INDUCTION OF PROCOAGULANT FUNCTION IN PORCINE ENDOTHELIAL-CELLS BY HUMAN NATURAL-KILLER-CELLS

NK cells may mediate effector functions other than target cell cytotox icity. To explore such noncytotoxic effector mechanisms, we tested whe ther human PBL and purified NK (CD56(+)) cells might induce expression of tissue factor by cultured porcine aortic endothelial cells. Tissue factor is the major coagulation factor that binds to factor VIIa and initiates coagulation. The addition of freshly isolated NK cells but n ot T cells to endothelial cells resulted in the induction of tissue fa ctor activity. NK-depleted (CD56(-)) effector cells did not induce tis sue factor activity; however, the combination of CD56(+) cells and NK- depleted cells induced tissue factor activity to the same extent as un separated cells. PBL induced tissue factor mRNA in porcine endothelial cells and NK depletion resulted in a significant decrease of the indu ction. Induction of tissue factor activity in porcine endothelial cell s by human NK cells required direct cell-to-cell contact, as transfer of supernatants from NK-endothelial cell cultures to secondary culture s did not induce tissue factor activity, and anti-LFA-1 alpha Abs inhi bited the induction of tissue factor activity. Induction of tissue fac tor activity in endothelial cells by NK cells may represent one of a v ariety of ways in which NK cells mediate noncytotoxic effects.