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Emergence of Anaplasma marginale antigenic variants during persistent rickettsemia

D M French1, W C Brown, G H Palmer

  • 1Program in Vector-Borne Diseases, Department of Veterinary Microbiology, Washington State University, Pullman, Washington 99164-7040, USA.

Infection and Immunity
|October 26, 1999
PubMed

Insights

Anaplasma marginale causes persistent cattle infections by varying its Major Surface Protein 2 (MSP2). This variation, driven by a single hypervariable region, allows the pathogen to evade the host immune response during rickettsemic cycles.

Area of Science:

  • Veterinary Microbiology
  • Immunology
  • Molecular Biology

Background:

  • Anaplasma marginale, an ehrlichial pathogen, causes cyclic rickettsemia in cattle.
  • During infection, A. marginale exhibits antigenic variation in its Major Surface Protein 2 (MSP2).

Purpose of the Study:

  • To investigate the structural basis of MSP2 antigenic variation in Anaplasma marginale.
  • To determine the role of MSP2 variation in the persistence of A. marginale infections.

Main Methods:

  • Cloning and sequencing of 17 full-length msp2 transcripts from cyclic rickettsemic cattle.
  • Comparative sequence analysis of MSP2 homologues across different ehrlichial species.

Main Results:

  • Emergent A. marginale variants possess a single, central hypervariable region in MSP2, encoding variant B-cell epitopes.
  • N- and C-terminal regions of MSP2 are conserved among A. marginale variants and similar to MSP2 homologues in the agent of human granulocytic ehrlichiosis.
  • Unlike other ehrlichial genogroup I pathogens, A. marginale MSP2 has a single hypervariable region.
  • The hypervariable region of MSP2 elicits immunogenic, variant-specific antibody responses during persistent infection.

Conclusions:

  • The single hypervariable region of A. marginale MSP2 is responsible for antigenic variation.
  • MSP2 antigenic variation is a key mechanism enabling Anaplasma marginale persistence in cattle.

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