The main source of MCP-1, GM-CSF, and IL-6 are fibroblasts, ECs, epithelial cells, etc. These cytokines may affect macrophages, neutrophils, and other immune cells via the JAK-STAT signaling pathway resulting in increased levels of suppressor of cytokine signaling (SOCS), and excessive cytokine production in severe COVID-19.177, 178, 179, 180. This evidence concerns the gene CSF2 and COVID-19.