Sera from humans with chronic Schistosoma mansoni infections (CHS) were chromatographed with CNBr-activated Sepharose 4 B conjugated with NP-40 extracts obtained from live 3 hr schistosomula. Both unbound (CHS(UB)) and bound (CHS(B)) fractions which contained IgG and IgM isotypes were characterized by ELISA, immunofluorescence, and complement-mediated in vitro killing assays. ELISA data showed that the CHS(B) fraction recognized schistosomula NP-40 extracts, whereas the CHS(UB) fraction did not. However, both CHS(UB) and CHS(B) fractions recognized 8 M urea adult worm extracts and 8 M urea egg extracts. By indirect immunofluorescence assay, the CHS(B) fraction recognized epitopes on the surface of live schistosomula 3 hr-29 days of age, whereas the CHS(UB) fraction showed surface fluorescence only on 24- and 29-day-old worms. The CHS(B) fraction mediated 95% killing of schistosomula in a complement dependent in vitro assay, the CHS(UB) fraction and the unfractionated CHS did not exhibit killing ability. The CHS(UB) fraction was able to titrate out the killing ability of the CHS(B) fraction in in vitro cytotoxic assays when mixed with the CHS(B) fraction at increasing concentrations. In passive immunization experiments, the CHS(B) fraction provided ~30% passive protection in mice when injected 1 day or 6 days after challenge and 20% protection when injected at 15 days, but failed to provide protection when administered ≥24 days after challenge. Unfractionated CHS failed to mediate passive protection.
ASJC Scopus subject areas
- Infectious Diseases