Modulation of transferrin synthesis, transferrin receptor expression, iNOSexpression and NO production in mouse macrophages by cytokines, either alone or in combination

Iron, an essential element for all living organisms, is central importance in a number of crucial metabolic pathways, including the regulation of immu ne function. Iron delivery to cells is accomplished by the complexing of ir on to transferrin (Tf), a monomeric iron-binding protein in the plasma, fol lowed by specific binding of Tf to cell-surface receptors, endocytosis of t he receptor ligand complexes and ultimately, release of iron fi om endosoma l vesicles to the cytoplasm. The purpose of this study was to evaluate the effect of cytokines, alone and in combination, on the factors that call aff ect the iron delivery in thioglycollate-elicited macrophages. In this study , IFN gamma induced a mai ked ina ease in Tf synthesis by macrophages, whil e IL-I, IL-6 and TNF alpha produced a more modest increase. Combinations of these cytokines were shown to be less effective in promoting macrophage Tf synthesis than the cytokines by themselves. IFN gamma alone and in combina tion with other cytokines was effective in inducing nitrite (NO) production and inducible nitric oxide synthetase (iNOS) expression in macrophages, wh ile IL-1, TNF alpha and IL-6 individually as well as in various combination s, were not. While all tested cytokines individually and in combination inh ibited the expression of the transferrin receptor (TfR) on macrophages, IFN gamma alone and in combination with other cytokines most strongly represse d the TfR expression. TfR localization in macrophages after IFN gamma stimu lation showed that TfR fluorescence was most intense in the perinuclear reg ion after 6 hours and scattered diffusely throughout the cytoplasm after 24 hours. This data suggests that IFN gamma may enhance iron uptake during th e early phase of macrophage activation, and in later phases, down-regulate TfR expression by inducing NO, thus contributing to intracellular oxidative stress reduction.