Aside from the role of CXCR7 in CXCL12-guided cell migration across the blood brain barrier (BBB), the higher CXCR7 cell surface expression on the HIV-susceptible CD14+ CD16+ monocytes might increase the likelihood of CXCR7 coreceptor use in subsequent infection cycles of CD14+ CD16+ monocytes. This evidence concerns the gene CXCL12 and infection.