Characterization of an Lyt-2+ alloreactive cytotoxic T cell clone specific for H-2Db that cross-reacts with I-Ek.

An alloreactive cytotoxic T cell clone (433) possessing the L3T4-, Lyt-2+ phenotype is described that shows a double specificity. It has been derived from unprimed BALB/c (H-2d) spleen cells by repetitive in vitro restimulation with C57BL/6(H-2b) cells. The specificity of clone 433 was determined in cytotoxicity and proliferation experiments. One specificity was for the class I antigen H-2Db and the second was for the class II antigen I-Ek. Inhibition of cytotoxicity with monoclonal antibodies confirmed these results. Cold target competition experiments demonstrated that the two specificities were mediated by the same cell population. Anti-Lyt-2 antibodies inhibited only the H-2Db- but not the I-Ek-specific lysis, suggesting a higher affinity of the antigen receptor for I-Ek than for Db. To our knowledge, this is the first description of a T cell clone that is specific for a class I antigen and cross-reacts heteroclitically with a class II antigen.