CCL2 and COVID-19: A study from the United Kingdom analyzed the characteristics of immune cells derived from the peripheral blood of patients with COVID-19, showing that immune response activity is correlated with the ratio of neutrophils to T cells, the increase of IL-6, IP-10, or MCP-1 in serum, and changes in the characteristics of CD14+ monocytes.7 This study supports the hypothesis that myeloid cells play a vital role in the early stages of SARS-CoV-2 infection and the abnormal differentiation promotes the progression of severe COVID-19.