Tactics of Mycobacterium avium subsp. paratuberculosis for intracellular survival in mononuclear phagocytes

Mycobacterium avium subsp. paratuberculosis Virulence: A Review

To propose a solution for control of Mycobacterium avium subsp. paratuberculosis (MAP) infections in animals as well as in humans, and develop effective prevention, diagnostic and treatment strategies, it is essential to understand the molecular mechanisms of MAP pathogenesis. In the present review, we discuss the mechanisms utilised by MAP to overcome the host defense system to achieve the virulence status. Putative MAP virulence genes are mentioned and their probable roles in view of other mycobacteria are discussed. This review provides information on MAP strain diversity, putative MAP virulence factors and highlights the knowledge gaps regarding MAP virulence mechanisms that may be important in control and prevention of paratuberculosis.

Application of Transcriptomics to Enhance Early Diagnostics of Mycobacterial Infections, with an Emphasis on Mycobacterium avium ssp. paratuberculosis

Mycobacteria cause a wide variety of disease in human and animals. Species that infect ruminants include M. bovis and M. avium ssp. paratuberculosis (MAP). MAP is the causative agent of Johne’s disease in ruminants, which is a chronic granulomatous enteric infection that leads to severe economic losses worldwide. Characteristic of MAP infection is the long, latent phase in which intermittent shedding can take place, while diagnostic tests are unable to reliably detect an infection in this stage. This leads to unnoticed dissemination within herds and the presence of many undetected, silent carriers, which makes the eradication of Johne’s disease difficult. To improve the control of MAP infection, research is aimed at improving early diagnosis. Transcriptomic approaches can be applied to characterize host-pathogen interactions during infection, and to develop novel biomarkers using transcriptional profiles. Studies have focused on the identification of specific RNAs that are expressed in different infection stages, which will assist in the development and clinical implementation of early diagnostic tests.

Johne's disease in cattle: an in vitro model to study early response to infection of Mycobacterium avium subsp. paratuberculosis using RNA-seq

Johne's disease is a chronic granulomatous enteritis caused by Mycobacterium avium subsp. paratubercolosis (MAP) which affects ruminants worldwide and has a significant economic impact. MAP has also been associated with human Crohn's disease, although this connection is not well established. MAP is highly adapted for survival within host macrophages and prevents macrophage activation, blocks phagosome acidification and maturation, and attenuates presentation of antigens to the immune system. The consequence is a very long silent infection before clinical signs are observed. The present work examined the transcriptome of bovine monocyte-derived macrophages (MDM) infected with the L1 strain of MAP at 2h, 6h and 24h post infection using RNA-seq. Pathway over-representation analysis of genes differentially expressed between infected vs. control MDM identified that immune related pathways were affected. Genes belonging to the cytokine-cytokine receptor interaction pathway and members of the JAK-STAT pathway, which is involved in the regulation of immune response, were up-regulated. However, in parallel inhibitors of immune functions were activated, including suppressor of cytokine signaling (SOCS) and cytokine-inducible SH2-containing protein (CISH), which most likely suppresses IFNγ and the JAK/STAT signaling cascade in infected MDM, which may favour MAP survival. After exposure, macrophages phagocytise pathogens, activate the complement cascade and the adaptive immune system through the antigen presentation process. However, data presented here suggest that genes related to phagocytosis and lysosome function are down regulated in MAP infected MDM. Genes of MHC class II and complement pathway were also down-regulated. This study therefore shows that MAP infection is associated with changes in expression of genes related to the host immune response that may affect its ability to survive and multiply inside the host cell.

Detection of Mycobacterium avium subsp. paratuberculosis in non-human primates

BACKGROUND

Due to a sporadic occurrence of Mycobacterium avium subsp. paratuberculosis (MAP) in non-human primates (NHP), the susceptibility of different NHP to MAP should be investigated.

METHODS

Fecal and tissue samples (ileum, ileocecal lymph node, bone marrow) of 20 animals (seven species) were analyzed by IS900-based PCRs and sequenced. Samples of MAP PCR positive NHP were further cultivated.

RESULTS

MAP DNA was detectable in two animals; the ileum of a cottontop tamarin and the bone marrow of a common marmoset. Cultivation of MAP failed. Sequence analysis revealed 100% homology to the MAP-K10 sequence. Pathohistological examinations offered no direct correlation to a MAP infection.

CONCLUSIONS

MAP was detected for the first time in a common marmoset. But as both NHP suffered from other diseases, an asymptomatic infection with MAP was assumed. The detection of MAP in the bone marrow might play a role in establishing latent paratuberculosis, as known from tuberculosis.

The immunoregulatory effects of co-infection with Fasciola hepatica: From bovine tuberculosis to Johne's disease

Fasciola hepatica (liver fluke) is a parasite prevalent in much of the world that causes the economically-important disease of fasciolosis in livestock. The threat that this disease poses extends beyond its direct effects due to the parasite's immunomodulatory effects. Research at this laboratory is focusing on whether this immunoregulation can, in animals infected with liver fluke, exert a bystander effect on concurrent infections in the host. It has already been established that F. hepatica infection reduces cell mediated immune responses to Mycobacterium bovis in cattle, and that the interaction between the two pathogens can be detected on an epidemiological scale. This review explores the immunological consequences of co-infection between F. hepatica and other bacterial infections. Arguments are presented suggesting that immunity of cattle to Mycobacterium avium subsp. paratuberculosis is also likely to be affected.

Host Transcriptional Profiles and Immunopathologic Response following Mycobacterium avium subsp. paratuberculosis Infection in Mice

Paratuberculosis or Johne’s disease is a chronic granulomatous enteropathy in ruminants caused by Mycobacterium avium subsp. paratuberculosis (MAP) infection. In the present study, we examined the host response to MAP infection in spleens of mice in order to investigate the host immunopathology accompanying host-pathogen interaction. Transcriptional profiles of the MAP-infected mice at 3 and 6 weeks p.i. showed severe histopathological changes, whereas those at 12 weeks p.i. displayed reduced lesion severity in the spleen and liver. MAP-infected mice at 3 and 6 weeks p.i. showed up-regulation of interferon-related genes, scavenger receptor, and complement components, suggesting an initial innate immune reaction, such as macrophage activation, bactericidal activity, and macrophage invasion of MAP. Concurrently, MAP-infected mice at 3 and 6 weeks p.i. were also suggested to express M2 macrophage phenotype with up-regulation of Mrc1, and Marco and down-regulation of MHC class II, Ccr7, and Irf5, and canonical pathways related to the T cell response including ICOS-ICOSL signaling in T helper cells, calcium-induced T lymphocyte apoptosis, and CD28 signaling in T helper cell. These results provide information which furthers the understanding of the immunopathologic response to MAP infection in mice, thereby providing insights valuable for research into the pathogenesis for MAP infection.

Effect of Penicillium mycotoxins on the cytokine gene expression, reactive oxygen species production, and phagocytosis of bovine macrophage (BoMacs) function

Bovine macrophages (BoMacs) were exposed to the following Penicillium mycotoxins (PM): citrinin (CIT), ochratoxin A (OTA), patulin (PAT), mycophenolic acid (MPA) and penicillic acid (PA). PM exposure at the concentration that inhibits proliferation by 25% (IC25) differentially for 24h altered the gene expression of various cytokines. OTA significantly induced IL-1α expression (p<0.05), while the expression of IL-6 was suppressed (p<0.01). MPA significantly induced the expression of IL-1α (p<0.05) and reduced the expression of IL-12α (p<0.01) and IL-10 (p<0.01). PAT significantly suppressed the expression of IL-23 (p<0.01), IL-10 (p<0.05) and TGF-β (p<0.05). Some PMs also affected reactive oxygen species (ROS) and phagocytosis of Mycobacterium avium ssp. Paratuberculosis (MAP) at higher concentrations. PAT and PA for example, significantly decreased the percent phagocytosis of MAP at 5.0 (p<0.01) and 15.6 μM (p<0.01), respectively, but only PA significantly suppressed PAM-3-stimulated ROS production at 62.5 (p<0.05) and 250.0 μM (p<0.01). OTA significantly increased the percent phagocytosis of MAP at 6.3 (p<0.05) and 12.5 μM (p<0.01). These findings suggest that exposure to sub-lethal concentrations of PMs can affect macrophage function, which could affect immunoregulation and innate disease resistance to pathogens.

Host responses to the pathogen Mycobacterium avium subsp. paratuberculosis and beneficial microbes exhibit host sex specificity

Differences between microbial pathogenesis in male and female hosts are well characterized in disease conditions connected to sexual transmission. However, limited biological insight is available on variances attributed to sex specificity in host-microbe interactions, and it is most often a minimized variable outside these transmission events. In this work, we studied two gut microbes-a pathogen, Mycobacterium avium subsp. paratuberculosis, and a probiotic, Lactobacillus animalis NP-51-and the interaction between each agent and the male and female gastrointestinal systems. This trial was conducted in BALB/c mice (n=5 per experimental group and per sex at a given time point), with analysis at four time points over 180 days. Host responses to M.avium subsp. paratuberculosis and L. animalis were sensitive to sex. Cytokines that were significantly different (P ≤ 0.05) betweenthe sexes included interleukin-1α/β (IL-1α/β), IL-17, IL-6, IL-10, IL-12, and gamma interferon (IFN-) and were dependent on experimental conditions. However, granulocyte-macrophage colony-stimulating factor (GM-CSF), vascular endothelial growth factor (VEGF), and IL-13/23 showed no sex specificity. A metabolomics study indicated a 0.5- to 2.0-fold (log2 scale) increase in short-chain fatty acids (butyrate and acetate) in males and greater increases in o-phosphocholine or histidine from female colon tissues; variances distinct to each sex were observed with age or long-term probiotic consumption. Two genera, Staphylococcus and Roseburia, were consistently overrepresented in females compared to males; other species were specific to one sex but fluctuated depending on experimental conditions. The differences observed suggest that male and female gut tissues and microbiota respond to newly introduced microorganisms differently and that gut-associated microorganisms with host immune system responses and metabolic activity are supported by biology distinct to the host sex.

The within host dynamics of Mycobacterium avium ssp. paratuberculosis infection in cattle: where time and place matter

Johne’s disease or paratuberculosis, caused by Mycobacterium avium subsp. paratuberculosis (MAP), occurs in domestic and wild animals worldwide, causing a significant economic loss to livestock industries. After a prolonged incubation time, infected cattle shed MAP bacilli into feces and spread the disease to an uninfected animal population. It is largely unknown how (or whether) the interplay between the pathogen and the host immunity determines timing of shedding after the long incubation time. Such information would provide an understanding of pathogenesis in individual animals and the epidemiology of MAP infection in animal populations. In this review, we summarize current knowledge of bovine Johne’s disease pathology, pathogenesis, immunology and genetics. We discuss knowledge gaps that direly need to be addressed to provide a science-based approach to diagnostics and (immuno)prophylaxis. These knowledge gaps are related to anatomical/clinical manifestation of MAP invasion, interaction of bacteria with phagocytes, granuloma formation, shedding, establishment and kinetics of adaptive immune responses in the pathogenesis of the disease. These topics are discussed at the molecular, cellular and tissue levels with special attention to the within host dynamics including the temporal and the spatial context relevant for the various host-pathogen interactions.

A comparison of cell mediators and serum cytokines transcript expression between male and female mice infected with Mycobacterium avium subspecies paratuberculosis and/or consuming probiotics

The gut immune system is complex, and dysregulation leads to a number of disorders including inflammatory bowel syndrome and (in livestock) Johne's disease. Previous work has demonstrated that males and females respond differently to treatment with pathologic and probiotic microorganisms, suggesting that a 'one-size-fits-all' approach to treat GIT inflammation may be inadequate. While we had observed significant differences between males and females in terms of cytokine production, it remains unclear how these changes occur. To better understand the mechanisms, transcript expression of genes important to gut immunoregulation were monitored from male and female BALB/c mice consuming the probiotic Lactobacillus animalis (1 × 10(6) CFU g(-1) ) and infected with the gut pathogen, Mycobacterium avium subspecies paratuberculosis (1 × 10(7) CFU). Expression of transcripts analyzed included those important to the immune system, intestinal cell differentiation, and/or regulation. Males generally displayed increased expression of Th 2 and B-cell mediators, and females showed repressed cytokine expression after MAP infection (IL-6, TNF-α, IL-1 among others). Additionally, regulation of pro-inflammatory mediators in female mice consuming probiotics suggests females responded positively to L. animalis when compared to males. Therefore, we speculate that studying mechanistic changes associated with sex and immunoregulation in gastrointestinal tissues could further elucidate host response to microorganisms.

Evidence of passive faecal shedding of Mycobacterium avium subsp. paratuberculosis in a Limousin cattle herd

It has been suggested that passive shedding of Mycobacterium avium subsp. paratuberculosis (MAP) in faeces may occur, but reliable data are missing. Passive shedding assumes the ingestion of MAP in contaminated feed and passive passage through the gastrointestinal tract without causing infection. In this study the presence of MAP in faeces in a closed herd of Limousin cattle was monitored for 53 months using quantitative real time PCR (qPCR) and culture. The initial prevalence of MAP in the herd was determined to be 63.4% and 4.9% using qPCR and culture, respectively. After the removal of two culture- and qPCR-positive (>10(4) MAP cells/g) cows, the prevalence of MAP using qPCR decreased to 42.1% and later to 15.6% and 6.7%. The continuous removal of suspected animals from the herd during the monitoring period minimised the presence of MAP in faeces to sporadic, which may have resulted from a decrease in the environmental infectious pressure. The findings suggest that the presence of low numbers of MAP in bovine faeces may not necessarily be caused by real infection, but rather by passive passage of MAP. This phenomenon should therefore be considered when interpreting MAP qPCR data.

Competition for antigen between Th1 and Th2 responses determines the timing of the immune response switch during Mycobaterium avium subspecies paratuberulosis infection in ruminants

Johne's disease (JD), a persistent and slow progressing infection of ruminants such as cows and sheep, is caused by slow replicating bacilli Mycobacterium avium subspecies paratuberculosis (MAP) infecting macrophages in the gut. Infected animals initially mount a cell-mediated CD4 T cell response against MAP which is characterized by the production of interferon (Th1 response). Over time, Th1 response diminishes in most animals and antibody response to MAP antigens becomes dominant (Th2 response). The switch from Th1 to Th2 response occurs concomitantly with disease progression and shedding of the bacteria in feces. Mechanisms controlling this Th1/Th2 switch remain poorly understood. Because Th1 and Th2 responses are known to cross-inhibit each other, it is unclear why initially strong Th1 response is lost over time. Using a novel mathematical model of the immune response to MAP infection we show that the ability of extracellular bacteria to persist outside of macrophages naturally leads to switch of the cellular response to antibody production. Several additional mechanisms may also contribute to the timing of the Th1/Th2 switch including the rate of proliferation of Th1/Th2 responses at the site of infection, efficiency at which immune responses cross-inhibit each other, and the rate at which Th1 response becomes exhausted over time. Our basic model reasonably well explains four different kinetic patterns of the Th1/Th2 responses in MAP-infected sheep by variability in the initial bacterial dose and the efficiency of the MAP-specific T cell responses. Taken together, our novel mathematical model identifies factors of bacterial and host origin that drive kinetics of the immune response to MAP and provides the basis for testing the impact of vaccination or early treatment on the duration of infection.

Mycobacterium avium subsp. paratuberculosis (MAP) is the causative agent of Johne's disease, a chronic enteric disease of ruminants such as sheep and cows. Due to early culling and reduction in milk production of affected animals, MAP inflicts high economic cost to diary farms. MAP infection has a long incubation period of several years, and during the asymptomatic stage a strong cellular (T helper 1) immune response is thought to control MAP replication. Over time, Th1 response is lost and ineffective antibody response driven by Th2 cells becomes predominant. We develop the first mathematical model of helper T cell response to MAP infection to understand impact of various mechanisms on the dynamics of the switch from Th1 to Th2 response. Our results suggest that in contrast to the generally held belief, Th1/Th2 switch may be driven by the accumulation of long-lived extracellular bacteria, and therefore, may be the consequence of the disease progression of MAP-infected animals and not its cause. Our model highlights limitations of our current understanding of regulation of helper T cell responses during MAP infection and identifies areas for future experimental research.

Effects of the probiotic Lactobacillus animalis in murine Mycobacterium avium subspecies paratuberculosis infection

Background

MAP is a suspected zoonotic pathogen and the causative agent of Johne’s Disease in cattle and other ruminant animals. With over $1 billion dollars in loss to the dairy industry due to Johne’s Disease, efforts to eliminate or reduce MAP from cattle are of importance. The purpose of this study was to determine if daily intake of probiotics could eliminate or reduce Johne’s Disease associated symptoms and pathogenesis by MAP. Post infection, animals are often asymptomatic carriers with limited shedding of the pathogen, proving early detection to be difficult. Disease and symptoms often appear 3–4 years after infection with antibiotic treatment proving ineffective. Symptoms include chronic gastrointestinal inflammation leading to severe weight-loss from poor feed and water intake cause a wasting disease. These symptoms are similar to those found in individuals with Crohn’s Disease (CD); MAP has been implicated by not proven to be the causative agent of CD. Probiotics administered to livestock animals, including dairy and beef cattle have demonstrated improvements in cattle performance and health. Our objectives included determining the benefits of Lactobacillus animalis (strain name: NP-51) in MAP infected BALB/c mice by evaluating systemic and gastrointestinal response by the host and gut microbiota. Male and female animals were fed 1×10⁶ CFU/g probiotics in sterile, powdered mouse chow daily and infected with 1 × 10⁷ CFU/ml MAP and compared to controls. Animals were evaluated for 180 days to assess acute and chronic stages of disease, with sample collection from animals every 45 days. MAP concentrations from liver and intestinal tissues were examined using real time-PCR methods and the expression of key inflammatory markers were measured during MAP infection (interferon-gamma [IFN-Υ], Interleukin-1α, IL-12, IL-10, IL-6, and Tumor necrosis factor alpha [TNF-α]).

Results

Our results demonstrate administration of probiotics reduces production of IFN-Υ and IL-6 while increasing TNF-α and IL-17 in chronic disease; healthful immune responses that reduce chronic inflammation associated to MAP infection.

Conclusions

We observed that the immune system’s response in the presence of probiotics to MAP contributes towards host health by influencing the activity of the immune system and gut microbial populations.

Use of the johnin PPD interferon-gamma assay in control of bovine paratuberculosis

Although the interferon-gamma (IFN-γ) assay for measurements of cell-mediated immune (CMI) responses to paratuberculosis PPD (johnin) has been available for close to 20 years, the assay has not yet emerged as the long desired test to identify infected animals at an early time point. Among other issues, this relates to problematic interpretation of the test results and maybe an over-expectation of what can be deducted from this kind of test given the chronic nature and slow development of infection of paratuberculosis. Over a number of years a modified IFN-γ assay with addition of recombinant bovine IL-12 to the PPDj stimulation of blood samples from the heifer group in more than 20 Danish dairy herds which also perform surveillance of MAP antibodies in milk have been performed. The results indicate that IFN-γ assay results are specific for paratuberculosis, but the IFN-γ assay result of an individual animal cannot establish whether the animal is infected or predict the future progression of disease in this animal. The IFN-γ assay should thus be used on a group of animals to test the level of exposure to paratuberculosis bacteria the animals have experienced, and thereby assist in maintaining rational in-herd management procedures and in the establishment of paratuberculosis status of a given herd. Indeed, for any diagnostic test applied in paratuberculosis, both the diagnostic target condition and the purpose of the diagnostic testing must be considered before any meaningful estimates of sensitivity or specificity can be given.

Current perspectives on Mycobacterium avium subsp. paratuberculosis, Johne's disease, and Crohn's disease: a review

Mycobacterium avium subsp. paratuberculosis (MAP) causes the disease of cattle, Johne's. The economic impact of this disease includes early culling of infected cattle, reduced milk yield, and weight loss of cattle sold for slaughter. There is a possible link between MAP and Crohn's disease, a human inflammatory bowel disease. MAP is also a potential human food borne pathogen because it survives current pasteurization treatments. We review the current knowledge of MAP, Johne's disease and Crohn's disease and note directions for future work with this organism including rapid and economical detection, effective management plans and preventative measures.

Assessment of live candidate vaccines for paratuberculosis in animal models and macrophages

Mycobacterium avium subsp. paratuberculosis (basonym M. paratuberculosis) is the causative agent of paratuberculosis, a chronic enteritis of ruminants. To control the considerable economic effect that paratuberculosis has on the livestock industry, a vaccine that induces protection with minimal side effects is required. We employed transposon mutagenesis and allelic exchange to develop three potential vaccine candidates, which were then tested for virulence with macrophages, mice, and goats. All three models identified the WAg906 mutant as being the most attenuated, but some differences in the levels of attenuation were evident among the models when testing the other strains. In a preliminary mouse vaccine experiment, limited protection was induced by WAg915, as evidenced by a reduced bacterial load in spleens and livers 12 weeks following intraperitoneal challenge with M. paratuberculosis K10. While we found macrophages and murine models to be rapid and cost-effective alternatives for the initial screening of M. paratuberculosis mutants for attenuation, it appears necessary to do the definitive assessment of attenuation with a ruminant model.

A bovine macrophage screening system for identifying attenuated transposon mutants of Mycobacterium avium subsp. paratuberculosis with vaccine potential

Johne's disease is a chronic granulomatous enteritis in ruminants caused by Mycobacterium avium subsp. paratuberculosis (MAP). The disease is responsible for considerable economic losses in the livestock industry and in particular within the dairy sector. A more effective vaccine against Johne's disease would be of major benefit. In this study, we developed an efficient procedure for identifying mutants of MAP with reduced virulence that are potential live vaccine candidates against Johne's disease. A mariner transposon was used to create random insertional libraries in two different MAP strains (989 and k10), an effective cattle macrophage survival system was developed, and a total of 1890 insertion mutants were screened by using a 96-prong multi-blot replicator (frogger) system. Two of the transposon mutants with poor survival ability in macrophages were tested in mice. These strains were found to be attenuated in vivo, thereby validating the further use of this macrophage screening system to identify MAP mutants with potential as candidate vaccines against Johne's disease.