Pokeweed mitogen induces IgE synthesis in the presence of a blocking antibody to the interferon-γ receptor

Background: Although pokeweed mitogen (PWEM) can induce peripheral blood mononuclear cells (PBMCs) to synthesize IgG, IgA, and IgM, such cultures fail to induce IgE synthesis. The present study examined the possibility that the stimulation of interferon-γ (IFN-γ) production plays a role in the failure of PWM to induce IgE synthesis. Methods: We examined PBMCs from eight normal control subjects for IFN-γ and IL-4 production. Since IFN-γ synthesis is known to inhibit IgE synthesis, we also examined the effect of a neutralizing anti-IFN-γ antibody and of two anti-IFN-γ receptor antibodies, monoclonal antibody (mAb) GIR208, which blocks cellular binding of IFN-γ, and mAB GIR94.5, which binds to the IFN-γ receptor but does not block the binding of IFN-γ to its receptor on PWM-stimulated PBMCs. Results: After stimulation with PWM, culture supernatants contained significantly more IFN-γ ( p = 0.001) and IL-4 ( P = 0.001) compared with supernatants from nonstimulated cultures. PWM-stimulated PBMCs also expressed higher levels of IFN-γ and IL-4 gene transcripts than unstimulated cells. When cultured in the presence of anti-IFN-γ, superantants from PWM-stimulated cultures also induced CD23 on Ramos B cells in an IL-4-dependent manner. In the presence of mAB GIR208 and a neutralizing anti-IFN-γ antibody, but not mAb GIR94.5, PWM stimulated PBMCs from eight normal control subjects and six patients with atopic dermatitis to produce IgE. Monoclonal antibody GIR208, however, did not enhance IgG synthesis. Furthermore, the exogenous addition of IFN-γ inhibited the IgE-stimulatory effect of mAb GIR208. Monoclonal antibody GIR208 was unable to induce purified B cells to synthesize IgE in the presence of IL-4. Conclusions: Thus unlike anti-CD40, mAb GIR208 does not act as a second signal for the induction of IgE synthesis. These results demonstrate that the induction of IFN-γ production contributes to the failure of PWM to stimulate synthesis of IgE in PBMCs from atopic and nonatopic donors.