title: Host-adaptation of Francisella tularensis alters the bacterium's surface-carbohydrates to hinder effectors of innate and adaptive immunity.
abstract: BACKGROUND
  The gram-negative bacterium Francisella tularensis survives in arthropods, fresh water amoeba, and mammals with both intracellular and extracellular phases and could reasonably be expected to express distinct phenotypes in these environments. The presence of a capsule on this bacterium has been controversial with some groups finding such a structure while other groups report that no capsule could be identified. Previously we reported in vitro culture conditions for this bacterium which, in contrast to typical methods, yielded a bacterial phenotype that mimics that of the bacterium's mammalian, extracellular phase.
  
  
  RESULTS
  SDS-PAGE and carbohydrate analysis of differentially-cultivated F. tularensis LVS revealed that bacteria displaying the host-adapted phenotype produce both longer polymers of LPS O-antigen (OAg) and additional HMW carbohydrates/glycoproteins that are reduced/absent in non-host-adapted bacteria. Analysis of wildtype and OAg-mutant bacteria indicated that the induced changes in surface carbohydrates involved both OAg and non-OAg species. To assess the impact of these HMW carbohydrates on the access of outer membrane constituents to antibody we used differentially-cultivated bacteria in vitro to immunoprecipitate antibodies directed against outer membrane moieties. We observed that the surface-carbohydrates induced during host-adaptation shield many outer membrane antigens from binding by antibody. Similar assays with normal mouse serum indicate that the induced HMW carbohydrates also impede complement deposition. Using an in vitro macrophage infection assay, we find that the bacterial HMW carbohydrate impedes TLR2-dependent, pro-inflammatory cytokine production by macrophages. Lastly we show that upon host-adaptation, the human-virulent strain, F. tularensis SchuS4 also induces capsule production with the effect of reducing macrophage-activation and accelerating tularemia pathogenesis in mice.
  
  
  CONCLUSIONS
  F. tularensis undergoes host-adaptation which includes production of multiple capsular materials. These capsules impede recognition of bacterial outer membrane constituents by antibody, complement, and Toll-Like Receptor 2. These changes in the host-pathogen interface have profound implications for pathogenesis and vaccine development.
authors.affiliation: Center for Immunology and Microbial Disease, Albany Medical College, Albany, New York, United States of America.
authors.forename: Tiffany M
authors.initials: TM
authors.lastname: Zarrella
authors.forename: Anju
authors.initials: A
authors.lastname: Singh
authors.forename: Constantine
authors.initials: C
authors.lastname: Bitsaktsis
authors.forename: Tabassum
authors.initials: T
authors.lastname: Rahman
authors.forename: Bikash
authors.initials: B
authors.lastname: Sahay
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Feustel
authors.forename: Edmund J
authors.initials: EJ
authors.lastname: Gosselin
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Sellati
authors.forename: Karsten R O
authors.initials: KR
authors.lastname: Hazlett
mesh_terms: D000222:Adaptation, Physiological / Q000276:immunology*; D056704:Adaptive Immunity; D000818:Animals; D000907:Antibodies, Bacterial / Q000276:immunology; D016667:Bacterial Capsules / Q000096:biosynthesis* / Q000737:chemistry; D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D003165:Complement System Proteins / Q000378:metabolism; D005110:Extracellular Space / Q000378:metabolism; D005604:Francisella tularensis / Q000166:cytology / Q000254:growth & development / Q000276:immunology* / Q000378:metabolism*; D006801:Humans; D007113:Immunity, Innate; D008070:Lipopolysaccharides / Q000096:biosynthesis* / Q000737:chemistry; D051379:Mice; D008970:Molecular Weight; D019081:O Antigens / Q000096:biosynthesis / Q000737:chemistry; D010641:Phenotype; D051195:Toll-Like Receptor 2 / Q000378:metabolism; D014406:Tularemia / Q000276:immunology / Q000382:microbiology
chemical_list: D000907:Antibodies, Bacterial; D001425:Bacterial Outer Membrane Proteins; D008070:Lipopolysaccharides; D019081:O Antigens; D051195:Toll-Like Receptor 2; D003165:Complement System Proteins