Activation of natural killer cells by the mAb YTA-1 that recognizes leukocyte function-associated antigen-1

The mAb YTA-1, which brightly stains CD3^–CD16⁺ large granularlymphocytes (LGL)/natural killer (NK) cells and CD8⁺ T cellsby immunofluorescence, is specific for leukocyte function-associatedantigen (LFA)-1. Some mAbs recognizing the LFA-1 chain (CD11a)or LFA-1ß chain (CD18) inhibited the binding of YTA-1to peripheral blood mononuclear cells. YTA-1 mAb could be chemicallycross-linked to 170 and 96 kDa molecules, whose molecular weightscorrespond to those of LFA-1 and ß respectively.YTA-1bound to COS-7 cells co-transfected with CD11a and CD18 cDNAs,but not to untransfected cells. Reactivities of YTA-1 to K562cells transfected with LFA-1 and ß(CD11a/CD18) cDNAsand to CHO cells transfected with Mac-1 (CD11b/CD18) or p150,95 (CD11c/CD18) cDNAs strongly suggest that YTA-1 recognizeseither LFA-1 or an epitope formed by a combination of LFA-1and ß. Treatment of fresh CD3^–CD16⁺ LGL withYTA-1 augmented cytolytic activity and induced proliferation.F(ab')₂ fragments of YTA-1 augmented NK cytotoxicity, indicatingthat the NK activating signal was transmitted through LFA-1without involvement of Fc receptor III. In contrast, the othermAbs against LFA-1 could not activate NK cells. These resultscollectively indicate that YTA-1 recognizes a unique epitopeof LFA-1, which is involved in activation of fresh NK cells.