CX3CR1 and viral infectious disease: It is noteworthy that, while most lineage-defining amino acids of the G protein were located in hypervariable regions, an amino acid substitution from N to G occurs at position 178 in the CCD of HRSV A. The CCD is devoid of glycosylation and contains a CX3C motif that facilitates binding to the receptor CX3CR1, playing key roles in virus infection and viral pathogenesis (Johnson et al. 2015).