Granulocyte colony-stimulating factor induces neutrophils to secrete macrophage colony-stimulating factor

In this work we provide evidence showing that granulocytes produce macropha ge colony-stimulating factor (M-CSF) from the band cell stage and secrete t his factor when induced to differentiate into polymorphonuclear cells by re combinant human granulocyte colony-stimulating factor (rhG-CSF). Using an e nriched population of myeloid band cells from murine bone marrow, we identi fied the presence of M-CSF with a chromophore-labelled monoclonal anti-M-CS F antibody. Using ELISA we detected the secretion of M-CSF in the supernata nts of cultures of enriched band cells when induced with rhG-CSF to differe ntiate into mature neutrophils. We also found that M-CSF is the only factor responsible for the colony forming activity in the supernatants and lysate s of band cells treated with rhG-CSF.