Xenogeneic mouse anti-human NK cytotoxicity is mediated via perforin

Natural killer (NK) cells have been identified among the cell populations thought to participate in delayed xenograft rejection. We investigated the relative contribution of perforin- and Fas ligand-pathways in mouse NK-mediated xenocytotoxicity generated in response to cytokine or xenoantigenic stimulation. Freshly isolated spleen cells exhibited little NK cell-mediated cytotoxicity against human PHA-stimulated peripheral blood mononuclear cells (PBMC) or the human NK-sensitive cell line, K562, despite efficiently lysing mouse NK-sensitive Yac-1 target cells. However, after incubation of mouse spleen cells for 7 to 10 days in the presence of mitomycin C-treated xenogeneic human PBMC or exogenous interleukin-2 (IL-2), the NK activity of cultured mouse adherent lymphocytes (A-NK) against human targets increased dramatically. A-NK cells generated in immunocompetent mice displayed significant lysis of human targets, as did effector cells generated in gld mice with a mutated Fas ligand. By contrast, the low cytotoxic activity of A-NK from perforin-deficient mice responding to K562 target cells suggested that NK xenocytotoxicity is perforin-mediated. Perforin-deficient mouse A-NK cells only lysed Fas-sensitive human PBMC and K562-Fas targets to a. minor extent. Overall, these data suggest that A-NK cell xenolysis is predominantly mediated by perforin, irrespective of the stimulus (cytokine or cellular) provided.