IMPAIRED SIGNALING IN ALLOANTIGEN-SPECIFIC CD8(-CELLS TOLERIZED IN-VIVO - EMPLOYING A MODEL OF L(D)-SPECIFIC TCR TRANSGENIC MICE TRANSPLANTED WITH ALLOGENIC HEARTS UNDER THE COVER OF A SHORT-TERM RAPAMYCIN TREATMENT() T)

Peripheral tolerance of T cells is necessary because thymic deletion i s not complete, and tissue-specific Ags exist outside the thymus, We h ave reported that persistent Ag is required to maintain peripheral tol erance in vivo. We suspect that the TCR signaling pathway in in vivo t olerized cells is compromised due to continuous exposure to the Ags, I n this study, the TCR signaling events in these cells were investigate d using TCR transgenic mice (2C mice) whose T cells are predominantly L(d) alloantigen-specific CD8 cells, The 2C mice were thymectomized an d then rendered tolerant to L(d) Ag by allogenic heart transplantation plus short-term treatment with rapamycin, We found that 1) the in viv o tolerized CD8 cells have compromised intracellular Ca2+ flux upon mi togen stimulation; and 2) their cellular tyrosine proteins fail to be phosphorylated properly upon TCR cross-linking, These results indicate that the signaling pathway in the in vivo tolerized CD8 cells is inde ed defective, We also found that 1) the tolerized CD8 cells have no ch aracteristic surface markers; and 2) the allograft is probably the pla ce where the rejection response is initiated according to the appearan ce of an early activation marker of T cells on graft-infiltrating cell s.