Immunological studies in human schistosomiasis. II. Antibodies cytotoxic for Schistosoma mansoni schistosomules

The esophageal gland mediates host immune evasion by the human parasite Schistosoma mansoni

Schistosomes are parasitic flatworms that cause schistosomiasis, a neglected tropical disease affecting over 200 million people. Schistosomes develop multiple body plans while navigating their complex life cycle, which involves two different hosts: a mammalian definitive host and a molluscan intermediate host. Their survival and propagation depend upon proliferation and differentiation of stem cells necessary for parasite homeostasis and reproduction. Infective larvae released from snails carry a handful of stem cells that serve as the likely source of new tissues as the parasite adapts to life inside the mammalian host; however, the role of these stem cells during this critical life cycle stage remains unclear. Here, we characterize stem cell fates during early intramammalian development. Surprisingly, we find that the esophageal gland, an accessory organ of the digestive tract, develops before the rest of the digestive system is formed and blood feeding is initiated, suggesting a role in processes beyond nutrient uptake. To explore such a role, we examine schistosomes that lack the esophageal gland due to knockdown of a forkhead-box transcription factor, Sm-foxA, which blocks development and maintenance of the esophageal gland, without affecting the development of other somatic tissues. Intriguingly, schistosomes lacking the esophageal gland die after transplantation into naive mice, but survive in immunodeficient mice lacking B cells. We show that parasites lacking the esophageal gland are unable to lyse ingested immune cells within the esophagus before passing them into the gut. These results unveil an immune-evasion mechanism mediated by the esophageal gland, which is essential for schistosome survival and pathogenesis.

Human schistosomiasis mansoni: immune responses during acute and chronic phases of the infection

Schistosoma mansoni infection may occur either as an acute infection in individuals who have recently visited an endemic area, with no previous contact with the parasite, or as a lasting chronic disease, if not interrupted by specific chemotherapy. The acute phase is characterized by symptoms such as fever, cough, diarrhea, anorexia, and arthralgias in combination with leukocytosis and eosinophilia, and a high cellular immune response to schistosome antigens especially those from the parasite's eggs. In the chronic phase, most patients living in endemic areas are asymptomatic, and their immune responses to egg antigens are modulated. A few develop periportal fibrosis of the liver, which may result in the hepatosplenic form of the disease. The humoral response (IgG, IgM and IgE) in acute patients to egg and worm antigens does not differ from the chronic phase. However, a high level of IgG and IgM antibodies to KLH were detected in acute patients. Acute patients express a considerably higher in vitro cellular responsiveness than do chronic patients, especially to egg antigens. They present a mixed profile of Th1 and Th2 cytokines. Ultrasound examinations of endemic population reveal a high heterogeneity between the patients as regards the presence and intensity of periportal fibrosis. Most patients are asymptomatic and their immune responses to schistosoma egg antigens (SEA) are modulated. In contrast, a high percentage of patients with incipient fibrosis (early stage of hepatosplenic) responded strongly to SEA. Patients with advanced hepatosplenic disease were likely to be non-responders to SEA. Most of the chronic patients presented a Th2 profile with low production of interferon-gamma (IFN-gamma). The intensity of infection favors the production of interleukin (IL)-10. After adjusting for age, sex, and intensity of infection, a strong correlation was observed between the production of IL-13 and the degree of fibrosis. Chronic asymptomatic patients and those with incipient fibrosis expressed very high levels of heterogeneity of their antibody responses. IgG response to soluble worm antigen preparation (SWAP) was distinct and significantly higher in hepatosplenic patients than in those asymptomatic or with incipient fibrosis. Levels of IgG4 to SEA were significantly higher in sera from patients with incipient fibrosis as compared to uninfected and hepatosplenic groups. Polyclonal idiotypic antibodies and their fragments F(ab')2, directly stimulate in culture T cells of schistosomiasis patients in presence of IL-1. Polyclonal idiotypic antibodies are able to modulate in vitro granuloma formation around SEA-polyacrylamide. The importance of idiotypes for protection or pathology in schistosomiasis is still not clear.

Complement regulation on the surface of cultured schistosomula and adult worms of Schistosoma mansoni

Cercaria and freshly prepared schistosomula of Schistosoma mansoni are highly sensitive to complement. However, early in their maturation, the schistosomula become resistant to complement killing. This conversion is preceded by a rapid and massive release of several acetabular proteases and of the glycocalyx coat. Thus, shedding of the glycocalyx which is a major immunogen and a strong activator of the alternative pathway of complement permits the parasite to escape immune damage. Mechanically transformed schistosomula, which were cultured in a defined synthetic medium and developed complement resistance, could be converted by proteolysis to complement sensitivity. Trypsin and pronase markedly increased the susceptibility of cultured schistosomula to complement. The trypsin-induced complement sensitivity persisted for at least 19 h without recovery of resistance. Similar treatment with trypsin produced complete killing of adult worms by complement in absence of antibodies. Efficient killing was obtained with normal human serum (NHS), with normal guinea pig serum (GpS), and with C4-depleted HS and C4-deficient GpS indicating that the killing was mediated by the cytolytic alternative pathway of complement. Larger quantities of C3b with intact alpha' chain could be demonstrated on trypsin-treated than on non-treated schistosomula. Antibodies which were raised in rabbits by immunization with the trypsin-released material bound to cultured (non-treated) schistosomula and to adult worms, and induced their killing in GpS and C4-deficient GpS. These results suggest that following release of the glycocalyx, the transforming schistosomula of S. mansoni spontaneously express a complement regulatory protein(s). A similar regulator is postulated to be present on the surface of adult worms. Such regulatory molecules may serve as good targets for immunotherapy, since antibodies directed to them will inhibit their regulatory activity and thus potentiate in vivo the lytic action of complement.

Schistosoma mansoni: killing of transformed schistosomula by the alternative pathway of human complement

The interaction of mechanically transformed schistosomula of Schistosoma mansoni with the alternative pathway of human complement was studied in vitro. To detect early changes in transformation, the schistosomula were prepared at a low temperature and used immediately. As shown previously, freshly transformed schistosomula were highly susceptible to killing by normal human serum and by C4-depleted normal human serum. This serum activity was concentration dependent and was markedly reduced on a twofold serum dilution. Upon incubation at 37 C in defined synthetic medium, schistosomula rapidly became refractory to killing by the alternative pathway of complement. After 1 hr of incubation at 37 C, the percentage of schistosomula which were resistant to killing increased from 16 to 85. This conversion was accompanied by a fivefold decrease in deposition of C3b on schistosomula which had been exposed to 37 C for 1 hr and then further incubated with C4-depleted normal human serum. The following events occurred concomitantly during incubation of freshly transformed schistosomula at 37 C with a half-life of 30-60 min: (1) Decrease in activation and consumption of the alternative pathway of complement by schistosomula; (2) appearance of a strong complement consuming activity in the supernatant of incubating schistosomula; and (3) shedding of protein- and carbohydrate-containing substances from the surface of schistosomula into the supernatant. Isolated external membranes of freshly transformed schistosomula consumed the alternative pathway of complement to a greater extent than membranes of schistosomula preincubated in medium at 37 C. The results demonstrate that transformed schistosomula acquire resistance to complement killing via the alternative pathway by shedding complement-activating substances.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation Of Specific Ige Antibody In Clonorchis Sinensis Infection

Serum IgE level and Clonorchis specific IgE in individuals with Clonorchis sinensis were determined by radioimmunosorbent(RIST) and radioallergosorbent technique(RAST) respectively. Highly significant elevations of serum IgE (P<0.001) and specific IgE antibodies (P<0.01) were observed in area from individuals with clonorchiasis. The mean values of serum IgE in individuals with clonorchiasis and healthy individuals were 2,372 IU/ml and 364 IU/ml respectively and specific IgE antibodies of both groups were 52.0 and 4.4%. A close correlation(r=0.9451) between serum IgE level and specific IgE antibodies were observed and correlation (r=0.6056) between serum IgE and EPG and between specific IgE and EPG(r=0.5693) were also observed.

In vitro study of immunological events in human and experimental schistosomiasis: relationships between cytotoxic antibodies and circulating Schistosoma antigens

Complement-dependent cytotoxic antibodies were found in 54% of Schistosoma mansoni infected patients from Burundi and in 69 to 78% of Schistosoma mansoni ninfected Brazilian patients. The levels of cytotoxic Ab were not statistically different in sera from infected mothers and from their newborn children, suggesting a transfer through the placenta. A sandwich radioimmunoassay (SRIA) and the Radioimmunoprecipitaion-PEG assay (RIPEGA) technique were used in order to detect respectively total schistosome circulating soluble antigens (CSA) and schistosome antigen '4' in sera from infected patients. An inverse relationship was found between the presence of cytotoxic Ab and both total CSA and antigen '4'. The cytotoxic Ab and total CSA levels were followed in five Erythrocebus patas monkeys for 30 weeks after Schistosoma mansoni infection. As in human schistosomiasis the presence of cytotoxic Ab was found to be inversely correlated with the presence of total CAS. The blocking role of Schistosoma mansoni antigens in a complexed form was suggested by the inhibitory effect of the ultracentrifugation pellet of infected human serum on the cytotoxic activity. Moreover, the CSA absorption of infected monkey serum by passage through an anti-CSA immunosorbent significantly increased the cytotoxic activity. Possible mechanisms for the inhibitory role of circulating immune complexes on complement-dependent cytotoxic activity are discussed.