There are four eIF2 kinases that phosphorylate eIF2α: (1) general control non-derepressible 2 (GCN2), which is upregulated by amino acid starvation; (2) protein kinase R (PKR), which is activated by viral infections; (3) PKR-like endoplasmic reticulum (ER) kinase (PERK), which is upregulated by ER stress; (4) heme-regulated eIF2α kinase (HRI), which is induced upon oxidative stress or mitochondrial dysfunction (Figure 1A). Here, EIF2AK2 is linked to viral infectious disease.