CD4 and HIV infectious disease: HIV replication in primary microglial cells from adults, infants, as well as fetal brain have been demonstrated in vitro.[41–45] Microglial cells functions are similar to macrophages and they express major receptors and co-receptors for HIV infections like CD4, CCR5, along with other chemokine receptors, viz., CCR3, CCR2b, CCR8, CXCR6, and CX3CR1.[18, 46–48] Presence of these receptors and co-receptors makes microglial cells vulnerable for HIV infection.