CD4 and lymphopenia: The cytokine storm in severe COVID-19 is characterized by Pedersen et al. [19] and decreased interferon (IFN)-γ expression in CD4+ T cells, lymphopenia (in CD4+ and CD8+ T cells), and increased cytokine levels (IL-6, IL-10, and TNF-α) were found to be associated with severe COVID-19, likely through increased pulmonary pathology, T-cell depletion, and CD4+ T cell dysfunction.