CD4 and COVID-19: Regarding PD-1 expression (Fig. 4C,D), convalescent COVID-19 plasma decreased PD-1 in CD4+ T cells (MFI) and in CD8+ T cells (%); moreover, anti-IFN-γ treatment rescued the expression of PD-1 in CD8+ T cells (%), suggesting that IFN-γ in convalescent COVID-19 plasma may inhibit the expression of PD-1 on CD8+ T cells.