SEARCH

SEARCH BY CITATION

Keywords:

  • Cytotoxic T cell;
  • gastrointestinal tract;
  • HIV;
  • mucosa-associated lymphoid tissue;
  • natural killer cells

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. HIV infection of the female reproductive tract: local inflammation leads to rapid viral dissemination
  5. Innate immune defenses in the female reproductive tract
  6. HIV-specific IgA in cervical secretions
  7. HIV-specific T cells, inflammation, and CD4 depletion in the lower female reproductive tract
  8. Sexually transmitted infections alter the mucosal microenvironment
  9. Exposure to semen induces inflammatory responses in the female genital tract
  10. The upper reproductive tract and HIV infection
  11. Changes in the upper reproductive tract during the menstrual cycle
  12. Uterine natural killer (NK) cells: a novel cell type with an unusual dual role
  13. Immunological parallels between the reproductive and gastrointestinal tracts
  14. Implications for studies on prevention of HIV infection and HIV immunopathogenesis
  15. Acknowledgments
  16. References

Citation Shacklett BL, Greenblatt RM. Immune responses to HIV in the female reproductive tract, immunologic parallels with the gastrointestinal tract, and research implications. Am J Reprod Immunol 2011; 65: 230–241

The female reproductive tract is a major site of mucosa-associated lymphoid tissue and susceptibility to HIV infection, yet the tissue site(s) of infection and the impact of HIV infection on this important mucosal tissue remain poorly understood. CD4+ T cells and other cell types expressing the major coreceptors for HIV, CCR5, and CXCR4 are abundant in both the lower reproductive tract (endocervix and vagina) and the upper tract (endocervix and uterus) and are highly susceptible to infection. Antiviral defenses in the female reproductive tract are mediated by a variety of soluble factors and by mucosal effector cells that differ phenotypically from their counterparts in blood. The immunologic characteristics of the female reproductive tract parallel those of the gut, where major HIV-related immunologic injury occurs. The susceptibility of the female reproductive tract to HIV infection and immunopathogenesis suggests important new avenues for further research.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. HIV infection of the female reproductive tract: local inflammation leads to rapid viral dissemination
  5. Innate immune defenses in the female reproductive tract
  6. HIV-specific IgA in cervical secretions
  7. HIV-specific T cells, inflammation, and CD4 depletion in the lower female reproductive tract
  8. Sexually transmitted infections alter the mucosal microenvironment
  9. Exposure to semen induces inflammatory responses in the female genital tract
  10. The upper reproductive tract and HIV infection
  11. Changes in the upper reproductive tract during the menstrual cycle
  12. Uterine natural killer (NK) cells: a novel cell type with an unusual dual role
  13. Immunological parallels between the reproductive and gastrointestinal tracts
  14. Implications for studies on prevention of HIV infection and HIV immunopathogenesis
  15. Acknowledgments
  16. References

Mucosal surfaces are the primary sites of most HIV transmission, and thus, these tissues are a focus of attention for efforts to prevent HIV infection.1 Several mechanisms have been proposed to explain how HIV crosses the epithelial barriers of the female genital tract, including direct passage of virus and/or infected cells through epithelial breaches, transcytosis of free virus across polarized epithelial cells, and binding and/or uptake by mucosal dendritic cells.2,3 Regardless of the mechanism(s) leading to infection via the reproductive mucosa, the rate of HIV transmission per high-risk sexual contact appears to be low.4 However, once infection is initiated, virus amplification occurs rapidly, aided by local inflammation.5 Systemic dissemination occurs prior to the development of the adaptive immune response,6 leading to massive depletion of CD4+ T cells, notably those lining the gastrointestinal mucosa.7–10 Like the gastrointestinal tract, tissues of the lower (ectocervix and vagina) and upper (endocervix and uterus) female reproductive tract contain partially activated, CD4+ memory cells expressing CCR5 and/or CXCR4, which can serve as targets for HIV. However, the effects of acute/early HIV infection on the reproductive tract have not been the focus of intensive study, while much attention has been devoted to the early effects of HIV infection on the gastrointestinal tract. This review summarizes literature on immune responses to HIV/simian immunodeficiency virus (SIV) in the female reproductive tract, highlighting immunologic parallels between the reproductive and gastrointestinal mucosal tissues.

HIV infection of the female reproductive tract: local inflammation leads to rapid viral dissemination

  1. Top of page
  2. Abstract
  3. Introduction
  4. HIV infection of the female reproductive tract: local inflammation leads to rapid viral dissemination
  5. Innate immune defenses in the female reproductive tract
  6. HIV-specific IgA in cervical secretions
  7. HIV-specific T cells, inflammation, and CD4 depletion in the lower female reproductive tract
  8. Sexually transmitted infections alter the mucosal microenvironment
  9. Exposure to semen induces inflammatory responses in the female genital tract
  10. The upper reproductive tract and HIV infection
  11. Changes in the upper reproductive tract during the menstrual cycle
  12. Uterine natural killer (NK) cells: a novel cell type with an unusual dual role
  13. Immunological parallels between the reproductive and gastrointestinal tracts
  14. Implications for studies on prevention of HIV infection and HIV immunopathogenesis
  15. Acknowledgments
  16. References

Detailed studies of acute SIV infection in rhesus macaques have revealed the mechanisms that lead to the rapid expansion of HIV/SIV in tissues, beginning with a small ‘founder’ population of cells near the initial site of entry in the endocervix. Li et al.5 employed a combination of in situ hybridization and immunohistochemistry to elucidate the cells and soluble factors participating in the earliest steps of SIV dissemination following cervicovaginal inoculation of macaques. At just 1 day post-infection, they found an accumulation in cervical mucosa of CD123+ plasmacytoid dendritic cells (pDC) expressing interferons α and β and producing the chemokines MIP-1α and MIP-1β. These chemokines, in turn, attract CD4+ T cells expressing the chemokine receptor CCR5, which serve as targets for SIV infection. This ‘inside-out’ signaling, involving innate and inflammatory responses in mucosal tissues, leads to rapid amplification and expansion of the infection.5

If an inflammatory cascade leads to rapid expansion of HIV/SIV infection in mucosal tissues, might the inhibition of local inflammatory responses prevent viral dissemination following HIV/SIV mucosal exposure? To address this question, Li et al. selected an antimicrobial compound, glycerol monolaurate (GML), which inhibits the production of proinflammatory cytokines and chemokines by vaginal epithelial cell cultures in vitro. Strikingly, rhesus macaques treated with 5% GML prior to a high-dose intravaginal challenge with SIV were completely protected from systemic viral infection.5 These findings demonstrate that innate immune defenses within mucosal tissues are, paradoxically, critical to the rapid dissemination of HIV/SIV within the host. They also suggest that microbicides designed to limit the host’s inflammatory response, rather than amplifying this response, may prove to be surprisingly effective at reducing HIV transmission. Furthermore, these findings imply that individuals who remain uninfected despite repeated mucosal exposure to HIV may respond to exposure by ‘immune quiescence’ rather than an active inflammatory response. Caution is warranted in the study of topical microbicides, as some inflammatory modulators have an additional, unique role in the female reproductive tract by which they influence the outcome of embryonic implantation and early growth.11

Innate immune defenses in the female reproductive tract

  1. Top of page
  2. Abstract
  3. Introduction
  4. HIV infection of the female reproductive tract: local inflammation leads to rapid viral dissemination
  5. Innate immune defenses in the female reproductive tract
  6. HIV-specific IgA in cervical secretions
  7. HIV-specific T cells, inflammation, and CD4 depletion in the lower female reproductive tract
  8. Sexually transmitted infections alter the mucosal microenvironment
  9. Exposure to semen induces inflammatory responses in the female genital tract
  10. The upper reproductive tract and HIV infection
  11. Changes in the upper reproductive tract during the menstrual cycle
  12. Uterine natural killer (NK) cells: a novel cell type with an unusual dual role
  13. Immunological parallels between the reproductive and gastrointestinal tracts
  14. Implications for studies on prevention of HIV infection and HIV immunopathogenesis
  15. Acknowledgments
  16. References

The female reproductive tract is equipped with a variety of physical and chemical defenses against viral infection (recently reviewed by Iwasaki12). The vagina and ectocervix are lined with multilayered squamous epithelium. In contrast, the upper reproductive tract, including the endocervix, uterine endometrium, and fallopian tubes, contains a less resilient monolayer of columnar epithelium. The endocervical canal is lined with mucus, which provides an additional defensive layer by trapping bacteria and viruses. Epithelial cells lining the reproductive tract produce a wide range of soluble factors with documented anti-HIV activity; these include secretory leukocyte protease inhibitor (SLPI13), lactoferrin,14 defensins,15,16 cytokines, and chemokines (e.g., RANTES and MIP-1β17).

The serine protease inhibitor Trappin-2/Elafin has antibacterial activity against Gram-positive and Gram-negative bacteria, as well as fungal pathogens.18 Intriguingly, a recent proteomics study identified this protein as a potential biomarker of protection against HIV acquisition.19 This study evaluated cervicovaginal lavage (CVL) samples from 315 women, including highly exposed, persistently seronegative (HEPS) commercial sex workers, HIV-positive women, and seronegative controls, using SELDI-TOF mass spectrometry. Trappin-2/Elafin was found to be significantly overexpressed in HEPS women when compared to both HIV-positive and seronegative control groups.

A related study found that Trappin-2 was constitutively produced by primary cells from multiple reproductive tract sites, including uterus, fallopian tube, cervix, and ectocervix.18 Levels of secreted Trappin-2/Elafin were higher in CVL samples from HIV-negative women than in samples from HIV-positive women, although these differences did not reach statistical significance. Recombinant Trappin-2/Elafin inhibited the infectivity of CXCR4- and CCR5-utilizing HIV strains in a TZM-bl assay.18

Other innate immune factors present in genital fluids include alpha and beta defensins and the antimicrobial peptide cathelicidin (LL-37). One recent study assessed the levels of these factors in cervicovaginal secretions from HEPS commercial sex workers.20 The presence of multiple sexually transmitted infections (including Chlamydia trachomatis, Neisseria gonorrheae, Trichomonas vaginalis, and candidiasis) was associated with the increased levels of human neutrophil peptide-1 (HNP-1), human β-defensin-2-3, and LL-37 in secretions. Levels of HNP-1 and LL-37 were strongly associated with in vitro HIV-neutralizing capacity of cervicovaginal secretions. However, in univariate analysis, the levels of these factors in secretions tended to be increased in high-risk women who eventually seroconverted, relative to those who remained uninfected.20

HIV-specific IgA in cervical secretions

  1. Top of page
  2. Abstract
  3. Introduction
  4. HIV infection of the female reproductive tract: local inflammation leads to rapid viral dissemination
  5. Innate immune defenses in the female reproductive tract
  6. HIV-specific IgA in cervical secretions
  7. HIV-specific T cells, inflammation, and CD4 depletion in the lower female reproductive tract
  8. Sexually transmitted infections alter the mucosal microenvironment
  9. Exposure to semen induces inflammatory responses in the female genital tract
  10. The upper reproductive tract and HIV infection
  11. Changes in the upper reproductive tract during the menstrual cycle
  12. Uterine natural killer (NK) cells: a novel cell type with an unusual dual role
  13. Immunological parallels between the reproductive and gastrointestinal tracts
  14. Implications for studies on prevention of HIV infection and HIV immunopathogenesis
  15. Acknowledgments
  16. References

The presence of mucosal IgA at the sites of potential HIV exposure in the female reproductive tract could theoretically provide an important barrier against infection. IgG is also abundant in the reproductive tract, where it may be produced in the vagina or transported from serum by paracellular diffusion.12 Intriguingly, several studies have reported the detection of HIV-specific immunoglobulin A (IgA) in cervicovaginal secretions from HEPS women.21 It has also been reported that such antibodies are capable of neutralizing primary strains of HIV in vitro22 and can block transcytosis of HIV across an intact epithelial monolayer.23 However, other studies of HEPS cohorts have failed to detect such antibodies and this topic remains controversial in the HIV field.24,25 Intriguingly, Tudor et al. recently described the construction of an antibody expression library derived from B cells isolated from the cervical mucosa of HEPS women. Antibodies derived from this library included IgA antibodies specific for the membrane-proximal region of gp41.26

HIV-specific T cells, inflammation, and CD4 depletion in the lower female reproductive tract

  1. Top of page
  2. Abstract
  3. Introduction
  4. HIV infection of the female reproductive tract: local inflammation leads to rapid viral dissemination
  5. Innate immune defenses in the female reproductive tract
  6. HIV-specific IgA in cervical secretions
  7. HIV-specific T cells, inflammation, and CD4 depletion in the lower female reproductive tract
  8. Sexually transmitted infections alter the mucosal microenvironment
  9. Exposure to semen induces inflammatory responses in the female genital tract
  10. The upper reproductive tract and HIV infection
  11. Changes in the upper reproductive tract during the menstrual cycle
  12. Uterine natural killer (NK) cells: a novel cell type with an unusual dual role
  13. Immunological parallels between the reproductive and gastrointestinal tracts
  14. Implications for studies on prevention of HIV infection and HIV immunopathogenesis
  15. Acknowledgments
  16. References

Very few studies have characterized HIV-specific T-cell responses in the female reproductive tract of chronically infected individuals, likely due to the challenges associated with obtaining fresh tissues for analysis. Accordingly, it has been difficult to obtain a clear picture of the T-cell repertoire in the female reproductive tract and the extent to which CD4+ and CD8+ T-cell populations mirror those found elsewhere in the body. Musey et al.27 compared the T-cell receptor clonality of HIV-specific CD8+ T cells from several mucosal sites and found that the majority of clones were shared between mucosal tissues and peripheral blood mononuclear cells (PBMC). They also identified several clones with CTL function that were CD4+, MHC class II-restricted and responded to peptides within the HIV Env protein.28

Recently, progress has been made in utilizing minimally invasive clinical specimens, notably cervical cytobrushes and CVL for immunological assays.29–36 Gumbi et al.32 studied the relationship between mucosal inflammation and HIV-specific CD8+ T-cell responses in the cervix. They found that increased levels of proinflammatory cytokines (i.e., TNF-α, IL-1β, IL-6, and IL-8) in CVL fluid were significantly associated with HIV shedding in the genital tract. Plasma viral load was also positively associated with viral shedding from the cervix. However, there was no association between the magnitude of HIV Gag-specific CD8+ T-cell responses in the cervix and viral shedding. There was also no correlation between HIV-specific T-cell response magnitudes at the cervix and in blood. These findings suggest that (i) genital inflammation may promote HIV replication and viral shedding, and (ii) HIV-specific T-cell responses in blood do not necessarily predict those in cervical mucosa.32

In a related study, Bebell et al.29 collected CVL and plasma samples from women in a longitudinal cohort in Durban, South Africa, including 44 women with acute HIV infection. Levels of IL-6, IL-10, and IL-12p70 in CVL were significantly greater in women with acute HIV infection than in pre-seroconversion samples from the same women or in CVL from HIV-negative controls. Importantly, cytokine levels in the genital tract were similar in women with acute HIV infection regardless of concurrent STI or bacterial vaginosis. Furthermore, elevated levels of IL-1β, IL-6, and IL-8 correlated with lower systemic CD4+ T-cell counts during acute HIV infection. Unfortunately, mucosal CD4+ T-cell depletion was not measured; nevertheless, these findings reveal that genital inflammation is associated with acute HIV infection and is significantly associated with systemic CD4+ T-cell depletion.29

Nkwanyana et al.34 evaluated the composition and yield of cytobrush-derived T cells from HIV-infected women and uninfected controls. In the HIV-positive women, yields of CD3+ T cells as well as CD19+ B cells were significantly greater than in uninfected controls, although CD4+ T cells were depleted relative to CD8+ T cells. The majority of cytobrush T cells had an effector memory (CD45RA-CCR7-CD27-) phenotype. There was a significant positive correlation between cytobrush T-cell counts and cervical concentrations of IL-1β, TNFα, and IL-12.

The low number of viable lymphocytes isolated from cytobrush specimens limits the range of experiments that may be performed to characterize HIV-specific T-cell responses at the cervical mucosa. To address this issue, Bere et al.30,31 compared several methods for in vitro expansion of cytobrush-derived T cells. Expansion with anti-CD3/28 beads and IL-2, IL-7, and IL-15 gave rise to the greatest expansion after 7 days, with an accumulation of central memory T cells.31 The same authors used polyclonally expanded T-cell lines from 16 HIV-positive women to assess the relationship between HIV Gag-specific responses in blood and cervix in Elispot assays.30 Both the total response magnitude and the peptide pools targeted were similar in both sites, and cervical responses to HIV Gag peptides were detected only in women with systemic Gag-specific responses >1000 spot-forming units/106 cells.30 This finding underscores the limitations inherent in cytobrush sampling, which typically yields between 0.01 and 1 × 106 viable cells per cytobrush.30,32

Although highly active antiretroviral therapy (HAART) is associated with the control of viremia and variable restoration of CD4+ T-cell counts in the periphery, little is known of the response to HAART in genital mucosa. In a recent cross-sectional study of 62 HIV-positive women, including 35 on HAART, Mkhize et al.33 demonstrated that HAART is associated with higher CD4+ T-cell percentages at the cervical mucosa. Genital tract HIV shedding was significantly associated with the amount of HIV RNA circulating in blood and was fully suppressed in HAART-compliant women. As previously reported, HAART was also associated with decreased HIV-specific CD8+ T-cell responses in blood. Surprisingly, however, Gag-specific T-cell responses in cervical mucosa were preserved in women on HAART. These findings may suggest that low levels of virus continue to replicate in cervical mucosa, even when virus reaches very low to undetectable levels in plasma and cervical secretions. Further studies will be required to address this issue.

Sexually transmitted infections alter the mucosal microenvironment

  1. Top of page
  2. Abstract
  3. Introduction
  4. HIV infection of the female reproductive tract: local inflammation leads to rapid viral dissemination
  5. Innate immune defenses in the female reproductive tract
  6. HIV-specific IgA in cervical secretions
  7. HIV-specific T cells, inflammation, and CD4 depletion in the lower female reproductive tract
  8. Sexually transmitted infections alter the mucosal microenvironment
  9. Exposure to semen induces inflammatory responses in the female genital tract
  10. The upper reproductive tract and HIV infection
  11. Changes in the upper reproductive tract during the menstrual cycle
  12. Uterine natural killer (NK) cells: a novel cell type with an unusual dual role
  13. Immunological parallels between the reproductive and gastrointestinal tracts
  14. Implications for studies on prevention of HIV infection and HIV immunopathogenesis
  15. Acknowledgments
  16. References

Other sexually transmitted infections are frequently present when HIV exposure occurs, and these infections may alter the mucosal immune environment in ways that facilitate HIV transmission (reviewed by Kaul et al.37). For example, infection with C. trachomatis, a pathogen of the columnar epithelium, results in increases in the number of CD4+ and CD8+ T cells, neutrophils, CD14+ monocytes, and CD83+ dendritic cells.38,39 Similarly, increased concentrations of a wide range of cytokines are found in genital tract tissues and secretions during infection with C. trachomatis, including INFγ, TNFα, IL-1α, IL-6, IL-8, and IL-10, contributing to an escalating inflammatory response. In contrast, human papillomavirus infections do not elicit an intense inflammatory response, but intraepithelial lesions produced by these viruses may impair barrier function and increase HIV access to susceptible cell types.40 Less invasive infections, such as bacterial vaginosis, also produce immunologic responses that may facilitate HIV transmission. St John et al. compared the effects of vaginal fluid from women with bacterial vaginosis or healthy controls on monocyte-derived dendritic cells. Fluids from women with bacterial vaginosis, but not controls, induced the production of IL-12 and IL-23, increased the expression of dendritic cell activation markers (HLA-DR, CD40, and CD83), and stimulated the proliferation of T cells in allogeneic mixed lymphocyte reactions.41 Chancroid is one of the STDs most closely associated with HIV transmission, perhaps owing to extensive disruption of the epithelial barrier, bleeding, and recruitment of susceptible cells.42 In addition, Humphreys et al.43 reported that experimental infection with Haemophilus ducreyi resulted in increased expression of HIV coreceptors by macrophages and CD4+ T-cells in chancroid lesions. Genital infections with herpes simplex viruses (HSV) lead to increases in cervical dendritic cells and CCR5-expressing CD4+ T cells.44 Additionally, some HSV proteins can transactivate HIV gene expression, while others can serve as immune modulators.45

Exposure to semen induces inflammatory responses in the female genital tract

  1. Top of page
  2. Abstract
  3. Introduction
  4. HIV infection of the female reproductive tract: local inflammation leads to rapid viral dissemination
  5. Innate immune defenses in the female reproductive tract
  6. HIV-specific IgA in cervical secretions
  7. HIV-specific T cells, inflammation, and CD4 depletion in the lower female reproductive tract
  8. Sexually transmitted infections alter the mucosal microenvironment
  9. Exposure to semen induces inflammatory responses in the female genital tract
  10. The upper reproductive tract and HIV infection
  11. Changes in the upper reproductive tract during the menstrual cycle
  12. Uterine natural killer (NK) cells: a novel cell type with an unusual dual role
  13. Immunological parallels between the reproductive and gastrointestinal tracts
  14. Implications for studies on prevention of HIV infection and HIV immunopathogenesis
  15. Acknowledgments
  16. References

While it is vital to elucidate the immunologic characteristics of the intact female genital tract, HIV exposure often occurs in the context of semen; thus, the effects of semen on these immunologic functions must also be understood. In addition to perturbations related to genital tract infections, semen and seminal plasma also alter the immunologic milieu of the female genital tract in a manner that facilitates conception and pregnancy.11 The proinflammatory effects of insemination are well documented and referred to as the ‘post-mating inflammatory response’ that is characterized by an increase in the synthesis of cytokines including GM-CSF, MCP-1 and IL-6 and the migration of macrophages, dendritic cells and granulocytes into the endometrial stroma.46 Leukocytes also migrate into the cervical epithelium, an occurrence that requires direct contact between seminal plasma and female genital tissues and is related to increases in GM-CSF, IL-6, and IL-8.46 Seminal fluid taken from healthy men, and free of leukocytes, significantly increased TGF-β1 and IL-1β levels in the supernatants of endometrial epithelial cell cultures.47 In mouse experiments, TGFβ was the principal elicitor of uterine inflammation following mating.48 The TGFβ1 content of semen is comparable to that of colostrum, the most potent biological source of this cytokine.46 Semen from healthy men also contains significant levels of IL-7, SDF1α, MCP-1, and IL-8.49 After insemination, TGFβ1 tends to limit Th1-type responses, including those to paternal alloantigens that could undermine fertility.50 Robertson et al.51 reported that exposure to semen results in increases in CD4+ CD25+ Foxp3+ regulatory T cells in mice and tolerance to paternal antigens. Thus, semen is a potent immune modulator in the cervix and uterus and its effects on susceptibility to HIV infection are largely undefined.

The upper reproductive tract and HIV infection

  1. Top of page
  2. Abstract
  3. Introduction
  4. HIV infection of the female reproductive tract: local inflammation leads to rapid viral dissemination
  5. Innate immune defenses in the female reproductive tract
  6. HIV-specific IgA in cervical secretions
  7. HIV-specific T cells, inflammation, and CD4 depletion in the lower female reproductive tract
  8. Sexually transmitted infections alter the mucosal microenvironment
  9. Exposure to semen induces inflammatory responses in the female genital tract
  10. The upper reproductive tract and HIV infection
  11. Changes in the upper reproductive tract during the menstrual cycle
  12. Uterine natural killer (NK) cells: a novel cell type with an unusual dual role
  13. Immunological parallels between the reproductive and gastrointestinal tracts
  14. Implications for studies on prevention of HIV infection and HIV immunopathogenesis
  15. Acknowledgments
  16. References

The common occurrence of sexual transmission of HIV to women via vaginal intercourse was debated early in the AIDS epidemic, and anal intercourse was implicated as a possible mode of male-to-female transmission in the few incidents that were recognized.52 Two key reports53,54 indicated that male-to-female transmission occurred more regularly, but in these studies, infection was detected in women who had undergone hysterectomy, and although these cross-sectional studies could not determine that hysterectomy preceded HIV transmission, the studies may have been interpreted as indicating that the upper genital tract was not a common site of HIV transmission. Most studies of HIV transmission to women, including studies of vaccine responses and microbicides, have focused on the lower genital tract.

The assumption that sexual HIV transmission to women occurs in the lower genital tract is not surprising because the upper tract is generally thought to be a sterile environment that is not easily accessed. However, MRI studies demonstrate that intravaginal gels reach the endocervix and uterus within minutes of application.55,56 Once in the uterus, non-oxynol gels produce significant disruption of the endometrium including focal absence of the uterine epithelium proximal to the cervix,55 hemorrhage, and areas of necrosis,55 as well as increased densities of CD8+ and Foxp3+ cells.57

The uterus contains a variety of cell types that are susceptible to HIV infection, including CD4+ T cells expressing CXCR4 and/or CCR5 as well as monocyte/macrophages. A polarized human endometrial epithelial cell line, HEC-1, has been shown to efficiently transcytose both X4 and R5 tropic strains of HIV,58,59 allowing the transfer of virus to susceptible target cells situated near the basolateral surface. Primary uterine epithelial cells can also transfer virus to CD4+ T cells in vitro.60 In one recent study, primary tissue explants derived from ectocervix and endometrium of HIV-negative premenopausal women were infected ex vivo with R5-tropic HIV and viral transcription levels in the two tissue types were compared using real-time polymerase chain reaction. Significantly higher levels of HIV transcription were detected in ectocervical tissues when compared to endometrial explants, suggesting that ectocervix may be more permissive than endometrium for HIV replication.61 This may be related to a relatively higher density of T cells and dendritic cells in the cervix, particularly the cervical transformation zone, when compared to the upper reproductive tract.61,62

Few studies have addressed HIV-specific T-cell responses in the upper female reproductive tract. White et al.63 measured HIV-specific cytotoxic T-cell (CTL) activity in PBMC and a variety of upper and lower reproductive tissues from three HIV-positive women, including one long-term non-progressor (LTNP) and two women on highly active antiretroviral therapy (HAART). HIV-specific T-cell responses were found in ovaries, endometrium, and endocervix of the LTNP, but such responses were not detected in the two women on HAART. Although limited in scope, these findings demonstrate that HIV-specific T-cell responses are present in the upper reproductive tract under some conditions and provide a basis for further study.

Changes in the upper reproductive tract during the menstrual cycle

  1. Top of page
  2. Abstract
  3. Introduction
  4. HIV infection of the female reproductive tract: local inflammation leads to rapid viral dissemination
  5. Innate immune defenses in the female reproductive tract
  6. HIV-specific IgA in cervical secretions
  7. HIV-specific T cells, inflammation, and CD4 depletion in the lower female reproductive tract
  8. Sexually transmitted infections alter the mucosal microenvironment
  9. Exposure to semen induces inflammatory responses in the female genital tract
  10. The upper reproductive tract and HIV infection
  11. Changes in the upper reproductive tract during the menstrual cycle
  12. Uterine natural killer (NK) cells: a novel cell type with an unusual dual role
  13. Immunological parallels between the reproductive and gastrointestinal tracts
  14. Implications for studies on prevention of HIV infection and HIV immunopathogenesis
  15. Acknowledgments
  16. References

The immune microenvironment of the uterine endometrium fluctuates during the menstrual cycle, and significant changes in cell populations, growth factors, cytokines, and adhesion molecules may be required to promote embryo implantation. There is a short window during the mid-secretory phase, limited to about 48 hr, during which conditions are favorable for implantation (for a review, see Aghajanova et al.64). This implantation window typically begins 6–10 days after the surge in luteinizing hormone (LH), roughly days 20–24 of an idealized menstrual cycle. Gene expression changes include the upregulation of endometrial growth factors, cytokines and adhesion molecules, coupled with the downregulation of genes associated with cell-mediated immunity and the classical complement pathway.

The hormonal fluctuations associated with the menstrual cycle regulate a variety of features of the reproductive tract that may directly impact susceptibility to HIV infection and persistence. Several years ago, White et al.65 demonstrated that cytolytic activity by CD8+ T cells in the upper reproductive tract, as measured by redirected lysis assays, was present during the proliferative phase of the menstrual cycle (prior to ovulation), yet absent during the secretory phase. Notably, in contrast to the upper reproductive tract, CTL activity in the cervix and vagina persisted throughout the menstrual cycle.66 Postmenopausal women also retained strong cytotoxic T-cell populations in the upper tract. Taken together, these observations suggest tight post-ovulatory regulation of cell-mediated immunity to facilitate the implantation of the semi-allogeneic embryo. It is proposed that these fluctuations might contribute to a cycle-dependent ‘window of vulnerability’ to HIV infection in the upper reproductive tract.67 Expression of CD4, CCR5, and CXCR4 by uterine epithelial cells and other cell types may also be temporally regulated during the menstrual cycle, with consequences for HIV infection and dissemination.68,69

Finally, the uterine endometrium also contains hormonally regulated, organized cellular aggregates, consisting of a B-cell core surrounded by CD8+ T cells and macrophages, which are located in the stratum basalis layer.70 Aggregate size is smallest during the proliferative phase of the menstrual cycle, largest during the secretory phase, and absent from postmenopausal women. Whether these structures play an active role in antiviral defense is currently unknown.

Uterine natural killer (NK) cells: a novel cell type with an unusual dual role

  1. Top of page
  2. Abstract
  3. Introduction
  4. HIV infection of the female reproductive tract: local inflammation leads to rapid viral dissemination
  5. Innate immune defenses in the female reproductive tract
  6. HIV-specific IgA in cervical secretions
  7. HIV-specific T cells, inflammation, and CD4 depletion in the lower female reproductive tract
  8. Sexually transmitted infections alter the mucosal microenvironment
  9. Exposure to semen induces inflammatory responses in the female genital tract
  10. The upper reproductive tract and HIV infection
  11. Changes in the upper reproductive tract during the menstrual cycle
  12. Uterine natural killer (NK) cells: a novel cell type with an unusual dual role
  13. Immunological parallels between the reproductive and gastrointestinal tracts
  14. Implications for studies on prevention of HIV infection and HIV immunopathogenesis
  15. Acknowledgments
  16. References

NK cells are distributed throughout the body and play a major role in immunosurveillance of virally infected and neoplastic cells. NK cells utilize a variety of effector mechanisms, including the release of cytolytic granules containing perforin and granzymes, the production and release of cytokines, and antibody-dependent cellular cytotoxicity (ADCC71). Uterine NK cells (uNK) differ in cell surface phenotype from their counterparts in peripheral blood, typically expressing CD56 but not CD16 or CD57. Their density in the uterine endometrium increases after ovulation. uNK cells appear to secrete a variety of cytokines and growth factors that help prepare the endometrium for embryo implantation. However, high uterine NK activity is also associated with recurrent miscarriage.72,73 The extent to which these unique cells may participate in antiviral defense in the reproductive tract is currently unknown.

Immunological parallels between the reproductive and gastrointestinal tracts

  1. Top of page
  2. Abstract
  3. Introduction
  4. HIV infection of the female reproductive tract: local inflammation leads to rapid viral dissemination
  5. Innate immune defenses in the female reproductive tract
  6. HIV-specific IgA in cervical secretions
  7. HIV-specific T cells, inflammation, and CD4 depletion in the lower female reproductive tract
  8. Sexually transmitted infections alter the mucosal microenvironment
  9. Exposure to semen induces inflammatory responses in the female genital tract
  10. The upper reproductive tract and HIV infection
  11. Changes in the upper reproductive tract during the menstrual cycle
  12. Uterine natural killer (NK) cells: a novel cell type with an unusual dual role
  13. Immunological parallels between the reproductive and gastrointestinal tracts
  14. Implications for studies on prevention of HIV infection and HIV immunopathogenesis
  15. Acknowledgments
  16. References

The gut, of course, differs considerably from endometrium in terms of location, morphology, and basic function (intake of nutrients and elimination of wastes). The endometrium’s function is to support implantation of the embryo and sustenance until the placenta is fully developed. However, the similarities between the tissues are numerous. Both sites have a dual role in maintaining a tolerogenic microenvironment while retaining rapid responsiveness to pathogens (Table I).12,74 The ectocervix and vagina, like the lower anorectal canal, are characterized as type II mucosal tissues, lined with stratified squamous epithelia and lacking organized mucosa-associated lymphoid tissue (MALT) structures. The endocervix and uterus, as well as the rectum and most of the large and small intestine, are characterized as type I mucosal tissues, lined with simple columnar epithelium. These tissues produce secretory immunoglobulin, type A (sIgA), and can have organized MALT structures, including hormonally regulated uterine cellular aggregates, lymphoid follicles in the rectum, and intestinal Peyer’s patches.

Table I.   Immunological Properties Shared by the Female Reproductive Tract and Gastrointestinal Tract
PropertyFemale reproductive tractGastrointestinal tract
  1. MALT, mucosa-associated lymphoid tissue; TCR, T-cell receptor; TLR, toll-like receptor; iNOS, inducible nitric oxide synthase; PRR, pattern recognition receptor; NLR, NOD-like receptor.

Major portal of entry for HIVActivated CD4+ cells expressing CCR5, CXCR4Activated CD4+ cells expressing CCR5, CXCR4
Presence of type I mucosa  Simple columnar epithelium  Secretory IgA  Presence of MALTEndocervix, uterusRectum, large and small intestine
Presence of type II mucosa  Stratified squamous epithelium  Major antibody: IgG  Absence of MALTEctocervix, vaginaLower anorectal canal
Mucus contributes to barrier functionProduced by vaginal epithelial cells, cervical cryptsProduced by goblet cells
Epithelial cells play multiple roles: barrier function, antigen presentation, cytokine secretion, and transcytosis of antigensYesYes
Beneficial endogenous floraLactobacilli prevent overgrowth of harmful bacteria Secretion of lactic acid maintains low pHRole in metabolism, vitamin synthesis Stimulate production of iNOS and IgA TLR engagement promotes epithelial homeostasis
Immunologic toleranceDirected toward preservation of conceptus Relies on complex mechanisms involving cytokines and TregDirected toward flora and food antigens Relies on complex mechanisms involving cytokines and Treg
Novel effector cell populationsUterine NK cells with unique phenotype TCR gamma delta cells Intraepithelial CD8+ T cells Th17 cellsGut NK cells with unique phenotype TCR gamma delta cells Intraepithelial CD8+ T cells Th17 cells
Innate effector moleculesSLPI, lactoferrin, defensins PRR (TLR, NLR) very important in defenseLysozyme, cathelicidins, defensins PRR (TLR, NLR) very important in defense
Sex steroid responsivenessSignificant modulation of tissue architecture, development of inducible MALTEstrogen receptor ligands affect crypt/villus architecture and may play a role in inflammatory bowel diseases

Both the reproductive and gastrointestinal tracts are protected by mucus layers, and by epithelial cells that play multiple roles in barrier function, antigen presentation, secretion of cytokines, chemokines, and growth factors, and transcytosis of macromolecules. Both tissue systems are extensively colonized by endogenous flora. These flora both prevent the overgrowth of pathogenic bacteria and provide useful ‘housekeeping’ functions; in the case of intestinal flora, these include the synthesis of vitamins and hormones, stimulation of inducible nitric oxide synthase75 and IgA76,77 production, and the maintenance of epithelial homeostasis through signaling of toll-like receptor (TLR) pathways.78

Both the reproductive and gastrointestinal tracts engage in immunological tolerance. In the reproductive tract, tolerance is related to the implantation and preservation of a semi-allogeneic embryo; in the GI tract, tolerance is maintained with respect to food antigens and commensal bacteria. At both sites, the mechanisms regulating tolerance are complex and appear to involve Foxp3+ regulatory T cells and immunosuppressive cytokines such as TGF-β.

Th17/CD4+ cells and IL-17 play important roles at each site. Depletion of Th17+ cells and lack of IL-17 are associated with impaired intestinal barrier function, as illustrated by the increased dissemination of Salmonella typhimurium in SIV-infected macaques.79,80 In humans, IL-17 and related cytokines are involved in a number of autoimmune and inflammatory disorders, including inflammatory bowel disease,81,82 conditions that, like HIV infection, are characterized by altered gut barrier function.83 In the female genital tract, Th17 cells and IL-17 are associated with increased IL-8 and endometriosis84 and have been implicated in spontaneous abortion.85

From the perspective of HIV infection, both the reproductive and gastrointestinal tracts serve as important portals of entry. Both tissues are rich in partially activated CD4+ memory T cells, many of which express CCR5 and/or CXCR4. Both harbor significant populations of HIV-specific memory CD8+ T cells. Our laboratories are currently studying HIV-specific CD8+ T-cell responses in blood, reproductive mucosa, and gastrointestinal mucosa of HIV-infected women.74,86 Although these studies are still preliminary, early results suggest that there are significant differences in antigen responsiveness between CD8+ T cells isolated from endometrial biopsy when compared to those from PBMC or the gastrointestinal tract of the same individuals (Fig. 1). Additional studies will be required to extend these results.

image

Figure 1.  CD8+ T-cell responses to HIV Gag peptides (left) and a mixture of immunodominant peptides derived from cytomegalovirus, Epstein–Barr virus, and Influenza A (C-E-F) (right). Freshly isolated lymphocytes from PBMC, endometrial biopsy, and sigmoid colon were tested in a cytokine flow cytometry assay for production of IFNγ and the cytolytic granule marker CD107a in response to peptide stimulation. Numbers in individual quadrants indicate the number of cells producing either IFNγ (upper left quadrant), CD107 (lower right quadrant) or both IFNγ and CD107 (upper right quadrant) in response to peptide stimulation. Assays were performed as described elsewhere.88,89 The samples used in this experiment were obtained from a premenopausal HIV-positive woman on long-term highly active antiretroviral therapy (9 years), with plasma viral load <75 copies/mL, blood CD4+ T-cell count 1180, from whom blood and tissue samples were obtained on day 24 of the menstrual cycle.

Download figure to PowerPoint

Implications for studies on prevention of HIV infection and HIV immunopathogenesis

  1. Top of page
  2. Abstract
  3. Introduction
  4. HIV infection of the female reproductive tract: local inflammation leads to rapid viral dissemination
  5. Innate immune defenses in the female reproductive tract
  6. HIV-specific IgA in cervical secretions
  7. HIV-specific T cells, inflammation, and CD4 depletion in the lower female reproductive tract
  8. Sexually transmitted infections alter the mucosal microenvironment
  9. Exposure to semen induces inflammatory responses in the female genital tract
  10. The upper reproductive tract and HIV infection
  11. Changes in the upper reproductive tract during the menstrual cycle
  12. Uterine natural killer (NK) cells: a novel cell type with an unusual dual role
  13. Immunological parallels between the reproductive and gastrointestinal tracts
  14. Implications for studies on prevention of HIV infection and HIV immunopathogenesis
  15. Acknowledgments
  16. References

Women are increasingly affected by the HIV epidemic worldwide and now account for nearly half the 33 million individuals living with HIV.87 In sub-Saharan Africa, women account for approximately 60% of HIV infections.87 As the HIV/AIDS epidemic enters its second quarter century, many questions remain unanswered concerning the disease process and many more studies are needed to advance our understanding of HIV pathogenesis in women.

Owing to the susceptibility of endocervical and endometrial cell populations, these tissues are potential sites of HIV infection. Current data do not indicate the relative frequency of any female genital site as the location of initial HIV infection, and it is possible that tissue-specific susceptibility to infection depends on the existence of factors such as sexually transmitted infections, trauma, ovulatory cycle, seminal plasma effects, or hormonal modulators of genital immune responses. Thus, the upper tract tissues should be considered in studies of HIV vaccines, microbicides, and other prevention interventions. Several studies point to a potential ‘window of vulnerability’ to HIV infection at 7–10 days following ovulation.67 Addressing this question in the laboratory will require detailed studies of mucosal immunity in women across the menstrual cycle and a better understanding of the influence of reproductive hormones on adaptive and innate mucosal immunity. A second and related area of interest is the potential influence of hormonal contraception on HIV transmission.

Because semen and seminal fluids influence female genital immunology, studies of the tissue effects of prevention modalities must also include evaluations of semen exposure. Studies of the postmenopausal genital tract, and HIV susceptibility and shedding are also needed, given the increased survival of HIV patients and the large number of women who are living with this infection worldwide.

The limited existing evidence indicates that HIV exerts parallel effects on mucosal lymphoid tissues in the gut and endometrium. Although the rapid CD4+ T-cell decline that occurs during acute HIV infection of the GI tract has been extensively studied, much less is known about the effects of acute HIV infection on reproductive tissues. Similarly, the role of immune activation and inflammation within the reproductive tract on HIV disease has not been thoroughly studied, nor have the effects of HAART on CD4+ T-cell repopulation in the reproductive mucosa. These questions should prompt further study because endometrial tissues are readily obtained and no enteric preparation is required. Because tissue sampling in human studies of infrequent HIV phenotypes, such as in acute infection, is often problematic, the use of endometrial sampling may provide an opportunity to obtain MALT tissues more readily.

Acknowledgments

  1. Top of page
  2. Abstract
  3. Introduction
  4. HIV infection of the female reproductive tract: local inflammation leads to rapid viral dissemination
  5. Innate immune defenses in the female reproductive tract
  6. HIV-specific IgA in cervical secretions
  7. HIV-specific T cells, inflammation, and CD4 depletion in the lower female reproductive tract
  8. Sexually transmitted infections alter the mucosal microenvironment
  9. Exposure to semen induces inflammatory responses in the female genital tract
  10. The upper reproductive tract and HIV infection
  11. Changes in the upper reproductive tract during the menstrual cycle
  12. Uterine natural killer (NK) cells: a novel cell type with an unusual dual role
  13. Immunological parallels between the reproductive and gastrointestinal tracts
  14. Implications for studies on prevention of HIV infection and HIV immunopathogenesis
  15. Acknowledgments
  16. References

The authors thank Drs. Linda Giudice, Warner C. Greene, Laura Napolitano, and Karen Smith-McCune, University of California at San Francisco, for their ongoing collaboration and Dr. Charles Wira, Dartmouth University, for thought-provoking discussions. B.L.S. thanks Dr. J.W. Critchfield, University of California at Davis, for contributing the data shown in Fig. 1. This research is supported by the National Institutes of Health (NIH-NIAID R01 AI-057020 and P01 AI-083050). This research was approved by the Institutional Review Board of UC Davis and the Committee for Human Subjects Research of UC San Francisco.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. HIV infection of the female reproductive tract: local inflammation leads to rapid viral dissemination
  5. Innate immune defenses in the female reproductive tract
  6. HIV-specific IgA in cervical secretions
  7. HIV-specific T cells, inflammation, and CD4 depletion in the lower female reproductive tract
  8. Sexually transmitted infections alter the mucosal microenvironment
  9. Exposure to semen induces inflammatory responses in the female genital tract
  10. The upper reproductive tract and HIV infection
  11. Changes in the upper reproductive tract during the menstrual cycle
  12. Uterine natural killer (NK) cells: a novel cell type with an unusual dual role
  13. Immunological parallels between the reproductive and gastrointestinal tracts
  14. Implications for studies on prevention of HIV infection and HIV immunopathogenesis
  15. Acknowledgments
  16. References
  • 1
    Haase AT: Targeting early infection to prevent HIV-1 mucosal transmission. Nature 2010; 464:217223.
  • 2
    Hladik F, Hope TJ: HIV infection of the genital mucosa in women. Curr HIV/AIDS Rep 2009; 6:2028.
  • 3
    Hladik F, McElrath MJ: Setting the stage: host invasion by HIV. Nat Rev Immunol 2008; 8:447457.
  • 4
    Quinn TC, Wawer MJ, Sewankambo N, Serwadda D, Li C, Wabwire-Mangen F, Meehan MO, Lutalo T, Gray RH: Viral load and heterosexual transmission of human immunodeficiency virus type 1. Rakai Project Study Group. N Engl J Med 2000; 342:921929.
  • 5
    Li Q, Estes JD, Schlievert PM, Duan L, Brosnahan AJ, Southern PJ, Reilly CS, Peterson ML, Schultz-Darken N, Brunner KG, Nephew KR, Pambuccian S, Lifson JD, Carlis JV, Haase AT: Glycerol monolaurate prevents mucosal SIV transmission. Nature 2009; 458:10341038.
  • 6
    Reynolds MR, Rakasz E, Skinner PJ, White C, Abel K, Ma ZM, Compton L, Napoe G, Wilson N, Miller CJ, Haase A, Watkins DI: CD8+ T-lymphocyte response to major immunodominant epitopes after vaginal exposure to simian immunodeficiency virus: too late and too little. J Virol 2005; 79:92289235.
  • 7
    Favre D, Lederer S, Kanwar B, Ma ZM, Proll S, Kasakow Z, Mold J, Swainson L, Barbour JD, Baskin CR, Palermo R, Pandrea I, Miller CJ, Katze MG, McCune JM: Critical loss of the balance between Th17 and T regulatory cell populations in pathogenic SIV infection. PLoS Pathog 2009; 5:e1000295.
  • 8
    Li Q, Duan L, Estes JD, Ma ZM, Rourke T, Wang Y, Reilly C, Carlis J, Miller CJ, Haase AT: Peak SIV replication in resting memory CD4+ T cells depletes gut lamina propria CD4+ T cells. Nature 2005; 434:11481152.
  • 9
    Mattapallil JJ, Douek DC, Hill B, Nishimura Y, Martin M, Roederer M: Massive infection and loss of memory CD4+ T cells in multiple tissues during acute SIV infection. Nature 2005; 434:10931097.
  • 10
    Veazey R, DeMaria M, Chalifoux L, Shvetz D, Pauley D, Knight H, Rosenzweig M, Johnson R, Desrosiers R, Lackner A: Gastrointestinal tract as a major site of CD4+ T cell depletion and viral replication in SIV infection. Science 1998; 280:427431.
  • 11
    Schuberth HJ, Taylor U, Zerbe H, Waberski D, Hunter R, Rath D: Immunological responses to semen in the female genital tract. Theriogenology 2008; 70:11741181.
  • 12
    Iwasaki A: Antiviral immune responses in the genital tract: clues for vaccines. Nat Rev Immunol 2010; 10:699711.
  • 13
    Fahey JV, Wira CR: Effect of menstrual status on antibacterial activity and secretory leukocyte protease inhibitor production by human uterine epithelial cells in culture. J Infect Dis 2002; 185:16061613.
  • 14
    Berkhout B, Floris R, Recio I, Visser S: The antiviral activity of the milk protein lactoferrin against the human immunodeficiency virus type 1. Biometals 2004; 17:291294.
  • 15
    Quinones-Mateu ME, Lederman MM, Feng Z, Chakraborty B, Weber J, Rangel HR, Marotta ML, Mirza M, Jiang B, Kiser P, Medvik K, Sieg SF, Weinberg A: Human epithelial beta-defensins 2 and 3 inhibit HIV-1 replication. AIDS 2003; 17:F39F48.
  • 16
    Sun L, Finnegan CM, Kish-Catalone T, Blumenthal R, Garzino-Demo P, La Terra Maggiore GM, Berrone S, Kleinman C, Wu Z, Abdelwahab S, Lu W, Garzino-Demo A: Human beta-defensins suppress human immunodeficiency virus infection: potential role in mucosal protection. J Virol 2005; 79:1431814329.
  • 17
    Fahey JV, Schaefer TM, Channon JY, Wira CR: Secretion of cytokines and chemokines by polarized human epithelial cells from the female reproductive tract. Hum Reprod 2005; 20:14391446.
  • 18
    Ghosh M, Shen Z, Fahey JV, Cu-Uvin S, Mayer K, Wira CR: Trappin-2/Elafin: a novel innate anti-human immunodeficiency virus-1 molecule of the human female reproductive tract. Immunology 2009; 129:207219.
  • 19
    Iqbal SM, Ball TB, Levinson P, Maranan L, Jaoko W, Wachihi C, Pak BJ, Podust VN, Broliden K, Hirbod T, Kaul R, Plummer FA: Elevated elafin/trappin-2 in the female genital tract is associated with protection against HIV acquisition. AIDS 2009; 23:16691677.
  • 20
    Levinson P, Kaul R, Kimani J, Ngugi E, Moses S, MacDonald KS, Broliden K, Hirbod T: Levels of innate immune factors in genital fluids: association of alpha defensins and LL-37 with genital infections and increased HIV acquisition. AIDS 2009; 23:309317.
  • 21
    Hirbod T, Kaul R, Reichard C, Kimani J, Ngugi E, Bwayo JJ, Nagelkerke N, Hasselrot K, Li B, Moses S, MacDonald KS, Broliden K: HIV-neutralizing immunoglobulin A and HIV-specific proliferation are independently associated with reduced HIV acquisition in Kenyan sex workers. AIDS 2008; 22:727735.
  • 22
    Devito C, Hinkula J, Kaul R, Lopalco L, Bwayo JJ, Plummer F, Clerici M, Broliden K: Mucosal and plasma IgA from HIV-exposed seronegative individuals neutralize a primary HIV-1 isolate. AIDS 2000; 14:19171920.
  • 23
    Belec L, Ghys PD, Hocini H, Nkengasong JN, Tranchot-Diallo J, Diallo MO, Ettiegne-Traore V, Maurice C, Becquart P, Matta M, Si-Mohamed A, Chomont N, Coulibaly IM, Wiktor SZ, Kazatchkine MD: Cervicovaginal secretory antibodies to human immunodeficiency virus type 1 (HIV-1) that block viral transcytosis through tight epithelial barriers in highly exposed HIV-1-seronegative African women. J Infect Dis 2001; 184:14121422.
  • 24
    Alexander R, Mestecky J: Neutralizing antibodies in mucosal secretions: IgG or IgA? Curr HIV Res 2007; 5:588593.
  • 25
    Broliden K: Innate molecular and anatomic mucosal barriers against HIV infection in the genital tract of HIV-exposed seronegative individuals. J Infect Dis 2010; 202(Suppl 3):S351S355.
  • 26
    Tudor D, Derrien M, Diomede L, Drillet AS, Houimel M, Moog C, Reynes JM, Lopalco L, Bomsel M: HIV-1 gp41-specific monoclonal mucosal IgAs derived from highly exposed but IgG-seronegative individuals block HIV-1 epithelial transcytosis and neutralize CD4(+) cell infection: an IgA gene and functional analysis. Mucosal Immunol 2009; 2:412426.
  • 27
    Musey L, Ding Y, Cao J, Lee J, Galloway C, Yuen A, Jerome KR, McElrath MJ: Ontogeny and specificities of mucosal and blood human immunodeficiency virus type 1-specific CD8(+) cytotoxic T lymphocytes. J Virol 2003; 77:291300.
  • 28
    Musey L, Hu Y, Eckert L, Christensen M, Karchmer T, McElrath MJ: HIV-1 induces cytotoxic T lymphocytes in the cervix of infected women. J Exp Med 1997; 185:293303.
  • 29
    Bebell LM, Passmore JA, Williamson C, Mlisana K, Iriogbe I, van Loggerenberg F, Karim QA, Karim SA: Relationship between levels of inflammatory cytokines in the genital tract and CD4+ cell counts in women with acute HIV-1 infection. J Infect Dis 2008; 198:710714.
  • 30
    Bere A, Denny L, Burgers WA, Passmore JA: Polyclonal expansion of cervical cytobrush-derived T cells to investigate HIV-specific responses in the female genital tract. Immunology 2010; 130:2333.
  • 31
    Bere A, Denny L, Hanekom W, Burgers WA, Passmore JA: Comparison of polyclonal expansion methods to improve the recovery of cervical cytobrush-derived T cells from the female genital tract of HIV-infected women. J Immunol Methods 2010; 354:6879.
  • 32
    Gumbi PP, Nkwanyana NN, Bere A, Burgers WA, Gray CM, Williamson AL, Hoffman M, Coetzee D, Denny L, Passmore JA: Impact of mucosal inflammation on cervical HIV-1-specific CD8 T cell responses in the female genital tract during chronic HIV infection. J Virol 2008; 82:85298536.
  • 33
    Mkhize NN, Gumbi PP, Liebenberg LJ, Ren Y, Smith P, Denny L, Passmore JA: Persistence of genital tract T cell responses in HIV-infected women on highly active antiretroviral therapy. J Virol 2010; 84:1076510772.
  • 34
    Nkwanyana NN, Gumbi PP, Roberts L, Denny L, Hanekom W, Soares A, Allan B, Williamson AL, Coetzee D, Olivier AJ, Burgers WA, Passmore JA: Impact of human immunodeficiency virus 1 infection and inflammation on the composition and yield of cervical mononuclear cells in the female genital tract. Immunology 2009; 128:e746e757.
  • 35
    Kaul R, Thottingal P, Kimani J, Kiama P, Waigwa CW, Bwayo JJ, Plummer FA, Rowland-Jones SL: Quantitative ex vivo analysis of functional virus-specific CD8 T lymphocytes in the blood and genital tract of HIV-infected women. AIDS 2003; 17:11391144.
  • 36
    Shacklett BL, Cu-Uvin S, Beadle TJ, Pace CA, Fast NM, Donahue SM, Caliendo AM, Flanigan TP, Carpenter CC, Nixon DF: Quantification of HIV-1-specific T-cell responses at the mucosal cervicovaginal surface. AIDS 2000; 14:19111915.
  • 37
    Kaul R, Pettengell C, Sheth PM, Sunderji S, Biringer A, MacDonald K, Walmsley S, Rebbapragada A: The genital tract immune milieu: an important determinant of HIV susceptibility and secondary transmission. J Reprod Immunol 2008; 77:3240.
  • 38
    Agrawal T, Vats V, Salhan S, Mittal A: The mucosal immune response to Chlamydia trachomatis infection of the reproductive tract in women. J Reprod Immunol 2009; 83:173178.
  • 39
    Mittal A, Rastogi S, Reddy BS, Verma S, Salhan S, Gupta E: Enhanced immunocompetent cells in chlamydial cervicitis. J Reprod Med 2004; 49:671677.
  • 40
    Smith-McCune KK, Shiboski S, Chirenje MZ, Magure T, Tuveson J, Ma Y, Da Costa M, Moscicki AB, Palefsky JM, Makunike-Mutasa R, Chipato T, van der Straten A, Sawaya GF: Type-specific cervico-vaginal human papillomavirus infection increases risk of HIV acquisition independent of other sexually transmitted infections. PLoS ONE 2010; 5:e10094.
  • 41
    St John EP, Martinson J, Simoes JA, Landay AL, Spear GT: Dendritic cell activation and maturation induced by mucosal fluid from women with bacterial vaginosis. Clin Immunol 2007; 125:95102.
  • 42
    Greenblatt RM, Lukehart SA, Plummer FA, Quinn TC, Critchlow CW, Ashley RL, D’Costa LJ, Ndinya-Achola JO, Corey L, Ronald AR, Holmes KK: Genital ulceration as a risk factor for human immunodeficiency virus infection. AIDS 1988; 2:4750.
  • 43
    Humphreys TL, Schnizlein-Bick CT, Katz BP, Baldridge LA, Hood AF, Hromas RA, Spinola SM: Evolution of the cutaneous immune response to experimental Haemophilus ducreyi infection and its relevance to HIV-1 acquisition. J Immunol 2002; 169:63166323.
  • 44
    Rebbapragada A, Wachihi C, Pettengell C, Sunderji S, Huibner S, Jaoko W, Ball B, Fowke K, Mazzulli T, Plummer FA, Kaul R: Negative mucosal synergy between Herpes simplex type 2 and HIV in the female genital tract. AIDS 2007; 21:589598.
  • 45
    Van de Perre P, Segondy M, Foulongne V, Ouedraogo A, Konate I, Huraux JM, Mayaud P, Nagot N: Herpes simplex virus and HIV-1: deciphering viral synergy. Lancet Infect Dis 2008; 8:490497.
  • 46
    Robertson SA: Seminal plasma and male factor signalling in the female reproductive tract. Cell Tissue Res 2005; 322:4352.
  • 47
    Ochsenkuhn R, Toth B, Nieschlag E, Artman E, Friese K, Thaler CJ: Seminal plasma stimulates cytokine production in endometrial epithelial cell cultures independently of the presence of leucocytes. Andrologia 2008; 40:364369.
  • 48
    Tremellen KP, Seamark RF, Robertson SA: Seminal transforming growth factor beta1 stimulates granulocyte-macrophage colony-stimulating factor production and inflammatory cell recruitment in the murine uterus. Biol Reprod 1998; 58:12171225.
  • 49
    Politch JA, Tucker L, Bowman FP, Anderson DJ: Concentrations and significance of cytokines and other immunologic factors in semen of healthy fertile men. Hum Reprod 2007; 22:29282935.
  • 50
    Robertson SA: Seminal fluid signaling in the female reproductive tract: lessons from rodents and pigs. J Anim Sci 2007; 85:E36E44.
  • 51
    Robertson SA, Guerin LR, Moldenhauer LM, Hayball JD: Activating T regulatory cells for tolerance in early pregnancy – the contribution of seminal fluid. J Reprod Immunol 2009; 83:109116.
  • 52
    Melbye M, Ingerslev J, Biggar RJ, Alexander S, Sarin PS, Goedert JJ, Zachariae E, Ebbesen P, Stenbjerg S: Anal intercourse as a possible factor in heterosexual transmission of HTLV-III to spouses of hemophiliacs. N Engl J Med 1985; 312:857.
  • 53
    Goedert JJ, Eyster ME, Biggar RJ, Blattner WA: Heterosexual transmission of human immunodeficiency virus: association with severe depletion of T-helper lymphocytes in men with hemophilia. AIDS Res Hum Retroviruses 1987; 3:355361.
  • 54
    Kreiss JK, Kitchen LW, Prince HE, Kasper CK, Essex M: Antibody to human T-lymphotropic virus type III in wives of hemophiliacs. Evidence for heterosexual transmission. Ann Intern Med 1985; 102:623626.
  • 55
    Dayal MB, Wheeler J, Williams CJ, Barnhart KT: Disruption of the upper female reproductive tract epithelium by nonoxynol-9. Contraception 2003; 68:273279.
  • 56
    Barnhart KT, Stolpen A, Pretorius ES, Malamud D: Distribution of a spermicide containing Nonoxynol-9 in the vaginal canal and the upper female reproductive tract. Hum Reprod 2001; 16:11511154.
  • 57
    Rahangdale L, Greenblatt RM, Perry J, Darragh TM, Kobayashi A, Smith-McCune KK: In vivo effects of nonoxynol-9 on endometrial immune cell populations. J Acquir Immune Defic Syndr 2009; 52:137139.
  • 58
    Saidi H, Magri G, Nasreddine N, Requena M, Belec L: R5- and X4-HIV-1 use differentially the endometrial epithelial cells HEC-1A to ensure their own spread: implication for mechanisms of sexual transmission. Virology 2007; 358:5568.
  • 59
    Saidi H, Magri G, Carbonneil C, Bouhlal H, Hocini H, Belec L: Apical interactions of HIV type 1 with polarized HEC-1 cell monolayer modulate R5-HIV type 1 spread by submucosal macrophages. AIDS Res Hum Retroviruses 2009; 25:497509.
  • 60
    Asin SN, Fanger MW, Wildt-Perinic D, Ware PL, Wira CR, Howell AL: Transmission of HIV-1 by primary human uterine epithelial cells and stromal fibroblasts. J Infect Dis 2004; 190:236245.
  • 61
    Asin SN, Eszterhas SK, Rollenhagen C, Heimberg AM, Howell AL: HIV type 1 infection in women: increased transcription of HIV type 1 in ectocervical tissue explants. J Infect Dis 2009; 200:965972.
  • 62
    Pudney J, Quayle AJ, Anderson DJ: Immunological microenvironments in the human vagina and cervix: mediators of cellular immunity are concentrated in the cervical transformation zone. Biol Reprod 2005; 73:12531263.
  • 63
    White HD, Musey LK, Andrews MM, Yeaman GR, DeMars LR, Manganiello PD, Howell AL, Wira CR, Green WR, McElrath MJ: Human immunodeficiency virus-specific and CD3-redirected cytotoxic T lymphocyte activity in the human female reproductive tract: lack of correlation between mucosa and peripheral blood. J Infect Dis 2001; 183:977983.
  • 64
    Aghajanova L, Hamilton AE, Giudice LC: Uterine receptivity to human embryonic implantation: histology, biomarkers, and transcriptomics. Semin Cell Dev Biol 2008; 19:204211.
  • 65
    White HD, Crassi KM, Givan AL, Stern JE, Gonzalez JL, Memoli VA, Green WR, Wira CR: CD3+ CD8+ CTL activity within the human female reproductive tract: influence of stage of the menstrual cycle and menopause. J Immunol 1997; 158:30173027.
  • 66
    White HD, Yeaman GR, Givan AL, Wira CR: Mucosal immunity in the human female reproductive tract: cytotoxic T lymphocyte function in the cervix and vagina of premenopausal and postmenopausal women. Am J Reprod Immunol 1997; 37:3038.
  • 67
    Wira CR, Fahey JV: A new strategy to understand how HIV infects women: identification of a window of vulnerability during the menstrual cycle. AIDS 2008; 22:19091917.
  • 68
    Yeaman GR, Howell AL, Weldon S, Demian DJ, Collins JE, O’Connell DM, Asin SN, Wira CR, Fanger MW: Human immunodeficiency virus receptor and coreceptor expression on human uterine epithelial cells: regulation of expression during the menstrual cycle and implications for human immunodeficiency virus infection. Immunology 2003; 109:137146.
  • 69
    Yeaman GR, Asin S, Weldon S, Demian DJ, Collins JE, Gonzalez JL, Wira CR, Fanger MW, Howell AL: Chemokine receptor expression in the human ectocervix: implications for infection by the human immunodeficiency virus-type I. Immunology 2004; 113:524533.
  • 70
    Yeaman GR, Guyre PM, Fanger MW, Collins JE, White HD, Rathbun W, Orndorff KA, Gonzalez J, Stern JE, Wira CR: Unique CD8+ T cell-rich lymphoid aggregates in human uterine endometrium. J Leukoc Biol 1997; 61:427435.
  • 71
    Yokoyama WM: Mistaken notions about natural killer cells. Nat Immunol 2008; 9:481485.
  • 72
    Wira CR, Fahey JV, Sentman CL, Pioli PA, Shen L: Innate and adaptive immunity in female genital tract: cellular responses and interactions. Immunol Rev 2005; 206:306335.
  • 73
    Saito S, Shiozaki A, Sasaki Y, Nakashima A, Shima T, Ito M: Regulatory T cells and regulatory natural killer (NK) cells play important roles in feto-maternal tolerance. Semin Immunopathol 2007; 29:115122.
  • 74
    Shacklett BL: Cell-mediated immunity to HIV in the female reproductive tract. J Reprod Immunol 2009; 83:190195.
  • 75
    Tezuka H, Abe Y, Iwata M, Takeuchi H, Ishikawa H, Matsushita M, Shiohara T, Akira S, Ohteki T: Regulation of IgA production by naturally occurring TNF/iNOS-producing dendritic cells. Nature 2007; 448:929933.
  • 76
    He B, Qiao X, Klasse PJ, Chiu A, Chadburn A, Knowles DM, Moore JP, Cerutti A: HIV-1 envelope triggers polyclonal Ig class switch recombination through a CD40-independent mechanism involving BAFF and C-type lectin receptors. J Immunol 2006; 176:39313941.
  • 77
    Macpherson AJ, Uhr T: Induction of protective IgA by intestinal dendritic cells carrying commensal bacteria. Science 2004; 303:16621665.
  • 78
    Rakoff-Nahoum S, Paglino J, Eslami-Varzaneh F, Edberg S, Medzhitov R: Recognition of commensal microflora by toll-like receptors is required for intestinal homeostasis. Cell 2004; 118:229241.
  • 79
    Raffatellu M, Santos RL, Verhoeven DE, George MD, Wilson RP, Winter SE, Godinez I, Sankaran S, Paixao TA, Gordon MA, Kolls JK, Dandekar S, Baumler AJ: Simian immunodeficiency virus-induced mucosal interleukin-17 deficiency promotes Salmonella dissemination from the gut. Nat Med 2008; 14:421428.
  • 80
    Dandekar S, George MD, Baumler AJ: Th17 cells, HIV and the gut mucosal barrier. Curr Opin HIV AIDS 2010; 5:173178.
  • 81
    Shen W, Durum SK: Synergy of IL-23 and Th17 cytokines: new light on inflammatory bowel disease. Neurochem Res 2010; 35:940946.
  • 82
    Rovedatti L, Kudo T, Biancheri P, Sarra M, Knowles CH, Rampton DS, Corazza GR, Monteleone G, Di Sabatino A, Macdonald TT: Differential regulation of interleukin 17 and interferon gamma production in inflammatory bowel disease. Gut 2009; 58:16291636.
  • 83
    Peron JP, de Oliveira AP, Rizzo LV: It takes guts for tolerance: the phenomenon of oral tolerance and the regulation of autoimmune response. Autoimmun Rev 2009; 9:14.
  • 84
    Hirata T, Osuga Y, Takamura M, Kodama A, Hirota Y, Koga K, Yoshino O, Harada M, Takemura Y, Yano T, Taketani Y: Recruitment of CCR6-expressing Th17 cells by CCL 20 secreted from IL-1 beta-, TNF-alpha-, and IL-17A-stimulated endometriotic stromal cells. Endocrinology 2010; 151:54685476.
  • 85
    Wang WJ, Hao CF, Yi L, Yin GJ, Bao SH, Qiu LH, Lin QD: Increased prevalence of T helper 17 (Th17) cells in peripheral blood and decidua in unexplained recurrent spontaneous abortion patients. J Reprod Immunol 2010; 84:164170.
  • 86
    Ferre AL, Lemongello D, Hunt PW, Morris MM, Garcia JC, Pollard RB, Yee HF Jr, Martin JN, Deeks SG, Shacklett BL: Immunodominant HIV-specific CD8+ T-cell responses are common to blood and gastrointestinal mucosa, and Gag-specific responses dominate in rectal mucosa of HIV controllers. J Virol 2010; 84:1035410365.
  • 87
    UNAIDS: AIDS Epidemic Update: November 2009. Geneva, Switzerland, UNAIDS, 2009, pp 1100.
  • 88
    Critchfield JW, Lemongello D, Walker DH, Garcia JC, Asmuth DM, Pollard RB, Shacklett BL: Multifunctional HIVgag Specific CD8+ T-cell Responses in Rectal Mucosa and PBMC During Chronic HIV-1 Infection. J Virol 2007; 81:54605471.
  • 89
    Ferre AL, Hunt PW, Critchfield JW, Young DH, Morris MM, Garcia JC, Pollard RB, Yee HF Jr, Martin JN, Deeks SG, Shacklett BL: Mucosal immune responses to HIV-1 in elite controllers: a potential correlate of immune control. Blood 2009; 113:39783989.