CD4 and COVID-19: The main findings of this study include the following: (1) the frequencies of CD3+ T cells, activated CD4+ T cells, and Treg cells were significantly higher in FIhi COVID-19 patients compared with FIlo subjects; (2) DEGs and GESA analysis identified downregulation of IFN-responsive genes as well as impaired IFN signaling pathways in dysregulated T cells and NK cells; and (3) the expression of IFN-responsive genes and S100A8 was negatively associated with FI values among 12 patients.