Quantitative receptor binding assay of interleukin-1 using a flow cytometer

Abstract

Interleukin-1 (IL-1) is a cytokine that mediates various immune responses and inflammation. IL-1 binds to its receptor molecules expressed on the responding cells to mediate these responses. We prepared fluorescein-labeled IL-1, and established a quantitative assay for receptor binding using a flow cytometer. Mouse thymocytes expressing IL-1 receptor molecules on their surface were employed in the assay. With this binding assay, we obtained IL-1 binding proportional to the quantity of IL-1 in the range of 2.5 to 100 units at a constant thymocyte number. This assay worked at the temperature between 25 and 45 t. This assay appeared to be more rapid, convenient and simple than the conventional binding assay using 125I-labeled IL-1 and thymocyte proliferation assay using phytohaemagglutinin as a coactivator. This method could be utilized in other researches regarding IL-1 activity or IL-1 receptor expression. Thus, IL-1 inhibitors isolated from febrile patient urine were analyzed by this method. IL-1 receptor expression on mouse thymocytes along with expressions of other surface markers was also studied.