CD4 and COVID-19: The levels of IFN-γand TNF-αin CD4+T cells are lower in the severe group than in the mild group, where the levels of granzyme B and perforin in CD8+T cells are higher in the severe group than in the mild group (76), implying that SARS-CoV-2 infection may impair CD4+T cells and over-activate CD8+T cells in different COVID-19 status.