IL2 and COVID-19: Shi et al. reported low levels of IL-2 in plasma and low expression of IL-2 receptor (IL-2R) in peripheral blood mononuclear cells (PBMCs) of critical COVID-19 patients, which may result in the remarkable decrease of CD8+ T-cells and lymphocytes in critical patients with COVID-19 pneumonia, and proposed that the progressive decrease of IL-2 in plasma may be a warning factor of disease deterioration [28].