In an attempt to produce allonatibodies to cytotoxic T-cell receptors, hyperimmune anti-lymphocyte antisera have been raised in mice of various strain combinations, and have been tested for their ability to block allogeneic cell-mediated lymphocytotoxicity (CML) in the absence of complement at the T killer cell level. Most of the sera failed to show any significant and reproducible inhibitory effects. However, among C3H anti-B10.BR antisera, some sera were found to be capable of significantly inhibiting CML. This effect was attributable to antibodies reacting with the killer population rather than the target cells, because the sera inhibited B10 anti-C3H CML but not C3H anti-b10 CML. Among mouse strains tested, A/J, BALB/c, B10, and B6 strains were sensitive to the inhibitory effect of the sera whereas AKR, CBA, C3H, and DBA/2 strains were insensitive. The sensitivity of killer cells to the inhibitory effect correlated well with the strain distribution of the Lyt-2.2 antigen. In the presence of complement, these same sera were toxic to 100% of spleen cells of AKR, BALB/c, B10, and DBA/2 strains, with comparable cytotoxic titers. Thus, the inhibitory activity of the sera could not be explained by nonspecific effects of high-titered antibodies. To study the relationship between the antigen(s) responsible for the blocking effect and Lyt-2-linked genes, killer cells from Lyt-2 congenic strains were tested and conventional anti-Lyt-2.2 antisera were raised in an appropriate congenic strain combination. Killer cells from B6, but not from B6.Ly2.1 animals, were significantly sensitive to the blocking effects of the inhibitory C3H anti-B10.BR sera. The conventional anti-Lyt.2.2 sera did produce CML blocking, although there was no apparent correlation between such blocking and the anti-Lyt-2.2 cytotoxic titer. These results thus indicate that the target molecules responsible for blocking of killer cells are encoded or regulated by genes that are closely linked to or identical with Lyt-2.

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