CCL2 and acute respiratory distress syndrome: SARS-CoV-2 has a series of mechanisms to escape the host immune system; however, similar to SARS, some patients with COVID-19 experience inflammatory storms caused by excessive cytokines in the late stage (21), especially a series of chemokines in the plasma, such as CXCL10, IP-10, CCL2, MCP-1, MIP-1a/CCL3 and TNF-α, which increase uncontrollably (22) and lead to acute respiratory distress syndrome (ARDS) and poor prognosis.