CD8A and viral infectious disease: The involvement of M1 mAChRs in the differentiation of CD8+ T cells into cytolytic T cells was first postulated by Zimring et al. (129), but it was later found that neither M1 nor M5 mAChRs are required for expansion of antigen-specific CD8+ T cells, in response to viral infection in C57BL/6 mice (130).