Monoclonal antibodies which react with lymphocyte-lysed target cells and which cross-react with complement-lysed ghosts.

Monoclonal antibodies were raised against a human natural killing system and screened against targets lysed either by human lymphocytes in antibody-dependent cellular cytotoxicity (ADCC), or by human complement. Two monoclonals were identified which bound specifically to both types of killed targets. More detailed studies with one antibody showed that it inhibited ADCC, both as intact antibody and as the F(ab')2 fragment. Intact antibody enhanced natural (NK) killing, although the F(ab')2 fragment inhibited NK killing. The data support the hypothesis that lymphocyte-mediated killing involves a complex analogous in nature to the complement membrane attack complex. In addition, the antibodies provide evidence to suggest that this complex has antigenic determinants in common with the complement membrane attack complex, and indicate the possibility that the two systems are derived from a common ancestor.