A simple and sensitive bioassay for the detection of IL-2 activity

A simple, one-step quantitative assay for the detection of biologically active interleukin-2 (IL-2) is described. It is based on culture of pure CD3+ T cells which have been positively selected from blood mononuclear cells by particle (M450)-bound anti-CD3 monoclonal antibody (mAb). During culture, activation of the T cells via CD3 will occur, leading to expression of IL-2 receptors but not IL-2 production. By adding IL-2 a proliferative response is evoked, giving a linear dose-response curve for IL-2 concentrations between 0.01-20 U/ml. The cells were unresponsive to IL-1, IL-4, tumor necrosis factor alpha (TNF-alpha), interferon-alpha (IFN-alpha), IFN-gamma, phytohemagglutinin and concanavalin A. The responsiveness to IL-2 was enhanced by TNF-alpha and inhibited by IFN-alpha, while the other tested lymphokines and mitogens did not influence the proliferative response. Antibodies to IL-2 and to IL-2 receptor suppressed the IL-2 response in a dose-dependent manner. The method is both simple and specific, and obviates the necessity for keeping assay cells in long term culture.