PROTECTIVE IMMUNITY INDUCED IN RAT SCHISTOSOMIASIS BY A SINGLE DOSE OF THE SM28GST RECOMBINANT ANTIGEN - EFFECTOR MECHANISMS INVOLVING IGE AND IGA ANTIBODIES

Rats immunized by a single dose of the recombinant Sm28GST antigen, using either aluminium hydroxide or Bacillus Calmette-Guerin adjuvant, were significantly protected (up to 59 % reduction in worm burden) against a challenge infection with Schistosoma mansoni cercariae. A follow-up study of the humoral response revealed the presence of high levels of IgE and IgA antibodies together with specific IgG. Sera from once Sm28GST-immunized rats induced a cytotoxic response for schistosomula targets in the presence of normal rat eosinophils, similar to the one induced by sera from twice immunized rats. Depletion or competition studies indicated the participation of both IgE and IgA antibodies in eosinophil-dependent cytotoxicity mechanisms. These results suggest the existence, in immunized rats exhibiting protection against schistosomiasis, of an original effector mechanism implying eosinophils and IgA antibodies, together with documented effector mechanisms involving IgE and eosinophils. In addition, they raise questions concerning the role of IgA antibodies in schistosomiasis.