CCL2 and COVID-19: Although there is no standard diagnosis recognition of CSS in COVID-19, it has been proposed that a sudden or rapid disease progression with multiple organ involvement, a significant decline of peripheral blood lymphocyte counts, and an increase of multiple cytokines, such as IL-1β, IL-2R, IL-6, IFN-c, CXCL-10, CCL-2, CCL-3, and TNF-α are the main biomarkers of CSS in COVID-19 patients (Gao et al., 2020).