CD4 and influenza: CD4+ Th and CD8+ CTLs are important in protection from infection by different viruses, including influenza (La Gruta and Turner, 2014; Lartey et al., 2015), HIV (Rosenberg et al., 1997; Blazevic et al., 2000), HPV (Stanley, 2006), and the Epstein–Barr virus (Pepperl et al., 1998).