title: Primary Structural Variation in Anaplasma marginale Msp2 Efficiently Generates Immune Escape Variants.
abstract: Antigenic variation allows microbial pathogens to evade immune clearance and establish persistent infection. Anaplasma marginale utilizes gene conversion of a repertoire of silent msp2 alleles into a single active expression site to encode unique Msp2 variants. As the genomic complement of msp2 alleles alone is insufficient to generate the number of variants required for persistence, A. marginale uses segmental gene conversion, in which oligonucleotide segments from multiple alleles are recombined into the expression site to generate a novel msp2 mosaic not represented elsewhere in the genome. Whether these segmental changes are sufficient to evade a broad antibody response is unknown. We addressed this question by identifying Msp2 variants that differed in primary structure within the immunogenic hypervariable region microdomains and tested whether they represented true antigenic variants. The minimal primary structural difference between variants was a single amino acid resulting from a codon insertion, and overall, the amino acid identity among paired microdomains ranged from 18 to 92%. Collectively, 89% of the expressed structural variants were also antigenic variants across all biological replicates, independent of a specific host major histocompatibility complex haplotype. Biological relevance is supported by the following: (i) all structural variants were expressed during infection of a natural host, (ii) the structural variation observed in the microdomains corresponded to the mean length of variants generated by segmental gene conversion, and (iii) antigenic variants were identified using a broad antibody response that developed during infection of a natural host. The findings demonstrate that segmental gene conversion efficiently generates Msp2 antigenic variants.
authors.affiliation: The Paul G. Allen School for Global Animal Health, Washington State University, Pullman, Washington, USA Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, Washington, USA telmo@vetmed.wsu.edu.
authors.forename: Telmo
authors.initials: T
authors.lastname: Graça
authors.affiliation: The Paul G. Allen School for Global Animal Health, Washington State University, Pullman, Washington, USA School of Electrical Engineering and Computer Science, Washington State University, Pullman, Washington, USA.
authors.forename: Lydia
authors.initials: L
authors.lastname: Paradiso
authors.affiliation: The Paul G. Allen School for Global Animal Health, Washington State University, Pullman, Washington, USA Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, Washington, USA School of Electrical Engineering and Computer Science, Washington State University, Pullman, Washington, USA.
authors.forename: Shira L
authors.initials: SL
authors.lastname: Broschat
authors.affiliation: The Paul G. Allen School for Global Animal Health, Washington State University, Pullman, Washington, USA Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, Washington, USA Animal Disease Research Unit, Agricultural Research Service, U.S. Department of Agriculture, Pullman, Washington, USA.
authors.forename: Susan M
authors.initials: SM
authors.lastname: Noh
authors.affiliation: The Paul G. Allen School for Global Animal Health, Washington State University, Pullman, Washington, USA Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, Washington, USA School of Electrical Engineering and Computer Science, Washington State University, Pullman, Washington, USA.
authors.forename: Guy H
authors.initials: GH
authors.lastname: Palmer
mesh_terms: D000595:Amino Acid Sequence; D042322:Anaplasma marginale / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D000712:Anaplasmosis / Q000276:immunology* / Q000382:microbiology; D000907:Antibodies, Bacterial / Q000276:immunology; D000940:Antigenic Variation; D000942:Antigens, Bacterial / Q000737:chemistry* / Q000235:genetics / Q000276:immunology*; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000276:immunology*; D006801:Humans; D057131:Immune Evasion; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment
chemical_list: D000907:Antibodies, Bacterial; D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; C450839:p44 protein, Anaplasma phagocytophila