CCL2 and COVID-19: ACE2-expressing cells in patients with COVID-19 express pro-inflammatory cytokines (PICs) including monocyte chemokine-1 (MCP-1), tumor growth factor-β1 (TGF-β1), tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6 [94]; these cytokines can cause cytokine storms and lead to multiple organ damage.