CX3CR1 and head and neck squamous cell carcinoma: Aim of this study was to analyze the individual distribution of circulating monocyte subsets in HNSCC patients as well as associated expression levels of adhesion molecules and chemokine receptors CD11a (integrin-α L; LFA-1), CD11b (integrin-α M; Mac-1), CD11c (integrin-α X), CX3CR1 (CX3CL1 receptor) and checkpoint molecule PD-L1 (programmed cell death ligand-1) using flow cytometry, all of which are known to be differentially expressed in response to different environmental conditions [22].