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-gamma 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-gamma 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-gamma by YT and activated NK cells. These findings further support the separation of signaling pathways that regulate cytotoxicity and IFN-gamma production in resting as well as activated NK cells.