title: Lactoferrin and surfactant protein A exhibit distinct binding specificity to F protein and differently modulate respiratory syncytial virus infection.
abstract: Surfactant protein A (SP-A) and lactoferrin (LF) play important roles in innate immune systems in the respiratory mucous membranes. We investigated how SP-A and LF act against respiratory syncytial virus (RSV) infection. The present study indicated that RSV-induced IL-8 secretion from HEp-2 cells was up-regulated by SP-A (170% of control) but down-regulated by LF (23% of control). RSV infectivity determined by viral titers and the uptake of FITC-labeled RSV were also increased by SP-A, but decreased by LF. To clarify the mechanism of these opposite effects, we examined the interactions of SP-A and LF with RSV F protein, the most important surface glycoprotein for viral penetration. RSV F protein was found to be the ligand for both SP-A and LF, but the manners of binding were different. LF directly interacted with the F(1) subunit, which involved antigenic sites of F protein. Contrarily, SP-A associated with the F(2) subunit, which was highly glycosylated. SP-A but not LF failed to interact with deglycosylated F protein. Moreover, SP-A initiated the hemolyzing fusion activity of F protein. These results suggest that SP-A and LF modulate RSV infection by different binding specificity to F protein.
mesh_terms: D002460:Cell Line; D006461:Hemolysis; D006801:Humans; D016209:Interleukin-8 / Q000096:biosynthesis; D007781:Lactoferrin / Q000378:metabolism*; D037662:Pulmonary Surfactant-Associated Protein A / Q000378:metabolism*; D018357:Respiratory Syncytial Virus Infections / Q000276:immunology*; D014764:Viral Proteins / Q000378:metabolism*
chemical_list: D016209:Interleukin-8; D037662:Pulmonary Surfactant-Associated Protein A; D014764:Viral Proteins; D007781:Lactoferrin