CD4 and HIV infectious disease: To date, five major CD4+ T helper cell subpopulations have been identified: Th1, Th2, Th17, Treg, and Tfh cells.285,286 The CD4 protein is one of the main receptors for HIV, and HIV infection invades CD4+ T cells mainly by binding to the CD4 protein.287 The determination of CD4+ T-cell counts can help monitor the immune status of HIV-infected patients.