Inhibition of primary and secondary IgE-response by a schistosome-derived inhibitory factor.

Schistosome-derived inhibitory factor (SDIF) previously shown to inhibit lymphocyte proliferation, markedly decreased the primary IgE response of rats immunized with dinitrophenylated ovalbumin (DNP-OVA) when injected either simultaneously or shortly after antigen administration. No effect however was observed when SDIF was injected before the immunization. An inhibition of non-IgE anti-DNP antibodies was also found in SDIF-treated rats although the decrease was lower than with IgE antibody. IgE responses of both low and high IgE responder rats were reduced but a lower dose of SDIF was required in the case of high IgE responder Brown Norway rats. When SDIF was only given at the time of priming, the secondary IgE response was no longer modified. However, the administration of SDIF together with the second injection of the antigen induced marked decrease in the secondary IgE response. The effects of SDIF on primary and secondary IgE responses could be attributed to the inhibitory activity of the parasite-derived factor on lymphocyte proliferation. The observed inhibition of secondary IgE antibody responses confers to SDIF a pharmacological interest in allergic diseases.