CD4 and infection: In this study, we investigated transcriptional and functional differences between primary memory CD4+ T-cell subsets enriched in Th17 (CCR4+CCR6+) and Th1 (CXCR3+CCR6−) polarized cells, subsets that we previously reported to be permissive and resistant to infection with R5 or X4 HIV strains, respectively [37].