Enhancement of the Antibody‐dependent Tumoricidal Activity of Human Monocytes by Human Monocytic Colony‐stimulating Factor

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Abstract
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.