HUMAN BASOPHILS RELEASE INTERLEUKIN-4 AFTER STIMULATION WITH SCHISTOSOMA-MANSONI EGG ANTIGEN

The elevated interleukin (IL)-4 and IgE production in Schistosoma mans oni infection seems to be induced essentially by the egg stage of the parasite. The underlying mechanism, however, is not known. Since basop hils from human peripheral blood can produce IL-4, we asked, whether s oluble S. mansoni egg antigens (SEA) would trigger basophils to releas e IL-4. Basophils from healthy human donors (n = 32) without prior his tory of schistosomiasis were incubated with SEA in the presence of IL- 3. In all donors, IL-4 was produced at different concentrations. The I L-4 production was dependent on the dose of SEA, was correlated with t he purity of the basophil preparation, and the IL-4 concentration in t he culture supernatant was maximal 5 h after stimulation with SEA. In addition to its IL-4-stimulatory effect, SEA triggered basophils to de granulate, thereby releasing histamine and sulfidoleukotrienes. Stripp ing of receptor-bound IgE from basophils inhibited both SEA- and anti- IgE-induced, but not ionomycin-induced IL-4 production. Moreover, rese nsitization 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 ind uced in basophils from nonexposed donors, basophils may play a role as an early source of IL-4 in S. mansoni infection.