Erythropoietin enhances endogenous haem oxygenase-1 and represses immune responses to ameliorate experimental autoimmune encephalomyelitis.

Both erythropoietin (EPO) and haem oxygenase-1 (HO-1), an anti-oxidative stress protein, have proven protective roles in experimental autoimmune encephalomyelitis (EAE), a reliable animal model of multiple sclerosis. In this study, EPO delivered intraperitoneally could reduce disease severity in myelin oligodendrocyte glycoprotein (MOG)–EAE mice. To assess the effect of EPO on endogenous HO-1 in EAE, we investigated expression of HO-1 mRNA by real-time polymerase chain reaction (RT–PCR), protein expression centrally and peripherally by Western blot and immunohistochemistry and mean fluorescence intensity of splenic HO-1 by flow cytometry. A significantly higher expression of HO-1 in both the central nervous system (CNS) and spleen was shown in EPO-treated MOG–EAE mice than in controls.We further examined the immunomodulatory effect of EPO in EAE, and via RT–PCR demonstrated significantly lower expression of interferon-γ, interleukin (IL)-23, IL-6 and IL-17 mRNA, and significantly higher expression of IL-4 and IL-10 mRNA in CNS of EPO-treated MOG–EAE mice than in controls. Using flow cytometry, we also observed a significantly decreased ratio of both T helper type 1 (Th1) and Th17 lymphocyte subsets isolated from CNS and a significantly increased ratio of splenic regulatory CD4 T cells in EPO-treated MOG–EAE mice. In addition, we demonstrated that MOG-specific T cell proliferation was lower in the EPO-treated group than in controls and showed amelioration of EAE by adoptive transfer of splenocytes from EPO-treated MOG–EAE mice. Together, our data show that in EAE, EPO induction of endogenous HO-1 and modulation of adaptive immunity both centrally and peripherally may involve the repression of inflammatory responses.