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The immunoprotective Anaplasma marginale major surface protein 2 is encoded by a polymorphic multigene family
G H Palmer1, G Eid, A F Barbet
1Department of Veterinary Microbiology and Pathology, Washington State University, Pullman 99164-7040.
Abstract:
An Anaplasma marginale Florida msp-2 gene was cloned and expressed in Escherichia coli. Pulsed-field gel electrophoresis and Southern blot analysis revealed the presence of multiple msp-2 gene copies that were widely distributed throughout the chromosomes of all three strains examined. Genomic polymorphism among copies was greatest in the 5' end of msp-2 but also occurred in 3' regions. The presence of gene-copy-specific epitopes was indicated by the reactivity of the cloned msp-2 copy with some, but not all, monoclonal antibodies that bound native MSP-2. Multiple antigenically distinct MSP-2 molecules were expressed within strains and were coexpressed by individual A. marginale organisms. These results suggest that expression of polymorphic msp-2 gene copies is responsible for the significant percentages of A. marginale organisms within strains that do not react with individual anti-MSP-2 monoclonal antibodies. Sequence analysis revealed highly significant MSP-2 homology with two rickettsial surface proteins, A. marginale MSP-4 and Cowdria ruminantium MAP-1. Immunization with MSP-4 has been shown to induce protective immunity in a manner similar to that of immunization with MSP-2. These findings support the hypothesis that A. marginale surface proteins are targets of protective immune responses but are antigenically polymorphic.
Insights
Anaplasma marginale expresses multiple, polymorphic msp-2 gene copies, leading to diverse surface protein variants. This antigenic variation in Anaplasma marginale MSP-2 molecules impacts immune responses and diagnostics.
Area of Science:
- Microbiology
- Immunology
- Molecular Biology
Background:
- Anaplasma marginale is an important tick-borne pathogen causing significant economic losses in cattle.
- The major surface protein 2 (MSP-2) of A. marginale is a key target for immune responses.
- Understanding the genetic diversity of MSP-2 is crucial for vaccine development and disease control.
Purpose of the Study:
- To investigate the genetic structure and expression of the msp-2 gene in Anaplasma marginale.
- To determine the antigenic variability of MSP-2 molecules within and between A. marginale strains.
- To explore the evolutionary relationship of MSP-2 with other rickettsial surface proteins.
Main Methods:
- Cloning and expression of the Anaplasma marginale Florida msp-2 gene in Escherichia coli.
- Pulsed-field gel electrophoresis and Southern blot analysis to examine msp-2 gene copy number and distribution.
- Monoclonal antibody binding assays to assess antigenic epitopes on expressed MSP-2.
- Sequence analysis to compare MSP-2 with homologous proteins in other rickettsial species.
Main Results:
- Multiple copies of the msp-2 gene were found distributed across the chromosomes of A. marginale strains.
- Genomic polymorphism was observed in both 5' and 3' regions of the msp-2 gene copies.
- Antigenically distinct MSP-2 molecules were expressed and co-expressed by individual A. marginale organisms.
- MSP-2 showed significant homology with rickettsial surface proteins MSP-4 and MAP-1.
Conclusions:
- The expression of polymorphic msp-2 gene copies contributes to the antigenic diversity of MSP-2 in A. marginale.
- This antigenic polymorphism explains why not all A. marginale organisms react with specific anti-MSP-2 monoclonal antibodies.
- A. marginale surface proteins, like MSP-2 and MSP-4, are likely targets of protective immunity and exhibit antigenic polymorphism.