Shedding of Mycobacterium bovis in the nasal mucus of cattle infected experimentally with tuberculosis by the intranasal and intratracheal routes

Four groups of six calves were infected experimentally with either a low dose of approximately 10(4) colony-forming units (cfu) or a high dose of approximately 10(6) cfu of Mycobacterium bovis. Each dose was delivered by the intranasal and intratracheal routes. More severe disease was observed in the groups inoculated with the high dose. Visible lesions were identified in 21 of the 24 animals, all of which also gave positive skin tests and interferon-gamma (IFN-gamma) responses. Nasal shedding was detected in 15 of the 24 animals and the frequency of shedding was influenced by both the route and the dose of infection; no shedding was observed in the group infected intratracheally with the low dose. Two of the 15 confirmed shedders had no visible lesions at postmortem examination; both of these calves gave IFN-gamma responses but only one was skin test positive.

Exposure to Mycobacterium avium induces low-level protection from Mycobacterium bovis infection but compromises diagnosis of disease in cattle

We assessed the effect of exposure to Mycobacterium avium on the development of immune responses and the pathogenesis of disease observed following Mycobacterium bovis challenge. A degree of protection against M. bovis was observed in calves which were pre-exposed to M. avium as assessed by the extent of lesions and bacterial load compared to the M. bovis alone group. The immune response following M. bovis challenge in cattle previously inoculated with M. avium was biased towards antigens (PPD) present in M. avium, whereas the response following M. bovis alone was biased towards antigens present in M. bovis, indicating an imprinting of memory to avian antigens on T lymphocytes. A consequence of the memory to M. avium antigens was failure to diagnose M. bovis infection by the skin test or the IFN(gamma) assay in some of the animals which had lesions of tuberculosis at necropsy. The use of M. bovis specific antigens ESAT-6 and CFP-10 increased IFN(gamma) test specificity in animals previously exposed to M. avium but the responses to these antigens were lower than those observed in animals exposed to M. bovis alone. The implication is that responses to M. avium, although providing some immunity, may mask diagnosis of M. bovis infection, even when specific antigens are employed, potentially contributing to disease transmission in the field.

Vaccination of cattle with Mycobacterium bovis culture filtrate proteins and CpG oligodeoxynucleotides induces protection against bovine tuberculosis

Culture filtrate protein (CFP) vaccines have been shown to be effective in small animal models for protecting against tuberculosis while immunisation with these types of vaccines in cattle has been less successful. A study was conducted in cattle to evaluate the ability of selected adjuvants and immunomodulators to stimulate protective immune responses to tuberculosis in animals vaccinated with Mycobacterium bovis CFP. Seven groups of cattle (n=5) were vaccinated with M. bovis CFP formulated with either Emulsigen or Polygen adjuvant alone or in combination with a specific oligodeoxynucleotides (ODN), polyinosinic acid: polycytidylic acid (poly I:C) or poly I:C and recombinant granulocyte-macrophage colony stimulating factor. Two additional groups were vaccinated subcutaneously with BCG or non-vaccinated. In contrast to the strong interferon-gamma (IFN-gamma) responses induced by BCG, the CFP vaccines induced strong antibody responses but weak IFN-gamma responses. The addition of CpG ODN to CFP significantly enhanced cell-mediated responses and elevated antibody responses to mycobacterial antigens. Of the CFP vaccinated groups, the strongest IFN-gamma responses to CFP vaccines were measured in animals vaccinated with CFP/Emulsigen+CpG or CFP/Polygen+CpG. The animals in these two groups, together with those in the BCG and non-vaccinated groups were challenged intratracheally with virulent M. bovis at 13 weeks after the first vaccination and protection was assessed, by examination for presence of tuberculous lesions in the lungs and lymph nodes, 13 weeks later at postmortem. While BCG gave the best overall protection against tuberculosis, significant protection was also seen in animals vaccinated with CFP/Emulsigen+CpG. These results establish an important role for CpG ODN in stimulating protective Th1 responses to tuberculosis in cattle and indicate that a sub-unit protein vaccine can protect these animals against tuberculosis.

Vaccination of neonatal calves with Mycobacterium bovis BCG induces protection against intranasal challenge with virulent M. bovis

Vaccination of neonates with Mycobacterium bovis bacillus Calmette-Guerin (BCG) may be a strategy that overcomes reduced vaccine efficacy associated with exposure to environmental mycobacteria in humans and cattle. Preliminary comparisons indicated that 2-week-old calves produced an immune response to vaccination at least as intense as that observed in adults. Subsequently, five gnotobiotic hysterotomy derived calves aged 1 day were inoculated with BCG and 3 months later were challenged intranasally with virulent M. bovis. The number of tissues with lesions and the pathological extent of these lesions was reduced significantly in vaccinates. Furthermore, lesions were evident in the lung or associated chest lymph nodes of four of five controls but none of five vaccinates. BCG vaccination reduced significantly the level of bacterial colonization. However, lesions in the head associated lymph nodes were observed in three of five BCG-vaccinated cattle. Levels of interferon gamma (IFN-gamma) detected by enzyme-linked immunosorbent assay (ELISA) or enzyme-linked immunospot (ELISPOT) in individual vaccinated animals at challenge did not correlate with subsequent resistance and in general immune responses post-challenge were lower in vaccinated calves. Low IL-10 responses were evident but IL-4 was not detected. Responses to ESAT-6 and/or CFP-10 were evident in four of four control calves that had lesions. Two of the BCG vaccinates with lesions did not produce a response to ESAT-6 and CFP-10, indicating that these antigens did not distinguish vaccinated immune animals from vaccinated animals with lesions. Overall, vaccination of neonatal calves with BCG induced significant protection against disease and has potential as a strategy for the reduction of the incidence of bovine tuberculosis.

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.

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.

Modulation of the bovine delayed-type hypersensitivity responses to defined mycobacterial antigens by a synthetic bacterial lipopeptide

The use of defined protein and peptide antigens can overcome specificity limitations of purified protein derivatives in the detection of bovine tuberculosis when the antigens are used in blood-based tests. Since the use of these specific antigens as skin test reagents could have practical advantages, we investigated the potential of Mycobacterium bovis-specific antigens to stimulate delayed-type hypersensitivity (DTH) responses in cattle experimentally infected with M. bovis. A cocktail of the recombinant antigens ESAT-6, MPB83, and MPB64 failed to stimulate in vivo DTH in cattle that had been experimentally infected with M. bovis despite the fact that the antigens were recognized in vitro by the same animals. However, it was possible to stimulate antigen-specific bovine DTH responses by using ESAT-6 in combination with a synthetic bacterial lipopeptide. This lipopeptide stimulated the release of the proinflammatory cytokine tumor necrosis factor alpha from monocyte-derived bovine dendritic cells in vitro, thereby providing a possible mechanism for its DTH-enhancing properties.

Use of the bovine model of tuberculosis for the development of improved vaccines and diagnostics

Over the past few years there has been a resurgence in research into bovine tuberculosis due to the sharp rise of the disease in countries such as Great Britain and to the continuing problem of wild-life reservoirs in countries such as New Zealand. One of the goals of this research is to develop cattle vaccines against TB. The initial testing of candidate vaccines is carried out in laboratory animals, initially mice and subsequently guinea pigs. A unique feature of the cattle vaccination programme is that candidate vaccines which show promise in laboratory models can then be tested in the natural host species, cattle, before progressing to clinical trials. This is a major advantage over the strategy for developing a vaccine for human tuberculosis where, of course, it is impossible to test a candidate vaccine by experimentally challenging the host species with the pathogen. The most commonly used model for testing vaccine candidates in cattle consists of an intra-tracheal challenge of between 10(3) and 10(4) colony forming units of Mycobacterium bovis. The pathology observed following challenge is similar to human tuberculosis giving rise to a marked granulomatous reaction and a predominantly cellular immune response. Using this model we have been able to make a number of significant advances towards a bovine TB vaccine. First we have developed antigen cocktails that, when used in a whole blood gamma interferon assay, can differentiate between M. bovis infected and BCG vaccinated animals. Next we have developed immune correlates of pathology, which allow us to assess whether the vaccine is protecting animals against challenge before post mortem examination. Finally we have been able to use the model to develop a vaccine that improves the efficacy of BCG against M. bovis challenge.

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.

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).

Immunogenicity of Mycobacterium tuberculosis RD1 region gene products in infected cattle

Current immuno-diagnostic tests for the detection of Mycobacterium bovis infection in cattle rely on the use of tuberculin PPD as antigens. However, the use of a cattle vaccine is effectively prohibited because BCG, the only potentially available cattle TB vaccine, compromises the current tuberculin test. The main objective of this study was to identify specific antigens, which could increase the test sensitivity to levels achieved with tuberculin. Our approach utilized the availability of the genome sequences of Mycobacterium tuberculosis and BCG by applying principles of comparative genomics to the identification of species-specific antigens. Eight open-reading frames (Rv3871 to Rv3878) encoding for putative antigens in the RD1 region of the M. tuberculosis genome, which is deleted in all strains of BCG, were selected and screened in the form of pools of synthetic peptides for immunological reactivity (antigen induced proliferation and IFN-gamma secretion) with peripheral blood mononuclear cells from cattle experimentally infected with M. bovis. Our results confirm the immunodominant role of two RD1 region products, CFP-10 (Rv3874) and ESAT-6 (Rv3875). In addition, we were able to identify 3 more antigens (Rv3871, Rv3872 and Rv3873), which induced immunological reactivity in PBMC from more than 50%M. bovis of infected cattle.

Development of detection methods for ruminant interleukin (IL)-12

Recombinant bovine IL-12 (rbo IL-12) was transiently expressed in COS-7 cells and shown to upregulate the synthesis of IFNgamma by bovine cells stimulated with a suboptimal concentration of mitogen in vitro. Mice were immunised with a plasmid encoding rbo IL-12 and boosted with rbo IL-12 and a number of monoclonal antibodies (mAb) were generated that reacted with rbo IL-12 in an ELISA. Some of these mAb neutralised the ability of rbo IL-12 to induce IFNgamma synthesis by bovine cells. A pair of mAb was identified that together could be used to detect both recombinant and natural bovine IL-12 by ELISA and a luminometric detection method was applied to the ELISA making it more sensitive. Using this method native bovine IL-12 was detected in supernatants of dendritic cells (DC) cultured in vitro with a synthetic lipopeptide known to stimulate secretion of IL-12 by human DC. The ELISA was also able to detect recombinant ovine IL-12 and, less effectively, recombinant human IL-12. In contrast, bovine IL-12 was not detected by a commercial human IL-12 ELISA kit. Intracytoplasmic IL-12 was detected in bovine DC using the antibodies described herein. The ability to detect ruminant IL-12 by three methods: ELISA, bioassay with neutralising mAb and cytoplasmic staining, will permit studies of the role of this important cytokine in the immunology and pathogenesis of animal diseases.

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.

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.

Effective DNA vaccination of cattle with the mycobacterial antigens MPB83 and MPB70 does not compromise the specificity of the comparative intradermal tuberculin skin test

The current tuberculin test and slaughter strategy for the control of bovine tuberculosis in cattle has failed to prevent a sharp rise in cases over recent years, especially in the south-west of England. A recent scientific review has concluded that the development of a cattle vaccine holds the best prospect for tuberculosis control in British herds. In order to continue with test and slaughter-based control strategies, the development of TB vaccines that do not compromise the specificity of the tuberculin skin test are required. This report describes results of cattle vaccination experiments with TB DNA vaccines expressing the mycobacterial antigens MPB70, MPB83, and Ag85A and constitutes the first published vaccination study with DNA vaccines undertaken in a target host species. All calves vaccinated with the MPB83 expressing plasmid demonstrated potent cellular immune responses, characterised by CD4(+) T cells producing interferon-gamma as well as humoral immunity characterised by IgG1 biased specific antibodies. Vaccination with MPB70 was less effective with immune responses only observed in half of the vaccinated animals, while vaccination with Ag85A did not result in vaccine-induced immune responses. Intramuscular vaccination was found to stimulate stronger cellular responses than intradermal immunisation. Significantly, the specificity of tuberculin skin testing was not compromised by DNA vaccination since none of the vaccinated calves showed positive skin test reactivity.

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.

Toward the development of diagnostic assays to discriminate between Mycobacterium bovis infection and bacille Calmette-Guérin vaccination in cattle

A scientific review of the recent sharp increase in bovine tuberculosis in Great Britain has concluded that the development of a cattle vaccine holds the best prospect for long-term disease control. It is important to develop a diagnostic test that differentiates between vaccinated and Mycobacterium bovis-infected animals, to ensure that test-and-slaughter control strategies can continue alongside vaccination. The mycobacterial antigens ESAT-6, MPB64, and MPB83 are expressed at high levels in M. bovis but are expressed at low levels or not at all in bacille Calmette-Guérin (BCG) Pasteur. Promiscuous bovine T cell epitopes of these antigens were identified and formulated into a peptide cocktail. This cocktail and a cocktail composed of recombinant forms of the 3 antigens was able to distinguish cattle infected with virulent M. bovis from those vaccinated with BCG and from those sensitized to avian tuberculin in lymphocyte transformation and interferon-gamma assays.

Antigen specificity in experimental bovine tuberculosis

This report describes the kinetics of T-cell responses to a panel of mycobacterial antigens (PPD-M, PPD-A, ESAT-6, Ag85, 38kD, MPB64, MPB70, MPB83, hsp16.1, hsp65, and hsp70) following experimental infection of cattle with Mycobacterium bovis. Increased antigen-specific lymphocyte proliferation, gamma interferon, and interleukin-2 responses were observed in all calves following infection. Positive lymphocyte proliferation and cytokine responses to PPD-M and ESAT-6 were observed throughout the infection period studied. In contrast, responses to all other antigens were more variable and were not constantly present, suggesting that antigen cocktails rather than individual antigens should be used for immunodiagnosis. The detection of cytokine responses in the absence of lymphocyte proliferation, particularly during the early stages of infection, suggests a role for antigen-specific cytokine readout systems in the early identification of M. bovis infection in cattle.

Bovine tuberculosis: immune responses in the peripheral blood and at the site of active disease

This report describes a comparison of immune responses in the peripheral blood and at the site of active disease in cattle 20 weeks after experimental infection with Mycobacterium bovis. Lymphocyte proliferation, and the production of interferon-gamma (IFN-gamma) and interleukin (IL)-2 were measured in response to tuberculin and a number of mycobacterial antigens, including ESAT-6, MPB64, MPB70, MPB83, hsp 16.1, hsp 65, hsp 70 and the 38 000 MW lipoprotein antigen. The level of transforming growth factor-beta (TGF-beta) was measured following stimulation of cells with tuberculin. Our results suggest little difference in the responses of peripheral blood and lymph node cells to most of the antigens used. However, tuberculin purified protein derivative (PPD) and ESAT-6 elicited stronger responses in the peripheral blood compared with lymph node cells. Investigation of the responding T-cell subpopulations in the peripheral blood showed that both CD4+ and, to a lesser extent, gammadelta T-cell receptor-positive (TCR+) T cells contributed to these responses. This is the first report to compare peripheral and local immune responses in bovine tuberculosis. Unlike cases of human tuberculosis where immune activity at the site of disease and anergy in the peripheral blood have been reported, our results suggest that for bovine tuberculosis immune responses occurring in the peripheral blood reflect those at the site of disease.

Enhancement of the T cell response to a mycobacterial peptide by conjugation to synthetic branched polypeptide

A peptide-based approach towards improving the immunodiagnosis of, and vaccination against, tuberculosis faces the problems of MHC restriction of T cell recognition and the poor immunogenicity of peptides in the absence of adjuvant. We sought to compensate this by the use of synthetic branched polypeptides of the poly[Lys-(Xi-DL-Alam)] type, containing a glutamic acid residue (EAK), and further modified either by succinylation (SucEAK) or acetylation (AcEAK). These carriers were conjugated to two permissively recognized peptides of Mycobacterium tuberculosis. The 38p350 - 369-SucEAK conjugate enhanced IFN-gamma production more than 13-fold (from 22.6 to 294 pg / ml, p = 0.001) in peripheral blood mononuclear cells from healthy subjects, and 8.7-fold (p = 0. 012) in cells from tuberculosis patients. The effect was dependent on the carrier used and on covalent linkage of SucEAK to 38p350 - 369. An increased response occurred best in cells from subjects bearing at least one HLA-DR allele for which 38p350 - 369 had high binding affinity and required cellular processing of the conjugate as inhibitors (chloroquine and wortmannin) blocked the IFN-gamma response. SucEAK conjugation of peptide 16p91 - 110 did not significantly increase IFN-gamma production, indicating that the ability of conjugation to enhance the response was peptide structure dependent. These data indicate that the use of SucEAK polymer coupled with permissively recognized peptides could contribute to the development of an improved immunodiagnostic or vaccine reagent for tuberculosis.

Development of diagnostic reagents to differentiate between Mycobacterium bovis BCG vaccination and M. bovis infection in cattle

In Great Britain a recent independent scientific review for the government has concluded that the development of a cattle vaccine against Mycobacterium bovis holds the best long-term prospect for tuberculosis control in British herds. A sine qua non for vaccination is the development of a complementary diagnostic test to differentiate between vaccinated animals and those infected with M. bovis so that test-and-slaughter-based control strategies can continue alongside vaccination. In order to assess the feasibility of developing a differential diagnostic test for a live vaccine, we chose M. bovis BCG Pasteur as a model system. Recombinant forms of antigens which are expressed in M. bovis but not, or only at low levels, in BCG Pasteur (ESAT-6, MPB64, MPB70, and MPB83) were produced. These reagents were tested either alone or in combination by using peripheral blood mononuclear cells from M. bovis-infected, BCG-vaccinated, and Mycobacterium avium-sensitized calves. All four antigens induced in vitro proliferation and gamma interferon responses only in M. bovis-infected animals. A cocktail composed of ESAT-6, MPB64, and MPB83 identified infected animals but not those vaccinated with BCG. In addition, promiscuous T-cell epitopes of ESAT-6, MPB64, and MPB83 were formulated into a peptide cocktail. In T-cell assays with this peptide cocktail, infected animals were identified with frequencies similar to those obtained in assays with the protein cocktail, while BCG-vaccinated or M. avium-sensitized animals did not respond. In summary, our results suggest that peptide and protein cocktails can be designed to discriminate between M. bovis infection and BCG vaccination.

The role of B cells in the establishment of T cell response in mice infected with an intracellular bacteria, Listeria monocytogenes

To clarify the role of B cells in the establishment of T cell response against intracellular bacteria, B-cell-deficient (muMT-/-) mice were infected with an intracellular bacteria, Listeria monocytogenes, and T cell response against the bacteria was analyzed. On day 6 of primary Listeria infection, spleen T cells of the muMT-/- mice showed significantly lower levels of proliferative response and IFN-gamma production than those of normal infected mice after in vitro stimulation with listerial antigen. Even in the secondary Listeria infection after immunization with viable bacteria, spleen T cells of the muMT-/- mice proliferated and produced IFN-gamma against listerial antigen at significantly lower levels than those of normal immunized mice. These results demonstrate participation of B cells in priming of Listeria-specific T cells in vivo. However, B cells failed to present Listeria antigen to Listeria-specific T cells in vitro unless Listeria antigen was solubilized. Furthermore, transfer of immune serum from Listeria-infected normal mice failed to enhance the Listeria-specific T cell response of muMT-/- mice. The results indicate that B cells support the T cell response against intracellular bacteria through a mechanism other than their Ig production or antigen presentation function.

Induction of cellular immunity to a mycobacterial antigen adsorbed on lamellar particles of lactide polymers

Microspheres prepared from synthetic, biodegradable poly (L-lactide) [PLA] and copolymers of lactide and glycolide such as poly (DL lactide co-glycolide) [PLG] have been widely investigated for controlled delivery of encapsulated vaccine antigens. In this study we describe novel lamellar microparticles produced from PLA to which protein antigens can be adsorbed. These particles when administered to mice, induced strong Th1-type T cell responses to the adsorbed 38 kDa protein antigen from M. tuberculosis characterised by high levels of Interferon-gamma. In addition to proteins, we were also able to adsorb synthetic peptides resulting in specific T cell proliferation. Induction of strong cellular immunity together with the versatility of antigen adsorption to these particles should make such lamellae a useful tool to deliver protective antigens from intracellular pathogens.