CCL4 and COVID-19: Patients with severe-to-critical COVID-19 have been shown to have elevated levels of C–C chemokine receptor type 5 (CCR5) ligands including C–C ligand (CCL) 3 (or MIP-1α), CCL4 (or MIP-1β), CCL5 (or RANTES), as well as interleukin (IL) 6 and IL-10 [[6], [7], [8], [9], [10]].