Comparison ofMycoplasma synoviaeisolates by immunoblotting

Mycoplasma agassizii strain variation and distinct host antibody responses explain differences between enzyme-linked immunosorbent assays and Western blot assays

The precarious status of desert (Gopherus agassizii) and gopher (G. polyphemus) tortoises has resulted in conservation efforts that now include health assessment as an important component of management decision-making. Mycoplasmal upper respiratory tract disease (URTD) is one of very few diseases in chelonians for which comprehensive and rigorously validated diagnostic tests exist. In this study, serum samples obtained from eight Gopherus tortoises documented at necropsy to (i) be enzyme-linked immunosorbent assay (ELISA) seropositive using the PS6 antigen, (ii) be infected with Mycoplasma agassizii as indicated by direct isolation of the pathogen from the respiratory surfaces, and (iii) have histological lesions of mycoplasmal URTD were used to evaluate four distinct clinical isolates of M. agassizii as antigens for ELISA and Western blot analyses. Each animal sample reacted in the Western blot with its homologous M. agassizii strain, but recognition of heterologous M. agassizii strains was variable. Further, individual animals varied significantly with respect to the specific proteins recognized by the humoral immune response. An additional 114 Gopherus serum samples were evaluated using ELISA antigens prepared from the four distinct M. agassizii strains; A₄₀₅ values were significantly correlated (r² goodness of fit range, 0.708 to 0.771; P < 0.0001) for all antigens tested. The results confirm that strain variation is responsible for the observed differences between Western blot binding patterns. Thus, reliance on a single M. agassizii strain as an antigen in Western blot assays may provide false-negative results. This could have adverse consequences for the well-being of these environmentally sensitive hosts if false-negative animals were relocated to sites consisting of true-negative populations.

Identification of major immunogenic proteins of Mycoplasma synoviae isolates

Mycoplasma synoviae isolates differ in patterns of immunogenic proteins, but most of them have not been identified yet. The main aim of this study was their identification in two closely related M. synoviae isolates, ULB 02/P4 and ULB 02/OV6, recovered recently from chickens in Slovenia. N-terminal sequencing identified 17 M. synoviae proteins. Amongst them were 14 major, highly expressed but previously unidentified proteins, including enzymes, chaperones and putative lipoproteins. ULB 02/P4 proteins with increasing molecular weight (M(w)) in the region above the lipoprotein MSPB (approximately 40 kDa) were elongation factor EF-Tu, enolase, NADH oxidase, haemagglutinin MSPA, ATP synthase beta chain, trigger factor, pyruvate kinase and chaperone DnaK. Enolase (approximately 47 kDa) seemed to be immunogenic for chickens infected with M. synoviae, whereas EF-Tu, which might cross-react with antibodies to the P1 adhesin of Mycoplasma pneumoniae, was not. ULB 02/OV6 synthesized several immunogenic proteins and those with M(w) of approximately 70, 78, 82, 90, 110 and 160 kDa, cross-reacted with antibodies to Mycoplasma gallisepticum. They remain to be identified, because besides putative lipoproteins, protein bands of 78, 82, 85 and 110 kDa contained also dehydrogenase PdhD, elongation factor EF-G, enzyme PtsG and putative neuraminidase, respectively.

Haemagglutinins of pathogenic avian mycoplasmas

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.

Molecular basis of the length variation in the N-terminal part of Mycoplasma synoviae hemagglutinin

Mycoplasma synoviae is a major avian pathogen that synthesizes hemagglutinin VlhA, an abundant immunodominant surface lipoprotein. In most M. synoviae strains, the VlhA protein cleaves into the N-terminal part, a lipoprotein MSPB, and a C-terminal part MSPA, which mediates binding to erythrocytes. VlhA is encoded by the vlhA gene of which the 5'-end is present in the genome as a single copy, which does not change its sequence during recombination of the vlhA gene with pseudogenes. In this study, sequence analyses of the 5'-end vlhA sequences of 30 M. synoviae isolates revealed a highly polymorphic region encoding the proline-rich repeats (PRR) in the N-terminal part of MSPB. Pathogenic strain K1968 had an insertion encoding sequence DNPQNPN in PRR, whereas strains F10-2AS, K2581, K3344 and five strains belonging to two related clusters of strains isolated recently from chickens in Slovenia lacked one PRR repeat of 19 amino acids. The predicted length variations correlated well with the lengths of the corresponding MSPB proteins detected in immunoblots with specific antibodies. Comparison of the 5'-end vlhA sequences of 30 M. synoviae strains showed 11 different types of vlhA sequences indicating that the analysis of this vlhA part is useful for strain differentiation. Distinct sequence motifs seem to be characteristic for vlhA genes of individual M. synoviae strains or clusters of strains and can be used as markers for tracing their spreading between poultry farms.

The characterization of Mycoplasma synoviae EF-Tu protein and proteins involved in hemadherence and their N-terminal amino acid sequences

An abundant cytoplasmic 43-kDa protein from Mycoplasma synoviae, a major pathogen from poultry, was identified as elongation factor Tu. The N-terminal amino acid sequence (AKLDFDRSKEHVNVGTIGHV) has 90% identity with the sequence of the Mycoplasma hominis elongation factor Tu protein. Monoclonal antibodies reacting with the M. synoviae elongation factor Tu protein also reacted with 43-kDa proteins from the avian Mycoplasma species Mycoplasma gallinarum, Mycoplasma gallinaceum, Mycoplasma pullorum, Mycoplasma cloacale, Mycoplasma iners and Mycoplasma meleagridis, but not with the proteins from Mycoplasma gallisepticum, Mycoplasma imitans or Mycoplasma iowae. In addition, two groups of phase variable integral membrane proteins, pMSA and pMSB, associated with hemadherence and pathogenicity of M. synoviae strains AAY-4 and ULB925 were identified. The cleavage of a larger hemagglutinating protein encoded by a gene homologous to the vlhA gene of M. synoviae generates pMSB1 and pMSA1 proteins defined by mAb 125 and by hemagglutination inhibiting mAb 3E10, respectively. The N-terminal amino acid sequences of pMSA proteins (SENKLI ... and SENETQ ...) probably indicate the cleavage site of the M. synoviae strain ULB 925 hemagglutinin.

The hemagglutination-positive phenotype of Mycoplasma synoviae induces experimental infectious synovitis in chickens more frequently than does the hemagglutination-negative phenotype

Inoculation with hemagglutination-positive (HA+) cultures of Mycoplasma synoviae AAY-4 induced acute synovitis significantly more frequently (P = 0.001) in chicken tibiotarsal-tarsometatarsal joints than did inoculation with HA-negative (HA-) cultures derived from the same clone of AAY-4. Immunoblotting analyses showed that HA+ cultures abundantly expressed two phase-variable hemadherence-associated surface membrane proteins of 53 kDa and 48 to 50 kDa defined by monoclonal antibodies. HA- cultures lacked the 53-kDa proteins and synthesized truncated 27- to 30-kDa forms of the 48- to 50-kDa proteins. Inoculation of cyclosporin A (CsA) into infected joints significantly decreased the frequency of acute synovitis (P = 0.001). Moreover, repeated intra-articular inoculation of CsA (three doses of 1 mg at 2-day intervals) significantly reduced the local antibody response to M. synoviae in the joints treated with CsA.

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

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.

Genomic, protein homogeneity and antigenic variability of Mycoplasma agalactiae

Eleven strains of Mycoplasma agalactiae differing in pathogenicity, animal species origin and geographic localisation, showed similar chromosome restriction profiles with four endonucleases. However the international reference strain PG2 showed a unique profile. The protein and antigenic variabilities of 31 strains of M. agalactiae were investigated using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting performed with naturally infected animal sera and purified antibodies against the 29 kDa protein. Protein profiles were similar but antigenic profiles could be separated into two main groups according to geographic origin: (i) strains isolated in south-west France and (ii) strains from north-east France. Some differences also occurred from strain to strain within each group. The antigenic profile variability found in immunoblotting, originated in two different phenomena: (i) some epitopes were expressed only in strains of one profile type and (ii) some other epitopes were common to all strains but located on several proteins which differed in number and molecular mass from one strain to another. The presence of epitopes which undergo phase variation in the same lineage of clones from a single cell is discussed.

Molecular epidemiology of Mycoplasma mycoides subsp. mycoides biotype Small Colony, the agent of contagious bovine pleuropneumonia

Restriction endonuclease analysis (REA) and immunoblotting were used to compare field strains of Mycoplasma mycoides subsp. mycoides biotype Small Colony from different parts of Europe and Africa. Of the 27 strains tested by REA, the European ones (n = 15), except 3 from the Iberian peninsula, differed strikingly from the African ones (n = 10). Vaccinal strains T1-SR and KH3J had a unique REA pattern. Polyclonal immunoblot profiles of 46 strains appeared fairly similar. However most of the Italian strains (22 out of 24) shared a characteristic, in the 100 kDa area, unlike that of the other European strains. Immunoprofiles of the reference strain PG1 and vaccinal strain T1-SR were different from the others. These results allowed the determination of possible links between different geographic region of enzootic contagious bovine pleuropneumonia.