CCR1 and COVID-19: Furthermore, COVID-derived PBMCs and monocytes had upregulated expression of migration markers, including endothelial adhesion molecules, including L-selectin and intercellular adhesion molecule 1 (ICAM1), and CC/CXC chemokine receptors (CCR1, CXCR1), as a function of the severity of COVID-19 (Fig. 1B and D).