It’s reported that there are newly recruited intraepithelial Ly6A+CCR9+CD4+ T cells in small intestines after infection with enteric viruses including murine norovirus and adenovirus, and those intraepithelial Ly6A+CCR9+CD4+ T cells play protective role in host defense against enteric viral infection by producing IL-18-dependent protective IFN-γ27. Here, CD4 is linked to infection.