Mycoplasma synoviae has two distinct phase-variable major membrane antigens, one of which is a putative hemagglutinin

Abstract

Mycoplasma synoviae is a major pathogen of poultry, causing synovitis and respiratory infection. A cluster of 45-to 50-kDa membrane proteins is immunodominant in strain WVU-1853. Four distinct proteins were identified in this cluster by high-pressure liquid chromatography. Monoclonal antibodies and monospecific antisera against each established that they fell into two groups, MSPA and MSPB, each containing two members distinguishable by a difference in hydrophobicity. A 25-to 30-kDa membrane protein (MSPC) was shown to be antigenically related to the MSPB proteins. Considerable variation in the size and expression of MSPA and MSPB was observed among different strains of M. synoviae. Examination of expression in colonies of strain WVU-1853 established that both MSPA and MSPB (and MSPC) were phase variable. Immunostaining of MSPB (and MSPC) with monoclonal antibodies exhibited quantal variation, with three distinct levels observed between and within colonies. Hemadsorption by M. synoviae colonies was also found to be phase variable, with some colonies exhibiting sectorial expression of hemadsorption. Monospecific antisera against MSPA inhibited hemagglutination, but neither monoclonal antibodies nor monospecific antisera against MSPB could inhibit hemagglutination. However, loss of the capacity to hemadsorb by individual clones was associated with loss of expression of both MSPA and MSPB. These findings have elucidated the complexity of structure, function, and expression of the 45-to 50-kDa membrane protein cluster of M. synoviae, and they suggest that all members of the cluster may be involved in adhesion.

The characterization ofMycoplasma synoviaeEF-Tu protein and proteins involved in hemadherence and their N-terminal amino acid sequences

“…Monoclonal antibodies (mAbs) recognizing major integral membrane proteins of M. synoviae were used. The mAb 125 (IgG 2b ) which reacts with immunodominant membrane proteins of 45–50 kDa [16], which are associated with hemadherence positive (HAD + ) phenotypes [2] and appear in the hemadherence negative (HAD − ) phenotypes as truncated (25–30‐kDa) forms [2, 4], was kindly provided by Dr. David H. Ley (North Carolina State University). We designated proteins reacting with mAb 125 as pMSB 1 .…”

“…Despite a strong antibody response in infected birds, colonization of the upper respiratory tract by M. synoviae persists and the infection becomes chronic. Factors which contribute to the chronic form of the disease are unknown but the immunodominant M. synoviae surface membrane proteins, which undergo phase variation in expression and are associated with hemadherence, may at least in part be involved [2–4]. Indeed, there is increasing evidence that immunodominant surface proteins undergo phase variable expression in many Mycoplasma species and are associated with the evasion of the immune response [5–7].…”

“…Indeed, there is increasing evidence that immunodominant surface proteins undergo phase variable expression in many Mycoplasma species and are associated with the evasion of the immune response [5–7]. M. synoviae has two major immunogenic membrane proteins, MSPA and MSPB, both of which are phase variable and coordinately involved in adhesion of the organism to erythrocytes [2]. Recently the vlhA gene encoding a variably expressed lipoprotein which is a hemagglutinin of M. synoviae (WVU 1853 strain) has been identified [7].…”

Gene conversion and concerted evolution in bacterial genomes

“…Combinatorial gene conversion has also been identified as one of the mechanisms participating in antigenic variation in M. synoviae , a pathogen for poultry. In this organism, MSPB (a lipoprotein) and MSPA (a haemagglutinin) are the main surface antigens; these display a high antigenic diversity [101]. Both antigens are encoded by a single gene ( vlhA1 ), which undergoes post‐translational cleavage and modification to yield MSPB and MSPA [102].…”

“…This process may generate 120 potential MSPA variants [80]; this is a conservative estimate, since the size of the full complement of vlh pseudogenes has not been determined yet. Although the exact frequency of antigenic variation for this protein has not been determined, it is frequent enough to be detected as sectored colonies that synthesize a variable antigen [101].…”