Human basophils release interleukin-4 after stimulation with Schistosoma mansoni egg antigen

The elevated interleukin (IL)-4 and IgE production in Schistosoma mansoni infection seems to be induced essentially by the egg stage of the parasite. The underlying mechanism, however, is not known. Since basophils from human peripheral blood can produce IL-4, we asked, whether soluble S. mansoni egg antigens (SEA) would trigger basophils to release IL-4. Basophils from healthy human donors (n = 32) without prior history of schistosomiasis were incubated with SEA in the presence of IL-3. In all donors, IL-4 was produced at different concentrations. The IL-4 production was dependent on the dose of SEA, was correlated with the purity of the basophil preparation, and the IL-4 concentration in the culture supernatant was maximal 5 h after stimulation with SEA. In addition to its IL-4-stimulatory effect, SEA triggered basophils to degranulate, thereby releasing histamine and sulfidoleukotrienes. Stripping of receptor-bound IgE from basophils inhibited both SEA- and anti-IgE-induced, but not ionomycin-induced IL-4 production. Moreover, resensitization of stripped basophils with stripping supernatants or human serum restored SEA-induced IL-4 production. This suggests that IgE is involved in the mechanism of IL-4 induction by SEA. Since IL-4 is induced in basophils from nonexposed donors, basophils may play a role as an early source of IL-4 in S. mansoni infection.