Activation of T lymphocytes by the Fc portion of immunoglobulin.

T lymphocytes are stimulated to release T-cell-replacing factors in response to Fc fragments of human IgG, Lyt 1+23- T cells are directly triggered to factor production by Fc subfragments, derived from intact Fc fragments by macrophage-dependent enzymatic cleavage. These factor(s) replace T cell function in two Fc-mediated immune responses; induction of polyclonal antibody synthesis, and potentiation of anti-SRBC responses.