Properties of Serine Proteases of Schistosoma mansoni Schistosomula Involved in the Regulation of IgE Synthesis

Abstract

The regulation of IgE synthesis in vitro and in vivo by schistosomula‐released products (SRP) has been shown to be dependent on the presence of serine proteases. The present paper concerns the characterization of the enzymes involved. The labelling of SRP with [³H]di‐isopropyl phosphofluoridate revealed two molecules, one major with an MW of 27,500 and one minor with an MW of 29,000. The same pattern was obtained by labelling of schistosomula or cercariac surfaces as well as of the total schistosomulum homogenate. The properties of these enzymes were studied by means of various specific substrates or inhibitors of serine proteases. The specificity was relatively narrow, but had some similarity with trypsin. When added to lymphoid rat cells in culture, SRI induced an increased expression of receptors for the Fc fragment of IgE (FcεRII). This suggests that the IgE‐enhancing property of SRP was due to serine protease activity which may act by enhancing the lymphocyte FcεRII.