Interleukin 2 Receptors Are Released by Cells in Vitro and in Vivo. I. Detection of Soluble IL 2 Receptors in Cell Culture Supernatants and in the Serum of Mice by an Immunoradiometric Assay

An immunoradiometric assay (IRMA) detecting nanogram amounts of soluble mouse interleukin 2 receptors (IL 2R) is described. The IRMA is based on the finding that the two monoclonal antibodies AMT-13 and 7D4 react with two different epitopes of the mouse IL 2R molecule. As detected by IRMA, T lymphoblasts and IL 2R+ leukemic cells when incubated release IL 2R in soluble form into the culture medium. In the serum of mice inoculated with syngeneic IL 2R+ leukemic cells, growing as a solid tumor, IL 2R were detectable. The results raise the question whether circulating IL 2R are involved in down-regulation of immune responses.