Strain differences in lymphocyte responses and in vitro suppressor cell induction between Schistosoma mansoni-infected C57BL/6 and CBA mice

T cell-mediated immunity in CBA mice during Schistosoma japonicum infection

Characterisation of the cellular immune response to schistosomiasis is well established for Schistosoma mansoni but a comprehensive description of T cell-mediated immune responses against S. japonicum infection is lacking. Accordingly, 20 CBA mice were infected with cercariae of S. japonicum and the immune response at different time points was determined. Mouse spleen and liver lymphocytes were isolated from the mice and stimulated with schistosomal adult worm antigen preparation (SWAP) and schistosomal soluble egg antigen (SEA). There was a relatively higher Th1 immune response to SWAP compared to SEA at the early phase of infection (up to week 5 post challenge). However, a Th2 immune response directed against SEA was dominant at week 6 post-infection, a time point when the highest IgG response against both SWAP and, especially, SEA was generated. The regulatory immune response was highest at the early phase of the immune response (up to week 5 post challenge) followed by a rapid decline at week 6-post infection. Before egg-laying, S. japonicum induced a regulatory T cell immune response which may limit the early Th1-mediated immune response that is believed to be protective in murine schistosomiasis. Following egg laying, the immune response was polarized to a Th2 immune response mainly directed against the eggs and this may contribute to parasite survival.

Tetraspanins on the surface of Schistosoma mansoni are protective antigens against schistosomiasis

Schistosomes are blood-dwelling flukes that infect 200 million people worldwide and are responsible for hundreds of thousands of deaths annually. Using a signal sequence trap, we cloned from Schistosoma mansoni two cDNAs, Sm-tsp-1 and Sm-tsp-2, encoding the tetraspanin (TSP) integral membrane proteins TSP-1 and TSP-2. We raised antibodies to recombinant TSP fusion proteins and showed that both proteins are exposed on the surface of S. mansoni. Recombinant TSP-2, but not TSP-1, is strongly recognized by IgG1 and IgG3 (but not IgE) from naturally resistant individuals but is not recognized by IgG from chronically infected or unexposed individuals. Vaccination of mice with the recombinant proteins followed by challenge infection with S. mansoni resulted in reductions of 57% and 64% (TSP-2) and 34% and 52% (TSP-1) for mean adult worm burdens and liver egg burdens, respectively, over two independent trials. Fecal egg counts were reduced by 65-69% in both test groups. TSP-2 in particular provided protection in excess of the 40% benchmark set by the World Health Organization for progression of schistosome vaccine antigens into clinical trials. When coupled with its selective recognition by naturally resistant people, TSP-2 seems to be an effective vaccine antigen against S. mansoni.

Two distinct pathological syndromes in male CBA/J inbred mice with chronic Schistosoma mansoni infections

Humans chronically infected with Schistosoma mansoni most commonly present with the relatively asymptomatic intestinal form of the disease, whereas a small minority develop hepatosplenism characterized by severe hepatic disease with portal hypertension. Investigation of hypotheses describing the pathogenic mechanisms underlying the clinical forms of the human disease has been limited by the absence of an animal model that predictably develops such a spectrum of disease. We report that inbred male CBA/J mice that are chronically infected with S. mansoni develop two distinct syndromes, hypersplenomegaly syndrome (HSS) and moderate splenomegaly syndrome (MSS). Pathologically and immunologically, MSS and HSS remarkably parallel the intestinal and hepatosplenic clinical forms, respectively, in humans. HSS affects approximately 20% of these mice and consists of massive splenomegaly, ascites, thymic atrophy, severe anemia, and cachexia. The remaining majority of mice with MSS develop moderate splenomegaly only. Histopathological features of HSS include 1) relatively extensive hepatic fibrosis and granulomatous inflammation, 2) splenic congestion, 3) lymph node plasmacytosis, and 4) worms and eggs in the pulmonary vasculature. Immunologically, the idiotypes present on antisoluble egg antigen antibodies from HSS mice are distinct from those from mice with acute infections or the chronic MSS infection. These idiotypic differences are similar to those observed in patients with intestinal and hepatosplenic forms of the disease and may have regulatory importance. Investigation of the cellular and molecular events that lead to the development of MSS and HSS may advance current understanding of the pathogenesis of the clinical forms of chronic schistosomiasis in humans.

Reduced lymphocyte response to mitogens in patients with Bancroftian filariasis

Peripheral blood lymphocytes from patients with acute and chronic Wuchereria bancrofti infections responded poorly to concanavalin A, phytohaemagglutinin and pokeweed mitogen when cultured in heat-inactivated pooled normal serum. The lymphocyte response to mitogens in carriers of microfilariae (mff) were normal. The suppression of transformation to mitogens was not reversible by the removal of plastic adherent cells. Incubation with mitogens and the adult filarial worm antigen (BmA) did not alter the mitogen response either in control subjects or in filarial patients. The possible mechanism of immunosuppression is discussed.

The inheritance of responses to schistosomiasis mansoni in two pairs of inbred strains of mice

Genetic differences in mice influence both the pathological and immunological responses to schistosomiasis mansoni. We have investigated the nature of the genetic factors influencing these responses by crossing two different pairs of strains of mice which vary in their response to infection, and measuring responses in the F1 hybrid and backcross offspring. The two pairs of parental strains differed with respect to faecal egg excretion, accumulation of eggs in the tissues, splenomegaly and pattern of antibody response. The numbers of adult worms which establish do not differ between strains. The inheritance of the responses measured was different in the two pairs of strains. The F1 hybrid from the C57BL/6/0la X BALB/c cross resembled the low-responding parental strain (C57BL/6/0la) with respect to faecal egg excretion, accumulation of eggs in the tissues and splenomegaly, and was intermediate in its pattern of antibody response. The F1 hybrid mice from the NIH X CBA/Ca cross resembled the high-responding strain (CBA/Ca) with respect to faecal egg excretion, accumulation of eggs in the tissues and splenomegaly, and had an earlier and greater antibody response than either parental strain. No evidence of single gene influence on any of these responses was seen in the backcross offspring. The differing patterns of inheritance and the absence of a bimodal distribution of responses in the backcross offspring indicate that each of these responses is influenced by multiple genes. The pattern of antibody response did not correlate between strains with any of the pathological responses. The positive correlation of egg accumulation in the tissues and faecal egg excretion suggests that there are genetic influences on the fecundity of the worms.

Induction of non-specific human suppressor cells in vitro by defined Onchocerca volvulus antigens

In the present study the activity of Onchocerca volvulus total antigens (OVA) on the proliferative response of human lymphocytes from healthy donors was investigated. Normal human lymphocytes were cultured for 72 h with polyclonal activators, phytohaemagglutinin (PHA) or pokeweed mitogen (PWM), together with OVA, and thymidine uptake was measured. The proliferation of normal lymphocytes was markedly inhibited by the parasite antigens. The inhibition was not attributable to a cytotoxic effect of OVA, since at least 80% viable cells were recovered at the end of cell cultures. The inhibition was not abrogated by removal of the adherent cell population. The passage of OVA through immunosorbent column containing human antibodies to O. volvulus significantly reduced the suppressive activity of OVA. The in vitro response to mitogens (PHA, PWM) of normal human lymphocytes was suppressed by co-culture with allogeneic or syngeneic lymphocytes, which had previously been exposed for 72 h to OVA. The suppression was not abrogated by the irradiation of mononuclear cells before the exposure to OVA. A significant reduction of the suppression was however observed when OVA pre-treated cells were T cell depleted by centrifugation of E rosettes. Thus, parasite antigens, which are recognized by antibodies in infected human sera may participate in the modulation of the cellular immune response during O. volvulus infection by inducing suppressor cells. This suppression could in addition contribute to the survival of the parasite in its host.

Suppression of mitogen-induced lymphocyte transformation by plasma from patients with hepatosplenic Schistosomiasis mansoni: role of immune complexes

Plasma from chronic or advanced hepatosplenic schistosomiasis (mansoni) patients (PCS) suppressed mitogen-induced responses of normal human peripheral blood mononuclear cells. 1 x 10(5) Ficoll-Hypaque isolated lymphocytes were cultured in 100 microliter RPMI 1640 media with 100 microliter plasma preparation and stimulated with phytohemagglutinin P (PHA), concanavalin A (Con A), pokeweed mitogen (PWM) and Staphylococcus aureus phage lysate (SPL). Compared to normal human plasma, dose-response experiments with 10-50% PCS uniformly inhibited the 72-h PHA, Con A and PWM responses with maximal suppression at 50% plasma concentration. At this concentration, the range of suppression was 42-60%. The inhibitory activity was unaffected by 56 degrees C, 30 min pretreatment of PCS. However, pre-culture of cells with PHA for 24 h prior to addition of 50% PCS abrogated the suppressor activity. Furthermore, 6-day cultures with PWM and SPL were not suppressed by 50% PCS. Plasma suppressor activity was nearly eliminated by pre-treatment of PCS with 4% (w/v) polyethylene glycol (PEG) in all cases. In the putative immune complexes in the PEG precipitates, Clq, C3, C4, IgG, IgM and IgA were identified in nearly all PCS samples. Schistosomal antigen was found in only two of 23 PCS samples tested and significant anti-schistosomal IgG antibodies were found in all PEG precipitates. The data suggest immune complexes (non-specific and specific) act to suppress 72-h mitogenic responses.