Evidence for distinct epitopes on human IgG with T cell proliferative and suppressor function.

The Fc or pFc' fragments of the human IgG were demonstrated to exert different effects on murine T lymphocyte subsets. Thus, murine lymph node (LN) T cells were specifically induced to proliferate in vitro to pFc' after priming in vivo. This proliferation could be inhibited, either by depleting the responding LN population of macrophages, or by monoclonal antibodies specific for responder haplotype Ia antigenic determinants. Priming in vivo and subsequent restimulation in vitro with Fc resulted in the activation of a suppressor T cell subpopulation which, in an antigen-specific manner, could highly suppress proliferative responses. T cell subset isolation showed that the pFc'-specific proliferation was performed by Lyt-1+2- cells whereas the suppressor Fc-specific cells were of Lyt-1-2+ phenotype. Our data demonstrate that distinct epitopes on the human gamma chain induce either Ir gene-restricted T cell proliferation (pFc' fragment) or T cell suppressor function (Fc fragment).