Interleukin-1 production by a cloned line of human monocyte-like cells (CM-SM). Correlation with state of differentiation.

Interleukin-1 (IL-1) production by the human monocyte-like cloned cell line CM-SM has been investigated as a function of the state of cell differentiation. CM-SM cells were induced to differentiate along the monocyte-macrophage lineage by bacterial lipopolysaccharides (LPS) or by 12-O-tetradecanoyl-phorbol-13-acetate (TPA). Cell differentiation was studied by various morphological, functional, cytochemical, and immunological variables, whereas IL-1 activity in the supernatants was measured by the lectin-primed thymocyte proliferation assay. Unstimulated CM-SM cells constitutively produced small amounts of IL-1, and most of the cells appeared relatively undifferentiated. LPS induced cell differentiation, but the effect was reversible, and the cells, in general, did not acquire a capacity for phagocytosis. IL-1 levels were increased about 10-fold over the controls. TPA induced further cell differentiation to macrophage-like cells capable of phagocytosis. IL-1 activity could not be measured directly in the supernatants owing to the synergistic effect of TPA in the assay system. Unequivocal removal of the phorbol was not achieved, but the data indicated that the 'real' levels of IL-1 in the TPA-induced cultures were not significantly higher than those from LPS-induced cultures.