IL-2 responsiveness of lectin-induced lymphoblasts: soluble IL-2 receptor release and differential in vitro effects of immunosuppressants.

Abstract We examined the mode of action of different immunosuppressants on the responsiveness of phytohemagglutinin (PHA)-induced lymphoblasts further stimulated by recombinant interleukin-2 (rIL-2). The stimulation of PHA blasts with rIL-2 resulted in an enhancement of tritiated thymidine ([ 3 H]TdR) incorporation and of soluble interleukin-2 receptor (sIL-2R) release. Cyclosporin A (CsA) and prednisolone inhibited in different ways the responsiveness of PHA pre-stimulated blood mononuclear cells (PBMC) to rIL-2, as measured by [ 3 H]TdR incorporation. The addition of CsA resulted in considerable enhancement of the release of sIL-2R, whereas the addition of prednisolone was associated with a similar enhancement only when the higher concentrations of rIL-2 were employed. EGTA, a calcium (Ca 2+ ) chelator, and verapamil, a Ca 2+ channel blocker, inhibited [ 3 H]TdR incorporation in a concentration-dependent manner. EGTA inhibited sIL-2R release in the same manner when used alone, and reversed the CsA- and prednisolone-induced enhancement of sIL-2R release by rIL-2 induced lymphoblasts, when used in combination with CsA or prednisolone. Verapamil had a similar but less striking effect. The effects of CsA and prednisolone were also studied in PHA-induced blasts originating from purified CD4 + or CD8 + lymphocytes. Stimulation of these blasts with rIL-2 resulted in higher [ 3 H]TdR incorporation by CD8 + blasts than by CD4 + blasts: however, no sIL-2R release was detected in supernatants of either CD4 + or of CD8 + blasts. Both CsA and prednisolone inhibited the rIL-2-induced enhancement of [ 3 H]TdR incorporation by both T-cell subsets. In summary, widely used immunosuppressants and Ca 2+ antagonists exert differential effects on an in vitro system of lymphocyte activation.