Mechanisms of attachment of Mycoplasma arthritidis to host cells in vitro

Surface lipoproteome of Mycoplasma hominis PG21 and differential expression after contact with human dendritic cells

Aim: To assess the lipoproteins that are involved in the interaction between Mycoplasma hominis and human dendritic cells. Materials & methods: The surface lipoproteome of M. hominis PG21 was characterized by using Triton X-114 extraction and LC–MS/MS identification. The transcriptional changes in lipoprotein genes upon contact with human dendritic cells were determined by using reverse transcription quantitative PCR after identification of reference genes suitable for normalization. Results: A large-scale overexpression of lipoprotein genes was observed with 21 upregulated transcripts. Seven genes of unknown function were M. hominis species specific and six genes were putatively associated with increased nutrient capture from the host cell and adhesion. Conclusion: M. hominis regulates lipoprotein gene expression and may use species-specific mechanisms during the host colonization process.

Comparative genomic analysis of seven Mycoplasma hyosynoviae strains

Infection with Mycoplasma hyosynoviae can result in debilitating arthritis in pigs, particularly those aged 10 weeks or older. Strategies for controlling this pathogen are becoming increasingly important due to the rise in the number of cases of arthritis that have been attributed to infection in recent years. In order to begin to develop interventions to prevent arthritis caused by M. hyosynoviae, more information regarding the specific proteins and potential virulence factors that its genome encodes was needed. However, the genome of this emerging swine pathogen had not been sequenced previously. In this report, we present a comparative analysis of the genomes of seven strains of M. hyosynoviae isolated from different locations in North America during the years 2010 to 2013. We identified several putative virulence factors that may contribute to the ability of this pathogen to adhere to host cells. Additionally, we discovered several prophage genes present within the genomes of three strains that show significant similarity to MAV1, a phage isolated from the related species, M. arthritidis. We also identified CRISPR-Cas and type III restriction and modification systems present in two strains that may contribute to their ability to defend against phage infection.

RGD motif of lipoprotein T, involved in adhesion of Mycoplasma conjunctivae to lamb synovial tissue cells

Lipoprotein T (LppT), a membrane-located 105-kDa lipoprotein of Mycoplasma conjunctivae, the etiological agent of infectious keratoconjunctivitis (IKC) of domestic sheep and wild Caprinae, was characterized. LppT was shown to promote cell attachment to LSM 192 primary lamb joint synovial cells. Adhesion of M. conjunctivae to LSM 192 cells is inhibited by antibodies directed against LppT. The RGD (Arg-Gly-Asp) motif of LppT was found to be a specific site for binding of M. conjunctivae to these eukaryotic host cells. Recombinant LppT fixed to polymethylmethacrylate slides binds LSM 192 cells, whereas LppT lacking the RGD site is deprived of binding capacity to LSM 192, and LppT containing RGE rather than RGD shows reduced binding. Synthetic nonapeptides derived from LppT containing RGD competitively inhibit binding of LSM 192 cells to LppT-coated slides, whereas nonapeptides containing RAD rather than RGD do not inhibit. RGD-containing, LppT-derived nonapeptides are able to directly inhibit binding of M. conjunctivae to LSM 192 cells by competitive inhibition, whereas the analogous nonapeptide containing RAD rather than RGD or the fibronectin-derived RGD hexapeptide has no inhibitory effect. These results reveal LppT as the first candidate of a RGD lectin in Mycoplasma species that is assumed to bind to beta integrins.

Proteomics inference of genes involved in host adaptation of Mycoplasma gallinarum

Different from most other host-specific mycoplasmas, Mycoplasma gallinarum has been isolated from various hosts, such as poultry, pig, cattle, and sheep. The wide distribution among different hosts, the low pathogenesis, and the weak host immunological responses suggest this mycoplasma has a unique host adaptation mechanism. In this study, we applied two-dimensional liquid chromatography electrospray ionization tandem mass spectrometry (2D LC-MS/MS) to characterize the protein profiling of M. gallinarum. Our results suggest that M. gallinarum possesses homologs of cytadhesin proteins found in other mycoplasmas lacking an organized tip organelle. Our results showed that there are possibly multiple aminopeptidase gene homologs present in M. gallinarum, which might be involved in nutrient acquisition of M. gallinarum. The information present here would be useful for future studies to identify genes responsible for the colonization and host adaptation properties of M. gallinarum.

Mutation of two Mycoplasma arthritidis surface lipoproteins with divergent functions in cytadherence

Mycoplasma arthritidis is a natural pathogen of rats, causing an acute polyarthritis. Previous studies identified two membrane-bound lipoproteins, Maa1 and Maa2, thought to be associated with cytadherence of M. arthritidis strain 158p10p9. We have since confirmed that Maa1 is a major adhesin, although the role of Maa2 has proven more elusive. Both proteins were capable of eliciting protective immunity in rats against challenge with the virulent strain 158p10p9, suggesting that they may be important in pathogenesis. The purpose of this study was to better understand the roles of Maa1 and Maa2 in cytadherence in vitro. Insertion mutants were created for both genes by transposon mutagenesis. In vitro adherence of the Maa1 mutant KOMaa1 to rat L2 lung cells was reduced to the level previously reported for a spontaneous low-adherence mutant of 158p10p9 in which Maa1 is truncated and nonfunctional. Surprisingly, adherence of the Maa2 mutant KOMaa2 was approximately fivefold greater than that of the wild type. Complementation of KOMaa1 and KOMaa2 with wild-type alleles of maa1 and maa2, respectively, returned adherence to wild-type levels. This work confirms our earlier observation that Maa1 is a major adhesin for M. arthritidis strain 158p10p9. Maa2, on the other hand, may play a suppressive or modulatory role, possibly serving to release organisms from microcolonies at certain stages of infection.

Association of Mycoplasma arthritidis mitogen with lethal toxicity but not with arthritis in mice

Mycoplasma arthritidis induces an acute to chronic arthritis in rodents. Arthritis induced in mice histologically resembles human rheumatoid arthritis and can be associated with lethal toxicity following systemic injection. The M. arthritidis mitogen (MAM) superantigen has long been implicated as having a role in pathogenesis, but its significance with respect to toxicity and arthritogenicity in mycoplasma-induced disease is unclear. To study the pathogenic significance of MAM, M. arthritidis mutants that overproduced or failed to produce MAM were developed. MAM overproduction and knockout mutants were more and less mitogenic, respectively, than the wild-type strain. The degree of mitogenic activity correlated with lethal toxicity in DBA/2J mice. In contrast, histopathological studies detected no correlation between MAM production and the severity of arthritis induced in DBA/2J and CBA/J mice.

Expression and immunogenicity of six putative variable surface proteins in Mycoplasma mycoides subsp. mycoides SC

Variable surface protein Vmm and five Vmm-type proteins from Mycoplasma mycoides subsp. mycoides SC were analysed to determine whether these proteins are expressed in vivo in animals affected by contagious bovine pleuropneumonia (CBPP) and in vitro. Recombinant versions of these proteins were constructed and expressed in Escherichia coli after mutation of the TGA Trp codons to TGG. These proteins were then analysed by dot and Western blotting with sera from CBPP-affected cattle. Furthermore, affinity-purified polyclonal antibodies to the recombinant proteins were used in Western and colony blotting to look for expression of the putative Vmm-type proteins in cultured M. mycoides SC. This study demonstrates that immunoglobulins in CBPP sera recognize all putative Vmm-type proteins tested, indicating that these proteins or their homologues are expressed by mycoplasmas during natural infections. Vmm and one of the putative Vmm-type proteins showed variable expression in vitro.

Inflammatory lipoproteins purified from a toxigenic and arthritogenic strain of Mycoplasma arthritidis are dependent on Toll-like receptor 2 and CD14

Mycoplasma arthritidis is a naturally occurring murine pathogen, and the disease model has been used extensively to understand inflammatory mechanisms. Recently, Triton X-114 extracts of a virulent strain of M. arthritidis were found to be more potent in activating macrophages than were those from an avirulent strain, suggesting a role in disease. Here, octyl glucoside extraction of cells was used to identify four distinct bioactive moieties, with molecular masses of approximately 41, 37, 34, and 17 kDa. Their bioactivities were resistant to proteinase K but were destroyed by alkaline hydrolysis and oxidation. As for MALP-2, all were dependent upon Toll-like receptor 2, but unlike MALP-2, they were also dependent upon CD14. The M. arthritidis lipoproteins exhibited infrared absorbances at 2,900 cm(-1) and 1,662 cm(-1), similar to those seen in Pam(3)-Cys-Ser-(Lys)(4). Edman degradation failed to reveal N-terminal sequences, suggesting that they were blocked and therefore might be triacylated. However, mass spectrometry of fragments revealed that the 41-kDa moiety, which binds to serum apolipoprotein A-1, had similarity with the recently described MlpD lipoprotein of M. arthritidis.

Bone and joint disease associated with primary immune deficiencies

Primary immune deficiencies (PIDs) are characterized by functional and/or quantitative abnormalities of one or more immune system components. Several bone and joint abnormalities can occur in patients with PID, with arthritis being the most common. Joint manifestations, of which arthritis is the most common, occur chiefly in humoral PIDs (agammaglobulinemia, common variable immunodeficiency, hyper-IgM syndromes, and IgA deficiency) and occasionally in other PIDs (chronic granulomatous disease and Wiskott-Aldrich syndrome). Monoarthritis or oligoarthritis is the usual pattern, although polyarthritis may occur, occasionally with nodules suggesting rheumatoid arthritis. Arthritis in patients with PID is usually infectious in nature, the most common causative organism being Mycoplasma, followed by Staphylococcus, Streptococcus, and Haemophilus. These bacteria can induce not only synovial infections, but also aseptic arthritogenic inflammatory responses. Arthritis having no demonstrable relation to chronic infection has been reported also and ascribed to dysimmunity-driven mechanisms that exhibit a number of specific features. Bone lesions are far less common and usually due to infections complicating humoral PID. Distinctive bone manifestations occur in a number of rare PIDs (e.g., hyper-IgE syndrome and Di George syndrome) and in syndromes characterized by spondyloepiphyseal dysplasia. Familiarity with PID syndromes both enhances the diagnostic capabilities of physicians and provides insight into the pathophysiology of bone and joint abnormalities associated with immune dysfunction. In children and occasionally in adults, a combination of bone and/or joint manifestations and hypogammaglobulinemia may indicate PID. When there is no evidence of lymphoproliferative disease, infection, or iatrogenic complications, investigations for PID should be obtained. PID-related arthritis is a unique model for studying the pathogenesis of presumably postinfectious arthritis and of inflammatory joint diseases including rheumatoid arthritis.

Mycoplasma arthritidis bacteriophage MAV1 prophage integration, deletions, and strain-related polymorphisms

Temperate bacteriophage MAV1 is found in certain highly virulent strains of Mycoplasma arthritidis. Integration sites, portions of the right and left prophage ends, and flanking DNA from eight prophages in seven M. arthritidis strains were characterized in this study. attb and attp sites conformed for the most part to the consensus sequence TATTTTT, although minor polymorphisms were noted. Prophages were integrated into similar sites in four strains, suggesting that these strains may have had a common ancestor. Two strains had three prophage copies each, and integration sites were identical. Two strains had two copies each. One of these shared two of the integration sites occupied in the three-copy strains, while the other shared one of these sites and harbored a second prophage in a unique site. Integration sites in the two strains with one prophage each were unique. Four MAV1 copies contained extensive substitutions within a region encoding a putative structural protein and the putative repressor protein. A 3-kb fragment was deleted from the right side of two of these copies. It is proposed that polymorphisms within MAV1 prophage integration sites and within the prophages themselves may help to identify phylogenetic relationships among virulent M. arthritidis strains.

Adherence to various host cell lines of Mycoplasma bovis strains differing in pathogenic and cultural features

Mycoplasma bovis is known to be responsible for pneumonia and arthritis in calves, as well as mastitis in dairy cows. Despite clear evidence of its pathogenic potential, little is known about mechanisms of cytadherence and the molecular factors involved. The purpose of this work was to compare adherence rates of M. bovis field strains to different host cell lines and study the effects of cloning and sub-culturing M. bovis strains on their adherence properties. Eighteen metabolically labeled M. bovis strains isolated from different pathological backgrounds were examined in adherence trials using four different host cell lines, i.e. embryonic bovine lung (EBL), embryonic bovine trachea (EBTr), Madin Darby bovine kidney (MDBK) and rabbit kidney (RK) cells. Although large interstrain variations in adherence rates (3.4-19.1%) were measured they could not be correlated to the pathological background (pneumonia, arthritis or mastitis). Adherence rates to the fibroblast cell line (EBTr) were significantly lower than those to the three epithelial cell lines (EBL, MDBK and RK). The only non-pathogenic strain (221/89) exhibited lower adherence rates than three isolates from clinical mastitis. Interestingly, adherence rates were significantly reduced after in vitro passaging. In contrast, no effect of single cloning of strains on adherence was observed. There was no general correlation between expression of variable surface proteins (Vsps) as monitored by immunoblotting and adherence rates, although alterations in Vsp expression profiles were seen as a consequence of passaging. As there is probably a large number of adhesins, variable and non-variable, on the surface of M. bovis cells the issue is very complex, and the most active components have yet to be identified.

Restoration of cytoadherence to an adherence-deficient mutant of Mycoplasma arthritidis by genetic complementation

Mycoplasma arthritidis causes a severe septic arthritis in rats under natural and experimental conditions. An earlier study implicated a membrane lipoprotein designated MAA1 in cytadherence of M. arthritidis. In addition, a spontaneous adherence-deficient mutant was shown to contain a nonsense mutation in the gene encoding MAA1, resulting in production of a truncated product, MAA1Delta. In the present study, a wild-type maa1 gene carried on transposon Tn4001T was introduced into the low-adherence mutant by polyethylene glycol-mediated transformation. The presence of the tranposon and the wild-type maa1 gene in the chromosome of transformants was confirmed by PCR and Southern hybridization. The latter procedure also confirmed that each transformant contained a single copy of the transposon. Western immunoblotting showed that transformants produced both wild-type MAA1 and MAA1Delta, indicating that the introduced wild-type maa1 gene was functional. This phenotype was stably maintained after multiple subcultures even in the absence of antibiotic selection. Finally, transformants were shown to adhere to rat L-2 lung cells in culture at wild-type levels, providing confirmation for an important role for MAA1 in adherence.

Characterization of P40, a cytadhesin of Mycoplasma agalactiae

An immunodominant protein, P40, of Mycoplasma agalactiae was analyzed genetically and functionally. The gene encoding P40 was cloned from type strain PG2, sequenced, submitted to point mutagenesis in order to convert mycoplasma-specific TGA(Trp) codon to the universal TGG(Trp) codon, and subsequently expressed in Escherichia coli. Nucleotide sequence-derived amino acid sequence comparisons revealed a similarity of P40 to the adhesin P50 of Mycoplasma hominis and to protein P89 of Spiroplasma citri, which is expected to be involved in adhesion. The amino acid sequence of P40 revealed a recognition site for a signal peptidase and strong antigenic and hydrophilic motifs in the C-terminal domain. Triton X-114 phase partitioning confirmed that P40 is a membrane protein. Fab fragments of antibodies directed against recombinant purified P40 significantly inhibited adherence of M. agalactiae strains PG2 to lamb joint synovial cells LSM 192. Sera taken sequentially from sheep infected with PG2 revealed that P40 induced a strong and persistent immune response that gave strong signals on immunoblots containing recombinant P40 even 3 months after infection. The gene encoding P40 was present in a single copy in all of the 26 field strains of M. agalactiae analyzed and was not detected in closely related mycoplasma species. P40 was expressed as a protein with an apparent molecular mass of 37 kDa on sodium dodecyl sulfate-acrylamide gels by all M. agalactiae strains except for serotype C strains, which showed nonsense mutations in their p40 genes.

Identification and functional mapping of the Mycoplasma fermentans P29 adhesin

Initial adherence interactions between mycoplasmas and mammalian cells are important for host colonization and may contribute to subsequent pathogenic processes. Despite significant progress toward understanding the role of specialized, complex tip structures in the adherence of some mycoplasmas, particularly those that infect humans, less is known about adhesins through which other mycoplasmas of this host bind to diverse cell types, even though simpler surface components are likely to be involved. We show by flow cytometric analysis that a soluble recombinant fusion protein (FP29), representing the abundant P29 surface lipoprotein of Mycoplasma fermentans, binds human HeLa cells and inhibits M. fermentans binding to these cells, in both a quantitative and a saturable manner, whereas analogous fusion proteins representing other mycoplasma surface proteins did not. Constructs representing nested N- or C-terminal truncations of FP29 allowed initial mapping of this specific adherence function to a central region of the P29 sequence containing a 36-amino-acid disulfide loop. A derivative of FP29 containing a mutation converting one participating Cys to Ser, precluding intrachain disulfide bond formation, retained full activity. Together these results suggest that the direct interaction of M. fermentans with a ligand on the HeLa cell surface involves a limited segment of the P29 surface lipoprotein and requires neither the disulfide bond nor the contribution of adjacent portions of the protein. Earlier results indicating phase-variable display of monoclonal antibody surface epitopes on P29, now recognized to be outside this ligand binding region, raise the possibility that variation of mycoplasma surface architecture might alter the presentation of the binding region and the adherence phenotype. Preliminary results further indicated that FP29 could inhibit binding to HeLa cells by Mycoplasma hominis, a distinct human mycoplasma species displaying the phase-variable adhesin Vaa, but not that by Mycoplasma capricolum, an organism infecting caprine species. This result raises the additional, testable possibility that a common host cell ligand for two human mycoplasma species may be recognized through structurally dissimilar adhesins that undergo phase variation by two distinct mechanisms, governing protein expression (Vaa) or surface masking (P29).

Molecular characterization of Mycoplasma arthritidis membrane lipoprotein MAA1

Genes encoding the Mycoplasma arthritidis surface-exposed lipoprotein MAA1 were cloned and sequenced from MAA1-expressing strains 158p10p9 and PG6, from a low-adherence (LA) variant derived from 158p10p9 that expresses a truncated version of MAA1 (MAA1Delta) and from two MAA1-negative strains, 158 and H39. The deduced amino acid sequences of maa1 from 158p10p9 and PG6 predicted, respectively, 86.5- and 86.4-kDa basic, largely hydrophilic lipoproteins with 29-amino-acid signal peptides and predicted cleavage sites for signal peptidase II (Ala-Ala-Ala downward arrowCys). The truncation in the LA variant resulted from a G-->T substitution at nucleotide 695, which created a premature stop codon. This, in turn, generated a predicted 26.6-kDa prolipoprotein (23.6 kDa after processing), consistent with an M(r) of approximately 24,000 calculated for MAA1Delta. Similarly, absence of MAA1 expression in H39 and 158 resulted from C-->A substitutions at nucleotide 208, generating premature stop codons at that site in both strains.

Molecular characterization of Mycoplasma arthritidis variable surface protein MAA2

Earlier studies implied a role for Mycoplasma arthritidis surface protein MAA2 in cytadherence and virulence and showed that it exhibited both size and phase variability. Here we report the further analysis of MAA2 and the cloning and sequencing of the maa2 gene from two M. arthritidis strains, 158p10p9 and H606, expressing two size variants of MAA2. Triton X-114 partitioning and metabolic labeling with [3H]palmitic acid suggested lipid modification of MAA2. Surface exposure of the C terminus was indicated by cleavage of monoclonal antibody-specific epitopes from intact cells by carboxypeptidase Y. The maa2 genes from both strains were highly conserved, consisting largely of six (for 158p10p9) or five (for H606) nearly identical, 264-bp tandem direct repeats. The deduced amino acid sequence predicted a largely hydrophilic, highly basic protein with a 29-amino-acid lipoprotein signal peptide. The maa2 gene was expressed in Escherichia coli from the lacZ promoter of vector pGEM-T. The recombinant product was approximately 3 kDa larger than the native protein, suggesting that the signal peptide was not processed in E. coli. The maa2 gene and upstream DNA sequences were cloned from M. arthritidis clonal variants differing in MAA2 expression state. Expression state correlated with the length of a poly(T) tract just upstream of a putative -10 box. Full-sized recombinant MAA2 was expressed in E. coli from genes derived from both ON and OFF expression variants, indicating that control of expression did not include alterations within the coding region.

Identification of a novel adhesin-like glycoprotein from Mycoplasma hyopneumoniae

This study identifies an adhesin-like glycoprotein, which was a 110 kDa protein (P110) under HPLC-GPC assay. This adhesin consisted of one P54 and two P28 subunits. In addition, N-glycosidase F could cleave all N-linked oligosaccharides on the P54 subunit. Experimental results indicated that P110 with native conformations significantly inhibited the adherence of biotin-labeled porcine tracheal epithelial cell extracts to the intact M. hyopneumoniae cells (p < 0.01). Furthermore, the biotin-labeled porcine tracheal epithelial cell extracts specifically bound to P54 and P28 subunits. This binding could be competitively inhibited by unlabeled porcine tracheal epithelial extracts and SPF porcine antisera against Mycoplasma hyopneumoniae. Both P54 and P28 subunits were constitutively expressed in different strains of M. hyopneumoniae. Their production was negligibly changed at various passages during in vitro cultivation. The significant role of this adhesin-like glycoprotein in the pathogenesis of swine pneumonia is under study.

Protection of rats against Mycoplasma arthritidis-induced arthritis by active and passive immunizations with two surface antigens

We previously identified two surface-exposed Mycoplasma arthritidis protein antigens, designated MAA1 and MAA2, that may be involved in cytadherence. Since adherence to host tissues is an important first step in most bacterial infections, we suggest that MAA1 and MAA2 may be virulence factors for M. arthritidis. In order to provide evidence for such a role, we conducted a series of experiments in which rats were actively immunized with each of these proteins purified from sodium dodecyl sulfate-polyacrylamide gels or passively immunized with poly- or monoclonal antibodies against MAA1 and MAA2. In each case, immunity against MAA1 and MAA2 conferred at least partial protection against M. arthritidis-induced disease. The greatest protection was achieved by passive immunization with monoclonal antibody A9a, directed against a surface-exposed epitope of putative adhesin MAA1. Because protective immunity in most bacterial infections is directed against major virulence factors, these results suggest that MAA1 and MAA2 may play a role in the pathogenesis of M. arthritidis-induced arthritis of rats, possibly by mediating initial colonization of joint tissues.

Molecular biology of mycoplasmas

Although mycoplasmas lack cell walls, they are in many respects similar to the gram-positive bacteria with which they share a common ancestor. The molecular biology of mycoplasmas is intriguing because the chromosome is uniquely small (< 600 kb in some species) and extremely A-T rich (as high as 75 mol% in some species). Perhaps to accommodate DNA with a lower G + C content, most mycoplasmas do not have the "universal" genetic code. In these species, TGA is not a stop codon; instead it encodes tryptophan at a frequency 10 times greater than TGG, the usual codon for this amino acid. Because of the presence of TGA codons, the translation of mycoplasmal proteins terminates prematurely when cloned genes are expressed in other eubacteria, such as Escherichia coli. Many mycoplasmas possess strikingly dynamic chromosomes in which high-frequency changes result from errors in DNA repair or replication and from highly active recombination systems. Often, high-frequency changes in the mycoplasmal chromosome are associated with antigenic and phase variation, which regulate the production of factors critical to disease pathogenesis.

Gene transfer in Mycoplasma arthritidis: transformation, conjugal transfer of Tn916, and evidence for a restriction system recognizing AGCT

Mycoplasma arthritidis is a rat pathogen causing a severe polyarthritis. The study of its pathogenic mechanisms has been hampered by the lack of genetic systems for use with M. arthritidis. Described here are procedures for genetic transformation of M. arthritidis and conjugal transfer of Tn916 from an enterococcal donor to M. arthritidis. The location of Tn916 insertion sites in the mycoplasmal chromosome was random, suggesting that Tn916 may be useful as an insertional mutagen in this organism. Additionally, a restriction and modification system was identified which presented a strong barrier to gene transfer. For transformation, the restriction system was circumvented by using DNA that was modified in vitro with the appropriate site-specific methylase (AluI).

Mechanisms and factors involved in Mycoplasma bovis adhesion to host cells

Mycoplasma (M.) bovis cytadhesion was studied using permanent embryonic bovine lung (EBL) cells as host system. Adherence rates were found to be strongly dependent on temperature and the mycoplasma-to-EBL ratio near the point of saturation of the attachment isotherm was determined to be 225 : 1. Mild trypsinization of viable M. bovis cells caused a measurable decrease of adherence indicating that surface proteins, among them the P26 antigen, played a major part as adhesion factors. Neuraminidase treatment of mycoplasmas led to a drastic reduction of adherence rates, which emphasizes the importance of sialyl moieties in adhesive interactions. The ability of the P26 antigen, a hydrophilic 32-kDa protein, to function as an adhesin was confirmed using a competitive adherence assay, in which the HPLC-purified protein was shown to reduce mycoplasma adhesion. These data complement previous findings obtained with the corresponding monoclonal antibody (MAb) 4F6. In further inhibition experiments, it could be demonstrated that MAb 1E5, which is directed against a common epitope of at least three members of the Vsp (variable surface protein) family of M. bovis, was also capable of decreasing mycoplasma attachment to EBL cells. This is the first evidence of possible involvement of Vsps in cytadhesion. In an effort to identify more putative adhesion proteins of this organism, the reverse adherence screening assay was used, a procedure based on the specific binding of labelled mammalian tissue culture cells to Western-blotted mycoplasmal proteins.

Association of lysogenic bacteriophage MAV1 with virulence of Mycoplasma arthritidis

Mycoplasma arthritidis causes a severe polyarthritis under natural conditions in rats and under experimental conditions in both rats and mice. Although the disease itself has been extensively studied, M. arthritidis virulence factors remain uncharacterized. Comparison of relative arthritogenicity of 20 strains of M. arthritidis revealed that the strains tended to fall into two groups, a highly arthritogenic group, inducing maximum arthritis scores of > or = 11 in rats, and a low-virulence group, inducing maximum scores of < 6. Chromosomal DNA from the more highly arthritogenic strains possessed sequences that hybridized by Southern analysis with a probe prepared from lysogenic M. arthritidis bacteriophage MAV1, while DNA from low-virulence strains did not. One of the low-virulence strains, 158, was experimentally lysogenized with MAV1. Lysogenized 158 showed a significant increase in arthritogenicity over nonlysogenized 158. These data suggest that MAV1 carries a factor that is important in pathogenesis of M. arthritidis-induced arthritis of rats.

Comparison of Mycoplasma arthritidis strains by enzyme-linked immunosorbent assay, immunoblotting, and DNA restriction analysis

Twenty Mycoplasma arthritidis strains or isolates were compared by a combination of enzyme-linked immunosorbent assay by an antiserum adsorption technique, Western immunoblotting, and restriction analysis of chromosomal DNA. Antigenic markers that defined strains related to strains 158p10p9, PG6, and H606 were identified. In addition, restriction analysis allowed all 20 strains to be divided into six groups. Results of restriction analysis corresponded generally with antigenic similarities, although the former did not allow grouping with as fine a precision as the latter. However, intrastrain antigenic variability, which is common among many Mycoplasma species, including M. arthritidis, introduced a complicating factor into our attempts at antigenic analysis. While serologic and antigenic analyses remain useful, we recommend that they be used with caution and in combination with other techniques for identifying and characterizing new isolates and newly acquired strains. Combinations of these techniques have proven to be useful in our laboratory for quality control and for uncovering interesting relationships among strains subjected to animal passage and their less virulent antecedents and among strains originally classified as the same but obtained from different sources and maintained, sometimes for decades, in different laboratories.

Antigen heterogeneity among isolates of Mycoplasma bovis is generated by high-frequency variation of diverse membrane surface proteins

The protein and antigen profiles of 11 isolates of Mycoplasma bovis were compared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot analysis of whole organisms. The isolates examined included the type strain PG45 and 10 other filter-cloned strains or purified isolates both from animals without clinical signs and from clinical cases of bovine mastitis, arthritis, or pneumonia. While the overall protein patterns visualized by silver staining were very similar, marked differences in the antigen banding profiles were detected by rabbit antiserum prepared against whole organisms from one of the strains analyzed. This antigenic heterogeneity was shown to be independent of the geographical origin, the type of clinical disease, and the site of isolation and was also observed among serial isolates from a single animal. Antigen profiles were further monitored throughout sequentially subcloned populations of the PG45 strain. This clonal analysis revealed a high-frequency variation in the expression levels of several prominent antigens. All of these variable antigens were defined by detergent-phase fractionation with Triton X-114 as amphiphilic integral membrane proteins. A subset of different-sized membrane proteins was identified by a monoclonal antibody raised against a PG45 subclone expressing a 63- and a 46-kDa variant antigen within that set. The selective susceptibility of these proteins to trypsin treatment of intact organisms and their ability to bind the monoclonal antibody in colony immunoblots demonstrated that they were exposed on the cell surface. In addition, their preferential recognition by serum antibodies from individual cattle with naturally induced M. bovis mastitis or arthritis confirmed that they were major immunogens of this organism. These studies establish that the apparent antigenic heterogeneity among M. bovis isolates reported here does not represent stable phenotypic strain differences generated from accumulated mutational events but reflects distinct expression patterns of diverse, highly variable membrane surface proteins.

A family of phase- and size-variant membrane surface lipoprotein antigens (Vsps) of Mycoplasma bovis

A set of strain- and size-variant highly immunogenic membrane surface protein antigens of Mycoplasma bovis, which has been identified by a monoclonal antibody, is shown in this report to make up a family of antigenically and structurally related lipid-modified proteins, designated Vsps (variable surface proteins). By systematic analysis of several isogenic clonal lineages of the type strain PG45, three members of this family have been identified, VspA, VspB, and VspC, each of which was shown to undergo independent high-frequency changes in size as well as noncoordinate phase variation between ON and OFF expression states. The monoclonal antibody-defined epitope common to VspA, VspB, and VspC was accessible on the cell surface in most, but not all, of the clonal populations analyzed and was present on a C-terminal limit tryptic fragment of each Vsp variant that was released from the membrane surface. VspA and VspC were distinguished from VspB by their selective detection with colloidal gold and by their distinctive reaction with a polyclonal antibody against M. bovis D490. VspA, VspB, and VspC were further distinguishable from one another by their characteristic patterns of degradation at carboxypeptidase Y pause sites. While these Vsp-specific structural fingerprints with an irregular periodic spacing were constant for similarly sized variants of a defined Vsp product, they showed distinct differences among variants differing in size. This variability included gain or loss of individual bands within distinct subsets of bands, as well as shifts of the entire banding patterns up- or downwards, indicating that insertions or deletions underlying Vsp size variation can occur at various locations either within the C-terminal domain or within other regions of these proteins. This was similarly confirmed by comparative epitope mapping analysis of tryptic cleavage products generated from different Vsp size variants. The Vsp family of M. bovis described in this study represents a newly discovered system of surface antigenic variation in mycoplasmas displaying features which closely resemble but are also different from the characteristics reported for the Vlp (variable lipoprotein) system of M. hyorhinis. The isogenic lineages established here provide key populations for subsequent analysis of corresponding genes to further elucidate Vsp structure and variation, which may have important relevance for a better understanding of the pathogenicity of this agent.