CD4 and HIV-1 infection: Myeloid-derived dendritic cells, including Langerhans cells, stimulate naïve CD4 T cells to mature into Th1 cells which express high levels of the receptor CCR5 (Abbas et al., 1996; Loetscher et al., 1998), potentially rendering them more susceptible to HIV-1 infection due to the HIV-1 co-receptor expression (Bleul et al., 1997; Kawamura et al., 2003; McClure et al., 2005; McKinnon and Kaul, 2012; Prodger et al., 2012; Lemos et al., 2014).