CD4 and demyelinating disease: As virus-reactive IFN-γ-producing Th1 cells are protective but IL-17-producing Th17 cells inhibit Th1 development and cytotoxic T cell function [65,168], FoxP3+CD4+ T cells together with Th17 cells may promote the pathogenesis of TMEV-induced demyelinating disease in an epitope-dependent manner (Figure 5).