CD4 and viral infectious disease: In response to a chronic viral infection the cxcr5 promoter in CXCR5+ CD8 T cell contains two Blimp-1 binding sites and one E2A binding site, in addition to binding sites at the bcl6 and tcf7 promoter similar to that of CD8 effector memory T cells and CD4 Tfh cells (13, 15, 48).