Studies of effector cell, antibody, and target cell interactions in natural cell-mediated cytotoxicity.

IgG antibodies bound to effector cells through Fc receptors were observed to determine the specificity of natural cell-mediated cytotoxicity (NCMC) against cultured target cells. When effector lymphocytes were isolated from the peripheral blood of most individuals, they already possessed natural antibodies specific for antigens on cultured cells. Since they lacked IgG antibodies specific for antigens on sheep red blood cell (SRBC) targets, natural cytotoxicity against SRBC was almost non-existent. Effector cells incubated in IgG anti-SRBC became specifically cytotoxic to SRBC. In the process, NCMC and antibody-dependent cell-mediated cytotoxicity was diminished, indicating that arming with anti-SRBC replaced natural antibodies and occupied Fc receptors on effector cells. Thus, treating effector cells with serum may result in increased or decreased cytotoxicity depending upon the specificity of antibodies within the serum. This type of modulation of NCMC occurs at the interaction between antibody Fc and Fc receptors and can explain blocking and unblocking.