CCL2 and COVID-19: Cytokine storm was observed in severe COVID-19 patients with high levels of various serum cytokines, such as IL-2, IL-7, IL-10, TNF-α, granulocyte-colony stimulating factor (G-CSF), interferon gamma-induced protein 10 (IP-10; CXCL10), and monocyte chemotactic protein-1 (MCP-1) (18–21).