FUNCTIONAL PROPERTIES OF Fc RECEPTOR - BEARING T CELLS

Human T lymphocytes were initially identified (1) and distinguished from B lymphocytes based on the ability of T cells to form spontaneous rosettes with sheep erythrocytes (E). 1 Within the E + subset, Moretta et al. (2) defined a discrete subpopulation of cells that bound IgG-coated erythrocytes (EA) via a specific cell surface receptor for the Fc region of IgG (FcR). This population was designated the T~, subset. These cells have been shown to mediate suppressor cell function (2), ant ibody-dependent cellular cytotoxicity (ADCC) (3), and natural killer (NK) cel l -mediated cytotoxicity (4, 5). Using monoclonal antibodies (mAb) against human T cell differentiation antigens, two antigenically and functionally distinct subsets o f E + cells have been identified. The majority of E + lymphocytes express the p a n T cell-associated antigens, CD3 and CD5; whereas a minor subset of E + cells lack CD3 (5-7). However, most IgG-FcR + cells are contained within this small CD3fraction (57). NK cel l -mediated cytotoxicity is confined to E + lymphocytes lacking the CD3 antigen (5). Based on these findings, it was unclear whether functions at tr ibuted to the T7 subset were mediated by the CD3(non-T) NK cell fraction or the very small proport ion of CD3 + T cells that express FcR for IgG. Recently, several mAb (ant i -Leul l , VEP 13, B73.1, and 3G8) have been produced (8-12) that specifically react with the IgG FcR expressed on NK cells and neutrophils. These antibodies do not react with the IgG FcR expressed on monocytes or B lymphocytes (8-10, 12). Essentially all NK and ADCC function is contained within the small fraction of lymphocytes that express this IgG FcR (i.e. CD16/Leu-1 1 antigen) (8-10, 12, 13). We (8, 12) and other investigators (9-1 1) reported that these anti-FcR antibodies did not react with a significant proport ion of CD3 + T lymphocytes isolated