IL6 and COVID-19: Currently, inflammation, cell-death- and coagulation-associated serum proteins such as CrP, LDH and IL-6 as well as D-Dimers are used to characterize COVID-19 severity and disease progression clinically; it remains to be assessed how MDSC frequencies in peripheral blood and/or airway fluids relate to these clinical serum markers and whether combined/composite biomarker scores composed of both serum proteins and cells (PMN-MDSCs and/or M-MDSCs) could be superior than clinical serum markers alone to monitor and predict the outcome and treatment response in COVID-19.