Mycoplasma hyopneumoniae inhibits the unfolded protein response to prevent host macrophage apoptosis and M2 polarization.

Enzootic pneumonia caused by Mycoplasma hyopneumoniae (M. hyopneumoniae) has inflicted substantial economic losses on the global pig industry. The progression of M. hyopneumoniae induced-pneumonia is associated with lung immune cell infiltration and extensive proinflammatory cytokine secretion. Our previous study established that M. hyopneumoniae disrupts the host unfolded protein response (UPR), a process vital for the survival and immune function of macrophages. In this study, we demonstrated that M. hyopneumoniae targets the UPR- and caspase-12-mediated endoplasmic reticulum (ER)-associated classical intrinsic apoptotic pathway to interfere with host cell apoptosis signaling, thereby preserving the survival of host tracheal epithelial cells (PTECs) and alveolar macrophages (PAMs) during the early stages of infection. Even in the presence of apoptosis inducers, host cells infected with M. hyopneumoniae exhibited an anti-apoptotic potential. Further analyses revealed that M. hyopneumoniae suppresses the three UPR branches and their induced apoptosis. Interestingly, while UPR activation typically drives host macrophages toward an M2 polarization phenotype, M. hyopneumoniae specifically obstructs this process to maintain a proinflammatory phenotype in the host macrophages. Overall, our findings propose that M. hyopneumoniae inhibits the host UPR to sustain macrophage survival and a proinflammatory phenotype, which may be implicated in its pathogenesis in inducing host pneumonia.

Designing a smallpox B-cell and T-cell multi-epitope subunit vaccine using a comprehensive immunoinformatics approach.

Smallpox is a highly contagious human disease caused by the variola virus. Although the disease was eliminated in 1979 due to its highly contagious nature and historical pathogenicity, with a mortality rate of up to 30%, this virus is an important candidate for biological weapons. Currently, vaccines are the critical measures to prevent this virus infection and spread. In this study, we designed a peptide vaccine using immunoinformatics tools, which have the potential to activate human immunity against variola virus infection efficiently. The design of peptides derives from vaccine-candidate proteins showing protective potential in vaccinia WR strains. Potential non-toxic and nonallergenic T-cell and B-cell binding and cytokine-inducing epitopes were then screened through a priority prediction using special linkers to connect B-cell epitopes and T-cell epitopes, and an appropriate adjuvant was added to the vaccine construction to enhance the immunogenicity of the peptide vaccine. The 3D structure display, docking, and free energy calculation analysis indicate that the binding affinity between the vaccine peptide and Toll-like receptor 3 is high, and the vaccine receptor complex is highly stable. Notably, the vaccine we designed is obtained from the protective protein of the vaccinia and combined with preventive measures to avoid side effects. This vaccine is highly likely to produce an effective and safe immune response against the variola virus infection in the body. IMPORTANCE: In this work, we designed a vaccine with a cluster of multiple T-cell/B-cell epitopes, which should be effective in inducing systematic immune responses against variola virus infection. Besides, this work also provides a reference in vaccine design for preventing monkeypox virus infection, which is currently prevalent.

Mycoplasma glycine cleavage system key subunit GcvH is an apoptosis inhibitor targeting host endoplasmic reticulum.

Mycoplasmas are minimal but notorious bacteria that infect humans and animals. These genome-reduced organisms have evolved strategies to overcome host apoptotic defense and establish persistent infection. Here, using Mycoplasma bovis as a model, we demonstrate that mycoplasma glycine cleavage system (GCS) H protein (GcvH) targets the endoplasmic reticulum (ER) to hijack host apoptosis facilitating bacterial infection. Mechanically, GcvH interacts with the ER-resident kinase Brsk2 and stabilizes it by blocking its autophagic degradation. Brsk2 subsequently disturbs unfolded protein response (UPR) signaling, thereby inhibiting the key apoptotic molecule CHOP expression and ER-mediated intrinsic apoptotic pathway. CHOP mediates a cross-talk between ER- and mitochondria-mediated intrinsic apoptosis. The GcvH N-terminal amino acid 31-35 region is necessary for GcvH interaction with Brsk2, as well as for GcvH to exert anti-apoptotic and potentially pro-infective functions. Notably, targeting Brsk2 to dampen apoptosis may be a conserved strategy for GCS-containing mycoplasmas. Our study reveals a novel role for the conserved metabolic route protein GcvH in Mycoplasma species. It also sheds light on how genome-reduced bacteria exploit a limited number of genomic proteins to resist host cell apoptosis thereby facilitating pathogenesis.

A candidate competitive ELISA based on monoclonal antibody 3A8 for diagnosis of contagious bovine pleuropneumonia.

For the development of a competitive ELISA (cELISA) to detect serum antibodies against the Mycoplasma mycoides subsp. Mycoides (Mmm) (strain PG1), the causative agent of contagious bovine pleuropneumonia (CBPP), all the proteins of this pathogen were analyzed. Then, a specific extracellular region of a transmembrane protein with the potential for diagnosis was identified. After that, a monoclonal antibody (Mab) named 3A8 was obtained using this extracellular region as an immunogen. Finally, a cELISA was established with the extracellular domain of this transmembrane protein as the coating antigen, Mab 3A8 as the competitive antibody, and HRP-labeled goat anti-mouse IgG as the enzyme-labeled antibody. This established method was used to detect the antibody dynamic regularity of goats which are artificially immunized Mmm and was also compared with a commercial ELISA kit. Further, the sera of 1011 different cattle from border provinces of China were monitored using a candidate Mab 3A8 cELISA. The detection results of known background sera used in this study indicate that a candidate diagnostic marker was successfully identified by analyzing all the coding proteins of Mmm in this research, and the cELISA established based on the Mab 3A8 against this protein can detect CBPP-positive serum with specificity and has no cross-reaction with other related epidemic disease-positive sera. In addition, we tested the sera collected from the border areas of China using the established ELISA, and no positive sample was detected. The research protocol of the CBPP cELISA established in this study is different from the traditional method, which can greatly reduce the investment of manpower and capital and save development time. We believe that this study's protocol could serve as a reference for the development of detection methods for mycoplasma and other complex pathogens. KEY POINTS: • A Mmm-specific diagnostic marker was obtained based on protein characteristics. • A cELISA was established for CBPP serum antibody detection. • The serological investigation was conducted for CBPP in the border areas of China.

Mycoplasma hyopneumoniae membrane protein Mhp271 interacts with host UPR protein GRP78 to facilitate infection.

The unfolded protein response (UPR) plays a crucial role in Mycoplasma hyopneumoniae (M. hyopneumoniae) pathogenesis. We previously demonstrated that M. hyopneumoniae interferes with the host UPR to foster bacterial adhesion and infection. However, the underlying molecular mechanism of this UPR modulation is unclear. Here, we report that M. hyopneumoniae membrane protein Mhp271 interacts with host GRP78, a master regulator of UPR localized to the porcine tracheal epithelial cells (PTECs) surface. The interaction of Mhp271 with GRP78 reduces the porcine beta-defensin 2 (PBD-2) production, thereby facilitating M. hyopneumoniae adherence and infection. Furthermore, the R1-2 repeat region of Mhp271 is crucial for GRP78 binding and the regulation of PBD-2 expression. Intriguingly, a coimmunoprecipitation (Co-IP) assay and molecular docking prediction indicated that the ATP, rather than the substrate-binding domain of GRP78, is targeted by Mhp271 R1-2. Overall, our findings identify host GRP78 as a target for M. hyopneumoniae Mhp271 modulating the host UPR to facilitate M. hyopneumoniae adherence and infection.

Development of an ELISA for distinguishing convalescent sera with Mycoplasma hyopneumoniae infection from hyperimmune sera responses to bacterin vaccination in pigs.

Vaccination with inactivated bacterin is the most popular and practical measure to control enzootic pneumonia. After immunisation with inactivated bacterin, Mycoplasma hyopneumoniae colonised on the respiratory tract and lung stimulates the humoural immune responses and produces IgG and IgA antibodies. ELISA is a widely used serological method to detect M. hyopneumoniae antibodies. However, commercial IgG-ELISA kit cannot distinguish between inactivated bacterin-induced hyperimmune sera and convalescent sera stimulated by natural infection. SIgA-ELISA method needs to collect nasal swabs, but collecting nasal swabs is not easy to operate. Establishment of a discriminative ELISA detecting humoural IgG from convalescent sera but not hyperimmune sera facilitates to evaluate the natural infection of M. hyopneumoniae after inactivated bacterin vaccination. We expressed and purified a recombinant protein named Mhp366-N which contains an epitope recognised by the convalescent sera but not hyperimmune sera. The developed discriminative IgG-ELISA could discriminate between inactivated bacterin-induced hyperimmune sera and convalescent sera and was reproducible, sensitive and specific to M. hyopneumoniae antibody produced by natural infection. Compared to SIgA-ELISA method, discriminative IgG-ELISA was more convenient to detect IgG antibody from sera than IgA from nasal swabs, although it has limited sensitivity in the early stages of infection. Additionally, to some extent, it has a potential to avoid the interference of maternally derived IgG antibodies. The established discriminative IgG-ELISA was efficient to judge the serological IgG antibodies induced from natural infection or inactivated vaccine stimulation and provided a useful method to investigate and evaluate the live organism infection after the application of inactivated bacterin.

Mycoplasma hyopneumoniae evades complement activation by binding to factor H via elongation factor thermo unstable (EF-Tu).

Mycoplasmas persist in the host for a long time, suggesting that they possess mechanisms for immune evasion. Factor H is a negative regulator of the complement system, which binds to host cells to avoid unexpected complement activation. In this study, we revealed that many mycoplasmas, such as Mycoplasma hyopneumoniae, Mycoplasma hyorhinis, Mycoplasma hyosynoviae, Mycoplasma gallisepticum, Mycoplasma pneumoniae, Mycoplasma genitalium, Mycoplasma flocculare, and Mycoplasma bovis could hijack factor H such that they present themselves as a host tissue and thus escape from complement attack. Furthermore, the mechanism of recruiting factor H was identified in M. hyopneumoniae. M. hyopneumoniae binds factor H via factor H binding proteins, such as elongation factor thermo unstable (EF-Tu), P146, pyruvate dehydrogenase (acetyl-transferring) E1 component subunit alpha (PdhA), P46, Pyruvate dehydrogenase E1 component subunit beta (PdhB), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and three different hypothetical proteins. The binding of factor H by EF-Tu further contributes to decreased C3 deposition on the M. hyopneumoniae surface and ultimately blocks further complement activation. In fact, binding of factor H occurs in a multifactorial manner; factor H is not only exploited by M. hyopneumoniae via its regulator activity to help mycoplasmas escape from complement killing, but also increases M. hyopneumoniae adhesion to swine tracheal epithelial cells, partially through EF-Tu. Meanwhile, the high sequence identity among EF-Tu proteins in the above-mentioned mycoplasmas implied the universality of the mechanism. This is the first report that mycoplasmas can escape complement killing by binding to factor H.

Functional Identification and Structural Analysis of a New Lipoate Protein Ligase in Mycoplasma hyopneumoniae.

Mycoplasma hyopneumoniae (M. hyopneumoniae) is the causative agent of pandemic pneumonia among pigs, namely, swine enzootic pneumonia. Although M. hyopneumoniae was first identified in 1965, little is known regarding its metabolic pathways, which might play a pivotal role during disease pathogenesis. Lipoate is an essential cofactor for enzymes important for central metabolism. However, the lipoate metabolism pathway in M. hyopneumoniae is definitely unclear. Here, we identified a novel gene, lpl, encoding a lipoate protein ligase in the genome of M. hyopneumoniae (Mhp-Lpl). This gene contains 1,032 base pairs and encodes a protein of 343 amino acids, which is between 7.5 and 36.09% identical to lipoate protein ligases (Lpls) of other species. Similar to its homologs in other species, Mhp-Lpl catalyzes the ATP-dependent activation of lipoate to lipoyl-AMP and the transfer of the activated lipoyl onto the lipoyl domains of M. hyopneumoniae GcvH (Mhp H) in vitro. Enzymatic and mutagenesis analysis indicate that residue K56 within the SKT sequence of Mhp H protein is the lipoyl moiety acceptor site. The three-dimensional structure showed typical lipoate protein ligase folding, with a large N-terminal domain and a small C-terminal domain. The large N-terminal domain is responsible for the full enzymatic activity of Mhp-Lpl. The identification and characterization of Mhp-Lpl will be beneficial to our understanding of M. hyopneumoniae metabolism. Summary: Lipoic acid is an essential cofactor for the activation of some enzyme complexes involved in key metabolic processes. Lipoate protein ligases (Lpls) are responsible for the metabolism of lipoic acid. To date, little is known regarding the Lpls in M. hyopneumoniae. In this study, we identified a lipoate protein ligase of M. hyopneumoniae. We further analyzed the function, overall structure and ligand-binding site of this protein. The lipoate acceptor site on M. hyopneumoniae GcvH was also identified. Together, these findings reveal that Lpl exists in M. hyopneumoniae and will provide a basis for further exploration of the pathway of lipoic acid metabolism in M. hyopneumoniae.

Mycoplasma hyopneumoniae Inhibits Porcine Beta-Defensin 2 Production by Blocking the Unfolded Protein Response To Facilitate Epithelial Adhesion and Infection.

Mycoplasma hyopneumoniae causes the disease porcine enzootic pneumonia, a highly contagious and chronic disease affecting pigs. Understanding the molecular mechanisms of its pathogenicity is critical for developing effective interventions to control this swine respiratory disease. Here, we describe a novel virulence mechanism by which M. hyopneumoniae interferes with the host unfolded protein response (UPR) and eventually facilitates bacterial adhesion and infection. We observed that M. hyopneumoniae infection suppressed the UPR target molecules GRP78 and CHOP by reducing PKR-like endoplasmic reticulum kinase/eukaryotic initiation factor 2 alpha (PERK/eIF2α) phosphorylation, ATF6 cleavage, and X-box binding protein 1 (XBP1) splicing. Interestingly, further analyses revealed that host UPR inhibition subsequently suppressed the NF-κB pathway, leading to the reduced production of porcine beta-defensin 2 (PBD-2), thus facilitating M. hyopneumoniae adherence and infection. This study provides new insights into the molecular pathogenesis of M. hyopneumoniae and sheds light upon its interactions with the host.

Comparative genomics analysis of Mycoplasma capricolum subsp. capripneumoniae 87001.

Mycoplasma capricolum subsp. capripneumoniae (Mccp), belongs to Mycoplasma mycoides cluster and is a causal pathogen of contagious caprine pleuropneumonia (CCPP). This paper presents the complete annotated genome sequence of Mccp Strain 87001-a strain that was isolated from pneumonia affected goats on a farm in China, and comparative genomics analysis of five Mccp genomes in addition to comparative genomics within Mycoplasma mycoides cluster. The Mccp strain 87001 genome consists of a single circular chromosome 1017333 bp in length and encodes 898 open reading frames (orfs) averaging 944 bp in length. Fifty eight potential virulence genes were identified, including variable surface lipoproteins, hemolysin A, and P60 surface lipoprotein. Comparative genomic analysis revealed eight virulence genes and four extracellular genes which remained unchanged in five Mccp genomes for forty years, which can be used as potential target for drug development and vaccine design. We revealed 183 Mccp unique genes as markers to distinguish Mccp with other mycoplasma strains from goats, and different virulence factors contributing to host specificity and different syndrome of bovine pathogens and caprine pathogens.

A Novel Lipoate-Protein Ligase, Mhp-LplJ, Is Required for Lipoic Acid Metabolism in Mycoplasma hyopneumoniae.

Lipoic acid is a conserved cofactor necessary for the activation of several critical enzyme complexes in the aerobic metabolism of 2-oxoacids and one-carbon metabolism. Lipoate metabolism enzymes are key for lipoic acid biosynthesis and salvage. In this study, we found that Mycoplasma hyopneumoniae (M. hyopneumoniae) Mhp-Lpl, which had been previously shown to have lipoate-protein ligase activity against glycine cleavage system H protein (GcvH) in vitro, did not lipoylate the lipoate-dependent subunit of dihydrolipoamide dehydrogenase (PdhD). Further studies indicated that a new putative lipoate-protein ligase in M. hyopneumoniae, MHP_RS00640 (Mhp-LplJ), catalyzes free lipoic acid attachment to PdhD in vitro. In a model organism, Mhp-LplJ exhibited lipoate and octanoate ligase activities against PdhD. When the enzyme activity of Mhp-LplJ was disrupted by lipoic acid analogs, 8-bromooctanoic acid (8-BrO) and 6,8-dichlorooctanoate (6,8-diClO), M. hyopneumoniae growth was arrested in vitro. Taken together, these results indicate that Mhp-LplJ plays a vital role in lipoic acid metabolism of M. hyopneumoniae, which is of great significance to further understand the metabolism of M. hyopneumoniae and develop new antimicrobials against it.

GroEL Protein (Heat Shock Protein 60) of Mycoplasma gallisepticum Induces Apoptosis in Host Cells by Interacting with Annexin A2.

Mycoplasma gallisepticum is an avian respiratory and reproductive tract pathogen that has a significant economic impact on the poultry industry worldwide. Although membrane proteins of Mycoplasma spp. are thought to play crucial roles in host interactions, very few have had their biochemical function defined. In this study, we found that the GroEL protein (heat shock protein 60) of Mycoplasma gallisepticum could induce apoptosis in peripheral blood mononuclear cells, and the underlying molecular mechanism was further determined. The GroEL gene from Mycoplasma gallisepticum was cloned and expressed in Escherichia coli to facilitate the functional analysis of recombinant protein. The purified GroEL protein was shown to adhere to peripheral blood mononuclear cells (PBMCs) and DF-1 cells and cause apoptosis in PBMCs. A protein pulldown assay coupled with mass spectrometry identified that annexin A2 possibly interacted with GroEL protein. Coimmunoprecipitation assays confirmed that GroEL proteins could bind to annexin A2, and confocal analysis further demonstrated that GroEL colocolized with annexin A2 in HEK293T cells and PBMCs. Moreover, annexin A2 expression was significantly induced by a recombinant GroEL protein in PBMCs, and knocking down annexin A2 expression resulted in significantly reduced apoptosis. Taken together, these data suggest that GroEL induces apoptosis in host cells by interacting with annexin A2, a novel virulence mechanism in Mycoplasma gallisepticum Our findings lead to a better understanding of molecular pathogenesis in Mycoplasma gallisepticum.

Elongation Factor Thermo Unstable (EF-Tu) Moonlights as an Adhesin on the Surface of Mycoplasma hyopneumoniae by Binding to Fibronectin.

Mycoplasma hyopneumoniae is a colonizing respiratory pathogen that can cause great economic losses to the pig industry worldwide. Although putative virulence factors have been reported, the pathogenesis of this species remains unclear. Here, we used the virulent M. hyopneumoniae strain 168 to infect swine tracheal epithelial cells (STEC) to identify the infection-associated factors by two-dimensional electrophoresis (2-DE). Whole proteins of M. hyopneumoniae were obtained and compared with samples cultured in broth. Six differentially expressed proteins with an increase in abundance of ≥1.5 in the cell infection group were successfully identified. A String network of virulence-associated proteins showed that all the six differential abundance proteins were involved in virulence of M. hyopneumoniae. One of the most important upregulated hubs in this network, elongation factor thermo unstable (EF-Tu), which showed a relatively higher expression in M. hyopneumoniae-infected STEC and obtained a higher score on mass spectrometry was successfully recombined. In addition to its canonical enzymatic activities in protein synthesis, EF-Tu was also reported to be located on the cell surface as an important adhesin in many other pathogens. The cell surface location of EF-Tu was then observed in M. hyopneumoniae with flow cytometry. Recombinant EF-Tu (rEF-Tu) was found to be able to adhere to STEC and anti-rEF-Tu antibody enclosed M. hyopneumoniae decreased adherence to STEC. In addition, surface plasmon resonance (SPR) analysis showed that rEF-Tu could bind to fibronectin with a specific and moderately strong interaction, a dissociation constant (KD) of 605 nM. Furthermore, the block of fibronectin in STEC also decreased the binding of M. hyopneumoniae to the cell surface. Collectively, these data imply EF-Tu as an important adhesin of M. hyopneumoniae and fibronectin as an indispensable receptor on STEC. The binding between EF-Tu with fibronectin contributes to the adhesion of M. hyopneumoniae to STEC. HIGHLIGHTS Elongation factor thermo unstable (EF-Tu) exists on the cell surface of M. hyopneumoniae.EF-Tu moonlights as an adhesin of M. hyopneumoniae.The adhesive effect of EF-Tu is partly meditated by fibronectin.

TLR2/MyD88/NF-κB signaling pathway regulates IL-1ß production in DF-1 cells exposed to Mycoplasma gallisepticum LAMPs.

Mycoplasma gallisepticum (M. gallisepticum) is one of the most important pathogens that cause chronic respiratory disease in chickens. M. gallisepticum-derived lipid-associated membrane proteins (LAMPs) are thought to be one of the major factors in mycoplasma pathogenesis and are potent inducers of the host innate immune response. However, the interaction of pathogenic M. gallisepticum-derived LAMPs with Toll-like receptors (TLRs) and the signaling pathways responsible for activating inflammation and NF-κB have not been fully elucidated. In this study, we found that IL-1ß expression was induced in DF-1 cells stimulated with M. gallisepticum LAMPs. Subcellular localization experiments using immunofluorescence assays (IFAs) showed p65 translocation from the cytoplasm to the nucleus in DF-1 cells following stimulation with M. gallisepticum LAMPs. Phosphorylation of p65 was detected in LAMP-stimulated DF-1 cells. Treatment with an NF-κB-specific inhibitor showed that NF-κB is required for M. gallisepticum LAMP-induced IL-1ß expression. In addition, the results indicated that TLR2 and myeloid differentiation primary-response protein 88 (MyD88)-dependent signaling pathways were involved in the activation of NF-κB by M. gallisepticum LAMPs. Together, these results provide evidence that M. gallisepticum LAMPs activate IL-1ß production through the NF-κB pathway via TLR2 and MyD88.

Mmm-derived lipid-associated membrane proteins activate IL-1ß production through the NF-κB pathway via TLR2, MyD88, and IRAK4.

Mycoplasma mycoides subsp.mycoides (Mmm) is a pathogen that causes pneumonia, otitis media, and arthritis in young calves. Its pathogenesis is attributed in part to excessive immune responses. Mmm-derived lipid-associated membrane proteins (LAMPs) are potent inducers of the host innate immune system; however, interactions between Mmm-derived LAMPs as pathogenic agents, toll-like receptors (TLRs), and the signaling pathways responsible for activating inflammation and nuclear factor (NF)-κB have not been fully elucidated. Here, we analyzed the expression kinetics of interleukin (IL)-1ß in Mmm-derived LAMP-stimulated embryonic bovine lung (EBL) cells and found that Mmm-derived LAMPs induced IL-1ß expression. Subcellular localization analysis revealed the nuclear translocation of the NF-κB p65 subunit after EBL cells were stimulated with Mmm-derived LAMPs. Furthermore, a specific inhibitor assay demonstrated that NF-κB is required for Mmm-derived LAMP-induced IL-1ß expression. Additionally, overexpression of TLR2, myeloid differentiation primary response gene 88 (MyD88), and IL-1 receptor-associated kinase 4 (IRAK4) increased IL-1ß expression during LAMP stimulation, and TLR2-neutralizing antibodies reduced IL-1ß expression in EBL cells during LAMP stimulation. Furthermore, LAMPs inhibited IL-1ß expression following transfection with dominant-negative MyD88 and IRAK4 variants. These results suggested that Mmm-derived LAMPs activate IL-1ß production through the NF-κB pathway via TLR2, MyD88, and IRAK4.

TLR2 mediates autophagy through ERK signaling pathway in Mycoplasma gallisepticum-infected RAW264.7 cells.

Toll-like receptor 2 (TLR2) plays a crucial role in early innate immune response of host to various microorganisms. Mycoplasma gallisepticum (MG) is one of the major pathogen that can cause chronic respiratory diseases in chickens, but the molecular mechanism of MG infection still remained unclear. In this study, we examined the typical hallmarks of autophagy and multiple signaling pathways by western blot, immunofluorescence microscopy and electron microscopy. The results indicated that infection of mouse macrophage cell line RAW264.7 with MG activated autophagy and mitogen-activated protein kinases (MAPKs). Silencing of TLR2 by siRNA substantially down-regulated MG-triggered autophagy in macrophages, and markedly reduced MG-induced extracellular regulated protein kinase (ERK) in macrophages but did not down-regulate c-Jun N-terminal kinase (JNK) and p38. Importantly, in macrophages, inhibition of ERK by PD98059 (ERK inhibitor) also significantly attenuated the level of autophagy upon MG infection, and the simultaneous treatment of TLR2 siRNA and PD98059 showed a similar effect on MG-induced autophagy as compared with TLR2 siRNA treatment alone. These findings thus demonstrate that TLR2 may mediate MG-induced autophagy through ERK signaling pathway in macrophage.

Linear antigenic mapping of flagellin (FliC) from Salmonella enterica serovar Enteritidis with yeast surface expression system.

Salmonella enterica serovar Enteritidis (S. Enteritidis) is a major cause of food-borne illness around the world and can have significant health implications in humans, poultry and other animals. Flagellin (FliC) is the primary component of bacterial flagella. It has been shown that the FliC of S. Enteritidis is a significant antigenic structure and can elicit strong humoral responses against S. Enteritidis infection in chickens. Here, we constructed a FliC antigen library using a yeast surface expression system. Yeast cells expressing FliC peptide antigens were labeled with chicken sera against S. Enteritidis and sorted using FACS. The analyses of FliC peptides revealed that the FliC linear antigenicity in chickens resided on three domains which were able to elicit strong humoral responses in vivo. Animal experiments further revealed that the antibodies elicited by these antigenic domains were able to significantly inhibit the invasion of S. Enteritidis into the liver and spleen of chickens. These findings will facilitate our better understanding of the humoral responses elicited by FliC in chickens upon infection by S. Enteritidis.

P19 contributes to Mycoplasma mycoides subsp. mycoides adhesion to EBL cells.

Mycoplasma mycoides subsp. mycoides (Mmm) is the causative agent of contagious bovine pleuropneumonia (CBPP). The virulent Mmm Ben-1 strain was isolated from the lung of a CBPP-infected cow in China in the 1950s. To attenuate the virulence of the Ben-1 strain and preserve its protective ability, the isolate was re-isolated after inoculation into the testicles of rabbits and into the rabbit thorax. As a result, after the subsequent isolates were continuously passaged 468 times in rabbits, its pathogenicity to cattle decreased. However, the molecular mechanisms leading to attenuation of the Mmm Ben-1 remain unknown. We compared the entire genomes of the Ben-1 strain and the 468 th generation strain passaged in rabbits (Ben-468) and discovered that a putative protein gene named p19 was absent from the Ben-468 strain. The p19 gene was cloned and expressed in Escherichia coli to obtain recombinant P19 (rP19). Western blot analysis demonstrated that the P19 protein is detected in the cell-membrane fraction, the cell-soluble cytosolic fraction and whole-cell lysate of the Mmm Ben-1 strain. The rP19 can interact with international standard serum against CBPP. Immunostaining visualised via confocal laser scanning microscopy indicated that P19 is able to adhere to embryonic bovine lung (EBL) cells, and this finding was also confirmed by a sandwich ELISA. We also found that anti-rP19 serum could inhibit the adhesion of the Mmm Ben-1 total proteins to EBL cells.

Changes in pathogenicity and immunogenicity of Mycoplasma mycoides subsp. mycoides strains revealed by comparative genomics analysis.

Mycoplasma mycoides subsp. mycoides is the causative agent of contagious bovine pleuropneumonia. A pathogenic strain BEN-1 was isolated from bovine lung and underwent continuous passages in rabbits for 468 generations. During this process, the strain's strong virulence became weak and, gradually, it lost the ability to confer protective immunity in cattle but developed virulence in rabbits. In order to gain insight into the mechanisms behind the reduction in virulence and the loss of immunogenicity, we sequenced five representative strains of the BEN series, including the original strain (BEN-1), the strain generation that first acquired virulence in rabbits (BEN-50), the two vaccine strain generations (BEN-181 and BEN-326), and the strain generation showing the greatest loss of immunogenicity (BEN-468). The gene mutation rate in the four different propagation stages varied greatly, and over half of variations observed in each generation were removed during the propagation process. However, the variation maintained in the BEN-468 generation might contribute to its changes in virulence and immunogenicity. We thus identified 18 genes associated with host adaptation, six genes contributing to virulence in cattle, and 35 genes participating in conferring immunity in cattle. These findings might help us optimize the vaccine to obtain more effective immunization results.

Antimicrobial susceptibility and molecular characterization of macrolide resistance of Mycoplasma bovis isolates from multiple provinces in China.

Mycoplasma bovis has spread widely throughout the world via animal movement and has become an important pathogen of bovine respiratory disease. However, the minimum inhibitory concentrations of antimicrobials for Mycoplasma bovis have not been studied in China. The objective of this study was to determine the prevalence and antibiotic resistance of Mycoplasma bovis isolated from young cattle with respiratory infection in China. Mycoplasma bovis was detected in 32/45 bovine respiratory infection outbreaks at beef farms in 8 provinces in China. The isolates were susceptible or had medium sensitivity to ciprofloxacin, enrofloxacin and doxycycline, but were frequently resistant to macrolides (13/32, 41%). An A2058G (Escherichia coli Numbering) mutation located in the rrnA operon in domain V of 23S rRNA was observed in strains that were resistant to macrolides. This single mutations at the rrnA operon in domain V of 23S rRNA may play an important role in the resistance of Mycoplasma bovis strains to macrolides.