The expression of CD80 and or CD86 on target cells is not associated with the intensity of cytotoxicity by human NK cells

NK cell-mediated cytotoxicity is influenced by triggering as well as inhibi tory signals. The identification of inhibitory signals provided by MHC clas s I molecules has recently attracted significant attention. Much less is kn own about putative triggering signals. Using purified populations of murine NK cells and a human NK cell line (YTC2), it was proposed that the CD80 ge ne product functions to trigger proliferation and cytotoxicity of NK cells. However, a recent study reported that transduction of CD80 gene into squam ous cell carcinomas of the head and neck targets did not result in enhanced proliferation or cytotoxicity of human adult NK cells. To elucidate these observations, we examined the possible co-stimulatory role of CD80 and CD86 molecules or both on fresh human NK cell-mediated cytotoxicity. By transfe cting cDNA of CD80 or CD86 into K562 cells, we established four different K 562 clones that express CD80 and/or CD86 or none. Using these K562 clones w e demonstrated that CD80 and/or CD86 molecules are not involved in purified human NK-mediated cytotoxicity;. In addition, the expression of CD80 and/o r CD86 on target K562 cells did not trigger fresh human NK cell proliferati on or lymphokine production. We conclude that the CD80 and/or CD86 molecule s are not associated with fresh human NK cell proliferation, lymphokine pro duction, or cytotoxicity.