Regulation of LPS induced IL‐12 production by IFN‐γ and IL‐4 through intracellular glutathione status in human alveolar macrophages
Interleukin‐12 (IL‐12) is secreted from monocytes and macrophages; it exerts pleiotropic effects on T cells and natural killer (NK) cells, and stimulates interferon‐γ (IFN‐γ) secretion. Glutathione tripeptide regulates the intracellular redox status and other aspects of cell physiology. We examined whether IFN‐γ and IL‐4 affect the balance between intracellular reduced glutathione (GSH) and oxidized (GSSG) glutathione, as this may affect IL‐12 production in human alveolar macrophages (AM). We used both AM from healthy non‐smokers obtained by bronchoalveolar lavage and the monocytic THP‐1 cell line in this study. Incubation of AM for 2 h with the GSH precursor N‐acetylcysteine (NAC) increased the intracellular GSH/GSSG ratio, and enhanced lipopolysaccharide (LPS)‐induced IL‐12 secretion by AM. In THP‐1 cells, NAC increased the GSH/GSSG ratio and the expression of LPS‐induced IL‐12 mRNA, whereas l‐buthionine‐[S,R]‐sulphoximine (BSO) decreased these. NAC and BSO offset their own effects on the intracellular GSH/GSSG ratio and the expression of LPS‐induced IL‐12 mRNA. Furthermore, exposure of AM to the helper T cell type 1 (Th1) cytokine IFN‐γ or the helper T cell type 2 (Th2) cytokine IL‐4 for 72 h increased and decreased the GSH/GSSG ratio, respectively. Lipopolysaccharide (LPS)‐induced secretion of IL‐12 in AM was enhanced by IFN‐γ but inhibited by IL‐4. These results suggest that IFN‐γ and IL‐4 oppositely affect the GSH/GSSG balance, which may regulate IL‐12 secretion from AM in response to LPS.