CD4 and COVID-19: (e-f) Immune activation and proliferation levels are summarized for healthy controls (HC, n = 7) and five longitudinal time points of the COVID-19 patient and are assessed as co-expression of HLA-DR and CD38 (e) and expression of Ki67 (f) in CD4+ and CD8+ T cells, co-expression of CD38 and Ki67 by TCR-γδ T cells (g), and co-expression of HLA-DR and CD38 in NK CD56dim cells (h).