Blocking activity of rat monoclonal antibodies in experimental schistosomiasis.

Rat IgG2c monoclonal antibodies have been produced after fusion of spleen cells from LOU/C rats infected with Schistosoma mansoni for 5 wk and IRF983F nonsecreting rat myeloma. The cell supernatant of an IgG2c-producing clone (IPLSm3), as well as ascitic fluids induced by this clone, revealed anti-S. mansoni activity detected by immunofluorescence on schistosomula sections. Antigenic analysis performed with IPLSm3 IgG2c antibody allowed to isolate onto the S. mansoni schistosomula surface a 38,000 dalton antigen previously characterized with the protective IPLSm1 IgG2a monoclonal antibody. Although IPLSm3 IgG2c did not exhibit any killing activity in vitro against schistosomula in the presence of complement, macrophages, or eosinophils, it was shown to strongly inhibit the eosinophil-dependent cytotoxicity mediated by IPLSm1 IgG2a antibodies. The blocking activity of IgG2c antibody was further demonstrated in vitro by the use of F(ab')2 fragments and in vivo by the inhibition of passively transferred immunity conferred by the IgG2a protective monoclonal antibody. These results indicate that blocking antibodies could play an important role in the expression of protective immunity during schistosome infection.