Distinct involvement of CD45 in antigen receptor signalling in CD4+ and CD8+ primary T cells

We demonstrate that pretreatment of primary CD4+, but not CD8+ T cells with anti‐CD45 inhibits activation signals induced through the T cell receptor for antigen (TCRαβ). Specifically, anti‐TCRαβ‐mediated tyrosine phosphorylation of phospholipase C‐γ1 is inhibited, and this in turn correlates with the inhibition of subsequent Ca2+ mobilization and DNA synthesis. In marked contrast, none of these activation parameters are affected by anti‐CD45 in CD8+ T cells. Perturbation of TCRαβ signalling in CD4+ cells is observed in conditions which do not detectably affect the level of CD45 expression, or its membrane distribution. Further, changes in the intrinsic phosphatase activity of CD45 are not detectable. While anti‐CD45 ablates TCRαβ signalling, anti‐CD3ϵ‐mediated activation is unaffected. This suggests that elements of the antigen receptor complex can be functionally uncoupled, and indicates that the requirements for CD45 in signalling through these two elements are different. The results demonstrate that the involvement of CD45 in coupling TCRαβ to second messenger‐generating pathways is under distinct physical and/or functional constraints in primary CD4+ and CD8+ T cells.