CCL2 and COVID-19: Higher plasma MCP3 levels have previously been shown to be elevated in SARS-CoV-2-infected patients with severe disease in comparison with those without (Yang et al., 2020), and transcriptome-wide association in lung tissue has found that higher expression of monocyte-macrophage CCR2, the receptor for MCP1 and MCP3, is associated with severe COVID-19 (Pairo-Castineira et al., 2021).