Signal transduction through the T cell receptor-CD3 complex: Evidence for heterogeneity in receptor coupling

T cell receptor-CD3 complex (TCR-CD3)-mediated signal transduction was analyzed in HPB-ALL and Jurkat T cell lines. Both cell lines express high levels of TCR-CD3 complex on the cell surface, but provide different model systems for TCR-CD3 signaling in T cells. Jurkat responds with both inositol phosphate generation and intracellular Ca²⁺ mobilization after triggering of TCR-CD3, whereas TCR-CD3 triggering of HPB-ALL induces Ca²⁺ mobilization without detectable inositol phosphate generation. By employing a permeabilized cell system, we show that the HPB-ALL line expressed normal levels of Ca²⁺-induced phospholipase C activity. However, the TCR-CD3 on this cell line seems to be uncoupled from phospholipase C activiation. In agreement with this result we also show, by analysis of protein kinase C-dependent phosphorylation of three distinct substrates, that TCR-CD3 in HPB-ALL is apparently uncoupled from protein kinase C activation. These findings may have implications for understanding signal-transducing pathways in T cells at various stages of differentiation.