CX3CR1 and respiratory syncytial virus bronchiolitis: RSV G CX3C-CX3CR1 interaction is associated with altered pulmonary leukocyte trafficking, altered Th1-type cytokine and C–C/CXC chemokine expression and increased pulmonary substance P levels [11], [14].Intriguingly, a variation in the CX3CR1 gene has been associated with increased risk for severe RSV bronchiolitis in children hospitalized for bronchiolitis, supporting the importance of G protein CX3C-CX3CR1 interaction in disease pathogenesis [19].