RETN and COVID-19: Neutrophil activation cytokines such as IL-8 and granulocyte colony-stimulating factor (G-CSF), together with neutrophil-derived effectors such as resistin (RETN), lipocalin-2 (LCN2), and hepatocyte growth factor (HGF), are elevated in the plasma from the severe COVID-19 patients compared to the mild/moderate patients (11, 12).