Interleukin 2 regulates the expression of Tac antigen on peripheral blood T lymphocytes.

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Abstract
The effect of OKT3 antibody and interleukin 2 (IL-2) on Tac antigen expression and the proliferation of human peripheral blood mononuclear leukocytes was investigated. OKT3 monoclonal antibody at low, nonmitogenic concentrations (25 pg/ml) or IL-2 alone at optimal concentrations (20 U/ml) did not induce IL-2 receptor expression, as measured by Tac antibody or by T cell proliferation. Costimulation with these concentrations of OKT3 antibody and IL-2 led to Tac antigen expression and T cell proliferation. The data suggest that the T cells are activated in 2 steps: OKT3 antibody at 25 pg/ml does not induce Tac antigen expression, but preactivates T cells to become responsive to IL-2. The addition of exogenous IL-2 then leads to expression of the IL-2 receptor, as recognized by Tac antibody, and to subsequent proliferation.