FUNCTIONAL INACTIVATION OF PRIMARY T-CELLS STIMULATED IN-VITRO IN THEPRESENCE OF CYCLOSPORINE

Cyclosporine (CsA) blocks in vitro polyclonal activation of primary mu rine T-cells in a complex manner. This cannot be completely reversed b y exogenous IL2, and leads to a partial blockade in expression of the IL2 receptor (p55 chain) and, more intensely, in CD69. In proliferatio n assays, T-cells recovered from CsA-treated cultures and washed free from CsA were markedly refractory to restimulation in the presence of fresh accessory cells. In cell titration restimulation assays, CsA-tre ated, but not control T-cells, were also markedly unresponsive to acce ssory cell-independent stimuli provided by immobilized anti-CD3 antibo dy or rIL2, combined to phorbol ester. CsA-treated, but not control ac tivated T-cells, undergo progressive cell death after drug removal and reculturing. In contrast, primary T-cells activated by a CsA-resistan t pathway (rIL2 plus phorbol ester) and treated with CsA did not devel op unresponsiveness, compared to controls. When primary T-cells were s timulated with rIL2 plus phorbol ester in the presence of the calcium ionophore ionomycin, treatment with CsA resulted in marked unresponsiv eness of the T-cells, compared to untreated controls. The data indicat e that primary activation of T-cells in vitro in the presence of CsA i nduces an unresponsive state which lasts independent of the presence o f CsA, and results in progressive cell death. We suggest that these ef fects could characterize one additional mechanism of CsA action in viv a.