Mononuclear cell-mediated enhancement of granulocyte function in man

Human monocyte-enriched mononuclear cells (MNC) (greater than 95% monocytes) powerfully stimulated the antibody-dependent killing of tumor cells by purified human neutrophils (NE) or eosinophils (EO). The enhancement was observed when the mononuclear cell to granulocyte ratio was as low as 1:100. Media conditioned by MNC also stimulated antibody-dependent killing by NE and EO as well as the uptake and killing of Candida albicans by NE. There was a heterogeneity amongst individuals in the capacity of their MNC to elaborate this factor, and approximately 15% of individuals did not produce detectable factor. Different factors in the MNC supernatant were involved in NE and EO activation. The EO-activating factor (AF) had a m.w. of approximately 27,000 and migrated as a single band on phenyl-Sepharose chromatography. The NE-AF had a m.w. of 22,000 and migrated as two distinct bands on phenyl-Sepharose chromatography. EO-colony-stimulating factor (CSF) co-purified with EO-AF, and granulocyte-macrophage-CSF co-purified with both bands of NE-AF. It is concluded that MNC elaborate CSF-like molecules that powerfully stimulate human granulocyte function.