Chronic Toxoplasma gondii Infection Alleviates Experimental Autoimmune Encephalomyelitis by the Immune Regulation Inducing Reduction in IL-17A/Th17 Via Upregulation of SOCS3

Experimental autoimmune encephalomyelitis (EAE) is a mouse model of multiple sclerosis (MS), a demyelinating autoimmune disease caused by the infiltration of a harmful autoreactive Th1 and Th17 cells. To mitigate MS, which is impossible to cure with medication only, immunomodulatory interventions that prevent Th17 cell activation are ideal. The objective of the present study was to analyze the effect of Toxoplasma gondii infection on the onset of EAE. Our results found that Toxoplasma gondii infection in the brain increases SOCS3 expression and decreases the phosphorylation of STAT3, resulting in reducing IL-17A and IL-23, which suppress the differentiation and expansion of pathogenic Th17 cells, an important factor in MS development. These immune responses resulted in a reduction in the clinical scoring of EAE induced by myelin oligodendrocyte glycoprotein 35–55 immunization. In the EAE group with T. gondii infection (Tg + EAE group), Th17-related immune responses that exacerbate the onset of EAE were reduced compared to those in the EAE group. This study suggests that the alleviation of EAE after T. gondii infection is regulated in a SOCS3/STAT3/IL-17A/blood–brain barrier integrity-dependent manner. Although parasite infection would not be permitted for MS treatment, this study using T. gondii infection identified potential targets that contribute to disease attenuation.