Human CD16 as a lysis receptor mediating direct natural killer cell cytotoxicity

In addition to their role in peptide antigen presentation, class I MHC prot eins also play a critical role in inhibiting natural killer (NK) cytotoxici ty through interaction with NK inhibitory receptors, Thus, NK cells are cyt otoxic to virus-infected and tumor cells that have lost class I MHC protein expression, However, the nature of the receptors involved in the triggerin g of lysis of target cells is poorly understood. CD16 (Fc gamma receptor II I) has been described as a receptor expressed on NK cells that facilitates antibody-dependent cellular cytotoxicity (ADCC) by binding to the Fc portio n of various antibodies. However, we show here that CD16 has a broader func tion and is directly involved in the lysis of some virus-infected cells and tumor cells, independent of antibody binding. The presence of a putative C D16 ligand on appropriate target cells has also been demonstrated by the us e of a CD16-Ig fusion protein.