IL-10 as an autocrine regulator of CSF secretion by monocytes: disparate effects on GM-CSF and G-CSF secretion

In previous studies of endogenous granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte colony-stimulating factor (G-CSF) production, we found several differences in the secretion pattern within and between different cell systems; for example, CSF secretion by endothelial cells is not affected by any major downregulatory factors, whereas monocyte CSF secretion is modulated by several mechanisms. In this study, we characterized the factors that inhibit CSF secretion by monocytes. Three cytokines have inhibitory effects: interleukin (IL)-4, IL-10, and IL-13. Among these, IL-4 and IL-10 have higher potency than IL-13. IL-4 and IL-13 affect GM-CSF and G-CSF secretion to the same extent. In contrast, exogenously added IL-10 has a stronger inhibitory effect on GM-CSF secretion than on G-CSF secretion. We also found that monocytes produce IL-10 with an autocrine downregulatory effect, and that this autocrine IL-10 reaches concentrations at which in most cases only GM-CSF (not G-CSF) secretion is significantly affected. We postulate that the disparate effect of IL-10 on monocyte secretion of the two CSFs reflects their physiological functions, with GM-CSF being mainly a proinflammatory cytokine working in the local compartment and G-CSF functioning mainly as a cell recruiting factor.