Characterization of macrophages and occurrence of T cells in intestinal lesions of subclinical paratuberculosis in goats

Defining the caprine γδ T cell WC1 multigenic array and evaluation of its expressed sequences and gene structure conservation among goat breeds and relative to cattle

Workshop cluster 1 (WC1) molecules are part of the scavenger receptor cysteine-rich (SRCR) superfamily and act as hybrid co-receptors for the γδ T cell receptor and as pattern recognition receptors for binding pathogens. These members of the CD163 gene family are expressed on γδ T cells in the blood of ruminants. While the presence of WC1⁺ γδ T cells in the blood of goats has been demonstrated using monoclonal antibodies, there was no information available about the goat WC1 gene family. The caprine WC1 multigenic array was characterized here for number, structure and expression of genes, and similarity to WC1 genes of cattle and among goat breeds. We found sequence for 17 complete WC1 genes and evidence for up to 30 SRCR a1 or d1 domains which represent distinct signature domains for individual genes. This suggests substantially more WC1 genes than in cattle. Moreover, goats had seven different WC1 gene structures of which 4 are unique to goats. Caprine WC1 genes also had multiple transcript splice variants of their intracytoplasmic domains that eliminated tyrosines shown previously to be important for signal transduction. The most distal WC1 SRCR a1 domains were highly conserved among goat breeds, but fewer were conserved between goats and cattle. Since goats have a greater number of WC1 genes and unique WC1 gene structures relative to cattle, goat WC1 molecules may have expanded functions. This finding may impact research on next-generation vaccines designed to stimulate γδ T cells.

HERV-W and Mycobacteriumavium subspecies paratuberculosis Are at Play in Pediatric Patients at Onset of Type 1 Diabetes

The etiology of T1D remains unknown, although a variety of etiological agents have been proposed as potential candidates to trigger autoimmunity in susceptible individuals. Emerging evidence has indicated that endogenous human retrovirus (HERV) may play a role in the disease etiopathogenesis; although several epigenetic mechanisms keep most HERVs silenced, environmental stimuli such as infections may contribute to the transcriptional reactivation of HERV-Wand thus promote pathological conditions. Previous studies have indicated that also Mycobacterium avium subspecies paratuberculosis (MAP) could be a potential risk factor for T1D, particularly in the Sardinian population. In the present study, the humoral response against HERV-W envelope and MAP-derived peptides was analyzed to investigate their potential role in T1D etiopathogenesis, in a Sardinian population at T1D onset (n = 26), T1D (45) and an age-matched healthy population (n = 45). For the first time, a high serum-prevalence of anti-Map and anti-HERV-W Abs was observed in pediatric patients at onset of T1D compared to T1D patients and healthy controls. Our results support the hypothesis that external infections and internal reactivations are involved in the etiology of T1D, and that HERV-W activation may be induced by infectious agents such as MAP.

Early response of monocyte-derived macrophages from vaccinated and non-vaccinated goats against in vitro infection with Mycobacterium avium subsp. paratuberculosis

Paratuberculosis is a disease of ruminants caused by Mycobacterium avium subsp. paratuberculosis (Map). Vaccination is the most cost-effective control method. However, despite the fact that macrophages are the main target cells for this pathogen, the precise mechanisms behind the response of the macrophage to Map infection and how it is modified by vaccination are yet poorly understood. The aim of this study was to investigate the effect of Silirum^® vaccination in the early immune response of caprine monocyte-derived macrophages (CaMØs). Peripheral blood mononuclear cells (PBMCs) were obtained from vaccinated and non-vaccinated goats, cultured in vitro until differentiation to macrophages and infected with Map. After a 24 h incubation, Map viability and DNA were assessed in culture by viable colony count and real time quantitative polymerase chain reaction (qPCR). In addition, Map phagocytosis and expression of IL-10, IL-12, IFN-γ, TNF-α, IL-17A, IL-1β, iNOS, IL-6 and MIP-1β were also evaluated through immunofluorescence labelling and reverse transcriptase qPCR (RT-qPCR), respectively. A significant reduction of Map viability was observed in both supernatants (P < 0.05) and CaMØs (P < 0.001) from the vaccinated group. Similarly, the percentage of infected CaMØs and the number of internalized Map by CaMØs (P < 0.0001) was higher in the vaccinated group. Finally, iNOS (P < 0.01) and IL-10 were significantly up-regulated in CaMØs from vaccinated goats, whereas only MIP-1β was up-regulated in non-vaccinated animals (P < 0.05). These results show that vaccination modifies the immune response of CaMØs, suggesting that the phagocytosis and microbiocidal activity of macrophages against Map is enhanced after vaccination.

Goat γδ T cell subpopulations defined by WC1 expression, responses to pathogens and cytokine production

The major functions of γδ T cells in mammals overlap with those of αβ T cells but differ in that γδ T cells are rapid responders and see different types of antigens. While γδ T cells have been shown to be a major population of circulating lymphocytes in artiodactyl species such as cattle, sheep, and pigs, less is known about these cells in goats, an important agricultural species. We have recently shown that WC1, a γδ T cell-specific family of hybrid pattern recognition receptors/co-receptors, is a multigenic family in goats expanded beyond what occurs in cattle. This study was conducted to address some of the limitations of previous studies in determining the proportions of γδ T cells, WC1⁺ γδ T cells as well as the WC1.1⁺ and WC1.2⁺ subpopulations in blood and to evaluate their responses to various pathogens. Previously, the proportion of caprine γδ T cells was determined using a monoclonal antibody (mAb) 86D that we show here does not react with all γδ T cells thereby underestimating their contribution to the lymphocyte population. Using a mAb reactive with the TCRδ constant region we found the proportion of γδ T cells in blood was not significantly less than that of either CD4 or CD8 T cells and did not decrease with age after 6 months. γδ T cells that expressed WC1 ranged from ~20 to 85% of the total γδ T cells. Less than half of those were classified as WC1.1⁺ or WC1.2⁺ by mAb staining thus indicating a third major WC1⁺ population. We found that naïve γδ T cells proliferated in cultures of PBMC stimulated with antigens of Leptospira or Mycobacterium avium paratuberculosis (MAP) more than they did in control medium cultures or in those stimulated with M. bovis BCG antigens and that the responding γδ T cells included both WC1⁺ and WC1^- cells. In ex vivo PMA/ionomycin-stimulated cultures of WC1^- γδ T cells but not WC1⁺ cells produced both IL-17 and IFNγ. In longterm cultures with Leptospira or MAP both WC1^- and WC1⁺ cells proliferated but only WC1^- γδ T cells produced IL-17. In conclusion, goats have a substantial number of WC1^- and WC1⁺ γδ T cells in PBMC that do not decrease with animal age after 6 months; both populations respond to bacterial antigens as naïve cells but in these cultures only the WC1^- γδ cells produc IL-17 and IFNγ .

Goat γδ T cells

Goats are important food animals and are disseminated globally because of their high adaptability to varying environmental conditions and feeding regimes that provide them with a comparative advantage. Productivity is impacted by infectious diseases; this then contributes to societal poverty, food insecurity, and international trade restrictions. Since γδ T cells have been shown to have vital roles in immune responses in other mammals we reviewed the literature regarding what is known about their functions, distribution in tissues and organs and their responses to a variety of infections in goats. It has been shown that caprine γδ T cells produce interferon-γ and IL-17, are found in a variety of lymphoid and nonlymphoid tissues and constitute a significant population of blood mononuclear cells. Their representation in tissues and their functional responses may be altered concomitant with infection. This review summarizes caprine γδ T cell responses to Brucella melitensis, Fasciola hepatica, Mycobacterium avium paratuberculosis, caprine arthritis encephalitis virus (CAEV), and Schistosoma bovis in infected or vaccinated goats. Caprine γδ T cells have also been evaluated in goats infected with M. caprae, Ehrilichia ruminantium, Haemonchus contortus and peste des petits ruminants (PPR) virus but found to have an unknown or limited response or role in either protective immunity or immunopathogenesis in those cases.

γδ T cells in livestock: Responses to pathogens and vaccine potential

The immediate objective of our research is to understand the molecular mechanisms underlying activation and potentiation of the protective functional response of WC1⁺ γδ T cells to pathogens afflicting livestock species. The long-term goal is to incorporate stimulation of these cells into the next generation of vaccine constructs. γδ T cells have roles in the immune response to many infectious diseases including viral, bacterial, protozoan and worm infections, and their functional responses overlap with those of canonical αβ T cells, for example they produce cytokines including interferon-γ and IL-17. Stimulation of non-conventional lymphocytes including γδ T cells and αβ natural killer T (NKT) cells has been shown to contribute to protective immunity in mammals, bridging the gap between the innate and adaptive immune responses. Because of their innate-like early response, understanding how to engage γδ T-cell responses has the potential to optimize strategies of those that aim to induce pro-inflammatory responses as discussed here.

Anti-HERV-WEnv antibodies are correlated with seroreactivity against Mycobacterium avium subsp. paratuberculosis in children and youths at T1D risk

Recent evidence points at the role that human endogenous retroviruses (HERVs) may play through the activation of genes integrated across the human genome. Although a variety of genetic/epigenetic mechanisms maintain most HERVs silenced, independent environmental stimuli including infections may transactivate endogenous elements favoring pathogenic conditions. Several studies associated exposures to Mycobacterium avium subsp. paratuberculosis (MAP) with increased anti-MAP seroreactivity in T1D patients. Here, we assessed humoral responses against HERV envelope antigens (HERV-K_Env and HERV-W_Env) and four MAP-derived peptides with human homologs in distinct populations: Sardinian children at T1D risk (rT1D) (n = 14), rT1D from mainland Italy (n = 54) and Polish youths with T1D (n = 74) or obesity unrelated to autoimmunity (OB) (n = 26). Unlike Sardinian rT1D, youths displayed increased anti-HERV-W_Env Abs prevalence compared to age-matched OB or healthy controls (24.32 vs. 11.54%, p = 0.02 for Polish T1D/OB and 31.48 vs. 11.90%, p = 0.0025 for Italian rT1D). Anti-HERV-K_Env responses showed variable trends across groups. A strong correlation between Abs levels against HERV-W_Env and homologous peptides was mirrored by time-related Abs patterns. Elevated values registered for HERV-W_Env overlaped with or preceded the detection of T1D diagnostic autoantibodies. These results support the hypothesis of MAP infection leading to HERV-W antigen expression and enhancing the production of autoantibodies in T1D.

Study of peritoneal macrophage immunophenotype in sheep experimentally infected with Fasciola hepatica

During Fasciola hepatica infection, the parasite has the capability to modulate the host immune response towards a non-protector Th2 type instead of Th1. This type of immune response is closely related to the alternative activation of macrophages (M2 profile) as has been shown in vivo in murine models. In this study, an experiment was carried out in order to evaluate the expression of CD68, CD14, CD206 and iNOS in cells present in the peritoneal fluid of sheep during early stages of infection with F. hepatica (1, 3, 9 and 18 days post-infection, dpi) by immunocytochemistry. To the authors' knowledge, this is the first report that studies the in vivo immunophenotype of macrophages from the peritoneal fluid of sheep infected with F. hepatica. Throughout the experiments the absolute number of leucocytes progressively increased, reaching its highest value at 18 dpi, mainly due to the increase of eosinophils. This immunocytochemical study had two purposes: 1) CD68 expression was assessed with Hansel counterstaining, to optimally identify peritoneal macrophages, eosinophils and lymphocytes; 2) expression of CD14, CD206 and iNOS was evaluated to identify alternative or classical pathways of macrophage activation. The results showed a significant increase in CD14 from day 3 dpi compared with the non-infected group. CD206 expression at all time-points showed a significant and dramatic increase in comparison with the uninfected group. On the other hand, iNOS expression showed little variation, and was significantly decreased at 18 dpi in comparison with the uninfected group. These results suggest that F. hepatica induces an alternative activation of peritoneal macrophages of sheep from the first day post-infection, which may facilitate parasite survival. This is the first report describing M2 activation of peritoneal macrophages in ruminants infected with F. hepatica.

Macrophage Subsets Within Granulomatous Intestinal Lesions in Bovine Paratuberculosis

Animals infected with Mycobacterium avium subspecies paratuberculosis show a variety of granulomatous lesions that range from focal forms, seen in the subclinical stages, to diffuse lesions associated with clinical signs. The aim of this study was to phenotypically characterize the macrophages present in the different lesion types using immunohistochemical methods. Lesions from a total of 23 animals with bovine paratuberculosis, natural and experimental, were examined by immunohistochemistry. Antibodies against inducible nitric oxide synthase (iNOS), tumor necrosis factor α (TNF-α), CD163, interleukin 10 (IL-10), transforming growth factor β (TGF-β), major histocompatibility complex (MHC) class II, natural resistance-associated macrophage protein 1 (Nramp-1), calprotectin, Ki-67, CD68, lysozyme, and ionized calcium-binding adaptor molecule 1 (Iba-1) molecules were employed. Samples were scored semiquantitatively using a complete histological score (H-score), reflecting the staining intensity and the percentage of immunolabeled macrophages. Differences in the H-score were seen depending on the lesion type. In focal lesions, with none or few acid-fast bacilli (AFB), macrophages were polarized toward M1 phenotype, with high H-scores for iNOS and TNF-α. Diffuse multibacillary lesions showed M2 differentiation, with high expression of CD163, IL-10, and TGF-β as well as Nramp-1 and MHC class II antigens. Macrophages in diffuse paucibacillary forms showed high H-scores for iNOS but low ones for TNF-α. Diffuse lesions, either multibacillary or paucibacillary, showed high calprotectin and low Ki-67 expression, suggesting a progressive character, while focal forms, with low H-scores for these antigens, would be consistent with latency. Lysozyme and CD68 expression were related to the amount of AFB. H-score for Iba-1 antibody was similar among all types. The findings of this study provide insights into the polarization status of macrophages and lesion development in bovine paratuberculosis.

Bovine Immunoinhibitory Receptors Contribute to Suppression of Mycobacterium avium subsp. paratuberculosis-Specific T-Cell Responses

Johne's disease (paratuberculosis) is a chronic enteritis in cattle that is caused by intracellular infection with Mycobacterium avium subsp. paratuberculosis. This infection is characterized by the functional exhaustion of T-cell responses to M. avium subsp. paratuberculosis antigens during late subclinical and clinical stages, presumably facilitating the persistence of this bacterium and the formation of clinical lesions. However, the mechanisms underlying T-cell exhaustion in Johne's disease are poorly understood. Thus, we performed expression and functional analyses of the immunoinhibitory molecules programmed death-1 (PD-1)/PD-ligand 1 (PD-L1) and lymphocyte activation gene 3 (LAG-3)/major histocompatibility complex class II (MHC-II) in M. avium subsp. paratuberculosis-infected cattle during the late subclinical stage. Flow cytometric analyses revealed the upregulation of PD-1 and LAG-3 in T cells in infected animals, which suffered progressive suppression of interferon gamma (IFN-γ) responses to the M. avium subsp. paratuberculosis antigen. In addition, PD-L1 and MHC-II were expressed on macrophages from infected animals, consistent with PD-1 and LAG-3 pathways contributing to the suppression of IFN-γ responses during the subclinical stages of M. avium subsp. paratuberculosis infection. Furthermore, dual blockade of PD-L1 and LAG-3 enhanced M. avium subsp. paratuberculosis-specific IFN-γ responses in blood from infected animals, and in vitro LAG-3 blockade enhanced IFN-γ production from M. avium subsp. paratuberculosis-specific CD4(+) and CD8(+) T cells. Taken together, the present data indicate that M. avium subsp. paratuberculosis-specific T-cell exhaustion is in part mediated by PD-1/PD-L1 and LAG-3/MHC-II interactions and that LAG-3 is a molecular target for the control of M. avium subsp. paratuberculosis-specific T-cell responses.

Characterization of a caprine model for the subclinical initial phase of Mycobacterium avium subsp. paratuberculosis infection

Background

Paratuberculosis caused by Mycobacterium avium subsp. paratuberculosis (MAP) is difficult to control due to a long phase of clinically non-apparent (latent) infection for which sensitive diagnostics are lacking. A defined animal model for this phase of the infection can help to investigate host-MAP interactions in apparently healthy animals and identify surrogate markers for disease progress and might also serve as challenge model for vaccines. To establish such a model in goats, different age at inoculation and doses of oral inoculum of MAP were compared. Clinical signs, faecal shedding as well as MAP-specific antibody, IFN-γ and IL-10 responses were used for in vivo monitoring. At necropsy, about one year after inoculation (pi), pathomorphological findings and bacterial organ burden (BOB) were scored.

Results

MAP infection manifested in 26/27 inoculated animals irrespective of age at inoculation and dose. Clinical signs developed in three goats. Faecal shedding, IFN-γ and antibody responses emerged 6, 10–14 and 14 wpi, respectively, and continued with large inter-individual variation. One year pi, lesions were detected in 26 and MAP was cultured from tissues of 23 goats. Positive animals subdivided in those with high and low overall BOB. Intestinal findings resembled paucibacillary lesions in 23 and multibacillary in 4 goats. Caseous and calcified granulomas predominated in intestinal LNN. BOB and lesion score corresponded well in intestinal mucosa and oGALT but not in intestinal LNN.

Conclusions

A defined experimental infection model for the clinically non-apparent phase of paratuberculosis was established in goats as suitable basis for future studies.

Cellular composition of granulomatous lesions in gut-associated lymphoid tissues of goats during the first year after experimental infection with Mycobacterium avium subsp. paratuberculosis

Mycobacterium avium subsp. paratuberculosis (MAP) causes lesions in naturally and experimentally infected ruminants which greatly differ in severity, cellular composition and number of mycobacteria. Morphologically distinct lesions are already found during the clinically inapparent phase of infection. The complex local host response and number of MAP were characterized at the initial sites of lesions, organized gut-associated lymphoid tissue, in experimentally infected goats. Tissues were collected at 3, 6, 9 and 12 month post-inoculation (mpi) from goat kids that had orally received 10 times 10mg of bacterial wet mass of MAP (JII-1961). The cellular composition of lesions in Peyer's patches in the jejunum and next to the ileocecal valve was evaluated in 21 MAP-inoculated goats, where lesions were compared with unaltered tissue of six control goats. CD68+, CD4+, CD8+, γδ T lymphocytes, B lymphocytes and plasma cells, MHC class II+ and CD25+ cells were demonstrated by immunohistochemistry in serial cryostat sections. At 3 mpi, extensive granulomatous infiltrates predominated, consisting of numerous epitheloid cells admixed with many CD4 and γδ T lymphocytes. Only single MAP were detected. This indicates a strong cellular immune reaction able to control MAP infection. γδ T lymphocytes were markedly increased in this type of lesion which may reflect their important role early in the pathogenesis of paratuberculosis. At 9 and 12 mpi, divergent lesions were observed which may reflect different outcomes of host-pathogen interactions. In five goats, minimal granulomatous lesions were surrounded by extensive lymphoplasmacytic infiltrates and no MAP were detected by immunohistochemistry. This was interpreted as effective host response that was able to eliminate MAP locally. In three goats, decreased numbers of lymphocytes, but extensive granulomatous infiltrates with numerous epitheloid cells containing increased numbers of mycobacteria were seen. This shift of the immune response resulted in uncontrolled mycobacterial multiplication. Focal and multifocal circumscribed granulomatous infiltrates of mainly epitheloid cells may represent sites of new infection, since they were observed in goats at all times after inoculation. Their presence in goats with minimal granulomatous lesions surrounded by extensive lymphoplasmacytic infiltrates may indicate that despite the local clearance, the infection may be perpetuated. The complex cellular immune reactions postulated for the pathogenesis of paratuberculosis were demonstrated at the local sites of infection. These early host-pathogen interactions are most likely essential for the eventual outcome of the MAP infection.

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.

Achados patológicos e imuno-histoquímicos em bovinos com doença granulomatosa sistêmica pelo consumo de Vicia villosa (Leg. Papilionoideae) no Rio Grande do Sul

A doença granulomatosa sistêmica associada ao consumo de Vicia villosa (Leg. Papilionoideae) foi diagnosticada em 5 bovinos no período de 2005 a 2008. Os bovinos apresentavam alopecia, lesões crostosas na pele, prurido, febre, queda da produção leiteira, anorexia e emagrecimento. O curso clínico médio da doença foi de 2 semanas. Dos bovinos analisados três morreram e dois foram eutanasiados. As lesões macroscópicas de alopecia e crostas na pele eram localizadas principalmente na face e pescoço. Observava-se nódulos multifocais a coalescentes branco-acinzentados que infiltravam vários órgãos especialmente em linfonodos, rins e coração. As lesões microscópicas consistiam na infiltração de linfócitos, macrófagos, células epitelioides, células gigantes multinucleadas, eosinófilos e plasmócitos. Linfonodos, rins, adrenal, baço e fígado de todos os bovinos apresentaram infiltrado granulomatoso, porém de intensidade variável. Nos testes imuno-histoquímicos dos órgãos com infiltrado inflamatório, as principais células visualizadas foram os linfócitos T, seguidos de macrófagos/células epitelioides/células gigantes multi-nucleadas e os linfócitos B foram raramente detectados nos locais de inflamação granulomatosa. O número reduzido de células marcadas por Ki-67 nas lesões granulomatosas, tende a indicar que a proliferação celular não foi responsável pela hipercelularidade das lesões e que o recrutamento de macrófagos e linfócitos para o local da inflamação provavelmente tenha sido o responsável pelo acúmulo de células no infiltrado inflamatório.

Development of a bovine ileal cannulation model to study the immune response and mechanisms of pathogenesis of paratuberculosis

An ileal cannulation model was developed in conjunction with a flow cytometric assay to gain a better understanding of the mechanisms of immunopathogenesis of Johne's disease caused by Mycobacterium avium subsp. paratuberculosis. Initial studies with calves showed that M. avium subsp. paratuberculosis DNA is detectable by PCR in ileal biopsies during the first months following experimental infection. Inflammatory lesions were not detected on endoscopic evaluation up to 8 months postexperimental infection. M. avium subsp. paratuberculosis DNA was detected in multiple tissues at necropsy 8 months postinfection. Examination of the activation status of epithelial lymphocytes from the jejunum and ileum from infected and control animals at necropsy revealed that none of the major subsets of lymphocytes (NK, CD2(+), and CD2(-) gammadelta T lymphocytes, or CD4 and CD8 alphabeta T lymphocytes) expressed activation molecules CD25, CD26, CD71, ACT1, or ACT16. Subsets of CD4 and CD8 T lymphocytes from control and infected animals expressed CD26. The majority of CD4 and CD8 T lymphocytes expressed CD45R0, the memory T-lymphocyte marker. An immune response to M. avium subsp. paratuberculosis was detected by 3 months postinfection, dominated by a strong proliferative response of CD4 memory T lymphocytes. The findings indicate an immune response develops following initial exposure to M. avium subsp. paratuberculosis that controls but does not eliminate the pathogen. This persistence of M. avium subsp. paratuberculosis possibly leads to erosion and dysregulation of protective immunity at later time points postinfection. Continuous access to the ileum offers an opportunity to elucidate the cellular and molecular events leading to immune dysregulation and development of chronic inflammatory ileitis.

Relationship between Mycobacterium avium subspecies paratuberculosis, IL-1alpha, and TRAF1 in primary bovine monocyte-derived macrophages

Mycobacterium avium subspecies paratuberculosis (MAP) is a facultative intracellular pathogen that resides in host macrophage cells. Presently, little is known about how MAP is able to subvert the normal bacteriocidal functions of infected macrophages. Previously, we reported that ileal tissues from MAP infected cattle contained high levels of interleukin-1 alpha (IL-1alpha) and tumor necrosis factor receptor-associated factor 1 (TRAF1), relative to ileal tissues from uninfected cattle. High-level expression of these two proteins could have profound effects on macrophage function, intracellular signaling, and apoptosis. We now demonstrate that high levels of TRAF1 protein are located primarily within macrophages infiltrating areas of MAP infection. We have also utilized cultured bovine monocyte-derived macrophage cells (MDM) either infected with live MAP or stimulated with recombinant IL-1alpha (rIL-1alpha) to determine if there is a relationship between IL-1alpha and TRAF1 expression. These studies have identified a dose dependent increase in TRAF1 protein levels in bovine MDM in response to infection with live MAP or following treatment with rIL-1alpha. Sustained TRAF1 protein expression was dependent upon interaction of rIL-1alpha with it's receptor and rIL-1beta was also able to enhance TRAF1 gene expression. Our results suggest that MAP may use the IL-1-TRAF1 system to enhance TRAF1 protein expression in infected bovine MDM. These novel results provide evidence for a new avenue of research on the effect of MAP and other intracellular pathogens on macrophage signaling and apoptosis.

Gene expression profiling of monocyte-derived macrophages following infection with Mycobacterium avium subspecies avium and Mycobacterium avium subspecies paratuberculosis

Mycobacterium avium subspecies paratuberculosis (MAP) and Mycobacterium avium subspecies avium (MAA) represent two closely related intracellular bacteria with vastly different associated pathologies. MAA can cause severe respiratory infections in immune compromised humans but is nonpathogenic in ruminants and is more readily controlled by the bovine immune system than MAP. MAP causes a fatal wasting syndrome in ruminants, typified by granulomatous enteritis localized in the small intestine. MAP has also been cited as a potential cause of human Crohn's disease. We used a bovine immune-specific microarray (BOTL-5) to compare the response of mature bovine monocyte-derived macrophages (MDM cells) to MAP and MAA. Statistical analysis of microarray data revealed 21 genes not appreciably expressed in resting MDM cells that were activated following infection with either MAA or MAP. Further analysis revealed 144 genes differentially expressed in MDM cells following infection with MAA and 99 genes differentially expressed following infection with MAP. Of these genes, 37 were affected by both types of mycobacteria, with three being affected in opposite directions. Over 41% of the differentially expressed genes in MAA and MAP infected MDM cells were members of, regulated by, or regulators of the MAPK pathways. Expression of selected genes was validated by quantitative real-time reverse transcriptase PCR and in several key genes (i.e., IL-2 receptor, tissue inhibitor of matrix metalloproteinases-1, and Fas-ligand) MAA was found to be a stronger activating factor than MAP. These gene expression patterns were correlated with prolonged activation of p38 MAPK and ERK1/2 by MAA, relative to MAP.

A comparison of ovine monocyte-derived macrophage function following infection with Mycobacterium avium ssp. avium and Mycobacterium avium ssp. paratuberculosis

Mycobacterium avium ssp. paratuberculosis causes Johne's disease in ruminants, whereas the antigenically and genetically similar subspecies Mycobacterium avium ssp. avium is less virulent. In this study, we compared one strain of each subspecies for its ability to survive, induce cytokines, suppress MHC class I and II expression and induce apoptosis or necrosis in ovine monocyte-derived macrophages. Both subspecies survived intracellularly and induced the secretion of IL-10. Low levels of TNF-alpha were detected after infection with both subspecies at 4 h. IL-12 was not upregulated after infection. Downregulation of MHC class I and II was evident in response to infection with both M. avium ssp. avium and M. avium ssp. paratuberculosis. No significant cytotoxicity was detectable in ovine macrophages after the addition of bacteria. M. avium ssp. paratuberculosis induced slightly more apoptosis than M. avium ssp. avium. Still the overall rate of apoptosis was very low and both subspecies suppressed LPS-induced macrophage apoptosis.