Loss of Fc receptors for IgG from human T lymphocytes exposed to IgG immune complexes

Abstract

SURFACE receptors for immunoglobulins (Ig) have been detected on mononuclear lymphoid cells of several animal species. They are present on monocytes, macrophages, T and B lymphocytes and on a third as yet poorly defined population of non-T non-B cells (‘null’ cells)¹. Early studies demonstrated mainly receptors for IgG, but binding of IgM and IgE to lymphoid populations has also been observed^2–6. In humans the presence of surface receptors for either IgM or IgG molecules distinguishes two distinct T cell populations (T_·M and T_·G respectively) which have clearly defined functional characteristics. T_·M cells help B cell differentiation induced by pokeweed mitogen^7,8, whereas T_·G cells suppress differentiation. T_·G lymphocytes only suppress following interaction with IgG immune complexes, perhaps indicating an important role for IgG-Fc receptors in the regulation of humoral responses⁸. Another recognised role for IgG-Fc receptors is to mediate the antibody-dependent cell-mediated cytotoxicity (ADCC)^9,10. This latter activity is associated with both T and ‘null’ lymphocytes^11,12. We report here that interaction between IgG immune complexes and IgG-Fc receptors present on human T_·G cells is followed by the irreversible disappearence of the Fc receptors. As a consequence of this ‘modulation’ T_·G lymphocytes lose most of their cytotoxic activity in an antibody-mediated cell killing system.