Expression of the Major Outer Membrane Protein (MOMP) of Chlamydophila abortus, Chlamydophila pecorum, and Chlamydia suis in Escherichia coli using an Arabinose-inducible Plasmid Vector

A modular vaccine platform enabled by decoration of bacterial outer membrane vesicles with biotinylated antigens

Engineered outer membrane vesicles (OMVs) derived from Gram-negative bacteria are a promising technology for the creation of non-infectious, nanoparticle vaccines against diverse pathogens. However, antigen display on OMVs can be difficult to control and highly variable due to bottlenecks in protein expression and localization to the outer membrane of the host cell, especially for bulky and/or complex antigens. Here, we describe a universal approach for avidin-based vaccine antigen crosslinking (AvidVax) whereby biotinylated antigens are linked to the exterior of OMVs whose surfaces are remodeled with multiple copies of a synthetic antigen-binding protein (SNAP) comprised of an outer membrane scaffold protein fused to a biotin-binding protein. We show that SNAP-OMVs can be readily decorated with a molecularly diverse array of biotinylated subunit antigens, including globular and membrane proteins, glycans and glycoconjugates, haptens, lipids, and short peptides. When the resulting OMV formulations are injected in mice, strong antigen-specific antibody responses are observed that depend on the physical coupling between the antigen and SNAP-OMV delivery vehicle. Overall, these results demonstrate AvidVax as a modular platform that enables rapid and simplified assembly of antigen-studded OMVs for application as vaccines against pathogenic threats.

Polymorphic membrane protein 20G: A promising diagnostic biomarker for specific detection of Chlamydia psittaci infection

Psittacosis is a zoonotic disease caused by Chlamydia psittaci (C. psittaci), leading to high risk for animal industry and human health. Lack of reliable commercial kits and effective vaccines is hampering control of C. psittaci infection. Polymorphic outer membrane protein Gs (PmpGs) are enriched in diverse C. psittaci, and its role are unclear during C. psittaci infection. In the present study, pmp20G gene was cloned into pET-28a vector and then the constructed plasmid was transferred into Escherichia coli Rossetta (DE3). After denaturation and renaturation, the recombinant Pmp20G-N was identified by SDS-PAGE and Western blot. Afterwards Pmp20G-N was used as the coating antigen to develop an indirect ELISA (I-ELISA) assay. Both the specificity and sensitivity of Pmp20G-N ELISA were 100%, while the MOMP-ELISA had 93.65% sensitivity and 98.94% specificity, respectively. The concordance between MOMP-ELISA and Pmp20G-N ELISA assay was 98.1%. Hence, Pmp20G-N ELISA has the potential to be a diagnostic antigen for detection C. psittaci antibody. However, further studies are needed to be done for differentiating C. psittaci from Chlamydia spp. and other C.psittaci-specific serovars using Pmp20G-N ELISA.

Recombinant expression of Chlamydia trachomatis major outer membrane protein in E. Coli outer membrane as a substrate for vaccine research

Background

Chlamydia trachomatis is a human pathogen which causes a number of pathologies, including genital tract infections in women that can result in tubal infertility. Prevention of infection and disease control might be achieved through vaccination; however, a safe, efficacious and cost-effective vaccine against C. trachomatis infection remains an unmet medical need. C. trachomatis major outer membrane protein (MOMP), a β-barrel integral outer membrane protein, is the most abundant antigen in the outer membrane of the bacterium and has been evaluated as a subunit vaccine candidate. Recombinant MOMP (rMOMP) expressed in E. coli cytoplasm forms inclusion bodies and rMOMP extracted from inclusion bodies results in a reduced level of protection compared to the native MOMP in a mouse challenge model.

Results

We sought to target the recombinant expression of MOMP to the E. coli outer membrane (OM). Successful surface expression was achieved with codon harmonization, utilization of low copy number vectors and promoters with moderate strength, suitable leader sequences and optimization of cell culture conditions. rMOMP was extracted from E. coli outer membrane, purified, and characterized biophysically. The OM expressed and purified rMOMP is immunogenic in mice and elicits antibodies that react to the native antigen, Chlamydia elementary body (EB).

Conclusions

C. trachomatis MOMP was functionally expressed on the surface of E. coli outer membrane. The OM expressed and purified rMOMP elicits antibodies that react to the native antigen, Chlamydia EB, in a mouse immunogenicity model. Surface expression of MOMP could provide useful reagents for vaccine research, and the methodology could serve as a platform to produce other outer membrane proteins recombinantly.

PCR-based diagnosis, molecular characterization and detection of atypical strains of avian Chlamydia psittaci in companion and wild birds

Chlamydiosis is one of the most important infectious diseases of birds. In this study, 253 clinical samples were taken from 27 bird species belonging to seven orders. Thirty-two (12.6%) samples were positive for Chlamydia psittaci major outer membrane gene (ompA) DNA by a nested polymerase chain reaction (PCR). Twelve nested PCR-positive specimens were typed by ompA gene-based PCR-restricted fragment length polymorphism, using CTU/CTL primers and AluI restriction enzyme. Four restriction patterns were identified, including genotype A (two specimens from an African grey parrot [Psittacus erithacus] and a lorikeet [Trichoglossus haematodus]), genotype B (two specimens from a rock dove [Columbia livia] and a canary [Serinus canaria]), a third new restriction pattern (six specimens from African grey parrots), and a fourth new restriction pattern (two specimens from a ring-necked parakeet [Psittacula krameri] and an Alexandrine parakeet [Psittacula eupatria]). The third and the fourth restriction patterns are suggested to be provisional genotypes I and J, respectively. Partial sequencing of the ompA gene of seven specimens completely correlated with the results of PCR-restricted fragment length polymorphism and confirmed the presence of genotypes A and B and the two new provisional genotypes I and J. The two new genotypes have the closest identity with C. psittaci genotype F and Chlamydia abortus, respectively. From an evolutionary perspective, both new genotypes, particularly genotype J, are intermediate between the two species, C. psittaci and C. abortus.

The surface-localised α-enolase of Mycoplasma suis is an adhesion protein

Mycoplasma suis belongs to the haemotrophic mycoplasmas which colonise red blood cells of a wide range of vertebrates. Adhesion to red blood cells is the crucial step in the unique lifecycle of M. suis. Due to the lack of a cultivation system, identification of adhesion structures has been difficult. So far, only one adhesion protein, i.e. MSG1 was identified. In order to determine further adhesion molecules of M. suis, we screened genomic M. suis libraries and performed Southern blot hybridisation analyses of genomic M. suis DNA. The α-enolase of M. suis was identified and analysed genetically and functionally. The encoding gene has 1623 bp in size. The deduced amino acid sequence showed an overall identity of 59.6-65.1% to α-enolases of other pathogenic mycoplasmas. The 540 aa M. suis α-enolase displays a size extension of about 90 aa in comparison to α-enolases of other mycoplasmas. Recombinant α-enolase expressed in Escherichia coli demonstrated immunogenicity in experimentally infected pigs. Immunoblot, confocal laser scanning microscopy and immune electron microscopy analysis using antibodies against recombinant α-enolase, indicate the membrane and surface localisation of native α-enolase in M. suis, though no typical signal sequences exist. Furthermore, we showed that recombinant α-enolase binds to porcine erythrocyte lysate in a dose-dependent manner. E. coli transformants which express α-enolase on their surface acquire the ability to adhere to porcine red blood cells. In conclusion, our observations indicate that α-enolase could be involved in the adhesion of M. suis to porcine red blood cells.

Identification of immunodominant linear B-cell epitopes within the major outer membrane protein of Chlamydia trachomatis

Chlamydia trachomatis is one of the most prevalent sexually transmitted pathogens. Chlamydial major outer membrane protein (MOMP) can induce strong cellular and humoral immune responses in murine models and has been regarded as a potential vaccine candidate. In this report, the amino acid sequence of MOMP was analyzed using computer-assisted techniques to scan B-cell epitopes, and three possible linear B-cell epitopes peptides (VLKTDVNKE, TKDASIDYHE, TRLIDERAAH) with high predicted antigenicity and high conservation were investigated. The DNA coding region for each potential epitope was cloned into pET32a(+) and expressed as Trx-His-tag fusion proteins in Escherichia coli. The fusion proteins were purified by Ni-NTA agarose beads and followed by SDS-PAGE and western blot analysis. We immunized mice with these three fusion proteins. The sera containing anti-epitope antibodies from the immunized mice could recognize C. trachomatis serovars D and E in ELISA. Antisera of these fusion proteins displayed an inhibitory effect on invasion of serovar E by in vitro neutralization assays. In addition, serum samples from convalescent C. trachomatis-infected patients were reactive with the epitope fusion proteins by western blot assay. Our results showed that the epitope sequences selected by bioinformatic analysis are highly conserved C. trachomatis MOMP B-cell epitopes, and could be good candidates for the development of subunit vaccines, which can be used in clinical diagnosis.

Antibodies to actin in autoimmune haemolytic anaemia

Background

In autoimmune haemolytic anaemia (AIHA), autoreactive antibodies directed against red blood cells are up-regulated, leading to erythrocyte death. Mycoplasma suis infections in pigs induce AIHA of both the warm and cold types. The aim of this study was to identify the target autoantigens of warm autoreactive IgG antibodies. Sera from experimentally M. suis-infected pigs were screened for autoreactivity.

Results

Actin-reactive antibodies were found in the sera of 95% of all animals tested. The reactivity was species-specific, i.e. reactivity with porcine actin was significantly higher than with rabbit actin. Sera of animals previously immunised with the M. suis adhesion protein MSG1 showed reactivity with actin prior to infection with M. suis indicating that molecular mimicry is involved in the specific autoreactive mechanism. A potentially cross-reactive epitope was detected.

Conclusions

This is the first report of autoreactive anti-actin antibodies involved in the pathogenesis of autoimmune haemolytic anaemia.

First identification and functional characterization of an immunogenic protein in unculturable haemotrophic Mycoplasmas (Mycoplasma suis HspA1)

The antigenic structures of the haemotrophic Mycoplasma suis, an epicellular parasite of porcine erythrocytes, are largely unknown due to its unculturability. In this study, serological proteome and mass spectrometry analyses allowed the characterization of M. suis proteins targeted by the porcine antibody response: two proteins with characteristics of heat shock proteins, two proteins with characteristics of glycolytic enzymes, a RNA helicase- and an actin-like protein. The DnaK-like protein of M. suis (HspA1) was further analysed genetically and functionally. Its encoding gene (M. suis a1 gene) is 1.830 bp in size and corresponds to a 67 kDa protein. Immunoelectron microscopy verified the surface accessibility of HspA1 in M. suis. Recombinant HspA1 expressed in Escherichia coli demonstrated ATPase activity and antigenicity in experimentally infected pigs. In conclusion, this first identification and recombinant expression of an antigenic protein of M. suis provides the basis for the development of vaccines and new in vitro diagnostic assays.

First LightCycler real-time PCR assay for the quantitative detection of Mycoplasma suis in clinical samples

Mycoplasma suis cannot be cultivated in vitro. Therefore, PCR-based methods are irreplaceable for the diagnosis of M. suis infections especially when clinical symptoms are not evident. Currently, no easy and reliable method allowing the quantitative detection of M. suis is available. This report describes the development of a quantitative LightCycler PCR assay based on the msg1 gene of M. suis (LC MSG1 PCR). No PCR signals were obtained with closely related haemotrophic and non-haemotrophic mycoplasmas, with other bacteria, and with M. suis-free blood and tissue arguing for a high analytical specificity. Test sensitivity was found to be 100%, and test specificity 96.7%. To test the diagnostic suitability of the LC MSG1 PCR, 25 pigs with clinical porcine eperythrozoonosis and 25 healthy pigs were investigated. All ill pigs revealed a positive real-time PCR result whereas only one healthy pig was detected to be M. suis-infected. M. suis was quantitatively detected in 19 blood specimens of 100 sows from Switzerland and in 17 of 160 post-weaning piglets from Germany. In conclusion, this new LC MSG1 PCR assay represents a powerful tool for the improvement of the current M. suis diagnosis and for prevalence and pathogenesis studies.

MSG1, a surface-localised protein of Mycoplasma suis is involved in the adhesion to erythrocytes

Mycoplasma suis is a member of the group of uncultivable haemoplasmas which colonise erythrocytes of a wide range of vertebrates. Adhesion to erythrocytes is the crucial step in the unique haemoplasma life cycle. Due to the lack of a cultivation system, no adhesion structures have been identified so far. In order to determine potential adhesion molecules of M. suis, we screened genomic M. suis libraries. The protein MSG1 with glyceraldehyde-3-phosphate dehydrogenase (GAPDH) similarity was identified. The encoding gene msg1 is 1011bp in size. The overall homology of the deduced amino acid sequence to GAPDHs of other pathogenic mycoplasmas ranged from 52.6% to 54.5%. Recombinant MSG1 expressed in Escherichia coli exhibited GAPDH activity. Immunoblot and immunoelectron microscopy analyses using antibodies against rMSG1 verified the membrane and surface localisation of native MSG1 in M. suis. Furthermore, we showed that rMSG1 binds to erythrocyte lysate in a dose-dependent manner. E. coli transformants which express MSG1 on their surface acquire the ability to adhere to porcine erythrocytes. This adhesion could be specifically and significantly inhibited by rMSG1 and antibodies to MSG1. In conclusion, our studies indicate that the membrane-associated MSG1 represents the first putative adhesion protein identified in the group of haemoplasmas.

Prevalence of chlamydiae in semen and genital tracts of bulls, rams and bucks

Chlamydiae infect male genital organs of ruminants. However, little is known about their prevalence. Hence, we investigated fresh and cryopreserved semen (bulls: n=304; rams: n=78; bucks: n=44) by polymerase chain reaction (PCR), as well as genital organs (bulls: n=13; rams: n=10; bucks: n=6) by immunohistochemistry (IHC) and PCR. Sera from bulls (n=104) and small ruminants (n=61) were tested by LPS and rMOMP (recombinant major outer membrane protein) ELISA and competitive ELISA (cELISA), respectively. Three PCR assays were compared in this study for detection of chlamydial DNA in semen: 16S rRNA, IGS-S (intergenic spacer 16S/23S-short), and IGS-L (intergenic spacer 16S/23S-long) PCRs. PCR sensitivity and inhibitory effects were determined by spiking semen with Chlamydophila (Cp.) abortus DNA. In bull semen, detection limits of the 16S, IGS-S and IGS-L PCRs were 10, 10, 100 templates, respectively. However, PCR sensitivity was reduced in ram and buck semen suggesting the presence of potential PCR inhibitors. Of 304 bull semen samples, the 16S PCR revealed DNA of chlamydiae in 20 samples (6.6%), including Cp. abortus (n=2), Cp. psittaci (n=1), Chlamydia suis (n=2), and Chlamydia-like organisms (n=15). In rams, one semen sample was positive for Chlamydia-like organism. All investigated male genital organs were negative for Chlamydia. Serology revealed 47.1% (49/104) positive bulls by LPS ELISA. Of these, 30 samples were positive by rMOMP ELISA, predominantly for Cp. pecorum. In small ruminants, cELISA displayed 34.8% (16/46) and 60% (9/15) positivity for Cp. abortus in rams and bucks, respectively. There was no correlation between serology and PCR of semen. The presence of chlamydiae in semen suggests the possibility of venereal transmission, although risk may be low in Switzerland.

Mycoplasma suis antigens recognized during humoral immune response in experimentally infected pigs

Today, serodiagnostic tests for Mycoplasma suis infections in pigs have low accuracies. The development of novel serodiagnostic strategies requires a detailed analysis of the humoral immune response elicited by M. suis and, in particular, the identification of antigenic proteins of the agent. For this study, indirect enzyme-linked immunosorbent assay (ELISA) and immunoblot analyses were performed using pre- and sequential postinoculation sera from M. suis-infected and mock-infected control pigs. M. suis purified from porcine blood served as the antigen. Eight M. suis-specific antigens (p33, p40, p45, p57, p61, p70, p73, and p83) were identified as targets of the immunoglobulin G (IgG) antibody response during experimental infection, with p40, p45, and p70 being the preferentially recognized M. suis antigens. Besides the M. suis-specific antigens, porcine immunoglobulins were identified in blood-derived M. suis preparations. By immunoglobulin depletion, the specificity of the M. suis antigen for use in indirect ELISA was significantly improved. M. suis-specific Western blot and ELISA reactions were observed in all infected pigs by 14 days postinfection at the latest and until week 14, the end of the experiments. During acute clinical attacks of eperythrozoonosis, a derailment of the antibody response, determined by decreases in both the M. suis net ELISA values and the numbers of M. suis-specific immunoblot bands, was accompanied by peaking levels of autoreactive IgG antibodies. In conclusion, the M. suis-specific antigens found to stimulate specific IgG antibodies are potentially useful for the development of novel serodiagnostic tests.

A New Escherichia coli Strain Producing Human Tumor Necrosis Factor

An Escherichia coli strain producing human tumor necrosis factor (TNF-alpha) was obtained using a semisynthetic gene partially optimized in respect of codon composition and a phage T7 promoter. The expression product was accumulated in cells as inclusion bodies in a yield of 50-70 mg/l of culture medium. The recombinant TNF-alpha in the form of inclusion bodies was used for immunization of rats to give a polyclonal antiserum. The resulting antibodies were specific under the immunoblotting conditions to the antigen used for the immunization. A dilution-based refolding procedure was developed; it provided a yield of soluble protein exceeding 85%.

Recombinant major outer membrane protein (MOMP) of Chlamydophila abortus, Chlamydophila pecorum, and Chlamydia suis as antigens to distinguish chlamydial species-specific antibodies in animal sera

Recombinant major outer membrane proteins (rMOMP) of Chlamydophila (Ch.) abortus, Ch. pecorum, and Chlamydia (C.) suis were used as antigens to distinguish chlamydial species-specific antibodies in (i) immune sera from six rabbits and three pigs raised against native purified elementary bodies, (ii) serum samples from 25 sows vaccinated with Ch. abortus, and (iii) 40 serum samples from four heifers experimentally infected with Ch. abortus. All post-exposition sera contained chlamydial antibodies as confirmed by strong ELISA seroreactivities against the chlamydial LPS. For the rMOMP ELISA mean IgG antibody levels were at least 5.8-fold higher with the particular rMOMP homologous to the chlamydial species used for immunisation or infection than with heterologous rMOMPs (P <0.001). Preferential rMOMP ELISA reactivities of sera were confirmed by Western blotting. The results suggest that the entire chlamydial rMOMP could provide a species-specific serodiagnostic antigen.