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

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Abstract
Complement-dependent cytotoxic antibodies (Ab) were found in 54% of S. mansoni infected patients from Burundi and in 69-78% of S. mansoni infected 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 radioimmunoprecipitation-PEG [polyethylene glycol] assay (RIPEGA) technique were used to detect total schistosome circulating soluble antigens (CSA) and schistosome antigen 4, respectively, in sera from infected patients. An inverse relationship was found between the presence of cytotoxic Ab and total CSA and antigen 4. The cytotoxic Ab and total CSA levels were followed in 5 Erythrocebus patas monkeys for 30 wk after S. mansoni infection. As in human schistosomiasis, the presence of cytotoxic Ab was inversely correlated with the presence of total CSA. The blocking role of S. mansoni antigens in a complexed form was suggested by the inhibitory effect of the ultracentrifugation pellet of infected human serum on the cytotoxic activity. 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.