CCR5 and AIDS: Among host factors that may contribute to variable HIV-AIDS susceptibility, significant attention has focused on the role of variations in genes that influence HIV transmission, such as the genes that encode CC chemokine receptor 5 (CCR5), the major HIV co-receptor required for cell entry of virus, and CCR5 chemokine ligands such as CC ligand 3 (CCL3) and its paralog CCL3L1 [10].