CD4 and infection: For example, HERVK13-int was up-regulated in 10 human virus data sets, including HIV-infected activated CD4+ T cells (HIVactivated CD4+T cell) and resting CD4+ T cells (HIVresting CD4+T cell), IAV, and HSV-1, which have already been shown to express HERVK during infection (Fig 1C) (Kwun et al, 2002; van der Kuyl, 2012).