Modulation of c-fms proto-oncogene expression in human blood monocytes and macrophages

The gene product of the c-fms proto-oncogene is a transmembrane protein with tyrosine-kinase activity that is obviously related to the receptor for the colony-stimulating-factor CSF-1. By Northern blot analysis, we investigated the expression of the cellular counterpart of v-fms in purified normal human blood mononuclear cells and different macrophage populations. The proto-oncogene c-fms expression was demonstrable in blood monocytes but not in blood lymphocytes. Short-term cultivated blood monocytes exhibited an increased expression of c-fms in comparison to freshly isolated blood monocytes, possibly due to a temporary down regulation of c-fms during the separation procedure of blood monocytes. A comparably high rate of fms-RNA expression was found in most of the analyzed samples of resident peritoneal macrophages, while resident alveolar macrophages showed a considerably lower level of c-fms expression. In this, alveolar macrophages resembled long-term cultivated adherent blood monocytes, which showed a down regulation of c-fms expression. By correlating these data obtained by Northern blot analysis with phenotypic properties of the analyzed monocyte/macrophage populations, it is concluded that different levels of c-fms expression in monocytes/macrophages correspond to their stage of differentiation and maturity.