CXCR6 and COVID-19: Interestingly, CXCR6 expression was reduced on NK and CD8 T cells, probably as a consequence of these cells homing to the lung, where the ligand of CXCR6, CXCL16, is highly expressed.32,33 Of note, a significant increase of CXCL16 has been described in the serum of COVID-19 patients.6