Induction of granulocyte and granulocyte‐macrophage colony‐stimulating factors from human monocytes stimulated by Fc fragments of human IgG

The effect of human IgG on human haemopolesis has been studied in vitro. Dialysed purified IgG stimulated haemopoletic colony growth by bone marrow mononuclear cells (MNC) but not by monocyte‐depleted MNC. Culture media, conditioned by IgG‐stimulated peripheral blood MNC, augmented formation of neutrophil‐macrophage, eosinophil, and megakaryocyte colonies by monocyte‐depleted marrow MNC. Serum‐free IgG‐conditioned media also contained colony‐stimulating activity (CSA). IgG Fc fragments and heat‐aggregated IgG promoted the secretion of CSA, but F(ab′)2 fragments, Fab fragments or ultracentrifuged IgG did not. In the cell‐selection studies, CSA was produced by highly enriched monocytes following stimulation with Fc fragments. The antiserum against human granulocyte colony‐stimulating factor (G‐CSF) and/or granulocyte‐macrophage CSF (GM‐CSF) neutralized the CSA produced by Fc fragment‐activated monocytes. Enzyme immunoassays showed G‐CSF and GM‐CSF in media conditioned by monocytes stimulated with the Fc fragments, heat‐aggregated IgG and anti‐D‐sensitized red blood cells (RBC). Northern hybridization analysis showed mRNA encoding G‐CSF and GM‐CSF in RNA extracted from MNC and monocytes cultured with the Fc fragments, but not in the RNA from unstimulated cells or monocyte‐depleted MNC. These results indicate that IgG Fc fragments, aggregated IgG and antigen‐antibody complexes induce monocytes to produce G‐CSF and GM‐CSF in vitro. The CSFs release induced by IgG may be involved in the in vivo regulatory network in haemopoiesis.