A modified in situ enzyme-linked immunosorbent assay for quantitating interleukin-2 activity employing monoclonal anti-IL-2 receptor antibody

The IL-2R ELISA recently described by Igietseme and Herscowitz (J. Immunol. Methods 97 (1987) 123) is a simple and reliable procedure for measuring the immunological activation of lymphocytes based on the expression of the early activation antigen, the interleukin-2 receptor (IL-2R). In the present report, this assay has now been adapted for the quantitation of IL-2 in culture supernatants and is based on the measurement of augmentation of IL-2R expression resulting from the exposure of sensitive cells (IL-2-dependent T cell line, CTLL-2, and mitogenic blasts) to IL-2. Under the conditions of these experiments, the magnitude of IL-2R expression appears to be directly proportional to the concentration of IL-2 in a given sample up to an optimum concentration beyond which no further increase in IL-2R expression is observed. Dose-response curves revealed that the assay correlates well with the proliferative response of the responder cells as measured by the [ 3H]thymidine ( 3H-TdR) uptake assay which is the commonly employed assay for quantitating IL-2. Using a simple mathematical formula, units of IL-2 activity could be assigned to unknown IL-2 preparations employed in these studies based on the activity contained in a standard IL-2 preparation. In an attempt to further simplify the procedure, a novel approach involving an in situ assay was designed and was found to be applicable for quantitating IL-2 by both the 3H-TdR uptake assay and the IL-2R ELISA. The assay can provide direct information about the immediate effect(s) of ligand-to-receptor binding and/or the effect(s) of ligand on the initial response of the cell. The assay could be adapted to quantitate the interleukins, in general.