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Evaluation of Anaplasma marginale major surface protein 3 (MSP3) as a diagnostic test antigen
1Department of Pathobiology, University of Florida, Gainesville 32611-0880, USA. ARALL@GNV.IFAS.UFL.EDU
Abstract:
An immunodominant surface protein, major surface protein 3 (MSP3), has been proposed as an antigen suitable for use in the diagnosis of bovine anaplasmosis. We further characterized MSP3 to examine its potential as a test antigen for the serological diagnosis of carrier cattle. The specificity of this antigen in detecting infected cattle as well as the conservation of MSP3 between strains of Anaplasma marginale was evaluated by using immunoblots of A. marginale proteins separated by one- and two-dimensional polyacrylamide gel electrophoreses. Immune sera from animals infected with Anaplasma ovis, Ehrlichia risticii, and Ehrlichia ewingii reacted with the MSP3 antigen of A. marginale. One-dimensional gel electrophoresis of A. marginale proteins demonstrated size polymorphism of MSP3 between different geographic isolates. Two-dimensional gel electrophoresis revealed at least three different antigens migrating at the 86-kDa molecular size, and sera from animals infected with different strains of A. marginale reacted with different 86-kDa antigens. These results indicate that MSP3 may share cross-reactive epitopes with antigens found in A. ovis and some Ehrlichia spp. In addition, MSP3 is not conserved between different isolates of A. marginale, and at least in the isolate from Florida, what was previously identified as MSP3 is actually a group of three or more 86-kDa antigens with different isoelectric points. The cross-reactivity of MSP3 with some Ehrlichia spp., the variability of MSP3 between isolates, and the multiple 86-kDa antigens recognized by various sera suggest that MSP3 is not a suitable candidate for use as a recombinant test antigen.
Insights
Major surface protein 3 (MSP3) is not suitable for diagnosing bovine anaplasmosis. Cross-reactivity with other bacteria and variability among Anaplasma marginale strains limit its diagnostic potential.
Area of Science:
- Veterinary Immunology
- Bacteriology
- Molecular Biology
Background:
- Bovine anaplasmosis diagnosis relies on identifying specific antigens.
- Major surface protein 3 (MSP3) was proposed as a potential diagnostic antigen.
- Further characterization is needed to assess MSP3's suitability for serological diagnosis.
Purpose of the Study:
- To evaluate the specificity and conservation of MSP3 in diagnosing bovine anaplasmosis.
- To assess MSP3's potential as a test antigen for carrier cattle.
Main Methods:
- Immunoblots of Anaplasma marginale proteins using one- and two-dimensional polyacrylamide gel electrophoresis.
- Testing immune sera from animals infected with A. marginale, Anaplasma ovis, Ehrlichia risticii, and Ehrlichia ewingii.
Main Results:
- MSP3 showed cross-reactivity with sera from animals infected with A. ovis and Ehrlichia spp.
- MSP3 exhibited size polymorphism between different geographic isolates of A. marginale.
- Two-dimensional gel electrophoresis revealed MSP3 to be a group of at least three 86-kDa antigens with varying isoelectric points.
Conclusions:
- MSP3 is not a suitable candidate for recombinant test antigen due to cross-reactivity and variability.
- The identified MSP3 antigen is a complex of multiple proteins, not a single conserved entity.
- Diagnostic strategies for bovine anaplasmosis require antigens with higher specificity and conservation.