Tumor-stimulated release of tumor necrosis factor-α by human monocyte-derived macrophages

Abstract

Tumor necrosis factor-α (TNF) release by monocytes and macrophages may be an important determinant of the physiologic response of the host to neoplastic disease; however, the mechanisms which regulate TNF release by macrophages in hosts with neoplastic diseases are poorly understood. The purpose of this study was to determine if cell membranes and growth medium from human leukemia cell lines and solid tumor cell lines induced TNF release by cultured human blood monocyte-derived macrophages. The capacity for TNF release and direct tumor killing was highest in monocytes cultured for 7 to 11 days. Cell membranes and culture media from K562 erythroleukemia and several small cell lung carcinoma cell lines, including H82, induced the release of up to 1500 TNF units per 10 6 macrophages over 24 hr. By contrast, allogeneic peripheral blood lymphocytes, cell membranes from normal mixed donor peripheral blood leukocytes, or growth medium from normal embryonic lung fibroblasts induced the release of little or no TNF during culture up to 24 hr, suggesting that this macrophage response was specific for tumor cells. Release of TNF by tumor-stimulated macrophages was gradual, peaking 24 hr following the addition of stimuli. Induction of macrophage TNF release was concentration dependent, with half-maximal TNF levels induced by 12.5 and 25 μg/ml cell membranes prepared from K562 and H82, respectively. Pretreatment of tumor cell membranes with polymixin B, which inhibits many of the actions of endotoxin, failed to neutralize tumor induction of TNF, suggesting that endotoxin was not responsible for this activity. Depletion of macrophages by treatment with 3C10 monoclonal antibody and complement abrogated tumor-induced TNF release, indicating that macrophages were the source of the secreted TNF. HPLC analysis of H82 growth medium demonstrated a single peak of macrophage activating activity with approximate 40-kDa molecular weight. We have demonstrated that cell membranes and growth medium from some human leukemia and solid tumor cell lines, but not from normal human cells, induce human peripheral blood monocytes and monocyte-derived macrophages to release functionally active TNF. This process may contribute to the host response to some neoplastic diseases.