CD4 and infection: During chronic infection, it is well recognized that there is a loss of CD8+ and CD4+ reactivity in the blood towards a range of peptides, compared with patients where infection has been resolved (Bowen & Walker, 2005a; Cox et al., 2005a; Day et al., 2003; Lauer et al., 2004; Lucas et al., 2007; Missale et al., 1996; Semmo et al., 2005, 2007).