Identification of a monocyte-derived factor which regulates synthesis of insulin receptors on activated T-lymphocytes...

The regulation of the insulin receptor on the activated T-lymphocyte was studied. It has been previously shown that the monocyte with its constitutive insulin receptor can signal the quiescent T-lymphocyte with respect to ambient insulin concentration which regulates the copies of insulin receptors synthesized during the lymphocyte activation event. In this communication it is shown that the vehicle by which the monocyte signals the T-lymphocyte is a soluble, small molecular weight protein. Initially a bioassay was established to test the putative monocyte-derived factor in which freshly prepared purified populations of monocytes were incubated with insulin, extensively washed, and replated with lymphocytes in microwells or across a 3 microns filter from lymphocytes using the appearance of insulin receptors on T lymphocytes responding to lectin as measured by a radioligand binding assay as the outcome variable. Dose response and time course relationships were established to develop the ideal conditions for the bioassay. It was shown that the monocyte-derived insulin receptor regulatory factor (MIRRF) could be readily detected in conditioned medium of insulin-incubated and then washed monocytes as a starting point for attempts at later purification. Using rats fed an essential fatty acid deficient diet (EFAD), incapable of generating standard prostanoids, it was demonstrated that the MIRRF was readily detectable in our standard bioassay revealing that the factor was not a member of the arachidonic acid family. Lastly, it was shown that MIRRF is cycloheximide sensitive and either is a protein or requires protein synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)