Dynamic changes in circulating and antigen-responsive T-cell subpopulations post-Mycobacterium bovis infection in cattle

A study of the incidence of bovine tuberculosis in the wild red deer herd of Exmoor

Bovine tuberculosis (bTB) is an infectious disease which thrives at the wildlife-livestock interface. Exmoor has the largest herd of wild red deer (Cervus elaphus) in England, and also a large number of dairy and beef farms. The population, health and well-being of the herd are managed by a combination of hunting with hounds and by stalking. This study used a serological assay to determine the incidence of bTB in the population of 106 wild red deer of Exmoor, the relationship between regional deer densities and the presence of bTB in deer, and domestic cattle. The overall number of bTB positive deer was 28.3% (30/106). Stalked deer had a slightly higher incidence of bTB (19 out of 55, 34.55%) than hunted deer (11 out of 51, 21.57%). There was no clear pattern of distribution except for one region which showed an incidence of 42.22% compared with 16.4% in the remainder of the moor. There was little difference in the incidence of bTB between male and female animals. The age of animals in the study ranged from < 1 year to over 10 years. There was no clear difference in the incidence across the age range (< 1 year- > 10 years) with the exception of a particularly high incidence in those animals aged 1 year or less. There was a significant correlation between the presence of deer with bTB and the number of farms reporting bTB positive cattle, but not between the regional population of red deer and bTB in deer or cattle.

In-depth systems biological evaluation of bovine alveolar macrophages suggests novel insights into molecular mechanisms underlying Mycobacterium bovis infection

OBJECTIVE

Bovine tuberculosis (bTB) is a chronic respiratory infectious disease of domestic livestock caused by intracellular Mycobacterium bovis infection, which causes ~$3 billion in annual losses to global agriculture. Providing novel tools for bTB managements requires a comprehensive understanding of the molecular regulatory mechanisms underlying the M. bovis infection. Nevertheless, a combination of different bioinformatics and systems biology methods was used in this study in order to clearly understand the molecular regulatory mechanisms of bTB, especially the immunomodulatory mechanisms of M. bovis infection.

METHODS

RNA-seq data were retrieved and processed from 78 (39 non-infected control vs. 39 M. bovis-infected samples) bovine alveolar macrophages (bAMs). Next, weighted gene co-expression network analysis (WGCNA) was performed to identify the co-expression modules in non-infected control bAMs as reference set. The WGCNA module preservation approach was then used to identify non-preserved modules between non-infected controls and M. bovis-infected samples (test set). Additionally, functional enrichment analysis was used to investigate the biological behavior of the non-preserved modules and to identify bTB-specific non-preserved modules. Co-expressed hub genes were identified based on module membership (MM) criteria of WGCNA in the non-preserved modules and then integrated with protein-protein interaction (PPI) networks to identify co-expressed hub genes/transcription factors (TFs) with the highest maximal clique centrality (MCC) score (hub-central genes).

RESULTS

As result, WGCNA analysis led to the identification of 21 modules in the non-infected control bAMs (reference set), among which the topological properties of 14 modules were altered in the M. bovis-infected bAMs (test set). Interestingly, 7 of the 14 non-preserved modules were directly related to the molecular mechanisms underlying the host immune response, immunosuppressive mechanisms of M. bovis, and bTB development. Moreover, among the co-expressed hub genes and TFs of the bTB-specific non-preserved modules, 260 genes/TFs had double centrality in both co-expression and PPI networks and played a crucial role in bAMs-M. bovis interactions. Some of these hub-central genes/TFs, including PSMC4, SRC, BCL2L1, VPS11, MDM2, IRF1, CDKN1A, NLRP3, TLR2, MMP9, ZAP70, LCK, TNF, CCL4, MMP1, CTLA4, ITK, IL6, IL1A, IL1B, CCL20, CD3E, NFKB1, EDN1, STAT1, TIMP1, PTGS2, TNFAIP3, BIRC3, MAPK8, VEGFA, VPS18, ICAM1, TBK1, CTSS, IL10, ACAA1, VPS33B, and HIF1A, had potential targets for inducing immunomodulatory mechanisms by M. bovis to evade the host defense response.

CONCLUSION

The present study provides an in-depth insight into the molecular regulatory mechanisms behind M. bovis infection through biological investigation of the candidate non-preserved modules directly related to bTB development. Furthermore, several hub-central genes/TFs were identified that were significant in determining the fate of M. bovis infection and could be promising targets for developing novel anti-bTB therapies and diagnosis strategies.

Cellular and Cytokine Responses in Lymph Node Granulomas of Bacillus Calmette Guérin (BCG)-Vaccinated and Non-vaccinated Cross-Breed Calves Naturally Infected With Mycobacterium bovis

Local immunological responses at the site of infections, such as at the lymph nodes and lungs, do play a role in containing infection caused by Mycobacterium bovis (M. bovis). This bovine tuberculosis (bTB) study was conducted to evaluate cellular and cytokine responses in the lymph nodes and lungs of BCG-vaccinated and non-vaccinated calves that were naturally infected with M. bovis. Immunohistochemical assays were used for examination of the responses of macrophages, T cells, cytokines and chemical mediators of 40 (22 vaccinated and 18 non-vaccinated) Holstein-Friesian-zebu crossbred calves that were naturally exposed for 1 year to a known bTB positive cattle herd. The incidence rates of bTB visible lesion were 68.2% (15/22) and 89% (16/18) in vaccinated and non-vaccinated calves, respectively. The local responses of CD4⁺ and CD8⁺ T cells, and those of IFN-γ and TNF-α within the lesions, were stronger (P < 0.05) in BCG-vaccinated calves than in non-vaccinated calves. However, there was no statistically significant difference between the two groups (P > 0.05) in the response of CD68⁺ cells. Thus, the findings of this study indicated stronger responses of a set of immunological cells and markers at the local granulomas of BCG-vaccinated calves than in non-vaccinated calves. Furthermore, BCG vaccination may also play a role in reducing the severity of the gross pathology at the primary site of infection.

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.

Gamma Delta T Cell Function in Ruminants

Gamma delta (γδ) T cells constitute a major lymphocyte population in peripheral blood and epithelial surfaces. They play nonredundant roles in host defense against diverse pathogens. Although γδ T cells share functional features with other cells of the immune system, their distinct methods of antigen recognition, rapid response, and tissue tropism make them a unique effector population. This review considers the current state of our knowledge on γδ T cell biology in ruminants and the important roles played by this nonconventional T cell population in protection against several infectious diseases of veterinary and zoonotic importance.

Characterization of γδ T Cell Effector/Memory Subsets Based on CD27 and CD45R Expression in Response to Mycobacterium bovis Infection

Tuberculosis (TB) remains a leading cause of death from infectious diseases worldwide. Mycobacterium bovis is the causative agent of bovine TB and zoonotic TB infection. γδ T cells are known to participate in the immune control of mycobacterial infections. Data in human and nonhuman primates suggest that mycobacterial infection regulates memory/effector phenotype and adaptive immune functions of γδ T cells. To date, the impact of M. bovis infection on bovine γδ T cells and their effector and memory differentiation remains unknown. In this study, we show that circulating γδ T cells from M. bovis-infected cattle can be differentiated based on the expression of CD27, which is indicative of their capacity to respond to virulent M. bovis infection: CD27⁺ γδ T cells proliferated in response to M. bovis Ag and, thus, may comprise the adaptive γδ T cell compartment in cattle. We further show that bovine M. bovis-specific γδ T cells express surface markers characteristic of central memory T cells (CD45R^-CD27⁺CD62L^hi) and that M. bovis-specific CD4 and γδ T cells both upregulate the expression of the tissue-homing receptors CXCR3 and CCR5 during infection. Our studies contribute significantly to our understanding of γδ T cell differentiation during TB infection and provide important insights into the link between phenotypic and functional subsets in the bovine. Accurate characterization of γδ T cell effector and memory-like responses induced during mycobacterial infection will contribute to improved strategies for harnessing the γδ T cell response in protection against TB for humans and animals.

Targeting the Mincle and TLR3 receptor using the dual agonist cationic adjuvant formulation 9 (CAF09) induces humoral and polyfunctional memory T cell responses in calves

There is a need for the rational design of safe and effective vaccines to protect against chronic bacterial pathogens such as Mycobacterium tuberculosis and Mycobacterium avium subsp. paratuberculosis in a number of species. One of the main challenges for vaccine development is the lack of safe adjuvants that induce protective immune responses. Cationic Adjuvant Formulation 01 (CAF01)—an adjuvant based on trehalose dibehenate (TDB) and targeting the Mincle receptor—has entered human trials based on promising pre-clinical results in a number of species. However, in cattle CAF01 only induces weak systemic immune responses. In this study, we tested the ability of three pattern recognition receptors, either alone or in combination, to activate bovine monocytes and macrophages. We found that addition of the TLR3 agonist, polyinosinic:polycytidylic acid (Poly(I:C)) to either one of the Mincle receptor agonists, TDB or monomycoloyl glycerol (MMG), enhanced monocyte activation, and calves vaccinated with CAF09 containing MMG and Poly(I:C) had increased cell-mediated and humoral immune response compared to CAF01 vaccinated animals. In contrast to the highly reactogenic Montanide ISA 61 VG, CAF09-primed T cells maintained a higher frequency of polyfunctional CD4+ T cells (IFN-γ⁺ TNF-α⁺ IL-2⁺). In conclusion, CAF09 supports the development of antibodies along with a high-quality cell-mediated immune response and is a promising alternative to oil-in-water adjuvant in cattle and other ruminants.

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.

Immunohistochemical detection of pro-inflammatory and anti-inflammatory cytokines in granulomas in cattle with natural Mycobacterium bovis infection

Cellular immune response was evaluated in lymph nodes and lung with different granulomatous lesions from cattle naturally infected with Mycobacterium bovis. For this purpose, we assessed pro-inflammatory and anti-inflammatory cytokines by immunohistochemical assays. Immunoreaction was observed for all the cytokines analyzed. Fourteen animals displayed advanced stage IV granulomas, with intense immunoreactivity to IFN-γ and TGF-β in areas of caseous necrosis, macrophages and lymphocytes. Seven animals showed stage III granuloma, with high immunoreactivity to IFN-γ (average of 44.5% immunoreactive cells) and moderate to TNF-α and to the anti-inflammatory cytokines IL-10 and TGF-β, in relation to the proliferation of fibroblasts in granuloma periphery We found satellite stage I granulomas in 4 bovines and stage II granulomas in 2 bovines, which exhibited low immunostaining response (-13%). Cytokine expression in stage III and IV granulomas was significant, with predominance of immunoreactivity to IFN-γ, thus suggesting a strong, longstanding local immune response mediated by macrophages and epithelioid cells. In addition, these two stages displayed lower reactivity to IL-10; which suggests a deficit of anti-inflammatory cytokines, suppressed immunity and persistence of the infection. High expression of TGF-β could indicate a chronic process with greater tissue damage and fibrosis. Numerous bacilli observed in necrotic areas in stage III and IV granulomas with low expression of IL-1β suggest failure in the immune response with bacterial multiplication. In this study, evidence of in situ presence of cytokines demonstrates these cytokines are involved in the development and evolution of bovine tuberculosis granulomas.

Differential Cell Composition and Cytokine Expression Within Lymph Node Granulomas from BCG-Vaccinated and Non-vaccinated Cattle Experimentally Infected with Mycobacterium bovis

Cattle vaccination against bovine tuberculosis (bTB) has been proposed as a supplementary method to help control the incidences of this disease. Bacillus Calmette-Guérin (BCG) is currently the only viable candidate vaccine for immunization of cattle against bTB, caused by Mycobacterium bovis (M. bovis). In an attempt to characterize the differences in the immune response following M. bovis infection between BCG-vaccinated and non-vaccinated animals, a combination of gross pathology, histopathology and immunohistochemical (IHC) analyses was used. BCG vaccination was found to significantly reduce the number of gross and microscopic lesions present within the lungs and lymph nodes. Additionally, the microscopically visible bacterial load of stages III and IV granulomas was reduced. IHC using cell surface markers revealed the number of CD68+ (macrophages), CD3+ (T lymphocytes) and WC1+ cells (γδ T cells) to be significantly reduced in lymph node granulomas of BCG-vaccinated animals, when compared to non-vaccinated animals. B lymphocytes (CD79a+) were significantly increased in BCG-vaccinated cattle for granulomas at stages II, III and IV. IHC staining for iNOS showed a higher expression in granulomas from BCG-vaccinated animals compared to non-vaccinated animals for all stages, being statistically significant in stages I and IV. TGFβ expression decreased alongside the granuloma development in non-vaccinated animals, whereas BCG-vaccinated animals showed a slight increase alongside lesion progression. IHC analysis of the cytokines IFN-γ and TNF-α demonstrated significantly increased expression within the lymph node granulomas of BCG-vaccinated cattle. This is suggestive of a protective role for IFN-γ and TNF-α in response to M. bovis infection. Findings shown in this study suggest that the use of BCG vaccine can reduce the number and severity of lesions, induce a different phenotypic response and increase the local expression of key cytokines related to protection.

The CD4(+) T cell methylome contributes to a distinct CD4(+) T cell transcriptional signature in Mycobacterium bovis-infected cattle

We hypothesised that epigenetic regulation of CD4⁺ T lymphocytes contributes to a shift toward a dysfunctional T cell phenotype which may impact on their ability to clear mycobacterial infection. Combined RNA-seq transcriptomic profiling and Reduced Representation Bisulfite Sequencing identified 193 significantly differentially expressed genes and 760 differentially methylated regions (DMRs), between CD4⁺ T cells from M. bovis infected and healthy cattle. 196 DMRs were located within 10 kb of annotated genes, including GATA3 and RORC, both of which encode transcription factors that promote T_H2 and T_H17 T helper cell subsets respectively. Gene-specific DNA methylation and gene expression levels for the TNFRSF4 and Interferon-γ genes were significantly negatively correlated suggesting a regulatory relationship. Pathway analysis of DMRs identified enrichment of genes involved in the anti-proliferative TGF-β signaling pathway and TGFB1 expression was significantly increased in peripheral blood leukocytes from TB-infected cattle. This first analysis of the bovine CD4⁺ T cell methylome suggests that DNA methylation directly contributes to a distinct gene expression signature in CD4⁺ T cells from cattle infected with M. bovis. Specific methylation changes proximal to key inflammatory gene loci may be critical to the emergence of a non-protective CD4⁺ T cell response during mycobacterial infection in cattle.

CD4+ and γδ T Cells are the main Producers of IL-22 and IL-17A in Lymphocytes from Mycobacterium bovis-infected Cattle

Gene transcription studies have identified dual roles for the cytokines IL-17A and IL-22 in bovine tuberculosis, where they show potential as both predictors of vaccine success and correlates of infection. To allow for a detailed investigation of the cell populations responsible for production of these cytokines, we have utilised a novel bovine IL-22 specific recombinant antibody for flow cytometry. Bovine tuberculin (PPDB) induced greater IL-22 and IL-17A production in Mycobacterium bovis (M. bovis)-infected cattle compared to non-infected controls, while PWM-induced cytokine levels were similar between the two groups. In M. bovis-infected animals, PPDB specific IL-22 and IL-17A responses were observed in both CD4+ T cell and γδ T cell populations. Although both cytokines were detected in both cell types, IL-22/IL-17A double producers were rare and confined mainly to the γδ T cell population. These results support previous gene transcription studies and extend the observation of increased IL-22 and IL-17A responses in M. bovis-infected animals to the level of protein production. We were also able to characterise the cell populations responsible for these disease-related cytokine responses. The data generated can be used to further our understanding of the immunopathology of bovine tuberculosis and to produce more sensitive and specific immune-diagnostic reagents.

Mesenteric lymph node granulomatous lesions in naturally infected wild boar (Sus scrofa) in Portugal--Histological, immunohistochemical and molecular aspects

Several studies have demonstrated that wildlife reservoirs of mycobacteria are responsible for the maintenance and spreading of the infection to livestock and wildlife counterparts. Recent data report the role of wild boar (Sus scrofa) as a reservoir for Mycobacterium bovis. This study was conducted to evaluate the chronic inflammatory response in the mesenteric lymph nodes (MLN) of wild boar with granulomatous lymphadenitis (n=30). Morphological parameters of the lesions were recorded. The expression of CD3 and CD79α molecules was evaluated by immunohistochemistry. Molecular genotyping and culture to identify mycobacteria were performed. The lesions consisted mainly of stage III and stage IV granulomas. CD3 and CD79α positive cells were observed in 15 (50%) and in 11 (36.6%) MLN, respectively. In these lesions, higher percentages of T lymphocytes were found and a limited number of animals exhibited a tendency for an increased percentage of B lymphocytes. Our results suggest that there are similar percentages and distribution patterns of CD3 and CD79α in the lesions, regardless of the presence of Mycobacterium avium subsp. paratuberculosis (Map), M. bovis or Map-M. bovis co-infection, and confirm that wild boar is both susceptible and could be an important Map and M. bovis wild reservoir in the study area.

Analysis of Cytokine Gene Expression using a Novel Chromogenic In-situ Hybridization Method in Pulmonary Granulomas of Cattle Infected Experimentally by Aerosolized Mycobacterium bovis

Mycobacterium bovis is the cause of tuberculosis in most animal species including cattle and is a serious zoonotic pathogen. In man, M. bovis infection can result in disease clinically indistinguishable from that caused by Mycobacterium tuberculosis, the cause of most human tuberculosis. Regardless of host, the typical lesion induced by M. bovis or M. tuberculosis is the tuberculoid granuloma. Tuberculoid granulomas are dynamic structures reflecting the interface between host and pathogen and, therefore, pass through various morphological stages (I to IV). Using a novel in-situ hybridization assay, transcription of various cytokine and chemokine genes was examined qualitatively and quantitatively using image analysis. In experimentally infected cattle, pulmonary granulomas of all stages were examined 150 days after aerosol exposure to M. bovis. Expression of mRNA encoding tumour necrosis factor (TNF)-α, transforming growth factor-β, interferon (IFN)-γ, interleukin (IL)-17A, IL-16, IL-10, CXCL9 and CXCL10 did not differ significantly between granulomas of different stages. However, relative expression of the various cytokines was characteristic of a Th1 response, with high TNF-α and IFN-γ expression and low IL-10 expression. Expression of IL-16 and the chemokines CXCL9 and CXCL10 was high, suggestive of granulomas actively involved in T-cell chemotaxis.

Bovine gamma delta T cells and the function of gamma delta T cell specific WC1 co-receptors

The study of γδ T cells in ruminants dates to the discovery of the γδ TCR in humans and mice. It is important since cattle offer an alternative model to the mouse for evaluating the role of γδ T cells in zoonotic disease research and for control of disease reservoirs in non-human animals. In addition, maintaining the health of cattle and other members of the order Artiodactyla is critical to meet the global human need for animal-source protein. In this review, we examine the bovine γδ T cell responses to Mycobacteria, which infects a third of the human population, and bovine γ and δ TCR diversity and the relationship to the TCR of human mycobacteria-responsive γδ T cells. We review the utilization of the γδ T cell specific scavenger receptor cysteine-rich (SRCR) glycoproteins known as WC1, and that are part of the CD163 family, which function as both γδ T cell activating co-receptors and pattern recognition receptors (PRR) for bovine γδ T cells and highlight the presence and evolution of this multigenic array, with potential for the same function, in birds, reptiles, jawless and bony fishes, and prototherian and eutherian mammals.

Comparative epigenetics: relevance to the regulation of production and health traits in cattle

With the development of genomic, transcriptomic and bioinformatic tools, recent advances in molecular technologies have significantly impacted bovine bioscience research and are revolutionising animal selection and breeding. Integration of epigenetic information represents yet another challenging molecular frontier. Epigenetics is the study of biochemical modifications to DNA and to histones, the proteins that provide stability to DNA. These epigenetic changes are induced by environmental stimuli; they alter gene expression and are potentially heritable. Epigenetics research holds the key to understanding how environmental factors contribute to phenotypic variation in traits of economic importance in cattle including development, nutrition, behaviour and health. In this review, we discuss the potential applications of epigenetics in bovine research, using breakthroughs in human and murine research to signpost the way.

Relevance of bovine tuberculosis research to the understanding of human disease: historical perspectives, approaches, and immunologic mechanisms

Pioneer studies on infectious disease and immunology by Jenner, Pasteur, Koch, Von Behring, Nocard, Roux, and Ehrlich forged a path for the dual-purpose with dual benefit approach, demonstrating a profound relevance of veterinary studies for biomedical applications. Tuberculosis (TB), primarily due to Mycobacterium tuberculosis in humans and Mycobacterium bovis in cattle, is an exemplary model for the demonstration of this concept. Early studies with cattle were instrumental in the development of the use of Koch's tuberculin as an in vivo measure of cell-mediated immunity for diagnostic purposes. Calmette and Guerin demonstrated the efficacy of an attenuated M. bovis strain (BCG) in cattle prior to use of this vaccine in humans. The interferon-γ release assay, now widely used for TB diagnosis in humans, was developed circa 1990 for use in the Australian bovine TB eradication program. More recently, M. bovis infection and vaccine efficacy studies with cattle have demonstrated a correlation of vaccine-elicited T cell central memory (TCM) responses to vaccine efficacy, correlation of specific antibody to mycobacterial burden and lesion severity, and detection of antigen-specific IL-17 responses to vaccination and infection. Additionally, positive prognostic indicators of bovine TB vaccine efficacy (i.e., responses measured after infection) include: reduced antigen-specific IFN-γ, iNOS, IL-4, and MIP1-α responses; reduced antigen-specific expansion of CD4(+) T cells; and a diminished activation profile on T cells within antigen stimulated cultures. Delayed type hypersensitivity and IFN-γ responses correlate with infection but do not necessarily correlate with lesion severity whereas antibody responses generally correlate with lesion severity. Recently, serologic tests have emerged for the detection of tuberculous animals, particularly elephants, captive cervids, and camelids. B cell aggregates are consistently detected within tuberculous lesions of humans, cattle, mice and various other species, suggesting a role for B cells in the immunopathogenesis of TB. Comparative immunology studies including partnerships of researchers with veterinary and medical perspectives will continue to provide mutual benefit to TB research in both man and animals.

Subunit vaccine consisting of multi-stage antigens has high protective efficacy against Mycobacterium tuberculosis infection in mice

To search for more effective tuberculosis (TB) subunit vaccines, antigens expressed in different growth stages of Mycobacterium tuberculosis (M. tuberculosis), such as RpfE (Rv2450c) produced in the stage of resuscitation, Mtb10.4 (Rv0288), Mtb8.4 (Rv1174c), ESAT6 (Rv3875), Ag85B (Rv1886c) mainly secreted by replicating bacilli, and HspX (Rv2031c) highly expressed in dormant bacilli, were selected to construct six fusion proteins: ESAT6-Ag85B-MPT64_190-198-Mtb8.4 (EAMM), Mtb10.4-HspX (MH), ESAT6-Mtb8.4, Mtb10.4-Ag85B, ESAT6-Ag85B, and ESAT6-RpfE. The six fusion proteins were separately emulsified in an adjuvant composed of N,N’-dimethyl-N, N’-dioctadecylammonium bromide (DDA), polyribocytidylic acid (poly I:C) and gelatin to construct subunit vaccines, and their protective effects against M. tuberculosis infection were evaluated in C57BL/6 mice. Furthermore, the boosting effects of EAMM and MH in the adjuvant of DDA plus trehalose 6,6'-dimycolate (TDM) on BCG-induced immunity were also evaluated. It was found that the six proteins were stably produced in E. coli and successfully purified by chromatography. Among them, EAMM presented the most effective protection against M. tuberculosis. Interestingly, the mice that received EAMM+MH had significantly lower bacterial counts in the lungs and spleens than the single protein vaccinated groups, and had the same effect as those that received BCG. In addition, EAMM and MH could improve BCG-primed protective efficacy against M. tuberculosis infection in mice. In conclusion, the combination of EAMM and MH containing antigens from both replicating and dormant stages of the bacilli could induce robust immunity against M. tuberculosis infection in mice and may serve as promising subunit vaccine candidate.

Comparison of immune peripheral blood cells in tuberculin reactor cattle that are seropositive or seronegative for Mycobacterium bovis antigens

Bovine tuberculosis (bTB) is a major economic problem in animal husbandry and is a public health risk in nonindustrialized countries. It is generally accepted that protection against TB is generated through cell-mediated immunity. Previous investigations have shown that WC1(+) γδ, CD4(+) and CD8(+) T-cell subpopulations are important in the immune response to bTB. It is known that changes in the immune balance from a dominant T helper 1 (Th1)-type response toward a more prominent Th2 response may be observed during disease progression. In this study, we aimed to investigate immune peripheral blood cells in tuberculin reactor cattle that are seropositive or seronegative for Mycobacterium bovis antigens, using flow cytometry and hematological analysis. The evaluation of the T cell subpopulations revealed a decrease in CD8(+) T cells of the seropositive and seronegative animals compared with the control animals (p=0.0001). Moreover, the seropositive group exhibited a lower percentage of CD8(+) T cells than the seronegative group. The percentage of B cells was significantly increased in the seropositive group compared with the seronegative group and the control group (p=0.0009). No difference was observed in the percentage of WC1(+) γδ and CD4(+) T cells among the groups. Furthermore, following 24h of peripheral blood culture with bovine purified protein derivative (PPD), both apparently infected groups showed an increase in the levels of cellular activation compared with the control group (p<0.0001). The seropositive group displayed a higher level of cellular activation than the seronegative group. In both apparently infected groups, the hematological analysis showed an increase in total leukocyte (p=0.0012), lymphocyte (p=0.0057), monocyte (p=0.0010) and neutrophil (p=0.0320) counts in comparison with the healthy animals. Our results demonstrated differences in immune peripheral blood cells of tuberculin reactor cattle that are seropositive or seronegative for M. bovis antigens, probably due to different stages of bTB among the groups. The percentages of CD8(+) T cells, B cells and the T cell activation levels may represent biomarkers for the progression of the disease. However, general characteristics shared by both apparently infected groups as lymphocytosis and monocytosis may also be indicative of the disease. Further experiments are required to understand the variations between cellular and humoral immunities throughout the course of bTB infection. A detailed knowledge of the peripheral blood cells involved in all stages of the bTB immune response of naturally infected cattle is essential for the optimal exploitation of diagnosis and vaccination models.

BCG vaccination of neonatal calves: potential roles for innate immune cells in the induction of protective immunity

Bovine tuberculosis is a disease of increasing incidence in the UK causing major economic losses and with significant impact on bovine and, potentially human health: the causative agent Mycobacterium bovis is a zoonotic pathogen. Neonatal vaccination with the attenuated M. bovis Bacille Calmette Guerin (BCG) vaccine confers a significant degree of protection in cattle, and is a widely used control strategy for human TB. The adaptive immune system is relatively immature in neonates and increased numbers of innate effector cells present in young animals and human infants may compensate for this, enabling effective immune responses to vaccination. Natural killer cells and subsets of γδ TCR+ T lymphocytes secrete high levels of interferon gamma and can interact with antigen presenting cells to promote both innate and adaptive immune responses. These cell populations may be pivotal in determining immune bias following neonatal vaccination with BCG.

Bovine γδ T cells: cells with multiple functions and important roles in immunity

The γδ T-cell receptor (TCR)-positive lymphocytes are a major circulating lymphocyte population in cattle, especially in young calves. In contrast, human and mice have low levels of circulating γδ TCR(+) T cells (γδ T cells). The majority of the circulating γδ T cells in ruminants express the workshop cluster 1 (WC1) molecule and are of the phenotype WC1(+) CD2(-) CD4(-) CD8(-). WC1 is a 220000 molecular weight glycoprotein with homology to the scavenger receptor cysteine-rich (SRCR) family, closely related to CD163. The existence of 13 members in the bovine WC1 gene family has recently been demonstrated and although murine and human orthologues to WC1 genes exist, functional gene products have not been identified in species other than ruminants and pigs. Highly diverse TCRδ usage has been reported, with expanded variable genes in cattle compared to humans and mice. Differential γ chain usage is evident between populations of bovine γδ T cells, this may have implications for functionality. There is a growing body of evidence that WC1(+) γδ T cells are important in immune responses to mycobacteria and may have important roles in T cell regulation and antigen presentation. In this review, we will summarize recent observations in γδ T cell biology and the importance of γδ T cells in immune responses to mycobacterial infections in cattle.

Increased IL-17 expression is associated with pathology in a bovine model of tuberculosis

The identification of bovine tuberculosis (bTB) biomarkers in specific stages of the disease will contribute to a better understanding of the immunopathology associated with tuberculosis and to improve the disease diagnosis and prognosis. The aim of this study was to understand the changing profile of the immune responses during the course of infection and to identify biomarkers associated with pathology. Here we describe the immune response developed in experimentally infected cattle with field Mycobacterium bovis strains. Blood samples were taken from each animal at different time points after M. bovis intratracheal infection and lymphocyte subset activation and cytokine mRNA expression were determined from peripheral blood mononuclear cells in response to purified protein derivative (PPDB). We found that CD4 and CD8 activation during the early stages of infection, together with IL-17 gene expression, were positively associated with pathology. The results of this study provide evidences of the role of IL-17 in the immunopathology of tuberculosis and support the use of IL-17 as a potential biomarker with predictive value of prognosis in bTB.

Tuberculosis immunity: opportunities from studies with cattle

Mycobacterium tuberculosis and M. bovis share >99% genetic identity and induce similar host responses and disease profiles upon infection. There is a rich history of codiscovery in the development of control measures applicable to both human and bovine tuberculosis (TB) including skin-testing procedures, M. bovis BCG vaccination, and interferon-γ release assays. The calf TB infection model offers several opportunities to further our understanding of TB immunopathogenesis. Recent observations include correlation of central memory immune responses with TB vaccine efficacy, association of SIRPα⁺ cells in ESAT-6:CFP10-elicited multinucleate giant cell formation, early γδ T cell responses to TB, antimycobacterial activity of memory CD4⁺ T cells via granulysin production, association of specific antibody with antigen burden, and suppression of innate immune gene expression in infected animals. Partnerships teaming researchers with veterinary and medical perspectives will continue to provide mutual benefit to TB research in man and animals.

Study of the immunological profile towards Mycobacterium bovis antigens in naturally infected cattle

A number of studies have determined the contribution of Th1 and Th2 responses to the protective immunity and pathology of Mycobacterium bovis infection. However, much of that information is derived from experimentally infecting cattle with M. bovis and few data from naturally infected animals are available. The aim of this study was to characterize the immunological profile towards M. bovis antigens of naturally infected cattle by measurement of cytokine mRNA expression in PBMC, and to determine which lymphocyte subsets are involved in recall responses of PBMC from M. bovis infected cattle to M. bovis antigens. Consistent with data from cattle experimentally infected with M. bovis, naturally infected animals were found to display a Th1 cytokine profile in response to M. bovis PPDB stimulation. Production of IFN-gamma mRNA by PBMC after PPDB stimulation statistically distinguishes between infected and healthy herds, suggesting that this molecule is usable as an M. bovis-infection marker. As happens in experimentally infected cows, CD4, CD8 and gammadeltaTCR cells from a herd naturally infected with M. bovis are the predominant T cell subsets expanded in response to PPDB.

Evaluation of granulysin and perforin as candidate biomarkers for protection following vaccination with Mycobacterium bovis BCG or M. bovisDeltaRD1

The development of improved vaccines against tuberculosis (TB) is directly linked to the investigation of new and better correlates of protection after vaccination against TB. Cloning and characterization of bovine homologues of the antimicrobial protein granulysin (Bo-lysin) and perforin by our group could be used as potential biomarkers for TB vaccination efficacy. In the present study, we examined the kinetics of granulysin, perforin, IFNgamma and Fas-L responses to Mycobacterium bovis purified protein derivative (PPD) stimulation by peripheral blood mononuclear cells from M. bovisDeltaRD1-, BCG- and non-vaccinated cattle. Gene expression profiles following PPD stimulation showed significant increases in transcripts for granulysin and IFNgamma in both CD4(+) and CD8(+) T cells in BCG-vaccinated as compared with non-vaccinated animals. Perforin and IFNgamma examined by flow cytometry, showed a difference of 1-2% more PPD-specific cells in BCG-vaccinated than non-vaccinated animals. In the vaccine trial, granulysin and perforin were significantly increased in both vaccine groups as compared with control after vaccination and challenge. IFNgamma expression was increased only after vaccination and secretion was higher in the control, non-protected group as compared with both vaccine groups demonstrating no correlation with protection upon vaccination. In summary, results shown here provide evidence that granulysin and perforin are prospective candidates as biomarkers of protection after vaccination against TB.

Enhanced secretion of interferon-gamma by bovine gammadelta T cells induced by coculture with Mycobacterium bovis-infected dendritic cells: evidence for reciprocal activating signals

Evidence suggests that gammadelta T cells form part of the innate immune response to Mycobacterium bovis infection. Dendritic cells (DCs) are capable of secreting high levels of interleukin-12 (IL-12) following infection with mycobacteria and can induce interferon-gamma (IFN-gamma) secretion by natural killer and gammadelta T cells We investigated the innate interactions occurring between WC1(+)gammadelta T cells and M. bovis-infected DCs. Following coculture with M. bovis-infected DCs, secretion of IFN-gamma and expression of CD25 and major histocompatibility complex class II on WC1(+)gammadelta T cells were significantly enhanced. Reciprocal enhancement of IL-12 secretion by the DCs was also observed and this interaction was found to be contact dependent. We hypothesize that there is an early, transient signal between the WC1(+)gammadelta T cells and the DCs, which promotes the synthesis of biologically active IL-12, and which is dependent upon cell-cell contact. Reciprocal signals including IL-12 are then delivered to WC1(+)gammadelta cells, which leads to the enhanced secretion of IFN-gamma, and the up-regulation of activation markers and antigen presentation molecules by the WC1(+)gammadelta T cells. These interactions are likely to form a critical part of the T helper type 1-conditioning response of DCs to M. bovis.

Bovine TB and the development of new vaccines

Bovine tuberculosis (bTB) is caused by Mycobacterium bovis. The incidence of bTB is increasing in cattle herds of developed countries that have a wild life reservoir of M. bovis, such as the UK, New Zealand and the USA. The increase in the incidence of bTB is thought to be due, at least in part, to a wildlife reservoir of M. bovis. M. bovis is also capable of infecting humans and on a worldwide basis, M. bovis is thought to account for up to 10% of cases of human TB [Cosivi O, Grange JM, Daborn CJ et al. Zoonotic tuberculosis due to Mycobacterium bovis in developing countries. Emerg Infect Dis 1998;4(1):59-70]. Thus, the increased incidence of bTB, besides being a major economic problem, poses an increased risk to human health. In the UK, the incidence of bTB continues to rise despite the use of the tuberculin test and slaughter control policy, highlighting the need for improved control strategies. Vaccination of cattle, in combination with more specific and sensitive diagnostic tests, is suggested as the most effective strategy for bovine TB control. The only vaccine currently available for human and bovine TB is the live attenuated Bacille Calmette Guerin (BCG). BCG is thought to confer protection through the induction of Th1 responses against mycobacteria. However, protection against TB conferred by BCG is variable and to this date the reasons for the successes and failures of BCG are not clear. Therefore, there is a need to develop vaccines that confer greater and more consistent protection against bTB than that afforded by BCG. Given that BCG is currently the only licensed vaccine against human TB, it is likely that any new vaccine or vaccination strategy will be based around BCG. In this review we discuss immune responses elicited by mycobacteria in cattle and the novel approaches emerging for the control of bovine TB based on our increasing knowledge of protective immune responses.

Lesion development and immunohistochemical changes in granulomas from cattle experimentally infected with Mycobacterium bovis

Mycobacterium bovis, the causative agent of bovine tuberculosis, persists within granulomas. Formation of granulomas involves a complex array of immune activation and cellular migration. To examine temporal changes in granuloma development, we inoculated 32 cattle with M. bovis of deer origin. Tissues from 4 calves each were examined at 15, 28, 42, 60, 90, 180, 270, and 370 days after inoculation. Granulomas in the medial retropharyngeal lymph node were staged (I-IV) on the basis of cellular composition and the presence or absence of necrosis and peripheral fibrosis. Immunohistochemistry for inducible nitric oxide synthase (iNOS), CD68, CD4, CD8, and gamma/delta T cells was performed. Fifteen days after inoculation only stage I granulomas were seen, while between 28 and 60 days, there was a steady progression through granuloma stages such that by day 60, granulomas of all 4 stages were seen. Acid-fast bacilli were present in moderate-to-large numbers in stage I granulomas 15-60 days after inoculation. Stage IV granulomas contained large numbers of acid-fast bacteria. Abundant iNOS immunoreactivity was associated with granulomas from day 15 through day 60 but was minimal from day 90 to the termination of the experiment. The relative number of CD4+ and CD68+ cells remained constant throughout the study. In contrast, at time points >60 days, numbers of CD8+ and gamma/delta T cells diminished. Tuberculous granulomas are dynamic lesions that follow an orderly progression through disease stages. Diminished expression of iNOS and reduced numbers of CD8+ and gamma/delta T cells late in the progression of tuberculous granulomas may represent a failure of the host response to control infection.

Induction of CD8 T cells against a novel epitope in TB10.4: correlation with mycobacterial virulence and the presence of a functional region of difference-1

Although infection with Mycobacterium tuberculosis (M.tb) induces a robust CD8 T cell response, the role of CD8 T cells in the defense against M.tb, and the mechanisms behind the induction of CD8 T cells, is still not clear. TB10.4 is a recently described Ag that is expressed by both bacillus Calmette-Guérin (BCG) and M.tb. In the present study, we describe a novel CD8 T cell epitope in TB10.4, TB10.4(3-11). We show that TB10.4(3-11)-specific CD8 T cells are induced at the onset of infection and are present throughout the infection in high numbers. TB10.4(3-11) CD8 T cells were recruited to the site of infection and expressed CD44, TNF-alpha, and IFN-gamma. In addition, TB10.4(3-11) CD8 T cells showed an up-regulation of FasL and LAMP-1/2 (CD107A/B), which correlated with a strong in vivo cytolytic activity. The induction of TB10.4(3-11)-specific CD8 T cells was less pronounced following infection with BCG compared to infection with M.tb. By using a rBCG expressing the genetic region of difference-1 (RD1), we show that the presence of a functional RD1 region increases the induction of TB10.4(3-11)-specific CD8 T cells as well as the bacterial virulence. Finally, as an M.tb variant lacking the genetic region RD1 also induced a significant amount of TB10.4(3-11)-specific CD8 T cells, and exhibited increased virulence compared with BCG, our data suggest that virulence in itself is also involved in generating a robust CD8 T cell response against mycobacterial epitopes, such as TB10.4(3-11).

Distribution and activation of T-lymphocyte subsets in tuberculous bovine lymph-node granulomas

The immune response against mycobacterial infections is dependant upon a complex interaction between T lymphocytes and macrophages in the context of the granuloma. For this study, we performed the analysis of 18 stage I or II, and 13 stage III or IV granulomas found in lymph nodes from 8 experimentally and 2 naturally infected cattle. T-cell subpopulations (CD3(+), CD4(+), CD8(+), WC1(+), CD25(+)) were investigated by immunohistochemistry. In the majority of stage I/II lesions, CD8(+) and CD25(+) cells were predominantly found in the lymphocytic outer region of the granuloma, suggesting a possible role for activated CD8(+) cells in the initial attempt to restrain the granuloma growth. CD4(+) T cells appeared equally distributed in the lymphocytic mantle and in the internal areas of the granulomas. WC1(+) cells appeared interspersed among the macrophages. We speculated that this could indicate a role for these 2 subsets in the maintenance and the maturation of the granuloma. In stage III/IV lesions, all of the T-cell subsets investigated appeared interspersed among the mononuclear component of the granulomas. In general terms, there was a higher density of CD8(+) cells compared with CD4(+) cells. However, there was no sense of rimming effect for any of the investigated cell populations.

Workshop cluster 1, a γδ T cell specific receptor is phosphorylated and down regulated by activation induced Src family kinase activity

Workshop cluster 1(+) gamma delta (WC1(+)gammadelta) T cells have been shown to play important roles in the immune response to infections. WC1 is a transmembrane glycoprotein, uniquely expressed on the surface of gammadelta T cells of ruminants and pigs. A role for WC1 in inducing a reversible growth arrest of gammadelta T cells has been previously demonstrated. WC1-induced growth inhibition has been shown to be overcome following gammadelta T cell activation with Concanavalin A (Con A). However, molecular mechanism(s) by which WC1 signalling might be modulated following activation have not been elucidated. In this paper we show that Con A activation of bovine lymphocytes induces the tyrosine phosphorylation of WC1 in a Src-family kinase-dependent manner. Src family kinases also phosphorylated WC1 in a COS-7 co-transfection system. Furthermore, a glutathione-S-transferase (GST)-WC1 cytoplasmic domain fusion protein was directly phosphorylated by recombinant Lck (rLck) in vitro. The Y(1303) of WC1 was identified by mutational analysis as the only one of the five WC1 tyrosine residues to be critical for Src family phosphorylation. The importance of activation-induced Src family activity for WC1 function was investigated with the Src-family specific inhibitor PP2. These studies show that the surface levels of WC1 are down regulated in a Src-family-dependent manner following activation of bovine lymphocytes. Down regulation of surface WC1 was accompanied by a Src-family-dependent accumulation of intracellular WC1. These data show that WC1 is modulated by activation-induced tyrosine phosphorylation thus providing a new insight into the signalling mechanisms by which WC1 and gammadelta T cell activation are regulated in this important and unique cell population.

The immunology of bovine tuberculosis and progression toward improved disease control strategies

Failure to remove cattle diseased with Mycobacterium bovis has immense financial implications for disease control, animal health and agricultural trade as well as the zoonotic risk to human health. Current disease control strategies based on DTH skin testing fail to detect all diseased cattle and additional measures are urgently needed to improve detection of disease and to prevent naïve animals becoming exposed to infection. Experimental models of bovine TB traditionally based on intra-nasal instillation, intra-tracheal inoculation or placed in-contact with infected cattle, have been further developed using aerosolised bacteria delivered to the respiratory tract, allowing field-like bovine TB to be recreated under controlled, experimental conditions. Experimental infection models have already been used to improve diagnostic tests. Specificity of DTH skin testing can be improved under experimental conditions, using recombinant ESAT-6, while laboratory assays such as IFN-gamma release have benefited from the use of defined proteins to improve assay specificity. In combination, antigen cocktails may also improve test sensitivity. There is a concerted international effort to evaluate vaccines for use in cattle populations and to define vaccination strategies which will eliminate disease from infected herds. DNA, protein and genetically modified vaccines inoculated in a single dose, given as prime-boost or injected concurrently, will elicit significant protection against challenge with M. bovis under controlled conditions. However, vaccines and vaccination strategies require evaluation under field conditions. Furthermore, complementary strategies are under development to differentiate immune responses that follow vaccination from those following disease. This paper describes those recent advances which may lead to the introduction of improved disease control strategies.

High Growth Rate Fails to Enhance Adaptive Immune Responses of Neonatal Calves and Is Associated with Reduced Lymphocyte Viability

The objective of the study was to evaluate the effects of 3 targeted growth rates on adaptive (i.e., antigen-specific) immune responses of preruminant, milk replacer-fed calves. Calves (9.1 +/- 2.4 d of age) were assigned randomly to one of 3 dietary treatments to achieve 3 targeted daily rates of gain [no growth (maintenance) = 0.0 kg/d, low growth = 0.55 kg/d, or high growth = 1.2 kg/d] over an 8-wk period. The NRC Nutrient Requirements of Dairy Cattle calf model computer program was used to estimate the milk replacer intakes needed to achieve target growth rates. All calves were fed a 30% crude protein, 20% fat, all-milk protein milk replacer reconstituted to 14% dry matter. Diets were formulated to ensure that protein would not be limiting. All calves were vaccinated 3 wk after initiation of dietary treatments with Mycobacterium bovis, strain bacillus Calmette-Guerin and ovalbumin. Growth rates for no-growth (0.11 kg/d), low-growth (0.58 kg/d), and high-growth (1.16 kg/d) calves differed throughout the experimental period. Blood glucose concentrations in high-growth calves increased with time and were higher than in low- and no-growth calves. Mononuclear and polymorphonuclear leukocyte percentages in peripheral blood were unaffected by growth rate but did change with advancing age. Percentages of CD4(+) T cells increased with age in no-growth and low-growth calves, a characteristic of maturation, but failed to increase in high-growth calves. Growth rate did not affect the percentages of CD45RO(+) (memory) CD4(+) and CD8(+) T cells, antigen (i.e., ovalbumin)-specific serum IgG concentrations, or antigen (i.e., purified protein derivative)-induced IFN-gamma and nitric oxide secretion by mononuclear cell cultures. Antigen-elicited cutaneous delayed-type hypersensitivity responses of no-growth calves exceeded responses of low-growth, but not high-growth, calves. In resting- and antigen-stimulated cell cultures, viabilities of CD4(+), CD8(+), and gammadeltaTCR(+) T cells from high-growth calves were lower than those of the same T cell subsets from no-growth and low-growth calves. Alternatively, resting cultures of mononuclear leukocytes from high-growth calves produced more nitric oxide than those from no-growth and low-growth calves. In conclusion, adaptive immune responses were affected minimally by growth rate. The results suggest that protein-energy malnutrition in the absence of weight loss is not detrimental to antigen-specific responses of neonatal vaccinated calves and that a high growth rate does not enhance these responses. The negative effect of a high growth rate on the viability of circulating T cell populations may influence infectious disease resistance of the calf.

Immunogenicity of Mycobacterium tuberculosis antigens in Mycobacterium bovis BCG-vaccinated and M. bovis-infected cattle

The development of novel vaccine strategies supplementing Mycobacterium bovis BCG (BCG) constitutes an urgent research challenge. To identify potential subunit vaccine candidates, we have tested a series of eight recently identified Mycobacterium tuberculosis antigens in M. bovis-infected and BCG-vaccinated cattle. These antigens were characterized on the basis of their ability to induce in vitro gamma interferon responses in infected or BCG-vaccinated calves. We were able to establish a hierarchy of these antigens based on how frequently they were recognized in both groups of animals. In particular, we were able to prioritize frequently recognized proteins like Rv0287, Rv1174, and Rv1196 for future evaluation as subunit vaccines to be used in BCG-protein heterologous prime-boost vaccination scenarios. In addition, the antigen most dominantly recognized in M. bovis-infected cattle in this study, Rv3616c, was significantly less frequently recognized by BCG vaccinees and could be a target to improve BCG, for example, by increasing its secretion, in a recombinant BCG vaccine.

Early antibody responses to experimental Mycobacterium bovis infection of cattle

Bovine tuberculosis persists as a costly zoonotic disease in numerous countries despite extensive eradication and control efforts. Sequential serum samples obtained from Mycobacterium bovis-infected cattle were evaluated for seroreactivity to mycobacterial antigens. Animals received M. bovis by aerosol, intratonsil, intranasal, or intratracheal inoculation. Assays included the multiantigen print immunoassay for determination of antigen recognition patterns, immunoblot analysis for sensitive kinetic studies, and the VetTB STAT-PAK test, a novel, rapid test based on lateral-flow technology. Responses to MPB83 were detected for all M. bovis-infected animals regardless of the route or strain of M. bovis used for inoculation. Other less commonly recognized antigens included ESAT-6, CFP-10, and MPB70. Responses to MPB83 were detectable as early as 4 weeks after inoculation, were boosted upon injection of purified protein derivatives for skin testing, and persisted throughout the course of each of the four challenge studies. MPB83-specific immunoglobulin M (IgM) was detected prior to MPB83-specific IgG detection; however, early IgM responses rapidly waned, suggesting a benefit of tests that detect both IgM- and IgG-specific antibodies. The VetTB STAT-PAK test detected responses in sera from 60% (15/25) of the animals by 7 weeks after challenge and detected responses in 96% (24/25) of the animals by 18 weeks. These findings demonstrate the potential for new-generation antibody-based tests for the early detection of M. bovis infection in cattle.

Lymphocyte subset distribution in apparently normal and single intradermal test-positive water buffaloes analyzed by flow cytometry

Monoclonal antibodies (mAbs) against bovine lymphocyte cell surface antigens namely, MHC Class I, MHC class II (DP, DQ and DR), CD3, CD4, CD8, gamma delta TCR, WC1N1 and WC1N2, were tested for their reactivity on apparently normal buffalo mononuclear cells prepared from spleen, lymph nodes and peripheral blood. All the mAbs cross-reacted with the buffalo mononuclear cells. The mean (+/-SD) CD4:CD8 cell ratio in the peripheral blood of apparently normal buffaloes was 1.08+/-0.049 while in the spleen and lymph nodes it was 0.90+/-0.080 and 1.81+/-0.430, respectively. The lymphocyte subsets in the buffaloes positive for tuberculosis by the single intra dermal (SID) test was found to be altered; the CD4 cells were reduced while the CD8 and gamma delta cells were increased. The mean CD4:CD8 ratio in the SID positive buffaloes was 0.36+/-0.010.

ESAT-6 peptide recognition by bovine CD8+ lymphocytes of naturally infected cows in herds from southern Italy

The aim of this study was to define epitopes of Mycobacterium bovis from ESAT-6 (early secretory antigen of 6 kDa) recognized by CD8+ T lymphocytes from cows naturally infected with Mycobacterium bovis. We found that bovine CD8+ T cells recognized 10 out of 11 ESAT-6 peptides tested.

Pathogenesis of bovine tuberculosis: the role of experimental models of infection

In many countries, test-and-slaughter policies based on tuberculin skin testing have made a significant impact on the control of bovine tuberculosis (caused by infection with Mycobacterium bovis). However, in some countries these policies have not proved as effective and improved disease control strategies are required (including improved diagnostic tests and development of vaccines). The host pathogen interactions in bovine tuberculosis are very complex. While studies of the disease in naturally infected field cases of bovine tuberculosis have provided valuable information, detailed knowledge can also be gained through studies of disease models. A number of studies have developed M. bovis infection models employing a range of routes and challenge doses. An early objective was assessment of vaccine efficiency, and models of infection remain central to current work in this area. Development of the intra-nasal and intra-tracheal models have also advanced our understanding of the kinetics of the immune response. In many of these studies, understanding of pathogenesis has been improved by definition of the cells that respond to infection and those that are instrumental in modulation of host responses. Experimental models of infection have been adapted to study cattle to cattle transmission, modeling one of the fundamental routes of infection. This review provides a historical perspective on the types of experimental models used in over 100 years of research and outlines new opportunities to refine those methods for bovine and human tuberculosis and to contribute to improved diagnostics, advanced understanding of immunology and vaccine design.

Advanced Granulomatous Lesions in Mycobacterium bovis-infected Cattle are Associated with Increased Expression of Type I Procollagen, γδ (WC1+) T Cells and CD 68+ Cells

The pathognomonic characteristic of tuberculosis (TB) is the formation of a tuberculous granuloma. The objective of this study was to classify lymph node granulomas from experimentally infected calves into different histopathological stages and characterize them further by studying cell types and markers of fibrosis associated with each of the stages. Four stages of granuloma were identified and mRNA and protein expression for cell markers, cytokines and pro-fibrotic markers were studied by immunohistochemistry (IHC) and in-situ hybridization (ISH). In advanced stage granulomas, there was an increase in the expression of TGF-beta, and of type I procollagen as demonstrated by IHC and ISH. As the granulomas advanced, there were fewer CD3+T cells and they tended to be more prominent towards the periphery of the lesions, with a steady increase in the number of CD68+ cells and gammadelta (WC1+) T cells. Granuloma classification and application of cell cytokine markers will assist in improving understanding of the pathogenesis of bovine TB and may help to identify the immunopathology of active disease versus contained or inactive disease. Such disease correlates may help to inform the development of improved diagnostic methods and support vaccine development programmes.

Immune responses in bovine tuberculosis: Towards new strategies for the diagnosis and control of disease

In several countries, bovine tuberculosis (caused by infection with Mycobacterium bovis) is a major economic problem with the potential to be a significant public health risk. Where traditional test-and-slaughter policies based on skin testing with tuberculin have not been fully successful, new tools including additional diagnostic tests and improved vaccines are required urgently. This paper considers how recent developments in knowledge of immune responses and mycobacterial antigens can be used in the logical development of more efficient strategies for the identification of infected cattle.