CD4 and HIV infectious disease: From early stages of HIV infection, the gastrointestinal tract is a target for HIV-induced pathology, with severe depletion of mucosal CD4 T cells (in particular Th17 cells), dendritic cells, and innate lymphoid cells (107, 163, 164) disrupting mucosal immunity and the intestinal epithelial architecture [reviewed in (2, 165)].