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Keywords:

  • Schistosoma japonicum;
  • pig;
  • liver;
  • granuloma;
  • immunohistochemistry

Summary

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Use of the pig as an animal model in schistosomiasis research is increasing, but knowledge of the porcine immune response to schistosome infection is still very limited. We investigated the immunohistology of different maturation stages of the Schistosoma japonicum egg granuloma in pigs. Liver sections from pigs experimentally infected with S.japonicum for 9, 12 or 21 weeks were examined by immunohistochemistry using a three-step streptavidin-biotin-complex/immunoperoxidase method or a two-step alkaline phosphatase-mediated system. All granulomas showed marked expression of major histocompatibility complex (MHC) class II in epithelioid macrophages and were dominated by T lymphocytes, comprising both CD4+ and CD8+ phenotypes, with consistently higher proportions noted for CD8+ cells. B lymphocytes, as identified by expression of CD21, were confined to lymphoid nodular structures primarily associated with mature granulomas. Early and mature granulomas contained numerous immunoglobulin (Ig)G+ plasma cells. Significant differences in immunohistology related to duration of infection were not observed. The results indicate that all stages of the hepatic S.japonicum egg granuloma in the pig manifests MHC class II-dependent CD4+ T cell activity concomitant with infiltration of CD8+ T cells. B cell activity preceding the effector cell stage appears to occur in granuloma-associated lymphoid nodules, whereas antibody, mainly IgG, is produced within the granuloma.


Introduction

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

The blood fluke Schistosoma japonicum poses a significant threat to human health in endemic regions in Asia (1). The pig is important in the zoonotic transmission of this trematode, and is also used as an experimental animal in schistosomiasis japonica research (2–4). Several studies have addressed different aspects of schistosomiasis japonica in pigs, such as clinical disease and pathology in experimental and natural infection, vertical transmission, chemotherapy and immunization (5–13). Studies in pigs on the principal lesion, the granuloma formed around S. japonicum eggs trapped in tissues, have only dealt with its histopathological characteristics (5,7,9,10), whereas immunohistological features of the granuloma have not been explored. The composition and regulation of the schistosome egg granuloma have been most extensively studied in the murine model of schistosomiasis mansoni, in which the granuloma is a delayed type hypersensitivity reaction mediated by major histocompatibility complex (MHC) class II-restricted CD4+ T cells specific for schistosome egg antigen (14,15). Also, S. japonicum-induced granulomas in mice are T cell-mediated reactions, involving CD4+ cells (16,17). The lack of basic knowledge about the porcine egg granuloma prompted the present study, in which we identified lymphocyte subpopulations, expression of MHC class II antigen and the presence of immunoglobulin (Ig) in hepatic granulomas induced by S. japonicum in the pig. In order to assess the variability of the cellular composition in relation to granuloma stage and duration of infection, we studied early, mature and involutional granulomas in pigs at 9–21 weeks postinfection (PI) with S. japonicum cercariae.

Materials and Methods

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Animals and study design

Twelve helminth-naive, specific pathogen-free (MS-SPF) Danish Landrace/Yorkshire/Duroc crossbred pigs (six castrated males and six females), aged 8–12 weeks at the start of the experiment, were used. Four of the pigs were uninfected controls. The other eight pigs were inoculated by intramuscular injection with Iscove’s medium-suspended cercariae of a Chinese mainland strain of S. japonicum originating from Zhejiang Province and maintained in Oncomelania hupensis hupensis snails at the Danish Bilharziasis Laboratory, Charlottenlund, Denmark, as previously described (18). For each inoculation, 850 cercariae were used. Four pigs were given a primary infection at the start of the experiment (week 0) and were necropsied at week 12 (n = 2) or week 21 (n = 2). Two pigs were inoculated at week 0, received a challenge infection at week 12 and were necropsied at week 21. The two remaining pigs received a primary infection at week 12 and were necropsied at week 21. The study design as outlined in Table 1.

Table 1.  Schematic presentation of the study design
Duration of infection (weeks)Number of pigsWeek
01221
  1. P, primary infection (850 S. japonicum cercariae); Ch, challenge infection (850 S. japonicum cercariae); N, necropsy.

92PN
122PN
212PN
212PChN
Control 122N
Control 212N

Tissues

The pigs were killed with pentobarbital intravenously. From each pig, small pieces of liver, portal lymph node and spleen tissue were removed at necropsy, mounted on strips of filter paper, snap-frozen in liquid nitrogen and stored at 70°C. Larger pieces of these organs were fixed in 10% neutral-buffered formalin, trimmed, conventionally processed and embedded in paraffin.

Primary antibodies (Abs) and immunohistochemical staining procedures

The monoclonal and polyclonal primary Abs used are presented in Table 2. For application of all monoclonal (m) Abs and for the anti-CD3ɛ polyclonal Ab, frozen tissue samples were embedded in OCT compound (Miles Laboratories Inc., Elkhart, IN, USA). Serial 4-µm thick cryostat sections were cut onto SuperFrost® Plus glass slides (Menzel-Gläser, Germany), air-dried and stored at –20°C until further processed. The sections were fixed in cold acetone (4°C) for 15 min and then air-dried. To reduce nonspecific protein binding, the sections were incubated with 20% normal goat serum for 30 min. The two-step alkaline phosphatase-conjugated EnVision™ method (Dako A/S, Glostrup, Denmark) was used to demonstrate immunoreactivity. Tissue sections were developed with Vector®Red Alkaline Phosphatase Substrate Kit (Vector Laboratories, Burlingame, CA, USA) and counterstained with haematoxylin.

Table 2.  Monoclonal and polyclonal antibodies used, their specificity, Ig isotype, optimal dilution for the immunohistochemical staining procedure, and a reference to their reactivity in pig cells/tissues
AntibodySpecificityIsotypeOptimal dilutionReference
  • a

    VMRD Inc., Pullman, WA, USA;

  • b

    Labor B. Glatthaar, Tübingen, Germany;

  • c

    c Dako A/S, Glostrup, Denmark;

  • d

    d Bethyl Laboratories Inc., Montgomery, TX, USA. Po, porcine; Hu, human.

Monoclonal
 H42AaPo MHC class IIIgG2a1 : 40 00019
 BB6-11C9aPo wCD21IgG11 : 100020
 PGBL22AaPo γδ T cell receptorIgG11 : 5021
 b38c6bPo CD4aIgG11 : 5020
 11/295/33–25bPo wCD8bIgG2a1 : 1020
 PGBL25AaPo wCD25IgG11 : 20022
Polyclonal
 A 0452 (rabbit)cHu CD3ɛ1 : 50023
 A100-104 A-7 (goat)dPo IgG1 : 900024
 A100-102 A-8 (goat)dPo IgA1 : 400024
 A100-100 A-7 (goat)dPo IgM1 : 10 00024

For the anti-Ig polyclonal Abs, serial 4-µm thick paraffin sections were cut onto SuperFrost® Plus glass slides. The sections were pretreated with 0·05% pronase (Dako A/S) for 10 min at 37°C for antigen retrieval. The slides were incubated with 3% H2O2 for 10 min to quench endogenous peroxidase activity, and with 2% normal horse serum for 30 min to block nonspecific protein binding. Immunoreactivity was detected with the streptavidin-biotin-complex/horseradish peroxidase method (DAKO A/S). The sections were developed with 3,3′ diaminobenzidine tetrahydrochloride (Dako A/S), and counterstained as above. Tris-buffered saline, 0·05 m, pH 7·6, was used for all dilutions and washes, with addition of 0·1% bovine serum albumin for dilution of the primary Abs. The immunoreactivity of all primary Abs was assessed in lymph node tissue, except for the anti-γδ T cell receptor mAb, which was assessed in spleen tissue. Optimal dilutions of the primary Abs were determined (Table 2). To ascertain the specificity of the tissue staining, sections were treated as above, but with replacement of the primary Ab with an equally diluted negative control serum from the same animal species.

Histopathological and immunohistochemical evaluation

The first and last section of each series of liver tissue, comprising approximately 10 sections, were stained with haematoxylin and eosin for morphological assessment, and the sections in between were used for immunostaining. In each infected pig, at least 50 granulomas with one or more eggs in their centres were classified according to developmental stage into early exudative–productive, mature productive, or late involutional stages, as previously described (9,10). Briefly, exudative–productive stage granulomas are large and show a central accumulation of eosinophils surrounded by loosely organized macrophages, epithelioid cells and giant cells, and marked infiltration of eosinophils, lymphocytes and plasma cells. Productive stage granulomas are well organized structures with epithelioid cells and giant cells in the centre and inflammatory cell infiltration mainly at the periphery. Concentric fibrosis is present to a variable degree. Involutional stage granulomas are small and show only slight peripheral cellular infiltration and usually prominent fibrosis. For each granuloma, the proportion of eosinophils, expressed as the percentage of all cells in the granuloma, was estimated, and any significant fibrosis was recorded.

For each of the eight infected pigs, the first 25 of the above classified granulomas that were encountered in the immunostained sections were examined, giving a total number of 200 granulomas examined for each antigen in question. The presence of immunostained cells was graded as none or occasional cells, and as proportions of all granuloma cells upwards at 10% intervals. The principal location (central, peripheral or diffuse) of the stained cells was determined. The average proportions of CD4+ and CD8+ cells for each granuloma stage and timepoint were compared.

Results

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Histopathology

Perioval granulomas were usually located in portal triads and interlobular septa, frequently obstructing portal and distributing veins. Affected vessels often showed obliterative phlebitis and periphlebitis. Portal and septal fibrosis and diffuse inflammatory cell infiltration to variable degrees were present in all infected pigs. Most granulomas were dominated by epithelioid cells mixed with variable numbers of multinucleated giant cells, showed infiltrates of eosinophils and small mononuclear cells, mainly lymphocytes and some plasma cells, and contained a single egg. Small, usually single lymphoid nodules were detected in approximately one-quarter of all granulomas. The nodules, subsequently referred to as granuloma-associated lymphoid nodules, were eccentrically located at the border of the granuloma, and were most consistently seen in connection with productive stage granulomas. The exudative–productive stage contained 30–50%, the productive stage 20% and the involutional stage 10–20% eosinophils, with no difference observed in relation to duration of infection.

At 9 weeks PI, only large, vigorous granulomas of the exudative–productive (29%) and the productive (71%) stage were present, and approximately one-third of them showed viable immature or mature eggs (Plate I, Figure 1). These two granuloma stages constituted 18% and 65%, respectively, of the granulomas at 12 weeks PI. In addition, some granulomas (17%) were involutional stage. Viable eggs were detected in 30% of the granulomas at this timepoint. At 21 weeks PI in single-infected pigs, only productive and involutional stage granulomas (70% and 30%, respectively) were found, and viable eggs were detected in only 6% of them. The challenge-infected pigs killed at the same timepoint differed in that they showed occasional exudative–productive stage granulomas, had a higher frequency of granulomas with viable eggs (18%) and showed a higher granuloma density.

image

Figure 1. Liver cryostat section. Exudative–productive stage granuloma with a mature, viable egg (arrow) and a small accumulation of eosinophils in the centre, surrounded by epithelioid macrophages. There is marked infiltration of lymphocytes, plasma cells and eosinophils. Single infection, 12 weeks PI, haematoxylin and eosin stain (× 138).

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Immunohistochemistry

Controls

The antiporcine wCD21 mAb stained follicular cells in the control lymph node as previously described (25), as well as cells in the peritrabecular sinuses. The antiporcine wCD25 mAb stained scattered cells mainly in the paracortical zone of the lymph node. The immunostaining obtained in the lymph node or spleen from the uninfected control pigs with all the other Abs was consistent with results of other studies in pigs (23,26–29).

Schistosoma japonicum-infected pigs

T cells: All granulomas contained T lymphocytes as identified by the expression of CD3ɛ, which is a marker for all T cells, with proportions decreasing from 40% to 60% in the exudative–productive and productive stages to 20% to 30% in the involutional stage (Plate I, Figure 2). Both the CD4+ and CD8+ subsets were represented, with the highest proportions recorded for CD8+ cells (Plate I, Figures 3 and 4). The ratio between the average proportions (CD4 : CD8) was approximately 0·5 in most instances, but increased to 1·0 in exudative–productive granulomas at 12 weeks PI and was reduced to 0·2 in involutional granulomas at 21 weeks PI in pigs that received only a single infection (Table 3). These changes in proportions between CD4+ and CD8+ cells were essentially due to changes in CD8+ cell numbers, since infiltration of CD4+ cells was relatively constant for each granuloma stage at the different timepoints examined. The T lymphocytes were mainly located in the peripheral zone of the granuloma but, consistently, a few cells intermingled with the epithelioid cells, sometimes forming a thin rim around the central egg. Occasional T cells occurred in the granuloma-associated lymphoid nodules. Approximately one-half of the granulomas at 9 weeks PI showed occasional γδ T cells at their periphery, whereafter the frequency of γδ T cell-containing granulomas was reduced with time to low levels at 21 weeks PI.

image

Figure 2. Liver cryostat section. Productive stage granuloma with prominent T cell infiltration in the peripheral zone, and a few T cells in the centre. Single infection, 9 weeks PI, anti-CD3ɛ polyclonal Ab, alkaline-phosphatase/EnVision™ stain, counterstained with haematoxylin (× 138).

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image

Figure 3. Liver cryostat section. Productive stage granuloma with infiltration of CD4+ T cells at the periphery. Single infection, 21 weeks PI, anti-CD4a monoclonal (m)Ab, alkaline-phosphatase/EnVision™ stain, counterstained with haematoxylin (× 138).

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image

Figure 4. Liver cryostat section. Productive stage granuloma with infiltration of CD8+ T cells at the periphery. Single infection, 21 weeks PI, anti-CD8b mAb, alkaline-phosphatase/EnVision™ stain, counterstained with haematoxylin (× 138).

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Table 3.  The ratio of the mean proportions of CD4+ and CD8+ cells in each granuloma stage at different timepoints after infection and after challenge
Duration of infection (weeks)Granuloma stage
Exudative– productiveProductiveInvolutional
  1. The results do not take into account the possible presence in the granulomas of double-expressing CD4+CD8+ cells, common in porcine tissues (see Discussion).

90·50·5
121·00·60·5
210·40·2
21 (+ challenge)0·50·6

B cells: Expression of CD21, a marker for mature B cells and follicular dendritic cells, was usually seen as a uniform staining of granuloma-associated lymphoid nodules (Plate I, Figure 5), and only occasional CD21+ cells were found within the granulomas themselves. Diffusely distributed cells positive for cytoplasmic IgG were commonly detected in the granulomas (Plate I, Figure 6). The IgG+ cells in general had the character of plasma cells, but a few larger cells resembling macrophages were also stained. The proportions of IgG+ cells were approximately 10% in exudative–productive and productive stage granulomas at any timepoint, whereas only a few IgG-containing cells were found in involutional granulomas. Cells with cytoplasmic IgA and IgM were infrequently detected in the granulomas, and only in low numbers.

image

Figure 5. Liver cryostat section. Productive stage granuloma with B cells distinctly located in lymphoid nodule at the periphery (arrow). Single infection, 12 weeks post PI, anti-wCD21 mAb, alkaline-phosphatase/EnVision™ stain, counterstained with haematoxylin (× 138).

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image

Figure 6. Liver paraffin section. Exudative–productive stage granuloma showing numerous IgG+ plasma cells in the peripheral zone. Primary + challenge infection, 21 weeks PI, anti-IgG polyclonal Ab, streptavidin-biotin-complex/peroxidase, counterstained with haematoxylin (× 138).

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MHC class II:

A strong MHC class II antigen expression was detected in the epithelioid macrophage-dominated zone of granulomas of all developmental stages, and was similar at the different timepoints examined (Plate I, Figure 7). In exudative–productive stage granulomas, the central accumulation of eosinophils was negative for MHC class II. MHC class II expression was also found in scattered mononuclear cells in the peripheral zone, and in most cells of the granuloma-associated lymphoid nodules. Individual cells were often difficult to distinguish in the granuloma centres due to high staining intensity, but multinucleated giant cells were usually weakly stained or were negative, as were most peripheral small mononuclear cells and fibroblasts.

image

Figure 7. Liver cryostat section. Involutional stage granuloma with marked staining for MHC class II in epithelioid macrophages in the centre and in scattered cells in the peripheral zone. Giant cells show only weak staining (arrow). Single infection, 12 weeks PI, anti-MHC class II mAb, alkaline-phosphatase/EnVision™ stain, counterstained with haematoxylin (× 138).

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Cell activation: Expression of CD25 (the interleukin-2 receptor), a marker for activated lymphocytes and macrophages, was found in approximately 10% of the cells in exudative–productive and productive stage granulomas at all timepoints, mainly in lymphocytes in the peripheral zone (Plate I, Figure 8). Involutional granulomas never showed more than occasional CD25+ cells.

image

Figure 8. Liver cryostat section. Small productive stage granuloma with scattered activated cells expressing the interleukin-2 receptor. The egg in the centre shows nonspecific staining (arrow). Primary + challenge infection, 21 weeks PI, anti-CD25 mAb, alkaline-phosphatase/EnVision™ stain, counterstained with haematoxylin (× 138).

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Discussion

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

In the present study, we used a panel of Abs for in situ demonstration of lymphocyte subsets, MHC class II expression and Igs during the development and involution of the hepatic perioval granuloma in S. japonicum-infected pigs. We found that the granulomas were dominated by CD3+ T lymphocytes of both CD4+ and CD8+ phenotypes, and showed a marked expression of MHC class II antigen, mainly in epithelioid cells. Participation of B lymphocytes was often prominent and was indicated by the presence of IgG-containing plasma cells within the granuloma, and of CD21+ cells in granuloma-associated lymphoid nodules.

Granuloma formation in murine schistosomiasis mansoni is mediated by soluble egg antigen (SEA)-specific MHC class II restricted CD4+ T helper (Th) cells, with predominance of the cytokine profile of the Th2 subset (15,30,31). S. japonicum-induced granuloma formation is also T cell-dependent, and associated with a Th2-like cytokine pattern in mice (16,17). Our demonstration of CD4+ T cells and MHC class II expression indicates a similar immunogenesis of the porcine hepatic S. japonicum-induced granuloma. Eosinophil infiltration in schistosome egg granulomas, often marked in the present study, has previously been linked to Th2-associated interleukin (IL)-5 production, promoting eosinophil differentiation, in other species (31). More specific support for a Th2-dominated response in pigs comes from a recent report showing elevated mRNA-expression for IL-4 and IL-10, but not for interferon (IFN)-γ, in intestine and liver of S. japonicum-infected pigs (32).

As in murine schistosomiasis mansoni, expression of both CD4 and CD8 antigen was apparent in granuloma cells in the present pigs. Pigs differ from many other species (e.g. humans and mice) in that significant numbers of extrathymic CD4+CD8+ double-positive (DP) T cells, in addition to CD4+ and CD8+ single-positive (SP) cells, normally are present in peripheral blood and secondary lymphoid tissues (33). Evidence indicates that these CD4+CD8+ DP cells in pigs functionally are MHC class II restricted CD4+ Th cells, which upon activation are induced to express CD8. Several features, such as expression of memory T cell markers, increase in number with the age of the pig and production of IFN-γ, suggest that the cells are comprised of memory cells (33). It is reasonable to assume that a proportion of the CD4+ and the CD8+ cells in the porcine granulomas may have been of this phenotype. Further studies employing a double-staining technique are warranted to explore this cell population in porcine schistosomiasis.

However, the generally higher proportions of CD8+ than of CD4+ cells that we observed in the granulomas indicate that a significant proportion of the CD8+ cells were of the CD4CD8+ SP phenotype, which in pigs comprises MHC class I-restricted cytotoxic/suppressor T cells as well as natural killer (NK) cells (34). Suppressor T cells and NK cells have both been proposed to be involved in the down-regulation of granuloma size in murine schistosomiasis mansoni (35,36). These concepts, however, have been questioned in other studies (15,37,38). In the murine model of S. japonicum, granuloma size has been shown to be down-regulated by T cells in the acute, but not in the chronic phase of infection (39). In the present study, we found a distinctly increased proportion of CD8+ cells in involutional granulomas in the single-infected pigs, but not in the challenged pigs at 21 weeks PI or at the earlier timepoints of infection. Although this suggests that CD8+ cells may have a role in granuloma involution, possibly via suppression of immunological activity, these results are difficult to interpret and further investigations are required.

In pigs, similar to ruminants, a large proportion of peripheral blood T lymphocytes are γδ T cells (40), which are a prominent feature of the perioval granulomas in S. bovis-infected goats, and have also been reported in S. mansoni-infected mice, but their function in this context is unknown (41,42). In the present pigs, however, γδ T cells occurred only in very low numbers in granulomas, making it unlikely that they constitute a functionally significant cell population of the hepatic S. japonicum-induced egg granuloma in pigs.

B cells and their products are not necessary for granuloma formation in murine schistosomiasis japonica, since granulomas formed in B cell-depleted mice are not morphologically different from those formed in intact mice, except for the absence of plasma cells (43). On the other hand, B cells and Abs appear essential for immunomodulation of S. japonicum-induced granulomas in mice, as indicated by a lack of modulation in the chronic stage of infection in B cell-depleted mice, and by induced modulation of granulomas in recipient mice after passive transfer of serum from chronically infected mice (39,43). In the murine S. mansoni model, B cells increase during the modulatory phase (44). Failure of granulomas in genetically B cell-deficient mice to undergo spontaneous modulation has also been demonstrated (45,46).

Our study provided evidence for B cell involvement in perioval granulomas in pigs. We detected granuloma-associated lymphoid nodules with marked expression of CD21 antigen in approximately one-quarter of the granulomas at all timepoints. The observed low frequency is likely to be an underestimation, since the small size and eccentric location of these usually single nodules gave a low probability for them to appear in the examined granulomas, which were selected on the basis of being centrally sectioned. MHC class II antigen was also expressed in these lymphoid nodules, probably by B cells, and occasional T cells were present. This pattern of immunostaining was very similar to that in lymphoid follicles of the control lymph node. The epitope CD21 is expressed by mature B cells and follicular dendritic cells in pigs and other species, but expression is lost during the differentiation of B cells into plasma cells (25,47). The granuloma-associated lymphoid nodules thus appear to be a site for B cell activity prior to the effector cell stage, and it seems likely that plasma cells within the granuloma may originate from these structures. To our knowledge, there is no record of similar events in schistosome infections in other animal species.

Within exudative–productive and productive stage granulomas, we consistently found IgG-containing cells, whereas only occasional cells were positive for cytoplasmic IgM or IgA. Our results thus suggest involvement of IgG in developing and maturing hepatic granulomas in pigs throughout the period of infection studied. Numerous IgG-containing cells have been demonstrated in hepatic granulomas in murine schistosomiasis japonica, whereas the prevalence of cells producing other isotypes appear not to have been reported in this model (43). Immunoglobulin G was the main isotype detected in hepatic egg granulomas in chronic human schistosomiasis mansoni (48), whereas a marked predominance of IgM-secreting cells in hepatic granulomas was demonstrated in both acute and chronic stages of murine S. mansoni infection (49). One function of Ab produced within the granulomas may be to neutralize antigens emanating from the egg, thus preventing release of these antigens to the surroundings of the granuloma (48). The locally produced Ab may also mediate cellular cytotoxicity by binding to Fc receptors on local macrophages and eosinophils (50).

We found that cells with morphological characteristics of epithelioid macrophages consistently expressed MHC class II in all granuloma stages at all timepoints. These results are consistent with observations on hepatic granulomas in the murine S. mansoni model, where MHC class II expression remains in the chronic stage of infection (51). Scattered mononuclear cells in the peripheral, T cell dominated zone of the granulomas also expressed MHC class II. The phenotype of these cells was not identified, but they may have been migrating macrophages, or possibly T lymphocytes, since some porcine T cells, especially CD8+ cytotoxic T cells, show expression of MHC class II, the functional significance of which is not known (19). The lack of cells expressing CD21 outside the granuloma-associated lymphoid nodules makes it unlikely that significant numbers of the scattered MHC class II-expressing cells were B cells.

Expression of CD25, the α chain of the IL-2 receptor, signals cell activation (22). This epitope is expressed by SEA-activated lymphocytes in the murine S. mansoni model (52), and SEA-stimulated cells from murine hepatic S. japonicum-induced granulomas produce IL-2 (53). Cell activation was indicated in the present pigs by a stable proportion of CD25+ cells, mostly lymphocytes, in exudative–productive and productive stage granulomas, whereas expression was lacking or only minor in involutional granulomas, consistent with the abatement of stimulation by egg antigens in this granuloma stage.

This first study of the immunohistology of the S. japonicum-induced hepatic granuloma in the pig has delineated some basic features of this complex tissue reaction. The results encourage further investigations addressing functional aspects of the granuloma, such as cytokine production and other regulatory mechanisms, in this model of schistosomiasis japonica.

Acknowledgements

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

We wish to express our sincere thanks to the Danish Bilharziasis Laboratory for providing the S.japonicum infections, and to Ms Briitta Ojava and Ms Christina Nilsson for their skilful technical assistance. This work was supported by the Danish National Research Foundation and by grant no. SWE-95-032 from the Swedish Agency for Research Cooperation with Developing Countries (SAREC).

References

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
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