CCR5 and HIV infectious disease: In line with anincreased susceptibility to HIV infection, PD-1 expression in this CD4 T cell subsetwas associated with increased activation and expression of the HIV co-receptor, CCR5.Rather than exhaustion, this population produced more IFN-g, MIP1-a, IL-4, IL-10, andIL-17a compared to PD-1low EI CD4 T cells.