DIFFERENTIAL-EFFECTS OF COSTIMULATOR SIGNALS AND INTERLEUKIN-2 ON T-CELL RECEPTOR-MEDIATED CELL-DEATH OF RESTING AND ACTIVATED CD4(-CELLS()MURINE SPLENIC T)

Postthymic T cell receptor (TCR)-mediated cell death offers the potent ial for creating antigen-specific transplant tolerance analogous to th ymic clonal deletion. Murine splenic CD4(+) T cells were rigorously pu rified by: (a) adherent cell depletion and (b) magnetic bead/monoclona l antibody (mAb) depletion of macrophages, Ia(+) cells, mu-chain(+) ce lls, NR cells, and CD8(+) T cells, CD4(+)s were typically >95% pure by flow cytometry. Resting CD4(+)s stimulated by plastic-immobilized ant i-TCR/CD3 mAb were shown to die in the absence of exogenous interleuki n (IL)-2. Blasting CD4(+)s showed dose-dependent cell death upon relig ation of TCR/CD3 in the presence of IL-2; however, withdrawal of IL-2 from blasting CD4(+)s also resulted in cell death. Cell death was show n to be apoptotic by flow cytometry DNA content analysis. Anti-CD28 mA b, co-immobilized with anti-TCR/CD3 mAb, inhibited cell death of resti ng CD4(+)s in the absence of exogenous IL-2; however, anti-CD28 mAb sh owed minimal cell death inhibition of CD4(+) blasts when TCR/CD3 was r eligated. In contrast, splenic adherent cells effectively inhibited ce ll death of blasting CD4(+)s induced by TCR/CD3 mAb religation. We con clude that TCR-mediated programmed cell death of highly purified splen ic CD4(+)s is dependent upon activation state, availability of IL-2, a nd accessory cell or CD28 costimulator signals. Furthermore, IL-2 acts to protect against cell death in both resting and activated CD4(+) T cells. IL-2 protection could be overcome by high concentrations of ant i-TCR/CD3 mAb, which results in cell death of CD4(+) blasts. In the ef fort to understand potential mechanisms of peripheral tolerance induct ion, these findings assist to distinguish and define conditions for an tigen receptor-mediated programmed cell death of mature CD4(+) T cells .