MPO and COVID-19: In line with these observations, Aschenbrenner et al performed transcriptomic profiling on whole blood samples and purified neutrophils from mild and severe COVID-19 patients and showed signatures associated with neutrophil activation (e.g. CD177, PADI4, ELANE and MPO) and immune suppression (e.g. ARG1 and CD274) were enriched in patients with severe disease (17).