A target structure for a series of human cloned natural killer cell lines is recognized by both anti-TNKtar and 4F2 monoclonal antibodies.

It was shown recently that a surface antigen termed TNKtar was likely to serve as a target molecule for three distinct human NK clones expressing the same clonotypic determinant (termed NKTa) present on a 90 KD recognition structure. In the present studies, we investigated whether TNKtar and a previously described antigen termed 4F2 were related. Parallel immunoprecipitations from membrane lysates of the same cells showed that both anti-TNKtar and 4F2 Mab precipitate a heterodimeric structure which resolves as two bands of identical m.w. (40 and 80 KD) in SDS-PAGE analysis under reducing conditions. Sequential immunoprecipitations demonstrated that the two antibodies are directed at the same molecule. However, one antibody did not block subsequent binding of the other, and vice versa, suggesting that anti-TNKtar and 4F2 Mab are directed at two distinct epitopes of the molecule. Functionally, it was found that 4F2 Mab was able, as well as anti-TNKtar, to selectively block cytotoxic function of JT9 cloned cells. Furthermore, as reported previously for anti-TNKtar, 4F2 had no effect when additional NKTa-NK clones were used as effector cells in cytotoxicity assays. Finally, cold target inhibition assays were performed by using cold target cells precoated with either anti-TNKtar or 4F2 Mab. These experiments showed that preincubation of target cells with either antibody blocked their ability to compete with their radiolabeled counterpart. Such results further strengthen the hypothesis that the activation antigen recognized by both anti-TNKtar and 4F2 Mab serves as a specific target structure for NKTa+ NK active clones. We discuss the importance of previous data concerning the 4F2 molecule in light of this functional role, which had not been identified previously.