The early lymphocyte proliferation response in sheep exposed to Mycobacterium avium subsp. paratuberculosis compared to infection status

Correlates of vaccine protection against Mycobacterium avium sub-species paratuberculosis infection revealed in a transcriptomic study of responses in Gudair® vaccinated sheep

A critical hindrance in the development of effective vaccine strategies to combat infectious disease is lack of knowledge about correlates of protection and of the host responses necessary for successful adaptive immunity. Often vaccine formulations are developed by stepwise experimentation, with incomplete investigation of the fundamental mechanisms of protection. Gudair^® is a commercially available vaccine registered for use in sheep and goats for controlling spread of Mycobacterium avium sub-species paratuberculosis (MAP) infections and reduces mortality by up to 90%. Here, using an experimental infection model in sheep, we have utilized a transcriptomics approach to identify white blood cell gene expression changes in vaccinated, MAP-exposed Merino sheep with a protective response in comparison to those vaccinated animals that failed to develop immunity to MAP infection. This methodology facilitated an overview of gene-associated functional pathway adaptations using an in-silico analysis approach. We identified a group of genes that were activated in the vaccine-protected animals and confirmed stability of expression in samples obtained from naturally exposed commercially maintained sheep. We propose these genes as correlates of vaccine induced protection.

Mycobacterium avium subsp. paratuberculosis exploits miRNA expression to modulate lipid metabolism and macrophage polarisation pathways during infection

Pathogenic mycobacteria including Mycobacterium avium subsp. paratuberculosis (MAP), the causative agent of Johne's disease, manipulate host macrophages to persist and cause disease. In mycobacterial infection, highly plastic macrophages, shift between inflammatory M1 and permissive M2 phenotypes which alter the disease outcome and allow bacteria to survive intracellularly. Here we examine the impact of MAP infection on polarised macrophages and how increased lipid availability alters macrophage phenotype and bacterial persistence. Further, we assess if host microRNA (miRNA) are sensitive to macrophage polarisation state and how MAP can drive their expression to overcome innate responses. Using in vitro MAP infection, we find that increasing lipid availability through supplementing culture media with exogenous lipid increases cellular nitric oxide production. Lipid-associated miRs -19a, -129, -24, and -24-3p are differentially expressed following macrophage polarisation and lipid supplementation and are further regulated during MAP infection. Collectively, our results highlight the importance of host lipid metabolism in MAP infection and demonstrate control of miRNA expression by MAP to favour intracellular persistence.

Influence of Heterologous and Homologous Vaccines, and Their Components, on the Host Immune Response and Protection Against Experimental Caprine Paratuberculosis

Vaccination against paratuberculosis, a chronic disease of ruminants caused by Mycobacterium avium subsp. paratuberculosis (Map), has been considered as the most effective control method. However, protection is incomplete, and the mechanisms operating in the response of the animals to vaccination are not fully understood. Therefore, this study analyzed the immune response and the effects on protection against Map infection, elicited by paratuberculosis (Silirum®) and tuberculosis (heat-inactivated M. bovis [HIMB]) vaccines and their components in a caprine experimental model. Fifty goat kids were divided into 10 groups (n = 5) according to their vaccination (Silirum®, HIMB and nonvaccinated), immunization (inactivated bacteria or adjuvant), and/or infection. Oral challenge with Map was performed 45 days postvaccination/immunization (dpv), and animals were euthanized at 190 dpv. Peripheral immune response and proportion of lymphocyte subpopulations were assessed monthly by enzyme-linked immunosorbent assay and flow cytometry analysis, respectively. Local immune response, proportion of tissue lymphocyte subpopulations, Map detection (polymerase chain reaction), and histological examination were conducted in gut-associated lymphoid tissues. All infected groups developed paratuberculosis granulomatous lesions despite vaccination or immunization. The Silirum® and HIMB-vaccinated groups showed a considerable lesion reduction consistent with a significant peripheral cellular and humoral immune response. Besides, a lower number of granulomas were observed in groups immunized with inactivated bacteria and adjuvants in comparison to nonvaccinated and infected group. However, despite not being significant, this reduction was even higher in adjuvant immunized groups, which developed milder granulomatous lesion with no detectable peripheral immune responses associated with immunization. No changes in the peripheral and local proportion of lymphocyte subsets or local immune response were detected in relation to either vaccination/immunization or infection. Despite that paratuberculosis and tuberculosis vaccination showed a partial and cross-protection against Map infection, respectively, only histological examination could assess the progression of infection in these animals. In addition, the pattern observed in the reduction of the lesions in adjuvant immunized groups suggests the possible involvement of a nonspecific immune response that reduces the development of granulomatous lesions.

Integrated Analysis of lncRNAs, mRNAs, and TFs to Identify Regulatory Networks Underlying MAP Infection in Cattle

Johne’s disease is a chronic infection of ruminants that burdens dairy herds with a significant economic loss. The pathogenesis of the disease has not been revealed clearly due to its complex nature. In order to achieve deeper biological insights into molecular mechanisms involved in MAP infection resulting in Johne’s disease, a system biology approach was used. As far as is known, this is the first study that considers lncRNAs, TFs, and mRNAs, simultaneously, to construct an integrated gene regulatory network involved in MAP infection. Weighted gene coexpression network analysis (WGCNA) and functional enrichment analysis were conducted to explore coexpression modules from which nonpreserved modules had altered connectivity patterns. After identification of hub and hub-hub genes as well as TFs and lncRNAs in the nonpreserved modules, integrated networks of lncRNA-mRNA-TF were constructed, and cis and trans targets of lncRNAs were identified. Both cis and trans targets of lncRNAs were found in eight nonpreserved modules. Twenty-one of 47 nonpreserved modules showed significant biological processes related to the immune system and MAP infection. Some of the MAP infection’s related pathways in the most important nonpreserved modules comprise “positive regulation of cytokine-mediated signaling pathway,” “negative regulation of leukocyte migration,” “T-cell differentiation,” “neutrophil activation,” and “defense response.” Furthermore, several genes were identified in these modules, including SLC11A1, MAPK8IP1, HMGCR, IFNGR1, CMPK2, CORO1A, IRF1, LDLR, BOLA-DMB, and BOLA-DMA, which are potentially associated with MAP pathogenesis. This study not only enhanced our knowledge of molecular mechanisms behind MAP infection but also highlighted several promising hub and hub-hub genes involved in macrophage-pathogen interaction.

Apoptosis levels in bovine Johne's disease ileal lesions and association with bacterial numbers

Johne’s disease (JD) is a chronic granulomatous enteritis caused by Mycobacterium avium subsp. paratuberculosis (MAP). While it is generally accepted that MAP employs immune subversion mechanisms, aspects of the host-pathogen relationship are not fully understood. We sampled 3 ileal tissue sections from 17 naturally infected cattle (n = 51 sections) to analyze differences in cell types, apoptosis, and phagocytic cells. Diffuse multibacillary (DM) was the most common lesion type (n = 17) followed by diffuse intermediate (DI; n = 15). DM lesions had significantly greater proportion of Treg cells (CD3⁺ FoxP3⁺⁾ relative to all CD3⁺ T cells as compared to DI forms (P < .05). CD68⁺ individual cell size was significantly smaller in DM than in diffuse lymphocytic (DL) forms (P < .05). Area of caspase-3 positivity (apoptosis) was greater in DM lesions than DL (P < .05) and DI (P < .0001), and was linked to higher numbers of MAP within the macrophage.

Developing smarter vaccines for paratuberculosis: From early biomarkers to vaccine design

Vaccines for paratuberculosis have been used for over a hundred years but the disease continues to affect ruminant health and livestock industries globally. Mycobacterium avium subspecies paratuberculosis which causes the disease also known as Johne's disease is a subversive pathogen able to undermine both innate and adaptive host defense mechanisms. This review focuses on early protective immune pathways that lead to some animals becoming resilient to infection to provide a road map for designing better vaccines and emphasizes the need for harnessing the potential of mucosal immunity.

Ovine Paratuberculosis Control in Australia Revisited

Simple Summary

Ovine Johne’s Disease (OJD) is caused by Mycobacterium avium subspecies paratuberculosis (MAP) and is a less serious animal health issue in Australia than it was 10–20 years ago, with abattoir surveillance confirming declining prevalence. Control strategies for paratuberculosis potentially include (i) test and cull programs; (ii) management interventions to reduce faecal–oral transmission; and/or (iii) vaccination to limit and suppress infection, with the decline in OJD concern in Australia mostly attributable to vaccination programs providing effective disease suppression. However, as disease spread has continued, control program extension renewal to encourage the safe and wider use of vaccination, plus address misinformation promulgated by some disaffected producers, is required. As vaccination for OJD has contributed significantly to the welfare of Australian sheep, the livelihoods of producers, and reduced risk of MAP entering the human food chain, it should be more widely adopted globally.

Abstract

OJD is no longer the serious animal health issue that it was for many Australian rural communities a decade and a half ago. Despite declining OJD prevalence as determined by abattoir surveillance, the disease continues to spread, with OJD extension programs required to continually address the misinformation promulgated by some disaffected producers as new areas have become affected. Improved regional and on-farm biosecurity, including the introduction of a risk-based trading system, may have contributed to improved attitudes to OJD control, although attitudinal differences between OJD endemic areas and where the disease is not well established remain. Declines in on-farm OJD prevalence are almost certainly attributable to the widespread uptake of vaccination programs, although encouraging the ongoing use of vaccination to prevent recrudescence and improved biosecurity when mortalities disappear, remains challenging. Vaccination has provided a robust strategy for managing OJD and contributed significantly to the health of Australian sheep and the lives of producers with affected properties. As vaccination offers a pathway to reduce the risk of MAP infection entering the human food chain from small ruminant products, it should be more widely adopted globally, accompanied by research efforts to improve efficacy and importantly, the safety of vaccination to both operators and livestock.

Mycobacterium avium subsp. paratuberculosis MAP1889c Protein Induces Maturation of Dendritic Cells and Drives Th2-biased Immune Responses

Mycobacterium avium subsp. paratuberculosis (MAP) is a causative agent of chronic granulomatous bowel disease in animals and is associated with various autoimmune diseases in humans including Crohn’s disease. A good understanding of the host-protective immune response and antibacterial immunity controlled by MAP and its components may contribute to the development of effective control strategies. MAP1889c was identified as a seroreactive antigen in Crohn’s disease patients. In this study, we investigated the immunological function of MAP1889c in dendritic cells (DCs). MAP1889c stimulated DCs to increase expression of co-stimulatory molecules (CD80 and CD86) and major histocompatibility complex (MHC) class molecules and to secret higher interleukin (IL)-10 and moderate IL-6, tumor necrosis factor (TNF)-α, and IL-12p70 levels through the Toll-like receptor (TLR) 4 pathway. MAP1889c-induced DC activation was mediated by mitogen-activated protein kinases (MAPKs), cAMPp-response element binding protein (CREB), and nuclear factor kappa B (NF-κB). In particular, the CREB signal was essential for MAP1889c-mediated IL-10 production but not TNF-α and IL-12p70. In addition, MAP1889c-matured DCs induced T cell proliferation and drove the Th2 response. Production of lipopolysaccharide (LPS)-mediated pro-inflammatory cytokines and anti-inflammatory cytokines was suppressed and enhanced respectively by MAP1889c pretreatment in DCs and T cells. Furthermore, treatment of MAP1889c in M. avium-infected macrophages promoted intracellular bacterial growth and IL-10 production. These findings suggest that MAP1889c modulates the host antimycobacterial response and may be a potential virulence factor during MAP infection.

Case definition terminology for paratuberculosis (Johne's disease)

Paratuberculosis (Johne's disease) is an economically significant condition caused by Mycobacterium avium subsp. paratuberculosis. However, difficulties in diagnosis and classification of individual animals with the condition have hampered research and impeded efforts to halt its progressive spread in the global livestock industry. Descriptive terms applied to individual animals and herds such as exposed, infected, diseased, clinical, sub-clinical, infectious and resistant need to be defined so that they can be incorporated consistently into well-understood and reproducible case definitions. These allow for consistent classification of individuals in a population for the purposes of analysis based on accurate counts. The outputs might include the incidence of cases, frequency distributions of the number of cases by age class or more sophisticated analyses involving statistical comparisons of immune responses in vaccine development studies, or gene frequencies or expression data from cases and controls in genomic investigations. It is necessary to have agreed definitions in order to be able to make valid comparisons and meta-analyses of experiments conducted over time by a given researcher, in different laboratories, by different researchers, and in different countries. In this paper, terms are applied systematically in an hierarchical flow chart to enable classification of individual animals. We propose descriptive terms for different stages in the pathogenesis of paratuberculosis to enable their use in different types of studies and to enable an independent assessment of the extent to which accepted definitions for stages of disease have been applied consistently in any given study. This will assist in the general interpretation of data between studies, and will facilitate future meta-analyses.

Variation in susceptibility of different breeds of sheep to Mycobacterium avium subspecies paratuberculosis following experimental inoculation

Exposure to Mycobacterium avium subspecies paratuberculosis (MAP) does not always lead to Johne’s disease. Understanding differences in disease susceptibility of individual animals is a key aspect to controlling mycobacterial diseases. This study was designed to examine the susceptibility or resistance of various breeds of sheep to MAP infection. Merino, Suffolk first cross Merino, Border Leicester, and Poll Dorset sheep were orally inoculated with MAP and monitored for 14 months. Clinical disease occurred more frequently in the Merino (42%) and Suffolk first cross Merino (36%) compared to the Border Leicester (12%) and Poll Dorset (11%) breeds. Infection risk, as determined by culture of gut and associated lymphoid tissues, ranged from 75% for the Suffolk first cross Merino to 47% for the Poll Dorset sheep. Significant differences were identified in the site in the intestines of the most severe histopathological lesions and the immune responses to infection between the breeds. However, there was no difference in faecal MAP shedding by clinical cases between breeds. All breeds tested were susceptible to MAP infection, as determined by infection and clinical disease development, although there were differences in the proportions of diseased animals between the breeds. Poll Dorset and Border Leicester sheep were more resilient to MAP infection but there was evidence that more animals could have developed disease if given more time. These findings provide evidence of potential differential disease susceptibility between breeds, further our understanding of disease pathogenesis and risks of disease spread, and may have an influence on control programs for paratuberculosis.

The role of IL-10 in Mycobacterium avium subsp. paratuberculosis infection

Mycobacterium avium subsp. paratuberculosis (MAP) is an intracellular pathogen and is the causative agent of Johne's disease of domestic and wild ruminants. Johne's disease is characterized by chronic granulomatous enteritis leading to substantial economic losses to the livestock sector across the world. MAP persistently survives in phagocytic cells, most commonly in macrophages by disrupting its early antibacterial activity. MAP triggers several signaling pathways after attachment to pathogen recognition receptors (PRRs) of phagocytic cells. MAP adopts a survival strategy to escape the host defence mechanisms via the activation of mitogen-activated protein kinase (MAPK) pathway. The signaling mechanism initiated through toll like receptor 2 (TLR2) activates MAPK-p38 results in up-regulation of interleukin-10 (IL-10), and subsequent repression of inflammatory cytokines. The anti-inflammatory response of IL-10 is mediated through membrane-bound IL-10 receptors, leading to trans-phosphorylation and activation of Janus Kinase (JAK) family receptor-associated tyrosine kinases (TyKs), that promotes the activation of latent transcription factors, signal transducer and activators of transcription 3 (STAT3). IL-10 is an important inhibitory cytokine playing its role in blocking phagosome maturation and apoptosis. In the current review, we describe the importance of IL-10 in early phases of the MAP infection and regulatory mechanisms of the IL-10 dependent pathways in paratuberculosis. We also highlight the strategies to target IL-10, MAPK and STAT3 in other infections caused by intracellular pathogens.

Macrophage polarization in cattle experimentally exposed to Mycobacterium avium subsp. paratuberculosis

Mycobacterium avium subspecies paratuberculosis (MAP), the causative agent of Johne's disease (JD) in cattle, has significant impacts on the livestock industry and has been implicated in the etiology of Crohn's disease. Macrophages play a key role in JD pathogenesis, which is driven by the manipulation of host immune mechanisms by MAP. A change in the macrophage microenvironment due to pathogenic or host-derived stimuli can lead to classical (M1) or alternative (M2) polarization of macrophages. In addition, prior exposure to antigenic stimuli has been reported to alter the response of macrophages to subsequent stimuli. However, macrophage polarization in response to MAP exposure and its possible implications have not been previously addressed. In this study, we have comprehensively examined monocyte/macrophage polarization and responsiveness to antigens from MAP-exposed and unexposed animals. At 3 years post-exposure, there was a heterogeneous macrophage activation pattern characterized by both classical and alternate phenotypes. Moreover, subsequent exposure of macrophages from MAP-exposed cattle to antigens from MAP and other mycobacterial species led to significant variation in the production of nitric oxide, interleukin-10 and tumour necrosis factor α. These results indicate the previously unreported possibility of changes in the activation state and responsiveness of circulating monocytes/macrophages from MAP-exposed cattle.

Predicting the Role of IL-10 in the Regulation of the Adaptive Immune Responses in Mycobacterium avium Subsp. paratuberculosis Infections Using Mathematical Models

Mycobacterium avium subsp. paratuberculosis (MAP) is an intracellular bacterial pathogen that causes Johne’s disease (JD) in cattle and other animals. The hallmark of MAP infection in the early stages is a strong protective cell-mediated immune response (Th1-type), characterized by antigen-specific γ-interferon (IFN-γ). The Th1 response wanes with disease progression and is supplanted by a non-protective humoral immune response (Th2-type). Interleukin-10 (IL-10) is believed to play a critical role in the regulation of host immune responses to MAP infection and potentially orchestrate the reversal of Th1/Th2 immune dominance during disease progression. However, how its role correlates with MAP infection remains to be completely deciphered. We developed mathematical models to explain probable mechanisms for IL-10 involvement in MAP infection. We tested our models with IL-4, IL-10, IFN-γ, and MAP fecal shedding data collected from calves that were experimentally infected and followed over a period of 360 days in the study of Stabel and Robbe-Austerman (2011). Our models predicted that IL-10 can have different roles during MAP infection, (i) it can suppress the Th1 expression, (ii) can enhance Th2 (IL-4) expression, and (iii) can suppress the Th1 expression in synergy with IL-4. In these predicted roles, suppression of Th1 responses was correlated with increased number of MAP. We also predicted that Th1-mediated responses (IFN-γ) can lead to high expression of IL-10 and that infection burden regulates Th2 suppression by the Th1 response. Our models highlight areas where more experimental data is required to refine our model assumptions, and further test and investigate the role of IL-10 in MAP infection.

CD4⁺ T-cells, γδ T-cells and B-cells are associated with lack of vaccine protection in Mycobacterium avium subspecies paratuberculosis infection

Vaccination is one of the strategies used to control the spread of Mycobacterium avium subspecies paratuberculosis (MAP) infection in livestock. Gudair(®) is a widely-used vaccine in sheep and goats and is the only vaccine approved for use in sheep in Australia and New Zealand. This vaccine reduces mortality due to MAP-infection by up to 90% but some sheep remain infectious by shedding MAP in faeces, despite vaccination. In this study, using an experimental infection model in sheep, our aim was to assess differences in immune parameters between vaccinated MAP-exposed sheep in which the vaccine was effective compared to those in which it failed to protect against infection. We assessed immune parameters such as MAP-specific IFNγ, IL-10 and lymphocyte proliferative responses and serum antibody levels. At the end of the trial, 72% of non-vaccinated sheep and 24% of vaccinated sheep were infected, as defined by the detection of viable MAP in intestinal tissues when the trial was terminated at 49 weeks post exposure. There were significant differences in the proliferation of CD4(+), B and γδ T-cells over time in vaccinated sheep in which the vaccine failed to protect against infection compared to the non-infected vaccinated sheep. There were no significant differences in the IFNγ response or serum antibody levels between the vaccinated infected and vaccinated non-infected sheep. These results emphasise the importance of specific lymphocyte subsets in protecting against MAP-infection, especially in vaccinated sheep, and that immune parameters other than the commonly used IFNγ and antibody tests are required when assessing vaccine efficacy.

Investigation of immunity in sheep following footrot infection and vaccination

Ovine footrot is a major disease affecting sheep welfare and production. The anaerobic Gram-negative bacterium Dichelobacter nodosus is the essential transmitting agent. Monovalent or bivalent vaccines induce high levels of D. nodosus antibodies and are the basis of several successful footrot treatment, control and eradication programs. Due to the rapid rate of disease transmission within a flock, the presence of therapeutic vaccination non-responders has major implications for a control program. The aim of this study was to assess the immunological basis of a therapeutic vaccination non-response. Sheep (n=120) were infected with D. nodosus in an artificial pen challenge. Once disease had established, animals were vaccinated with a serogroup specific D. nodosus fimbrial vaccine. Based on the response to therapeutic vaccination, animals were allocated into one of three groups: (i) TVNR where disease persisted despite vaccination (ii) non-diseased, where disease never established and (iii) TVR, where disease was established but resolved with vaccination. Factors related to both the innate and adaptive immune pathways were assessed. These included antigen-specific serum antibodies, interferon-γ, interleukin-10, proliferation of lymphocyte subsets and phagocytic activity of leukocytes. There was no significant difference between the three groups of sheep for any of these parameters. All three groups of sheep produced antibody in excess of a previously published minimum antibody titre required for protection. Opsonising activity in sera from the three groups of sheep was also not significantly different and phagocytic cells from sheep from all three groups were able to destroy D. nodosus intracellularly. These findings show that the measured systemic adaptive and innate immune responses were unlikely to be the cause of a therapeutic vaccination non-response. They also show that the accepted minimum protective titre may be incorrect and may need further examination.

Lymphoproliferative and gamma interferon responses to stress-regulated Mycobacterium avium subsp. paratuberculosis recombinant proteins

Johne's disease in ruminants is a chronic infection of the intestines caused by Mycobacterium avium subsp. paratuberculosis. An important strategy to control disease is early detection, and a potentially efficient method for early detection is measurement of cell-mediated immune responses developed by the host in response to exposure or infection. One method is to measure lymphoproliferation and cytokine release from the host cells when exposed to the organism or parts of the organism. In this study, 10 recombinant M. avium subsp. paratuberculosis proteins known to be upregulated under in vitro stress conditions were evaluated by examining their ability to evoke memory as a result of exposure by vaccination or oral challenge with live Mycobacterium avium subsp. paratuberculosis. Out of 10 proteins, MAP2698c was found to induce higher cell-mediated immune responses in vaccinated and challenged sheep in comparison to healthy controls. The findings suggest that not all stress-regulated proteins have the diagnostic potential to detect cell-mediated immune responses in ovine paratuberculosis.

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.

Apoptosis of lymph node and peripheral blood cells in ovine Johne's disease

Ovine Johne's disease (OJD) is a degenerative wasting condition of ruminants caused by Mycobacterium avium subsp. paratuberculosis (MAP). Similar to other pathogenic mycobacterial infections it is a slow-progressing chronic disease and subclinically infected individuals can spread the disease while appearing healthy. MAP infects macrophages and the host responds by mounting a cell-mediated immune response. Disease progression is associated with immune dysfunction but the reasons are unknown. Increasing our current knowledge of the immunological mechanisms involved in disease progression, including apoptotic responses, may allow advancements in the area of early diagnosis, identification of resistant animals and disease control. We describe lymphocyte apoptosis in peripheral blood mononuclear cells (PBMC) and lymph node cells from sheep exposed to MAP as well as from healthy non-exposed sheep. Apoptosis in intestinal lymph node cells from MAP-exposed infected sheep, but not in MAP-exposed uninfected sheep, increased in response to MAP antigen. In this first longitudinal study of lymphocyte apoptosis using an experimental infection model of MAP infection, we found that there was a transient increase of ex vivo PBMC apoptosis in MAP-exposed sheep soon after exposure to MAP (4 months post inoculation). MAP antigen-specific apoptosis occurred later, at 12 months post inoculation. The cells involved were mainly γδ and CD4(+) T cells. Antigen-mediated lymphocyte apoptosis during mycobacterial disease progression could contribute to the immune dysfunction in Johne's disease.

In vivo and in vitro expression pattern of Toll-like receptors in Mycobacterium avium subspecies paratuberculosis infection

Johne's disease (JD) caused by Mycobacterium avium subspecies paratuberculosis (MAP) is a chronic infectious disease of ruminants. Activation of the Toll-like receptors (TLR) in response to microbial stimuli, including MAP, initiates responses in immune cells of the blood and within peripheral tissues. TLR2, 4 and 9 are believed to play a critical role in the initiation of immune responses against mycobacteria. In this study we report on the in vivo expression pattern of these receptors in sheep and cattle experimentally exposed to MAP. Experiments using the mouse macrophage cell line, RAW 264.7, and on isolated bovine monocytes were also carried out to assess the expression pattern of TLR2 and 4 in response to MAP and the non-pathogenic mycobacterial strain, M. smegmatis. Results from the in vivo study showed that there was a significant upregulation of TLR2 (P<0.05) at early time-points post-inoculation in the peripheral blood cells of sheep exposed to MAP S strain that went on to develop severe (multibacillary) disease. However, in the cattle during the initial months post-exposure to MAP C strain, TLR2 was significantly downregulated (P<0.05). TLR4 was significantly upregulated (P<0.05) at later stages (12 months post-inoculation) in MAP-exposed sheep with multibacillary disease; however significant differences in TLR4 expression were not observed in cattle. Expression of TLR9 was unchanged in MAP-exposed sheep and cattle. In vitro studies on mouse macrophages supported the findings of in vivo TLR2 gene expression increases seen in the sheep, in that the TLR2 receptor expression in response to MAP-infection was significantly increased in comparison to cells infected with a non-virulent mycobacterium, M. smegmatis. A likely role for TLR2 in the pathogenesis of Johne's disease is proposed.

Cellular and humoral immunogenicity of Mycobacterium avium subsp. paratuberculosis specific lipopentapeptide antigens

Paratuberculosis caused by Mycobacterium avium subsp. paratuberculosis (MAP) is a chronic infectious disease affecting domestic and wild ruminants. Antigens currently used for the diagnosis of paratuberculosis are whole-cell derived crude preparations. The identification of MAP-specific antigens for the specific and early diagnosis of this infection is strongly needed. This study assessed the ability of the MAP-specific synthetic lipopeptide antigen Para-LP-01 to invoke specific serum antibody (Ab) and cell-mediated immune (CMI) responses in sheep experimentally exposed to MAP S strain. Responses were compared to those elicited by the crude whole-cell derived MAP 316v antigen (316v). Para-LP-01 induced a significant serum Ab response in MAP-infected sheep in comparison with unexposed or uninfected sheep, but failed to induce detectable CMI responses including production of IFN-γ, IL-10 and lymphoproliferation, unlike 316v which invoked both CMI and serum Ab responses in MAP-exposed sheep. Para-LP-01 is a suitable antigen for serodiagnosis of MAP-infection in sheep. The differential induction of humoral and CMI responses by lipid based antigens could enhance current understanding of the role played by cell-wall associated lipid antigens in the pathogenesis of MAP-infection.

Innate immune markers that distinguish red deer (Cervus elaphus) selected for resistant or susceptible genotypes for Johne's disease

While many factors contribute to resistance and susceptibility to infectious disease, a major component is the genotype of the host and the way in which it is expressed. Johne’s disease is a chronic inflammatory bowel disease affecting ruminants and is caused by infection with Mycobacterium avium subspecies paratuberculosis (MAP). We have previously identified red deer breeds (Cervus elaphus) that are resistant; have a low rate of MAP infection and do not progress to develop Johne’s disease. In contrast, susceptible breeds have a high rate of MAP infection as seen by seroconversion and progress to develop clinical Johne’s disease. The aim of this study was to determine if immunological differences exist between animals of resistant or susceptible breeds. Macrophage cultures were derived from the monocytes of deer genotypically defined as resistant or susceptible to the development of Johne’s disease. Following in vitro infection of the cells with MAP, the expression of candidate genes was assessed by quantitative PCR as well as infection rate and cell death rate. The results indicate that macrophages from susceptible animals show a significantly higher upregulation of inflammatory genes (iNOS, IL-1α, TNF-α and IL-23p19) than the macrophages from resistant animals. Cells from resistant animals had a higher rate of apoptosis at 24 hours post infection (hpi) compared to macrophages from susceptible animals. The excessive expression of inflammatory mRNA transcripts in susceptible animals could cause inefficient clearing of the mycobacterial organism and the establishment of disease. Controlled upregulation of inflammatory pathways coupled with programmed cell death in the macrophages of resistant animals may predispose the host to a protective immune response against this mycobacterial pathogen.

Expression of genes associated with the antigen presentation and processing pathway are consistently regulated in early Mycobacterium avium subsp. paratuberculosis infection

The primary objective of this study was to evaluate early gene expression profiles associated with paratuberculosis in cattle exposed to known infectious doses of Mycobacterium avium sub-species paratuberculosis (MAP). A Johne's disease experimental infection field trial was conducted on a mixed population of Holstein and Holstein Red cattle. Blood samples from four MAP exposed and four unexposed cattle, selected based on IFNγ expressions were taken at 9, 13 and 21 weeks and RNA processed to Affymetrix GeneChip™ Bovine Genome arrays. Ontological analysis revealed consistent differences in gene expression between MAP exposed and control animals. A stark variation was observed in expression of a number of genes along antigen presentation pathways, suggesting that MAP exposure potentially results in the host immune response switching to a CD8(+) biased antigen presentation profile. This requires further in-depth analysis since it exposes a hitherto unconfirmed association between MAP exposure and in vivo MHC gene modulation.

Differences in the peripheral immune response between lambs and adult ewes experimentally infected with Mycobacterium avium subspecies paratuberculosis

The peripheral immune response, and its relationship with the outcome of the infection according to the age of the animal, has been investigated in young lambs and adult ewes experimentally infected with two different doses of Mycobacterium avium subspecies paratuberculosis (Map). Sixteen 1.5-month-old lambs out of 24 and 23 adult ewes out of 30 were orally challenged with an ovine Map field isolate. Animals were divided into two groups: HD, infected with a higher dose of Map and LD, with a lower dose. The remaining animals were used as uninfected control groups. Animals were euthanized at 110-120 and 210-220 days post-infection (dpi). Along the experiment, the humoral response and the specific and non-specific IFN-γ production were assessed. An intradermal skin test (IDT), using avian PPD, was also performed at 90 and 195 dpi. Samples of intestine and related lymphoid tissue were taken for histological, bacteriological and PCR studies. The Ab and IFN-γ production as well as the IDT response appeared earlier and with more intensity in the adult ewes compared to the lambs. The basal non-specific IFN-γ levels increased only in the adult ewes from the HD group. Animals from the LD and HD groups were positive to PCR; however, lesions consistent with paratuberculosis were exclusively observed in the HD group, both in lambs and in adult sheep, but they only progressed to more advanced stages in the former. These results suggest that the peripheral immune response induced by Map infection in the adult ewes is more efficient to control the progression of the infection than in lambs. This could likely be due to the existence of previous contacts with Map or other mycobacteria in the adult sheep compared to the young lambs.

Indoleamine 2,3-dioxygenase, tryptophan catabolism, and Mycobacterium avium subsp. paratuberculosis: a model for chronic mycobacterial infections

Virulent mycobacterial infections progress slowly, with a latent period that leads to clinical disease in a proportion of cases. Mycobacterium avium subsp. paratuberculosis is an intracellular pathogen that causes paratuberculosis or Johne's disease (JD), a chronic intestinal disease of ruminants. Indoleamine 2,3-dioxygenase (IDO), an enzyme that regulates tryptophan metabolism, was originally reported to have a role in intracellular pathogen killing and has since been shown to have an important immunoregulatory role in chronic immune diseases. Here we demonstrate an association between increased IDO levels and progression to clinical mycobacterial disease in a natural host, characterizing gene expression, protein localization, and functional effects. IDO mRNA levels were significantly increased in M. avium subsp. paratuberculosis-infected monocytic cells. Levels of both IDO gene and protein expression were significantly upregulated within the affected tissues of sheep with JD, particularly at the site of primary infection, the ileum, of animals with severe multibacillary disease. Lesion severity was correlated with the level of IDO gene expression. IDO gene expression was also increased in the peripheral blood cells of M. avium subsp. paratuberculosis-exposed sheep and cattle. IDO breaks down tryptophan, and systemic increases were functional, as shown by decreased plasma tryptophan levels, which correlated with the onset of clinical signs, a stage well known to be associated with Th1 immunosuppression. IDO may be involved in downregulating immune responses to M. avium subsp. paratuberculosis and other virulent mycobacteria, which may be an example of the pathogen harnessing host immunoregulatory pathways to aid survival. These findings raise new questions about the host-mycobacterium interactions in the progression from latent to clinical disease.

Comparative immunological and microbiological aspects of paratuberculosis as a model mycobacterial infection

Paratuberculosis or Johne's disease of livestock, which is caused by Mycobacterium avium subsp. paratuberculosis (MAP), has increased in prevalence and expanded in geographic and host ranges over about 100 years. The slow and progressive spread of MAP reflects its substantial adaptation to its hosts, the technical limitations of diagnosis, the lack of practical therapeutic approaches, the lack of a vaccine that prevents transmission and the complexity and difficulty of the on-farm control strategies needed to prevent infection. More recently evidence has accumulated for an association of MAP with Crohn's disease in humans, adding to the pressure on animal health authorities to take precautions by controlling paratuberculosis. Mycobacterial infections invoke complex immune responses but the essential determinants of virulence and pathogenesis are far from clear. In this review we compare the features of major diseases in humans and animals that are caused by the pathogenic mycobacteria M. ulcerans, M. avium subsp. avium, M. leprae, M. tuberculosis and MAP. We seek to answer key questions: are the common mycobacterial infections of humans and animals useful "models" for each other, or are the differences between them too great to enable meaningful extrapolation? To simplify this, the immunopathogenesis of mycobacterial infections will be defined at cellular, tissue, animal and population levels and the key events at each level will be discussed. Many pathogenic processes are similar between divergent mycobacterial diseases, and at variance between virulent and avirulent isolates of mycobacteria, suggesting that the research on the pathogenesis of one mycobacterial disease will be informative for the others.

Candidate gene and genome-wide association studies of Mycobacterium avium subsp. paratuberculosis infection in cattle and sheep: a review

Paratuberculosis (Johne's disease), caused by Mycobacterium avium subspecies paratuberculosis, is responsible for significant economic losses in livestock industries worldwide. This organism is also of public health concern due to an unconfirmed link to Crohn's disease. Susceptibility to paratuberculosis has been suggested to have a genetic component. In livestock, a number of candidate genes have been studied, selected on their association to susceptibility in other mycobacterial diseases, their known role in disease pathogenesis or links to susceptibility of humans to Crohn's disease. These genes include solute carrier family 11 member 1 (SLC11A1, formerly NRAMP1), toll-like receptors, caspase associated recruitment domain 15 (CARD15, formerly NOD2), major histocompatibility complex (MHC) and cytokines (interleukin-10 and interferon-gamma) and their receptors. Genome wide association studies have attempted to confirm associations found and identify new genes involved in pathogenesis and susceptibility. There are a number of limitations and difficulties in these approaches, some peculiar to paratuberculosis but others generally applicable to identification of genetic associations for complex traits. The technical approaches and available information for paratuberculosis have expanded rapidly, particularly relating to sheep and cattle. Here we review the current published evidence for a genetic association with paratuberculosis susceptibility, technological advances that have progressed the field and potential avenues for future research.

Does a Th1 over Th2 dominancy really exist in the early stages of Mycobacterium avium subspecies paratuberculosis infections?

The immune response of ruminants to Johne's disease has been long associated with a cell mediated immune (CMI) response in the early stages of infection with a switch to an antibody response later as the disease manifests. This study examines the immune response in sheep to Mycobacterium avium subspecies paratuberculosis (Map) infections, specifically the antigen-specific interferon gamma (IFN-γ) and antibody responses as surrogates of T helper-1 (Th1) and Th2 immunity. The difference in IFN-γ production between paucibacillary and multibacillary diseased animals was also examined. The results show that sheep are more likely to have a combined antibody and IFN-γ response (seen in 50% of the animals) rather than a switch from an IFN-γ to antibody response (39%). Multibacillary diseased animals were found to have a decrease in functional ability to produce IFN-γ from cells stimulated with MAP-specific antigens and non-specific mitogens. This indicates that the immune responses to Map infections are more complex than thought, where both antibody and cellular immunity may play key roles in the early stages of disease manifestation or resistance. The loss of the cellular response in multibacillary animals may be an indication that the entire immune response is dysfunctional, with the cell mediated responses becoming affected first.

Optimisation of culture of Mycobacterium avium subspecies paratuberculosis from blood samples

Mycobacterium avium subspecies paratuberculosis (MAP) is the causative agent of Johne's disease or paratuberculosis, a chronic enteritis of ruminants, and has been suggested to play a role in Crohn's disease in humans. While disease expression is primarily in the gastrointestinal tract, isolation of MAP or MAP DNA at distant sites indicates that disseminated infections also occur. This is the first study to compare, optimise and critically evaluate different methods of concentrating MAP from spiked blood samples to enable its culture. Whole blood, erythrocytes, but not plasma, delayed the growth of MAP in BACTEC 12B medium. Culture of MAP from buffy coats (concentrated leukocytes) after lysis of erythrocytes and washing of the cells was an effective preparatory method. Several antibiotics were evaluated to reduce contamination of the slow growing MAP cultures with microbes which were derived from the skin during venipuncture, but were detrimental to the growth of MAP. However, decontamination of erythrocyte-lysed washed buffy coat samples in 0.75% hexadecylpyridinium chloride (HPC) for 72 h prior to inoculation of culture media did not inhibit the growth of MAP. The prepared samples can be stored at -80 degrees C prior to batch culture. MAP was isolated from the blood of 2 of 23 sheep 20 months after experimental inoculation. The optimised method has an analytical sensitivity of at least 10(1) MAP per ml of spiked whole blood and will enable trials to determine the incidence, duration and magnitude of mycobacteraemia in infected animals and humans.