatment of TB
  8. The clinical relevance of vitamin D in TB
  9. The role of NO in resistance against and control of TB
  10. Interventions targeting cell-mediated immunity in TB patients co-infected with HIV and helminths
  11. Therapeutic implications of effector mechanisms against Mtb induced by cytotoxic T lymphocytes
  12. Cytokines as adjuvant immunotherapy in the treatment of active TB
  13. Concluding remarks
  14. Conflict of interest statement
  15. Acknowledgements
  16. References

Before the availability of chemotherapy, nutritional supplementation was an important part of care in a Sanatorium, although the relative contribution of food supplementation to the cure of TB during this time is controversial [48, 49]. As care, diet and sanitation improved during late 19th and early 20th century in countries that today have a relatively low incidence of TB, the disease burden declined even before the introduction of the BCG vaccination and the development of antibiotics, underlining the importance of social factors and nutrition in reducing the spread of TB [50]. In a large epidemiological study, being underweight (body mass index <18.5 kg m−2) and having a low serum albumin level (<3.5 g dL−1) were found to be strong risk factors for TB whereas low vitamin A levels and iron status were not [51]. Decreased levels of vitamins and trace elements during active TB have been demonstrated in a number of clinical studies, but it is difficult to determine whether these deficiencies or malnutrition in general were the cause or result of TB [52]. In a clinical trial conducted in Tanzania including 887 adult patients with pulmonary TB, multiple micronutrient supplementation (vitamins A, B-complex, C and E and selenium) reduced the risk of TB recurrence together with an increase in CD4 counts, but without any effects on mortality [53]. The divergent results from nutritional intervention studies, for example investigating the effect of vitamin A [54-56], may be due to the composition and doses as well as inclusion criteria [52, 57].

What are the immunological mechanisms that underlie the effect on Mtb of nutritional interventions? The mechanisms of action of arginine, NO and antimicrobial peptides produced as a response to vitamin D are better understood than those of other micronutrients [58, 59]. The host response to TB involves production of molecules through protein synthesis and secretion, and the mediators produced also increase catabolism [60]. Although the precise mechanisms of the dietary effect and which dietary factors are most important are unknown, impaired macrophage activation and reduced T cell-dependent production of protective cytokines are linked to malnutrition in general and protein calorie deficiency in particular [61].

Some recent interventional studies of patients with active TB investigating multivitamin/mineral supplementation as well as specific treatment with vitamin D and trace elements have shown promising results [62, 63]. Even though the contribution of dietary supplementation must be seen in the perspective of the effective TB drugs available [57, 64], supplementation of nutrients may shorten the duration of treatment, as well as increase extent of recovery in TB patients [53, 65]. Nutritional supplementation may also be important in highly endemic areas to prevent the development of active disease upon exposure (Fig. 1, I1); in such areas, the majority of patients are malnourished even before the onset of TB and thus immune defence is impaired.

The clinical relevance of vitamin D in TB

  1. Top of page
  2. Abstract
  3. Introduction
  4. Immunological ‘checkpoints’ of Mtb infection
  5. Innate immune mechanisms during TB infection
  6. Targeting host immunity for prevention and cure of TB
  7. Nutritional supplementation in the treatment of TB
  8. The clinical relevance of vitamin D in TB
  9. The role of NO in resistance against and control of TB
  10. Interventions targeting cell-mediated immunity in TB patients co-infected with HIV and helminths
  11. Therapeutic implications of effector mechanisms against Mtb induced by cytotoxic T lymphocytes
  12. Cytokines as adjuvant immunotherapy in the treatment of active TB
  13. Concluding remarks
  14. Conflict of interest statement
  15. Acknowledgements
  16. References

Interest in the possibility of vitamin D supplementation for patients with TB has increased since the finding in 2006 that TLR activation upregulates the expression of the vitamin D receptor (VDR) and the vitamin D hydroxylase genes in human macrophages, leading to induction of the antimicrobial peptide LL-37 and enhanced killing of intracellular Mtb [66]. The active metabolite of vitamin D, vitamin D3 (also known as calcitriol), induces potent antibacterial effects including production of NO and antimicrobial peptides such as LL-37 as well as stimulation of autophagy [34]. The effect of vitamin D3 may also be modulated by VDR polymorphisms involving the tt genotype of the TaqI allele [62].

Several randomized trials have been conducted to investigate the effect of vitamin D3 in patients with active TB [62, 67]. In one trial performed in the UK, patients with smear-positive TB (= 146) were assigned randomly to high-dose (2.5 mg) vitamin D3 or placebo every other week for 6 weeks. There was no effect on the primary outcome of time to culture conversion, but a significant effect was observed in the subgroup analysis of vitamin D3-supplemented patients with the tt genotype (5/12 patients) of TaqI in the VDR [62]. In a recently published follow-up analysis, it was shown that vitamin D3 supplementation accelerated the resolution of inflammatory responses unrelated to the TaqI genotype [58]. In a larger West-African trial, a lower vitamin D3 dose in patients with active TB had no effect on the reduction of a clinical severity score or mortality, which were the primary and secondary outcomes respectively [67]. In addition, there was a trend towards an effect on the primary outcome in HIV-negative individuals and those with initially low vitamin D levels, as well as higher mortality in HIV-infected individuals. Vitamin D may be beneficial in some patients with active TB and vitamin D deficiency (VDD), in particular in those with certain VDR polymorphisms as well as in cases of MDR/Multidrug-resistant TB where it may contribute to the relatively weak efficacy of second-line drugs. Larger multicentre trials are urgently needed to verify these possibilities.

Association studies of VDD in TB patients and healthy control subjects have shown inconsistent results. A study from Guinea-Bissau showed a higher prevalence of VDD [25(OH)D(3) ≤ 25 nmol L−1] in healthy individuals relative to TB patients, but the mean serum level of vitamin D was lower in the TB group [68]. In a recent trial conducted in South Africa, the number of TB cases was found to increase after the winter season, when the lowest mean serum levels of vitamin D are observed in the population. In this study, more than 60% of patients (n = 370) with active or latent TB had inadequate vitamin D levels, and VDD was strongly associated with HIV co-infection [69]. Amongst healthy individuals with latent TB, 37%–52% exhibited VDD compared with 75%–86% in the active TB group depending on whether they were HIV positive or not [69]. The findings of a study from Greenland demonstrated that both high and low serum vitamin D levels were associated with TB [70]. Vitamin D levels increased during the first 2 months of treatment of active TB in a trial conducted in Tanzania, indicating that vitamin D levels may normalize spontaneously during treatment, at least in this setting [71]. Although low serum levels of vitamin D may be a contributing risk factor for developing active TB at the population level, there are clearly large groups of healthy individuals with low levels of vitamin D who will not develop disease. Thus, in terms of prevention and causality, the relative importance of VDD for the risk of developing TB remains to be established.

The role of NO in resistance against and control of TB

  1. Top of page
  2. Abstract
  3. Introduction
  4. Immunological ‘checkpoints’ of Mtb infection
  5. Innate immune mechanisms during TB infection
  6. Targeting host immunity for prevention and cure of TB
  7. Nutritional supplementation in the treatment of TB
  8. The clinical relevance of vitamin D in TB
  9. The role of NO in resistance against and control of TB
  10. Interventions targeting cell-mediated immunity in TB patients co-infected with HIV and helminths
  11. Therapeutic implications of effector mechanisms against Mtb induced by cytotoxic T lymphocytes
  12. Cytokines as adjuvant immunotherapy in the treatment of active TB
  13. Concluding remarks
  14. Conflict of interest statement
  15. Acknowledgements
  16. References

In macrophages activated by Th1-mediated cytokines such as IFN-γ and TNF-α, NO is produced in large amounts from the amino acid arginine via the enzyme inducible NO synthase (iNOS) (Fig. 2) [72, 73]. On the other hand, transforming growth factor (TGF)-ß, IL-4 and IL-10 suppress the induction of iNOS [72, 74] and increase arginase activity in alternatively activated macrophages. Mtb may increase arginase activity, which would lead to competition with iNOS for its substrate arginine [75-77]. It was recently shown that, in addition to iNOS, arginase is present in biopsy material from human TB patients [78]. Other Mtb defence strategies include inhibiting iNOS recruitment to the phagosomal membrane thereby avoiding NO exposure [79]. In a mouse model, NO has been well established as a key molecule in host resistance against active and latent TB [80]. Production of NO has been confirmed in human TB, but its relative importance is debated. The presence of iNOS and nitrotyrosine in macrophages has been shown at the site of TB infection in humans [37, 81-84]. Measurements of NO in exhaled air and NO metabolites in urine from TB patients indicate that human macrophages are also partly dependent on NO production for control of Mtb [82, 83]. Furthermore, it has been shown that polymorphisms in the promoter for iNOS may have a role in the regulation of NO production as well as in the host defence against the disease [18]. The bicyclic nitroimidazole PA-824, the active metabolites of which generate reactive nitrogen intermediates (RNIs), was shown to largely mediate the anaerobic microbicidal effect against Mtb [85-88]. The results of recent clinical trials of this drug have been promising [87, 89].

image

Figure 2. Macrophage polarization. Stimulation of macrophages with IFN-γ, TNF-α or IL-1β will result in the M1 phenotype, with upregulation of iNOS, NO production and antimicrobial activity. Stimulation with IL-4, IL-10 or TGF-β will generate the M2 phenotype, with increased arginase activity promoting tissue repair, but not bacterial killing [72, 73].

Download figure to PowerPoint

Pathogenic mycobacteria have several antioxidant systems [90-92] and are inherently more resistant than nonpathogenic mycobacteria to RNIs. Clinical strains exhibit a variable susceptibility to NO although acidified nitrite was mostly used in early studies and modern NO-donating substances or macrophage-based assays may be more suitable for assessing this effect [90, 93, 94]. Moreover, recently published results indicate that part of the mechanism of action of INH may involve NO production from the bacteria [95]. We have recently shown that clinical isolates have a variable resistance to NO, and that reduced NO susceptibility is correlated with INH resistance [96]. Targeting bacterial factors that inhibit an effective antioxidative antimycobacterial response might lead to novel treatment of TB. Catalase peroxidase katG, the alkyl hydroperoxide reductase subunit C, superoxide dismutase, haem proteins, bacterial proteases, thioredoxin and lipoamide dehydrogenase can all scavenge ROS and RNS and reduce redox stress due to the host immune response [97-105].

It has been postulated that during the early phase of human TB exposure, an efficient innate response and high levels of NO from alveolar macrophages may kill Mtb even before infection occurs. In addition, other effector molecules such as granulysin from natural killer (NK) cells, LL-37 from macrophages and ROS from recruited neutrophils may contribute to this effect. In the host, if innate immunity and NO levels are inadequate to eradicate the bacteria (Fig. 1, checkpoint 1), a latent infection is established where cell-mediated immunity in most cases keeps the infection under control indefinitely. However, in latently infected individuals with malnutrition and l-arginine deficiency, as well as reduced levels of NO and subsequent loss of control of the infection, active disease may develop. In case of insufficient levels of NO production due to a poor CMI response or NO resistance, or because of the virulence of the bacterial strain, bacterial replication will continue and cause active disease. Some potential strategies for NO-based therapies are shown in Fig. 3.

image

Figure 3. Future NO-based therapeutic options. Four main areas can be identified as targets for new NO-based intervention: (i) immunization to prepare the host for an early and strong NO response to Mtb exposure; (ii) therapeutic strategies to increase NO production postexposure, either by l-arginine supplementation or iNOS upregulation by proinflammatory cytokines; (iii) bacterial defence mechanisms against NO and other antibacterial agents; (iv) immune modulatory therapies that release intracellular bacteria by inhibition of cell-mediated immunity or NO production – this could be combined with new drugs to shorten treatment and achieve sterilization.

Download figure to PowerPoint

To evaluate the role of NO, we initiated a double-blind randomized trial of arginine supplementation combined with chemotherapy in 120 smear-positive TB patients in Gondar, Ethiopia and observed an increased sputum smear conversion and reduced clinical symptoms in HIV-negative patients [106]. In a subsequent clinical trial in the same area, we noticed that addition of a food supplement rich in arginine (peanuts) had a clinical effect in HIV-positive TB patients, and that nutritional supplementation per se was beneficial for the clinical outcome [107]. Studies by Yeo et al. in patients with malaria indicate that the arginine dose can be increased considerably [108]. l-arginine is a semi-essential amino acid which is taken up from arginine-rich food such as nuts and is obtained from endogenous sources such as citrulline [59]. In TB patients, arginase activity may warrant high doses of l-arginine to overcome deficiency due to prediagnosis malnutrition and TB-related anorexia.

Interventions targeting cell-mediated immunity in TB patients co-infected with HIV and helminths

  1. Top of page
  2. Abstract
  3. Introduction
  4. Immunological ‘checkpoints’ of Mtb infection
  5. Innate immune mechanisms during TB infection
  6. Targeting host immunity for prevention and cure of TB
  7. Nutritional supplementation in the treatment of TB
  8. The clinical relevance of vitamin D in TB
  9. The role of NO in resistance against and control of TB
  10. Interventions targeting cell-mediated immunity in TB patients co-infected with HIV and helminths
  11. Therapeutic implications of effector mechanisms against Mtb induced by cytotoxic T lymphocytes
  12. Cytokines as adjuvant immunotherapy in the treatment of active TB
  13. Concluding remarks
  14. Conflict of interest statement
  15. Acknowledgements
  16. References

An obvious way to reduce the risk of developing active TB is early detection and treatment of HIV, the greatest risk factor for TB in highly endemic areas [14]. It is important to note that TB is often unidentified in HIV-positive individuals due to atypical presentation [9, 109-111]. TB increases the replication of HIV, particularly locally in the lung, by activating CD4+ T cells and enhancing production of proinflammatory cytokines such as TNF-α. HIV in turn increases the susceptibility to TB by selectively depleting protective CD4+ T cells [112, 113]. The early initiation of antiretroviral therapy in TB/HIV co-infected patients with low CD4 counts is important as it has been shown to significantly reduce mortality [114, 115]. Clearly, early treatment of HIV is vital both to prevent development of active TB from latent infection, and reduce mortality in patients with established TB/HIV co-infection (Fig. 1).

In countries in which TB is common, helminth infections, which are often asymptomatic, are also highly prevalent. Similar to TB, it has been estimated that intestinal parasites infect up to one-third of the global population [116]. It has been proposed that chronic worm infection might make the host more vulnerable to TB [117, 118]; however, there is a relative lack of clinical data to support this notion [119-121]. We have recently published a small observational study, demonstrating that asymptomatic worm infection affects host immunity in TB patients, and that approximately 30% of these patients have concurrent worm infection [122]. Furthermore, in a case–control study at the same site, the prevalence of worms in patients with active TB was twice as high as in their healthy close (household) contacts. [118].

The issue of co-infection may be complicated by the fact that Mtb/helminth co-infected patients are often also HIV positive [123] The results of a recent meta-analysis indicated that deworming may slow progression of HIV [124]; in the few clinical trials conducted there was a trend towards reduced viral HIV loads and increased CD4 counts as the short-term outcome [125-127]. In one of these studies in Kenya, 299 of 1551 (19%) screened HIV-positive patients were also helminth (A. lumbricoides) co-infected. In the group of worm-infected patients treated with the anthelmintic albendazole, a significant effect on CD4 counts was observed after 3 month as well as a reduction in IL-10 production [126, 128]. A possible explanation of the beneficial effect of deworming may be that chronic helminth infection increases intestinal permeability which in turn increases bacterial translocation and subsequently increases immune activation and HIV replication [129].

The persistence and outcome of active TB in the host following helminth infection is considered to be linked to immunoregulatory mechanisms such as expansion of Treg cells producing IL-10 and TGF-ß, attenuation of Mtb-specific Th1 responses [117, 118, 121] and increased Th2 response with production of IL-4 which in turn could mediate alternative macrophage activation (Fig. 2) [130]. A decreased Th1 response to TB and leprosy associated with worm infection has been shown in clinical studies [131, 132]. Furthermore, filarial infection was found to cause attenuated Th1 and Th17 responses in Mtb/helminth co-infected patients, which could be reversed by antifilarial treatment [133, 134]. With regard to the preventive effect of deworming, Elias et al. [135] showed in an Ethiopian study that albendazole treatment of PPD-negative and worm-positive, healthy individuals prior to BCG vaccination resulted in increased levels of the Th1-type cytokines IL-12 and IFN-γ, and reduced levels of the immunoregulatory cytokine TGF-ß. In conclusion, experimental and clinical data suggest that deworming can have a role both in the prevention and treatment of active TB, probably by redirecting the adaptive immune response to a CMI response and efficiently clearing Mtb from the tissues.

Therapeutic implications of effector mechanisms against Mtb induced by cytotoxic T lymphocytes

  1. Top of page
  2. Abstract
  3. Introduction
  4. Immunological ‘checkpoints’ of Mtb infection
  5. Innate immune mechanisms during TB infection
  6. Targeting host immunity for prevention and cure of TB
  7. Nutritional supplementation in the treatment of TB
  8. The clinical relevance of vitamin D in TB
  9. The role of NO in resistance against and control of TB
  10. Interventions targeting cell-mediated immunity in TB patients co-infected with HIV and helminths
  11. Therapeutic implications of effector mechanisms against Mtb induced by cytotoxic T lymphocytes
  12. Cytokines as adjuvant immunotherapy in the treatment of active TB
  13. Concluding remarks
  14. Conflict of interest statement
  15. Acknowledgements
  16. References

Experimental studies have established that cytotoxic T lymphocytes (CTLs) – primarily CD8+ T cells – are required for optimum host immunity against TB [136, 137]. However, supportive data from TB patients are scarce, and there have been no parallel observations of a link between CD4+ cells and HIV co-infection, confirming the relative importance of CD8+ T cells [137].

Mtb-infected macrophages can be recognized and killed by human CD8+ T cells following activation mediated by recognition of the class I MHC complex, and antigen-specific CD8+ T cells have been observed in patients with active TB [138, 139]. The major mechanisms of action of lymphocyte-mediated cytotoxicity include the release of cytotoxic granules containing perforin, granzyme proteases and granulysin, and the induction of apoptosis by the Fas ligand (CD95L) on the CTL and Fas on the target cell [137, 140-142]. The CTL-mediated lysis of infected cells results in the release of the pathogen into the extracellular environment, where the bacteria can be taken up by freshly recruited, activated macrophages, that are better able to kill them [136]. Expression of membrane TNF, or secretion of TNF by CTLs, may promote TNF receptor-induced apoptosis of the target cells mediated by the TNF-related apoptosis-inducing ligand (TRAIL) [143], but data in human cells from TB patients are lacking. On the other hand, granulysin, produced from CD8+ CTLs and NK cells, has been shown to directly kill intracellular Mtb together with perforin [141, 142, 144]. Perforin induces a nonselective pore in the plasma membrane of infected cells and granulysin is subsequently delivered to the cytoplasm where it kills Mtb by attacking the bacterial membrane [141]. In addition to the cytolytic capacity, CD8+ T cells can produce the proinflammatory cytokines IFN-γ and TNF-α, highlighting the overlapping effects of CD4+ and CD8+ T cells [137].

Findings from animal models lacking critical mediators of cytolysis, such as perforin, granzyme or CD95L, are inconsistent, which is partly due to the fact that these molecules are not specific for CD8+ T cells, but are also expressed by NK cells, γδ T cells and some CD4+ T cells [145, 146]. From studies of human biopsy material, it is clear that granulysin is produced in active TB, where it is mainly colocalized with perforin in CD8+ T cells surrounding the granuloma [147, 148]. In contrast to cells expressing granulysin, granzyme A-expressing CD3+ T cells were shown to be significantly upregulated in immunopathological studies of lesions from TB patients [149]. Stimulation of T cells from tuberculin-positive individuals in vitro using Mtb to induce production of granzyme A and B, granulysin, perforin and CD95L (Fas ligand) in CD4+ as well as CD8+ T cells, and both cell subsets were able to lyse Mtb-infected monocytes [150].

Although it is possible to isolate Mtb-specific CD8+ CTLs in vitro, and their activity can be detected and localized in vivo, the relative importance of their cytolytic activity in patients with TB is largely unknown [137]. This should warrant further clinical studies before CTL-based effector mechanisms such as granulysin can be translated into new therapeutic strategies. Pathways regulating CTL effector mechanisms may be important to consider in future vaccine development as well as for developing drugs that stimulate cytolytic CTL activity.

Cytokines as adjuvant immunotherapy in the treatment of active TB

  1. Top of page
  2. Abstract
  3. Introduction
  4. Immunological ‘checkpoints’ of Mtb infection
  5. Innate immune mechanisms during TB infection
  6. Targeting host immunity for prevention and cure of TB
  7. Nutritional supplementation in the treatment of TB
  8. The clinical relevance of vitamin D in TB
  9. The role of NO in resistance against and control of TB
  10. Interventions targeting cell-mediated immunity in TB patients co-infected with HIV and helminths
  11. Therapeutic implications of effector mechanisms against Mtb induced by cytotoxic T lymphocytes
  12. Cytokines as adjuvant immunotherapy in the treatment of active TB
  13. Concluding remarks
  14. Conflict of interest statement
  15. Acknowledgements
  16. References

Strategies for adjuvant immunotherapy have involved stimulation of a favourable immune response using Mycobacterium vaccae, immunosuppression to reduce inflammation with drugs that affect production of TNF-α and effector cytokines (IL2, INF) to enhance antimycobacterial effector mechanisms such as IL-2 and IFN-γ [151]. The timing of immunotherapy needs to be considered carefully and should probably primarily have a sterilizing effect which could be maximized if it is initiated when the bacillary load has been reduced by effective antimycobacterial drugs. Of note, there are large gaps in the understanding of host immune mechanisms against TB, which may affect the use of cytokines as adjuvant immunotherapy [8]. It is clear that mouse models have limited value regarding the development of the granuloma because of differences from human disease with regard to the organization of cells, lack of giant cells and lack of caseous necrosis [8]. In the mouse model, IFN-γ, which increases the killing capacity of macrophages, and TNF-α, which is produced by T cells and macrophages, expressed in early-stage TB at the site of disease and essential for granuloma maintenance, are key molecules for host defence and control of Mtb in the T cell/macrophage immune axis [5]. One of the first large-scale randomized trials of adjuvant IL-2 therapy in 110 Ugandan HIV-negative TB patients showed no effect on the sputum conversion which was the primary outcome. The rationale for the treatment relied mainly on animal models, in which IL-2 strongly induced IFN-γ production and was a potent growth factor in T cells [152]. One possible cause of the unfavourable response is an unexpected increase in the activity of CD25+ Treg cells, which may counteract the proinflammatory reaction. IFN-γ administered by aerosol in five MDR patients showed some effect on sputum conversion, but results from follow-up trials were inconclusive [153]. In most TB patients, single cytokine therapy is unlikely to be very effective, but may be essential for patients with defects in the IFNγ–IL-12 immune pathway [19]. An approach to provide a stimulus that targets a suitable host response instead of using single cytokines, has been extensively investigated by therapeutic vaccination with M. vaccae. The rationale for this treatment, that it would enhance the Th1 response and suppress the Th2 response, has not yet been proven beneficial in clinical trials [154]. Another possible strategy could be to downregulate the Th2 and Treg responses to gain a more effective Th1 response [107, 151, 155]. Adjuvant IL-7 therapy may impair TGF-ß production, as shown in HIV-positive patients [156]. A novel strategy that has been investigated in several clinical trials is to administer high-dose corticosteroids or TNF-α inhibitors to induce therapeutic disruption of granulomas to increase the accessibility of antimycobacterial drugs [153, 157, 158].

Concluding remarks

  1. Top of page
  2. Abstract
  3. Introduction
  4. Immunological ‘checkpoints’ of Mtb infection
  5. Innate immune mechanisms during TB infection
  6. Targeting host immunity for prevention and cure of TB
  7. Nutritional supplementation in the treatment of TB
  8. The clinical relevance of vitamin D in TB
  9. The role of NO in resistance against and control of TB
  10. Interventions targeting cell-mediated immunity in TB patients co-infected with HIV and helminths
  11. Therapeutic implications of effector mechanisms against Mtb induced by cytotoxic T lymphocytes
  12. Cytokines as adjuvant immunotherapy in the treatment of active TB
  13. Concluding remarks
  14. Conflict of interest statement
  15. Acknowledgements
  16. References

Because of considerable biological variation, there might be a role for individualized treatment strategies in TB. The sources of variation include the virulence of Mtb, host response, nutrition and co-infection (e.g. with HIV), and pharmacokinetics of anti-TB chemotherapy. Individualized medicine is likely to have an impact on the outcome of TB treatment by optimizing antibiotic therapy through therapeutic drug monitoring and by enhancing the host immune response. A way of shortening the therapeutic regimen is to ‘hit hard and early’ with many bactericidal drugs when Mtb is at the extracellular stage. Such strategies combined with an improved host response through nutritional support, deworming and treatment of HIV, may reduce the long treatment period which is mainly designed to reduce the risk of relapse. In patients with resistant TB, it is important to consider strategies to optimize the immune response, as they might be at least as effective as some second-line drugs. In the future, with the availability of assays to measure nutritional status, host immunity and drug concentrations, it may be possible to tailor an individualized regimen to optimize both the host response and the effects of the available bactericidal drugs.

Acknowledgements

  1. Top of page
  2. Abstract
  3. Introduction
  4. Immunological ‘checkpoints’ of Mtb infection
  5. Innate immune mechanisms during TB infection
  6. Targeting host immunity for prevention and cure of TB
  7. Nutritional supplementation in the treatment of TB
  8. The clinical relevance of vitamin D in TB
  9. The role of NO in resistance against and control of TB
  10. Interventions targeting cell-mediated immunity in TB patients co-infected with HIV and helminths
  11. Therapeutic implications of effector mechanisms against Mtb induced by cytotoxic T lymphocytes
  12. Cytokines as adjuvant immunotherapy in the treatment of active TB
  13. Concluding remarks
  14. Conflict of interest statement
  15. Acknowledgements
  16. References

This work was supported in part by grants from the Swedish Research Council (ML and OS), the Heart-Lung Foundation (ML, TS and OS), the Swedish International Development Agency (OS), European developing countries clinical trial partnership (EDCTP), the Swedish Society of Medicine (TS), the Medical Research Council of Southeast Sweden (TS), the M&M Wallenberg Foundation (TS), the R Söderberg Foundation (OS) and the B&M Gates Foundation (ML).

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Immunological ‘checkpoints’ of Mtb infection
  5. Innate immune mechanisms during TB infection
  6. Targeting host immunity for prevention and cure of TB
  7. Nutritional supplementation in the treatment of TB
  8. The clinical relevance of vitamin D in TB
  9. The role of NO in resistance against and control of TB
  10. Interventions targeting cell-mediated immunity in TB patients co-infected with HIV and helminths
  11. Therapeutic implications of effector mechanisms against Mtb induced by cytotoxic T lymphocytes
  12. Cytokines as adjuvant immunotherapy in the treatment of active TB
  13. Concluding remarks
  14. Conflict of interest statement
  15. Acknowledgements
  16. References
  • 1
    WHO. Global tuberculosis report 2011. (www.who.int/tb/publications/global_report/2011/gtbr11_full.pdf). 2011. Accessed January 23, 2013.
  • 2
    Mack U, Migliori GB, Sester M et al. LTBI: latent tuberculosis infection or lasting immune responses to M. tuberculosis? A TBNET consensus statement. The European respiratory journal: official journal of the European Society for Clinical Respiratory Physiology 2009; 33: 95673.
  • 3
    Skrahina A, Hurevich H, Zalutskaya A et al. Alarming levels of drug-resistant tuberculosis in Belarus: results of a survey in Minsk. Eur Respir J 2012; 39: 142531.
  • 4
    Dorhoi A, Reece ST, Kaufmann SH. For better or for worse: the immune response against Mycobacterium tuberculosis balances pathology and protection. Immunol Rev 2011; 240: 23551.
  • 5
    Cooper AM. Cell-mediated immune responses in tuberculosis. Annu Rev Immunol 2009; 27: 393422.
  • 6
    Ernst JD. The immunological life cycle of tuberculosis. Nat Rev Immunol 2012; 12: 58191.
  • 7
    Philips JA, Ernst JD. Tuberculosis pathogenesis and immunity. Annual review of pathology 2012; 7: 35384.
  • 8
    Russell DG, Barry CE 3rd, Flynn JL. Tuberculosis: what we don't know can, and does, hurt us. Science 2010; 328: 8526.
  • 9
    Lawn SD, Wood R, Wilkinson RJ. Changing concepts of “latent tuberculosis infection” in patients living with HIV infection. Clin Dev Immunol; 2011; doi: 10.1155/2011/980594
  • 10
    Achkar JM, Jenny-Avital ER. Incipient and subclinical tuberculosis: defining early disease states in the context of host immune response. J Infect Dis 2011; 204(Suppl 4): S117986.
  • 11
    Achkar JM, Sherpa T, Cohen HW, Holzman RS. Differences in clinical presentation among persons with pulmonary tuberculosis: a comparison of documented and undocumented foreign-born versus US-born persons. Clin Infect Dis 2008; 47: 127783.
  • 12
    Dheda K, Schwander SK, Zhu B, van Zyl-Smit RN, Zhang Y. The immunology of tuberculosis: from bench to bedside. Respirology 2010; 15: 43350.
  • 13
    Natarajan K, Kundu M, Sharma P, Basu J. Innate immune responses to M. tuberculosis infection. Tuberculosis (Edinb) 2011; 91: 42731.
  • 14
    Suthar AB, Lawn SD, Del Amo J et al. Antiretroviral therapy for prevention of tuberculosis in adults with HIV: a systematic review and meta-analysis. PLoS medicine 2012; 9: e1001270.
  • 15
    Keane J, Gershon S, Wise RP et al. Tuberculosis associated with infliximab, a tumor necrosis factor alpha-neutralizing agent. N Engl J Med 2001; 345: 1098104.
  • 16
    Solovic I, Sester M, Gomez-Reino JJ et al. The risk of tuberculosis related to tumour necrosis factor antagonist therapies: a TBNET consensus statement. The European respiratory journal: official journal of the European Society for Clinical Respiratory Physiology 2010; 36: 1185206.
  • 17
    Wallis RS. Tumour necrosis factor antagonists: structure, function, and tuberculosis risks. Lancet Infect Dis 2008; 8: 60111.
  • 18
    Moller M, Hoal EG. Current findings, challenges and novel approaches in human genetic susceptibility to tuberculosis. Tuberculosis (Edinb) 2010; 90: 7183.
  • 19
    Casanova JL, Abel L. Genetic dissection of immunity to mycobacteria: the human model. Annu Rev Immunol 2002; 20: 581620.
  • 20
    Stein CM. Genetic epidemiology of tuberculosis susceptibility: impact of study design. PLoS Pathog 2011; 7: e1001189.
  • 21
    Luebeck Disaster. Am J Public Health Nations Health 1932; 22: 2967.
  • 22
    Rieder HL. Clarification of the Luebeck infant tuberculosis. Pneumologie 2003; 57: 4025.
  • 23
    Morrison J, Pai M, Hopewell PC. Tuberculosis and latent tuberculosis infection in close contacts of people with pulmonary tuberculosis in low-income and middle-income countries: a systematic review and meta-analysis. Lancet Infect Dis 2008; 8: 35968.
  • 24
    Wolf AJ, Desvignes L, Linas B et al. Initiation of the adaptive immune response to Mycobacterium tuberculosis depends on antigen production in the local lymph node, not the lungs. J Exp Med 2008; 205: 10515.
  • 25
    Lin PL, Rodgers M, Smith L et al. Quantitative comparison of active and latent tuberculosis in the cynomolgus macaque model. Infect Immun 2009; 77: 463142.
  • 26
    Dorman SE, Hatem CL, Tyagi S et al. Susceptibility to tuberculosis: clues from studies with inbred and outbred New Zealand white rabbits. Infect Immun 2004; 72: 17005.
  • 27
    Brighenti S, Lerm M. How Mycobacterium tuberculosis Manipulates Innate and Adaptive Immunity – New Views of an Old Topic. In: Cardona DP-J, ed. Understanding Tuberculosis - Analyzing the Origin of Mycobacterium Tuberculosis Pathogenicity. Rijeka, Croatia: InTech, 2012; 20734.
  • 28
    Welin A, Winberg ME, Abdalla H et al. Incorporation of Mycobacterium tuberculosis lipoarabinomannan into macrophage membrane rafts is a prerequisite for the phagosomal maturation block. Infect Immun 2008; 76: 28827.
  • 29
    Welin A, Raffetseder J, Eklund D, Stendahl O, Lerm M. Importance of Phagosomal functionality for growth restriction of Mycobacterium tuberculosis in primary human macrophages. J Innate Immun 2011; 3: 50818.
  • 30
    Velmurugan K, Chen B, Miller JL et al. Mycobacterium tuberculosis nuoG is a virulence gene that inhibits apoptosis of infected host cells. PLoS Pathog 2007; 3: e110.
  • 31
    Carlsson F, Kim J, Dumitru C et al. Host-detrimental role of Esx-1-mediated inflammasome activation in mycobacterial infection. PLoS Pathog 2010; 6: e1000895.
  • 32
    Welin A, Eklund D, Stendahl O, Lerm M. Human macrophages infected with a high burden of ESAT-6-expressing M. tuberculosis undergo caspase-1- and cathepsin B-independent necrosis. PLoS ONE 2011; 6: e20302.
  • 33
    Davis JM, Ramakrishnan L. The role of the granuloma in expansion and dissemination of early tuberculous infection. Cell 2009; 136: 3749.
  • 34
    Kim JJ, Lee HM, Shin DM et al. Host cell autophagy activated by antibiotics is required for their effective antimycobacterial drug action. Cell Host Microbe 2012; 11: 45768.
  • 35
    Cederlund A, Agerberth B, Bergman P. Specificity in killing pathogens is mediated by distinct repertoires of human neutrophil peptides. J Innate Immun 2010; 2: 50821.
  • 36
    Hernandez-Pando R, Jeyanathan M, Mengistu G et al. Persistence of DNA from Mycobacterium tuberculosis in superficially normal lung tissue during latent infection. Lancet 2000; 356: 21338.
  • 37
    Schon T, Elmberger G, Negesse Y, Pando RH, Sundqvist T, Britton S. Local production of nitric oxide in patients with tuberculosis. Int J Tuberc Lung Dis 2004; 8: 11347.
  • 38
    Stewart GR, Newton SM, Wilkinson KA et al. The stress-responsive chaperone alpha-crystallin 2 is required for pathogenesis of Mycobacterium tuberculosis. Mol Microbiol 2005; 55: 112737.
  • 39
    Nace G, Evankovich J, Eid R, Tsung A. Dendritic cells and damage-associated molecular patterns: endogenous danger signals linking innate and adaptive immunity. J Innate Immun 2012; 4: 615.
  • 40
    Comas I, Chakravartti J, Small PM et al. Human T cell epitopes of Mycobacterium tuberculosis are evolutionarily hyperconserved. Nat Genet 2010; 42: 498503.
  • 41
    Romagnoli A, Etna MP, Giacomini E, et al. ESX-1 dependent impairment of autophagic flux by Mycobacterium tuberculosis in human dendritic cells. Autophagy 2012; 8: 135770.
  • 42
    Persson YA, Blomgran-Julinder R, Rahman S, Zheng L, Stendahl O. Mycobacterium tuberculosis-induced apoptotic neutrophils trigger a pro-inflammatory response in macrophages through release of heat shock protein 72, acting in synergy with the bacteria. Microbes and infection/Institut Pasteur 2008; 10: 23340.
  • 43
    Zheng L, He M, Long M, Blomgran R, Stendahl O. Pathogen-induced apoptotic neutrophils express heat shock proteins and elicit activation of human macrophages. J Immunol 2004; 173: 631926.
  • 44
    Hedlund S, Persson A, Vujic A, Che KF, Stendahl O, Larsson M. Dendritic cell activation by sensing Mycobacterium tuberculosis-induced apoptotic neutrophils via DC-SIGN. Hum Immunol 2010; 71: 53540.
  • 45
    Keane J, Remold HG, Kornfeld H. Virulent Mycobacterium tuberculosis strains evade apoptosis of infected alveolar macrophages. J Immunol 2000; 164: 201620.
  • 46
    Briken V, Miller JL. Living on the edge: inhibition of host cell apoptosis by Mycobacterium tuberculosis. Future microbiology 2008; 3: 41522.
  • 47
    Blomgran R, Desvignes L, Briken V, Ernst JD. Mycobacterium tuberculosis inhibits neutrophil apoptosis, leading to delayed activation of naive CD4 T cells. Cell Host Microbe 2012; 11: 8190.
  • 48
    Daniel TM. The history of tuberculosis. Respir Med 2006; 100: 186270.
  • 49
    Ramakrishnan CV, Rajendran K, Jacob PG, Fox W, Radhakrishna S. The role of diet in the treatment of pulmonary tuberculosis. An evaluation in a controlled chemotherapy study in home and sanatorium patients in South India. Bull World Health Organ 1961; 25: 33959.
  • 50
    Snowden FM. Emerging and reemerging diseases: a historical perspective. Immunol Rev 2008; 225: 926.
  • 51
    Cegielski JP, Arab L, Cornoni-Huntley J. Nutritional risk factors for tuberculosis among adults in the United States, 1971-1992. Am J Epidemiol 2012; 176: 40922.
  • 52
    Sinclair D, Abba K, Grobler L, Sudarsanam TD. Nutritional supplements for people being treated for active tuberculosis. Cochrane Database Syst Rev 2011; 11: CD006086.
  • 53
    Villamor E, Mugusi F, Urassa W et al. A trial of the effect of micronutrient supplementation on treatment outcome, T cell counts, morbidity, and mortality in adults with pulmonary tuberculosis. J Infect Dis 2008; 197: 1499505.
  • 54
    Visser ME, Grewal HM, Swart EC et al. The effect of vitamin A and zinc supplementation on treatment outcomes in pulmonary tuberculosis: a randomized controlled trial. Am J Clin Nutr 2011; 93: 93100.
  • 55
    Lawson L, Thacher TD, Yassin MA et al. Randomized controlled trial of zinc and vitamin A as co-adjuvants for the treatment of pulmonary tuberculosis. Trop Med Int Health 2010; 15: 148190.
  • 56
    Karyadi E, West CE, Schultink W et al. A double-blind, placebo-controlled study of vitamin A and zinc supplementation in persons with tuberculosis in Indonesia: effects on clinical response and nutritional status. Am J Clin Nutr 2002; 75: 7207.
  • 57
    Benn CS, Friis H, Wejse C. Should micronutrient supplementation be integrated into the case management of tuberculosis? J Infect Dis 2008; 197: 14879.
  • 58
    Coussens AK, Wilkinson RJ, Hanifa Y et al. Vitamin D accelerates resolution of inflammatory responses during tuberculosis treatment. Proc Natl Acad Sci USA 2012; 109: 1544954.
  • 59
    Ralph AP, Kelly PM, Anstey NM. L-arginine and vitamin D: novel adjunctive immunotherapies in tuberculosis. Trends Microbiol 2008; 16: 33644.
  • 60
    Schaible UE, Kaufmann SH. Malnutrition and infection: complex mechanisms and global impacts. PLoS Med 2007; 4: e115.
  • 61
    Cegielski JP, McMurray DN. The relationship between malnutrition and tuberculosis: evidence from studies in humans and experimental animals. The international journal of tuberculosis and lung disease: the official journal of the International Union against Tuberculosis and Lung Disease 2004; 8: 28698.
  • 62
    Martineau AR, Timms PM, Bothamley GH et al. High-dose vitamin D(3) during intensive-phase antimicrobial treatment of pulmonary tuberculosis: a double-blind randomised controlled trial. Lancet 2011; 377: 24250.
  • 63
    Sudarsanam TD, John J, Kang G et al. Pilot randomized trial of nutritional supplementation in patients with tuberculosis and HIV-tuberculosis coinfection receiving directly observed short-course chemotherapy for tuberculosis. Trop Med Int Health 2011; 16: 699706.
  • 64
    McMurray DN, Bartow RA, Mintzer CL, Hernandez-Frontera E. Micronutrient status and immune function in tuberculosis. Ann N Y Acad Sci 1990; 587: 5969.
  • 65
    Gupta KB, Gupta R, Atreja A, Verma M, Vishvkarma S. Tuberculosis and nutrition. Lung India: official organ of Indian Chest Society 2009; 26: 916.
  • 66
    Liu PT, Stenger S, Li H et al. Toll-like receptor triggering of a vitamin D-mediated human antimicrobial response. Science 2006; 311: 17703.
  • 67
    Wejse C, Gomes VF, Rabna P et al. Vitamin D as supplementary treatment for tuberculosis: a double-blind, randomized, placebo-controlled trial. Am J Respir Crit Care Med 2009; 179: 84350.
  • 68
    Wejse C, Olesen R, Rabna P et al. Serum 25-hydroxyvitamin D in a West African population of tuberculosis patients and unmatched healthy controls. Am J Clin Nutr 2007; 86: 137683.
  • 69
    Martineau AR, Nhamoyebonde S, Oni T et al. Reciprocal seasonal variation in vitamin D status and tuberculosis notifications in Cape Town, South Africa. Proc Natl Acad Sci USA 2011; 108: 190137.
  • 70
    Nielsen NO, Skifte T, Andersson M et al. Both high and low serum vitamin D concentrations are associated with tuberculosis: a case-control study in Greenland. Br J Nutr 2010; 104: 148791.
  • 71
    Tostmann A, Wielders JP, Kibiki GS, Verhoef H, Boeree MJ, van der Ven AJ. Serum 25-hydroxy-vitamin D3 concentrations increase during tuberculosis treatment in Tanzania. Int J Tuberc Lung Dis 2010; 14: 114752.
  • 72
    Bogdan C. Nitric oxide and the immune response. Nat Immunol 2001; 2: 90716.
  • 73
    Benoit M, Desnues B, Mege JL. Macrophage polarization in bacterial infections. J Immunol 2008; 181: 37339.
  • 74
    Chan ED, Morris KR, Belisle JT et al. Induction of inducible nitric oxide synthase-NO* by lipoarabinomannan of Mycobacterium tuberculosis is mediated by MEK1-ERK, MKK7-JNK, and NF-kappaB signaling pathways. Infect Immun 2001; 69: 200110.
  • 75
    Qualls JE, Neale G, Smith AM et al. Arginine usage in mycobacteria-infected macrophages depends on autocrine-paracrine cytokine signaling. Sci Signal 2010; 3: ra62.
  • 76
    El Kasmi KC, Qualls JE, Pesce JT et al. Toll-like receptor-induced arginase 1 in macrophages thwarts effective immunity against intracellular pathogens. Nat Immunol 2008; 9: 1399406.
  • 77
    Hesse M, Modolell M, La Flamme AC et al. Differential regulation of nitric oxide synthase-2 and arginase-1 by type 1/type 2 cytokines in vivo: granulomatous pathology is shaped by the pattern of L-arginine metabolism. J Immunol 2001; 167: 653344.
  • 78
    Pessanha AP, Martins RA, Mattos-Guaraldi AL, Vianna A, Moreira LO. Arginase-1 expression in granulomas of tuberculosis patients. FEMS Immunol Med Microbiol 2012; 66: 26568.
  • 79
    Davis AS, Vergne I, Master SS, Kyei GB, Chua J, Deretic V. Mechanism of inducible nitric oxide synthase exclusion from mycobacterial phagosomes. PLoS Pathog 2007; 3: e186.
  • 80
    Chan ED, Chan J, Schluger NW. What is the role of nitric oxide in murine and human host defense against tuberculosis?Current knowledge. Am J Respir Cell Mol Biol 2001; 25: 60612.
  • 81
    Nicholson S, Bonecini-Almeida Mda G, Lapa e Silva JR,et al. . Inducible nitric oxide synthase in pulmonary alveolar macrophages from patients with tuberculosis. J Exp Med 1996; 183: 2293302.
  • 82
    Wang CH, Liu CY, Lin HC, Yu CT, Chung KF, Kuo HP. Increased exhaled nitric oxide in active pulmonary tuberculosis due to inducible NO synthase upregulation in alveolar macrophages. Eur Respir J 1998; 11: 80915.
  • 83
    Schon T, Gebre N, Sundqvist T, Aderaye G, Britton S. Effects of HIV co-infection and chemotherapy on the urinary levels of nitric oxide metabolites in patients with pulmonary tuberculosis. Scand J Infect Dis 1999; 31: 1236.
  • 84
    Choi HS, Rai PR, Chu HW, Cool C, Chan ED. Analysis of nitric oxide synthase and nitrotyrosine expression in human pulmonary tuberculosis. Am J Respir Crit Care Med 2002; 166: 17886.
  • 85
    Nathan C. Microbiology. An antibiotic mimics immunity. Science 2008; 322: 13378.
  • 86
    Gurumurthy M, Mukherjee T, Dowd CS et al. Substrate specificity of the deazaflavin-dependent nitroreductase from Mycobacterium tuberculosis responsible for the bioreductive activation of bicyclic nitroimidazoles. The FEBS journal 2012; 279: 11325.
  • 87
    Singh R, Manjunatha U, Boshoff HI et al. PA-824 kills nonreplicating Mycobacterium tuberculosis by intracellular NO release. Science 2008; 322: 13925.
  • 88
    Manjunatha U, Boshoff HI, Barry CE. The mechanism of action of PA-824: novel insights from transcriptional profiling. Communicative & integrative biology 2009; 2: 2158.
  • 89
    Diacon AH, Dawson R, von Groote-Bidlingmaier F et al. 14-day bactericidal activity of PA-824, bedaquiline, pyrazinamide, and moxifloxacin combinations: a randomised trial. Lancet 2012; 380: 98693.
  • 90
    O'Brien L, Carmichael J, Lowrie DB, Andrew PW. Strains of Mycobacterium tuberculosis differ in susceptibility to reactive nitrogen intermediates in vitro. Infect Immun 1994; 62: 518790.
  • 91
    Rhoades ER, Orme IM. Susceptibility of a panel of virulent strains of Mycobacterium tuberculosis to reactive nitrogen intermediates. Infect Immun 1997; 65: 118995.
  • 92
    Yu K, Mitchell C, Xing Y, Magliozzo RS, Bloom BR, Chan J. Toxicity of nitrogen oxides and related oxidants on mycobacteria: M. tuberculosis is resistant to peroxynitrite anion. Tuber Lung Dis 1999; 79: 1918.
  • 93
    Inumaru VT, Nogueira PA, Butuem IV, Riley LW, Ferrazoli L. Reactive nitrogen intermediate susceptibility of Mycobacterium tuberculosis genotypes in an urban setting. Int J Tuberc Lung Dis 2009; 13: 6658.
  • 94
    Friedman CR, Quinn GC, Kreiswirth BN et al. Widespread dissemination of a drug-susceptible strain of Mycobacterium tuberculosis. J Infect Dis 1997; 176: 47884.
  • 95
    Timmins GS, Master S, Rusnak F, Deretic V. Nitric oxide generated from isoniazid activation by KatG: source of nitric oxide and activity against Mycobacterium tuberculosis. Antimicrob Agents Chemother 2004; 48: 30069.
  • 96
    Idh J, Mekonnen M, Abate E et al. Resistance to first-line anti-TB drugs is associated with reduced nitric oxide susceptibility in Mycobacterium tuberculosis. PLoS ONE 2012; 7: e39891.
  • 97
    Wengenack NL, Jensen MP, Rusnak F, Stern MK. Mycobacterium tuberculosis KatG is a peroxynitritase. Biochem Biophys Res Commun 1999; 256: 4857.
  • 98
    Ribeiro-Guimaraes ML, Pessolani MC. Comparative genomics of mycobacterial proteases. Microb Pathog 2007; 43: 1738.
  • 99
    Venugopal A, Bryk R, Shi S et al. Virulence of Mycobacterium tuberculosis depends on lipoamide dehydrogenase, a member of three multienzyme complexes. Cell Host Microbe 2011; 9: 2131.
  • 100
    Bryk R, Griffin P, Nathan C. Peroxynitrite reductase activity of bacterial peroxiredoxins. Nature 2000; 407: 2115.
  • 101
    Milani M, Pesce A, Ouellet H, Guertin M, Bolognesi M. Truncated hemoglobins and nitric oxide action. IUBMB Life 2003; 55: 6237.
    Direct Link:
  • 102
    Biswas T, Small J, Vandal O et al. Structural insight into serine protease Rv3671c that Protects M. tuberculosis from oxidative and acidic stress. Structure 2010; 18: 135363.
  • 103
    Stewart GR, Ehrt S, Riley LW, Dale JW, McFadden J. Deletion of the putative antioxidant noxR1 does not alter the virulence of Mycobacterium tuberculosis H37Rv. Tuber Lung Dis 2000; 80: 23742.
  • 104
    Ruan J, St John G, Ehrt S, Riley L, Nathan C. noxR3, a novel gene from Mycobacterium tuberculosis, protects Salmonella typhimurium from nitrosative and oxidative stress. Infect Immun 1999; 67: 327683.
  • 105
    Ehrt S, Shiloh MU, Ruan J et al. A novel antioxidant gene from Mycobacterium tuberculosis. J Exp Med 1997; 186: 188596.
  • 106
    Schon T, Elias D, Moges F et al. Arginine as an adjuvant to chemotherapy improves clinical outcome in active tuberculosis. Eur Respir J 2003; 21: 4838.
  • 107
    Schon T, Idh J, Westman A et al. Effects of a food supplement rich in arginine in patients with smear positive pulmonary tuberculosis–a randomised trial. Tuberculosis (Edinb) 2011; 91: 3707.
  • 108
    Yeo TW, Lampah DA, Gitawati R et al. Safety profile of L-arginine infusion in moderately severe falciparum malaria. PLoS ONE 2008; 3: e2347.
  • 109
    Barry CE 3rd, Boshoff HI, Dartois V et al. The spectrum of latent tuberculosis: rethinking the biology and intervention strategies. Nat Rev Microbiol 2009; 7: 84555.
  • 110
    Lawn SD, Wood R. Tuberculosis in antiretroviral treatment services in resource-limited settings: addressing the challenges of screening and diagnosis. J Infect Dis 2011; 204(Suppl 4): S115967.
  • 111
    Lawn SD, Nicol MP. Xpert(R) MTB/RIF assay: development, evaluation and implementation of a new rapid molecular diagnostic for tuberculosis and rifampicin resistance. Future Microbiol 2011; 6: 106782.
  • 112
    Lawn SD, Butera ST, Shinnick TM. Tuberculosis unleashed: the impact of human immunodeficiency virus infection on the host granulomatous response to Mycobacterium tuberculosis. Microbes Infect 2002; 4: 63546.
  • 113
    Diedrich CR, Flynn JL. HIV-1/mycobacterium tuberculosis coinfection immunology: how does HIV-1 exacerbate tuberculosis? Infect Immun 2011; 79: 140717.
  • 114
    Torok ME, Farrar JJ. When to start antiretroviral therapy in HIV-associated tuberculosis. N Engl J Med 2011; 365: 153840.
  • 115
    Lawn SD, Torok ME, Wood R. Optimum time to start antiretroviral therapy during HIV-associated opportunistic infections. Curr Opin Infect Dis 2011; 24: 3442.
  • 116
    Albonico M, Crompton DW, Savioli L. Control strategies for human intestinal nematode infections. Adv Parasitol 1999; 42: 277341.
  • 117
    Elias D, Britton S, Kassu A, Akuffo H. Chronic helminth infections may negatively influence immunity against tuberculosis and other diseases of public health importance. Expert review of anti-infective therapy 2007; 5: 47584.
  • 118
    Elias D, Mengistu G, Akuffo H, Britton S. Are intestinal helminths risk factors for developing active tuberculosis? Trop Med Int Health 2006; 11: 5518.
  • 119
    Borkow G, Weisman Z, Leng Q et al. Helminths, human immunodeficiency virus and tuberculosis. Scand J Infect Dis 2001; 33: 56871.
  • 120
    Bentwich Z. Good worms or bad worms: do worm infections affect the epidemiological patterns of other diseases? Parasitol Today 2000; 16: 312.
  • 121
    Rafi W, Ribeiro-Rodrigues R, Ellner JJ, Salgame P. Coinfection-helminthes and tuberculosis. Curr Opin HIV AIDS 2012; 7: 23944.
  • 122
    Abate E, Belayneh M, Gelaw A et al. The impact of asymptomatic helminth co-infection in patients with newly diagnosed tuberculosis in north-west ethiopia. PLoS ONE 2012; 7: e42901.
  • 123
    Mouser EE, Pollakis G, Paxton WA. Effects of helminths and Mycobacterium tuberculosis infection on HIV-1: a cellular immunological perspective. Current opinion in HIV and AIDS 2012; 7: 2607.
  • 124
    Sangare LR, Herrin BR, John-Stewart G, Walson JL. Species-specific treatment effects of helminth/HIV-1 co-infection: a systematic review and meta-analysis. Parasitology 2011; 138: 154658.
  • 125
    Wolday D, Mayaan S, Mariam ZG et al. Treatment of intestinal worms is associated with decreased HIV plasma viral load. J Acquir Immune Defic Syndr 2002; 31: 5662.
  • 126
    Walson JL, Otieno PA, Mbuchi M et al. Albendazole treatment of HIV-1 and helminth co-infection: a randomized, double-blind, placebo-controlled trial. AIDS 2008; 22: 16019.
  • 127
    Walson JL, Herrin BR, John-Stewart G. Deworming helminth co-infected individuals for delaying HIV disease progression. Cochrane Database Syst Rev 2009; 3: CD006419.
  • 128
    Blish CA, Sangare L, Herrin BR, Richardson BA, John-Stewart G, Walson JL. Changes in plasma cytokines after treatment of ascaris lumbricoides infection in individuals with HIV-1 infection. J Infect Dis 2010; 201: 181621.
  • 129
    Sandler NG, Douek DC. Microbial translocation in HIV infection: causes, consequences and treatment opportunities. Nat Rev Microbiol 2012; 10: 65566.
  • 130
    Potian JA, Rafi W, Bhatt K, McBride A, Gause WC, Salgame P. Preexisting helminth infection induces inhibition of innate pulmonary anti-tuberculosis defense by engaging the IL-4 receptor pathway. J Exp Med 2011; 208: 186374.
  • 131
    Resende Co T, Hirsch CS, Toossi Z, Dietze R, Ribeiro-Rodrigues R. Intestinal helminth co-infection has a negative impact on both anti-Mycobacterium tuberculosis immunity and clinical response to tuberculosis therapy. Clin Exp Immunol 2007; 147: 4552.
  • 132
    Diniz LM, Magalhaes EF, Pereira FE, Dietze R, Ribeiro-Rodrigues R. Presence of intestinal helminths decreases T helper type 1 responses in tuberculoid leprosy patients and may increase the risk for multi-bacillary leprosy. Clin Exp Immunol 2010; 161: 14250.
  • 133
    Babu S, Bhat SQ, Kumar NP et al. Attenuation of toll-like receptor expression and function in latent tuberculosis by coexistent filarial infection with restoration following antifilarial chemotherapy. PLoS Negl Trop Dis 2009; 3: e489.
  • 134
    Babu S, Kumaraswami V, Nutman TB. Alternatively activated and immunoregulatory monocytes in human filarial infections. J Infect Dis 2009; 199: 182737.
  • 135
    Elias D, Britton S, Aseffa A, Engers H, Akuffo H. Poor immunogenicity of BCG in helminth infected population is associated with increased in vitro TGF-beta production. Vaccine 2008; 26: 3897902.
  • 136
    Smith SM, Dockrell HM. Role of CD8 T cells in mycobacterial infections. Immunol Cell Biol 2000; 78: 32533.
  • 137
    Woodworth JS, Behar SM. Mycobacterium tuberculosis-specific CD8+ T cells and their role in immunity. Crit Rev Immunol 2006; 26: 31752.
  • 138
    Mohagheghpour N, Gammon D, Kawamura LM, van Vollenhoven A, Benike CJ, Engleman EG. CTL response to Mycobacterium tuberculosis: identification of an immunogenic epitope in the 19-kDa lipoprotein. J Immunol 1998; 161: 24006.
  • 139
    Lalvani A, Brookes R, Wilkinson RJ et al. Human cytolytic and interferon gamma-secreting CD8+ T lymphocytes specific for Mycobacterium tuberculosis. Proc Natl Acad Sci USA 1998; 95: 2705.
  • 140
    Nagata S. Fas ligand-induced apoptosis. Annu Rev Genet 1999; 33: 2955.
  • 141
    Stenger S, Hanson DA, Teitelbaum R et al. An antimicrobial activity of cytolytic T cells mediated by granulysin. Science 1998; 282: 1215.
  • 142
    Stenger S, Cytolytic T. Cells in the immune response to mycobacterium tuberculosis. Scand J Infect Dis 2001; 33: 4837.
  • 143
    Griffith TS, Lynch DH. TRAIL: a molecule with multiple receptors and control mechanisms. Curr Opin Immunol 1998; 10: 55963.
  • 144
    Cho S, Mehra V, Thoma-Uszynski S et al. Antimicrobial activity of MHC class I-restricted CD8+ T cells in human tuberculosis. Proc Natl Acad Sci USA 2000; 97: 122105.
  • 145
    Tascon RE, Stavropoulos E, Lukacs KV, Colston MJ. Protection against Mycobacterium tuberculosis infection by CD8+ T cells requires the production of gamma interferon. Infect Immun 1998; 66: 8304.
  • 146
    Feng CG, Britton WJ. CD4+ and CD8+ T cells mediate adoptive immunity to aerosol infection of Mycobacterium bovis bacillus Calmette-Guerin. J Infect Dis 2000; 181: 18469.
  • 147
    Brighenti S, Andersson J. Local immune responses in human tuberculosis: learning from the site of infection. J Infect Dis 2012; 205(Suppl 2): S31624.
  • 148
    Rahman S, Gudetta B, Fink J et al. Compartmentalization of immune responses in human tuberculosis: few CD8+ effector T cells but elevated levels of FoxP3+ regulatory t cells in the granulomatous lesions. Am J Pathol 2009; 174: 221124.
  • 149
    Andersson J, Samarina A, Fink J, Rahman S, Grundstrom S. Impaired expression of perforin and granulysin in CD8+ T cells at the site of infection in human chronic pulmonary tuberculosis. Infect Immun 2007; 75: 521022.
  • 150
    Canaday DH, Wilkinson RJ, Li Q, Harding CV, Silver RF, Boom WH. CD4(+) and CD8(+) T cells kill intracellular Mycobacterium tuberculosis by a perforin and Fas/Fas ligand-independent mechanism. J Immunol 2001; 167: 273442.
  • 151
    Barnes PF. Immunotherapy for tuberculosis: wave of the future or tilting at windmills? Am J Respir Crit Care Med 2003; 168: 1423.
  • 152
    Johnson JL, Ssekasanvu E, Okwera A et al. Randomized trial of adjunctive interleukin-2 in adults with pulmonary tuberculosis. Am J Respir Crit Care Med 2003; 168: 18591.
  • 153
    Wallis RS. Reconsidering adjuvant immunotherapy for tuberculosis. Clin Infect Dis 2005; 41: 2018.
  • 154
    Mwinga A, Nunn A, Ngwira B et al. Mycobacterium vaccae (SRL172) immunotherapy as an adjunct to standard antituberculosis treatment in HIV-infected adults with pulmonary tuberculosis: a randomised placebo-controlled trial. Lancet 2002; 360: 10505.
  • 155
    Ellner JJ. Immunoregulation in TB: observations and implications. Clin Transl Sci 2010; 3: 238.
  • 156
    Levy Y, Lacabaratz C, Weiss L et al. Enhanced T cell recovery in HIV-1-infected adults through IL-7 treatment. J Clin Investig 2009; 119: 9971007.
  • 157
    Wallis RS, Kyambadde P, Johnson JL et al. A study of the safety, immunology, virology, and microbiology of adjunctive etanercept in HIV-1-associated tuberculosis. AIDS 2004; 18: 25764.
  • 158
    Mayanja-Kizza H, Jones-Lopez E, Okwera A et al. Immunoadjuvant prednisolone therapy for HIV-associated tuberculosis: a phase 2 clinical trial in Uganda. J Infect Dis 2005; 191: 85665.