Modulation of antigen-induced B and T cell responses by antigen-specific IgE antibodies

Ag-specific IgE Abs not only mediate immediate hypersensitivity through mast cell activation, but also enhance in vitro Ag presentation and in vivo specific Ab responses in mice. To delineate the role of IgE Ab in the modulation of Ag-specific responses, spleen cells from OVA-sensitized BALB/C mice were cultured together with OVA-specific IgE (or IgG isotypes). OVA-dependent proliferative responses and anti-OVA IgE production were enhanced in the presence of anti-OVA IgE. A significant decrease in IFN-gamma secretion in OVA-stimulated cultures was observed in the presence of anti-OVA IgE, but no changes in IL-4 production were detected. Anti-OVA IgG isotypes or anti-TNP IgE showed no significant effect on any of these Ag-dependent responses. Addition of anti-CD23 Ab abolished these effects of anti-OVA IgE. Further, OVA-sensitized spleen cells from CD23-deficient mice responded to in vitro stimulation with OVA, but demonstrated no modulation by anti-OVA IgE. These results demonstrate that Ag-specific IgE not only augments Ag presentation and T cell proliferation, but also alters the pattern of cytokine production and increases specific IgE synthesis. These modulatory effects of Ag-specific IgE appear to be mediated by binding to Fc epsilon RII/CD23.