CCL2 and COVID-19: Compared to patients with mild COVID-19, those with a severe form of the illness would experience a cytokine storm and be characterized by increased levels of CRP, IL-6, granulocyte colony-stimulating factor, interferon-inducible protein-10, monocyte chemotactic protein-1, macrophage inflammatory protein-1α/β, IL-8, and other cytokines, which can promote chemotaxis or the apoptosis of peripheral blood lymphocyte subsets, leading to a decrease in cell number (45–48).