PRF1 and COVID-19: Finally, direct comparison of effector molecule expression levels between NK cells and T cells as well as between COVID-19 and influenza patients revealed similarities but also slightly different patterns between the two diseases: Granzyme A and B were significantly increased in CD56brightCD16- NK cells and CD4+ T cells in COVID-19 patients (Figure S3D), while granzyme B and perforin levels were significantly higher in NK cells and T cells in influenza patients (Figure S3F).