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Home / Equine Research Bank / Infect Immun / Molecular basis for antigenic variation of a protective stra...
Infection and immunity1998; 66(8); 3682-3688; doi: 10.1128/IAI.66.8.3682-3688.1998

Molecular basis for antigenic variation of a protective strain-specific antigen of Ehrlichia risticii.

Abstract: Ehrlichia risticii, the causative agent of Potomac horse fever, has recently been isolated from many vaccinated horses with typical clinical signs of the disease. The heterogeneity of the E. risticii isolates obtained from the vaccinated horses necessitates the identification of the molecular basis of strain variations to elucidate the vaccine failure and to aid in the development of an efficient vaccine against this disease. As an attempt, two major cross-reacting surface antigen genes of 50- and 85-kDa antigens, present separately in strains 25-D (isolated in 1984) and 90-12 (isolated in 1990 from a vaccinated horse), respectively, were cloned and sequenced. A comparative sequence analysis revealed differences and similarities between these two antigens with strain-specific sizes (SSA). The 2.5- and 1.6-kb genes coding for the 85- and 50-kDa proteins, respectively, contained many different tandem repeats. The identical repeat motifs were more frequent in the middle of both genes, but the numbers and positions of the repeats were altogether different in the genes. Many of these direct repeats of both genes had exact sequence homology and coded for the same amino acids. The homology of the 5'- and 3'-flanking regions of the two genes was greater than that of the regions in the central part of the genes. A comparative analysis of the deduced amino acid sequences of these two antigen genes indicated eight common domains, which were designated identical domains. Although the sequence homologies of these identical domains were the same, the positions of the domains in their respective strains were completely different. This finding might be one of the bases of antigenic variation between the strains. In addition, there were a few unique regions in both antigen genes where no sequence homology existed. These specific regions were designated unique domains. The 50-kDa protein had two such unique domains, and the 85-kDa protein had six such unique domains. The presence of such unique domains contributed to the large size variation of these SSA. The cross-reactivity of recombinant proteins confirmed the presence of conserved epitopes between these two antigens. The SSA have been determined to be apparent protective antigens of E. risticii.
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Publication Date: 1998-07-23 PubMed ID: 9673249PubMed Central: PMC108402DOI: 10.1128/IAI.66.8.3682-3688.1998Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

This research investigates the molecular basis for antigenic variation in Ehrlichia risticii, the bacteria causing Potomac horse fever, due to observed differences in strains acquired from vaccinated horses. Two major surface antigen genes in separate strain samples were cloned, sequenced, and compared to help understand why the current vaccination may be ineffective and aid in developing a better vaccine.

Investigated Antigen Genes

  • The two major surface antigen genes (from strains 25-D and 90-12) that the research focused on are the 50-kDa and 85-kDa antigens.
  • These genes were found to contain numerous dissimilar tandem repeats – short sequences of DNA that is repeated back-to-back.
  • Although the types of tandem repetitions found in the middle parts of both genes were the same, the numbers and positions of the repetitions varied significantly.

Comparative Sequence Analysis

  • The researchers carried out a comparative analysis on the sequence of these two antigen genes, revealing both dissimilarities and similarities.
  • Despite their sequence homologies being the same, the identical domains were found in completely different positions in their respective strains, which could be a reason for the antigenic variation between the strains.
  • There were also unique regions present in both genes where no sequence homology existed; these were named unique domains.
  • These unique domains may contribute to significant size variations of the strain-specific antigens.

Potential Implications

  • Both proteins were found to consistently react, confirming the presence of conserved epitopes (parts of antigens that antibodies recognise) between these two antigens.
  • It has been determined that the strain-specific antigens are potential protective antigens of E. risticii.
  • The research may assist in understanding the molecular basis of the observed strain variations and could aid in creating a more effective vaccine.

Cite This Article

APA
Biswas B, Vemulapalli R, Dutta SK. (1998). Molecular basis for antigenic variation of a protective strain-specific antigen of Ehrlichia risticii. Infect Immun, 66(8), 3682-3688. https://doi.org/10.1128/IAI.66.8.3682-3688.1998

Publication

Infection and immunity
ISSN: 0019-9567
NlmUniqueID: 0246127
Country: United States
Language: English
Volume: 66
Issue: 8
Pages: 3682-3688

Researcher Affiliations

Biswas, B
  • Virginia-Maryland Regional College of Veterinary Medicine, University of Maryland, College Park, Maryland 20742, USA.
Vemulapalli, R
    Dutta, S K

      MeSH Terms

      • Amino Acid Sequence
      • Antigenic Variation / genetics
      • Antigens, Bacterial / analysis
      • Antigens, Bacterial / genetics
      • Antigens, Surface / analysis
      • Antigens, Surface / genetics
      • Base Sequence
      • Cell Line
      • Cloning, Molecular
      • DNA, Bacterial
      • Ehrlichia / genetics
      • Ehrlichia / immunology
      • Genes, Bacterial
      • Humans
      • Molecular Sequence Data
      • Recombinant Fusion Proteins / analysis
      • Recombinant Fusion Proteins / genetics
      • Sequence Analysis, DNA

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