Culture of human monocytes with granulocyte-macrophage colony-stimulating factor results in enhancement of IFN-gamma receptors but suppression of IFN-gamma-induced expression of the gene IP-10.

The initiation and promulgation of chronic inflammation are controlled in part by the various pro-inflammatory and anti-inflammatory cytokines present at the site of injury. IFN-gamma and granulocyte-macrophage CSF (GM-CSF) are two cytokines that can contribute to the inflammatory state and possess both pro- and anti-inflammatory properties. However, the characterization of the interaction between GM-CSF-cultured monocytes and IFN-gamma is poorly documented. In this report we show that culture of human peripheral blood monocytes for up to 6 days in the presence of GM-CSF results in an eightfold increase in the level of IFN-gamma R expression, as determined by radioligand binding. The IFN-gamma R on these cells maintains a specificity typical of that observed in fresh monocytes. Only IFN-gamma, not IFN-alpha or -beta, blocks the binding of IFN-gamma to its receptor, and anti-IFN-gamma R antibodies block at least 80% of binding of IFN-gamma to these cultured cells. However, in spite of increased receptor expression, GM-CSF-cultured monocytes have a diminished response to IFN-gamma, as measured by the induction of the gene for IP-10 (a member of the platelet factor-4/IL-8 family). On the other hand, IFN-gamma-induced activation of the DNA-binding protein FcRF gamma is maintained in GM-CSF-cultured monocytes. Therefore, suppression of IFN-gamma-mediated IP-10 induction is not the result of a global abrogation of signal transduction across the IFN-gamma R but a more selective inhibition that appears to occur downstream of the receptor.