CD4 and infection: This phenomenon is probably attributable to two different observations: (i) infections with BCRF1-deficient viruses led to higher levels of Th1 cytokines (Figure 4A) suggesting that increased Th1 cytokine secretion by CD4+ T cells boosted NK cell activity, and (ii) rescue experiments indicated a direct inhibitory effect of vIL-10, as well as hIL-10, on NK and CD4+ T cell activity (Figure 4B).