title: Mechanism of serum resistance among Brucella abortus isolates.
abstract: It was shown in this study that complement-resistant Brucella abortus used were unable to activate complement in the absence of specific antibody. Complement-resistant isolates possessed O-antigen, but complement-sensitive organisms used are O-antigen deficient. Since B. abortus LPS does not activate the alternative pathway of complement, we concluded that activation of bovine complement must be due to some other mechanism. In this study, it was shown that bovine C1 binds to the outer membrane proteins of B. abortus. Isolated outer membrane proteins of both smooth (O-antigen positive) and rough (O-antigen negative) B. abortus used bind to C1q. However, only rough isolates were killed by complement. All of the O-antigen positive B. abortus isolates were complement-resistant. We propose that O-antigen shields outer membrane proteins and blocks C1q binding.
authors.affiliation: Department of Microbiology and Cell Science, IFAS, University of Florida, Gainesville 32611, USA.
authors.forename: F C
authors.initials: FC
authors.lastname: Eisenschenk
authors.forename: J J
authors.initials: JJ
authors.lastname: Houle
authors.forename: E M
authors.initials: EM
authors.lastname: Hoffmann
mesh_terms: D000818:Animals; D000907:Antibodies, Bacterial / Q000737:chemistry; D000911:Antibodies, Monoclonal; D001425:Bacterial Outer Membrane Proteins / Q000276:immunology; D015153:Blotting, Western / Q000662:veterinary; D002003:Brucella abortus / Q000276:immunology* / Q000472:pathogenicity; D002007:Brucellosis, Bovine / Q000276:immunology*; D002417:Cattle; D015922:Complement C1q / Q000276:immunology*; D015941:Complement Hemolytic Activity Assay / Q000662:veterinary; D004591:Electrophoresis, Polyacrylamide Gel / Q000662:veterinary; D019081:O Antigens / Q000276:immunology
chemical_list: D000907:Antibodies, Bacterial; D000911:Antibodies, Monoclonal; D001425:Bacterial Outer Membrane Proteins; D019081:O Antigens; D015922:Complement C1q