CX3CR1 and COVID-19: More mature CD62L−NKG2A− CD56dim NK cells express higher levels of CX3CR1 compared with less mature NKG2A+ and CD62L+ CD56dim NK cells (44), and the CX3CR1 ligand CX3CL1 was one of the few chemokines that were not induced in BAL from COVID-19 patients (25).