Mouse alloantibodies capable of blocking cytotoxic T cell function. III. Studies of the mechanism of blocking of CML by anti-Lyt-2 antibodies.

Attempts were made to analyze the mechanism of action of anti-Lyt-2 antibody in blocking of CML in the absence of complement. Preincubation of killer cells with anti-Lyt-2 antibody followed by washing was found to abrogate the inhibitory effect of the antibody on target cell lysis, whereas an equivalent amount of the antibody present throughout the culture period caused marked inhibition. The failure of pretreatment with anti-Lyt-2 antibody to cause inhibition of CML might be due to rapid turnover of Lyt-2 molecules. Delayed addition of the anti-Lyt-2 antibody to CML cultures decreased the inhibition observed, which indicated that the antibody must be present during early stages of killing in order to exert significant inhibitory effects. The partitioning of CML according to requirements for divalent cations showed that anti-Lyt-2 antibody acts on killer cells during the Mg++-dependent stage of killing. In addition, the antibody was shown to be capable of reversing certain events occurring during this stage. These data are consistent with a role for Lyt-2 molecules during the antigen recognition stage of cell-mediated lysis. However, the exact function of the Lyt-2 molecule remains unknown.