Related Experiment Videos
Haemagglutinins of pathogenic avian mycoplasmas
1Biotechnical Faculty, Department of Animal Sciences, University of Ljubljana, Groblje 3, 1230 Domzale, Slovenia.
Abstract:
The pathogenic avian mycoplasmas, Mycoplasma gallisepticum, Mycoplasma synoviae, Mycoplasma meleagridis, Mycoplasma iowae and Mycoplasma imitans, synthesize haemagglutinins that are immunogenic, variably expressed, surface proteins. The haemagglutinins of M. gallisepticum (pMGA), M. synoviae (VlhA) and M. imitans are lipoproteins, encoded by related multigene families that appear to have arisen by horizontal gene transfer. M. gallisepticum also has genes encoding cytadhesins in its genome but these are present as a single copies, while the pMGA gene family contains 30 to 70 genes. The switch in expression of distinct pMGA genes (e.g. pMGA1.1 to pMGA1.9) generates antigenic variation, which is thought to be important in immune evasion but also has significance in the preparation of M. gallisepticum antigens for serological diagnosis. In the majority of M. synoviae strains, post-translational cleavage of the VlhA protein generates an amino-terminal part (the lipoprotein MSPB) and a carboxyl-terminal part (MSPA), which mediates binding to erythrocytes. The 5'vlhA gene region, which encodes proline-rich repeats in the amino-terminal part of MSPB, is highly polymorphic among M. synoviae strains. Insertions or deletions in the part of vlhA encoding the proline-rich repeats cause MSPB length variation in different M. synoviae strains. Recombination between the 5'vlhA gene and pseudogenes in the genome generates changes in antigenic determinants in the carboxyl two-thirds of the MSPB molecule, and in MSPA, resulting in changes in the domains involved in the binding of M. synoviae to erythrocytes. Variant haemagglutinins of M. gallisepticum (pMGA1.7) and M. synoviae (diverse VlhA forms) share sequences that may be responsible for antigenic cross-reactions between M. gallisepticum and M. synoviae. Shared epitopes have been demonstrated using specific antibodies against MSPB that also recognize proteins of M. gallisepticum and of M. iowae (serotype N). Size and antigenic variants have also been reported for M. meleagridis and M. iowae proteins, but it is not known if these are their haemagglutinins. Advances in the molecular characterization of M. gallisepticum (pMGA, pvpA) and M. synoviae (vlhA) genes and their sequencing in numerous strains is likely to enable significantly improved epidemiological studies and improved tracing of M. gallisepticum and M. synoviae strains in different flocks.
Insights
Pathogenic avian mycoplasmas produce variable surface proteins called haemagglutinins. Molecular characterization of these avian mycoplasma haemagglutinin genes aids in understanding immune evasion and improving disease tracing in poultry flocks.
Area of Science:
- Veterinary Microbiology
- Immunology
- Molecular Biology
Background:
- Pathogenic avian mycoplasmas, including Mycoplasma gallisepticum and Mycoplasma synoviae, synthesize immunogenic surface proteins known as haemagglutinins.
- These haemagglutinins are lipoproteins encoded by multigene families, suggesting horizontal gene transfer as their origin.
Purpose of the Study:
- To investigate the molecular characteristics of haemagglutinins in pathogenic avian mycoplasmas.
- To understand the mechanisms of antigenic variation and immune evasion employed by these pathogens.
- To explore the potential for improved serological diagnosis and epidemiological studies.
Main Methods:
- Molecular characterization and sequencing of haemagglutinin genes (pMGA, vlhA) in various avian mycoplasma strains.
- Analysis of gene families, post-translational modifications, and genetic variations (polymorphisms, insertions, deletions, recombination).
- Investigation of antigenic cross-reactivity using specific antibodies.
Main Results:
- Mycoplasma gallisepticum (pMGA) and Mycoplasma synoviae (VlhA) haemagglutinins exhibit significant antigenic variation due to gene switching and polymorphisms.
- Post-translational cleavage and recombination events contribute to the diversity of VlhA in Mycoplasma synoviae.
- Shared epitopes between Mycoplasma gallisepticum and Mycoplasma synoviae haemagglutinins were identified, suggesting potential cross-reactivity.
Conclusions:
- Molecular insights into avian mycoplasma haemagglutinins are crucial for understanding their pathogenesis and immune evasion strategies.
- Advances in gene sequencing facilitate enhanced epidemiological studies for tracing Mycoplasma gallisepticum and Mycoplasma synoviae strains.
- The identified antigenic variations and cross-reactivities have implications for serological diagnostics and vaccine development.