A soluble form of the interleukin 4 receptor in biological fluids

Murine biological fluids and murine cell culture supernatants were analyzed for the presence of soluble murine interleukin 4 receptor (sIL4R) with the use of two monoclonal antibodies directed against the receptor. Mouse urine, serum, ascitic fluid, and cell culture supernatants contained varying levels of immunoreactive protein. All of the immunoreactive protein possessed interleukin 4 (IL 4) binding activity. Following partial purification of ascitic fluid a protein was isolated that binds IL 4 with high affinity. This data is consistent with the fact that murine biological fluids contain a soluble version of the murine IL 4 receptor that arises via secretion of the soluble receptor and/or via shedding of the extracellular portion of the full-length receptor from the cell surface.