Innate immune response of bovine mammary epithelial cells to Mycoplasma bovis

Mycoplasma bovis mastitis in dairy cattle

Mycoplasma bovis has recently been identified increasingly in dairy cows causing huge economic losses to the dairy industry. M. bovis is a causative agent for mastitis, pneumonia, endometritis, endocarditis, arthritis, otitis media, and many other clinical symptoms in cattle. However, some infected cows are asymptomatic or may not shed the pathogen for weeks to years. This characteristic of M. bovis, along with the lack of adequate testing and identification methods in many parts of the world until recently, has allowed the M. bovis to be largely undetected despite its increased prevalence in dairy farms. Due to growing levels of antimicrobial resistance among wild-type M. bovis isolates and lack of cell walls in mycoplasmas that enable them to be intrinsically resistant to beta-lactam antibiotics that are widely used in dairy farms, there is no effective treatment for M. bovis mastitis. Similarly, there is no commercially available effective vaccine for M. bovis mastitis. The major constraint to developing effective intervention tools is limited knowledge of the virulence factors and mechanisms of the pathogenesis of M. bovis mastitis. There is lack of quick and reliable diagnostic methods with high specificity and sensitivity for M. bovis. This review is a summary of the current state of knowledge of the virulence factors, pathogenesis, clinical manifestations, diagnosis, and control of M. bovis mastitis in dairy cows.

Expression, Regulation, and Function of β-Defensins in the Bovine Mammary Glands: Current Knowledge and Future Perspectives

β-Defensins are cationic antimicrobial peptides (AMPs) that play an important role in the innate immune defense of bovines. They are constitutively expressed in mammary glands and induced differently in response to pathogens. Their expression is influenced by various factors, including hormones, plant-derived compounds, and dietary energy imbalance. The toll-like receptors (TLRs)/nuclear factor-kappa B (NF-κB) pathway plays a crucial role in β-defensin induction, while alternative pathways such as mitogen-activated protein kinase (MAPK) and epigenetic regulation also make substantial contributions. β-Defensins exhibit bactericidal activity against a wide range of pathogens, including two major mastitis pathogens, Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), primarily through membrane disruption. β-Defensins have low cytotoxicity to host cells and demonstrate immunomodulatory properties, and pathogens also display minimal resistance to these AMPs. Given the increasing concern in antimicrobial resistance, the potential of β-defensins as natural antimicrobials has garnered considerable attention. This article provides an overview of the characteristics of bovine β-defensins, their expression pathways, their mode of action, and factors influencing their expression in the mammary glands of cattle. Additionally, it identifies the current gaps in research within this field and suggests areas that require further investigation. Understanding the regulation and function of β-defensins offers valuable insights to develop effective strategies for strengthening the immune system of mammary glands, reducing the reliance on synthetic antimicrobials, and explore novel natural antimicrobial alternatives.

Characteristics of Mycoplasma bovis, Mycoplasma arginini, and Mycoplasma californicum on immunological response of bovine synovial cells

Mycoplasma arthritis in calves caused by M. bovis exhibits joint swelling, lameness, and immobility. In contrast to M. bovis, M. arginini, and M. californicum which were similarly isolated from the affected joints, only induced mild inflammation. The changes in pathogenesis that depended on species, however, remained unknown. This investigation aims to examine the characteristics of immune responses to M. bovis, M. arginini, and M. californicum in synovial cells. Intracellular M. bovis was detected by gentamicin assay, but M. arginini and M. californicum were not detected. M. bovis-infected synovial cells were encouraged to proliferate and had their apoptosis suppressed. We suggest that M. bovis invaded and inhibited apoptosis of synovial to evade host immunity, which led to long term survival in joints. M. bovis infection significantly increased IL-6 mRNA expression compared to control, although M. arginini and M. californicum infection were comparable to control. We suggest that M. arginini and M. californicum have low abilities to induce inflammation in joints and therefore do not cause severe pathology. Our findings are the first to show the variations in synovial cell immune responses to M. bovis, M. arginini, and M. californicum, which are thought to be related to the pathogenicity of arthritis.

Interactions between polycyclic musks and human lactoferrin: Multi-spectroscopic methods and docking simulation

Galaxolide (1,3,4,6,7,8-hexahydro-4,6,6,7,8-hexamethylcyclopenta-γ-2-benzopyrane; HHCB) and Tonalide (7-acetyl-1,1,3,4,4,6-hexamethyl-1,2,3,4-tetrahydronaphthalene; AHTN) are "pseudo-persistent" pollutants that can cause DNA damage, endocrine disruption, organ toxicity, and reproductive toxicity in humans. HHCB and AHTN are readily enriched in breast milk, so exposure of infants to HHCB and AHTN is of concern. Here, the molecular mechanisms through which HHCB and AHTN interact with human lactoferrin (HLF) are investigated using computational simulations and spectroscopic methods to identify indirectly how HHCB and AHTN may harm infants. Molecular docking and kinetic simulation studies indicated that HHCB and AHTN can interact with and alter the secondary HLF structure. The fluorescence quenching of HLF by HHCB, AHTN was static with the forming of HLF-HHCB, HLF-AHTN complex, and accompanied by non-radiative energy transfer and that 1:1 complexes form through interaction forces. Time-resolved fluorescence spectroscopy indicated that binding to small molecules does not markedly change the HLF fluorescence lifetime. Three-dimensional fluorescence spectroscopy indicated that HHCB and AHTN alter the peptide chain backbone structure of HLF. Ultraviolet-visible absorption spectroscopy, simultaneous fluorescence spectroscopy, Fourier-transform infrared spectroscopy, and circular dichroism spectroscopy indicated that HHCB and AHTN change the secondary HLF conformation. Antimicrobial activity experiments indicated that polycyclic musks decrease lactoferrin activity and interact with HLF. These results improve our understanding of the mechanisms involved in the toxicities of polycyclic musks bound to HLF at the molecular level and provide theoretical support for mother-and-child health risk assessments.

A Novel TLR4-SYK Interaction Axis Plays an Essential Role in the Innate Immunity Response in Bovine Mammary Epithelial Cells

Mammary gland epithelium, as the first line of defense for bovine mammary gland immunity, is crucial in the process of mammary glands’ innate immunity, especially that of bovine mammary epithelial cells (bMECs). Our previous studies successfully marked SYK as an important candidate gene for mastitis traits via GWAS and preliminarily confirmed that SYK expression is down-regulated in bMECs with LPS (E. coli) stimulation, but its work mechanism is still unclear. In this study, for the first time, in vivo, TLR4 and SYK were colocalized and had a high correlation in mastitis mammary epithelium; protein−protein interaction results also confirmed that there was a direct interaction between them in mastitis tissue, suggesting that SYK participates in the immune regulation of the TLR4 cascade for bovine mastitis. In vitro, TLR4 also interacts with SYK in LPS (E. coli)-stimulated or GBS (S. agalactiae)-infected bMECs, respectively. Moreover, TLR4 mRNA expression and protein levels were little affected in bMECsSYK- with LPS stimulation or GBS infection, indicating that SYK is an important downstream element of the TLR4 cascade in bMECs. Interestingly, IL-1β, IL-8, NF-κB and NLRP3 expression in LPS-stimulated or GBS-infected bMECsSYK- were significantly higher than in the control group, while AKT1 expression was down-regulated, implying that SYK could inhibit the IL-1β, IL-8, NF-κB and NLRP3 expression and alleviate inflammation in bMECs with LPS and GBS. Taken together, our solid evidence supports that TLR4/SYK/NF-κB signal axis in bMECs regulates the innate immunity response to LPS or GBS.

Integrated Analysis of Transcriptome mRNA and miRNA Profiles Reveals Self-Protective Mechanism of Bovine MECs Induced by LPS

Many studies have investigated the molecular crosstalk between mastitis-pathogens and cows by either miRNA or mRNA profiles. Here, we employed both miRNA and mRNA profiles to understand the mechanisms of the response of bovine mammary epithelial cells (bMECs) to lipopolysaccharide (LPS) by RNA-Seq. The total expression level of miRNAs increased while mRNAs reduced after LPS treatment. About 41 differentially expressed mRNAs and 45 differentially expressed miRNAs involved in inflammation were screened out. We found the NFκB-dependent chemokine, CXCL1, CXCL3, CXCL6, IL8, and CX3CL1 to be strongly induced. The anti-apoptosis was active because BCL2A1 and BIRC3 significantly increased with a higher expression. The effects of anti-microbe and inflammation were weakly activated because TNF, IL1, CCL20, CFB, S100A, MMP9, and NOS2A significantly increased but with a low expression, IL6 and β-defensin decreased. These activities were supervised by the NFKBIA to avoid excessive damage to bMECs. The bta-let-7a-5p, bta-miR-30a-5p, bta-miR-125b, and bta-miR-100 were essential to regulate infection process in bMECs after LPS induction. Moreover, the lactation potential of bMECs was undermined due to significantly downregulated SOSTDC1, WNT7B, MSX1, and bta-miR-2425-5p. In summary, bMECs may not be good at going head-to-head with the pathogens; they seem to be mainly charged with sending out signals for help and anti-apoptosis for maintaining lives after LPS induction.

Regularity of Toll-Like Receptors in Bovine Mammary Epithelial Cells Induced by Mycoplasma bovis

Mastitis is one of the most common and significant infectious diseases in dairy cattle and is responsible for significant financial losses for the dairy industry globally. An important pathogen of bovine mastitis, Mycoplasma bovis (M. bovis) has a high infection rate, requires a long course of treatment, and is difficult to cure. Bovine mammary epithelial cells (BMECs) are the first line of defense of the mammary gland, and their natural immune system plays a critical role in resisting M. bovis infection. This study aimed to explore and demonstrate the regularity of Toll-like receptors (TLRs) activation during M. bovis infection and their function during M. bovis mastitis. An in vitro model of M. bovis-induced mastitis showed that the expression of IL-6, IL-8, and TNF-α increased significantly following infection. M. bovis infection also upregulated the expression of TLR1/2/6 on the cell membrane and TLR3/9 in the cytoplasm. There is a crosstalk effect between TLR1–TLR2 and TLR2–TLR6. Furthermore, M. bovis infection was found to activate the TLR1/2/6/9/MyD88/NF-κB and TLR3/TRIF/IRF signal transduction pathways, which in turn activate inflammatory factors. These findings lay the theoretical foundation for understanding the pathogenesis of M. bovis, permitting the development of effective measures for preventing and controlling M. bovis mastitis.

Aclonifen induces bovine mammary gland epithelial cell death by disrupting calcium homeostasis and inducing ROS production

Herbicides play key roles in agriculture. Aclonifen is a diphenyl ether herbicide that is widely used for sunflower, potato, corn, and wheat crops. Since it has a long half-life, it is considered persistent and can easily accumulate in the environment. Therefore, livestock and humans are at risk of exposure to aclonifen. Importantly, aclonifen is toxic to several mammals such as rats, mice, and dogs. However, the toxicity of aclonifen in cattle remains unclear. Therefore, we sought to investigate its toxicity in cattle using bovine mammary gland epithelial cells (MAC-T). We found that aclonifen induces sub-G1 phase arrest and represses MAC-T proliferation. In addition, aclonifen caused mitochondrial dysfunction, as evidenced by excessive ROS production and loss of mitochondrial membrane potential. Furthermore, cytosolic and mitochondrial calcium homeostases were disrupted after aclonifen treatment. Moreover, aclonifen treatment caused alterations in the PI3K/AKT and MAPK signaling pathways, which are involved in the regulation of cell survival and death. In conclusion, aclonifen causes MAC-T cell death through mitochondrial dysfunction and the collapse of calcium homeostasis.

Mycoplasma bovis Mastitis

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Mycoplasma bovis mastitis (MBM) is highly contagious and causes significant economic losses through reduction in milk quantity and quality, culling and treatment costs.

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Adhesion and invasion are among the most important virulence mechanisms to establish infection in the mammary gland.

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M. bovis can elicit both humoral and cellular immune responses during mammary gland infection.

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There is no effective commercial vaccine against MBM to date and early detection and isolation/culling remains vital control measure for MBM in dairy farms.

Bovine mycoplasmoses, which is mostly caused by Mycoplasma bovis, is a significant problem in the dairy and beef industry. Mycoplasmal mastitis has a global occurrence with notable effects in the United States and Europe. The pathogen was first detected in a mastitis case in California, United States, and regarded as major contagious mastitis. It is highly contagious and resistant to antibiotics and lack cell wall rendering certain group of antibiotics ineffective. Outbreaks mostly originate from introduction of diseased dairy cows to a farm and poor hygienic practices that help to maintain cow to cow transmission. Rapid detection scheme is needed to be in place in dairy farms to devise preventive measures and stop future outbreaks. However; early detection is hampered by the fastidious growth of M. bovis and the need for specialized equipment and reagents in laboratory settings. Intramammary Mycoplasma bovis infections cause elevation in milk somatic cell count which is one of the important factors to determine milk quality for grading and hence dictates milk price. There are multiple attributes of M. bovis regarded as virulence factors such as adhesion to and invasion into host cells, avoidance of phagocytosis, resistance to killing by the alternative complement system, biofilm formation, and hydrogen peroxide production.

Nevertheless, there are still undetermined virulence factors that hamper the development of sustainable control tools such as effective vaccine. To date, most vaccine trials have failed, and there is no commercial M. bovis mastitis vaccine. Mycoplasma bovis has been shown to modulate both humoral and cellular immune response during bovine mastitis. In the future, research seeking new immunogenic and protective vaccine targets are highly recommended to control this important dairy cattle disease worldwide.

Effects of intra-articular inoculation with Mycoplasma bovis on immunological responses in calf joints

Mycoplasma arthritis that caused by Mycoplasma bovis exhibit severe lameness. This disease is difficult to cure with antibiotics, but the detailed pathological mechanisms have not been fully clarified. In this study, we examined the effects of intra-articular inoculation with M. bovis on immunological responses in calf joints. We inoculated three calves each with M. bovis or phosphate buffer saline (control) into the right stifle joint and dissected them at 15 days postinoculation. Mycoplasma bovis-inoculated calves exhibited swelling of the stifle joint, increases in synovial fluid, fibrin deposition, and cartilage thinning. Intracellular M. bovis was detected in synovial tissues analyzed by immunohistochemistry and transmission electron microscopy. Messenger RNA expressions of interleukin (IL)-1β, IL-6, IL-8, IL-12p40, and IL-17A in synovial fluid cells and synovial tissues from M. bovis-inoculated calves were significantly higher than those from control calves. Protein levels of these cytokines in synovial fluid from M. bovis-inoculated calves were markedly higher than those from control calves. Our study clarified that inoculation with M. bovis into the stifle joint induced the production of inflammatory cytokines by synovial fluid cells and synovial tissues, causing a severe inflammatory response in joints. Additionally, M. bovis could invade cells in synovial tissues, which may have aided it in evading antibiotics and host immune surveillance.

A Review of the Neutrophil Extracellular Traps (NETs) from Cow, Sheep and Goat Models

This review provides insight into the importance of understanding NETosis in cows, sheep, and goats in light of the importance to their health, welfare and use as animal models. Neutrophils are essential to innate immunity, pathogen infection, and inflammatory diseases. The relevance of NETosis as a conserved innate immune response mechanism and the translational implications for public health are presented. Increased understanding of NETosis in ruminants will contribute to the prediction of pathologies and design of strategic interventions targeting NETs. This will help to control pathogens such as coronaviruses and inflammatory diseases such as mastitis that impact all mammals, including humans. Definition of unique attributes of NETosis in ruminants, in comparison to what has been observed in humans, has significant translational implications for one health and global food security, and thus warrants further study.

In Silico Identification of Novel Immunogenic Secreted Proteins of Mycoplasma bovis from Secretome Data and Experimental Verification

Mycoplasma bovis is a major pathogen, responsible for bovine respiratory diseases worldwide. The present lack of effective control measures leaves cattle owners at considerable perpetual risk of M. bovis outbreaks. In this study, we identified M. bovis secreted immunogenic proteins in silico as potential candidates for novel diagnostic agents and vaccines. We used immunoinformatics to analyze 438 M. bovis proteins previously identified with a label-free proteomics analysis of virulent M. bovis HB0801 (P1) and its attenuated P150 strains. The subcellular localization of these proteins was preliminarily screened and 59 proteins were found to be secreted extracellular proteins. Twenty-seven of these proteins contained a large number of predictive T-cell epitopes presented by major histocompatibility complex (MHC) class I and II molecules. Twenty-two of these 27 proteins had a high number of conformational B-cell epitopes, predicted from the corresponding 3D structural templates, including one unique to P1, two unique to P150, and 19 common to both strains. Five proteins were selected for further validation, and two of these, MbovP274 and MbovP570, were successfully expressed and purified. Both were confirmed to be secretory and highly immunogenic proteins that induced a mouse antibody response, reacted with cattle serum positive for M. bovis infection, and significantly increased the production of interleukin 8 (IL-8), IL-12 and interferon γ (IFN-γ) during the secretion of these three cytokines by both M. bovis mutants of these genes. These results should be useful in the development of novel immunological agents against M. bovis infection.

Persistence in Livestock Mycoplasmas—a Key Role in Infection and Pathogenesis

Purpose of Review

Mycoplasma, economically important pathogens in livestock, often establishes immunologically complex persistent infections that drive their pathogenesis and complicate prophylaxis and therapy of the caused diseases. In this review, we summarize some of the recent findings concerning cellular and molecular persistence mechanisms related to the pathogenesis of mycoplasma infections in livestock.

Recent Findings

Data from recent studies prove several mechanisms including intracellular lifestyle, immune dysregulation, and autoimmunity as well as microcolony and biofilm formation and apoptosis of different host cell types as important persistence mechanisms in several clinically significant Mycoplasma species, i.e., M. bovis, M. gallisepticum, M. hyopneumoniae, and M. suis.

Summary

Evasion of the immune system and the establishment of persistent infections are key features in the pathogenesis of livestock mycoplasmas. In-depth knowledge of the underlying mechanisms will provide the basis for the development of therapy and prophylaxis strategies against mycoplasma infections.

Bovine Epithelial in vitro Infection Models for Mycoplasma bovis

Mycoplasma bovis causes bovine mycoplasmosis. The major clinical manifestations are pneumonia and mastitis. Recently an increase in the severity of mastitis cases was reported in Switzerland. At the molecular level, there is limited understanding of the mechanisms of pathogenicity of M. bovis. Host–pathogen interactions were primarily studied using primary bovine blood cells. Therefore, little is known about the impact of M. bovis on other cell types present in infected tissues. Clear in vitro phenotypes linked to the virulence of M. bovis strains or tissue predilection of specific M. bovis strains have not yet been described. We adapted bovine in vitro systems to investigate infection of epithelial cells with M. bovis using a cell line (MDBK: Madin-Darby bovine kidney cells) and two primary cells (PECT: bovine embryonic turbinate cells and bMec: bovine mammary gland epithelial cells). Two strains isolated before and after the emergence of severe mastitis cases were selected. Strain JF4278 isolated from a cow with mastitis and pneumonia in 2008 and strain L22/93 isolated in 1993 were used to assess the virulence of M. bovis genotypes toward epithelial cells with particular emphasis on mammary gland cells. Our findings indicate that M. bovis is able to adhere to and invade different epithelial cell types. Higher titers of JF4278 than L22/93 were observed in co-cultures with cells. The differences in titers reached between the two strains was more prominent for bMec cells than for MDBK and PECT cells. Moreover, M. bovis strain L22/93 induced apoptosis in MDBK cells and cytotoxicity in PECT cells but not in bMec cells. Dose-dependent variations in proliferation of primary epithelial cells were observed after M. bovis infection. Nevertheless, an indisputable phenotype that could be related to the increased virulence toward mammary gland cells is not obvious.

Allergic airway sensitization impairs antibacterial IgG antibody responses during bacterial respiratory tract infections

BACKGROUND

Mycoplasma pneumoniae, an atypical human pathogen, has been associated with asthma initiation and exacerbation. Asthmatic patients have been reported to have higher carriage rates of M pneumoniae compared with nonasthmatic subjects and are at greater risk for invasive respiratory infections.

OBJECTIVE

We sought to study whether prior allergen sensitization affects the host response to chronic bacterial infection.

METHODS

BALB/cJ and IL-4 receptor α^-/- mice were sensitized with ovalbumin (OVA) and then infected with M pneumoniae or Streptococcus pneumoniae. Immune parameters were analyzed at 30 days postinfection and included cellular profiles in bronchoalveolar lavage fluid (BALF) and serum IgG and IgE antibody levels to whole bacterial lysate, recombinant P1 adhesin, and OVA. Total lung RNA was examined for transcript levels, and BALF was examined for cytokine protein profiles.

RESULTS

Anti-M pneumoniae antibody responses were decreased in allergen-sensitized, M pneumoniae-infected animals compared with control animals, but OVA-specific IgG responses were unaffected. Similar decreases in anti-S pneumoniae antibody levels were found in OVA-sensitized animals. However, M pneumoniae, but not S pneumoniae, infection augmented anti-OVA IgE antibody responses. Loss of IL-4 receptor signaling partially restored anti-M pneumoniae antibody responses in IgG_2a and IgG_2b subclasses. Inflammatory cytokine levels in BALF from OVA-sensitized, M pneumoniae-infected or S pneumoniae-infected animals were reduced compared with those in uninfected OVA-sensitized control animals. Unexpectedly, airway hyperreactivity to methacholine was essentially ablated in M pneumoniae-infected, OVA-sensitized animals.

CONCLUSIONS

An established type 2-biased host immune response impairs the host immune response to respiratory bacterial infection in a largely pathogen-independent manner. Some pathogens, such as M pneumoniae, can augment ongoing allergic responses and inhibit pulmonary type 2 cytokine responses and allergic airway hyperreactivity.