title: Impact of alginate-producing Pseudomonas aeruginosa on alveolar macrophage apoptotic cell clearance.
abstract: Pseudomonas aeruginosa infection is a hallmark of lung disease in cystic fibrosis. Acute infection with P. aeruginosa profoundly inhibits alveolar macrophage clearance of apoptotic cells (efferocytosis) via direct effect of virulence factors. During chronic infection, P. aeruginosa evades host defense by decreased virulence, which includes the production or, in the case of mucoidy, overproduction of alginate. The impact of alginate on innate immunity, in particular on macrophage clearance of apoptotic cells is not known. We hypothesized that P. aeruginosa strains that exhibit reduced virulence impair macrophage clearance of apoptotic cells and we investigated if the polysaccharide alginate produced by mucoid P. aeruginosa is sufficient to inhibit alveolar macrophage efferocytosis. Rat alveolar or human peripheral blood monocyte (THP-1)-derived macrophage cell lines were exposed in vitro to exogenous alginate or to wild type or alginate-overproducing mucoid P. aeruginosa prior to challenge with apoptotic human Jurkat T-lymphocytes. The importance of LPS contamination and that of structural integrity of alginate polymers was tested using alginate of different purities and alginate lyase, respectively. Alginate inhibited alveolar macrophage efferocytosis in a dose- and time-dependent manner. This effect was augmented but not exclusively attributed to lipopolysaccharide (LPS) present in alginates. Alginate-producing P. aeruginosa inhibited macrophage efferocytosis by more than 50%. A mannuronic-specific alginate lyase did not restore efferocytosis inhibited by exogenous guluronic-rich marine alginate, but had a marked beneficial effect on efferocytosis of alveolar macrophages exposed to mucoid P. aeruginosa. Despite decreased virulence, mucoid P. aeruginosa may contribute to chronic airway inflammation through significant inhibition of alveolar clearance of apoptotic cells and debris. The mechanism by which mucoid bacteria inhibit efferocytosis may involve alginate production and synergy with LPS, suggesting that alginate lyase may be an attractive therapeutic approach to airway inflammation in cystic fibrosis and other chronic obstructive pulmonary diseases characterized by P. aeruginosa colonization.
authors.affiliation: Department of Pediatrics, Pediatric Pulmonology, Indiana University Purdue University Indianapolis, Indianapolis, IN.
authors.forename: Charlie A
authors.initials: CA
authors.lastname: McCaslin
authors.affiliation: Department of Medicine, School of Medicine, Indiana University Purdue University Indianapolis, Indianapolis, IN.
authors.forename: Daniela N
authors.initials: DN
authors.lastname: Petrusca
authors.affiliation: Department of Medicine, School of Medicine, Indiana University Purdue University Indianapolis, Indianapolis, IN.
authors.forename: Christophe
authors.initials: C
authors.lastname: Poirier
authors.affiliation: Department of Medicine, School of Medicine, Indiana University Purdue University Indianapolis, Indianapolis, IN.
authors.forename: Karina A
authors.initials: KA
authors.lastname: Serban
authors.affiliation: Department of Biology; Indiana University Purdue University Indianapolis, Indianapolis, IN.
authors.forename: Gregory G
authors.initials: GG
authors.lastname: Anderson
authors.affiliation: Department of Medicine, School of Medicine, Indiana University Purdue University Indianapolis, Indianapolis, IN.|Richard L. Roudebush Veteran Affairs Medical Center, Indianapolis, IN.
authors.forename: Irina
authors.initials: I
authors.lastname: Petrache
mesh_terms: D000464:Alginates / Q000494:pharmacology*; D000704:Analysis of Variance; D000818:Animals; D017209:Apoptosis / Q000187:drug effects* / Q000276:immunology; D002478:Cells, Cultured; D003550:Cystic Fibrosis / Q000188:drug therapy / Q000276:immunology / Q000382:microbiology*; D020723:Glucuronic Acid / Q000096:biosynthesis / Q000494:pharmacology; D006603:Hexuronic Acids / Q000494:pharmacology; D007113:Immunity, Innate / Q000502:physiology; D008070:Lipopolysaccharides / Q000494:pharmacology; D016676:Macrophages, Alveolar / Q000187:drug effects* / Q000382:microbiology; D011133:Polysaccharide-Lyases / Q000494:pharmacology; D011552:Pseudomonas Infections / Q000188:drug therapy / Q000276:immunology / Q000382:microbiology*; D011550:Pseudomonas aeruginosa / Q000378:metabolism* / Q000472:pathogenicity; D051381:Rats; D014774:Virulence
chemical_list: D000464:Alginates; D006603:Hexuronic Acids; D008070:Lipopolysaccharides; D020723:Glucuronic Acid; D011133:Polysaccharide-Lyases; C016158:poly(beta-D-mannuronate) lyase
keywords: Alginate lyase; Cystic fibrosis; Efferocytosis; Macrophage; Mucoid; Phagocytosis; Pseudomonas aeruginosa