CD4 and HIV infectious disease: Furthermore as highlighted earlier, the epithelial surface expresses all the receptors necessary for HIV infection including CD4, CCR5, CXCR4 [64, 65], and various other G protein-coupled coreceptors (GPCRs) known to mediate entry of HIV into cells (including CCR2b, CXCR6, and GPR1) [63, 66].