IFNG and COVID-19: Compared with that in the non-COVID-19 group, the levels of Interleukin-2 (IL-2), Interleukin-6 (IL-6), Interferon-gamma (IFN-γ) and tumor necrosis factor-alpha (TNF-α) were significantly increased in the COVID-19 group (P < 0.05; Table 5).