CCR4 and HIV infectious disease: Studies by our group [37], confirmed by others [38, 50], demonstrated that CCR4+CCR6+Th17 and CXCR3+CCR6+Th1Th17 cells are highly permissive, while CXCR3+CCR6−Th1 are relatively resistant to R5 and X4 HIV infection, and CCR4+CCR6−Th2 are permissive to X4 HIV only [37].