Evidently, IL-4 produced by Th2 cells and natural killer T (NKT) cells is critical for antiviral CD8+ T-cell (IFN-γ- and TNF-α–secreting cell) functions and antibody development during early viral infections, all of which are essential for inhibiting the establishment of persistent virus infections [60,61]. The gene discussed is IFNG; the disease is viral infectious disease.