Infection induces antibodies against the cercarial secretions, but not against the cercarial elastases of Schistosoma mansoni, Schistosoma haematobium, Schistosoma japonicum and Trichobilharzia ocellata

Cercarial secretions from different species of the parasite Schistosoma and from Trichobilharzia ocellata contain a proteolytic activity, cercarial el astase, which was demonstrated by a 30 kDa band in gelatin gels. Sera of pa tients infected with Schistosoma mansoni, Schistosoma haematobium or Schist osoma japonicum contain immunoglobulin G which react in ELISA with cercaria l secretions from all schistosomes and cross-react among the different para site species. In Western blots, however, infection sera from patients, as w ell as heavily infected mice or rabbits, did not react with a 30-kDa protei n. Moreover, when sections from infected snails (Biomphalaria, Bulinus and Lymnaea) were analysed by immunofluorescence using the same infection sera, only the tegument of the developing cercariae was recognized, but not the acetabular glands. In contrast, when antisera against purified cercarial el astase from either S. mansoni or S. haematobium were tested with sections o f infected Biomphalaria or Bulinus fluorescence was strong in the preacetab ular glands of the cercariae of either species, but undetectable with the t egument. Cross-reactivity of both antisera extended to T. ocellata-infected Lymnaea, but not to S. japonicum-infected Oncomelania. In conclusion, alth ough immunization with purified cercarial elastase results in antibody prod uction, the enzyme does not induce an apparent antibody response following natural infection.