Antibody bound to the surface antigen MPB83 ofMycobacterium bovisenhances survival against high dose and low dose challenge

Cationic pH-sensitive liposome-based subunit tuberculosis vaccine induces protection in mice challenged with Mycobacterium tuberculosis

Tuberculosis (TB) has been and still is a global emergency for centuries. Prevention of disease through vaccination would have a major impact on disease prevalence, but the only available current vaccine, BCG, has insufficient impact. In this article, a novel subunit vaccine against TB was developed, using the Ag85B-ESAT6-Rv2034 fusion antigen, two adjuvants - CpG and MPLA, and a cationic pH-sensitive liposome as a delivery system, representing a new TB vaccine delivery strategy not previously reported for TB. In vitro in human dendritic cells (DCs), the adjuvanted formulation induced a significant increase in the production of (innate) cytokines and chemokines compared to the liposome without additional adjuvants. In vivo, the new vaccine administrated subcutaneously significantly reduced Mycobacterium tuberculosis (Mtb) bacterial load in the lungs and spleens of mice, significantly outperforming results from mice vaccinated with the antigen mixed with adjuvants without liposomes. In-depth analysis underpinned the vaccine's effectiveness in terms of its capacity to induce polyfunctional CD4+ and CD8+ T-cell responses, both considered essential for controlling Mtb infection. Also noteworthy was the differential abundance of various CD69+ B-cell subpopulations, which included IL17-A-producing B-cells. The vaccine stimulated robust antigen-specific antibody titers, further extending its potential as a novel protective agent against TB.

Antibodies as clinical tools for tuberculosis

Tuberculosis (TB) is a leading cause of morbidity and mortality worldwide. Global research efforts to improve TB control are hindered by insufficient understanding of the role that antibodies play in protective immunity and pathogenesis. This impacts knowledge of rational and optimal vaccine design, appropriate diagnostic biomarkers, and development of therapeutics. Traditional approaches for the prevention and diagnosis of TB may be less efficacious in high prevalence, remote, and resource-poor settings. An improved understanding of the immune response to the causative agent of TB, Mycobacterium tuberculosis (Mtb), will be crucial for developing better vaccines, therapeutics, and diagnostics. While memory CD4+ T cells and cells and cytokine interferon gamma (IFN-g) have been the main identified correlates of protection in TB, mounting evidence suggests that other types of immunity may also have important roles. TB serology has identified antibodies and functional characteristics that may help diagnose Mtb infection and distinguish between different TB disease states. To date, no serological tests meet the World Health Organization (WHO) requirements for TB diagnosis, but multiplex assays show promise for improving the sensitivity and specificity of TB serodiagnosis. Monoclonal antibody (mAb) therapies and serum passive infusion studies in murine models of TB have also demonstrated some protective outcomes. However, animal models that better reflect the human immune response to Mtb are necessary to fully assess the clinical utility of antibody-based TB prophylactics and therapeutics. Candidate TB vaccines are not designed to elicit an Mtb-specific antibody response, but evidence suggests BCG and novel TB vaccines may induce protective Mtb antibodies. The potential of the humoral immune response in TB monitoring and control is being investigated and these studies provide important insight into the functional role of antibody-mediated immunity against TB. In this review, we describe the current state of development of antibody-based clinical tools for TB, with a focus on diagnostic, therapeutic, and vaccine-based applications.

B-Cells and Antibodies as Contributors to Effector Immune Responses in Tuberculosis

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), is still a major threat to mankind, urgently requiring improved vaccination and therapeutic strategies to reduce TB-disease burden. Most present vaccination strategies mainly aim to induce cell-mediated immunity (CMI), yet a series of independent studies has shown that B-cells and antibodies (Abs) may contribute significantly to reduce the mycobacterial burden. Although early studies using B-cell knock out animals did not support a major role for B-cells, more recent studies have provided new evidence that B-cells and Abs can contribute significantly to host defense against Mtb. B-cells and Abs exist in many different functional subsets, each equipped with unique functional properties. In this review, we will summarize current evidence on the contribution of B-cells and Abs to immunity toward Mtb, their potential utility as biomarkers, and their functional contribution to Mtb control.

The phenotypic and functional study of tissue B cells in respiratory system provided important information for diseases and development of vaccines

The field of tissue-resident B cells has received increasing attention, yet the feature of tissue B cells in respiratory system is unclear. Here, we first show that non-circulating B cells obtained from nasal, trachea and lung tissues are numerically and phenotypically distinct from their circulating counterparts. Analysis of single cell transcriptome sequence identified multiple differentially expressed genes between non-circulating B cells and circulating B cells, which illustrated their heterogeneity. Furthermore, we found high expression of CXCR3 on non-circulating B cells, and the chemokine CXCL11 was also up-regulated in the respiratory tissues, suggesting that CXCR3-CXCL11 axis might accelerate the local resident of non-circulating B cells in respiratory tract. Interestingly, intranasal immunization with BCG in mice elicited a sustained humoral immune response via induction of IgA and IgG Abs, which revealed the role of B cells. Meanwhile, tissue-resident B cells, IgA⁺ and IgG⁺ memory B cells (MBCs) in respiratory tissues, as well as plasma cells in bone marrow, were expanded and maintained, and these subsets probably developed into antibody-producing cells to participate in the local humoral immunity. Our data illustrate the phenotype and function of tissue B cells in the upper and lower airways, provide references for the prospective development of vaccines.

Mucosal Therapy of Multi-Drug Resistant Tuberculosis With IgA and Interferon-γ

New evidence has been emerging that antibodies can be protective in various experimental models of tuberculosis. Here, we report on protection against multidrug-resistant Mycobacterium tuberculosis (MDR-TB) infection using a combination of the human monoclonal IgA 2E9 antibody against the alpha-crystallin (Acr, HspX) antigen and mouse interferon-gamma in mice transgenic for the human IgA receptor, CD89. The effect of the combined mucosal IgA and IFN-γ; treatment was strongest (50-fold reduction) when therapy was applied at the time of infection, but a statistically significant reduction of lung bacterial load was observed even when the therapy was initiated once the infection had already been established. The protection involving enhanced phagocytosis and then neutrophil mediated killing of infected cells was IgA isotype mediated, because treatment with an IgG version of 2E9 antibody was not effective in human IgG receptor CD64 transgenic mice. The Acr antigen specificity of IgA antibodies for protection in humans has been indicated by their elevated serum levels in latent tuberculosis unlike the lack of IgA antibodies against the virulence-associated MPT64 antigen. Our results represent the first evidence for potential translation of mucosal immunotherapy for the management of MDR-TB.

Emerging Themes for the Role of Antibodies in Tuberculosis

The best way to debunk a scientific dogma is to throw irrefutable evidence at it. This is especially true if the dogma in question has been nurtured over many decades, as is the case with the apparent redundancy of antibodies (Abs) against intracellular pathogens. Although not fully compelling yet, that ‘hard core’ evidence is nevertheless now slowly beginning to emerge. This is true for several clinically relevant infections but none more so than Mycobacterium tuberculosis, the archetype intracellular pathogen that poses a great health challenge to the mankind. Here, prompted by a spate of recent high-profile reports on the effects of Abs in various experimental models of tuberculosis, we step back and take a critical look at the progress that has been made in the last 5 years and highlight some of the strengths and shortcomings of the presented evidence. We conclude that the tide of the opinion has begun to turn in favour of Abs but we also caution against overinterpreting the currently available limited evidence. For, until definitive evidence that can withstand even the most rigorous of experimental tests is produced, the dogma may yet survive. Or indeed, we may find that the truth is hidden somewhere in between the dogma and the unfulfilled scientific prophecy.

Tuberculosis vaccine candidates based on mycobacterial cell envelope components

Even after decades searching for a new and more effective vaccine against tuberculosis, the scientific community is still pursuing this goal due to the complexity of its causative agent, Mycobacterium tuberculosis (Mtb). Mtb is a microorganism with a robust variety of survival mechanisms that allow it to remain in the host for years. The structure and nature of the Mtb envelope play a leading role in its resistance and survival. Mtb has a perfect machinery that allows it to modulate the immune response in its favor and to adapt to the host's environmental conditions in order to remain alive until the moment to reactivate its normal growing state. Mtb cell envelope protein, carbohydrate and lipid components have been the subject of interest for developing new vaccines because most of them are responsible for the pathogenicity and virulence of the bacteria. Many indirect evidences, mainly derived from the use of monoclonal antibodies, support the potential protective role of Mtb envelope components. Subunit and DNA vaccines, lipid extracts, liposomes and membrane vesicle formulations are some examples of technologies used, with encouraging results, to evaluate the potential of these antigens in the protective response against Mtb.

A significant therapeutic effect of immunoglobulins administered alone, or in combination with conventional chemotherapy, in experimental pulmonary tuberculosis caused by drug-sensitive or drug-resistant strains

The recommended chemotherapy for drug-sensitive tuberculosis (TB) consists of four different antibiotics administrated for 6 months. This long treatment leads to significant compliance problems and consequently to recrudescence of the disease and to the development of multidrug-resistant (MDR) strains. Thus, new alternatives are needed to shorten or simplify the treatment of TB. Antibodies have therapeutic effects in animal models of TB, so their use as adjuvants in drug-sensitive and MDR TB is an interesting alternative. To assess the effect of antibodies, BALB/c mice with active late disease 60 days after infection with drug-sensitive TB strain H37Rv were treated with intravenous immunoglobulin (IVIg), alone or in combination with conventional chemotherapy. When compared with control non-treated animals, IVIg alone produced a significantly decreased burden of pulmonary bacilli. This decrease was even greater when IVIg was used in combination with conventional chemotherapy. The combined therapy also significantly reduced tissue damage (pneumonia) when compared to infected animals treated only with antibiotics. IVIg treatment also caused decreased bacillary burdens in mice infected with an MDR strain. In vitro experiments suggested that improving phagocytosis by efficient opsonization is perhaps the principal mechanism of this beneficial therapeutic effect.

Th1 cytokines, true functional signatures for protective immunity against TB?

The lack of an effective preventative vaccine against tuberculosis (TB) presents a great challenge to TB control. Since it takes an extremely long time to accurately determine the protective efficacy of TB vaccines, there is a great need to identify the surrogate signatures of protection to facilitate vaccine development. Unfortunately, antigen-specific Th1 cytokines that are currently used to evaluate the protective efficacy of the TB vaccine, do not align with the protection and failure of TB vaccine candidates in clinical trials. In this review, we discuss the limitation of current Th1 cytokines as surrogates of protection and address the potential elements that should be considered to finalize the true functional signatures of protective immunity against TB.

Human isotype-dependent inhibitory antibody responses against Mycobacterium tuberculosis

Accumulating evidence from experimental animal models suggests that antibodies play a protective role against tuberculosis (TB). However, little is known about the antibodies generated upon Mycobacterium tuberculosis (MTB) exposure in humans. Here, we performed a molecular and functional characterization of the human B‐cell response to MTB by generating recombinant monoclonal antibodies from single isolated B cells of untreated adult patients with acute pulmonary TB and from MTB‐exposed healthcare workers. The data suggest that the acute plasmablast response to MTB originates from reactivated memory B cells and indicates a mucosal origin. Through functional analyses, we identified MTB inhibitory antibodies against mycobacterial antigens including virulence factors that play important roles in host cell infection. The inhibitory activity of anti‐MTB antibodies was directly linked to their isotype. Monoclonal as well as purified serum IgA antibodies showed MTB blocking activity independently of Fc alpha receptor expression, whereas IgG antibodies promoted the host cell infection. Together, the data provide molecular insights into the human antibody response to MTB and may thereby facilitate the design of protective vaccination strategies.

B cells and antibodies in the defense against Mycobacterium tuberculosis infection

Better understanding of the immunological components and their interactions necessary to prevent or control Mycobacterium tuberculosis (Mtb) infection in humans is critical for tuberculosis (TB) vaccine development strategies. Although the contributory role of humoral immunity in the protection against Mtb infection and disease is less defined than the role of T cells, it has been well-established for many other intracellular pathogens. Here we update and discuss the increasing evidence and the mechanisms of B cells and antibodies in the defense against Mtb infection. We posit that B cells and antibodies have a variety of potential protective roles at each stage of Mtb infection and postulate that such roles should be considered in the development strategies for TB vaccines and other immune-based interventions.

The role of B cells and humoral immunity in Mycobacterium tuberculosis infection

Mycobacterium tuberculosis remains a major public health burden. It is generally thought that while B cell- and antibody-mediated immunity plays an important role in host defense against extracellular pathogens, the primary control of intracellular microbes derives from cellular immune mechanisms. Studies on the immune regulatory mechanisms during infection with M. tuberculosis, a facultative intracellular organism, has established the importance of cell-mediated immunity in host defense during tuberculous infection. Emerging evidence suggest a role for B cell and humoral immunity in the control of intracellular pathogens, including obligatory species, through interactions with the cell-mediated immune compartment. Recent studies have shown that B cells and antibodies can significantly impact on the development of immune responses to the tubercle bacillus. In this review, we present experimental evidence supporting the notion that the importance of humoral and cellular immunity in host defense may not be entirely determined by the niche of the pathogen. A comprehensive approach that examines both humoral and cellular immunity could lead to better understanding of the immune response to M. tuberculosis.

Vaccines to prevent tuberculosis infection rather than disease: Physiological and immunological aspects

There is increasing enthusiasm and optimism that a vaccine could be developed that prevents infection rather than disease. In this article I discuss the fact that despite this optimism nothing has been produced so far that seems to have this capability, and moreover even the borderline between when infection ends and disease begins has not even been defined. To be effective such a vaccine, or at least the immunity it would generate, would have to work within the confines of the pulmonary physiological systems, which are complex. To date much of the emphasis here has turned away from T cell mediated immunity and towards establishing specific antibodies in the lungs. Here, I argue that with the exception of a possible exclusionary function, most claims of a protective role of antibody are completely over-blown. Finally, even if we had a potential "anti-infection" vaccine, how would we test and validate it?

Role of B cells and antibodies in acquired immunity against Mycobacterium tuberculosis

Accumulating evidence has documented a role for B cells and antibodies (Abs) in the immunity against Mycobacterium tuberculosis (Mtb). Passive transfer studies with monoclonal antibodies (mAbs) against mycobacterial antigens have shown protection against the tubercle bacillus. B cells and Abs are believed to contribute to an enhanced immune response against Mtb by modulating various immunological components in the infected host including the T-cell compartment. Nevertheless, the extent and contribution of B cells and Abs to protection against Mtb remains uncertain. In this article we summarize the most relevant findings supporting the role of B cells and Abs in the defense against Mtb and discuss the potential mechanisms of protection.

Development of novel carrier(s) mediated tuberculosis vaccine: more than a tour de force

Despite worldwide availability of the vaccines against most of the infectious diseases, BCG and various programs such as Directly Observed Treatment Short course (DOTS) to prevent tuberculosis still remains one of the most deadly forms of the disease affecting millions of people globally. The evolution of multi drug resistant strains (MDR) has increased the complexity further. Although currently available marketed BCG vaccine has shown sufficient protection against childhood tuberculosis, it has failed to prevent the most common form of disease i.e., pulmonary tuberculosis in adults. However, various vaccine candidates have already entered phase I clinical trials and have shown promising outcomes. The most prominent amongst them is the heterologous prime-boost approach, which shows a great promise towards designing and development of a new efficacious tuberculosis vaccine. It has also been shown that the use of various viral and non-viral vectors as carriers for the potential vaccine candidates will further boost their effect on subsequent immunization. In this review, we briefly summarize the potential of a few novel nano-carriers for developing effective vaccination strategies against tuberculosis.

The human antibody response to the surface of Mycobacterium tuberculosis

Background

Vaccine-induced human antibodies to surface components of Haemophilus influenzae and Streptococcus pneumonia are correlated with protection. Monoclonal antibodies to surface components of Mycobacterium tuberculosis are also protective in animal models. We have characterized human antibodies that bind to the surface of live M. tuberculosis.

Methods

Plasma from humans with latent tuberculosis (TB) infection (n = 23), active TB disease (n = 40), and uninfected controls (n = 9) were assayed by ELISA for reactivity to the live M. tuberculosis surface and to inactivated M. tuberculosis fractions (whole cell lysate, lipoarabinomannan, cell wall, and secreted proteins).

Results

When compared to uninfected controls, patients with active TB disease had higher antibody titers to the surface of live M. tuberculosis (Δ = 0.72 log₁₀), whole cell lysate (Δ = 0.82 log₁₀), and secreted proteins (Δ = 0.62 log₁₀), though there was substantial overlap between the two groups. Individuals with active disease had higher relative IgG avidity (Δ = 1.4 to 2.6) to all inactivated fractions. Surprisingly, the relative IgG avidity to the live M. tuberculosis surface was lower in the active disease group than in uninfected controls (Δ = –1.53, p = 0.004). Patients with active disease had higher IgG than IgM titers for all inactivated fractions (ratios, 2.8 to 10.1), but equal IgG and IgM titers to the live M. tuberculosis surface (ratio, 1.1). Higher antibody titers to the M. tuberculosis surface were observed in active disease patients who were BCG-vaccinated (Δ = 0.55 log₁₀, p = 0.008), foreign-born (Δ = 0.61 log₁₀, p = 0.004), or HIV-seronegative (Δ = 0.60 log₁₀, p = 0.04). Higher relative IgG avidity scores to the M. tuberculosis surface were also observed in active disease patients who were BCG-vaccinated (Δ = 1.12, p<0.001) and foreign-born (Δ = 0.87, p = 0.01).

Conclusions/Significance

Humans with active TB disease produce antibodies to the surface of M. tuberculosis with low avidity and with a low IgG/IgM ratio. Highly-avid IgG antibodies to the M. tuberculosis surface may be an appropriate target for future TB vaccines.

Antibody-mediated immunity against tuberculosis: implications for vaccine development

There is an urgent need for new and better vaccines against tuberculosis (TB). Current vaccine design strategies are generally focused on the enhancement of cell-mediated immunity. Antibody-based approaches are not being considered, mostly due to the paradigm that humoral immunity plays little role in the protection against intracellular pathogens. Here, we reappraise and update the increasing evidence for antibody-mediated immunity against Mycobacterium tuberculosis, discuss the complexity of antibody responses to mycobacteria, and address mechanism of protection. Based on these findings and discussions, we challenge the common belief that immunity against M. tuberculosis relies solely on cellular defense mechanisms, and posit that induction of antibody-mediated immunity should be included in TB vaccine development strategies.

Immunogenicity of mycobacterial vesicles in humans: identification of a new tuberculosis antibody biomarker

Biomarkers for active tuberculosis (TB) are urgently needed. Mycobacteria produce membrane vesicles (MVs) that contain concentrated immune-modulatory factors that are released into the host. We evaluated the human immune responses to BCG and Mycobacterium tuberculosis MVs to characterize the antibody responses and identify potentially novel TB biomarkers. Serological responses to MVs were evaluated by ELISAs and immunoblots with sera from 16 sputum smear-positive, 12 smear-negative HIV uninfected pulmonary TB patients and 16 BCG vaccinated Tuberculin skin-test positive controls with and without latent tuberculosis infection. MVs from both BCG and M. tuberculosis induced similar responses and were strongly immunogenic in TB patients but not in controls. Several MV-associated antigens appear to induce robust antibody responses, in particular the arabinomanan portion of the cell wall glycolipid lipoarabinomannan. Three proteins at ≈ 36, 25, and 23 kDa were simultaneously recognized by sera from 16/16 smear-positive, 9/12 smear-negative TB patients and 0/16 controls. These results provide promise and encouragement that antibody responses to proteins enriched in MVs of pathogenic mycobacteria may constitute a novel TB biomarker signature that could have diagnostic information.

The secreted lipoprotein, MPT83, of Mycobacterium tuberculosis is recognized during human tuberculosis and stimulates protective immunity in mice

The long-term control of tuberculosis (TB) will require the development of more effective anti-TB vaccines, as the only licensed vaccine, Mycobacterium bovis bacille Calmette-Guérin (BCG), has limited protective efficacy against infectious pulmonary TB. Subunit vaccines have an improved safety profile over live, attenuated vaccines, such as BCG, and may be used in immuno-compromised individuals. MPT83 (Rv2873) is a secreted mycobacterial lipoprotein expressed on the surface of Mycobacterium tuberculosis. In this study, we examined whether recombinant MPT83 is recognized during human and murine M. tuberculosis infection. We assessed the immunogenicity and protective efficacy of MPT83 as a protein vaccine, with monophosphyl lipid A (MPLA) in dimethyl-dioctadecyl ammonium bromide (DDA) as adjuvant, or as a DNA vaccine in C57BL/6 mice and mapped the T cell epitopes with peptide scanning. We demonstrated that rMPT83 was recognised by strong proliferative and Interferon (IFN)-γ-secreting T cell responses in peripheral blood mononuclear cells (PBMC) from patients with active TB, but not from healthy, tuberculin skin test-negative control subjects. MPT83 also stimulated strong IFN-γ T cell responses during experimental murine M. tuberculosis infection. Immunization with either rMPT83 in MPLA/DDA or DNA-MPT83 stimulated antigen-specific T cell responses, and we identified MPT83_127–135 (PTNAAFDKL) as the dominant H-2^b-restricted CD8⁺ T cell epitope within MPT83. Further, immunization of C57BL/6 mice with rMPT83/MPLA/DDA or DNA-MPT83 stimulated significant levels of protection in the lungs and spleens against aerosol challenge with M. tuberculosis. Interestingly, immunization with rMPT83 in MPLA/DDA primed for stronger IFN-γ T cell responses to the whole protein following challenge, while DNA-MPT83 primed for stronger CD8⁺ T cell responses to MPT83_127–135. Therefore MPT83 is a protective T cell antigen commonly recognized during human M. tuberculosis infection and should be considered for inclusion in future TB subunit vaccines.

Use of recombinant proteins MPB70 or MPB83 as capture antigens in ELISAs to confirm bovine tuberculosis infections in Brazil

The objective was to evaluate the use of two indirect IgG-ELISA tests (with recombinant proteins MPB70 or MPB83, respectively, as capture antigens) as confirmatory tests for diagnosis of bovine tuberculosis in a herd of naturally infected dairy cows. Results for ELISA-MPB70 and ELISA-MPB83 were similar (kappa statistic=0.92) on Days 0 (day of intradermal injection with purified protein derivatives, PPD), 7, and 21. The kappa statistic between ELISA and the Comparative Intradermal Tuberculin Test, as well as ELISA sensitivity and specificity (relative to culture or PCR as standards) were: 0.7, 34.4% and 75% on Day 0; 0.25, 53.8% and 66.6% on Day 7; and 0.01, 1.8% and 77.7% on Day 21, respectively. In conclusion, although ELISAs using MPB70 or MPB83 as antigens were not reliable indicators of infection status, especially on Days 7 and 21, they were of potential value as complementary tools to intradermal PPD testing.

A novel human IgA monoclonal antibody protects against tuberculosis

Abs have been shown to be protective in passive immunotherapy of tuberculous infection using mouse experimental models. In this study, we report on the properties of a novel human IgA1, constructed using a single-chain variable fragment clone (2E9), selected from an Ab phage library. The purified Ab monomer revealed high binding affinities for the mycobacterial α-crystallin Ag and for the human FcαRI (CD89) IgA receptor. Intranasal inoculations with 2E9IgA1 and recombinant mouse IFN-γ significantly inhibited pulmonary H37Rv infection in mice transgenic for human CD89 but not in CD89-negative littermate controls, suggesting that binding to CD89 was necessary for the IgA-imparted passive protection. 2E9IgA1 added to human whole-blood or monocyte cultures inhibited luciferase-tagged H37Rv infection although not for all tested blood donors. Inhibition by 2E9IgA1 was synergistic with human rIFN-γ in cultures of purified human monocytes but not in whole-blood cultures. The demonstration of the mandatory role of FcαRI (CD89) for human IgA-mediated protection is important for understanding of the mechanisms involved and also for translation of this approach toward development of passive immunotherapy of tuberculosis.

Potential application of new diagnostic methods for controlling bovine tuberculosis in Brazil

Bovine tuberculosis, a chronic infection in cattle caused by Mycobacterium bovis, remains an economic and public health problem for several countries. Due to its economic impact on international trade, contagious nature, and implications for human health, global programs to eradicate the disease were implemented worldwide. Those programs are based on slaughtering PPD-reactive animals. Despite the National Programs in Brazil, complete eradication has not been achieved, and the disease remains, albeit at a lower prevalence. The central purpose of this review is to address diagnostic tests for tuberculosis. Considering the course of the infection in cattle, at least two tests, ideally complementary to one another, may be necessary for an adequate diagnosis: the first based on the cellular response, and the second capable of identifying anergic animals by detection of specific anti-M.bovis antibodies.

Non-acylated Mycobacterium bovis glycoprotein MPB83 binds to TLR1/2 and stimulates production of matrix metalloproteinase 9

A variety of Mycobacterium tuberculosis cell wall components induce expression of matrix metalloproteinase 9 (MMP-9) by monocytic cells and levels of MMP-9 in vivo positively correlate with severity of disease. Toll-like receptor (TLR)2 mediates cellular responses to acylated molecules but can also mediate responsiveness to diverse molecular structures, including non-acylated native viral and bacterial proteins. MPT/B-83 is a cell-associated lipoglycoprotein common to M. tuberculosis and M. bovis and an important antigen during infection of cattle. Since MPB83 is acylated and glycosylated, we investigated whether MPB83 would induce MMP-9 expression via interaction with TLR2, and assessed the contribution of the lipid, glycan and polypeptide components to its activity. Acylated peptide derived from MPB83 stimulated MMP-9 expression by human macrophage cells via interaction with both TLR2 and TLR1, but not TLR4. Lesser induction was found with secreted (non-acylated, but glycosylated) MPB83 protein purified from culture of M. bovis. Stimulation of cells with MPB83 induced TNF-α production which acted to upregulate MMP-9 expression. Surprisingly, recombinant MPB83 protein devoid of any post-translational modification also induced MMP-9 expression. Direct interaction of RecMPB83 with TLR2 was demonstrated by surface plasmon-resonance. MPB83 may act as a virulence factor through TLR2 mediated induction of MMP-9.

The protective role of antibody responses during Mycobacterium tuberculosis infection

Tuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb) is one of the most important infectious diseases globally. Immune effector mechanisms that lead to protection or development of clinical disease are not fully known. It is generally accepted that cell-mediated immunity (CMI) plays a pivotal role in controlling Mtb infection, whereas antibody responses are believed to have no protective role. This generalization is based mainly on early classical experiments that lacked standard protocols, and the T helper type 1 (Th1)/Th2 paradigm. According to the Th1/Th2 paradigm Th1 cells protect the host from intracellular pathogens, whereas Th2 cells protect form extracellular pathogens. During the last two decades, the Th1/Th2 paradigm has dominated not only our understanding of immunity to infectious pathogens but also our approach to vaccine design. However, the last few years have seen major discrepancies in this model. Convincing evidence for the protective role of antibodies against several intracellular pathogens has been established. Studies of B cell-deficient mice, severe combined immunodeficiency (SCID) mice, passive immunization using monoclonal (mAb) and polyclonal antibodies and immune responses against specific mycobacterial antigens in experimental animals reveal that, in addition to a significant immunomodulatory effect on CMI, antibodies play an essential protective role against mycobacterial infections. In this review, our current understanding of the essential role of antibodies during Mtb infections, limitations of the Th1/Th2 model and the unfolding interdependence and mutual regulatory relationships between the humoral and CMI will be presented and discussed.

Prophylactic effect of administration of human gamma globulins in a mouse model of tuberculosis

The protective effect of human gamma globulins on Mycobacterium tuberculosis infection was evaluated in a mouse model of intratracheal infection. Animals receiving human gamma globulins intranasally, 2h before intratracheal challenge showed a significant decrease in lung bacilli load compared to non-treated animals in different time intervals of up to 2 months after challenge. The same effect was obtained when M. tuberculosis was pre-incubated with the gamma globulin before challenge. The protective effect of the gamma-globulin formulation was abolished after pre-incubation with M. tuberculosis. These results suggest a potential role of specific antibodies in the defence against mycobacterial infections.

How could we have better vaccines against tuberculosis?

BACKGROUND

Tuberculosis (TB), an infirmity that mainly affects the respiratory system, is the world's second deadliest infectious disease, with > 9 million new cases diagnosed in 2006. One-third of the world's population is now infected with the TB bacillus. According to the WHO, an estimated 1.7 million people died from TB in 2006. More precisely, every 15 seconds, one person dies due to TB worldwide.

OBJECTIVE

To review some of the key advances in the field of TB immunology and to discuss potential means for the development of new generation vaccines against TB disease.

METHODS

Systematic review of the published literature in various journals.

RESULTS/CONCLUSION

The current TB vaccine Bacillus Calmette-Guérin, developed > 85 years ago, reduces the risk of severe forms of TB in early childhood but is not very effective in preventing pulmonary TB in adolescents and adults, the populations with the highest rates of TB disease. TB is changing and evolving, making the development of new vaccines more crucial to controlling the pandemic. Rigorous research using cutting edge vaccine technology is occurring worldwide to combat TB, and various vaccination strategies, especially prime-boost, have been pursued by many scientists.

Antibody responses of cervids (Cervus elaphus) following experimental Mycobacterium bovis infection and the implications for immunodiagnosis

Captive and free-ranging wildlife animals are implicated in the maintenance and transmission of bovine tuberculosis and therefore pose a significant obstacle to eradication of the disease from domestic livestock. The current antemortem diagnostic method, the intradermal tuberculin skin test, is impractical for routine use with many wild animals. Antibody-based assays are particularly attractive because the animals are handled only once and immediate processing of the sample is not required. This report characterizes the antibody responses of red deer-elk hybrids (Cervus elaphus) against Mycobacterium bovis and subsequently evaluates the diagnostic performance of select antigens in a rapid-test format. Sequential serum samples were collected from 10 animals experimentally infected with M. bovis and 5 noninfected animals over a 7-month period postinfection (p.i.). Samples were evaluated by enzyme-linked immunosorbent assays, immunoblot analyses, and multiantigen print immunoassays for seroreactivity to mycobacterial antigens. Although all infected animals produced antibodies to M. bovis protein antigens, there was significant animal-to-animal variation in the kinetics and magnitudes of responses and the antigens recognized. The most frequently recognized antigens included MPB83, ESAT-6, CFP10, and MPB70. Responses to some antigens, such as MPB83, were consistently detected as early as 4 weeks after inoculation, whereas other antigens were detected only much later (>140 days p.i.). Antibody responses were boosted by injection of tuberculin for intradermal tuberculin skin testing. Comparison of single-antigen (fluorescence polarization assay) with multiantigen (CervidTB STAT-PAK) rapid tests demonstrated that a highly sensitive and specific serodiagnostic test for tuberculosis in cervids will require multiple and carefully selected seroreactive antigens covering a broad spectrum of antibody specificities.

Determinants of natural immunity against tuberculosis in an endemic setting: factors operating at the level of macrophage-Mycobacterium tuberculosis interaction

We aimed to delineate factors operating at the interface of macrophage-mycobacterium interaction which could determine the fate of a 'subclinical' infection in healthy people of a tuberculosis-endemic region. Ten study subjects (blood donors) were classified as 'high' or 'low' responders based on the ability of their monocyte-derived macrophages to restrict or promote an infection with Mycobacterium tuberculosis. Bacterial multiplication between days 4 and 8 in high responder macrophages was significantly lower (P < 0.02) than low responders. All donor sera were positive for antibodies against cell-membrane antigens of M. tuberculosis and bacilli opsonized with heat-inactivated sera were coated with IgG. In low responder macrophages, multiplication of opsonized bacilli was significantly less (P < 0.04) than that of unopsonized bacilli. The levels of tumour necrosis factor (TNF)-alpha and interleukin (IL)-12 produced by infected high responder macrophages was significantly higher (P < 0.05) than low responders. However, infection with opsonized bacilli enhanced the production of IL-12 in low responders to its level in high responders. The antibody level against membrane antigens was also significantly higher (P < 0.05) in high responders, although the antigens recognized by two categories of sera were not remarkably different. Production of certain other cytokines (IL-1beta, IL-4, IL-6 and IL-10) or reactive oxygen species (H2O2 and NO) by macrophages of high and low responders did not differ significantly. The study highlights the heterogeneity of Indian subjects with respect to their capability in handling subclinical infection with M. tuberculosis and the prominent role that TNF-alpha, opsonizing antibodies and, to a certain extent, IL-12 may play in containing it.

Mucosal immunization with recombinant heparin-binding haemagglutinin adhesin suppresses extrapulmonary dissemination of Mycobacterium bovis bacillus Calmette-Guérin (BCG) in infected mice

It is generally accepted that cellular immunity plays a critical role in the protection against Mycobacterium tuberculosis, an intracellular pathogen. Recently, however, an increasing number of reports indicate the important contribution of humoral immunity against mycobacterial infection. Since M. tuberculosis establishes its primary lesion in the lung, induction of humoral immunity in the airway tract by mucosal immunization regime could provide protective immunity against tuberculosis. In this study, mycobacterial heparin-binding haemagglutinin adhesin (HBHA) was used as an immunization antigen because HBHA is an essential virulence factor required for the infection of lung epithelial cells and extrapulmonary dissemination of mycobacteria. The effects of intranasal immunization with a yeast-expressed recombinant (r) HBHA co-administered with a mucosal adjuvant cholera toxin (CT) on the induction of humoral and cellular immunity were examined, and its protective efficacy against pulmonary challenge infection with Mycobacterium bovis bacillus Calmette-Guérin (BCG) was evaluated. HBHA-specific antibodies were induced in serum and airway tract of immunized mice, which specifically recognized native HBHA expressed on M. bovis BCG. Th1-type immunity against mycobacterial antigens was also enhanced in the lung of immunized mice after pulmonary BCG infection. Furthermore, the immunization suppressed bacterial load in the spleen after pulmonary BCG infection. These results indicate that systemic and local humoral immunity induced by the HBHA-based mucosal vaccine impairs extrapulmonary dissemination, thus providing immune protection against mycobacterial infection.

Monoclonal antibodies to Mycobacterium tuberculosis CDC 1551 reveal subcellular localization of MPT51

Mycobacterium tuberculosis CDC 1551, a highly immunogenic outbreak strain, previously reported to have unique surface distribution of capsular polysaccharide, was used to generate novel monoclonal antibodies (mabs) to surface mycobacterial targets. Two immunoglobulin G1 (IgG1) mAbs, 16a1 and 16a6 were generated. The mAbs originated from the same B cell, bound strongly to whole cell M. tuberculosis CDC1551 and to its cell wall, membrane and cytosol fractions recognizing a 90kDa protein. Immunoprecipitation using mAb 16a1 isolated a protein with amino acid peptide sequences matching MPT51 from the cytosol. This immunogenic protein of unknown function was previously reported only in culture filtrates of M. tuberculosis. Our findings suggest for the first time that this protein is found within the M. tuberculosis cell.

Immunological options for the treatment of tuberculosis: evaluation of novel therapeutic approaches

The emergence of multidrug-resistant tuberculosis strains and the coinfection with HIV, together with advances in immunology, have led to renewed interest regarding ways to exploit the immune responses against Mycobacterium tuberculosis therapeutically. Here we review the fundamentals of tuberculosis therapy in view of the epidemiological and clinical challenges, and explore the experience with immune-based therapies for the treatment of active tuberculosis. These immune-based therapies are discussed here with the aim of assessing their potential use as adjuncts to chemotherapy.

IL-4 depletion enhances host resistance and passive IgA protection against tuberculosis infection in BALB/c mice

The influence of Th2 cytokines in tuberculosis has been a matter of dispute. Here we report that IL-4 has a profound regulatory effect on the infection of BALB/c mice with Mycobacterium tuberculosis. Depletion of IL-4 with a neutralizing mAb caused only evanescent reduction of lung infection, but when combined with i.n. inoculations of IgA anti-mycobacterial alpha-crystallin mAb and mouse rIFN-gamma, we observed a 40-fold reduction of the bacterial counts in the lungs at 3 wks following i.n. infection (p<0.001). In genetically deficient IL-4-/- BALB/c mice, infection in both lung and spleen was substantially reduced for up to 8 wks without further treatment. Reconstitution of IL-4-/- mice with rIL-4 increased bacterial counts to wild-type levels and made the mice refractory to protection by IgA/IFN-gamma. Analysis of the lungs showed increased granulomatous infiltration and proinflammatory mediators in anti-IL-4/IgA/IFN-gamma-treated and infected mice. We conclude that the action of IL-4 in tuberculosis is targeted at macrophages and that it may include an antagonistic effect on their IgA/IFN-gamma-induced activation and nitric oxide production. The described novel immunotherapy, combining treatments with anti-IL-4, IgA antibody and IFN-gamma, has potential for translation toward the passive immunoprophylaxis of tuberculosis.

Humoral and cellular immune responses in sheep immunized with a 22 kilodalton exported protein of Mycobacterium avium subspecies paratuberculosis

An immunogenic 22 kilodalton exported Mycobacterium avium subspecies paratuberculosis (MAP) lipoprotein (P22) was previously identified, and found to belong to the LppX/LprAFG family of mycobacterial lipoproteins. N-terminal polyhistidine-tagged P22 was produced and purified from Escherichia coli. Antibody recognition of P22, and interferon-gamma (IFN-gamma) responses in vitro using blood from a sheep vaccinated with Neoparasec, confirmed its immunogenicity. To evaluate the immunogenicity of P22 in vivo, five sheep were immunized with a single dose containing 0.8 mg recombinant P22 protein in adjuvant. Blood was collected at 4, 13 and 29 weeks post-immunization (p.i.) and tested for anti-P22 antibodies and P22-specific IFN-gamma production. P22-specific antibodies were detected by Western blot analysis in all five Neoparasec-immunized sheep at the three time points. Three out of five P22-immunized sheep produced P22-specific antibodies for up to 13 weeks p.i., and two gave a response at 29 weeks p.i. Recombinant P22 was able to stimulate significant IFN-gamma production in blood of P22-immunized sheep at 13 and 29 weeks p.i. Recombinant P22 also elicited an IFN-gamma response in blood of sheep immunized with Neoparasec.

A case for passive immunoprophylaxis against tuberculosis

HIV-associated tuberculosis is escalating ominously in Africa and southeast Asia despite existing control measures. Therefore, new approaches to tuberculosis control need to be explored. We discuss the potential use of passive immunoprophylaxis with antibodies in tuberculosis control. Although the predominant type of active host resistance is T-cell mediated, recent results in mouse experimental models suggest that monoclonal antibodies to certain antigens (eg, Acr or lipoarabinomannan) can impart substantial passive protection against tuberculous infection. These results are corroborated by data from other laboratories on passive vaccination against a number of intracellular microbial pathogens. Further work is needed to develop human (or humanised) antibody reagents, to increase their protective efficacy, and to expand our understanding of the mechanisms of antibody action.

Vaccine Approaches to Prevent Tuberculosis

Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), is one of the main killers among infectious pathogens in the world and represents an important factor that sustain poverty in developing countries. Failure of the BCG vaccine to protect in endemic regions, and increasing problems with multi-drug-resistant TB calls for development of better vaccines to prevent reactivation of tuberculosis. It has been estimated that an effective post-exposure vaccine will prevent 30-40% of the TB cases. New vaccines should also prevent development of TB in HIV-infected individuals. Recent characterization of M. tuberculosis H37Rv by proteomic methods has revealed a large number of novel secreted proteins that should be investigated in mouse models for latent and slowly progressive TB. There is an important balance between control of infection and tissue destruction in TB, and M. tuberculosis has developed strategies to prevent immune-mediated sterilization. Central to this strategy is inhibition of apoptosis of macrophages. Development of novel vaccines should therefore take into consideration the effects on central markers to obtain a better picture of regulation of immunity, including FasL and Bcl-2 which are essential in regulation of apoptosis.

Mycobacterium tuberculosis malate synthase is a laminin-binding adhesin

Mycobacterium tuberculosis (M. tb) uses the glyoxalate bypass for intracellular survival in vivo. These studies provide evidence that the M. tb malate synthase (MS) has adapted to function as an adhesin which binds to laminin and fibronectin. This binding is achieved via the unique C-terminal region of the M. tb MS. The ability to function as an adhesin necessitates extracellular localization. We provide evidence that despite the absence of a Sec-translocation signal sequence the M. tb MS is secreted/excreted, and is anchored on the cell wall by an undefined mechanism. The MS of Mycobacterium smegmatis is cytoplasmic but the M. tb MS expressed in M. smegmatis localizes to the cell wall and enhances the adherence of the bacteria to lung epithelial A549 cells. Antibodies to the C-terminal laminin/fibronectin-binding domain interfere with the binding of the M. tb MS to laminin and fibronectin and reduce the adherence of M. tb to A549 cells. Coupled to the earlier evidence of in vivo expression of M. tb MS during active but not latent infection in humans, these studies show that a housekeeping enzyme of M. tb contributes to its armamentarium of virulence promoting factors.

The role of antibody-mediated immunity in defense against Mycobacterium tuberculosis: advances toward a novel vaccine strategy

Antibody-mediated immunity has been historically considered to have no role in host-defense against Mycobacterium tuberculosis. In recent years, studies from our group as well as others have challenged this traditional thinking. Using monoclonal antibodies, researchers demonstrated that antibodies can modify various aspects of mycobacterial infection to the benefit of the host. A review of recent experimental evidence in support of a role for antibodies in host-defense against mycobacterial infections is presented. Challenges to the field and an outline of future directions with particular attention to research leading to the development of a novel vaccine strategy, are emphasized.

Passive serum therapy with polyclonal antibodies against Mycobacterium tuberculosis protects against post-chemotherapy relapse of tuberculosis infection in SCID mice

We investigated the protective role of immune-sera against reactivation of Mycobacterium tuberculosis infection in SCID mice and found that passive immunization with sera obtained from mice treated with detoxified M. tuberculosis extracts (delivered in liposomes in a composition known as RUTI) exerted significant protection. Our SCID mouse model consisted of aerosol infection by M. tuberculosis, followed by 3 to 8weeks of chemotherapy with isoniazid+rifampicin (INH+RIF) (25 and 10mg/kg, respectively). After infection and antibiotic administration, two groups of mice were treated for up to 10weeks with intraperitoneal passive immunization using hyperimmune serum (HS) obtained from mice infected with M. tuberculosis, treated with chemotherapy (INH+RIF) for 8weeks and inoculated with RUTI (HS group) or with normal serum (CT group). Significant differences were found between HS and CT groups in the number of bacilli in the lungs (3.68+/-2.02 vs. 5.72+/-1.41log(10) c.f.u.), extent of pulmonary granulomatomous infiltration (10.33+/-0.67 vs. 31.2+/-1.77%), and percentage of animals without pulmonary abscesses (16.7% vs. 45.5%). These data strongly suggest a protective role of specific antibodies against lung dissemination of M. tuberculosis infection.

Intranasal IFNgamma extends passive IgA antibody protection of mice against Mycobacterium tuberculosis lung infection

Intranasal inoculation of mice with monoclonal IgA against the alpha-crystallin (acr1) antigen can diminish the tuberculous infection in the lungs. As this effect has been observed only over a short-term, we investigated if it could be extended by inoculation of IFNgamma 3 days before infection, and further co-inoculations with IgA, at 2 h before and 2 and 7 days after aerosol infection with Mycobacterium tuberculosis H37Rv. This treatment reduced the lung infection at 4 weeks more than either IgA or IFNgamma alone (i.e. 17-fold, from 4.2 x 10(7) to 2.5 x 10(6) CFU, P = 0.006), accompanied also by lower granulomatous infiltration of the lungs. IFNgamma added prior to infection of mouse peritoneal macrophages with IgA-opsonized bacilli resulted in a synergistic increase of nitric oxide and TNFalpha production and a 2-3 fold decrease in bacterial counts. Our improved results suggest, that combined treatment with IFNgamma and IgA could be developed towards prophylactic treatment of AIDS patients, or as an adjunct to chemotherapy.

Mucosal immunotherapy of tuberculosis: is there a value in passive IgA?

Immunotherapeutic approaches, which have been considered for tuberculosis (TB), include immuno-potentiating or suppressing agents, cytokines, antibodies, DNA vaccines, non-pathogenic mycobacteria and mycobacterial extracts. While most or all of these potential agents showed at least some degree of promise in various experimental models, few progressed to clinical trials, yielding only moderately encouraging, though controversial results. Consequently, further research is required, as the need for an immunological agent, adjunct to chemotherapy, remains strongly justified. Its purpose is to shorten the currently protracted (6-9 months) drug treatment and thus increase compliance rates, which are most disappointing in areas with the highest disease prevalence. Using a mouse model of Mycobacterium tuberculosis (Mtb) infection, we recently reported, that an intranasally given monoclonal IgA antibody significantly reduced the bacterial load in the infected lungs, and that this protective effect of IgA could be further extended by co-inoculation with interferon gamma (IFNgamma). In this review, we describe the main features of IgA and its cellular receptors, the extent and possible mechanisms of passive vaccination with an IgA monoclonal antibody against the alpha-crystallin antigen of Mtb and discuss the potentials of this approach in the wider context of immunotherapy of TB.

A Reappraisal of Humoral Immunity Based on Mechanisms of Antibody‐Mediated Protection Against Intracellular Pathogens

Sometime in the mid to late twentieth century the study of antibody-mediated immunity (AMI) entered the doldrums, as many immunologists believed that the function of AMI was well understood, and was no longer deserving of intensive investigation. However, beginning in the 1990s studies using monoclonal antibodies (mAbs) revealed new functions for antibodies, including direct antimicrobial effects and their ability to modify host inflammatory and cellular responses. Furthermore, the demonstration that mAbs to several intracellular bacterial and fungal pathogens were protective issued a serious challenge to the paradigm that host defense against such microbes was strictly governed by cell-mediated immunity (CMI). Hence, a new view of AMI is emerging. This view is based on the concept that a major function of antibody (Ab) is to amplify or subdue the inflammatory response to a microbe. In this regard, the "damage-response framework" of microbial pathogenesis provides a new conceptual viewpoint for understanding mechanisms of AMI. According to this view, the ability of an Ab to affect the outcome of a host-microbe interaction is a function of its capacity to modify the damage ensuing from such an interaction. In fact, it is increasingly apparent that the efficacy of an Ab cannot be defined either by immunoglobulin or epitope characteristics alone, but rather by a complex function of Ab variables, such as specificity, isotype, and amount, host variables, such as genetic background and immune status, and microbial variables, such as inoculum, mechanisms of avoiding host immune surveillance and pathogenic strategy. Consequently, far from being understood, recent findings in AMI imply a system with unfathomable complexity and the field is poised for a long overdue renaissance.

Peripheral blood and pleural fluid mononuclear cell responses to low-molecular-mass secretory polypeptides of Mycobacterium tuberculosis in human models of immunity to tuberculosis

A total of 104 polypeptides were purified from the low-molecular-mass secretory proteome of Mycobacterium tuberculosis H(37)Rv using a combination of anion exchange column chromatography and high resolution preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by electroelution. The goal of this study was to identify polypeptides from a low-molecular-mass secretory proteome recognized by human subjects infected with M. tuberculosis and to ascertain the differences in specificity of antigen recognition by the peripheral blood mononuclear cells (PBMCs) and pleural fluid mononuclear cells (PFMCs) of these individuals. The study identified CFP-8 (Rv0496), CFP-11 (Rv2433c), CFP-14.5 (Rv2445c), and CFP-31 (Rv0831c) as novel T-cell antigens apart from previously characterized ESAT-6, TB10.4, CFP10, GroES, MTSP14, MTSP17, CFP21, MPT64, Ag85A, and Ag85B on the basis of recognition by PBMCs of tuberculosis contacts and treated tuberculosis patients. Further, polypeptides prominently recognized by PFMCs of tuberculous pleurisy patients were the same as those recognized by PBMCs of healthy contacts and treated tuberculosis patients. The results of our study indicate the homogeneity of antigenic target recognition by lymphocytes at the site of infection and at the periphery in the human subjects studied and the need to evaluate these antigenic targets as components of future antituberculous vaccines.

Reduced expression of antigenic proteins MPB70 and MPB83 in Mycobacterium bovis BCG strains due to a start codon mutation in sigK

Mycobacterium bovis Bacille Calmette-Guerin (BCG) strains are genetically and phenotypically heterogeneous. Expression of the antigenic proteins MPB70 and MPB83 is known to vary considerably across BCG strains; however, the reason for this phenotypic difference has remained unknown. By immunoblot, we separated BCG into high- and low-producing strains. By quantitative reverse transcription polymerase chain reaction (RT-PCR), we determined that transcription of the antigen-encoding genes, mpb70 and mpb83, follows the same strain pattern with mRNA levels reduced over 50-fold in low-producing strains. Transcriptome comparison of the same BCG strains by DNA microarray revealed two gene regions consistently downregulated in low-producing strains compared with high-producing strains, one including mpb70 (Rv2875) and mpb83 (Rv2873) and a second that includes the predicted sigma factor, sigK. DNA sequence analysis revealed a point mutation in the start codon of sigK in all low-producing BCG strains. Complementation of a low-producing strain, BCG Pasteur, with wild-type sigK fully restored MPB70 and MPB83 production. Microarray-based analysis and confirmatory RT-PCR of the complemented strains revealed an upregulation in gene transcription limited to the sigK and the mpb83/mpb70 gene regions. These data demonstrate that a mutation of sigK is responsible for decreased expression of MPB70 and MPB83 in low-producing BCG strains and provide clues into the role of Mycobacterium tuberculosis SigK.