title: The Borrelia hermsii factor H binding protein FhbA is not required for infectivity in mice or for resistance to human complement in vitro.
abstract: The primary causative agent of tick-borne relapsing fever in North America is Borrelia hermsii. It has been hypothesized that B. hermsii evades complement-mediated destruction by binding factor H (FH), a host-derived negative regulator of complement. In vitro, B. hermsii produces a single FH binding protein designated FhbA (FH binding protein A). The properties and ligand binding activity of FhbA suggest that it plays multiple roles in pathogenesis. It binds plasminogen and has been identified as a significant target of a B1b B cell-mediated IgM response in mice. FhbA has also been explored as a potential diagnostic antigen for B. hermsii infection in humans. The ability to test the hypothesis that FhbA is a critical virulence factor in vivo has been hampered by the lack of well-developed systems for the genetic manipulation of the relapsing fever spirochetes. In this report, we have successfully generated a B. hermsii fhbA deletion mutant (the B. hermsii YORΔfhbA strain) through allelic exchange mutagenesis. Deletion of fhbA abolished FH binding by the YORΔfhbA strain and eliminated cleavage of C3b on the cell surface. However, the YORΔfhbA strain remained infectious in mice and retained resistance to killing in vitro by human complement. Collectively, these results indicate that B. hermsii employs an FhbA/FH-independent mechanism of complement evasion that allows for resistance to killing by human complement and persistence in mice.
authors.affiliation: Department of Microbiology and Immunology, Virginia Commonwealth University Medical Center, Richmond, Virginia, USA.
authors.forename: Lindy M
authors.initials: LM
authors.lastname: Fine
authors.affiliation: Department of Microbiology and Immunology, Virginia Commonwealth University Medical Center, Richmond, Virginia, USA.
authors.forename: Daniel P
authors.initials: DP
authors.lastname: Miller
authors.affiliation: Department of Microbiology and Immunology, Virginia Commonwealth University Medical Center, Richmond, Virginia, USA.
authors.forename: Katherine L
authors.initials: KL
authors.lastname: Mallory
authors.affiliation: Department of Microbiology and Immunology, Virginia Commonwealth University Medical Center, Richmond, Virginia, USA.
authors.forename: Brittney K
authors.initials: BK
authors.lastname: Tegels
authors.affiliation: Department of Microbiology and Immunology, Virginia Commonwealth University Medical Center, Richmond, Virginia, USA.
authors.forename: Christopher G
authors.initials: CG
authors.lastname: Earnhart
authors.affiliation: Department of Microbiology and Immunology, Virginia Commonwealth University Medical Center, Richmond, Virginia, USA Center for the Study of Biological Complexity, Virginia Commonwealth University Medical Center, Richmond, Virginia, USA rmarconi@vcu.edu.
authors.forename: Richard T
authors.initials: RT
authors.lastname: Marconi
mesh_terms: D000818:Animals; D001770:Blood Bactericidal Activity; D001898:Borrelia / Q000235:genetics / Q000276:immunology*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D003165:Complement System Proteins / Q000276:immunology*; D004195:Disease Models, Animal; D017353:Gene Deletion; D006801:Humans; D051379:Mice; D012061:Relapsing Fever / Q000276:immunology* / Q000382:microbiology*; D037521:Virulence Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; C510009:FH-binding protein A, Borrelia hermsii; D037521:Virulence Factors; D003165:Complement System Proteins