The human immune system efficiently controls most of the viral infections through strong sterilizing immunity mediated by various innate (non-specific; e.g., NK cells, gamma-delta T cells, MAIT cells) and adaptive (virus-specific; e.g., CD4+ Th1, Tfh, Th17 cells, CD8+ cytotoxic T cells, B cells) immune cell types. Here, CD4 is linked to viral infectious disease.