TGF-beta(1) differentially regulates IL-2 expression and [H-3]-thymidine incorporation in CD3 epsilon mAb- and CD28 mAb-activated splenocytes and thymocytes

Transforming growth Factor-beta, (TGF-beta(1)) is a critical bifunctional r egulator of inflammatory responses. Evidence strongly suggests that these r egulatory consequences are, at least in part, a result of profound pleiotro pic effects on T lymphocyte effector function. The mechanisms underlying th e contradictory biological effects of TGF-beta(1) remain ambiguous. The obj ective of the present studies was to test the hypothesis that the concentra tion of TGF-beta(1) and the temporal relationship between activation of the T cell receptor (TCR) and the TGF-beta receptor regulate the effect of TGF -beta(1) on T lymphocyte activation and proliferation. Toward this end, we have quantified the concentration- and time-dependent effect of TGF-beta(1) on interleukin-2 (IL-2) protein secretion as an index of T lymphocyte acti vation and [H-3]-thymidine incorporation as an index of cell proliferation in primary splenocytes and thymocytes. Our results suggest that TCF-beta(1) stimulates IL-2 production at low concentrations (0.1-1 pg/ml) and convers ely inhibits IL-2 production at high concentrations (1-10 ng/ml) in CD3 eps ilon monoclonal antibody (mAb) +/- CD28 mAb-activated splenocytes. Addition ally, concentrations of TGF-beta(1) that simulate IL-2 production in CD3 ep silon mAb + CD28 mAb-activated splenocytes concominantly inhibit splenocyte proliferation under similar conditions. Furthermore, we provide evidence s uggesting that the effects of TGF-beta(1) on T lymphocytes are dependent up on the temporal relationship between activation of the TCR and the TGF-beta receptor. A time-dependent loss of a stimulatory effect and a concomitant gain of an inhibitory response by TGF-beta(1) on IL-2 production in respons e to CD3 epsilon and CD28 mAbs is observed when TGF-beta(1) is added follow ing T lymphocyte activation. In summary, these data unequivocally demonstra te that the orchestration of paradoxical effects of TGF-beta(1) on T-lympho cyte function is dependent upon the concentration of TGF-beta(1) and the te mporal relationship between activation of signaling through the TCR and the TGF-beta receptor. Future mechanistic studies addressing the putative role that these factors play in modulating the effects of TGF-beta(1).