CD4 and HIV infectious disease: Of note, the classically described HIV receptor CD4, in conjunction with the coreceptors CCR5 and CXCR4, remain as canonical cellular receptors for HIV infection in all cell types in humans, with the exception of epithelial cells and brain astrocytes, which can be infected and harbor HIV provirus via syncytial fusion without any expression of the CD4 receptor on the cell surface [10,17,18,19].