Time course and cellular localization of interleukin-10 mRNA and protein expression in autoimmune inflammation of the rat central nervous system.

Experimental autoimmune encephalomyelitis of the Lewis rat is a T-cell-mediated autoimmune disease of the central nervous system characterized by a self-limiting monophasic course. In this study, we analyzed the expression of the anti-inflammatory cytokine interleukin (IL)-10 at the mRNA and protein level in experimental autoimmune encephalomyelitis actively induced with the encephalitogenic 68-86 peptide of guinea pig myelin basic protein. Semiquantitative reverse transcriptase-polymerase chain reaction revealed that IL-10 mRNA expression peaked during the acute phase of the disease at days 11 and 13. IL-10 mRNA was synchronously induced with mRNA for the proinflammatory cytokine interferon-gamma. Immunocytochemistry with a monoclonal antibody against rat IL-10 showed that the peak of IL-10 mRNA was accompanied by an abundant expression of IL-10 protein during the acute stage of the disease. Both in situ hybridization and double labeling immunocytochemistry in combination with confocal microscopy identified T cells, macrophages/microglia, and astrocytes as major cellular sources of IL-10 in vivo. The early peak of IL-10 production was unexpected in light of its well-documented anti-inflammatory properties. Additional studies are required to determine whether endogenous IL-10 contributes to rapid clinical remission typical for Lewis rat experimental autoimmune encephalomyelitis or if it plays other, yet undefined, roles in central nervous system autoimmunity.