PIVOTAL ROLE OF ENDOGENOUS TNF-ALPHA IN THE INDUCTION OF FUNCTIONAL INACTIVATION AND APOPTOSIS IN NK CELLS

The interaction of purified nonactivated human NK cells with target ce lls overnight results in functional anergy and apoptosis in NK cells a nd in a change of the NK phenotype from CD16(+)CD56(+)CD69(-) to CD16( dim/-)CD56(+/dim/-)CD69(+). These studies suggested that signaling tri ggered by the FcR CD16 may be implicated in target cell-mediated anerg y/apoptosis of NK cells, We hypothesized that triggering CD16 by anti- CD16 Ab should result in NK cells exhibiting functional and phenotypic Properties similar to those obtained following triggering of NK cells with target cells, The findings demonstrate that the anti-CD16 mAb-tr eated NK cells acquired the CD16(-)CD56(+/dim)CD69(+)Fas(+) phenotype and lost their cytotoxic function, a significant number of the NK cell s underwent apoptosis, and a selective induction of TNF-alpha synthesi s and secretion was observed, The coaddition of IL-2 to anti-CD16 Ab-t reated NK cells resulted in enhanced secretion of TNF-alpha and augmen tation of the frequency of cell death. However, a minor subset of NK c ells exhibited potent cytotoxic function and proliferated, The anti-CD 16-induced effects in NK cells were largely abrogated by the addition of either anti-TNF-alpha Ab or TNF-binding protein in the cultures, Th ere was an enhancement of NK cell killing following the addition of ex ogenous TNF-alpha into the culture, Cytochalasin B selectively trigger ed the secretion of TNF-alpha and significantly augmented the frequenc y of apoptosis of anti-CD16-treated NK cells, These findings demonstra te an important and pivotal role of endogenous TNF-alpha synthesis and secretion by NK cells in the induction of functional anergy and apopt osis in anti-CD16-treated NK cells.