C1R and COVID-19: A number of studies have shown that the sign of COVID-19 was the cytokine storm with elevated levels of interleukin-6 (IL-6), IL-1β, complement C1r (C1R), tumor necrosis factor-alpha (TNF-α), chemokine (C-C-motif) ligand 2 (CCL2), and granulocyte-macrophage colony-stimulating factor (GM-CSF) [12].