In the present study, we have investigated the molecular basis for the immunoregulatory function of CD8 cells after autologous mixed lymphocyte reaction (AMLR) activation. We demonstrated that the CD8+CD45R+, but not the CD8+CD45R− subset of cells effected suppression following AMLR activation. In contrast, cytotoxic activity against alloantigens resided in both the CD8+CD45R+ and CD8+CD45R− subsets of cells. Biochemical analysis showed that on CD8 cells, the 220‐kDa isoform of the LCA/T200 antigen family was better represented than the 200‐kDa isoform, when compared to CD4 cells. The density of the CD45R antigen increased on CD8 cells following activation in AMLR and treatment of AMLR‐activated CD8 cells with either anti‐CD45R antibody or anti‐CD3 antibody abolished the suppressor function of these cells. In contrast, treatment of AMLR‐activated CD4 cells with anti‐CD45R, but not anti‐CD3 antibody, abolished the suppressor/inducer function of these cells. The results suggest that the CD45R antigen as well as CD3 T cell receptor complex have an important role in the suppressor function of AMLR‐activated CD8 cells.
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