Effects of interferon-β on microglial functions as inflammatory and antigen presenting cells in the central nervous system

Abstract

Interferon-β (IFNβ) reduces exacerbations of the relapsing-remitting form of multiple sclerosis (MS), but the exact mechanisms by which it exerts its beneficial effects are unknown. In this study, we examined the effects of IFNβ on microglial functions, as either antigen presenting cells or effector cells for inflammatory demyelination. IFNβ significantly suppressed the expression of class II MHC antigen and the co-stimulatory molecule B7-1 in microglia. It also suppressed microglial IL-12 production and differentiation of myelin oligodendrocyte glycoprotein (MOG)-sensitized T cells into the T helper 1 phenotype, which use microglia as antigen presenting cells. However, IFNβ significantly and dose-dependently enhanced the production of inflammatory mediators for demyelination, such as TNFα, IL-1β, IL-6, and nitric oxide (NO). The upregulation of inflammatory mediators was effectively suppressed with a phosphodiesterase inhibitor. Thus, IFNβ may exert its suppressive effects in the induction phase, but not in the effector phase of MS. Side effects of IFNβ treatment may be due to elevation of pro-inflammatory cytokines, and may be reduced by co-treatment with phosphodiesterase inhibitors.