Comparison of Experimental Infection of Normal and Immunosuppressed Chickens with Mycoplasma gallisepticum

Development and Evaluation of Mycoplasma gallisepticum Challenge Model in Layer Pullets

Manufacturers of Mycoplasma gallisepticum (MG) modified live vaccines usually recommend a single application at 8 wk of age. This makes 12-16-wk-old layer pullets suitable for challenge studies intended to evaluate these vaccines. Numerous challenge models in different poultry species and ages have been reported. However, there is not an established layer pullet challenge model for this age. The aim of this study is to develop a suitable challenge model in 12-wk-old layer pullets. MG Rlow strain was used as the challenge strain, and its ability to induce clinical signs and lesions in 12-wk-old Hy-Line W-36 layer pullets was evaluated. Three different doses (low, 7.95 × 104 color-changing units [CCU]/bird; medium, 7.95 × 106 CCU/bird; and high, 7.95 × 108 CCU/bird) via three different routes (eye drop, fine spray, and contact infection) were compared and evaluated using different parameters. At 14 days post-challenge, there were no mortalities in any of the groups throughout the study. Layer pullets directly challenged with the high dose via the fine spray route showed the clearest and most consistent results (clinical signs, positive quantitative real-time PCR [qPCR], seroconversion, air sac scoring, and histopathological changes of the tracheal mucosa). Medium and low challenge doses applied via fine spray or eye drop did not show consistent results. Rlow strain was able to spread to the contact infection birds, as confirmed by the positive qPCR results; however, none of the contact-infected birds showed any clinical signs or gross or microscopic lesions. Our results suggest that a high dose (7.95 × 108 CCU/bird) administered through a fine spray route is the model of choice in any future MG vaccine evaluation trials in 12-wk-old layer pullets.

Unmasking the dynamics of Mycoplasma gallisepticum: deciphering HD11 macrophage polarization for innovative infection control strategies

Mycoplasma gallisepticum (MG) is a highly contagious avian respiratory pathogen characterized by rapid spread, widespread distribution, and long-term persistence of infection. Previous studies have shown that chicken macrophage HD11 cells play a critical role in the replication and immunomodulation of MG. Macrophages are multifunctional immunomodulatory cells that polarize into different functions and morphologies in response to exogenous stimuli. However, the effect of MG infection on HD11 polarization is not well understood. In this study, we observed a time-dependent increase in both the expression of the MG-related virulence protein pMGA1.2 and the copy number of MG upon MG infection. Polarization studies revealed an upregulation of M1-type marker genes in MG-infected HD11 cells, suggesting that MG mainly induces HD11 macrophages towards M1-type polarization. Furthermore, MG activated the inflammatory vesicle NLRP3 signaling pathway, and NLRP3 inhibitors affected the expression of M1 and M2 marker genes, indicating the crucial regulatory role of the NLRP3 signaling pathway in MG-induced polarization of HD11 macrophages. Our findings reveal a novel mechanism of MG infection, namely the polarization of MG-infected HD11 macrophages. This discovery suggests that altering the macrophage phenotype to inhibit MG infection may be an effective control strategy. These findings provide new perspectives on the pathogenic mechanism and control measures of MG.

Inflammatory responses and barrier disruption in the trachea of chicks following Mycoplasma gallisepticum infection: a focus on the TNF-α-NF-κB/MLCK pathway

Mycoplasma gallisepticum (MG) can induce persistent inflammatory damage to the tracheal mucosa of poultry and cause chronic respiratory diseases in chickens. To further investigate the mechanism of MG-induced injury to the tracheal mucosa, we used chick embryo tracheal organ culture (TOC) as a model to study the invasion and reproduction of MG, the effect of MG on tracheal morphology, and the potential factors that promote MG tissue invasion. The results showed that MG infection significantly damaged the tracheal epithelial structure and weakened tracheal epithelial barrier function; MG also increased the occurrence of bacterial displacement, with a significant (p < 0.05) increase in the bacterial load of the infected TOCs at 5 and 7 days post-infection. In addition, MG significantly (p < 0.05) increased the expression levels of inflammatory cytokines, such as TNF-α, interleukin-1β (IL-1β), and IL-6, and activated the NF-κB signalling pathway, leading to increased nuclear translocation of NF-κB p65. Simultaneously, the map kinase pathway (MAPK) was activated. This activation might be associated with increased myosin light chain (MLC) phosphorylation, which could lead to actin-myosin contraction and disruption of tight junction (TJ) protein function, potentially compromising epithelial barrier integrity and further catalysing MG migration into tissues. Overall, our results contribute to a better understanding of the interaction between MG and the host, provide insight into the mechanisms of damage to the tracheal mucosa induced by MG infection, and provide new insights into the possible pathways involved in Mycoplasma gallisepticum infection in vivo.

Andrographolide restored production performances and serum biochemical indexes and attenuated organs damage in Mycoplasma gallisepticum-infected broilers

1. This study aimed to study the preventive and therapeutic effects of andrographolide (Andro) during Mycoplasma gallisepticum HS strain (MG) infection in ArborAcres (AA) broilers.2. The minimum inhibitory concentration (MIC) of Andro against MG was measured. Broiler body weight, feed efficiency, morbidity, cure rate and mortality were recorded during the experiment. Air sac lesion scores and immune organ index were calculated. Expression of pMGA1.2 in lung tissue and serum biochemical indices were examined. Histopathological examinations of immune organs, liver, trachea and lung tissue were conducted by Haematoxylin and Eosin stain.3. MIC was 3.75 μg/mL and Andro significantly inhibited the expression of pMGA1.2 (P ≤ 0.05). Compared with control MG-infected group, Andro low-dose and high-dose prevention reduced the morbidity of chronic respiratory disease in 40.00% and 50.00%, respectively. Mortality of C, D and E group was 16.67%, 10.00% and 6.67%, respectively. Cure rate of E, F, G and H group was 92.00%, 92.86%, 93.33% and 100.0%, respectively. Compared with control MG-infected group, Andro treatment significantly increased average weight gain (AWG), relative weight gain rate (RWG) and feed conversion rate (FCR) at 18 to 24 days (P ≤ 0.05). Compared with control group, Andro alone treatment significantly increased AWG in broilers (P ≤ 0.05).4. Compared with control MG-infected group, Andro significantly attenuated MG-induced air sac lesion, immune organs, liver, trachea and lung damage in broilers. Andro alone treatment did not induce abnormal morphological changes in these organs in healthy broilers. Serum biochemical analysis results showed, comparing with control MG-infected group, Andro significantly decreased the content of total protein, albumin, globulin, alanine aminotransferase, aspartate aminotransferase, total bilirubin, urea, creatinine, uric acid, total cholesterol, and increased the albumin/globulin ratio and content of alkaline phosphatase, apolipoprotein B and apolipoprotein A-I in a dose-dependent manner (P ≤ 0.05).5. Andro could act as a potential agent against MG infection in broilers.

Polypharmacology-based approach for screening TCM against coinfection of Mycoplasma gallisepticum and Escherichia coli

Natural products and their unique polypharmacology offer significant advantages for finding novel therapeutics particularly for the treatment of complex diseases. Meanwhile, Traditional Chinese Medicine exerts overall clinical benefits through a multi-component and multi-target approach. In this study, we used the previously established co-infection model of Mycoplasma gallisepticum and Escherichia coli as a representative of complex diseases. A new combination consisting of 6 herbs were obtained by using network pharmacology combined with transcriptomic analysis to reverse screen TCMs from the Chinese medicine database, containing Isatdis Radix, Forsythia Fructus, Ginkgo Folium, Mori Cortex, Licorice, and Radix Salviae. The results of therapeutic trials showed that the Chinese herbal compounds screened by the target network played a good therapeutic effect in the case of co-infection. In summary, these data suggested a new method to validate target combinations of natural products that can be used to optimize their multiple structure-activity relationships to obtain drug-like natural product derivatives.

Evaluation of Glycyrrhizic Acid Therapeutic Effect and Safety in Mycoplasma gallisepticum (HS Strain)-Infected Arbor Acres Broilers

This study was conducted to evaluate the therapeutic effects and safety of GA in MG-infected broilers. Our results showed that the minimum inhibitory concentration of GA was 31.25 μg/mL. Moreover, GA inhibited the expression of MG adhesion protein (pMGA1.2) in the broilers' lungs. GA treatment clearly decreased the morbidity of CRD and mortality in the MG-infected broilers. Compared with the model group, GA treatment significantly decreased gross air sac lesion scores and increased average weight gain and feed conversion rate in the MG-infected broilers. Histopathological examination showed GA treatment attenuated MG-induced trachea, immune organ and liver damage in the broilers. Moreover, GA treatment alone did not induce abnormal morphological changes in these organs in the healthy broilers. Compared with the model group, serum biochemical results showed GA treatment significantly decreased the content of total protein, albumin, globulin, alanine aminotransferase, aspartate aminotransferase, total bilirubin, creatinine, uric acid, total cholesterol, and increased the content of albumin/globulin, alkaline phosphatase, apolipoprotein B and apolipoprotein A-I. In conclusion, GA displayed a significant therapeutic efficacy regarding MG infection and had no adverse effects on the broilers (100 mg/kg/d).

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.

Methylsulfonylmethane ameliorates inflammation via NF-κB and ERK/JNK-MAPK signaling pathway in chicken trachea and HD11 cells during Mycoplasma gallisepticum infection

Mycoplasma gallisepticum (MG) is an avian pathogen that commonly causes respiratory diseases in poultry. Methylsulfonylmethane (MSM) is a sulfur-containing natural compound that could alleviate inflammatory injury through its excellent anti-inflammatory and antioxidant properties. However, it is still unclear whether MSM prevents MG infection. The purpose of this study is to determine whether MSM has mitigative effects on MG-induced inflammatory injury in chicken and chicken like macrophages (HD11 cells). In this research, White Leghorn chickens and HD11 cells were used to build the MG-infection model. Besides, the protective effects of MSM against MG infection were evaluated by detecting MG colonization, histopathological changes, oxidative stress and inflammatory injury of trachea, and HD11 cells. The results revealed that MG infection induced inflammatory injury and oxidative stress in trachea and HD11 cells. However, MSM treatment significantly ameliorated oxidative stress, partially alleviated the abnormal morphological changes and reduced MG colonization under MG infection. Moreover, MSM reduced the mRNA expression of proinflammatory cytokines-related genes and decreased the number of death cells under MG infection. Importantly, the protective effects of MSM were associated with suppression of nuclear factor-kappa B (NF-κB) and extracellular signal-related kinases (ERK)/Jun amino terminal kinases (JNK)-mitogen-activated protein kinases (MAPK) pathway in trachea and HD11 cells. These results proved that MSM has protective effects on MG-induced inflammation in chicken, and supplied a better strategy for the protective intervention of this disease.

An overview of pharmacological activities of baicalin and its aglycone baicalein: New insights into molecular mechanisms and signaling pathways

The flavonoids, baicalin, and its aglycone baicalein possess multi-fold therapeutic properties and are mainly found in the roots of Oroxylum indicum (L.) Kurz and Scutellaria baicalensis Georgi. These flavonoids have been reported to possess various pharmacological properties, including antibacterial, antiviral, anticancer, anticonvulsant, anti-oxidant, hepatoprotective, and neuroprotective effects. The pharmacological properties of baicalin and baicalein are due to their abilities to scavenge reactive oxygen species (ROS) and interaction with various signaling molecules associated with apoptosis, inflammation, autophagy, cell cycle, mitochondrial dynamics, and cytoprotection. In this review, we summarized the molecular mechanisms underlying the chemopreventive and chemotherapeutic applications of baicalin and baicalein in the treatment of cancer and inflammatory diseases. In addition, the preventive effects of baicalin and baicalein on mitochondrial dynamics and functions were highlighted with a particular emphasis on their anti-oxidative and cytoprotective properties. The current review highlights could be useful for future prospective studies to further improve the pharmacological applications of baicalein and baicalin. These studies should define the threshold for optimal drug exposure, dose optimization and focus on therapeutic drug monitoring, objective disease markers, and baicalin/baicalein drug levels.

Baicalin alleviates Mycoplasma gallisepticum-induced oxidative stress and inflammation via modulating NLRP3 inflammasome-autophagy pathway

Baicalin is a well-known flavonoid compound, possess therapeutic potential against inflammatory diseases. Previous studies reported that Mycoplasma gallisepticum (MG) induced inflammatory response and immune dysregulation inside the host body. However, the underlying molecular mechanisms of baicalin against MG-infected chicken-like macrophages (HD11 cells) are still illusive. Oxidant status and total reactive oxygen species (ROS) were detected by ELISA assays and flow cytometry respectively. Mitochondrial membrane potential (ΔΨ_M) was evaluated by immunofluorescence microscopy. Transmission electron microscopy was used for ultrastructural analysis. The hallmarks of inflammation and autophagy were determined by western blotting. Oxidative stress and reactive oxygen species (ROS) were significantly enhanced in the MG-infected HD11 cells. MG infection caused disruption in the mitochondrial membrane potential (ΔΨ_M) compared to the control conditions. Meanwhile, baicalin treatment reduced MG-induced reactive oxygen species (ROS), oxidative stress and alleviated the disruption in ΔΨ_M. The activities of inflammatory markers were significantly enhanced in the MG-infected HD11 cells. Increased protein expressions of TLR-2-NF-κB pathway, NLRP3-inflammasome and autophagy-related proteins were detected in the MG-infected HD11 cells. Besides, baicalin treatment significantly reduced the protein expressions of TLR-2-NF-κB pathway and NLRP3 inflammasome. While, the autophagy-related proteins were significantly enhanced with baicalin treatment in a dose-dependent manner in the MG-infected HD11 cells. The results showed that baicalin prevented HD11 cells from MG-induced oxidative stress and inflammation via the opposite modulation of TLR-2-NF-κB-mediated NLRP3-inflammasome pathway and autophagy, and baicalin could be a promising candidate for the prevention of inflammatory effects caused by MG-infection in macrophages.

Pharmacokinetic/pharmacodynamic profiles of baicalin against Mycoplasma gallisepticum in an in vivo infection model

Mycoplasma gallisepticum (M. gallisepticum), a devastating avian pathogen that commonly causes chronic respiratory disease in chicken, is responsible for tremendous economic losses to the poultry industry. Baicalin is the main constituent of Scutellaria baicalensis that shows potential therapeutic effects against M. gallisepticum. However, the pharmacokinetic/pharmacodynamics (PK/PD) profiles of baicalin against M. gallisepticum are not well understood. The main objective of the present study was to determine the relationship between the PK/PD index and efficacy of baicalin in the M. gallisepticum infection model in chickens. The experiments were carried out on 10-day-old chickens that were challenged with M. gallisepticum in the bilateral air sacs. While, baicalin was orally administrated once in a day for 3 consecutive days, started from d 3 postinfection. Ultra-performance liquid chromatography (UPLC) was used to evaluate the PK parameters of baicalin at doses of 200, 400, and 600 mg/kg in M. gallisepticum-infected chickens. Real-time PCR (RT-PCR) was used for the quantitative detection of M. gallisepticum in lungs. The PK and PD data were fitted to WinNonlin software to evaluate the PK/PD profiles of baicalin against M. gallisepticum. The minimum inhibitory concentration (MIC) of baicalin against M. gallisepticum strain R_low was 31.25 µg/mL. The in vivo data suggested that baicalin concentration in the lung tissues was higher than plasma (1.21–1.73 times higher). The ratios of AUC_24h/MIC of baicalin against bacteriostatic, bactericidal, and eradication were 0.62, 1.33, and 1.49 h, respectively. In conclusion, these results provided potential reference for future clinical dose selection of baicalin and evaluation of susceptibility breakpoints.

Effects of immunosuppression on the efficacy of vaccination against Mycoplasma gallisepticum infection in chickens

Immunosuppression can increase the susceptibility of chickens to other disease-causing pathogens and interfere with the efficacy of vaccination against those pathogens. Chicken anaemia virus (CAV) and infectious bursal disease virus (IBDV) are common causes of immunosuppression in chickens. Immunosuppression was induced by experimental infection with either CAV or IBDV to assess the effect of immunosuppression on the efficacy of vaccination with Mycoplasma gallisepticum strain ts-304 against infection with virulent M. gallisepticum, a common bacterial pathogen of chickens worldwide. Birds were experimentally infected with either CAV or IBDV at 1 week of age, before vaccination and challenge with M. gallisepticum to examine the effect of immunosuppression at the time of vaccination, or at 6 weeks of age, after vaccination against M. gallisepticum but before challenge with virulent M. gallisepticum, to investigate the effect of immunosuppression at the time of challenge. All birds were vaccinated with a single dose of the ts-304 vaccine at 3 weeks of age and experimentally challenged with the virulent M. gallisepticum strain Ap3AS at 8 weeks of age. In immunosuppressed chickens there was a reduction in protection offered by the ts-304 vaccine at two weeks after challenge, as measured by tracheal mucosal thicknesses, serum antibody levels against M. gallisepticum, air sac lesion scores and virulent M. gallisepticum load in the trachea. Immunosuppressed birds with detectable serum antibodies against M. gallisepticum were less likely to have tracheal lesions. This study has shown that immunosuppression caused by infection with CAV or IBDV can interfere with vaccination against mycoplasmosis in chickens.

Arachidonic acid metabolism is elevated in Mycoplasma gallisepticum and Escherichia coli co-infection and induces LTC4 in serum as the biomarker for detecting poultry respiratory disease

Outbreaks of multiple respiratory diseases with high morbidity and mortality have been frequently reported in poultry industry. Metabolic profiling has showed widespread usage in metabolic and infectious disease for identifying biomarkers and understanding of complex mechanisms. In this study, the non-targeted metabolomics were used on Mycoplasma gallisepticum (MG) and Escherichia coli (E.coli) co-infection model in serum, which showed that Leukotriene C4 (LTC4), Leukotriene D4 (LTD4), Chenodeoxycholate, Linoleate and numerous energy metabolites were varied significantly. KEGG enrichment analysis revealed that the metabolic pathways of linoleic acid, taurine and arachidonic acid (AA) were upregulated. To further characterize the consequences of co-infection, we performed an AA metabolic network pathway with metabolic products and enzyme genes. The results showed that the expression of LTC4 increased extremely significant and accompanied with different degree of infection. Meanwhile, the AA network performed the changes and differences of various metabolites in the pathway when multiple respiratory diseases occurred. Taken together, co-infection induces distinct alterations in the serum metabolome owing to the activation of AA metabolism. Furthermore, LTC4 in serum could be used as the biomarker for detecting poultry respiratory disease.

Abbreviations

MG: Mycoplasma gallisepticum; E.coli: Escherichia coli; AA: Arachidonic acid; LTC4: Leukotriene C4; CRD: chronic respiratory diseases; KEGG: Kyoto Encyclopedia of Genes and Genomes; LTs: leukotrienes; PGs: prostaglandins; NO: nitric oxide; HIS: histamine; PCA: Principal Component Analysis; PLS-DA: Partial Least Squares Discriminant Analysis; CCU: color change unit; UPLC: ultra-performance liquid chromatography; MS: mass spectrometry; DEMs: differentially expressed metabolites; ELISA: enzyme-linked immunosorbent assay; SD: standard deviation; VIP: Variable importance in the projection

Baicalin attenuated Mycoplasma gallisepticum-induced immune impairment in chicken bursa of fabricius through modulation of autophagy and inhibited inflammation and apoptosis

BACKGROUND

Mycoplasma gallisepticum (MG) is the primary etiologic agent of chronic respiratory disease in poultry. However, the mechanism underlying MG-induced immune dysregulation in chicken is still elusive. Baicalin shows excellent anti-bacterial, anti-inflammatory, anti-carcinogenic and anti-viral properties. In the present study, the preventive effects of baicalin against immune impairment in chicken bursa of fabricius (BF) were studied in an MG infection model.

RESULTS

Histopathological examination showed increased inflammatory cell infiltrations and fragmented nuclei in the model group. Ultrastructural analysis revealed the phenomenon of apoptosis in bursal cells, along with the deformation of mitochondrial membrane and swollen mitochondria in the model group. However, these abnormal morphological changes were partially alleviated by baicalin. Meanwhile, baicalin treatment attenuated the level of proinflammatory cytokines, and suppressed nuclear factor-kappa B expression at both protein and mRNA level. Terminal deoxynucleotidyl transferase-mediated dUTP nick endlabeling assay showed extensive apoptosis in BF in the model group. The mRNA and protein expression levels of apoptosis-related genes were upregulated in BF, while baicalin treatment significantly alleviated apoptosis in BF. In addition, alterations in mRNA and protein expression levels of autophagy-related genes and mitochondrial dynamics proteins were significantly alleviated by baicalin. Moreover, baicalin treatment significantly attenuated MG-induced decrease in CD8⁺ cells and reduced bacterial load in chicken BF compared to the model group.

CONCLUSIONS

These results suggested that baicalin could effectively inhibit MG-induced immune impairment and alleviate inflammatory responses and apoptosis in chicken BF. © 2020 Society of Chemical Industry.

Polydatin attenuates Mycoplasma gallisepticum (HS strain)-induced inflammation injury via inhibiting the TLR6/ MyD88/NF-κB pathway

Mycoplasma gallisepticum (MG) infection is the main cause of chronic respiratory disease (CRD) characterized by severe respiratory inflammation in chickens. Polydatin (PD) is a resveratrol glycoside isolated from Polygonum cuspidatum, which has prominent anti-inflammatory effect. The purpose of this study was to investigate the therapeutic effect of PD against MG-induced inflammation in chicken and its underlying mechanism. Histopathological analysis showed that PD treatment (15, 30, and 45 mg/kg) apparently alleviated MG-induced pathological changes of chicken embryonic lung. In chicken embryo fibroblast (DF-1) cells, PD treatment (15, 30, and 60 μg/mL) could effectively suppress MG propagation, promote MG-infected cell proliferation and cell cycle progress, and inhibit MG-induced cell apoptosis. ELISA and qPCR assays showed that PD treatment significantly suppressed the expression of interleukin-6 (IL-6), IL-1β and tumor necrosis factor-α (TNF-α) induced by MG both in vivo and in vitro. Besides, molecular studies indicated that the MG-induced levels of toll-like receptor-6 TLR6, myeloid differentiation-88 (MyD88) and nuclear factor κB (NF-κB) were significantly decreased by PD treatment. Moreover, immunofluorescence analysis showed that PD treatment restrained the MG-induced NF-κB-p65 nuclear translocation. Taken together, these results indicate the protective effects of PD against MG-induced inflammation injury in chicken were mainly by inhibiting the TLR6/MyD88/NF-κB pathway.

Baicalin inhibits inflammation caused by coinfection of Mycoplasma gallisepticum and Escherichia coli involving IL-17 signaling pathway

Coinfection of Mycoplasma gallisepticum (MG) and Escherichia coli (E. coli) is frequently reported in poultry farms. Baicalin possess various pharmacological properties such as anti-inflammatory, anticancer, and antioxidant, etc. However, the protective effects of baicalin against coinfection of MG and E. coli are still elusive. In this study, baicalin (450 mg/kg) treatment was started on day 13 after infection and continued for 5 d. Histopathological examination, qRT-PCR, ELISA, and molecular docking technique were used to evaluate the effects of baicalin on MG and E. coli coinfection in chicken lung and trachea. The results showed that coinfection caused severe lesions in the lung and tracheal tissues. However, baicalin treatment partially alleviated these lesions in coinfection group. Histopathological examination showed the alveolar spaces and mucosal layer thickening was restored and cilia gradually recovered with baicalin treatment compared in coinfection group and MG-infection group. Meanwhile, IL-17 singling pathway–related genes were significantly reduced (P < 0.05) in baicalin treatment group in lung, including IL-17C, TRAF6, NF-κB, CXCL1, CXCL2, MMP1, GM-CSF, and MUC5AC. The activities of cytokines and chemokines (CXCL1, CXCL2, MMP1, GMCSF, and MUC5AC) were decreased significantly (P < 0.05) in baicalin-treated group. The molecular docking of baicalin and NF-κB showed the highest fitness score and interaction. From these results, it has been suggested that baicalin proved effective against coinfection of MG and E. coli in chicken and provided scientific basis for further dose–response and drug–target interaction studies.

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.

Mycoplasma gallisepticum Infection Impaired the Structural Integrity and Immune Function of Bursa of Fabricius in Chicken: Implication of Oxidative Stress and Apoptosis

Mycoplasma gallisepticum (MG) induces a dysregulated immune response in the lungs and air ways of poultry. However, the mechanism of MG-induced immune dysregulation is still not completely understood. In the present study, the effect of MG-infection on chicken bursa of fabricius (BOF) is investigated. Histopathology, electron microscopy, TUNEL assay, qRT-PCR and western blot were employed to examine the hallmarks of oxidative stress and apoptosis. The data revealed that MG-infection induced oxidative stress and decreased antioxidant responses in BOF tissues compared to control group. Histopathological study showed pathological changes including reduction in lymphocytes and increased inflammatory cell infiltration in MG-infection group. Ultrastructural assessment represents obvious signs of apoptosis such as mitochondrial swelling, shrinkage of nuclear membrane and fragmentation of nucleus. Increased cytokine activities were observed in MG-infection group compared to control group. Meanwhile, the mRNA and protein expression level of apoptosis-related genes were significantly (p < 0.05) upregulated in MG-infection group. Terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assay further confirmed that MG induced apoptosis in BOF tissues as TUNEL-stained positive nuclei were remarkably increased in MG-infection group. In addition, MG-infection significantly reduced the number of CD8⁺ lymphocytes in chicken BOF at day 7. Moreover, bacterial load significantly increased at day 3 and day 7 in MG-infection group compared to control group. These results suggested that MG-infection impaired the structural integrity, induced oxidative stress and apoptosis in chicken BOF tissues, which could be the possible causes of damage to immune function in chicken BOF.