CD4 and infection: The preferential infection of memory and naive T-cells by R5 and X4 C-HIV Envs, respectively, could be influenced by the variation in the proportion of cells that express CCR5 and CXCR4 (Additional file 1: Table S2) as CD45RO− cells had a higher proportion of CD4+ T-cells expressing CXCR4 compared to CD45RO+ cells, which had higher proportions of CD4+ T-cells expressing CCR5.