Molecular characterization of a ribonucleotide reductase (nrdF) gene fragment of Mycoplasma hyopneumoniae and assessment of the recombinant product as an experimental vaccine for enzootic pneumonia

Sequence TTKF ↓ QE defines the site of proteolytic cleavage in Mhp683 protein, a novel glycosaminoglycan and cilium adhesin of Mycoplasma hyopneumoniae

Mycoplasma hyopneumoniae colonizes the ciliated respiratory epithelium of swine, disrupting mucociliary function and inducing chronic inflammation. P97 and P102 family members are major surface proteins of M. hyopneumoniae and play key roles in colonizing cilia via interactions with glycosaminoglycans and mucin. The p102 paralog, mhp683, and homologs in strains from different geographic origins encode a 135-kDa pre-protein (P135) that is cleaved into three fragments identified here as P45(683), P48(683), and P50(683). A peptide sequence (TTKF↓QE) was identified surrounding both cleavage sites in Mhp683. N-terminal sequences of P48(683) and P50(683), determined by Edman degradation and mass spectrometry, confirmed cleavage after the phenylalanine residue. A similar proteolytic cleavage site was identified by mass spectrometry in another paralog of the P97/P102 family. Trypsin digestion and surface biotinylation studies showed that P45(683), P48(683), and P50(683) reside on the M. hyopneumoniae cell surface. Binding assays of recombinant proteins F1(683)-F5(683), spanning Mhp683, showed saturable and dose-dependent binding to biotinylated heparin that was inhibited by unlabeled heparin, fucoidan, and mucin. F1(683)-F5(683) also bound porcine epithelial cilia, and antisera to F2(683) and F5(683) significantly inhibited cilium binding by M. hyopneumoniae cells. These data suggest that P45(683), P48(683), and P50(683) each display cilium- and proteoglycan-binding sites. Mhp683 is the first characterized glycosaminoglycan-binding member of the P102 family.

Production and characterization of recombinant transmembrane proteins from Mycoplasma hyopneumoniae

Mycoplasma hyopneumoniae is the etiological agent of swine enzootic pneumonia (EP), a chronic respiratory disease which causes significant economic losses to the swine industry worldwide. More efficient strategies for controlling this disease are necessary. In this study, we cloned17 genes coding for transmembrane proteins from M. hyopneumoniae, among which six were successfully expressed in Escherichia coli and had their immunogenic and antigenic properties evaluated. All proteins were immunogenic in mice and sera from naturally infected pigs reacted with the recombinant proteins, suggesting that they are expressed during infection. These antigens may contribute for the development of new recombinant vaccines and diagnostic tests against EP.

A processed multidomain mycoplasma hyopneumoniae adhesin binds fibronectin, plasminogen, and swine respiratory cilia

Porcine enzootic pneumonia is a chronic respiratory disease that affects swine. The etiological agent of the disease, Mycoplasma hyopneumoniae, is a bacterium that adheres to cilia of the swine respiratory tract, resulting in loss of cilia and epithelial cell damage. A M. hyopneumoniae protein P116, encoded by mhp108, was investigated as a potential adhesin. Examination of P116 expression using proteomic analyses observed P116 as a full-length protein and also as fragments, ranging from 17 to 70 kDa in size. A variety of pathogenic bacterial species have been shown to bind the extracellular matrix component fibronectin as an adherence mechanism. M. hyopneumoniae cells were found to bind fibronectin in a dose-dependent and saturable manner. Surface plasmon resonance was used to show that a recombinant C-terminal domain of P116 bound fibronectin at physiologically relevant concentrations (K(D) 24 ± 6 nm). Plasmin(ogen)-binding proteins are also expressed by many bacterial pathogens, facilitating extracellular matrix degradation. M. hyopneumoniae cells were found to also bind plasminogen in a dose-dependent and saturable manner; the C-terminal domain of P116 binds to plasminogen (K(D) 44 ± 5 nm). Plasminogen binding was abolished when the C-terminal lysine of P116 was deleted, implicating this residue as part of the plasminogen binding site. P116 fragments adhere to the PK15 porcine kidney epithelial-like cell line and swine respiratory cilia. Collectively these data suggest that P116 is an important adhesin and virulence factor of M. hyopneumoniae.

Development of non-antibiotic-resistant, chromosomally based, constitutive and inducible expression systems for aroA-attenuated Salmonella enterica Serovar Typhimurium

Live-vaccine delivery systems expressing two model antigens from Mycoplasma hyopneumoniae, F2(P97) (Adh) and NrdF, were constructed using Salmonella enterica serovar Typhimurium aroA (STM-1), and immunogenicity in mice was evaluated. Recombinant plasmid-based expression (PBE) and chromosomally based expression (CBE) systems were constructed. The PBE system was formed by cloning both antigen genes into pJLA507 to create an operon downstream of temperature-inducible promoters. Constitutive CBE was achieved using a promoter-trapping technique whereby the promoterless operon was stably integrated into the chromosome of STM-1, and the expression of antigens was assessed. The chromosomal position of the operon was mapped in four clones. Inducible CBE was obtained by using the in vivo-induced sspA promoter and recombining the expression construct into aroD. Dual expression of the antigens was detected in all systems, with PBE producing much larger quantities of both antigens. The stability of antigen expression after in vivo passage was 100% for all CBE strains recovered. PBE and CBE strains were selected for comparison in a vaccination trial. The vaccine strains were delivered orally into mice, and significant systemic immunoglobulin M (IgM) and IgG responses against both antigens were detected among all CBE groups. No significant immune response was detected using PBE strains. Expression of recombinant antigens in S. enterica serovar Typhimurium aroA from chromosomally located strong promoters without the use of antibiotic resistance markers is a reliable and effective method of inducing a significant immune response.

Vaccines for Mycoplasma diseases in animals and man

Vaccines for important mycoplasma diseases, including contagious bovine and caprine pleuropneumonia, have been used for centuries, consisting mainly of infected tissue or fluids which are inoculated into sites at which the risk of severe infection is slight, such as the tail and bridge of the nose. Surprisingly, little progress has been made in developing safe, defined and protective alternatives, the vaccines today still consisting of mildly attenuated strains serially passaged in eggs or in culture. Ill-defined temperature-sensitive mutants are widely used for mycoplasmoses in poultry despite uncertainty about their mode of protection. Inactivated vaccines for enzootic pneumonia appear to have improved pig health worldwide, but disease reduction has been generally modest. Ironically, attempts to develop subunit preparations have often led to exacerbation of disease, particularly in human atypical pneumonia. Promising results have been seen in DNA vaccine technology, which has been applied to the development of mycoplasma vaccines for porcine enzootic pneumonia, but field trials still seem a long way off. No commercial vaccines exist for Mycoplasma bovis, despite evidence that this is a major cause of calf pneumonia, mastitis and arthritis.

Epitope mapping of Mycoplasma hyopneumoniae using phage displayed peptide libraries and the immune responses of the selected phagotopes

Phage display techniques have been widely employed to map the epitope structures which served as the basis for developing molecular vaccines. In the present study, we applied this technique to map the epitopes of Mycoplasma hyopneumoniae, the etiologic agent causing swine enzootic pneumonia, and evaluated directly the immune responses in mice of the selected phage-displayed epitopes (phagotopes). Two phage-displayed random peptide libraries were biopanned with the protein A-purified IgG of the rabbit anti-M. hyopneumoniae hyperimmune serum and the selected phage clones were sequenced and analyzed. Some of the inserts of the selected phagotopes showed a good match with the known proteins of M. hyopneumoniae. Others, which did not match with any known proteins, but shared extensive homology with each other, were clustered and classified as the conformational epitopes of M. hyopneumoniae. To evaluate the potential of using these phagotopes as effective vaccines, several phage clones were chosen to immunize mice. IgA coproantibody, IgA in bronchoalveolar lavage fluid and serum IgG responses were assayed. The serum raised by the phage clones clearly recognized several major mycoplasmal proteins indicating that the phagotope-induced immune responses were antigen-specific. The stronger IgG1 response revealed that the immune responses of the epitope-displaying phage were mainly through Th2 activation. The growth inhibition assay showed that the selected phage clones CS4 and varphi58 are potential vaccine candidates and suggested that the mycoplasmal 97 kDa, 56 kDa, 30 kDa and 23 kDa proteins may play important roles in the immune responses. The present work demonstrates that the whole epitope profile of a microorganism can be obtained through screening the phage displayed peptide libraries with the hyperimmune serum and reveals the potential of using epitope-displaying phages as peptide vaccines.

Induction of enzootic pneumonia in pigs by the administration of an aerosol of in vitro-cultured Mycoplasma hyopneumoniae

The aim of this study was to establish whether enzootic pneumonia could be induced reliably in piglets by administering an aerosolised culture of Mycoplasma hyopneumoniae. Groups of five M hyopneumoniaefree Landrace x Large White piglets weaned at 11 to 14 days of age were exposed to aerosols of in vitro cultures of a virulent strain of M hyopneumoniae. In three separate trials, 14 of 15 pigs exposed to the bacteria developed pneumonia, but pigs exposed to the culture medium alone did not develop the disease. Lung pathology, both gross and histological, indicated acute disease. Ten of the pigs were tested for seroconversion by Western blot and they were all positive. The growth rates of the infected pigs were significantly reduced and the water consumption of the infected groups was also depressed. M hyopneumoniae was recovered from eight of the 15 infected pigs.

Oral immunization of swine with attenuated Salmonella typhimurium aroA SL3261 expressing a recombinant antigen of Mycoplasma hyopneumoniae (NrdF) primes the immune system for a NrdF specific secretory IgA response in the lungs

Salmonella typhimurium SL3261 (aroA mutant) expressing a recombinant Mycoplasma hyopneumoniae antigen was used to orally immunize swine against porcine enzootic pneumonia. This construct, designated S. typhimurium aro A SL3261 (pKF1), expressed a recombinant protein containing the carboxy-terminal 11 kDa of a 42 kDa M. hyopneumoniae NrdF ribonucleotide reductase R2 subunit protein. Here we demonstrate that this antigen is present in all seven geographically diverse strains of M. hyopneumoniae tested, and is recognized by the swine immune system after experimental infection with the virulent M. hyopneumoniae Beaufort strain. The immune response of swine orally immunized twice with S. typhimurium SL3261 (pKF1) on day 0 and day 14 was evaluated. Oral immunization with S. typhimurium SL3261 (pKF1) primed the immune system to elicit a significant (P<0.05) secretory IgA response against the 15 kDa NrdF antigen in the respiratory tract of swine, post-challenge, compared to control groups. Blood lymphocytes from swine immunized with S. typhimurium SL3261 (pKF1) proliferated significantly (P<0.05) following stimulation with M. hyopneumoniae whole-cell extracts compared to control groups 14 days post-vaccination. Following challenge with virulent M. hyopneumoniae, swine immunized with S. typhimurium SL3261 (pKF1) showed higher average daily weight gains and reduced lung pathology compared to control groups.

Protective effect of vaccination with culture supernate of M. hyopneumoniae against experimental infection in pigs

The protective activity of Mycoplasma hyopneumoniae inactivated vaccine prepared from sedimented whole cells and cell-free culture supernates was evaluated experimentally using hysterectomy-produced, colostrum-deprived pigs in which mycoplasmal pneumonia had been induced. The culture supernate vaccine containing less than 10(1) colour-changing units (CCU)/0.2 ml of M. hyopneumoniae significantly (P < 0.05) reduced the percentage of lung lesions compared to controls (3.2 +/- 3.9 vs. 12.2 +/- 2.2%), whereas the sedimented whole cells vaccine containing 10(10) CCU/0.2 ml of organisms provided variable protection (18.7 +/- 16.5 vs. 12.2 +/- 2.2%). Serum from the pigs vaccinated with culture supernate reacted with six protein bands of 97, 89, 65, 46, 42 and 41 kDa by immunoblot analysis. From these results, we conclude that vaccination with culture supernate of M. hyopneumoniae can provide protection against M. hyopneumoniae infection and that these antigens in the culture supernate may be closely related to the reduction of lung lesions.

A physical and genetic map of the Mycoplasma hyopneumoniae strain J genome

A macrorestriction map of the genome of Mycoplasma hyopneumoniae strain J, the type strain of the causative agent of enzootic pneumonia in pigs, was constructed using pulsed-field gel electrophoresis (PFGE) and DNA hybridization. The size of the genome as determined by PFGE was approximately 1070 kb. Assembly of the M. hyopneumoniae genomic map was facilitated and complimented by the simultaneous construction of an ordered cosmid library. Five contigs of overlapping cosmids were assembled, which together represent coverage of approximately 728 kb. Forty-two genetic markers (including three types of repeated elements) were placed on the M. hyopneumoniae map. Closer examination of an ApaI restriction fragment contained entirely within a single cosmid insert suggests that the genome size may be overestimated by PFGE.

Molecular biology and pathogenicity of mycoplasmas

The recent sequencing of the entire genomes of Mycoplasma genitalium and M. pneumoniae has attracted considerable attention to the molecular biology of mycoplasmas, the smallest self-replicating organisms. It appears that we are now much closer to the goal of defining, in molecular terms, the entire machinery of a self-replicating cell. Comparative genomics based on comparison of the genomic makeup of mycoplasmal genomes with those of other bacteria, has opened new ways of looking at the evolutionary history of the mycoplasmas. There is now solid genetic support for the hypothesis that mycoplasmas have evolved as a branch of gram-positive bacteria by a process of reductive evolution. During this process, the mycoplasmas lost considerable portions of their ancestors' chromosomes but retained the genes essential for life. Thus, the mycoplasmal genomes carry a high percentage of conserved genes, greatly facilitating gene annotation. The significant genome compaction that occurred in mycoplasmas was made possible by adopting a parasitic mode of life. The supply of nutrients from their hosts apparently enabled mycoplasmas to lose, during evolution, the genes for many assimilative processes. During their evolution and adaptation to a parasitic mode of life, the mycoplasmas have developed various genetic systems providing a highly plastic set of variable surface proteins to evade the host immune system. The uniqueness of the mycoplasmal systems is manifested by the presence of highly mutable modules combined with an ability to expand the antigenic repertoire by generating structural alternatives, all compressed into limited genomic sequences. In the absence of a cell wall and a periplasmic space, the majority of surface variable antigens in mycoplasmas are lipoproteins. Apart from providing specific antimycoplasmal defense, the host immune system is also involved in the development of pathogenic lesions and exacerbation of mycoplasma induced diseases. Mycoplasmas are able to stimulate as well as suppress lymphocytes in a nonspecific, polyclonal manner, both in vitro and in vivo. As well as to affecting various subsets of lymphocytes, mycoplasmas and mycoplasma-derived cell components modulate the activities of monocytes/macrophages and NK cells and trigger the production of a wide variety of up-regulating and down-regulating cytokines and chemokines. Mycoplasma-mediated secretion of proinflammatory cytokines, such as tumor necrosis factor alpha, interleukin-1 (IL-1), and IL-6, by macrophages and of up-regulating cytokines by mitogenically stimulated lymphocytes plays a major role in mycoplasma-induced immune system modulation and inflammatory responses.

Reiterated repeat region variability in the ciliary adhesin gene of Mycoplasma hyopneumoniae

Mycoplasma hyopneumoniae is a highly prevalent pathogen which colonizes the ciliated epithelial lining of the porcine respiratory tract. Expression libraries constructed from genomic DNA of the non-pathogenic strain M. hyopneumoniae J were screened with porcine hyperimmune antiserum against M. hyopneumoniae. One clone expressed a 28 kDa protein which was also reactive with monospecific antiserum raised against a putative M. hyopneumoniae-specific 94 kDa antigen derived from strain J. Trypsin digestion of whole M. hyopneumoniae cells showed the 94 kDa antigen to be surface-accessible. DNA sequence analysis of the gene encoding the 94 kDa antigen revealed greater than 90% homology to two adhesin genes, encoding P97 and Mhp1, cloned from pathogenic strain 232 and strain P5722 of M. hyopneumoniae, respectively. Two regions of repetitive DNA sequence were identified in the gene encoding the 94 kDa antigen. The first encoded the deduced amino acid sequence A(T)-K-P-E(V)-A(T) arranged as nine tandem repeats (RR1). The second region of repetitive DNA sequence encoded the deduced amino acid sequence G-A(E,S)-P-N(S)-Q-G-K-K-A-E arranged as five tandem repeats (RR2). Comparison of the three M. hyopneumoniae adhesin genes revealed that the genes encoding P97 and Mhp1, and the strain J gene encoding the 94 kDa antigen contained 15, 12 and 9 tandem repeats, respectively, in RR1, and 4, 5 and 5 tandem repeats, respectively, in RR2. Southern hybridization analysis of EcoRI-digested genomic DNA probed with an 820 bp fragment spanning RR1 and RR2 identified a strongly hybridizing fragment ranging in size from 2.15 to 2.30 kb among seven geographically diverse strains of M. hyopneumoniae but failed to hybridize with DNA from four strains of Mycoplasma hyorhinis or Mycoplasma flocculare strain Ms42. PCR primers flanking the DNA sequence encoding RR1 and RR2 were used to amplify DNA from the seven strains of M. hyopneumoniae and DNA sequence analysis of the amplification products showed that the number of tandem amino acid repeats in RR1 varied considerably between strains. RR1 from M. hyopneumoniae strains YZ, Beaufort, Sue, OMZ407 and C1735/2 comprised 11, 15, 12, 15 and 8 tandem copies, respectively, of the 5-aa repeat whilst RR2 comprised 4, 3, 4, 3 and 4 tandem copies, respectively, of the 10-aa repeat. Two putative integrin binding sites (L-E-T and R-X-X-X-D) were identified in the 94 kDa ciliary adhesin. Variability in the number of amino acid repeats in RR1 amongst strains of M. hyopneumoniae may influence ciliary binding.

Serum and mucosal antibody responses and protection in pigs vaccinated against Mycoplasma hyopneumoniae with vaccines containing a denatured membrane antigen pool and adjuvant

OBJECTIVE

To investigate the protective efficacy of a pool of denatured membrane protein antigens of Mycoplasma hyopneumoniae (J strain) in the molecular size range 70 to 85 kDa (F3 antigen) in combination with adjuvants for pigs challenged with M hyopneumoniae.

DESIGN

A vaccine efficacy experiment with assessment of serum and respiratory tract antibody responses.

PROCEDURE

F3 antigens were emulsified with five different adjuvants. To groups of three pigs per vaccine, four vaccines were given by intramuscular injection, and two vaccines, including one of those given intramuscularly, were given by intraperitoneal injection.

RESULTS

Compared to six unvaccinated pigs, animals vaccinated with F3 antigen displayed significantly reduced pneumonia (54% reduction in mean lung score) following experimental challenge. Analysis of post-vaccination, pre-challenge IgG and IgA ELISA antibody absorbances in serum and respiratory tract washings revealed no correlation with lung score. Six weeks after challenge, pigs previously vaccinated intramuscularly mostly demonstrated greater IgG and IgA responses in respiratory tract washings, and greater IgG serum antibody responses, than those vaccinated by intraperitoneal injection.

CONCLUSION

Pigs vaccinated with M hyponeumoniae antigens in the molecular size range of 70 to 85 kDa showed a significant reduction in lung lesions compared with unvaccinated control animals after experimental challenge. IgG and IgA antibody concentrations in serum and respiratory tract washings after vaccination do not provide a useful prognostic indicator of protection from enzootic pneumonia.

Oral immunization of mice with attenuated Salmonella typhimurium aroA expressing a recombinant Mycoplasma hyopneumoniae antigen (NrdF)

Mycoplasma hyopneumoniae is the etiological agent of porcine enzootic pneumonia, a commercially expensive respiratory disease of swine. Salmonella typhimurium SL3261 was used as a live carrier of plasmid pKF1, which encodes a 15-kDa recombinant M. hyopneumoniae protein. This expressed recombinant protein consists of the carboxy-terminal 11 kDa of a 42-kDa M. hyopneumoniae NrdF ribonucleotide reductase R2 subunit protein. Rabbit anti-15-kDa serum was able to inhibit the growth of viable M. hyopneumoniae J in vitro. When used as a live oral vaccine, S. typhimurium SL3261(pKF1) induced a significant secretory immunoglobulin A immune response in the lungs of mice orally immunized against the M. hyopneumoniae antigen. Utilization of live oral vaccines expressing potentially protective M. hyopneumoniae proteins, such as the NrdF antigen, which can stimulate a lung mucosal response against surface-accessible proteins may provide a cost-effective alternative to the present control strategies used for porcine enzootic pneumonia.