The LLT1 receptor induces IFN-γ production by human natural killer cells

Natural killer cell functions are regulated by signals through activating and inhibitory receptors. These receptors belong to the immunoglobulin superfamily or the lectin superfamily. We have previously identified a lectin-like transcript, LLT1, expressed in human NK cells. In the present study, we have generated a monoclonal antibody, L9.7, that specifically binds LLT1 receptor and studied the functional role of LLT1 in human NK cells. Binding of mAb L9.7 to surface LLT1 induced IFN-γ production, but did not modulate cytotoxicity by YT cells, a human NK cell line. We further demonstrate that in resting NK cells as well as in IL-2 activated NK cells LLT1 induced IFN-γ production, but not cytotoxicity. Excess amounts of L9.7 mAb failed to increase natural or antibody-dependent cell-mediated cytolytic activity, whereas minimal amounts achieved maximal production of IFN-γ by YT and activated NK cells. These findings further support the separation of signaling pathways that regulate cytotoxicity and IFN-γ production in resting as well as activated NK cells.