Temporal development of autoreactive Th1 responses and endogenous presentation of self myelin epitopes by central nervous system-resident APCs in theiler's virus-infected mice

Theiler's murine encephalomyelitis virus (TMEV)-induced demyelinating disease is a chronic-progressive, immune-mediated CNS demyelinating disease and a relevant model of multiple sclerosis. Myelin destruction is initiated by TMEV-specific CD4⁺ T cells targeting persistently infected CNS-resident APCs leading to activation of myelin epitope-specific CD4⁺ T cells via epitope spreading. We examined the temporal development of virus- and myelin-specific T cell responses and acquisition of virus and myelin epitopes by CNS-resident APCs during the chronic disease course. CD4⁺ T cell responses to virus epitopes arise within 1 wk after infection and persist over a > 300-day period. In contrast, myelin-specific T cell responses are first apparent ~50-60 days postinfection, appear in an ordered progression associated with their relative encephalitogenic dominance, and also persist. Consistent with disease initiation by virus-specific CD4⁺ T cells, CNS mononuclear cells from TMEV-infected SJL mice endogenously process and present virus epitopes throughout the disease course, while myelin epitopes are presented only after initiation of myelin damage (> 50-60 days postinfection). Activated F4/80⁺ APCs expressing high levels of MHC class II and B7 costimulatory molecules and ingested myelin debris chronically accumulate in the CNS. These results suggest a process of autoimmune induction in which virus-specific T cell-mediated bystander myelin destruction leads to the recruitment and activation of infiltrating and CNS-resident APCs that process and present endogenous myelin epitopes to autoreactive T cells in a hierarchical order.