A glycoprotein from Schistosoma mansoni eggs binds non‐antigen‐specific immunoglobulin E and releases interleukin‐4 from human basophils

We have recently shown that soluble extracts from Schistosoma mansoni eggs (SmEA) triggered basophils from nonsensitized donors to rapidly release interleukin (IL)-4. Assuming that this mechanism might play a role in vivo in biasing the immune response towards a Th2 phenotype, we determined basic properties of the IL-4-inducing activity contained in SmEA. Sensitivity to pepsin digestion indicated protein nature. Binding to and specific elution from Concanavalin A-sepharose suggested that this protein contains mannose residues, thus being a glycoprotein. The IL-4-inducing activity was stable for 30 min at room temperature towards shifting the pH between 3 and 10. When incubated at 100 degrees C, it was stable at pH 3, but less stable at neutral and alkaline pH. Electroelution from an SDS-PAGE gel indicated an apparent molecular weight of the IL-4-inducing activity between 31 and 66 kDa. Although binding to purified human immunoglobulin E (IgE) and activating basophils IgE-dependently, SmEA appears to activate basophils in a non-antigen-specific way, since the cells were purified from noninfected donors. Because the IL-4-inducing activity was found to be released from eggs, it could be an important factor in the environment of the eggs skewing the immune response towards the Th2 phenotype.