Mouse natural killer (NK) cell activity against human cell lines is not influenced by superinfection of the target cell with xenotropic murine c‐type virus

Mouse natural killer (NK) cells can lyse a variety of syngeneic, allogeneic and xenogeneic target cells in short‐term ⁵¹Cr release assays. The target specificity of NK cells is not known, but endogenous C‐type viral antigens have been suggested as possible target structures. To test this hypothesis, human lymphoid lines were superinfected with xenotropic mouse C‐type virus either by repeated passage through nude mice or by in vitro superinfection with the supernatants of nude‐mouse‐passaged lines. The appearance of surface‐associated MuLV antigens after superinfection was confirmed in a complement‐dependent cytotoxtcity test. Subsequently, the NK sensitivity of each infected line was compared with its non‐infected counterpart in direct cytolytic and competition assays, None of these two assay systems showed a consistent difference in NK sensitivity of infected and non‐infected cell lines. These findings do not lend support to the concept that murine C‐type viral antigens are responsible for NK sensitivity.