CD4 and COVID-19: Consistent with the ability of CD4+ T cells to regulate the recruitment and function of phagocytes in peripheral tissues (De Biasi et al., 2020; Grant et al., 2021), severe COVID-19 in adults have shown to be associated with changes in the function of two different CD4+ T cell profiles; FoxP3+ regulatory T cells (Tregs) and TH17 cells.