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 (CHSUB) and bound (CHSB) fractions which contained
IgG and
IgM isotypes were characterized by ELISA, immunofluorescence, and
complement-mediated in vitro killing assays. ELISA data showed that the CHSB fraction recognized schistosomula
NP-40 extracts, whereas the CHSUB fraction did not. However, both CHSUB and CHSB fractions recognized 8 M
urea adult worm extracts and 8 M
urea egg extracts. By indirect immunofluorescence assay, the CHSB fraction recognized
epitopes on the surface of live schistosomula 3 hr-29 days of age, whereas the CHSUB fraction showed surface fluorescence only on 24- and 29-day-old worms. The CHSB fraction mediated 95% killing of schistosomula in a
complement dependent in vitro assay, the CHSUB fraction and the unfractionated CHS did not exhibit killing ability. The CHSUB fraction was able to titrate out the killing ability of the CHSB fraction in in vitro cytotoxic assays when mixed with the CHSB fraction at increasing concentrations. In passive immunization experiments, the CHSB fraction provided approximately 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 greater than or equal to 24 days after challenge. Unfractionated CHS failed to mediate passive protection.