INDUCTION OF IGG3 SECRETION BY INTERFERON GAMMA - A MODEL FOR T-CELL INDEPENDENT CLASS SWITCHING IN RESPONSE TO T-CELL INDEPENDENT TYPE-2 ANTIGENS

T cell-independent type 2 (TI-2), in contrast to T-dependent, antigens stimulate the production of murine IgG3. To investigate a possible role for cytokines in mediating the induction of this IgG subclass, we established an in vitro polyclonal model system for studying TI-2 antigen-mediated B cell activation by using dextran-conjugated anti-IgD antibody (alpha-delta-dex). We demonstrate that interferon-gamma (IFN-gamma) stimulates, and interleukin 4 inhibits, the expression of IgG3 by alpha-delta-dex-activated cells. The production of IFN-gamma by non-T cells in response to bacterial products, possibly capsular polysaccharides, may provide an explanation underlying the ability of TI antigens, which are unable to directly stimulate T cell-derived cytokines to induce Ig isotype switching.