Interleukin 2 receptors are released by cells in vitro and in viva. 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 IL2R molecule. As detected by IRMA, T lymphoblasts and IL2R⁺ leukemic cells when incubated release IL2R in soluble form into the culture medium. In the serum of mice inoculated with syngeneic IL2R⁺ leukemic cells, growing as a solid tumor, IL2R were detectable. The results raise the question whether circulating IL2R are involved in down-regulation of immune responses.