Humans express natural cytotoxic (NC) cell activity that is similar to murine NC cell activity.

The expression of natural cytotoxic (NC) activity is well defined in mice, but poorly defined in humans. In this paper we report that humans express naturally occurring cytotoxic cell activity that recognizes and lyses murine targets that are sensitive to lysis mediated by murine NC cells, but not murine targets that are resistant to lysis by murine NC cells. We present data showing that these naturally occurring human cytotoxic cells and murine NC cells have similar lytic mechanisms. Both the human cytotoxic cells described here, and murine NC cells, use tumor necrosis factor (TNF) to mediate the lysis of sensitive targets. Moreover, targets that resist murine NC-mediated lysis by a protein synthesis-dependent post-recognitive mechanism use a similar mechanism to prevent lysis mediated by naturally occurring human cytotoxic cells. In addition to the similarity of naturally occurring human cytotoxic cells and murine NC cells in their specificity and lytic mechanism, naturally occurring human cytotoxic cells and murine NC cells are also similar in that their activity is both associated with a monocyte lineage and age independent. Taken together, these data indicate that humans express NC activity.