Roles of the Chemokine Receptor CX3CR1 in the Pathogenesis of RSV Infections

CX3CR1 is a chemokine receptor expressed on respiratory epithelial and immune cells and has been identified as a host factor important for infections with respiratory syncytial virus (RSV). In this review, we discuss the roles CX3CR1 plays in the pathogenesis of RSV infections as a viral entry receptor and regulator of immune cell trafficking. The conserved CX3C motif of the RSV G glycoprotein binds to CX3CR1 to mediate viral attachment and entry into respiratory epithelial cells. Furthermore, soluble G protein (sG) can bind to CX3CR1 and competitively interfere with cell signaling induced by the chemokine CX3CL1, resulting in inhibition of immune cell recruitment to the site of infection. In addition, sG engages TLR2 on epithelial cells, activating MyD88-NF-κB signaling and priming the NLRP3 inflammasome, which enhances viral dissemination through pyroptotic cell death. CX3CR1 signaling should be viewed as one of several overlapping host factors that—along with developmental changes in interferon and STAT3 signaling, airway anatomy, inflammasome activity, and tissue-resident memory responses—contribute to differential disease outcomes of RSV infection. A more complete molecular understanding of RSV-CX3CR1 interactions and downstream host responses may enable the development of improved prevention and treatment strategies.