Combination of metformin with sodium selenite induces a functional phenotypic switch of human GM-CSF monocyte-derived macrophages

•Combined Metformin/Selenium modulates respiratory burst and phagocytosis in LPS-activated GM-CSF monocyte-derived macrophages.•Metformin/Selenium also regulates killing capacity and expression of NADH dehydrogenase (Complex I) in human LPS-activated GM-MDM.•Metformin/Selenium combination induces a switch into “M2”-associated arginase.•Metformin/Selenium together immunomodulate differently the expression of CD14, CD80, CD86 and HLA-DR.•Selenium markedly influences the effects of metformin on the functional activity of human GM-MDM.•Selenium modulates metformin effects on surface expression of co-stimulatory, activation and presentation molecules on GM-MDM.