Mycoplasma hyopneumoniae evades phagocytic uptake by porcine alveolar macrophages in vitro

Research Progress on Immune Evasion of Mycoplasma hyopneumoniae

As the main pathogen associated with enzootic pneumonia (EP), Mycoplasma hyopneumoniae (Mhp) is globally prevalent and inflicts huge financial losses on the worldwide swine industry each year. However, the pathogenicity of Mhp has not been fully explained to date. Mhp invasion usually leads to long-term chronic infection and persistent lung colonization, suggesting that Mhp has developed effective immune evasion strategies. In this review, we offer more detailed information than was previously available about its immune evasion mechanisms through a systematic summary of the extant findings. Genetic mutation and post-translational protein processing confer Mhp the ability to alter its surface antigens. With the help of adhesins, Mhp can achieve cell invasion. And Mhp can modulate the host immune system through the induction of inflammation, incomplete autophagy, apoptosis, and the suppression of immune cell or immune effector activity. Furthermore, we offer the latest views on how we may treat Mhp infections and develop novel vaccines.

Unveiling the stealthy tactics: mycoplasma's immune evasion strategies

Mycoplasmas, the smallest known self-replicating organisms, possess a simple structure, lack a cell wall, and have limited metabolic pathways. They are responsible for causing acute or chronic infections in humans and animals, with a significant number of species exhibiting pathogenicity. Although the innate and adaptive immune responses can effectively combat this pathogen, mycoplasmas are capable of persisting in the host, indicating that the immune system fails to eliminate them completely. Recent studies have shed light on the intricate and sophisticated defense mechanisms developed by mycoplasmas during their long-term co-evolution with the host. These evasion strategies encompass various tactics, including invasion, biofilm formation, and modulation of immune responses, such as inhibition of immune cell activity, suppression of immune cell function, and resistance against immune molecules. Additionally, antigen variation and molecular mimicry are also crucial immune evasion strategies. This review comprehensively summarizes the evasion mechanisms employed by mycoplasmas, providing valuable insights into the pathogenesis of mycoplasma infections.

Interactions of Mycoplasma hyopneumoniae and/or Mycoplasma hyorhinis with Streptococcus suis Serotype 2 Using In Vitro Co-Infection Models with Swine Cells

Bacterial and/or viral co-infections are very common in swine production and cause severe economic losses. Mycoplasma hyopneumoniae, Mycoplasma hyorhinis and Streptococcus suis are pathogenic bacteria that may be found simultaneously in the respiratory tracts of pigs. In the present study, the interactions of S. suis with epithelial and phagocytic cells in the presence or absence of a pre-infection with M. hyopneumoniae and/or M. hyorhinis were studied. Results showed relatively limited interactions between these pathogens. A previous infection with one or both mycoplasmas did not influence the adhesion or invasion properties of S. suis in epithelial cells or its resistance to phagocytosis (including intracellular survival) by macrophages and dendritic cells. The most important effect observed during the co-infection was a clear increment in toxicity for the cells. An increase in the relative expression of the pro-inflammatory cytokines IL-6 and CXCL8 was also observed; however, this was the consequence of an additive effect due to the presence of different pathogens rather than a synergic effect. It may be hypothesized that if one or both mycoplasmas are present along with S. suis in the lower respiratory tract at the same time, then increased damage to epithelial cells and phagocytes, as well as an increased release of pro-inflammatory cytokines, may eventually enhance the invasive properties of S. suis. However, more studies should be carried out to confirm this hypothesis.

Development of a Versatile Toolbox for Genetic Manipulation of Sporothrix brasiliensis

Sporothrix brasiliensis has emerged as the most virulent species in the Sporothrix schenckii complex, accounting for sporotrichosis. Albeit the new insights into the understanding of host-pathogen interactions and comparative genomics of this fungi, the lack of genetic tools has hindered significant advances in this field of research. Here, we established an Agrobacterium tumefaciens-mediated transformation (ATMT) system to transform different strains of S. brasiliensis. We report parameters that account for a transformation efficiency of 3,179 ± 1,171 transformants/co-cultivation, which include the use of A. tumefaciens AGL-1 in a 2:1 ratio (bacteria:fungi) during 72 h at 26°C. Our data show that a single-copy transgene is transferred to S. brasiliensis that is mitotically stable in 99% of cells after 10 generations without selective pressure. In addition, we created a plasmid toolkit that allows the establishment of fusion proteins of any S. brasiliensis gene of interest with sGFP or mCherry under the control of the GAPDH or H2A endogenous promoters. These modules allow different levels of expression of the desired fusion. Moreover, we successfully targeted these fluorescent proteins to the nucleus and used fluorescence-tagged strains to assess phagocytosis. Overall, our data show that the ATMT system is an easy-to-use and efficient genetic toolbox for studies on recombinant expression and gene function in S. brasiliensis. IMPORTANCE Sporotrichosis is the most prevalent subcutaneous mycosis worldwide and has recently become a public health concern. Although immunocompetent hosts are also prone to sporotrichosis, immunodeficient hosts often develop a more severe and disseminated form of disease. To date, the Rio de Janeiro state in Brazil is the most significant feline zoonotic transmission epicenter in the world, with more than 4,000 human and feline diagnosed cases. Cats play an essential role in the S. brasiliensis infection due to their high susceptibility and transmissibility to other felines and humans. S. brasiliensis is the most virulent etiological agent of sporotrichosis, causing the most severe clinical manifestations. Despite the increasing incidence of sporotrichosis, the identification of virulence traits important for disease establishment, development, and severity has been lacking. In this work, we established an efficient genetic toolbox to manipulate S. brasiliensis that will guide future studies to define new virulence mechanisms and a better understanding of host-pathogen interactions from a molecular perspective.

Incomplete autophagy promotes the proliferation of Mycoplasma hyopneumoniae through the JNK and Akt pathways in porcine alveolar macrophages

Autophagy is an important conserved homeostatic process related to nutrient and energy deficiency and organelle damage in diverse eukaryotic cells and has been reported to play an important role in cellular responses to pathogens and bacterial replication. The respiratory bacterium Mycoplasma hyopneumoniae has been identified to enter porcine alveolar macrophages, which are considered important immune cells. However, little is known about the role of autophagy in the pathogenesis of M. hyopneumoniae infection of porcine alveolar macrophages. Our experiments demonstrated that M. hyopneumoniae infection enhanced the formation of autophagosomes in porcine alveolar macrophages but prevented the fusion of autophagosomes with lysosomes, thereby blocking autophagic flux and preventing the acidification and destruction of M. hyopneumoniae in low-pH surroundings. In addition, using different autophagy regulators to intervene in the autophagy process, we found that incomplete autophagy promoted the intracellular proliferation of M. hyopneumoniae. We also found that blocking the phosphorylation of JNK and Akt downregulated the autophagy induced by M. hyopneumoniae, but pathways related to two mitogen-activated protein kinases (Erk1/2 and p38) did not affect the process. Collectively, M. hyopneumoniae induced incomplete autophagy in porcine alveolar macrophages through the JNK and Akt signalling pathways; conversely, incomplete autophagy prevented M. hyopneumoniae from entering and degrading lysosomes to realize the proliferation of M. hyopneumoniae in porcine alveolar macrophages. These findings raise the possibility that targeting the autophagic pathway may be effective for the prevention or treatment of M. hyopneumoniae infection.

Neutrophil and M2-polarized Macrophage Infiltration, Expression of IL-8 and Apoptosis in Mycoplasma hyopneumoniae Pneumonia in Swine

Mycoplasma hyopneumoniae (Mhp) is the primary pathogen of porcine enzootic pneumonia (PEP). Consolidated lung tissue from the cranioventral lung lobes of 15 pigs with PEP was collected for quantitative polymerase chain reaction, histopathology and immunohistochemistry. Histopathology revealed the co-existence of bronchial-associated lymphoid tissue hyperplasia with intra-alveolar neutrophils and macrophage infiltration in lesions of suppurative bronchopneumonia. Immunolabelling of infiltrated macrophages with CD163/CD204 indicated the presence of M2-polarized macrophages. Mhp antigen was detected on respiratory epithelial cells and in phagocytosed neutrophils. The intensity of Mhp immunolabelling and number of CD163/CD204-positive macrophages were correlated with the Mhp load in lung tissue (r = 0.87, 0.56, P <0.05). IL-8 immunolabelling was mainly found in neutrophils and correlated with Mhp load, Mhp immunolabelling and histological lesion score (r = 0.70, 0.66, 0.64, P <0.05), respectively. Apoptosis was seen in intra-alveolar cells and was correlated with Mhp load (r = 0.62, P <0.05). It is postulated that IL-8 attracts neutrophils to the lesions, while M2-polarized macrophages are a major source of IL-10 and promote a Th2-type immune response.

Pathogenicity & virulence of Mycoplasma hyopneumoniae

Mycoplasma hyopneumoniae: is the etiological agent of porcine enzootic pneumonia (EP), a disease that impacts the swine industry worldwide. Pathogen-induced damage, as well as the elicited host-response, contribute to disease. Here, we provide an overview of EP epidemiology, control and prevention, and a more in-depth review of M. hyopneumoniae pathogenicity determinants, highlighting some molecular mechanisms of pathogen-host interactions relevant for pathogenesis. Based on recent functional, immunological, and comparative “omics” results, we discuss the roles of many known or putative M. hyopneumoniae virulence factors, along with host molecules involved in EP. Moreover, the known molecular bases of pathogenicity mechanisms, including M. hyopneumoniae adhesion to host respiratory epithelium, protein secretion, cell damage, host microbicidal response and its modulation, and maintenance of M. hyopneumoniae homeostasis during infection are described. Recent findings regarding M. hyopneumoniae pathogenicity determinants also contribute to the development of novel diagnostic tests, vaccines, and treatments for EP.

Perspectives for improvement of Mycoplasma hyopneumoniae vaccines in pigs

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

Genomic Variability and Post-translational Protein Processing Enhance the Immune Evasion of Mycoplasma hyopneumoniae and Its Interaction With the Porcine Immune System

Mycoplasma hyopneumoniae (M. hyopneumoniae, Mhp) is a geographically widespread and economically devastating pathogen that colonizes ciliated epithelium; the infection of Mhp can damnify the mucociliary functions as well as leading to Mycoplasma pneumonia of swine (MPS). MPS is a chronic respiratory infectious disease with high infectivity, and the mortality can be increased by secondary infections as the host immunity gets down-regulated during Mhp infection. The host immune responses are regarded as the main driving force for the disease development, while MPS is prone to attack repeatedly in farms even with vaccination or other treatments. As one of the smallest microorganisms with limited genome scale and metabolic pathways, Mhp can use several mechanisms to achieve immune evasion effect and derive enough nutrients from its host, indicating that there is a strong interaction between Mhp and porcine organism. In this review, we summarized the immune evasion mechanisms from genomic variability and post-translational protein processing. Besides, Mhp can induce the immune cells apoptosis by reactive oxygen species production, excessive nitric oxide (NO) release and caspase activation, and stimulate the release of cytokines to regulate inflammation. This article seeks to provide some new points to reveal the complicated interaction between the pathogen and host immune system with Mhp as a typical example, further providing some new strategies for the vaccine development against Mhp 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.

Upregulation of PD-L1 Expression by Prostaglandin E2 and the Enhancement of IFN-γ by Anti-PD-L1 Antibody Combined With a COX-2 Inhibitor in Mycoplasma bovis Infection

Bovine mycoplasmosis caused by Mycoplasma bovis results in pneumonia and mastitis in cattle. We previously demonstrated that the programmed death 1 (PD-1)/PD-ligand 1 (PD-L1) pathway is involved in immune dysfunction during M. bovis infection and that prostaglandin E₂ (PGE₂) suppressed immune responses and upregulated PD-L1 expression in Johne's disease, a bacterial infection in cattle. In this study, we investigated the role of PGE₂ in immune dysfunction and the relationship between PGE₂ and the PD-1/PD-L1 pathway in M. bovis infection. In vitro stimulation with M. bovis upregulated the expressions of PGE₂ and PD-L1 presumably via Toll-like receptor 2 in bovine peripheral blood mononuclear cells (PBMCs). PGE₂ levels of peripheral blood in infected cattle were significantly increased compared with those in uninfected cattle. Remarkably, plasma PGE₂ levels were positively correlated with the proportions of PD-L1⁺ monocytes in M. bovis-infected cattle. Additionally, plasma PGE₂ production in infected cattle was negatively correlated with M. bovis-specific interferon (IFN)-γ production from PBMCs. These results suggest that PGE₂ could be one of the inducers of PD-L1 expression and could be involved in immunosuppression during M. bovis infection. In vitro blockade assays using anti-bovine PD-L1 antibody and a cyclooxygenase 2 inhibitor significantly upregulated the M. bovis-specific IFN-γ response. Our study findings might contribute to the development of novel therapeutic strategies for bovine mycoplasmosis that target PGE₂ and the PD-1/PD-L1 pathway.