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 int erleukin (IL)-4. Assuming that this mechanism might play a role in vivo in biasing the immune response towards a Th2 phenotype, we determined basic pr operties of the IL-4-inducing activity contained in SmEA. Sensitivity to pe psin digestion indicated protein nature. Binding to and specific elution fr om Concanavalin A-sepharose suggested that this protein contains mannose re sidues, thus being a glycoprotein. The IL-4-inducing activity was stable fo r 30 min at room temperature towards shifting the pH between 3 and 10. When incubated at 100 degreesC, it was stable at pH 3, but less stable at neutr al and alkaline pH. Electroelution from an SDS-PAGE gel indicated an appare nt molecular weight of the IL-4-inducing activity between 31 and 66 kDa. Al though binding to purified human immunoglobulin E (IgE) and activating baso phils IgE-dependently, SmEA appears to activate basophils in a non-antigen- specific way, since the cells were purified from noninfected donors. Becaus e the IL-4-inducing activity was found to be released from eggs, it could b e an important factor in the environment of the eggs skewing the immune res ponse towards the Th2 phenotype.