Immunologic Pathways in Protective versus Maladaptive Host Responses to Attenuated and Pathogenic Strains of Mycoplasma gallisepticum

Transcriptomic analysis of the effects of tylosin on the protective immunity provided by the Mycoplasma gallisepticum vaccine Vaxsafe MG ts-304

The antimicrobial tylosin is commonly used to control mycoplasma infections, sometimes in combination with vaccination. However, the efficacy of a live mycoplasma vaccine, when combined with subsequent antimicrobial treatment, against the effects of subsequent infection with a virulent strain is unknown. This study employed differential gene expression analysis to evaluate the effects of tylosin on the protection provided by the live attenuated Vaxsafe MG ts-304 vaccine, which has been shown to be safe and to provide long-term protective immunity against infection with Mycoplasma gallisepticum. The transcriptional profiles of the tracheal mucosa revealed significantly enhanced inflammation, immune cell proliferation and adaptive immune responses in unvaccinated, untreated birds and in unvaccinated birds treated with tylosin 2 weeks after infection with virulent M. gallisepticum. These responses, indicative of the typical immune dysregulation caused by infection with M. gallisepticum, were less severe in the unvaccinated, tylosin-treated birds than in the unvaccinated, untreated birds. This was attributable to the effect of residual levels of tylosin in the tracheal mucosa on replication of virulent M. gallisepticum. These responses were not detected in vaccinated, tylosin-treated birds or in vaccinated, untreated birds after infection. The tracheal mucosal transcriptional profiles of these birds resembled those of unvaccinated, untreated, uninfected birds, suggesting a rapid and protective secondary immune response and effective vaccination. Overall, these results show that, although tylosin treatment reduced the duration of immunity, the initial protective immunity induced by Vaxsafe MG ts-304 lasted for at least 22 weeks after vaccination, even after the administration of tylosin for 16 weeks following vaccination.

Immune Evasion of Mycoplasma gallisepticum: An Overview

Mycoplasma gallisepticum is one of the smallest self-replicating organisms. It causes chronic respiratory disease, leading to significant economic losses in poultry industry. Following M. gallisepticum invasion, the pathogen can persist in the host owing to its immune evasion, resulting in long-term chronic infection. The strategies of immune evasion by mycoplasmas are very complex and recent research has unraveled these sophisticated mechanisms. The antigens of M. gallisepticum exhibit high-frequency changes in size and expression cycle, allowing them to evade the activation of the host humoral immune response. M. gallisepticum can invade non-phagocytic chicken cells and also regulate microRNAs to modulate cell proliferation, inflammation, and apoptosis in tracheal epithelial cells during the disease process. M. gallisepticum has been shown to transiently activate the inflammatory response and then inhibit it by suppressing key inflammatory mediators, avoiding being cleared. The regulation and activation of immune cells are important for host response against mycoplasma infection. However, M. gallisepticum has been shown to interfere with the functions of macrophages and lymphocytes, compromising their defense capabilities. In addition, the pathogen can cause immunological damage to organs by inducing an inflammatory response, cell apoptosis, and oxidative stress, leading to immunosuppression in the host. This review comprehensively summarizes these evasion tactics employed by M. gallisepticum, providing valuable insights into better prevention and control of mycoplasma infection.

Drug sensitivity and genome-wide analysis of two strains of Mycoplasma gallisepticum with different biofilm intensity

Mycoplasma gallisepticum (MG) is one of the major causative agents of chronic respiratory diseases in poultry. The biofilms of MG are highly correlated to its chronic infection. However data on genes involved in biofilm formation ability are still scarse. MG strains with distinct biofilm intensity were screened by crystal violet staining morphotyped and characterized for the drug sensitivity. Two MG strains NX-01 and NX-02 showed contrasted ability to biofilm formation. The biofilm formation ability of NX-01 strain was significantly higher than that of NX-02 strain (p < 0.01). The drug sensitivity test showed that the stronger the ability of MG stain to form biofilms, the weaker its sensitivity to 17 antibiotic drugs. Moreover, putative key genes related to biofilm formation were screened by genome-wide analysis. A total of 13 genes and proteins related to biofilm formation, including ManB, oppA, oppD, PDH, eno, RelA, msbA, deoA, gapA, rpoS, Adhesin P1 precursor, S-adenosine methionine synthetase, and methionyl tRNA synthetase were identified. There were five major discrepancies between the two isolated MG strains and the five NCBI-published MG strains. These findings provide potential targets for inhibiting the formation of biofilm of MG, and lay a foundation for treating chronic infection.

Comparative Transcriptome Analysis Reveals the Innate Immune Response to Mycoplasma gallisepticum Infection in Chicken Embryos and Newly Hatched Chicks

Mycoplasma gallisepticum (MG) is a major cause of chronic respiratory diseases in chickens, with both horizontal and vertical transmission modes and varying degrees of impact on different ages. The innate immune response is crucial in resisting MG infection. Therefore, this study aimed to investigate the innate immune response of chicken embryos and newly hatched chicks to MG infection using comparative RNA-seq analysis. We found that MG infection caused weight loss and immune damage in both chicken embryos and chicks. Transcriptome sequencing analysis revealed that infected chicken embryos had a stronger immune response than chicks, as evidenced by the higher number of differentially expressed genes associated with innate immunity and inflammation. Toll-like receptor and cytokine-mediated pathways were the primary immune response pathways in both embryos and chicks. Furthermore, TLR7 signaling may play an essential role in the innate immune response to MG infection. Overall, this study sheds light on the development of innate immunity to MG infection in chickens and can help in devising disease control strategies.

Tracheal cellular immune response in chickens inoculated with Mycoplasma synoviae vaccine, MS-H or its parent strain 86079/7NS

Mycoplasma synoviae causes respiratory tract disease in chickens characterised by mild to moderate lymphoplasmacytic infiltration of the tracheal mucosa. MS-H (Vaxsafe1 MS, Bioproperties Pty Ltd.) is an effective live attenuated vaccine for M. synoviae, but the immunological basis for its mechanism of protection has not been investigated, and the phenotypes of lymphocytes and associated cytokines involved in the local adaptive immune response have not been described previously. In this study, specific-pathogen-free chickens were inoculated intra-ocularly at 3 weeks of age with either M. synoviae vaccine strain MS-H or vaccine parent strain 86079/7NS (7NS), or remained uninoculated. At 2-, 7- and 21 days post-inoculation (dpi), tracheal mucosal pathology, infiltrating lymphocytes subsets and transcription levels of mRNA encoding 8 cytokines were assessed using light microscopy, indirect immunofluorescent staining and RT-qPCR, respectively. After inoculation, tracheal mucosal thickness, tracheal mucosal lesions, and numbers of infiltrating CD4⁺CD25^- cells, B-cells, and macrophages were greater in MS-H- and 7NS-inoculated chickens compared with non-inoculated. Inoculation with 7NS induced up-regulation of IFN-γ, while vaccination with MS-H induced up-regulation of IL-17A, when compared with non-inoculated birds. Both inoculated groups had a moderate infiltrate of CD4⁺CD25⁺ T cells in the tracheal mucosa. These findings reveal that the tracheal local cellular response after MS-H inoculation is dominated by a Th-17 response, while that of 7NS-inoculated chickens is dominated by a Th-1 type response.

Study on the mechanism of Mycoplasma gallisepticum infection on chicken tracheal mucosa injury

ABSTRACTMycoplasma gallisepticum (MG) is a pathogenic microorganism that causes serious harm to the poultry industry. It is mainly adsorbed on the cilia and mucosa of respiratory epithelial cells, causing tracheal mucosal damage or cilia loss, causing chronic respiratory disease (CRD). In order to study the effect of MG infection on chicken tracheal mucosa injury and explore its possible mechanism, specific-pathogen-free (SPF) chickens were challenged with Mycoplasma gallisepticum wild-type strain MG-HY. Then, transcriptome sequencing analysis was performed to study the mechanism of MG tracheal mucosal damage. During infection, MG localizes and proliferates in the chicken trachea, and induces mucosal damage. A total of 3112 significantly (P < 0.01) differentially expressed genes (DEGs) were selected by RNA-seq, including 1646 up-regulated genes and 1466 down-regulated genes. Functional analysis showed increased expression levels of genes involved in immune defense response and mechanical barrier of tracheal mucosa in infected chicks. The expression level of pro-inflammatory cytokines (TNF-α) increased, activating the upstream protein Ras of the ERK-MLCK signaling pathway, Ras causing ERK phosphorylation levels to rise and MLCK activation, thus causing phosphationalization of MLC, and further regulating the expression and mucous distribution of tight junction protein (TJ), leading to tracheal mucosal injury in chicks. The results of qRT-PCR assay and immunohistochemical analysis were consistent with the results of transcriptome analysis. Overall, Our findings provide a basis for further research on the underlying mechanism of chick tracheal mucosal damage caused by MG infection, and help to understand how MG induces respiratory immune damage in birds.

A Computational Reverse Vaccinology Approach for the Design and Development of Multi-Epitopic Vaccine Against Avian Pathogen Mycoplasma gallisepticum

Avian mycoplasma is a bacterial disease causing chronic respiratory disease (CRD) in poultry industries with high economic losses. The eradication of this disease still remains as a challenge. A multi-epitope prophylactic vaccine aiming the antigenic proteins of Mycoplasma gallisepticum can be a capable candidate to eradicate this infection. The present study is focused to design a multi-epitope vaccine candidate consisting of cytotoxic T-cell (CTL), helper T-cell (HTL), and B-cell epitopes of antigenic proteins, using immunoinformatics strategies. The multi-epitopic vaccine was designed, and its tertiary model was predcited, which was further refined and validated by computational tools. After initial validation, molecular docking was performed between multi-epitope vaccine construct and chicken TLR-2 and 5 receptors, which predicted effective binding. The in silico results specify the structural stability, precise specificity, and immunogenic response of the designed multi-epitope vaccine, and it could be an appropriate vaccine candidate for the M. gallisepticum infection.

gga-miR-142-3p negatively regulates Mycoplasma gallisepticum (HS strain)-induced inflammatory cytokine production via the NF-κB and MAPK signaling by targeting TAB2

OBJECTIVE

Mycoplasma gallisepticum (MG), a notorious avian pathogen, leads to considerable economic losses in the poultry industry. MG infection is characterized by severe, uncontrollable inflammation and host DNA damage. Micro ribonucleic acids (miRNAs) have emerged as important regulators in microbial pathogenesis. However, the role of miRNAs in MG infection is poorly characterized. In this study, we validated the functional roles of gga-miR-142-3p.

METHODS

The relative expression of gga-miR-142-3p in the lungs of the MG-infected chicken embryos and the MG-infected chicken embryonic fibroblast cell line (DF-1) was determined by reverse transcription quantitative real-time PCR analysis. Bioinformatics database was used to analysis the target gene of gga-miR-142-3p. The luciferase reporter assay as well as gene expression analysis were conducted to validate the target gene. To further explore the biological functions of gga-miR-142-3p upon MG infection, the cell proliferation was quantified using Cell Counting Kit-8 (CCK-8). Meanwhile, cell cycle analysis and apoptosis were measured using a flow cytometer.

RESULTS

gga-miR-142-3p was significantly upregulated in both MG-infected chicken-embryo lungs and the DF-1 cells. gga-miR-142-3p over expression significantly downregulated the expression of pro-inflammatory cytokines, including interleukin-1β, interleukin-6 and tumor necrosis factor alpha after MG infection. Meanwhile, gga-miR-142-3p enhanced the host defense against MG infection by facilitating cell proliferation, promoting cell progression and inhibiting cell apoptosis. Interestingly, TAB2 knockdown groups show similar results, whereas, TAB2 over-expression groups and gga-miR-142-3p inhibitor groups had thoroughly opposite results. The expression of p-p65 in nuclear factor kappa B (NF-κB) and p-p38 in the mitogen-activated protein kinase (MAPK) pathway was decreased when gga-miR-142-3p was over-expressed.

CONCLUSION

Upon MG infection, upregulation of gga-miR-142-3p alleviates inflammation by negatively regulating the signaling pathways of NF-κB and MAPKs by targeting TAB2 and facilitates cell proliferation by inhibiting cell apoptosis and promoting cell cycle progression to defend against MG infection.

Mucosal immune responses in the trachea after chronic infection with Mycoplasma gallisepticum in unvaccinated and vaccinated mature chickens

Tracheitis associated with the chronic respiratory disease in chickens caused by Mycoplasma gallisepticum is marked by infiltration of leukocytes into the mucosa. Although cytokines/chemokines are known to play a key role in the recruitment, differentiation, and proliferation of leukocytes, those that are produced and secreted into the trachea during the chronic stages of infection with M. gallisepticum have not been described previously. In this study, the levels of transcription in the trachea of genes encoding a panel of 13 cytokines/chemokines were quantified after experimental infection with the M. gallisepticum wild-type strain Ap3AS in unvaccinated chickens and chickens vaccinated 40-, 48- or 57-weeks previously with the novel attenuated strain ts-304. These transcriptional levels in unvaccinated/infected and vaccinated/infected chickens were compared with those of unvaccinated/uninfected and vaccinated/uninfected chickens. Pathological changes and subsets of leukocytes infiltrating the tracheal mucosa were concurrently assessed by histopathological examination and indirect immunofluorescent staining. After infection, unvaccinated birds had a significant increase in tracheal mucosal thickness and in transcription of genes for cytokines/chemokines, including those for IFN-γ, IL-17, RANTES (CCLi4), and CXCL-14, and significant downregulation of IL-2 gene transcription. B cells, CD3⁺ or CD4⁺ cells and macrophages (KUL01⁺ ) accumulated in the mucosa but CD8⁺ cells were not detected. In vaccinated birds, the levels of transcription of the genes for IL-6, IL-2, RANTES and CXCL-14 were significantly lower after infection than in the unvaccinated/infected and/or unvaccinated/uninfected birds, while the transcription of the IFN-γ gene was significantly upregulated, and there were aggregations of B cells in the tracheal mucosa. These observations indicated that M. gallisepticum may have suppressed Th2 responses by upregulating secretion of IFN-γ and IL-17 by CD4⁺ cells and induced immune dysregulation characterized by depletion of CD8⁺ cells and downregulation of IL-2 in the tracheas of unvaccinated birds. The ts-304 vaccine appeared to induce long-term protection against this immune dysregulation. TAKE AWAY: The ts-304 vaccine-induced long-term protection against immune dysregulation caused by M. gallisepticum Detection of B cells and plasma cells in the tracheal mucosa suggested that long-term protection is mediated by mucosal B cell memory Infection of unvaccinated birds with M. gallisepticum resulted in CD8⁺ cell depletion and downregulation of IL-2 in the tracheal mucosa, suggestive of immune dysregulation Infection of unvaccinated birds with M. gallisepticum resulted in upregulation of IFN-γ and infiltration of CD4⁺ cells and antigen presenting cells (B and KUL01⁺ cells) into the tracheal mucosa, suggesting enhanced antigen processing and presentation during chronic infection Th2 responses to infection with M. gallisepticum may be dampened by CD4⁺ cells through upregulation of IFN-γ and IL-17 during chronic infection.

Transcriptomic Analysis of Long-Term Protective Immunity Induced by Vaccination With Mycoplasma gallisepticum Strain ts-304

Live attenuated vaccines are commonly used to control Mycoplasma gallisepticum infections in chickens. M. gallisepticum ts-304 is a novel live attenuated vaccine strain that has been shown to be safe and effective. In this study, the transcriptional profiles of genes in the tracheal mucosa in chickens challenged with the M. gallisepticum wild-type strain Ap3AS at 57 weeks after vaccination with ts-304 were explored and compared with the profiles of unvaccinated chickens that had been challenged with strain Ap3AS, unvaccinated and unchallenged chickens, and vaccinated but unchallenged chickens. At two weeks after challenge, pair-wise comparisons of transcription in vaccinated-only, vaccinated-and-challenged and unvaccinated and unchallenged birds detected no differences. However, the challenged-only birds had significant up-regulation in the transcription of genes and enrichment of gene ontologies, pathways and protein classes involved in infiltration and proliferation of inflammatory cells and immune responses mediated through enhanced cytokine and chemokine production and signaling, while those predicted to be involved in formation and motor movement of cilia and formation of the cellular cytoskeleton were significantly down-regulated. The transcriptional changes associated with the inflammatory response were less severe in these mature birds than in the relatively young birds examined in a previous study. The findings of this study demonstrated that vaccination with the attenuated M. gallisepticum strain ts-304 protects against the transcriptional changes associated with the inflammatory response and pathological changes in the tracheal mucosa caused by infection with M. gallisepticum in chickens for at least 57 weeks after vaccination.

Current status of vaccine research, development, and challenges of vaccines for Mycoplasma gallisepticum

Mycoplasma gallisepticum (MG) is an important avian pathogen that causes significant economic losses in the poultry industry. Surprisingly, the limited protection and adverse reactions caused by the vaccines, including live vaccines, bacterin-based (killed) vaccines, and recombinant viral vaccines is still a major concern. Mycoplasma gallisepticum strains vary in infectivity and virulence and infection may sometimes unapparent and goes undetected. Although extensive research has been carried out on the biology of this pathogen, information is lacking about the type of immune response that confers protection and selection of appropriate protective antigens and adjuvants. Regardless of numerous efforts focused on the development of safe and effective vaccine for the control of MG, the use of modern DNA vaccine technology selected in silico approaches for the use of conserved recombinant proteins may be a better choice for the preparation of novel effective vaccines. More research is needed to characterize and elucidate MG products modulating MG-host interactions. These products could be used as a reference for the preparation and development of vaccines to control MG infections in poultry flocks.

Differential Response of the Chicken Trachea to Chronic Infection with Virulent Mycoplasma gallisepticum Strain Ap3AS and Vaxsafe MG (Strain ts-304): a Transcriptional Profile

Mycoplasma gallisepticum is the primary etiological agent of chronic respiratory disease in chickens. Live attenuated vaccines are most commonly used in the field to control the disease, but current vaccines have some limitations. Vaxsafe MG (strain ts-304) is a new vaccine candidate that is efficacious at a lower dose than the current commercial vaccine strain ts-11, from which it is derived. In this study, the transcriptional profiles of the trachea of unvaccinated chickens and chickens vaccinated with strain ts-304 were compared 2 weeks after challenge with M. gallisepticum strain Ap3AS during the chronic stage of infection. After challenge, genes, gene ontologies, pathways, and protein classes involved in inflammation, cytokine production and signaling, and cell proliferation were upregulated, while those involved in formation and motor movement of cilia, formation of intercellular junctional complexes, and formation of the cytoskeleton were downregulated in the unvaccinated birds compared to the vaccinated birds, reflecting immune dysregulation and the pathological changes induced in the trachea by infection with M. gallisepticum Vaccination appears to protect the structural and functional integrity of the tracheal mucosa 2 weeks after infection with M. gallisepticum.

Transcriptional and Pathological Host Responses to Coinfection with Virulent or Attenuated Mycoplasma gallisepticum and Low-Pathogenic Avian Influenza A Virus in Chickens

The avian pathogen Mycoplasma gallisepticum, the etiological agent of chronic respiratory disease in chickens, exhibits enhanced pathogenesis in the presence of a copathogen such as low-pathogenic avian influenza virus (LPAIV). To further investigate the intricacies of this copathogenesis, chickens were monoinfected or coinfected with either virulent M. gallisepticum strain R_low or LPAIV H3N8 (A/duck/Ukraine/1963), with assessment of tracheal histopathology, pathogen load, and transcriptomic host responses to infection by RNA sequencing. Chickens coinfected with M. gallisepticum R_low followed by LPAIV H3N8 exhibited significantly more severe tracheal lesions and mucosal thickening than chickens infected with LPAIV H3N8 alone and greater viral loads than chickens infected first with H3N8 and subsequently with M. gallisepticum R_low Recovery of live M. gallisepticum was significantly higher in chickens infected first with LPAIV H3N8 and then with M. gallisepticum R_low, compared to chickens given a mock infection followed by M. gallisepticum R_low The transcriptional responses to monoinfection and coinfection with M. gallisepticum and LPAIV highlighted the involvement of differential expression of genes such as Toll-like receptor 15, Toll-like receptor 21, and matrix metallopeptidase 1. Pathway and gene ontology analyses of these differentially expressed genes suggest that coinfection with virulent M. gallisepticum and LPAIV induces decreases in the expression of genes related to ciliary activity in vivo and alters multiple immune-related signaling cascades. These data aid in the understanding of the relationship between M. gallisepticum and LPAIV during copathogenesis in the natural host and may contribute to further understanding of copathogen infections of humans and other animals.