Interleukin 2 leads to dose-dependent expression of the alpha chain of the IL-2 receptor on CD25-negative T lymphocytes in the absence of exogenous antigenic stimulation.

Expression of the alpha chain of the interleukin 2 receptor on T lymphocytes is restricted, increasing in the setting of activation, particularly after antigenic stimulation via the TCR. The effects of IL-2 in vitro on the expression of CD25 and proliferation as well as the cytokine induction in CD25-depleted T cells were studied. CD25-depleted and PBMC of healthy donors were cultured for 7 days with 0, 10, or 100 IU/ml of IL-2. Phenotypic analysis and measurement of cytokines in the culture supernatants were performed. IL-2 led to a dose-dependent induction of the IL-2R alpha chain on both CD4 and CD8 T lymphocytes. In the CD25-depleted cultures, IL-2 treatment (100 IU/ml) increased the percentage of CD4 T cells expressing CD25 by 30.6% (P = 0.05) and of CD8 T cells by 48.2% (P = 0.01) on day 7 compared to no treatment. In the PBMC cultures the increase on day 7 was 36.4% for CD4 (P = 0.01) and 50.8% (P = 0.025) for CD8 T lymphocytes. The patterns of cytokine induction in the CD25-depleted and control cultures were similar with increases of IFN-gamma, GM-CSF, IL-16, TNF alpha, and soluble IL-2 receptor in the IL-2-containing cultures. CFSE experiments demonstrated the proliferative capacity of both CD25-positive and -negative T cells. Interleukin 2 alone can lead to a dose-dependent induction of the alpha chain of its receptor on resting CD4 and CD8 T lymphocytes. IL-2 as a sole stimulant is also associated with generation of a cytokine milieu that includes IFN-gamma, GM-CSF, IL-16, and TNF alpha.