Schistosoma mansoni: kinetics and class specificity of hypergammaglobulinemia induced during murine infection

IL-10R blockade during chronic schistosomiasis mansoni results in the loss of B cells from the liver and the development of severe pulmonary disease

In schistosomiasis patients, parasite eggs trapped in hepatic sinusoids become foci for CD4+ T cell-orchestrated granulomatous cellular infiltrates. Since the immune response is unable to clear the infection, the liver is subjected to ongoing cycles of focal inflammation and healing that lead to vascular obstruction and tissue fibrosis. This is mitigated by regulatory mechanisms that develop over time and which minimize the inflammatory response to newly deposited eggs. Exploring changes in the hepatic inflammatory infiltrate over time in infected mice, we found an accumulation of schistosome egg antigen-specific IgG1-secreting plasma cells during chronic infection. This population was significantly diminished by blockade of the receptor for IL-10, a cytokine implicated in plasma cell development. Strikingly, IL-10R blockade precipitated the development of portal hypertension and the accumulation of parasite eggs in the lungs and heart. This did not reflect more aggressive Th2 cell responsiveness, increased hepatic fibrosis, or the emergence of Th1 or Th17 responses. Rather, a role for antibody in the prevention of severe disease was suggested by the finding that pulmonary involvement was also apparent in mice unable to secrete class switched antibody. A major effect of anti-IL-10R treatment was the loss of a myeloid population that stained positively for surface IgG1, and which exhibited characteristics of regulatory/anti-inflammatory macrophages. This finding suggests that antibody may promote protective effects within the liver through local interactions with macrophages. In summary, our data describe a role for IL-10-dependent B cell responses in the regulation of tissue damage during a chronic helminth infection.

IgE expression on the surface of B1 and B2 lymphocytes in experimental murine schistosomiasis

In a previous study we monitored the distribution and phenotype expression of B1 cells during the evolution of experimental murine schistosomiasis mansoni and we proposed that the B1 cells were heterogeneous: a fraction which originated in the spleen and followed the migratory pathway to mesenteric ganglia, while the other was the resident peritoneal B1-cell pool. In the present study, we have addressed the question of whether these two B1-lymphocyte populations are involved in the production of the late Ig isotype IgE, which is present in high levels in schistosomal infection. Lymphocyte expression of surface markers and immunoglobulins were monitored by immunofluorescence flow cytometry. Both in the spleen and mesenteric ganglia, the B1 and B2 cells were induced to switch from IgM to IgE in the early Th2-dominated phase of the disease, with an increase of IgE in its later phases. Conversely, peritoneal B1-IgM+ switched to the remaining IgE+ present in high numbers in the peritoneal cavity throughout the disease. We correlated the efficient induction of the expression of late Ig isotypes by B1 cells with high levels of inflammatory cytokines due to the intense host response to the presence of worms and their eggs in the abdominal cavity. In conclusion, B1 cells have a different switch behavior from IgM to IgE indicating that these cell sub-populations depend on the microenvironment.

CD4+ T cell-mediated granulomatous pathology in schistosomiasis is downregulated by a B cell-dependent mechanism requiring Fc receptor signaling

The effector functions of CD4+ T lymphocytes are generally thought to be controlled by distinct populations of regulatory T cells and their soluble products. The role of B cells in the regulation of CD4-dependent host responses is less well understood. Hepatic egg granuloma formation and fibrosis in murine schistosomiasis are dependent on CD4+ lymphocytes, and previous studies have implicated CD8+ T cells or cross-regulatory cytokines produced by T helper (Th) lymphocytes as controlling elements of this pathologic process. In this report, we demonstrate that B cell-deficient (muMT) mice exposed to Schistosoma mansoni develop augmented tissue pathology and, more importantly, fail to undergo the spontaneous downmodulation in disease normally observed during late stages of infection. Unexpectedly, B cell deficiency did not significantly alter T cell proliferative response or cause a shift in the Th1/Th2 balance. Since schistosome-infected Fc receptor-deficient (FcR gamma chain knockout) mice display the same exacerbated egg pathology as that observed in infected muMT mice, the B cell- dependent regulatory mechanism revealed by these experiments appears to require receptor-mediated cell triggering. Together, the data demonstrate that humoral immune response/FcR interactions can play a major role in negatively controlling inflammatory disease induced by CD4+ T cells.

Neutral glycolipids of Schistosoma mansoni as feasible antigens in the detection of schistosomiasis

The neutral glycolipid fraction from mouse-propagated, Schistosoma mansoni adult worms has been investigated as to its chromatographic and antigenic properties, and whether it fulfills the serodiagnostic antigen requirements of sensitivity and specificity in the detection of schistosomiasis. Serological analyses were performed by thin-layer chromatography immunostaining and ELISA. In the acute-phase form of mouse schistosomiasis, the kinetics of development of neutral glycolipid-specific antibody levels was correlated with the intensity of the initial infection and the response was dominated by IgG, as represented by the subclass IgG1. With the experimental animal helminthiases screened, glycolipid antigenicity fulfilled the fundamental traits for a serodiagnostic reagent. In the chronic-phase form of human schistosomiasis mansoni, neutral glycolipid-specific antibody levels were not correlated with the intensity of infection, as estimated from the faecal content of parasite eggs, whilst the isotypic response was dominated by IgM and IgG, the latter represented primarily by IgG1 and secondarily by IgG3. With other human helminthiases, glycolipid antigenicity was incomplete, in that, the specificity was only partially fulfilled. The reason for this incomplete specificity has been clarified, in part, by the detection of cryptic schistosomiasis infections in the cohorts of African patient sera examined.

Increased CD4+ T cell-dependent anti-erythrocyte antibody levels following the onset of parasite egg production in Schistosoma mansoni infected mice

Anaemia has been reported to be a symptom of schistosomiasis mansoni. In other chronic infectious diseases, anti-red blood cell (RBC) antibodies have been suggested or shown to play a role in anaemia by participating in either complement or macrophage-dependent RBC elimination. To examine whether such a situation could be contributing to the anaemia of schistosomiasis, we examined RBC taken from infected mice for surface-bound antibodies. Our data show that prior to the onset of egg production infected mice have plasma haemoglobin levels that are indistinguishable from age matched controls (AMC). However, consistent with previous reports, following the initiation of egg laying, infected mice have significantly lower haemoglobin levels than AMC. Surface-bound IgM, IgG1 and IgG3 on RBC from infected mice increased markedly after egg laying began. Levels of RBC-associated IgG2b were similar on RBC from infected and normal mice. Antibody production against RBC was Th cell-dependent since it did not occur in mice depleted of CD4+ cells. Antibodies eluted from RBC of infected mice bound to isolated membranes of RBC from AMC and to a soluble extract of schistosome eggs. Furthermore, antibodies in serum from mice carrying patent infections bound to the membranes of RBC from normal mice. Taken together, these data suggest that schistosome eggs induce an antibody response which may cross react with a RBC surface antigen.

Schistosoma mansoni: analysis of monoclonal antibodies reactive with gut-associated antigens

The analysis of a series of monoclonal antibodies (mAbs) developed in our laboratory against gut-associated antigens of Schistosoma mansoni is described. It was found that mAbs that recognized epitopes of antigens in the gut and on the eggshell were mainly of the IgM isotype; these epitopes are likely to be carbohydrate in composition. Of a number of mAbs that were reactive with antigens important to the human humoral immune response, 75% appeared to be reactive with the circulating cathodic antigen.

Polyclonal activation of B lymphocytes during experimental infection with Schistosoma mansoni

A significant polyclonal activation of B lymphocytes was observed during experimental infection of C57BL/10J mice with Schistosoma mansoni. The isotypic pattern of this expansion, assessed by the Protein-A plaque-forming cell method, was compared with and found to differ from those occurring after infection by Trypanosoma cruzi or injection of bacterial LPS. In the infection of S. mansoni an early expansion of most immunoglobulin isotypes occurs together with a late, sustained expansion of IgG1-secreting cells. High levels of polyclonal B cell activation were observed after adoptive transfer of spleen cells from infected mice to isogenic recipients pre-treated with hydroxyurea.

Role of cytokines and CD4+ T-cell subsets in the regulation of parasite immunity and disease

CD4+ T cells have been separated into two subsets, designated TH1 and TH2, based upon the repertoire of lymphokines that they produce following stimulation. We have analyzed the role of these T-cell subsets in two chronic parasitic infections, leishmaniasis and schistosomiasis. In both diseases, we found a strong association with TH1 stimulation and protection, and TH2 stimulation and immunopathology. In addition, certain parasite antigens appeared to be strongly linked with either TH1 or TH2 cell development. This led to the establishment of protective T-cell lines and clones in a L. major model, from which we identified a new candidate antigen for vaccination against Leishmania parasites. Moreover, we show that protection against L. major infection can be significantly augmented by coadministration of IFN-gamma with antigen, a lymphokine known to inhibit TH2 cell proliferation. In S. mansoni-infected mice, animals with a patent infection exhibit an overwhelming TH2 response, while animals protectively immunized with irradiated cercariae preferentially produce IFN-gamma, a lymphokine associated with TH1 cell stimulation. In addition, we show that ablation of schistosome-induced eosinophilia by in vivo anti-IL-5 monoclonal treatment fails to reduce the protection induced by irradiated cercariae. Similarly, anti-IL-5 treatment resulted in egg-induced granulomas nearly devoid of eosinophils, but only caused a marginal reduction in granuloma size. These results demonstrate that an understanding of the factors controlling TH1 and TH2 development will significantly facilitate the identification and development of vaccines for parasitic infections.

Immunopathology of Schistosoma mansoni infection

Schistosomiasis mansoni is a chronic helminthic disease that affects about 100 million people in the tropics. The worms have a life span of 5 to 10 years, and they live in the mesenteric veins of the host. Lightly infected individuals are asymptomatic or manifest mild intestinal symptoms. Heavily infected individuals often develop severe morbidity with hepatosplenomegaly, sometimes with a fatal outcome. Morbidity is attributed to the strong humoral and T-cell-mediated host immune responses developed to a variety of parasite antigens and expressed as tissue inflammations. The immunopathology includes dermatitis, immune complex-mediated kidney disease, and, chiefly, T-cell-mediated granuloma formation and fibrosis around disseminated parasite eggs. This review describes the mechanisms of induction and expression of immunopathology in infected persons and experimental animals. Immunoregulatory mechanisms that modulate the enhanced immune responses and may ameliorate excessive morbidity are discussed.

Delayed isotype switching in Dirofilaria immitis infection

The anti-microfilarial immunoglobulin response in Dirofilaria immitis infection was investigated serially in a naturally infected dog. Spontaneous clearance of microfilariae was associated with IgM opsonizing antibodies which promoted in vitro killing of microfilariae by granulocytes. Over a 6- to 11-month period, there was a shift to a predominantly IgG response. The addition of fresh non-immune serum markedly enhanced killing mediated by both IgM and IgG. The findings document conversion from IgM to IgG isotype with chronic infection, and suggest that isotype switching in canine D. immitis infection is delayed relative to that seen in bacterial or viral infections.

[Evolution of immunoglobulins involved in the immune response of mice to Schistosoma mansoni]

Foi estudada a evolução das imunoglobulinas envolvidas na resposta imune de camundongos ao Schistosoma mansoni durante oito semanas de infecção, utilizando soros pluri-específicos como reativos biológicos e a técnica da imunoeletroforese bidimensional. Os resultados expressaram modulação da resposta imune humoral, tanto em soros de animais parasitados (I) como nos normais, tomados como controle (C). Aumentos relativos dos níveis de imunoglobulinas entre estes dois grupos foram constatados pela relação I/C. Foi possível verificar o aparecimento de uma resposta primária, ocorrida entre o início da doença e a segunda semana de infecção, constituída de IgM e IgA, e uma secundária, iniciada na sexta semana de infecção, constituída pelas IgA; IgG1 e IgM, com aumentos relativos de 4.5; 3 e 2 vezes normal.

[Schistosomiasis mansoni. II. Evolution of the levels of serum proteins and the electrophoretic profile by quantitative immunoelectrophoresis technics]

Camundongos Swiss foram infectados com 100 cercárias da linhagem mineira (BH) do Schistosoma mansoni e sacrificados semanalmente no período de 8 semanas de infecção. Os níveis de proteínas séricas totais destes animais não diferiram dos apresentados pelos animais controles. Os níveis de albumina sérica determinados por "Rocket immunoelectrophoresis" acharam-se diminuídos nas 5.ª, 6.ª e 7.ª semanas de infecção. O perfil obtido por imunoeletroforese cruzada revelou alterações em componentes séricos com mobilidade nas regiões de gama, beta e em menor grau de alfa-globulinas, após a oviposição do parasito.

Opisthorchis viverrini: partial success in adoptively transferring immunity with spleen cells and serum in the hamster

Three groups of golden Syrian hamsters received intraperitoneally either, (1) 1 x 10(7) spleen cells, (2) 0.5 ml. serum or, (3) 1 x 10(7) spleen cells plus 0.5 ml. serum, from donors infected 6 weeks previously with 25 Opisthorchis viverrini metacercariae, one day before and at the same time as challenge with 25 metacercariae. Three groups of control animals received the same quantities of spleen cells, serum or an admixture of both from normal non-infected donors in the same manner followed by challenge with 25 metacercariae. Animals were killed six weeks after challenge, livers and extrahepatic biliary systems carefully removed, and liver worm burdens estimated. Additionally, parasitic egg counts were performed on pooled faeces samples collected one hour prior to death. Animals receiving spleen cells, serum, or an admixture of both, from normal non-infected donors had mean worm burdens of 11.44, 12.00 and 12.66, respectively. Animals receiving spleen cells, serum, or both, from infected donors had mean worm burdens of 9.88, 7.77 and 12.00, respectively. There were no significant differences in mean worm burdens between control and experimental groups. However, a substantial reduction in parasitic faecal egg counts and subsequently mean egg production per worm was observed in all 3 groups of animals receiving spleen cells, serum, or both, from infected donors when compared to their respective control groups. These findings are discussed in relation to adoptive transfer studies performed with other helminths and their possible relevance to naturally acquired immunity is commented on.

Kinetics of classes and sub-classes of total immunoglobulins and specific antibodies to Schistosoma mansoni during murine infection

During the course of Schistosoma mansoni murine infection there is a dramatic increase of some immunoglobulins and S. mansoni-specific antibodies. The most substantial response is initiated after 40 days of infection and results in a prolonged increase of total IgG1, IgM and IgA. The maximum increase is respectively 26, 14 and 3-fold the basic immunoglobulin level in control mice. Some anti-S. mansoni classes and sub-classes were studied by an original radio-immunoadsorbent test. Anti-S. mansoni IgG1 and IgM antibodies appear and increase at the same time as that of total IgG1 and IgM. Anti-S. mansoni IgA antibodies appear later (80th day) and correspond to a second peak of total IgA.

Experimental renal disease due to schistosomiasis

Although there is a marked variability in the development of renal lesions among individual animal models of schistosomal infections, much has been learned about the mechanisms leading to renal injury. The lesions in S. mansoni and S. japonicum infections correspond quite closely to the immune complex type of lesions, with complement involvement. The main antigens involved seem to be polysacharides of worm-gut origin, but participation of other antigens (including soluble egg antigens) cannot be excluded. Many observations testify to the localization of immune complexes, preformed in circulation, but the possibility that antigens, filtered through glomeruli, deposit incapillary walls first and bind with corresponding antibodies later on should be considered also. Deoxyribonucleic acids also may play a role in the pathogenesis. The perpetuation of the lesions is probably due to constant supply of antigens. In some models, renal pathology was related to the dose of infection, but in others there was no relation to worm burden. Renal pathology in S. haematobium infections is different, being related to the lower urinary tract, with obstructive lesions causing pyelonephritis and hydronephrosis.