Fc Fragment Activation of T Lymphocytes. I. Fc Fragments Trigger Lyt 1+23- T Lymphocytes to Release a Helper T Cell-replacing Activity

Fc fragments of human IgG stimulate both proliferation and polyclonal antibody formation by B lymphocytes. T lymphocytes, although not proliferating in response to Fc fragments, are triggered to produce a T cell-replacing factor, which substitutes for T cells in the Fc fragment-induced polyclonal response. The factor is produced within 24 hr after Fc stimulation. Neither Fab fragments nor whole IgG have the capacity to stimulate the release of this activity. This material is a product of Lyt 1+23-, Ia-T lymphocytes and requires Ia+ adherent accessory cells for production. The role of the accessory cell is to process the Fc fragments to biologically active 14,000-daltons subfragments, which directly trigger T cells to factor production. This material has been called (Fc)TRF to distinguish it from other T cell factors.