A recombinant chimera composed of repeat region RR1 of Mycoplasma hyopneumoniae adhesin with Pseudomonas exotoxin: in vivo evaluation of specific IgG response in mice and pigs

Characterization of the pig lower respiratory tract antibiotic resistome

Respiratory diseases and its treatments are highly concerned in both the pig industry and human health. However, the composition and distribution of antibiotic resistance genes (ARGs) in swine lower respiratory tract microbiome remain unknown. The relationships of ARGs with mobile genetic elements (MGEs) and lung health are unclear. Here, we characterize antibiotic resistomes of the swine lower respiratory tract microbiome containing 1228 open reading frames belonging to 372 ARGs using 745 metagenomes from 675 experimental pigs. Twelve ARGs conferring resistance to tetracycline are related to an MGE Tn916 family, and multiple types of ARGs are related to a transposase gene tnpA. Most of the linkage complexes between ARGs and MGEs (the Tn916 family and tnpA) are also observed in pig gut microbiomes and human lung microbiomes, suggesting the high risk of these MGEs mediating ARG transfer to both human and pig health. Gammaproteobacteria are the major ARG carriers, within which Escherichia coli harbored >50 ARGs and >10 MGEs. Although the microbial compositions structure the compositions of ARGs, we identify 73 ARGs whose relative abundances are significantly associated with the severity of lung lesions. Our results provide the first overview of ARG profiles in the swine lower respiratory tract microbiome.

Oral Immunization with Attenuated Salmonella Choleraesuis Expressing the P42 and P97 Antigens Protects Mice against Mycoplasma hyopneumoniae Challenge

Mycoplasma hyopneumoniae (M. hyopneumoniae, Mhp) is the etiological agent of swine enzootic pneumonia (EP), which has been associated with considerable economic losses due to reduced daily weight gain and feed efficiency. Adhesion to the cilia is important for Mhp to colonize the respiratory epithelium. Therefore, a successful vaccine must induce broad Mhp-specific immune responses at the mucosal surface. Recombinant attenuated Salmonella strains are believed to act as powerful live vaccine vectors that are able to elicit mucosal immune responses against various pathogens. To develop efficacious and inexpensive vaccines against Mhp, the immune responses and protection induced by recombinant attenuated Salmonella vaccines based on the P42 and P97 antigens of Mhp were evaluated. In general, the oral inoculation of recombinant rSC0016(pS-P42) or rSC0016(pS-P97) resulted in strong mucosal immunity, cell-mediated immunity, and humoral immunity, which was a mixed Th1/Th2-type response. In addition, the levels of specific IL-4 and IFN-γ in the immunized mice were increased, and the proliferation of lymphocytes was also enhanced, confirming the production of a good cellular immune response. Finally, both vaccine candidate strains were able to improve the weight loss of mice after a challenge and reduce clinical symptoms, lung pathological damage, and the inflammatory cell infiltration. These results suggest that the delivery of protective antigens with recombinant attenuated Salmonella vectors may be an effective means by which to combat Mhp infection. IMPORTANCE Mhp is the main pathogen of porcine enzootic pneumonia, a highly infectious and economically significant respiratory disease that affects pigs of all ages. As the target tissue of Mhp infections are the mucosal sites of the respiratory tract, the induction of protective immunity at the mucosal tissues is the most efficient strategy by which to block disease transmission. Because the stimulation of mucosal immune responses is efficient, Salmonella-vector oral vaccines are expected to be especially useful against mucosal-invading pathogens. In this study, we expressed the immunogenic proteins of P42 and P97 with the attenuated Salmonella Choleraesuis vector rSC0016, thereby generating a low-cost and more effective vaccine candidate against Mhp by inducing significant mucosal, humoral and cellular immunity. Furthermore, rSC0016(pS-P42) effectively prevents Mhp-induced weight loss and the pulmonary inflammation of mice. Because of the effectiveness of rSC0016(pS-P42) against Mhp infection in mice, this novel vaccine candidate strain shows great potential for its use in the pig breeding industry.

Inactivated Pseudomonas PE(ΔIII) exotoxin fused to neutralizing epitopes of PEDV S proteins produces a specific immune response in mice

Porcine epidemic diarrhea (PED) caused by the porcine epidemic diarrhea virus (PEDV), is a severe infectious and devastating swine disease that leads to serious economic losses in the swine industry worldwide. An increased number of PED cases caused by variant PEDV have been reported in many countries since 2010. S protein is the main immunogenic protein containing some B-cell epitopes that can induce neutralizing antibodies of PEDV. In this study, the construction, expression and purification of Pseudomonas aeruginosa exotoxin A (PE) without domain III (PEΔIII) as a vector was performed for the delivery of PEDV S-A or S-B. PE(ΔIII) PEDV S-A and PE(ΔIII) PEDV S-B recombinant proteins were confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analysis. The immunogenicity of PEDV S-A and PEDV S-B subunit vaccines were evaluated in mice. The results showed that PEDV-S-B vaccine could not only induce specific humoral and Th1 type-dominant cellular immune responses, but also stimulate PEDV-specific mucosal immune responses in mice. PEDV-S-B subunit vaccine is a novel candidate mucosal vaccine against PEDV infection.

Perspectives for improvement of Mycoplasma hyopneumoniae vaccines in pigs

Mycoplasma hyopneumoniae (M. hyopneumoniae) is one of the primary agents involved in the porcine respiratory disease complex, economically one of the most important diseases in pigs worldwide. The pathogen adheres to the ciliated epithelium of the trachea, bronchi, and bronchioles, causes damage to the mucosal clearance system, modulates the immune system and renders the animal more susceptible to other respiratory infections. The pathogenesis is very complex and not yet fully understood. Cell-mediated and likely also mucosal humoral responses are considered important for protection, although infected animals are not able to rapidly clear the pathogen from the respiratory tract. Vaccination is frequently practiced worldwide to control M. hyopneumoniae infections and the associated performance losses, animal welfare issues, and treatment costs. Commercial vaccines are mostly bacterins that are administered intramuscularly. However, the commercial vaccines provide only partial protection, they do not prevent infection and have a limited effect on transmission. Therefore, there is a need for novel vaccines that confer a better protection. The present paper gives a short overview of the pathogenesis and immune responses following M. hyopneumoniae infection, outlines the major limitations of the commercial vaccines and reviews the different experimental M. hyopneumoniae vaccines that have been developed and tested in mice and pigs. Most experimental subunit, DNA and vector vaccines are based on the P97 adhesin or other factors that are important for pathogen survival and pathogenesis. Other studies focused on bacterins combined with novel adjuvants. Very few efforts have been directed towards the development of attenuated vaccines, although such vaccines may have great potential. As cell-mediated and likely also humoral mucosal responses are important for protection, new vaccines should aim to target these arms of the immune response. The selection of proper antigens, administration route and type of adjuvant and carrier molecule is essential for success. Also practical aspects, such as cost of the vaccine, ease of production, transport and administration, and possible combination with vaccines against other porcine pathogens, are important. Possible avenues for further research to develop better vaccines and to achieve a more sustainable control of M. hyopneumoniae infections are discussed.

Analysis of swine antigen-specific antibody responses to Mycoplasma hyopneumoniae infection determined by protein microarray

Pigs harbor several different species of mycoplasmas, of which Mycoplasma hyopneumoniae presents the most significant economic impact on the swine industry. While ELISAs are the predominant diagnostic assay to measure antibody responses during infection with M. hyopneumoniae, the assay itself is only a rough estimate of the total antibody response. It lends little information on pathogen-wide antigen-specific responses. In addition, antibody responses to M. hyopneumoniae as measured by ELISA are slow to develop in infected swine. Our goal was to determine if a protein microarray could be more sensitive and informative of the serological responses of pigs to M. hyopneumoniae infection. The gene sequences of approximately 50 M. hyopneumoniae surface proteins or protein fragments were cloned, mutated to remove UGA codons, expressed in Escherichia coli and purified. The arrays were used to interrogate pig sera from various sources. Sera from naturally-infected swine gave some variability in antigen-specific responses, but, unexpectedly, the responses against the C-terminal portion of the major adhesin P97 was weak in all animals, including those that were experimentally infected. In two of four 118-day experimentally-infected caesarian-derived colostrum-deprived pigs, the strongest antibody responses occurred on days 30 and 54 against members of the P97/P102 paralog families. Our Day 0 results in the other two animals indicate that although thought to be mycoplasma free by all known criteria (serology and PCR), they may have harbored an inapparent Mycoplasma infection. In summary, the protein microarray has the potential to identify new targets for assay development to enhance sensitivity of antibody-based assays.

Update on Mycoplasma hyopneumoniae infections in pigs: Knowledge gaps for improved disease control

Mycoplasma hyopneumoniae (M. hyopneumoniae) is the primary pathogen of enzootic pneumonia, a chronic respiratory disease in pigs. Infections occur worldwide and cause major economic losses to the pig industry. The present paper reviews the current knowledge on M. hyopneumoniae infections, with emphasis on identification and analysis of knowledge gaps for optimizing control of the disease. Close contact between infected and susceptible pigs is the main route of M. hyopneumoniae transmission. Management and housing conditions predisposing for infection or disease are known, but further research is needed to better understand M. hyopneumoniae transmission patterns in modern pig production systems, and to assess the importance of the breeding population for downstream disease control. The organism is primarily found on the mucosal surface of the trachea, bronchi and bronchioles. Different adhesins and lipoproteins are involved in the adherence process. However, a clear picture of the virulence and pathogenicity of M. hyopneumoniae is still missing. The role of glycerol metabolism, myoinositol metabolism and the Mycoplasma Ig binding protein-Mycoplasma Ig protease system should be further investigated for their contribution to virulence. The destruction of the mucociliary apparatus, together with modulating the immune response, enhances the susceptibility of infected pigs to secondary pathogens. Clinical signs and severity of lesions depend on different factors, such as management, environmental conditions and likely also M. hyopneumoniae strain. The potential impact of strain variability on disease severity is not well defined. Diagnostics could be improved by developing tests that may detect virulent strains, by improving sampling in live animals and by designing ELISAs allowing discrimination between infected and vaccinated pigs. The currently available vaccines are often cost-efficient, but the ongoing research on developing new vaccines that confer protective immunity and reduce transmission should be continued, as well as optimization of protocols to eliminate M. hyopneumoniae from pig herds.

Development of Mycoplasma hyopneumoniae Recombinant Vaccines

Mycoplasma hyopneumoniae is the etiological agent of swine enzootic pneumonia (EP), a disease that affects swine production worldwide. Vaccination is the most cost-effective strategy for the control and prevention of the disease. Research using genome-based approach has the potential to elucidate the biology and pathogenesis of M. hyopneumoniae and contribute to the development of more effective vaccines. Here, we describe the protocol for developing M. hyopneumoniae recombinant vaccines using reverse vaccinology approaches.

Evaluation of recombinant Mycoplasma hyopneumoniae P97/P102 paralogs formulated with selected adjuvants as vaccines against mycoplasmal pneumonia in pigs

Pig responses to recombinant subunit vaccines containing fragments of eight multifunctional adhesins of the Mycoplasma hyopneumoniae (Mhp) P97/P102 paralog family formulated with Alhydrogel(®) or Montanide™ Gel01 were compared with a commercial bacterin following experimental challenge. Pigs, vaccinated intramuscularly at 9, 12 and 15 weeks of age with either of the recombinant formulations (n=10 per group) or Suvaxyn(®) M. hyo (n=12), were challenged with Mhp strain Hillcrest at 17 weeks of age. Unvaccinated, challenged pigs (n=12) served as a control group. Coughing was assessed daily. Antigen-specific antibody responses were monitored by ELISA in serum and tracheobronchial lavage fluid (TBLF), while TBLF was also assayed for cytokine responses (ELISA) and bacterial load (qPCR). At slaughter, gross and histopathology of lungs were quantified and damage to epithelial cilia in the porcine trachea was evaluated by scanning electron microscopy. Suvaxyn(®) M. hyo administration induced significant serological responses against Mhp strain 232 whole cell lysates (wcl) and recombinant antigen F3P216, but not against the remaining vaccine subunit antigens. Alhydrogel(®) and Montanide™ Gel01-adjuvanted antigen induced significant antigen-specific IgG responses, with the latter adjuvant eliciting comparable Mhp strain 232 wcl specific IgG responses to Suvaxyn(®) M. hyo. No significant post-vaccination antigen-specific mucosal responses were detected with the recombinant vaccinates. Suvaxyn(®) M. hyo was superior in reducing clinical signs, lung lesion severity and bacterial load but the recombinant formulations offered comparable protection against cilial damage. Lower IL-1β, TNF-α and IL-6 responses after challenge were associated with reduced lung lesion severity in Suvaxyn(®) M. hyo vaccinates, while elevated pathology scores in recombinant vaccinates corresponded to cytokine levels that were similarly elevated as in unvaccinated pigs. This study highlights the need for continued research into protective antigens and vaccination strategies that will prevent Mhp colonisation and establishment of infection.

A recombinant chimera comprising the R1 and R2 repeat regions of M. hyopneumoniae P97 and the N-terminal region of A. pleuropneumoniae ApxIII elicits immune responses

Background

Infection by Mycoplasma hyopneumoniae and Actinobacillus pleuropneumoniae, either alone or together, causes serious respiratory diseases in pigs.

Results

To develop an efficient multi-disease subunit vaccine against these pathogens, we produced a chimeric protein called Ap97, which comprises a deletion derivative of the N-terminal region of the A. pleuropneumoniae ApxIII toxin (ApxN) and the R1 and R2 repeats of M. hyopneumoniae P97 adhesin (P97C), using an E. coli expression system.

The levels of both IgG1 and IgG2a isotypes specific for ApxN and P97C in the sera of Ap97-immunized mice increased, and Ap97 induced the secretion of IL-4 and IFN-γ by mouse splenocytes. Antisera from mice and pigs immunized with Ap97 readily reacted with both native ApxIII and P97 proteins. In addition, immunization with the Ap97 vaccine effectively protected pigs against challenge with both pathogens.

Conclusions

These findings suggest that Ap97 confers immunogenicity, and is an effective vaccine that protects pigs against infection by M. hyopneumoniae and A. pleuropneumoniae.

Immunogenicity of IMS 1113 plus soluble subunit and chimeric proteins containing Mycoplasma hyopneumoniae P97 C-terminal repeat regions

The surface adhesin P97 mediates the adherence of Mycoplasma hyopneumoniae to swine cilia. Two reiterated repeats R1 and R2 are located at the C-terminus of P97. The purpose of this study was to evaluate the immunogenicity of Montanide adjuvant IMS 1113 plus soluble subunit proteins rR1, rR1R2 and their chimeric forms coupled with B subunit of the heat-labile enterotoxin of Escherichia coli (LTB). Each recombinant protein in this study was capable of eliciting anti-R1 specific humoral antibodies (IgG), mucosal antibodies (IgG and IgA) and IFN-γ production. The chimeric protein rLTBR1R2 elicited the quickest humoral antibody response among the recombinant proteins. Serum and bronchoalveolar lavage analysis revealed that each recombinant protein was capable of inducing both Th1 and Th2 responses. Importantly, all of the proteins induced an anti-R1-specific Th2-biased response in both humoral and mucosal compartments, similar to the response observed in a natural infection or vaccination process. These observations indicate that rR1, rR1R2, rLTBR1 and rLTBR1R2 with IMS 1113 might represent a promising subunit vaccine strategy against porcine enzootic pneumonia in pigs.

Mycoplasma hyopneumoniae: from disease to vaccine development

Mycoplasma hyopneumoniae is the etiological agent of swine enzootic pneumonia (EP), a disease that affects swine production worldwide. Vaccination is the most cost-effective strategy for the control and prevention of the disease. Despite efforts to control M. hyopneumoniae infection, significant economic losses in pig production continue to occur. The results of genome-based research have the potential to help understand the biology and pathogenesis of M. hyopneumoniae, and contribute to the development of more effective vaccines and diagnostic tests. In this review, the characteristics of M. hyopneumoniae related to pathogenesis and control measures will be discussed. Special emphasis will be placed on vaccination strategies that have been proposed with the use of reverse vaccinology approaches.

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.

B subunit ofEscherichia coliheat-labile enterotoxin as adjuvant of humoral immune response in recombinant BCG vaccination

The B subunit of Escherichia coli heat-labile enterotoxin (LTB), a nontoxic molecule with potent biological properties, is a powerful mucosal and parenteral adjuvant that induces a strong immune response against co-administered or coupled antigens. In this paper, the effect of LTB on the humoral immune response to recombinant BCG (rBCG) vaccination was evaluated. Isogenic mice were immunized with rBCG expressing the R1 repeat region of the P97 adhesin of Mycoplasma hyopneumoniae alone (rBCG/R1) or fused to LTB (rBCG/LTBR1). Anti-R1 systemic antibody levels (IgG1, IgG2a, IgG2b, IgG3, IgM, and IgA) were measured by ELISA using recombinant R1 as antigen. With the exception of IgM, LTB doubled the anti-R1 antibody levels in rBCG vaccination. The IgG1/IgG2a mean ratio showed that both rBCG/LTBR1 and rBCG/R1 induced a mixed Th1/Th2 immune response. Interestingly, anti-R1 serum IgA was induced only by rBCG/LTBR1. These results demonstrate that LTB has an adjuvant effect on the humoral immune response to recombinant antigens expressed in BCG.

Evaluation of the immunogenicity of the P97R1 adhesin of Mycoplasma hyopneumoniae as a mucosal vaccine in mice

The immunogenicity of P97 adhesin repeat region R1 (P97R1) of Mycoplasma hyopneumoniae, an important pathogenesis-associated region of P97, was evaluated in mice as a mucosal vaccine. Mice were immunized orally with attenuated Salmonella typhimurium aroA strain CS332 harbouring a eukaryotic or prokaryotic expression vector encoding P97R1. Local and systemic immune responses were analysed by ELISA on mouse sera, lung washes and splenocyte supernatants following splenocyte stimulation with specific antigens in vitro. Although no P97R1-specific antibody responses were detected in serum and lung washes, significant gamma interferon was produced by P97R1-stimulated splenocytes from mice immunized orally with S. typhimurium aroA harbouring either expression system, indicating induction of a cell-mediated immune response. These results suggested that live bacterial vectors carrying DNA vaccines or expressing heterologous antigens preferentially induce a Th1 response. Surprisingly, however, mice immunized with the vaccine carrier S. typhimurium aroA CS332 induced serum IgG, but not mucosal IgA, against P97R1 or S. typhimurium aroA CS332 whole-cell lysate, emphasizing the importance of assessing the suitability of attenuated S. typhimurium antigen-carrier delivery vectors in the mouse model prior to their evaluation as potential vaccines in the target species, which in this instance was pigs.

A recombinant chimera composed of R1 repeat region of Mycoplasma hyopneumoniae P97 adhesin with Escherichia coli heat-labile enterotoxin B subunit elicits immune response in mice

Swine mycoplasmal pneumonia (SMP), caused by fastidious bacterium Mycoplasma hyopneumoniae, is the most important respiratory disease in swine breeding. The commonly used vaccines to control this disease consist of inactivated whole cells (bacterins), whose production cost is high and the efficiency is limited. The objective of this study was to develop and to evaluate in BALB/c mice a recombinant subunit vaccine (rLTBR1) containing the R1 region of P97 adhesin of M. hyopneumoniae (R1) fused to the B subunit of the heat-labile enterotoxin of Escherichia coli (LTB). rLTBR1 formed functional oligomers that presented high affinity to GM1 ganglioside. Mice inoculated with rLTBR1 by intranasal (IN) or intramuscular (IM) route produced high levels of anti-R1 systemic and mucosal antibodies (IgA), which recognized the native P97. On the other hand, mice inoculated with the inactivated whole cell vaccine did not produce anti-R1 antibodies. The administration route influenced the modulation of the immune response by LTB, showing that IM rLTBR1 induced Th2-biased immune responses and IN rLTBR1 induced Th1-biased immune responses. rLTBR1 administrated by IN route also induced IFN-gamma secretion by lymphocytes. rLTBR1 may constitute a new strategy for preventing infection by M. hyopneumoniae and may have potential for developing vaccines against other infectious diseases as well.

Fusion protein vaccine by domains of bacterial exotoxin linked with a tumor antigen generates potent immunologic responses and antitumor effects

Antigen-specific immunotherapy represents an attractive approach for cancer treatment because of the capacity to eradicate systemic tumors at multiple sites in the body while retaining the requisite specificity to discriminate between neoplastic and nonneoplastic cells. It has been shown that certain domains of bacterial exotoxins facilitate translocation from extracellular and vesicular compartments into the cytoplasm. This feature provides an opportunity to enhance class I and/or II presentation of exogenous antigen to T lymphocytes. We investigated previously whether the translocation domain (domain II) of Pseudomonas aeruginosa exotoxin A with a model tumor antigen, human papillomavirus type 16 E7, in the context of a DNA vaccine could enhance vaccine potency. We then attempted to determine whether this chimeric molecule could also generate strong antigen-specific immunologic responses and enhance the potency of cancer vaccine in the protein format. Our results show that vaccination with the PE(DeltaIII)-E7-KDEL3 fusion protein enhances MHC class I and II presentation of E7, leading to dramatic increases in the number of E7-specific CD8+ and CD4+ T-cell precursors and markedly raised titers of E7-specific antibodies. Furthermore, the PE(DeltaIII)-E7-KDEL3 protein generates potent antitumor effects against s.c. E7-expressing tumors and preestablished E7-expressing metastatic lung tumors. Further, mice immunized with PE(DeltaIII)-E7-KDEL3 protein vaccine also retained long-term immunologic responses and antitumor effects. Our results indicate that retrograde-fusion protein via the delivery domains of exotoxins with an antigen greatly enhances in vivo antigen-specific immunologic responses and represents a novel strategy to improve cancer vaccine potency.