Enhancement of the antibody-dependent tumoricidal activity of human monocytes by human monocytic colony-stimulating factor.

Human monocytic colony-stimulating factor (hM-CSF) stimulates mature cells as well as progenitor cells of human monocyte lineage. In the present study, we investigated the effect of completely purified native hM-CSF on the tumoricidal activity of human monocytes against Raji (Burkitt lymphoma-derived cell line) using a chromium release assay. Preincubation of human peripheral blood monocytes with hM-CSF for 48 h markedly enhanced their antibody-dependent cellular cytotoxicity (ADCC). This enhancing effect was dependent on the concentration of hM-CSF, and maximal enhancement was achieved at the concentration of 66 ng/ml. The number of receptor sites on monocytes against the Fc portion of immunoglobulin G increased 2- to 4-fold during 48 h incubation with hM-CSF. These results suggest that hM-CSF stimulates monocyte-ADCC by increasing the number of Fc receptor sites on human monocytes.