FAS-MEDIATED CYTOTOXICITY BY FRESHLY ISOLATED NATURAL-KILLER-CELLS

The expression of Fas ligand on natural killer (NK) cells and Fas-medi ated cytotoxicity by NK cells was investigated. Fas ligand mRNA was ex pressed in freshly isolated NK cells but not in T cells. Furthermore, the Fas ligand was detected on the cell surface of NK cells by stainin g with soluble Fas molecule. We analyzed the cytolytic activity of NK cells against thymocyte targets from normal and lpr mice, and found th at the NK cells killed thymocytes from normal mice but not from lpr mi ce. On the other hand, splenic T cells did not show any cytotoxicity a gainst either of the thymocyte targets. Similarly, NK cells exhibited cytotoxicity against transfectants expressing Fas antigen but not agai nst parental cells or transfectants expressing a mutant Fas antigen wi th deleted cytoplasmic region. These results demonstrated that NK cell s express Fas ligand and possess the capability of killing target cell s expressing Fas antigen on their surface. This finding suggests that NK cells play an important role by eliminating Fas-expressing cells ei ther constitutively or inducibly in peripheral lymphoid organs.