DIFFERENTIAL ACTIVATION OF PHOSPHOLIPASE C-GAMMA-1 AND MITOGEN-ACTIVATED PROTEIN-KINASE IN NAIVE AND ANTIGEN-PRIMED CD4 T-CELLS BY THE PEPTIDE MHC LIGAND

In this study, we determined the functional and biochemical difference s in naive and primed CD4 T cells that expressed a TCR specific for th e pigeon cytochrome c (pcc) peptide presented by I-E(k) MHC class II m olecules, Naive CD4 T cells expressing the transgenic TCR were isolate d from the peripheral lymphoid organs of transgenic mice and stimulate d with pee peptide and IL-2 for 10 to 14 days. After this culture peri od, the Ag-primed cells were quiescent, as judged by the lack of expre ssion of the early activation marker CD69, low expression of CD25 (IL- 2R), and failure to incorporate thymidine, The primed cells required 1 0-fold less peptide than naive cells to achieve the same degree of pro liferation and for the induction of CD69, Primed cells also mobilized calcium more efficiently with regard to Ag dose and magnitude of the r esponse, The biochemical signal-transduction events in naive and prime d T cells were compared by stimulating them with different concentrati ons of pee peptide presented by adherent E(k)-transfected fibroblasts. It was found that tyrosine phosphorylation and activation of mitogen- activated protein kinase (MAPK) in primed cells required 10-fold less Ag and occurred more rapidly and intensively, Interestingly, peptide s timulation induced tyrosine phosphorylation of phospholipase C (PLC)-g amma 1 exclusively in primed cells, RasGAP was also more efficiently t yrosine phosphorylated in primed cells, By contrast, She was tyrosine phosphorylated to the same extent in naive and primed cells, P13Kp85 w as not tyrosine-phosphorylated in naive and primed cells either before or after peptide stimulation, We propose that the higher sensitivity of the primed cells to Ag stimulation is most likely dependent, at lea st in part, on the more efficient activation of PLC-gamma 1, MAPK, and calcium-dependent pathways.