More exact quantification of interleukin-2 production by addition of anti-Tac monoclonal antibody to cultures of stimulated lymphocytes.

Human T-cells produce interleukin-2 (IL-2) in response to in vitro stimulation with mitogens and antigens. Precise measurement of IL-2 production in vitro is hampered by binding of IL-2 to IL-2 receptors on activated T-cells which results in IL-2 consumption. In an attempt to prevent IL-2 consumption, we supplemented the cultures with anti-Tac, a monoclonal antibody that functionally blocks the human lymphocyte receptor for IL-2. Addition of anti-Tac to cultures of mitogen-stimulated peripheral blood mononuclear cells resulted in a 2-4-fold increase of maximal levels of IL-2 in the supernatants. No decline of IL-2 concentrations beyond 18-24 h of culture was observed, indicating that anti-Tac effectively blocked IL-2 consumption. Comparison of the kinetics of IL-2 accumulation in the presence and absence of anti-Tac revealed that IL-2 consumption by mitogen-stimulated cells occurred as early as 6 h after culture initiation. Addition of anti-Tac to cultures of antigen-stimulated cells similarly resulted in higher IL-2 levels in the culture supernatants, and prevented the rapid decline of IL-2 concentrations at prolonged culture time. We conclude that addition of anti-Tac to lymphocyte cultures enables more exact quantification of in vitro IL-2 production, presumably by blocking IL-2 consumption. This finding offers new possibilities for the study of abnormalities of IL-2 production in different disease conditions.