CCR5 is widely expressed on T lymphocytes, macrophages, microglia, and dendritic cells and plays a critical role in inducing migration of immune cells to sites of infection and injury in response to elevated levels of certain C-C-chemokine ligands (MIP-1α/CCL3, MIP-1β/CCL4, CCL5/RANTES) [31]. This evidence concerns the gene CCL4 and infection.