IFNG and COVID-19: Furthermore, virus-specific T cells from severe cases presented with a central memory phenotype and high levels of interferon (IFN)-γ, tumor necrosis factor (TNF)-α, and interleukin (IL)-2 compared with that of the mild group.29 Zhou et al.30 reported that CD69, CD38, and CD44 are highly expressed on CD4+ and CD8+ T cells of patients with COVID-19 compared with healthy controls.