title: Variability in the 28-kDa surface antigen protein multigene locus of isolates of the emerging disease agent Ehrlichia chaffeensis suggests that it plays a role in immune evasion.
abstract: Infections caused by rickettsial pathogens persist in vertebrate hosts for long periods of time, despite the active host immune response. We recently described the multigene locus encoding 28 kDa surface antigen proteins (28 kDa SAPs) for two closely related rickettsials, Ehrlichia chaffeensis and Ehrlichia canis (Reddy, G. R., et al. (1998) Biochem. Biophys. Res. Commun. 247, 636-643), that share extensive structural homology to antigenic variant surface protein genes of Neisseria and Borrelia species. In this study, we describe motifs for recombinase binding sites and a high frequency of repeat elements in the cloned 28 kDa SAP genes. The locus for two newly established E. chaffeensis isolates also was characterized, and immunological specificity of the 28 kDa SAPs was investigated. The study identified variant forms of the 28 kDa SAPs and extensive restriction fragment length polymorphisms among isolates. The molecular data suggest that the locus is influenced by short-term evolutionary changes such as genetic recombinations leading to the generation of antigenic variants. Antigenic variation could contribute to the mechanism of immune evasion and the emergence of new diseases.
authors.affiliation: Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan 66506, USA. rganta@vet.ksu.edu
authors.forename: G R
authors.initials: GR
authors.lastname: Reddy
authors.forename: C P
authors.initials: CP
authors.lastname: Streck
mesh_terms: D000595:Amino Acid Sequence; D000942:Antigens, Bacterial / Q000235:genetics* / Q000276:immunology; D001483:Base Sequence; D018469:Ehrlichia chaffeensis / Q000235:genetics* / Q000276:immunology / Q000472:pathogenicity; D014644:Genetic Variation; D006801:Humans; D007107:Immune System / Q000382:microbiology*; D008969:Molecular Sequence Data; D005810:Multigene Family; D014774:Virulence / Q000235:genetics / Q000276:immunology
chemical_list: D000942:Antigens, Bacterial