RETN and COVID-19: Studies have identified serum IL-10 and testosterone levels in males, serum ACE2 levels, and even an activated neutrophil signature containing a combination of several serum factors (granulocyte colony-stimulating factor (G-CSF) and interleukin-8 (IL-8)) and neutrophil-derived effectors (resistin (RETN), lipocalin-2 (LCN2), and hepatocyte growth factor (HGF)) as predictive of outcome in COVID-19 patients [7–9].