Later development of Fas ligand-mediated cytotoxicity as compared with granule-mediated cytotoxicity during the maturation of natural killer cells

We classified CD56(+) CD3(-) natural killer (NR) cells into CD2(-) CD56(dim) (CD2(-) NK), CD2(+) CD56(dim) (CD2(+) NK) and CD2(+) CD56(bright) populations, and investigated mainly functional differences between the former two populations. CD2(-) and CD2(+) NK cells were the same in their morphology and several surface molecules except for CD2. The percentages of CD2(-) NK cells in total NK cells were higher in the cord blood and bone marrow than in the peripheral blood of adults or children. Freshly isolated CD2(-) NK cells had CD2 in the cytoplasm, and gradually expressed it on the surface upon incubation with interleukin-2 (IL-2). These results demonstrated that CD2 is an antigen which appears on the surface during the maturation of NK cells. The granule-mediated cytotoxicities, which are mainly performed by the perforin molecule, of CD2(+) NK cells against K562 and Daudi cells were higher than those of CD2(-) NK cells, and they were inhibited to the levels of CD2(-) NK cells by the addition of a blocking anti-CD2 monoclonal antibody (mAb). Fas ligand (Fast) mRNA was expressed in freshly isolated CD2(+) NK cells but not in the CD2(-) NK cells. Neither freshly isolated NK populations showed FasL-mediated cytotoxicity, and only CD2(+) NE( cells lysed Fas-transfected targets after the 24-hr incubation with IL-2, Based on these results, CD2(-) NK cells have already developed granule-mediated cytotoxicity equal to that of CD2(+) NK cells except for the CD2-associated activity, but they, unlike CD2(+) NK tells, totally lack Fast-mediated cytotoxicity. These findings suggest that Fast-mediated cytotoxicity may be acquired at more mature stages of NK-cell maturation than granule-mediated cytotoxicity.