Lymphocytes consist of the immune system including B cells, which mediate the humoral immunity by secreting pathogen-neutralizing antibodies and proinflammatory cytokines (plasm cells) [5] and providing long-lasting protection (memory B cells) [6]; T cells, which induce cellular immunity by inducing virus-infected cell death (CD8+ T cells) [7,8] and modifying the activity of other immune cells to clear infection (CD4+ T cells) [9,10,11,12]; and natural killer (NK) cells, which participate in innate immune responses, especially to viral infections [13]. The gene discussed is CD4; the disease is infection.