CCL2 and COVID-19: In the latter condition, monocyte chemoattractant protein-1 (MCP-1 = chemokine ligand 2, CCL2) was identified among the biomarkers most strongly associated with post-acute sequelae of COVID-19 (PASC) (Phetsouphanh et al., 2021) and is involved in the recruitment and transformation of microglial cells, as well as in leukocyte trafficking across the BBB (Weiss et al., 1998).