Mouse alloantibodies capable of blocking cytotoxic T cell function. V. The majority of I region-specific CTL are Lyt-2+ but are relatively resistant to anti-Lyt-2 blocking.

In an attempt to solve the conflict concerning the correlation between the Lyt-2 phenotype of T cells subsets and the type of the MHC antigens involved in the recognition by T cells, class 2 (I region) antigen-specific CTL were studied for their Lyt phenotypes and the sensitivity to the blocking effects of anti-Lyt-2,3 antibodies. To avoid contamination by CTL to class 1 antigens such as Qa antigens, A.TH anti-A. TL attackers and A.TH anti-A attackers were tested on LPS blasts of the A strain and the A.TL stain, respectively. By using these combinations, it was shown that the majority of I region-specific killers were Thy-1+, Lyt-1+23+. Specific target cell lysis by these cells were, however, found to be far less sensitive to the blocking effects of various monoclonal antibodies to the Lyt-2,3 antigens than conventional class 1-specific CTL. This conclusion was drawn by directly comparing the sensitivity of the I region-specific and K region-specific killing by identical numbers of the same attacker cells (A.TH anti-A). No significant difference was seen between the primary and the hyperimmune CTL. Lyt-2-, Thy-1+ killer cells with I region specificity could be induced when Lyt-2-depleted A.TH responder cells were stimulated in vitro. Such Lyt-2- killer cells were not induced to the H-2K alloantigen.