Antigen specificity in experimental bovine tuberculosis

Identification of leptospiral protein antigens recognized by WC1+ γδ T cell subsets as target for development of recombinant vaccines

Pathogenic Leptospira species cause leptospirosis, a neglected zoonotic disease recognized as a global public health problem. It is also the cause of the most common cattle infection that results in major economic losses due to reproductive problems. γδ T cells play a role in the protective immune response in livestock species against Leptospira while human γδ T cells also respond to Leptospira. Thus, activation of γδ T cells has emerged as a potential component in the optimization of vaccine strategies. Bovine γδ T cells proliferate and produce IFN-γ in response to vaccination with inactivated leptospires and this response is mediated by a specific subpopulation of the WC1-bearing γδ T cells. WC1 molecules are members of the group B scavenger receptor cysteine rich (SRCR) superfamily and are composed of multiple SRCR domains, of which particular extracellular domains act as ligands for Leptospira. Since WC1 molecules function as both pattern recognition receptors and γδ TCR coreceptors, the WC1 system has been proposed as a novel target to engage γδ T cells. Here, we demonstrate the involvement of leptospiral protein antigens in the activation of WC1⁺ γδ T cells and identified two leptospiral outer membrane proteins able to interact directly with them. Interestingly, we show that the protein-specific γδ T cell response is composed of WC1.1⁺ and WC1.2⁺ subsets, although a greater number of WC1.1⁺ ???? T-cell respond. Identification of protein antigens will enhance our understanding of the role γδ T cells play in the leptospiral immune response and in recombinant vaccine development.

Augmentation of DTH reaction of mycobacterial antigenic cocktail using synthetic mycobacterial 19-kDa lipoprotein as a TLR-stimulant

The current study proposed that previously characterized individual antigenic proteins could represent potential replacement for conventional purified protein derivative (PPD) in tuberculosis skin testing when used in cocktails triggered by suitable TLR-stimulants that would provide the missing pro-inflammatory stimulus. Three different cocktails of previously selected antigens, including C1 (ESAT-6/CPF-10/MPB-83); C2 (ESAT-6/MPB-64/MPB-83); and C3 (CPF-10/MPB-64/MPB-83), were evaluated in vitro using lymphocytic proliferation and IFN-γ production assays, as well as mRNA and protein expression levels of TNF-α, IL-12p40, and IL-2 as pro-inflammatory molecules. C1 showed the highest significant induction of pro-inflammatory molecules as compared to other cocktails, yet still significantly lower than that induced by conventional PPD. Interestingly, inclusion of the synthetic Mycobacterium tuberculosis 19-kDa lipoprotein (Pam3Cys-SSNKSTTGSGETTTA) as a TLR-stimulant resulted in obvious augmentation of C1-induced pro-inflammatory molecules to levels comparable to that of PPD. In addition, skin testing using sensitized guinea pig model revealed comparable significant reaction to that of conventional PPD. ESAT-6/CPF-10/MPB-83 cocktail is suggested as a potential alternative skin-testing reagent when used in combination with the M. tuberculosis 19-kDa lipoprotein as a TLR-stimulant.

Use of antigen-specific interleukin-2 to differentiate between cattle vaccinated with Mycobacterium bovis BCG and cattle infected with M. bovis

We describe here the application of a novel bovine interleukin-2 (IL-2) enzyme-linked immunosorbent assay (ELISA) for the measurement of antigen-specific IL-2 in cattle naturally infected with Mycobacterium bovis and in cattle vaccinated with Mycobacterium bovis BCG and then experimentally challenged with pathogenic M. bovis. Supernatants from whole-blood cultures stimulated with mycobacterial antigen (bovine purified protein derivative [PPDB] or the peptide cocktail ESAT6-CFP10) were assessed using a sandwich ELISA consisting of a new recombinant monoclonal fragment capture antibody and a commercially available polyclonal anti-bovine-IL-2. The production of IL-2 was compared to the production of gamma interferon (IFN-γ) in the same antigen-stimulated whole-blood supernatants. The data show that cattle infected with M. bovis produced quantifiable levels of antigen-specific IL-2, while IL-2 levels in cattle vaccinated with M. bovis BCG did not. Furthermore, cattle vaccinated with M. bovis BCG and then challenged with pathogenic M. bovis displayed a more rapid induction of IL-2 but ultimately had lower levels of infection-induced IL-2 than did unvaccinated challenge control cattle. These data suggest that IL-2 responses are not detectable post-BCG vaccination and that these responses may require infection with virulent M. bovis to develop. This may be useful to differentiate infected cattle from uninfected or BCG-vaccinated cattle, although the overall sensitivity is relatively low, particularly in single intradermal comparative cervical tuberculin (SICCT)-negative infected animals. Furthermore, the strength of the IL-2 response may correlate with pathology, which poses interesting questions on the immunobiology of bovine tuberculosis in contrast to human tuberculosis, which is discussed.

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.

Purified protein derivatives of tuberculin--past, present, and future

The tuberculin skin test, which involves monitoring the immune reaction to an injection of purified protein derivative (PPD), has been the most widely used method for detecting infection with Mycobacterium tuberculosis since its development in 1930s. Until recently, the molecular composition of PPD was unknown. This thwarted the discovery of improved skin testing reagents and drastically hindered efforts to define the mechanism of action. Proteomic evaluation of PPD combined with a detailed analysis in the guinea pig model of tuberculosis led to further definition of the molecular composition of PPD. This communication reviews the history and current status of PPD, in addition to describing candidate next-generation PPD reagents, based on the use of an individual protein or protein cocktails.

T-Cell and Antibody Responses to Mycobacterial Antigens in Tuberculin Skin-Test-Positive Bos indicus and Bos taurus Cattle in Ethiopia

Higher IFN-γ responses to mycobacterial antigens were observed in Bos taurus (Holsteins) than in Bos indicus (Zebu) cattle which could due to differences in antigen recognition profiles between the two breeds. The present study was conducted to evaluate mycobacterial antigen recognition profiles of the two breeds. Twenty-three mycobacterial antigens were tested on 46 skin test positive (24 Zebu and 22 Holstein) using enzyme-linked immunospot assay (ELISPOT) and multiple antigen print immunoassay (MAPIA). Herds from which the study cattle obtained were tested for Fasciola antibody. The T cells from both breeds recognized most of the mycobacterial antigens at lower and comparable frequencies. However, antigens such as CFP-10, ESAT-6, Rv0287, Rv0288, MPB87, Acr-2, Rv3616c, and Rv3879c were recognized at higher frequencies in zebu while higher frequencies of T cell responses were observed to Hsp65 in both breeds. Furthermore, comparable antibody responses were observed in both breeds; MPB83 being the sero-dominant antigen in both breeds. The prevalence of Fasciola antibody was 81% and similar in both breeds. This piece of work could not lead to a definitive conclusion if there are differences in mycobacterial recognition profiles between the two breeds warranting for further similar studies using sound sample size from the two breeds.

Three protein cocktails mediate delayed-type hypersensitivity responses indistinguishable from that elicited by purified protein derivative in the guinea pig model of Mycobacterium tuberculosis infection

Purified protein derivative (PPD) is a widely used reagent for the diagnosis of Mycobacterium tuberculosis infection. Recently, the molecular composition of PPD was defined, with hundreds of mycobacterial protein representatives making up PPD. Which, if any, of these specific products drive the potency of PPD remains in question. In this study, two proteins (DnaK and GroEL2) previously identified as dominant proteins in PPD were tested for the capacity to induce delayed-type hypersensitivity (DTH) responses in H37Rv-infected or BCG-vaccinated guinea pigs. These two proteins were used in pull-down assays to identify interacting PPD products. Six proteins were identified as interacting partners with DnaK and GroEL2, i.e., Rv0009, Rv0475, Rv0569, Rv0685, Rv2626c, and Rv2632c. These six proteins were tested alone and in combination with DnaK and GroEL2 for the capacity to induce a DTH response in the guinea pig model. From these studies, two cocktails, DnaK/GroEL2/Rv0009 and DnaK/GroEL2/Rv0685, were found to induce DTH responses in H37Rv-infected or BCG-vaccinated guinea pigs that were indistinguishable from DTH responses driven by a PPD injection. The mechanism by which DTH responses were induced was elucidated by histologic examination, analysis of activated CD4(+)/CD8(+) T cells, and cytokine mRNA expression at the site of the DTH response. PPD and the protein cocktails tested induced strong DTH responses in H37Rv-infected guinea pigs. Ex vivo phenotyping of T cells at the DTH site indicated that this response is mediated by activated CD4(+) and CD8(+) T cells, with increases in gamma interferon and tumor necrosis factor alpha, but not interleukin-10, at the site of the DTH response. Our results demonstrate for the first time that the PPD response can be mimicked at the molecular level with defined protein cocktails. The use of this defined product will allow a more thorough understanding of the DTH response and may provide a platform for more rapid and sensitive second-generation skin test reagents for the diagnosis of M. tuberculosis infection.

Comparison of tuberculin activity using the interferon-gamma assay for the diagnosis of bovine tuberculosis

In this study, interferon-gamma (IFN-gamma) responses in whole blood cultures stimulated with tuberculins from different sources were compared with regard to their diagnostic reliability in cattle experimentally and naturally infected with Mycobacterium bovis. The IFN-gamma responses to different concentrations of purified protein derivatives (PPDs) from M bovis and Mycobacterium avium were quantified. Significant differences (P<0.05) between sources and concentrations of PPDs used for stimulation were detected, indicating a need for standardisation of PPDs used in the IFN-gamma assay. Additionally, a tool named'relative potency 30' that allows rapid comparison of batches and sources of PPDs was defined.

Identification of novel Mycobacterium bovis antigens by dissection of crude protein fractions

Culture filtrate and cell extracts from Mycobacterium bovis cultures contain molecules which could promote protective immunity to tuberculosis in animals. Different protein fractions of M. bovis cultures were obtained by elution electrophoresis and were tested in experimentally infected cattle. The fractions that elicited gamma interferon (IFN-gamma) responses were resolved by two-dimensional gel electrophoresis, and individual proteins were identified by matrix-assisted laser desorption ionization-time of flight mass spectrometry. The open reading frames were cloned, expressed as their recombinant forms, and retested with naturally and experimentally infected animals. Eleven protein fractions were highly reactive, from which the Rv1636, HspX, Rv0138, Rv2524, EsxI, and Rv3740 recombinant proteins were obtained. EsxI and HspX were the antigens most recognized by the IFN-gamma release assay. In summary, a proteomic approach allowed the identification of novel antigens useful for the diagnosis of bovine tuberculosis.

Viral booster vaccines improve Mycobacterium bovis BCG-induced protection against bovine tuberculosis

Previous work with small-animal laboratory models of tuberculosis has shown that vaccination strategies based on heterologous prime-boost protocols using Mycobacterium bovis bacillus Calmette-Guérin (BCG) to prime and modified vaccinia virus Ankara strain (MVA85A) or recombinant attenuated adenoviruses (Ad85A) expressing the mycobacterial antigen Ag85A to boost may increase the protective efficacy of BCG. Here we report the first efficacy data on using these vaccines in cattle, a natural target species of tuberculous infection. Protection was determined by measuring development of disease as an end point after M. bovis challenge. Either Ad85A or MVA85A boosting resulted in protection superior to that given by BCG alone: boosting BCG with MVA85A or Ad85A induced significant reduction in pathology in four/eight parameters assessed, while BCG vaccination alone did so in only one parameter studied. Protection was particularly evident in the lungs of vaccinated animals (median lung scores for naïve and BCG-, BCG/MVA85A-, and BCG/Ad85A-vaccinated animals were 10.5, 5, 2.5, and 0, respectively). The bacterial loads in lymph node tissues were also reduced after viral boosting of BCG-vaccinated calves compared to those in BCG-only-vaccinated animals. Analysis of vaccine-induced immunity identified memory responses measured by cultured enzyme-linked immunospot assay as well as in vitro interleukin-17 production as predictors of vaccination success, as both responses, measured before challenge, correlated positively with the degree of protection. Therefore, this study provides evidence of improved protection against tuberculosis by viral booster vaccination in a natural target species and has prioritized potential correlates of vaccine efficacy for further evaluation. These findings also have implications for human tuberculosis vaccine development.

Searching for proteins of Mycobacterium avium subspecies paratuberculosis with diagnostic potential by comparative qualitative proteomic analysis of mycobacterial tuberculins

Accurate immunodiagnosis of bovine paratuberculosis is among others hampered by the lack of specific antigens. One of the most frequently used antigen preparations is purified protein derivative (PPD), also known as tuberculin. This crude extract has limitations when used in diagnostic assays due to the presence of cross-reactive antigens. The aim of the current study was to systematically analyze the qualitative protein composition of PPD of the major mycobacterial pathogens. One-dimensional gel electrophoresis followed by tandem mass spectrometry analysis of PPD from Mycobacterium avium subspecies paratuberculosis (MAP), Mycobacterium avium subspecies avium (MAA) and Mycobacterium bovis (MB) identified 156, 95 and 132 proteins, respectively. Comparative sequence analysis led to the selection of a MAP-specific protein (MAP1718c), and finally heterologous expression in Escherichia coli of this and other diagnostic candidate proteins (MAP3515c and MAP1138c (LprG)) enabled evaluation of their immunogenicity. Lymphocyte proliferation responses did not indicate substantial diagnostic potential of the antigens tested. In contrast serum antibody levels for MAP1138c in paratuberculosis infected cows (N=20) were significantly higher (p<0.01) than in control animals (N=20), despite the conserved nature of this protein. In conclusion, this study showed that a combination of proteomics and genomics, starting from complex protein mixtures, present in tuberculins, can reveal novel proteins aiding the development of immunodiagnostics for mycobacterial diseases.

A single dose of vitamin D enhances immunity to mycobacteria

RATIONALE

Vitamin D was used to treat tuberculosis (TB) in the preantibiotic era. Prospective studies to evaluate the effect of vitamin D supplementation on antimycobacterial immunity have not previously been performed.

OBJECTIVES

To determine the effect of vitamin D supplementation on antimycobacterial immunity and vitamin D status.

METHODS

A double-blind randomized controlled trial was conducted in 192 healthy adult TB contacts in London, United Kingdom. Participants were randomized to receive a single oral dose of 2.5 mg vitamin D or placebo and followed up at 6 weeks.

MEASUREMENTS AND MAIN RESULTS

The primary outcome measure was assessed with a functional whole blood assay (BCG-lux assay), which measures the ability of whole blood to restrict luminescence, and thus growth, of recombinant reporter mycobacteria in vitro; the readout is expressed as a luminescence ratio (luminescence postinfection/baseline luminescence). IFN-gamma responses to the Mycobacterium tuberculosis antigens early secretory antigenic target-6 and culture filtrate protein 10 were determined with a second whole blood assay. Vitamin D supplementation significantly enhanced the ability of participants' whole blood to restrict BCG-lux luminescence in vitro compared with placebo (mean luminescence ratio at follow-up, 0.57, vs. 0.71, respectively; 95% confidence interval for difference, 0.01-0.25; p=0.03) but did not affect antigen-stimulated IFN-gamma secretion.

CONCLUSIONS

A single oral dose of 2.5 mg vitamin D significantly enhanced the ability of participants' whole blood to restrict BCG-lux luminescence in vitro without affecting antigen-stimulated IFN-gamma responses. Clinical trials should be performed to determine whether vitamin D supplementation prevents reactivation of latent TB infection. Clinical trial registered with www.clinicaltrials.gov (NCT 00157066).

Neutrophil-mediated innate immune resistance to mycobacteria

Neutrophils contain antimicrobial peptides with antituberculous activity, but their contribution to immune resistance to tuberculosis (TB) infection has not been previously investigated to our knowledge. We determined differential white cell counts in peripheral blood of 189 adults who had come into contact with patients diagnosed with active TB in London, United Kingdom, and evaluated them for evidence of TB infection and capacity to restrict mycobacterial growth in whole-blood assays. Risk of TB infection was inversely and independently associated with peripheral blood neutrophil count in contacts of patients diagnosed with pulmonary TB. The ability of whole blood to restrict growth of Mycobacterium bovis bacille Calmette Guérin and Mycobacterium tuberculosis was impaired 7.3- and 3.1-fold, respectively, by neutrophil depletion. In microbiological media, human neutrophil peptides (HNPs) 1-3 killed M. tuberculosis. The neutrophil peptides cathelicidin LL-37 and lipocalin 2 restricted growth of the organism, the latter in an iron-dependent manner. Black African participants had lower neutrophil counts and lower circulating concentrations of HNP1-3 and lipocalin 2 than south Asian and white participants. Neutrophils contribute substantially to innate resistance to TB infection, an activity associated with their antimicrobial peptides. Elucidation of the regulation of neutrophil antimicrobial peptides could facilitate prevention and treatment of TB.

Antigen-specific proliferation and activation of peripheral blood mononuclear cells from Mycobacterium bovis-infected reindeer

To evaluate antigen-specific proliferative and activation-associated responses from Mycobacterium bovis-infected reindeer, blood mononuclear cells from M. bovis- (n = 10) and non-infected reindeer (n = 4) were stimulated with a recombinant early secretory antigenic target-6 and culture filtrate protein-10 fusion protein (rESAT6:CFP10), M. bovis purified protein derivative, pokeweed mitogen, or medium alone and evaluated by flow cytometry using dye tracker analysis and cell surface marker staining. gammadelta TCR+ and CD8+ cells, but not CD4+ cells, from M. bovis-infected reindeer proliferated in response to specific antigen stimulation. Expression (i.e., mean fluorescence intensity) of CD44 was increased and CD62L decreased on proliferative as compared to non-proliferative fractions in antigen- and mitogen-stimulated cultures. In response rESAT6:CFP10 stimulation, MHC II fluorescence intensity was increased on CD4+, gammadelta TCR+, CD172a+, and IgM+ cells from infected reindeer as compared to that of non-stimulated cells from the same reindeer. Recombinant ESAT6:CFP10 stimulation also induced expansion of a CD172a+, MHC II+ population within mononuclear cell cultures from M. bovis-infected reindeer. Despite a moderate challenge dose and extended duration of incubation, experimental infection of reindeer was generally limited to lymph nodes draining the inoculation site, suggestive of host resistance to progressive disease. Present in vitro findings, therefore, may be predictive of host responses by reindeer that limit progression to disseminated disease.

Progress in the development of vaccines and diagnostic reagents to control tuberculosis in cattle

The sharp rise of bovine tuberculosis (TB) in Great Britain and the continuing problem of wild life reservoirs in countries such as New Zealand and Great Britain have resulted in increased research efforts into the disease. Two of the goals of this research are to develop (1) cattle vaccines against TB and (2) associated diagnostic reagents that can differentiate between vaccinated and infected animals (differential diagnosis). This review summarises recent progress and describes efforts to increase the protective efficacy of the only potential TB vaccine currently available, Mycobacterium bovis BCG, and to develop specific reagents for differential diagnosis. Vaccination strategies based on DNA or protein subunit vaccination, vaccination with live viral vectors as well as heterologous prime-boost scenarios are discussed. In addition, we outline results from studies aimed at developing diagnostic reagents to allow the distinction of vaccinated from infected animals, for example antigens that are not expressed by vaccines like Mycobacterium bovis Bacille-Calmette-Guérin, but recognised strongly in Mycobacterium bovis infected cattle.

Advances in bovine tuberculosis diagnosis and pathogenesis: What policy makers need to know

The mainstay of tuberculosis diagnosis in cattle and deer has been the tuberculin skin test. Recent advances have allowed the incorporation of blood based assays to the diagnostic arsenal for both cattle and deer. Use of defined and specific antigens has allowed for improved specificity of cell mediated assays in both cattle and deer and advances in antibody tests for tuberculosis have potential for use in free-ranging and captive cervid populations. Combined use of blood-based assays with skin testing will require further understanding of the effect of skin testing on the accuracy of blood based assays. Models of experimental infection of cattle have allowed for increased understanding of natural disease pathogenesis. Differences likely exist; however, between cattle and deer in both disease distribution and primary route of inoculation in naturally infected animals.

Protective immunity against Mycobacterium bovis induced by vaccination with Rv3109c--a member of the esat-6 gene family

In a number of clinical studies the current TB vaccine, Mycobacterium bovis bacille Calmette-Guerin (BCG), has provided little or no protection against pulmonary tuberculosis in cattle and man. A new generation of vaccines is therefore required to replace or supplement BCG. Safety concerns surrounding a number of strategies make protein subunits an attractive approach. Moreover, novel prime-boost strategies based on primary immunisations with BCG are not only showing promise but also present a clear strategy for testing new TB vaccines in clinical studies. We report the evaluation of six protein vaccine candidates for their ability to induce protective immunity in a murine virulent M. bovis challenge model. One protein (Rv3019c) induced reproducibly significant protection in the spleen and lungs approaching that induced by BCG. Detailed analysis of antigen-specific T cell responses revealed that despite robust responses in the spleen and lungs of vaccinated mice, there was no correlation between these responses and the protective efficacy of the vaccine. Significantly, Rv3019c also stimulated IFN-gamma responses in PBMC from BCG vaccinated cattle, indicating its potential for use in a heterologous prime-boost strategy in conjunction with BCG in the target species.

Analysis of possible factors affecting the specificity of the gamma interferon test in tuberculosis-free cattle herds

Bovine tuberculosis (TB) is still a zoonotic problem in the world. Despite the fact that eradication programs for bovine TB are being implemented in many countries, it remains a public health problem. These programs are mainly based on a single intradermal tuberculin test using bovine tuberculin purified protein derivative (PPD), isolation, and slaughtering of infected animals. The aim of this study was to assess the specificity of the gamma interferon (IFN-gamma) test in TB-free cattle herds, by using not only Australian tuberculins but also tuberculins produced at our institute, and to correlate the response with the type of production (beef cattle, dairy cattle, and a dual-purpose breed), the housing system, and the age of the animals. We studied 800 animals selected from 20 TB- and paratuberculosis-free herds. The animals were tested in parallel, after stimulation with Australian tuberculins and tuberculins produced at our institute, by using the skin test and two IFN-gamma assays. The results of this trial showed that the specificity of the IFN-gamma test is higher than that of the skin test (96.8%) and ranges from 97.3% (using only Australian tuberculins) to 98.6% (using tuberculins produced at our institute). We found that different categories of cattle could influence the specificity of the skin test but that these differences tended to be reduced in the IFN-gamma assay, especially when Italian PPDs were used.

1,25-dihydroxyvitamin D3 and development of tuberculosis in cattle

This report describes the presence and activity of 1,25-dihydroxyvitamin D3 (1,25-D3) in experimental bovine tuberculosis. Animals that went on to develop tuberculous lesions exhibited a rapid transient increase in serum 1,25-D3 within the first 2 weeks following infection with Mycobacterium bovis. 1,25-D3-positive mononuclear cells were later identified in all tuberculous granulomas by immunohistochemical staining of postmortem lymph node tissue. These results suggest a role for 1,25-D3 both at the onset of infection and in the development of the granuloma in these infected animals. Using a monoclonal antibody to the vitamin D receptor (VDR) as a VDR agonist, we confirmed that activation of the vitamin D pathway profoundly depresses antigen-specific, but not mitogenic, bovine peripheral blood T-cell responses (proliferation and gamma interferon production). Investigation of the mechanism of this suppression showed that the VDR antibody modified the expression of CD80 by accessory cells, such that a significant positive correlation between T-cell proliferation and accessory cell CD80 emerged.

Cellular immune responses induced in cattle by heterologous prime-boost vaccination using recombinant viruses and bacille Calmette-Guérin

The development of novel vaccine strategies to replace or supplement bacille Calmette-Guérin (BCG) is urgently required. Here we study, in cattle, the use of heterologous prime-boost strategies based on vaccination with BCG and the mycobacterial mycolyl transferase Ag85A (Rv3804c) expressed either in recombinant modified vaccinia virus Ankara (MVA85A) or attenuated fowlpox strain FP9 (FP85A). Five different vaccination schedules were tested in the first experiment: MVA85A followed by BCG (group 1); BCG followed by MVA85A (group 2); BCG followed by FP85A and then MVA85A (group 3); MVA85A followed by MVA85A and then FP85A (group 4); and FP85A followed by FP85A and then MVA85A (group 5). Vaccine-induced levels of cellular immunity were assessed by determining interferon-gamma (IFN-gamma) responses in vitro. Prime-boost protocols, using recombinant MVA and BCG in combination (groups 1-3), resulted in significantly higher frequencies of Ag85-specific IFN-gamma-secreting cells than the two viral vectors used in combination (P=0.0055), or BCG used alone (groups 2 and 3, P=0.04). The T-cell repertoires of the calves in all five groups were significantly broader following heterologous booster immunizations than after the primary immunization. In a second experiment, the effects of BCG\MVA85A heterologous prime-boost vaccination were compared with BCG\BCG homologous revaccination. The results suggested a higher Ag85A-specific response with a wider T-cell repertoire in the MVA85A-boosted calves than in the BCG\BCG-vaccinated calves. In conclusion therefore, the present report demonstrates the effectiveness of heterologous prime-boost strategies based on recombinant MVA and BCG to induce strong cellular immune responses in cattle and prioritise such vaccination strategies for rapid assessment of protective efficacy in this natural target species of tuberculosis.

Gamma interferon-based immunodiagnosis of tuberculosis: comparison between whole-blood and enzyme-linked immunospot methods

The gamma interferon secretion levels of 52 adults whose T cells had been stimulated with the Mycobacterium tuberculosis antigens CFP-10 and ESAT-6 were measured by enzyme-linked immunospot methods and a whole-blood-based assay. The test results correlated well (r = 0.689, P < 0.0001). Its simple format and use of only small volumes of blood make the whole-blood assay suitable for pediatric practice and field trials.

Use of mycobacterial peptides and recombinant proteins for the diagnosis of bovine tuberculosis in skin test-positive cattle

More accurate tests are required to test cattle which have reacted positively in the tuberculin skin test. For this purpose, a range of mycobacterial antigens, MPB59, MPB64, MPB70, MPB83, ESAT-6 and CFP10, were used either as recombinant proteins or as synthetic peptides in the whole blood interferon-gamma (IFN-gamma) test. Groups of uninfected cattle with typical 'non-specificity' problems were targeted, in particular animals with skin tuberculosis, animals vaccinated against Johne's disease and animals that were positive in the standard purified protein derivative (PPD)-based IFN-gamma test. The two study groups consisted of 74 Mycobacterium bovis-culture positive animals and 72 uninfected animals, all of which tested positive in the caudal fold tuberculin skin test eight to 28 days before the blood test. The use of combinations of ESAT-6 and CFP10 antigens, either as recombinant proteins or peptides, detected similar percentages of M bovis-infected animals as the PPD-based IFN-gamma test, but produced significantly fewer false positive reactions. The PPD-based IFN-gamma test was very effective in differentiating animals vaccinated against Johne's disease that were skin-test positive from those with bovine tuberculosis, and the use of PPD or specific mycobacterial antigens minimised the number of false positive reactions in animals with skin tuberculosis.

Identification of Mycobacterium bovis antigens by analysis of bovine T-cell responses after infection with a virulent strain

Purification and characterization of individual antigenic proteins are essential for the understanding of the pathogenic mechanisms of mycobacteria and the immune response against them. In the present study, we used anion-exchange chromatography to fractionate cell extracts and culture supernatant proteins from Mycobacterium bovis to identify T-cell-stimulating antigens. These fractions were incubated with peripheral blood mononuclear cells (PBMC) from M. bovis-infected cattle in lymphoproliferation assays. This procedure does not denature proteins and permits the testing of mixtures of potential antigens that could be later identified. We characterized protein fractions with high stimulation indices from both culture supernatants and cell extracts. Proteins were identified by two-dimensional gel electrophoresis followed by N-terminal sequencing or MALDI-TOF. Culture supernatant fractions containing low molecular weight proteins such as ESAT6 and CFP10 and other proteins (85B, MPB70), and the novel antigens TPX and TRB-B were associated with a high stimulation index. These results reinforce the concept that some low molecular weight proteins such as ESAT6 and CFP10 play an important role in immune responses. Also, Rv3747 and L7/L12 were identified in high stimulation index cell extract fractions. These data show that protein fractions with high lymphoproliferative activity for bovine PBMC can be characterized and antigens which have been already described and new protein antigens can also be identified in these fractions.

Mycobacterium bovis AN5 antigens vary in their ability to induce nitric oxide production in blood monocytes of experimentally infected cattle

Reactive nitrogen intermediates (RNI) are the principal effector molecules of activated monocyte/macrophage populations, responsible for killing and inhibiting the growth of virulent mycobacteria. In vitro nitrite production by blood monocytes of cattle inoculated with live Mycobacterium bovis AN5 was assessed from 0 day through 45 weeks post inoculation (PI). High in vitro nitrite production was observed at the 8th and 12th weeks PI in sensitized cattle but reactivity had fallen by the 20th week PI. To assess the in vitro nitrite producing ability of monocytes induced by individual polypeptides within culture filtrate antigens (CFA) of M. bovis AN5, cellular blotting was performed using peripheral blood mononuclear cells (PBMC) at the 12th week PI. It was observed that polypeptides of MW 70, 65, 60, 25, 24 and 22 kDa of CFA induced high nitrite production by blood monocytes while many polypeptides had little or no effect.

DNA injection in combination with electroporation: a novel method for vaccination of farmed ruminants

Injection of plasmid DNA encoding antigens into rodents followed by electroporation improved the immune response when compared with injection without electroporation (Widera et al. J Immunol 2000;164:4635-40; Zucchelli et al. J Virol 2000;74:11598-607; Kadowaki et al. Vaccine 2000;18:2779-88). The present study describes the extension of this technology to farm animals, by injecting plasmid DNA encoding mycobacterial antigens (MPB70, Ag85B and Hsp65) into the muscles of goats and cattle using two different types of electrodes, both allowing DNA delivery at the site of electroporation. The animals were vaccinated under local anaesthesia without any observed immediate or long-term distress or discomfort, or any behavioural signs of muscle damage or pathological changes after the electroporation. DNA-injected and electroporated goats showed increased humoral response after the primary vaccination when compared with nonelectroporated animals. Improved T-cell responses following electroporation were observed in hsp65 DNA-vaccinated cattle. DNA injection with or without electroporation did not compromise the specificity of the tuberculin skin test. In conclusion, a protocol applying in vivo electroporation free of side effects to farmed ruminants was established. In addition, we show that DNA vaccination in combination with electroporation can improve the primary immune responses to the encoded antigens.

Vaccination with DNA vaccines encoding MPB70 or MPB83 or a MPB70 DNA prime-protein boost does not protect cattle against bovine tuberculosis

SETTING

Bovine tuberculosis is a problem in a number of countries and protection of cattle by vaccination could be an important control strategy.

OBJECTIVES

To determine the ability of DNA vaccines, which express the mycobacterial antigens MPB83 and MPB70 and a DNA prime-protein boost strategy to stimulate immune responses in cattle and protect against bovine tuberculosis.

DESIGN

Groups of cattle (n=10) were vaccinated with MPB83 DNA, MPB70 DNA, or MPB70 DNA followed by MPB70 protein or injected with BCG or control plasmid DNA. Animals were challenged intratracheally with virulent Mycobacterium bovis at 13 weeks and protection assessed 17 weeks later at postmortem.

RESULTS

In contrast to the strong cellular immune responses induced by BCG, the DNA vaccines induced minimal interferon-gamma (IFN-gamma) and interleukin-2 (IL-2) responses. Cattle primed with MPB70 DNA and boosted with MPB70 protein induced a strong antibody response and a weak IFN-gamma response. BCG gave significant reduction in four pathological parameters of disease while the DNA vaccines and MPB70 DNA/protein did not protect animals against challenge with M. bovis. Moreover, cattle vaccinated with MPB70 DNA/protein had a significantly higher proportion of animals with severe lung lesions (>100 lesions) than the MPB70 DNA alone or the control group. Increased bovine PPD-specific IL-4 mRNA expression in cattle, post-challenge, correlated with the presence of tuberculous lung lesions.

CONCLUSION

Vaccination of calves with MPB70 or MPB83 DNA vaccines or with a more immunogenic MPB70 DNA prime-protein boost strategy did not induce protection against bovine tuberculosis.

Expression of L-Selectin (CD62L), CD44, and CD25 on activated bovine T cells

Mycobacterium bovis infection of cattle represents a natural host-pathogen interaction and, in addition to its economic and zoonotic impact, represents a model for human tuberculosis. Extravasation and trafficking of activated lymphocytes to inflammatory sites is modulated by differential expression of multiple surface adhesion molecules. However, effects of M. bovis infection on adhesion molecule expression have not been characterized. To determine these changes, peripheral blood mononuclear cells from M. bovis-infected cattle were stimulated with M. bovis purified protein derivative (PPD) or pokeweed mitogen (PWM) and evaluated concurrently for proliferation and activation marker expression. Stimulation with PPD or PWM increased CD25 and CD44 mean fluorescence intensity (MFI) and decreased CD62L MFI on CD4(+) cells from infected animals. CD62L MFI on PPD- and PWM-stimulated gammadelta T-cell receptor-positive (TCR(+)) and CD8(+) cells was also reduced compared to that of nonstimulated gammadelta TCR(+) and CD8(+) cells. Using a flow cytometry-based proliferation assay, it was determined that proliferating cells, regardless of lymphocyte subset, exhibited increased expression of CD25 and CD44 and decreased expression of CD62L compared to cells that had not proliferated. In contrast to proliferation, activation-induced apoptosis of CD4(+) cells resulted in a significant down regulation of CD44 expression. Lymphocytes obtained from lungs of M. bovis-infected cattle also had reduced expression of CD44 compared to lymphocytes from lungs of noninfected cattle. These alterations in surface molecule expression upon activation likely impact trafficking to sites of inflammation and the functional capacity of these cells within tuberculous granulomas.

Identification of novel Mycobacterium tuberculosis antigens with potential as diagnostic reagents or subunit vaccine candidates by comparative genomics

An independent review for the British government has concluded that the development of a cattle vaccine against Mycobacterium bovis holds the best long-term prospects for tuberculosis control in British herds. The development of complementary diagnostic tests to differentiate between vaccinated and infected animals is necessary to allow the continuation of test-and-slaughter-based control policies alongside vaccination. Vaccination with M. bovis bacillus Calmette-Guérin (BCG), the only available vaccine, results in tuberculin purified protein derivative sensitivity and has shown varying vaccine efficacies in cattle. Thus, identification of more-specific reagents to distinguish between vaccination and infection, as well as the identification of subunit vaccine candidates for improved tuberculosis vaccines, is a research priority. In the present study, we applied comparative genomics to identify M. bovis-Mycobacterium tuberculosis antigens whose genes had been deleted in BCG Pasteur. In total, 13 open reading frames (ORFs) from the RD1, RD2, and RD14 regions of the M. tuberculosis genome were selected. Pools of overlapping peptides spanning these ORFs were tested in M. bovis-infected (n = 22), BCG-vaccinated (n = 6), and unvaccinated (n = 10) control cattle. All were recognized in infected cattle, with responder frequencies varying between 16 and 86%. In particular, eight highly immunogenic antigens were identified whose potentials as diagnostic reagents or as subunit vaccines warrant further study (Rv1983, Rv1986, Rv3872, Rv3873, Rv3878, Rv3879c, Rv1979c, and Rv1769).

Purification, biochemical characterization and immunogenicity of SA5K, a secretion antigen of Mycobacterium tuberculosis

Mycobacterium tuberculosis (MTB) secretory proteins are generally considered important antigens for immune protection against tuberculosis (TB). An 8.3-kDa secretory antigen of MTB and Mycobacterium bovis bacillus Calmette-Guérin (BCG), called SA5K, was recently identified and cloned in our laboratory. In this report, recombinant SA5K containing a histidine hexamer was expressed in Escherichia coli and purified to investigate its biochemical structure and to establish whether it was immunogenic for healthy sensitized and nonsensitized human donors and for patients infected with MTB. The protein nucleotide sequence was shown to be identical in BCG and in MTB. SA5K revealed an abnormal electrophoretic mobility in SDS-PAGE that made it look lighter than it is in Western blotting. While recombinant SA5K was poorly recognized by T lymphocytes from patients with pulmonary TB, it elicited proliferation of CD4+ T lymphocytes in the vast majority of healthy individuals sensitized to mycobacterial antigens by BCG vaccination. At a serum dilution of 1 : 80, antibodies reacting against recombinant SA5K were found in 67% of sera from TB patients and in 73% of sera from healthy subjects. The percentage of positive subjects dropped at higher serum dilutions, but no significant difference in the recognition rate was observed between TB patients and healthy donors and between healthy vaccinated and nonvaccinated subjects. Owing to the high percentage of sera from healthy subjects who recognized SA5K in Western blotting, the antigen seems to exhibit, at least in the present form, a poor specificity for an employment for a serodiagnosis of TB.

Vaccination of guinea pigs with DNA encoding the mycobacterial antigen MPB83 influences pulmonary pathology but not hematogenous spread following aerogenic infection with Mycobacterium bovis

Protection of cattle against bovine tuberculosis by vaccination could be an important control strategy in countries where there is persistent Mycobacterium bovis infection in wildlife and in developing countries where it is not economical to implement a tuberculin test and slaughter control program. The main aim of such a vaccination strategy would be to reduce transmission of infection by reducing the lung pathology caused by infection and preventing seeding of the organism to organs from which M. bovis could be excreted. Recent reports of successful DNA vaccination against Mycobacterium tuberculosis in small-animal models have suggested that DNA vaccines act by reducing lung pathology without sensitizing animals to tuberculin testing. We therefore evaluated the ability of vaccines consisting of DNA encoding the mycobacterial antigens MPB83 and 85A to reduce lung pathology and prevent hematogenous spread in guinea pigs challenged with a low dose of aerosolized M. bovis. Vaccination with MPB83 DNA reduced the severity of pulmonary lesions, as assessed by histopathology, and resembled M. bovis BCG vaccination in this respect. However, unlike BCG vaccination, MPB83 DNA vaccination did not protect challenged guinea pigs from hematogenous spread of organisms to the spleen. In contrast, vaccination with antigen 85A DNA, a promising DNA vaccine for human tuberculosis, had no measurable protective effect against infection with M. bovis.

Human T cell responses to peptides of the Mycobacterium leprae 45-kD serine-rich antigen

In order to identify T cell epitopes within the Mycobacterium leprae 45-kD serine-rich antigen, we analysed responses to overlapping 17-mer peptides encompassing the whole antigen in non-exposed UK controls, Pakistani leprosy patients and tuberculosis patients in both the United Kingdom and Pakistan. This antigen has been described as M. leprae-specific, although it has a hypothetical homologue in M. tuberculosis. Human peripheral blood mononuclear cells were stimulated with peptide for 5 days and IFN-gamma measured in supernatants by ELISA. Some peptides were recognized more frequently by T cells from tuberculoid leprosy patients than those from UK controls, suggesting that such T cell epitopes might have diagnostic potential, while other peptides induced greater responses among UK control subjects. Short-term cell lines confirmed that these assays detected specific T cell recognition of these peptides. However, many tuberculosis patients also recognized these potentially specific peptides suggesting that there could be a true homologue present in M. tuberculosis.

Modulation of Mycobacterium bovis-specific responses of bovine peripheral blood mononuclear cells by 1,25-dihydroxyvitamin D(3)

Historically, administration of vitamin D has been considered beneficial in the treatment of tuberculosis. The interaction of this vitamin [i.e., 1,25-dihdroxyvitamin D(3) [1,25(OH)(2)D(3)]] with the antitubercular immune response, however, is not clear. In the present study, in vitro recall responses of peripheral blood mononuclear cells (PBMC) from cattle infected with Mycobacterium bovis were used to study the immune-modulatory effects of 1,25(OH)(2)D(3) on M. bovis-specific responses in vitro. Addition of 1 or 10 nM 1,25(OH)(2)D(3) inhibited M. bovis-specific proliferative responses of PBMC from M. bovis-infected cattle, affecting predominantly the CD4(+) cell subset. In addition, 1,25(OH)(2)D(3) inhibited M. bovis-specific gamma interferon (IFN-gamma) production yet enhanced M. bovis-specific nitric oxide (NO) production. Lymphocyte apoptosis, measured by flow cytometry using annexin-V staining, was diminished by addition of 1,25(OH)(2)D(3) to PBMC cultures. These findings support the current hypothesis that 1,25(OH)(2)D(3) enhances mycobacterial killing by increasing NO production, a potent antimicrobial mechanism of activated macrophages, and suggest that 1,25(OH)(2)D(3) limits host damage by decreasing M. bovis-induced IFN-gamma production.

Intranasal BCG vaccination protects BALB/c mice against virulent Mycobacterium bovis and accelerates production of IFN-gamma in their lungs

Local immune reactivity in the lungs of BALB/c mice was studied following (i) intranasal (i.n.) vaccination with Mycobacterium bovis BCG, (ii) intravenous (i.v.) challenge with a virulent M. bovis field isolate and (iii) i.n. vaccination with M. bovis BCG followed by i.v. challenge with an M. bovis field isolate. The results demonstrated that i.n. vaccination with BCG induced a high degree of protection against systemic M. bovis challenge, and that this protection correlated with a rapid production of IFN-gamma after M. bovis challenge by lung T cells from vaccinated mice.

BOVIGAM: an in vitro cellular diagnostic test for bovine tuberculosis

BOVIGAM which is based on the detection of gamma interferon (IFN- gamma) is a rapid, laboratory assay of a cell mediated immune response that may be used for the detection of tuberculosis (TB) infection in animals. Whole blood is first incubated overnight with bovine PPD, avian PPD or negative control antigens, and IFN- gamma in the supernatant plasma is then measured by EIA. TB infection is indicated by a predominant IFN- gamma response to bovine PPD. Since 1988, BOVIGAM has been extensively trialed on more than 200 000 cattle in Australia, Brazil, Ireland, Northern Ireland, Italy, New Zealand, Romania, Spain and the USA. Sensitivity has varied between 81.8% and 100% for culture-confirmed bovine TB and specificity between 94% and 100%. The IFN- gamma assay detects M. bovis infection earlier than the skin test and in New Zealand is applied to detect skin-test negative cattle with TB, where after slaughter a significant number of IFN- gamma reactors have TB. BOVIGAM is also approved in New Zealand for serial testing skin test positive cattle when non-specificity is suspected. Cattle are tested 7-30 days after a positive caudal fold test. The boosting effect of the skin test on T-cell activity allows blood to be cultured with PPD up to 30 h after collection without effecting accuracy. The BOVIGAM results are not affected by poor nutritional condition and are only mildly and briefly affected by dexamethasone treatment and parturition. IFN- gamma responses of cattle vaccinated with BCG are dose-dependent and short-lived. The BOVIGAM kit is now used routinely in many countries for the detection of M. bovis infected cattle, buffalo and goats.

Immune responses in bovine tuberculosis

Knowledge of the immune responses which develop in cattle following infection with Mycobacterium bovis is essential both to the understanding of disease pathogenesis and to the logical development of immune-dependent tools, such as diagnostic tests and vaccines, which can be used to combat the disease. Studies of field cases of bovine tuberculosis (TB) and of experimental bovine models of M. bovis infection have indicated that cell-mediated immune responses (CMI) predominate within a spectrum of immunity which exists. This paper reviews aspects of recent research and indicates how knowledge of T-cell antigenic targets in bovine TB along with increasing knowledge of T-cell subpopulations and their interactions with M. bovis -infected macrophages provides opportunities for the development of better methods for disease control.

Use of synthetic peptides derived from the antigens ESAT-6 and CFP-10 for differential diagnosis of bovine tuberculosis in cattle

In Great Britain an independent scientific review for the government has concluded that the development of a cattle vaccine against Mycobacterium bovis infection holds the best long-term prospect for tuberculosis control in British herds. A precondition for vaccination is the development of a complementary diagnostic test to differentiate between vaccinated animals and those infected with M. bovis so that testing and slaughter-based control strategies can continue alongside vaccination. To date bacillus Calmette-Guérin (BCG), an attenuated strain of M. bovis, is the only available vaccine for the prevention of tuberculosis. However, tests based on tuberculin purified protein derivative cannot distinguish between M. bovis infection and BCG vaccination. Therefore, specific antigens expressed by M. bovis but absent from BCG constitute prime candidates for differential diagnostic reagents. Recently, two such antigens, ESAT-6 and CFP-10, have been reported to be promising candidates as diagnostic reagents for the detection of M. bovis infection in cattle. Here we report the identification of promiscuous peptides of CFP-10 that were recognized by M. bovis-infected cattle. Five of these peptides were formulated into a peptide cocktail together with five peptides derived from ESAT-6. Using this peptide cocktail in T-cell assays, M. bovis-infected animals were detected, while BCG-vaccinated or Mycobacterium avium-sensitized animals did not respond. The sensitivity of the peptide cocktail as an antigen in a whole-blood gamma interferon assay was determined using naturally infected field reactor cattle, and the specificity was determined using blood from BCG-vaccinated and noninfected, nonvaccinated animals. The sensitivity of the assay in cattle with confirmed tuberculosis was found to be 77.9%, with a specificity of 100% in BCG-vaccinated or nonvaccinated animals. This compares favorably with the specificity of tuberculin when tested in noninfected or vaccinated animals. In summary, our results demonstrate that this peptide cocktail can discriminate between M. bovis infection and BCG vaccination with a high degree of sensitivity and specificity.

Antigen recognition and immunomodulation by gamma delta T cells in bovine tuberculosis

This report describes the in vitro proliferative responses of peripheral blood gammadelta T cells to defined mycobacterial protein Ags and the immunomodulatory effect of gammadelta T cells in cattle infected with Mycobacterium bovis. gammadelta T cell responses were specific to M. bovis infection because they were detected in cattle either experimentally or naturally infected with M. bovis, but were not present in uninfected controls. Proliferating gammadelta T cell cultures produced enhanced levels of IFN-gamma and TGF-beta, but not IL-2 in response to the more immunodominant mycobacterial AGS: Depletion of gammadelta T cells from PBMC resulted in an increased Ag-specific proliferation in half the animals tested, indicating a suppressive effect of gammadelta T cells upon other (alphabeta) T cell responses. Because gammadelta T cells constitute a major T cell population in the peripheral blood of cattle, the activities of gammadelta T cells described in this report could make a significant contribution to the immune response in bovine tuberculosis.

Lymphocyte subset proliferative responses of Mycobacterium bovis-infected cattle to purified protein derivative

Despite highly successful eradication efforts in several countries, Mycobacterium bovis infection of cattle remains a significant health concern worldwide. Immune mechanisms of resistance to and/or clearance of M. bovis infection of cattle, however, are unclear. Recent studies have provided evidence supporting a role for CD4(+), CD8(+), and gammadelta TCR(+) T cells in the response of cattle to M. bovis. In the present study, we utilized a flow cytometric-based proliferation assay to determine the relative contribution of individual lymphocyte subsets in the response to M. bovis infection and/or sensitization with mycobacterial purified protein derivative (PPD). Peripheral blood mononuclear cells (PBMC) from M. bovis-infected cattle proliferated in response to in vitro stimulation with M. bovis PPD. CD4(+) T cells and gammadelta TCR(+) cells were the predominate subsets of lymphocytes responding to PPD. gammadelta TCR(+) cells also proliferated in non-stimulated cultures; however, the gammadelta TCR(+) cell proliferative response of infected cattle was significantly (p<0.05) greater in PPD-stimulated cultures as compared to non-stimulated cultures. Intradermal injection of PPD for comparative cervical testing (CCT) induced a boost in the in vitro proliferative response of CD4(+) but not gammadelta TCR(+) cells of infected cattle. Administration of PPD for CCT also boosted interferon-gamma (IFN-gamma) production by PBMC of infected cattle following in vitro stimulation with M. bovis PPD. Injection of PPD for CCT did not, however, elicit a proliferative or IFN-gamma response in cells isolated from non-infected cattle. These data indicate that CD4(+) and gammadelta TCR(+) cells of M. bovis-infected cattle proliferate in a recall response to M. bovis PPD and that the CD4(+) cell response is boosted by intradermal injection with PPD for CCT.

Distinct response kinetics of gamma interferon and interleukin-4 in bovine tuberculosis

This study shows that gamma interferon (IFN-gamma) and interleukin-4 (IL-4) cytokine responses are produced by peripheral blood cells in cattle infected with Mycobacterium bovis. The different kinetics of the IFN-gamma and IL-4 responses to bovine tuberculin and to ESAT-6 following experimental intratracheal infection with M. bovis are described. An early increase in IFN-gamma was observed that was maintained throughout the period studied. In contrast, the IL-4 response was delayed and confined to a peak of activity lasting 6 to 8 weeks. Interestingly, an experimental challenge of cattle with a lower dose of M. bovis which did not result in the development of lesions, positive DTH skin test, or substantial IFN-gamma responses nevertheless generated strong specific IL-4 responses. Investigation of naturally infected M. bovis field reactors showed increased IFN-gamma and IL-4 responses compared to uninfected cattle and that both of these cytokines were equally able to differentiate infected from uninfected animals. The magnitude of the M. bovis-induced IL-4 responses were found to be similar to the antigen-specific IL-4 responses of cattle infected with the parasitic nematode Onchocerca ochengi, further supporting the presence of this type 2 cytokine in bovine tuberculosis.