PRF1 and neoplasm: Figure 1A shows percent positive cells by flow analysis of common NK surface markers. There was no difference between the LTV and 3.3 cells in cell surface expression of most of the NK markers examined. However, the expression of NK activating receptors, NKp44 and CD16, was significantly higher in LTV cells than in parental cells. Figure 1B shows expression of NK proteins associated with tumor killing (perforin and granzymes) in whole cell lysate from 3.3 and LTV cells.