Antibody-Dependent Complement-Mediated Killing of Schistosomula in Intraperitoneal Diffusion Chambers in Mice

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Abstract
The present investigations were designed to determine the biologic role of the different host defense mechanisms against schistosomiasis mansoni that are independent of direct cell-parasite contact. Schistosomula were placed in Millipore chambers of 0.22-µm pore size and were implanted i.p. into immune and nonimmune age- and sex-matched control mice. Significant degree of mortality was detected on recovery of the implanted schistosomula at 24 hr; the mean dead organisms in immune animals was 30 ± 4% as compared to 10 ± 2% in control mice (p < 0.01). This effect on the implanted schistosomula into immune mice was confirmed by injecting these organisms into normal recipients and by recovering those that mature to adult worms. The ability of immune mice to kill significant numbers of implanted schistosomula was dependent on the intensity of infection and developed only after 8 weeks, which parallels the onset of protective immunity in vivo. Adoptive transfer of immune sera to normal recipients resulted in a mean of 23 ± 2% dead schistosomula in the recipient mice, which represents approximately 65% of the protection detected in the donor animals. Depletion of the eosinophils or neutrophils in the immune mice did not alter their ability to kill significant numbers of the implanted schistosomula. Cobra venom factor treatment, on the other hand, resulted in abrogation of the significant schistosomula killing detected in immune mice or in animals adoptively transferred with immune serum. These results demonstrate that specific acquired immunity to schistosomiasis in vivo is partially mediated by humoral factors and is dependent on the presence of complement. The Millipore chambers may help elucidate the significance of the many mechanisms which have already been described for host immune responses against the multicellular parasite Schistosoma mansoni.