title: Surfactant protein A, but not surfactant protein D, is an opsonin for influenza A virus phagocytosis by rat alveolar macrophages.
abstract: Surfactant protein A (SP-A) and surfactant protein D (SP-D) are collectins, and both proteins were shown to interact with influenza A virus and alveolar macrophages. However, it is not known whether SP-A and SP-D can serve as opsonins for the phagocytosis of influenza A virus by alveolar macrophages. In the present study, we investigated the opsonic activities of SP-A and SP-D for phagocytosis of fluorescein isothiocyanate (FITC)-labeled influenza A (H3N2) virus by rat alveolar macrophages using flow cytometry. SP-A enhanced the association of the virus with macrophages in a dose-dependent manner, reaching a maximum at an SP-A concentration of 60 microg/ml. An approximate threefold increase in association of influenza A virus with alveolar macrophages in the presence of SP-A over control incubations which contained no SP-A was observed. Half of the total cell-associated fluorescence could be quenched as demonstrated using the extracellular quenching dye trypan blue. These results indicate that SP-A mediates internalization of FITC-labeled influenza A (H3N2) virus by alveolar macrophages. Removal of the carbohydrate moiety of SP-A by N-glycosidase F treatment or cleavage of its sialic acid residues by neuraminidase abolished the enhancement of the phagocytosis of FITC-labeled influenza A virus by alveolar macrophages. Mannan, a mannose homopolysaccharide known to bind to the carbohydrate-binding domain of SP-A, did not affect the SP-A-mediated phagocytosis of FITC-labeled influenza by alveolar macrophages. In contrast, SP-D neither enhanced the association of FITC-labeled influenza A virus with alveolar macrophages nor affected the opsonic activity of SP-A for FITC-labeled influenza A (H3N2) virus at the SP-D concentrations tested. It is concluded that SP-A acts via its sialic acid residues as an opsonin in the phagocytosis of influenza A virus by alveolar macrophages.
authors.affiliation: Regional Public Health Laboratory Groningen, The Netherlands.
authors.forename: C A
authors.initials: CA
authors.lastname: Benne
authors.forename: B
authors.initials: B
authors.lastname: Benaissa-Trouw
authors.forename: J A
authors.initials: JA
authors.lastname: van Strijp
authors.forename: C A
authors.initials: CA
authors.lastname: Kraaijeveld
authors.forename: J F
authors.initials: JF
authors.lastname: van Iwaarden
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000276:immunology* / Q000502:physiology; D016650:Fluorescein-5-isothiocyanate; D006023:Glycoproteins / Q000276:immunology* / Q000502:physiology; D006801:Humans; D009980:Influenza A virus / Q000276:immunology*; D016676:Macrophages, Alveolar / Q000276:immunology*; D008297:Male; D009844:Oligosaccharides / Q000494:pharmacology; D009895:Opsonin Proteins / Q000502:physiology*; D010587:Phagocytosis / Q000187:drug effects*; D011510:Proteolipids / Q000276:immunology* / Q000502:physiology; D037662:Pulmonary Surfactant-Associated Protein A; D037663:Pulmonary Surfactant-Associated Protein D; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000276:immunology* / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar
chemical_list: D002352:Carrier Proteins; D006023:Glycoproteins; D009844:Oligosaccharides; D009895:Opsonin Proteins; D011510:Proteolipids; D037662:Pulmonary Surfactant-Associated Protein A; D037663:Pulmonary Surfactant-Associated Protein D; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants; D016650:Fluorescein-5-isothiocyanate