Evidence that schistosome MHC antigens are not synthesized by the parasite but are acquired from the host as intact glycoproteins.

Schistosoma mansoni schistosomula recovered from the lungs of mice have previously been shown to express serologically detectable products of the major histocompatibility complex (MHC). To determine whether these determinants are products of the schistosome genome, DNA from cercariae and adult worms of the parasite was probed with a 32P-cDNA clone encoding a human class I MHC antigen. Although this probe hybridized to mouse DNA, no hybridization was observed with DNA isolated from schistosomes, indicating that there are no DNA sequences homologous to class I MHC antigens in the parasite genome. The class I MHC antigens found on schistosomes were characterized in a further series of experiments. Two monoclonal antibodies known to recognize spatially distinct determinants of H-2Kk both bound to lung-stage schistosomula recovered from mice expressing this haplotype, suggesting that a significant portion of the H-2K molecule is present at the larval surface. Furthermore, both antibodies precipitated from lysates of 125I-lactoperoxidase-labeled lung-stage schistosomula, a molecule of approximately 45,000 daltons similar in mobility to H-2Kk precipitated from 125I-labeled mouse spleen cells. These results support the hypothesis that the class I MHC antigens expressed on S. mansoni are not synthesized by the parasite but are acquired from the host as intact glycoproteins.