MPO and COVID-19: The neutrophil-to-lymphocyte ratio in the thrombus (tNLR, calculated as ratio of MPO+ cell/mm2 count over the sum of CD3+ and CD20+ cells/mm2) was significantly different between the groups: thrombi of COVID-19 patients had a three-fold higher tNLR than control patients (respectively, median tNLR 30.3, [IQR 25.9–44.4] vs. 10.7, [IQR 8.1–19.0], p ≤ 0.01), (Fig. 4D).