IFNG and COVID-19: In the severe COVID-19 group, the correlation coefficients between IL-4 and IL-2, CD16+CD56+ NK cells and CD3+ T cells, CD16+CD56+ NK cells and CD3+CD4+ T cells, CD16+CD56+ NK cells and CD3+CD8+ T cells, TNF-α and IL-2, TNF-α and IL-4, and TNF-α and IFN-γ were 0.961, 0.804, 0.659, 0.848, 0.733, 0.7, and 0.629, respectively.