title: Expression of major surface protein 2 antigenic variants during acute Anaplasma marginale rickettsemia.
abstract: Antigenic variants of Anaplasma marginale major surface protein 2 (MSP-2), a target of protective immune responses, have been detected by use of copy-specific monoclonal antibodies reactive with some, but not all, organisms during acute rickettsemia. The presence of polymorphic msp-2 genes was confirmed by cloning and sequencing two gene copies, 11.2 and DF5, each of which encodes a full-length MSP-2 with a unique amino acid sequence. Transcription of msp-2 genes during acute rickettsemia was analyzed by use of cDNA cloning of hybrid-selected msp-2 mRNA. Sequencing of cDNA clones, designated AR1 to AR14, indicated that DF5 msp-2 was transcribed during acute rickettsemia. Two classes of variant msp-2 genes were also transcribed during acute rickettsemia. The first class of variant transcripts, typified by clones AR3, AR4, AR7, and AR14, each encoded a single or small number of amino acid substitutions relative to DF5. The second type, AR5, encoded a large region of amino acid polymorphism, including additions, deletions, and substitutions, as compared to DF5. Specific antibody directed against the AR5 polymorphic region bound a unique MSP-2 expressed on A. marginale that was not recognized by antibody generated against DF5. Similarly, anti-AR5 peptide antibody reacted with a different MSP-2 that was not bound by anti-DF5 antibody. This expression confirmed that variant msp-2 transcripts encode structurally distinct MSP-2 molecules which bear unique B-cell epitopes. These results support the hypothesis that the large msp-2 gene family, which constitutes a minimum of 1% of the genome, encodes antigenic variants critical to evasion of protective immune response directed against surface MSP-2 epitopes.
authors.affiliation: Department of Infectious Diseases, University of Florida, Gainesville, USA.
authors.forename: G
authors.initials: G
authors.lastname: Eid
authors.forename: D M
authors.initials: DM
authors.lastname: French
authors.forename: A M
authors.initials: AM
authors.lastname: Lundgren
authors.forename: A F
authors.initials: AF
authors.lastname: Barbet
authors.forename: T F
authors.initials: TF
authors.lastname: McElwain
authors.forename: G H
authors.initials: GH
authors.lastname: Palmer
mesh_terms: D000208:Acute Disease; D000595:Amino Acid Sequence; D000709:Anaplasma / Q000276:immunology*; D000712:Anaplasmosis / Q000276:immunology*; D000818:Animals; D000942:Antigens, Bacterial / Q000032:analysis / Q000235:genetics*; D000954:Antigens, Surface / Q000235:genetics; D016470:Bacteremia / Q000276:immunology*; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D002417:Cattle; D003001:Cloning, Molecular; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000032:analysis
chemical_list: D000942:Antigens, Bacterial; D000954:Antigens, Surface; D001426:Bacterial Proteins; D012333:RNA, Messenger