Mycobacterium leprae infection in monocyte-derived dendritic cells and its influence on antigen-presenting function

Identification of potential biomarkers of leprosy: A study based on GEO datasets

Leprosy has a high rate of cripplehood and lacks available early effective diagnosis methods for prevention and treatment, thus novel effective molecule markers are urgently required. In this study, we conducted bioinformatics analysis with leprosy and normal samples acquired from the GEO database(GSE84893, GSE74481, GSE17763, GSE16844 and GSE443). Through WGCNA analysis, 85 hub genes were screened(GS > 0.7 and MM > 0.8). Through DEG analysis, 82 up-regulated and 3 down-regulated genes were screened(|Log2FC| > 3 and FDR < 0.05). Then 49 intersection genes were considered as crucial and subjected to GO annotation, KEGG pathway and PPI analysis to determine the biological significance in the pathogenesis of leprosy. Finally, we identified a gene-pathway network, suggesting ITK, CD48, IL2RG, CCR5, FGR, JAK3, STAT1, LCK, PTPRC, CXCR4 can be used as biomarkers and these genes are active in 6 immune system pathways, including Chemokine signaling pathway, Th1 and Th2 cell differentiation, Th17 cell differentiation, T cell receptor signaling pathway, Natural killer cell mediated cytotoxicity and Leukocyte transendothelial migration. We identified 10 crucial gene markers and related important pathways that acted as essential components in the etiology of leprosy. Our study provides potential targets for diagnostic biomarkers and therapy of leprosy.

Protective Efficacy of BCG Vaccine against Mycobacterium leprae and Non-Tuberculous Mycobacterial Infections

The genus mycobacterium includes several species that are known to cause infections in humans. The microorganisms are classified into tuberculous and non-tuberculous based on their morphological characteristics, defined by the dynamic relationship between the host defenses and the infectious agent. Non-tuberculous mycobacteria (NTM) include all the species of mycobacterium other than the ones that cause tuberculosis (TB). The group of NTM contains almost 200 different species and they are found in soil, water, animals—both domestic and wild—milk and food products, and from plumbed water resources such as sewers and showerhead sprays. A systematic review of Medline between 1946 and 2014 showed an 81% decline in TB incidence rates with a simultaneous 94% increase in infections caused by NTM. Prevalence of infections due to NTM has increased relative to infections caused by TB owing to the stringent prevention and control programs in Western countries such as the USA and Canada. While the spread of typical mycobacterial infections such as TB and leprosy involves human contact, NTM seem to spread easily from the environment without the risk of acquiring from a human contact except in the case of M. abscessus in patients with cystic fibrosis, where human transmission as well as transmission through fomites and aerosols has been recorded. NTM are opportunistic in their infectious processes, making immunocompromised individuals such as those with other systemic infections such as HIV, immunodeficiencies, pulmonary disease, or usage of medications such as long-term corticosteroids/TNF-α inhibitors more susceptible. This review provides insight on pathogenesis, treatment, and BCG vaccine efficacy against M. leprae and some important NTM infections.

Production of antibiotic resistance gene-free urease-deficient recombinant BCG that secretes antigenic protein applicable for practical use in tuberculosis vaccination

Mycobacterium bovis BCG has been the only practical vaccine for tuberculosis. However, BCG cannot fully prevent adult pulmonary tuberculosis. Therefore, the improvement of BCG vaccine is necessary. We previously produced recombinant (r) BCG (BCG-PEST) for the better control of tuberculosis. BCG-PEST was developed by introducing PEST-Heat Shock Protein (HSP)70-Major Membrane Protein (MMP)-II-PEST fusion gene into urease-deficient rBCG using antibiotic-resistant gene for the selection of rBCG. HSP70-MMPII fusion protein is highly immunogenic and PEST sequence was added to enhance processing of the fusion protein. Although BCG-PEST effectively inhibited intrapulmonary growth of Mycobacterium tuberculosis (MTB), BCG with antibiotic-resistant gene is not appropriate for human use. Therefore, we produced antibiotic-resistant gene-free rBCG. We generated leucine-biosynthetic gene (leuD)-deficient BCG and introduced the fusion gene with leuD as the selection marker and named this rBCG as BCG-LeuPH. BCG-LeuPH activated human naïve T cells of both CD4 and CD8 subsets and efficiently inhibited aerosol-challenged MTB in mice. These results indicate that leuD can replace antibiotic-resistant gene for the selection of vaccine candidates of rBCG for human use.

In search of biomarkers for leprosy by unraveling the host immune response to Mycobacterium leprae

Mycobacterium leprae, the causative agent of leprosy, is still actively transmitted in endemic areas reflected by the fairly stable number of new cases detected each year. Recognizing the signs and symptoms of leprosy is challenging, especially at an early stage. Improved diagnostic tools, based on sensitive and specific biomarkers, that facilitate diagnosis of leprosy are therefore urgently needed. In this review, we address the challenges that leprosy biomarker research is facing by reviewing cell types reported to be involved in host immunity to M leprae. These cell types can be associated with different possible fates of M leprae infection being either protective immunity, or pathogenic immune responses inducing nerve damage. Unraveling these responses will facilitate the search for biomarkers. Implications for further studies to disentangle the complex interplay between host responses that lead to leprosy disease are discussed, providing leads for the identification of new biomarkers to improve leprosy diagnostics.

Intrinsic activation of the vitamin D antimicrobial pathway by M. leprae infection is inhibited by type I IFN

Following infection, virulent mycobacteria persist and grow within the macrophage, suggesting that the intrinsic activation of an innate antimicrobial response is subverted by the intracellular pathogen. For Mycobacterium leprae, the intracellular bacterium that causes leprosy, the addition of exogenous innate or adaptive immune ligands to the infected monocytes/macrophages was required to detect a vitamin D-dependent antimicrobial activity. We investigated whether there is an intrinsic immune response to M. leprae in macrophages that is inhibited by the pathogen. Upon infection of monocytes with M. leprae, there was no upregulation of CYP27B1 nor its enzymatic activity converting the inactive prohormone form of vitamin D (25-hydroxyvitamin D) to the bioactive form (1,25α-dihydroxyvitamin D). Given that M. leprae-induced type I interferon (IFN) inhibited monocyte activation, we blocked the type I IFN receptor (IFNAR), revealing the intrinsic capacity of monocytes to recognize M. leprae and upregulate CYP27B1. Consistent with these in vitro studies, an inverse relationship between expression of CYP27B1 vs. type I IFN downstream gene OAS1 was detected in leprosy patient lesions, leading us to study cytokine-derived macrophages (MΦ) to model cellular responses at the site of disease. Infection of IL-15-derived MΦ, similar to MΦ in lesions from the self-limited form of leprosy, with M. leprae did not inhibit induction of the vitamin D antimicrobial pathway. In contrast, infection of IL-10-derived MΦ, similar to MΦ in lesions from patients with the progressive form of leprosy, resulted in induction of type I IFN and suppression of the vitamin D directed pathway. Importantly, blockade of the type I IFN response in infected IL-10 MΦ decreased M. leprae viability. These results indicate that M. leprae evades the intrinsic capacity of human monocytes/MΦ to activate the vitamin D-mediated antimicrobial pathway via the induction of type I IFN.

Our macrophages are equipped with the ability to detect and kill invading pathogens, and yet, these cells of the innate immune system are still subject to infection by intracellular bacterium. In particular, mycobacterium, the type of intracellular bacteria responsible for diseases such as tuberculosis and leprosy, are very successful at establishing infection within macrophages. By studying Mycobacterium leprae, the etiological agent of leprosy, we describe an immune evasion mechanism whereby this bacterial pathogen utilizes our own antiviral immune response against the macrophage. Type I interferons (IFN) are a major part of our immune response to viral infections; however, this response will also suppress our ability to fight opportunistic bacterial infection. During infection of our macrophages, M. leprae induces an aberrant type I IFN response that subsequently suppresses our macrophage’s ability to activate the vitamin D-mediated antimicrobial pathway, a critical antimicrobial response for containment of mycobacterium. Thus, understanding how these pathogens can evade our immune response will be important for the development of new therapies against these chronic infections.

Innate Immune Responses in Leprosy

Leprosy is an infectious disease that may present different clinical forms depending on host immune response to Mycobacterium leprae. Several studies have clarified the role of various T cell populations in leprosy; however, recent evidences suggest that local innate immune mechanisms are key determinants in driving the disease to its different clinical manifestations. Leprosy is an ideal model to study the immunoregulatory role of innate immune molecules and its interaction with nervous system, which can affect homeostasis and contribute to the development of inflammatory episodes during the course of the disease. Macrophages, dendritic cells, neutrophils, and keratinocytes are the major cell populations studied and the comprehension of the complex networking created by cytokine release, lipid and iron metabolism, as well as antimicrobial effector pathways might provide data that will help in the development of new strategies for leprosy management.

Serum Levels of Migration Inhibitory Factor (MIF) and In Situ Expression of MIF and Its Receptor CD74 in Lepromatous Leprosy Patients: A Preliminary Report

Leprosy is a chronic disease caused by Mycobacterium leprae that affects the skin and peripheral nerves. It may present as one of two distinct poles: the self-limiting tuberculoid leprosy and the highly infectious lepromatous leprosy (LL) characterized by M. leprae-specific absence of cellular immune response. The pro-inflammatory cytokine macrophage migration inhibitory factor (MIF) enhance the bactericide activities of macrophages after interaction with its receptor, CD74. Importantly, MIF also possesses chemoattractant properties, and it is a key factor in situ for the activation of macrophages and in blood to promote leukocytes migration. MIF-mediated activation of macrophages is a key process for the elimination of pathogens such as Mycobacterium tuberculosis; however, its participation for the clearance of M. leprae is unclear. The aim of this study was to evaluate the serum levels of MIF as well as MIF and CD74 expression in skin lesions of LL and compare it with healthy skin (HSk) taken from subjects attending to dermatological consult. Samples of serum and skin biopsies were taken from 39 LL patients and compared with 36 serum samples of healthy subjects (HS) and 10 biopsies of HSk. Serum samples were analyzed by ELISA and skin biopsies by immunohistochemistry (IHC). IHC smears were observed in 12 100× microscopic fields, in which percentage of stained cells and staining intensity were evaluated. Both variables were used to calculate a semi-quantitative expression score that ranged from 0 to 3+. We found no differences in MIF levels between LL patients and HS in sera. In addition, MIF was observed in over 75% of cells with high intensity in the skin of patients and HSk. Although we found no differences in MIF expression between the groups, a CD74 score statistically higher was found in LL skin than HSk (p < 0.001); this was the result of a higher percentage of cells positive for CD74 (p < 0.001). As a conclusion, we found that CD74-positive cells are intensely recruited to the skin with LL lesions. In this manner, MIF signaling may be enhanced in the skin of LL patients due to increased expression of its receptor, but further studies are required.

Enhanced protective efficacy against tuberculosis provided by a recombinant urease deficient BCG expressing heat shock protein 70-major membrane protein-II having PEST sequence

Enhancement of the T cell-stimulating ability of Mycobacterium bovis BCG (BCG) is necessary to develop an effective tuberculosis vaccine. For this purpose, we introduced the PEST-HSP70-major membrane protein-II (MMPII)-PEST fusion gene into ureC-gene depleted recombinant (r) BCG to produce BCG-PEST. The PEST sequence is involved in the proteasomal processing of antigens. BCG-PEST secreted the PEST-HSP70-MMPII-PEST fusion protein and more efficiently activated human monocyte-derived dendritic cells (DCs) in terms of phenotypic changes and cytokine productions than an empty-vector-introduced BCG or HSP70-MMPII gene-introduced ureC gene-depleted BCG (BCG-DHTM). Autologous human naïve CD8⁺ T cells and naïve CD4⁺ T cells were effectively activated by BCG-PEST and produced IFN-γ in an antigen-specific manner through DCs. These T cell activations were closely associated with phagosomal maturation and intraproteasomal protein degradation in antigen-presenting cells. Furthermore, BCG-PEST produced long-lasting memory-type T cells in C57BL/6 mice more efficiently than control rBCGs. Moreover, a single subcutaneous injection of BCG-PEST more effectively reduced the multiplication of subsequent aerosol-challenged Mycobacterium tuberculosis of the standard H37Rv strain and clinically isolated Beijing strain in the lungs than control rBCGs. The vaccination effect of BCG-PEST lasted for at least 6months. These results indicate that BCG-PEST may be able to efficiently control the spread of tuberculosis in human.

Expression profile of Rab5, Rab7, tryptophan aspartate-containing coat protein, leprae lipoarabinomannan, and phenolic glycolipid-1 on the failure of the phagolysosome process in macrophages of leprosy patients as a viability marker of Mycobacterium leprae

OBJECTIVE/BACKGROUND

Phagolysosome process in macrophage of leprosy patients' is important in the early phase of eliminating Mycobacterium leprae invasion. This study was to clarify the involvement of Rab5, Rab7, and trytophan aspartate-containing coat protein (TACO) from host macrophage and leprae lipoarabinomannan (Lep-LAM) and phenolic glycolipid-1 (PGL-1) from M. leprae cell wall as the reflection of phagolysosome process in relation to 16 subunit ribosomal RNA (16S rRNA) M. leprae as a marker of viability of M. leprae.

METHODS

Using a cross sectional design study, skin biopsies were obtained from 47 newly diagnosed, untreated leprosy at Dr Soetomo Hospital, Surabaya, Indonesia. RNA isolation and complementary DNA synthesis were performed. Samples were divided into two groups: 16S rRNA M. leprae-positive and 16S rRNA M. leprae-negative. The expressions of Rab5, Rab7, TACO, Lep-LAM, and PGL-1 were assessed with an immunohistochemistry technique.

RESULT

Using Mann-Whitney U analysis, a significant difference in the expression profile of Rab5, Rab7, Lep-LAM, and PGL-1 was found (p<.05), but there was no significant difference of TACO between the two groups (p>.05). Spearman analysis revealed that there was a significant correlation between the score of Rab5, Rab7, Lep-LAM, and PGL-1 and the score of 16S rRNA M. leprae (p<.05).

CONCLUSION

In M. leprae infection, Rab5, Rab7, and Lep-LAM play important roles in the failure of phagolysosome process via a membrane trafficking pathway, while PGL-1 plays a role via blocking lysosomal activities. These inventions might be used for the development of an early diagnostic device in the future.

Genetic Variation in Toll-Interacting Protein Is Associated With Leprosy Susceptibility and Cutaneous Expression of Interleukin 1 Receptor Antagonist

Leprosy is a chronic disease characterized by skin and peripheral nerve pathology and immune responses that fail to control Mycobacterium leprae. Toll-interacting protein (TOLLIP) regulates Toll-like receptor (TLR) and interleukin 1 receptor (IL-1R) signaling against mycobacteria. We analyzed messenger RNA (mRNA) expression of candidate immune genes in skin biopsy specimens from 85 individuals with leprosy. TOLLIP mRNA was highly and specifically correlated with IL-1R antagonist (IL-1Ra). In a case-control gene-association study with 477 cases and 1021 controls in Nepal, TOLLIP single-nucleotide polymorphism rs3793964 TT genotype was associated with increased susceptibility to leprosy (recessive, P = 1.4 × 10(-3)) and with increased skin expression of TOLLIP and IL-1Ra. Stimulation of TOLLIP-deficient monocytes with M. leprae produced significantly less IL-1Ra (P < .001), compared with control. These data suggest that M. leprae upregulates IL-1Ra by a TOLLIP-dependent mechanism. Inhibition of TOLLIP may decrease an individual's susceptibility to leprosy and offer a novel therapeutic target for IL-1-dependent diseases.

Activation and cytokine profile of monocyte derived dendritic cells in leprosy: in vitro stimulation by sonicated Mycobacterium leprae induces decreased level of IL-12p70 in lepromatous leprosy

Dendritic cells (DCs) play a pivotal role in the connection of innate and adaptive immunity of hosts to mycobacterial infection. Studies on the interaction of monocyte-derived DCs (MO-DCs) using Mycobacterium leprae in leprosy patients are rare. The present study demonstrated that the differentiation of MOs to DCs was similar in all forms of leprosy compared to normal healthy individuals. In vitro stimulation of immature MO-DCs with sonicated M. leprae induced variable degrees of DC maturation as determined by the increased expression of HLA-DR, CD40, CD80 and CD86, but not CD83, in all studied groups. The production of different cytokines by the MO-DCs appeared similar in all of the studied groups under similar conditions. However, the production of interleukin (IL)-12p70 by MO-DCs from lepromatous (LL) leprosy patients after in vitro stimulation with M. leprae was lower than tuberculoid leprosy patients and healthy individuals, even after CD40 ligation with CD40 ligand-transfected cells. The present cumulative findings suggest that the MO-DCs of LL patients are generally a weak producer of IL-12p70 despite the moderate activating properties ofM. leprae. These results may explain the poor M. leprae-specific cell-mediated immunity in the LL type of leprosy.

Paracoccidioides brasiliensis interferes on dendritic cells maturation by inhibiting PGE2 production

Paracoccidioidomycosis (PCM) is a systemic mycosis, endemic in most Latin American countries, especially in Brazil, whose etiologic agent is the thermodimorphic fungus of the genus Paracoccidioides, comprising cryptic species of Paracoccidioides brasiliensis, S1, PS2, PS3 and Paracoccidioides lutzii. The mechanisms involved in the initial interaction of the fungus with cells of the innate immune response, as dendritic cells (DCs), deserve to be studied. Prostaglandins (PGs) are eicosanoids that play an important role in modulating functions of immune cells including DCs. Here we found that human immature DCs derived from the differentiation of monocytes cultured with GM-CSF and IL-4 release substantial concentrations of PGE₂, which, however, were significantly inhibited after challenge with P. brasiliensis. In vitro blocking of pattern recognition receptors (PRRs) by monoclonal antibodies showed the involvement of mannose receptor (MR) in PGE₂ inhibition by the fungus. In addition, phenotyping assays showed that after challenge with the fungus, DCs do not change their phenotype of immature cells to mature ones, as well as do not produce IL-12 p70 or adequate concentrations of TNF-α. Assays using exogenous PGE₂ confirmed an association between PGE₂ inhibition and failure of cells to phenotypically mature in response to P. brasiliensis. We conclude that a P. brasiliensis evasion mechanism exists associated to a dysregulation on DC maturation. These findings may provide novel information for the understanding of the complex interplay between the host and this fungus.

Playing hide-and-seek with host macrophages through the use of mycobacterial cell envelope phthiocerol dimycocerosates and phenolic glycolipids

Mycobacterial pathogens, including Mycobacterium tuberculosis, the etiological agent of tuberculosis (TB), have evolved a remarkable ability to evade the immune system in order to survive and to colonize the host. Among the most important evasion strategies is the capacity of these bacilli to parasitize host macrophages, since these are major effector cells against intracellular pathogens that can be used as long-term cellular reservoirs. Mycobacterial pathogens employ an array of virulence factors that manipulate macrophage function to survive and establish infection. Until recently, however, the role of mycobacterial cell envelope lipids as virulence factors in macrophage subversion has remained elusive. Here, we will address exclusively the proposed role for phthiocerol dimycocerosates (DIM) in the modulation of the resident macrophage response and that of phenolic glycolipids (PGL) in the regulation of the recruitment and phenotype of incoming macrophage precursors to the site of infection. We will provide a unique perspective of potential additional functions for these lipids, and highlight obstacles and opportunities to further understand their role in the pathogenesis of TB and other mycobacterial diseases.

Manipulation of the mononuclear phagocyte system by Mycobacterium tuberculosis

Over the past 20 years, there has been an emerging appreciation about the role of the mononuclear phagocyte system (MPS) to control and eradicate pathogens. Likewise, there have been significant advances in dissecting the mechanisms involved in the microbial subversion of MPS cells, mainly affecting their differentiation and effector functions. Mycobacterium tuberculosis is a chronic bacterial pathogen that represents an enigma to the field because of its remarkable ability to thrive in humans. One reason is that M. tuberculosis renders a defective MPS compartment, which is perhaps the most ingenious strategy for survival in the host given the prominence of these cells to modulate microenvironments, their function as sentinels and orchestrators of the immune response, and their pathogenic role as reservoirs for microbial persistence. In this article, the principal strategies used by M. tuberculosis to subvert the MPS compartment are presented along with emerging concepts.

Polyclonal activation of naïve T cells by urease deficient-recombinant BCG that produced protein complex composed of heat shock protein 70, CysO and major membrane protein-II

BACKGROUND

Mycobacterium bovis bacillus Calmette-Guérin (BCG) is known to be only partially effective in inhibiting M. tuberculosis (MTB) multiplication in human. A new recombinant (r) urease-deficient BCG (BCG-dHCM) that secretes protein composed of heat shock protein (HSP)70, MTB-derived CysO and major membrane protein (MMP)-II was produced for the efficient production of interferon gamma (IFN-γ) which is an essential element for mycobacteriocidal action and inhibition of neutrophil accumulation in lungs.

METHODS

Human monocyte-derived dendritic cells (DC) and macrophages were differentiated from human monocytes, infected with BCG and autologous T cells-stimulating activity of different constructs of BCG was assessed. C57BL/6 mice were used to test the effectiveness of BCG for the production of T cells responsive to MTB-derived antigens (Ags).

RESULTS

BCG-dHCM intracellularly secreted HSP70-CysO-MMP-II fusion protein, and activated DC by up-regulating Major Histcompatibility Complex (MHC), CD86 and CD83 molecules and enhanced various cytokines production from DC and macrophages. BCG-dHCM activated naïve T cells of both CD4 and CD8 subsets through DC, and memory type CD4+ T cells through macrophages in a manner dependent on MHC and CD86 molecules. These T cell activations were inhibited by the pre-treatment of Ag-presenting cells (APCs) with chloroquine. The single and primary BCG-dHCM-inoculation produced long lasting T cells responsive to in vitro secondarily stimulation with HSP70, CysO, MMP-II and H37Rv-derived cytosolic protein, and partially inhibited the replication of aerosol-challenged MTB.

CONCLUSIONS

The results indicate that introduction of different type of immunogenic molecules into a urease-deficient rBCG is useful for providing polyclonal T cell activating ability to BCG and for production of T cells responsive to secondary stimulation.

B cells in teleost fish act as pivotal initiating APCs in priming adaptive immunity: an evolutionary perspective on the origin of the B-1 cell subset and B7 molecules

The long-held paradigm that B cells cannot uptake nonspecific particulate Ags for the initiation of primary adaptive immunity has been challenged by the recent discovery that teleost B cells have potent phagocytic and microbicidal abilities. This discovery provides preliminary clues that primitive B cells might act as initiating APCs in priming adaptive immunity. In this study, zebrafish B cells clearly showed a potent Ag-presenting ability to both soluble Ags and bacterial particles to prime naive CD4(+) T cell activation. This finding demonstrates the innate-like nature of teleost B cells in the interface of innate and adaptive immunity, indicating that they might consist of a major population of initiating APCs whose performance is similar to that of dendritic cells. Given the functional similarities between teleost B cells and the mammalian B-1 subset, we hypothesize that B-1 lineage and teleost B cells might originate from a common ancestor with potent phagocytic and initiating APC capacities. In addition, CD80/86 and CD83 costimulatory signals were identified as being essential for B cell-initiated adaptive immunity. This result suggests that the costimulatory mechanism originated as early as the origin of adaptive immunity and is conserved throughout vertebrate evolution. In fish, only a single CD80/86 copy exists, which is similar to mammalian CD86 rather than to CD80. Thus, CD86 might be a more primordial B7 family member that originated from fish. This study provides valuable insights into the evolutionary history of professional APCs, B cell lineages, and the costimulatory mechanism underlying adaptive immunity as a whole.

Leprosy as a model of immunity

ABSTRACT: Leprosy displays a spectrum of clinical manifestations, such as lepromatous and tuberculoid leprosy, and type I and II lepra reactions, which are thought to be a reflection of the host’s immunological response against Mycobacterium leprae. Therefore, differential recognition of M. leprae, as well as its degraded components, and subsequent activation of cellular immunity will be an important factor for the clinical manifestation of leprosy. Although M. leprae mainly parasitizes tissue macrophages in the dermis and the Schwann cells of peripheral nerves, the presence of M. leprae in other organs, such as the liver, may also play important roles in the further modification of seesaw-like bipolar phenotypes of leprosy. Thus, leprosy is an exciting model for investigating the role of the human immune system in host defense and susceptibility to infection.

Efficient activation of human T cells of both CD4 and CD8 subsets by urease-deficient recombinant Mycobacterium bovis BCG that produced a heat shock protein 70-M. tuberculosis-derived major membrane protein II fusion protein

For the purpose of obtaining Mycobacterium bovis bacillus Calmette-Guérin (BCG) capable of activating human naive T cells, urease-deficient BCG expressing a fusion protein composed of Mycobacterium tuberculosis-derived major membrane protein II (MMP-II) and heat shock protein 70 (HSP70) of BCG (BCG-DHTM) was produced. BCG-DHTM secreted the HSP70-MMP-II fusion protein and effectively activated human monocyte-derived dendritic cells (DCs) by inducing phenotypic changes and enhanced cytokine production. BCG-DHTM-infected DCs activated naive T cells of both CD4 and naive CD8 subsets, in an antigen (Ag)-dependent manner. The T cell activation induced by BCG-DHTM was inhibited by the pretreatment of DCs with chloroquine. The naive CD8(+) T cell activation was mediated by the transporter associated with antigen presentation (TAP) and the proteosome-dependent cytosolic cross-priming pathway. Memory CD8(+) T cells and perforin-producing effector CD8(+) T cells were efficiently produced from the naive T cell population by BCG-DHTM stimulation. Single primary infection with BCG-DHTM in C57BL/6 mice efficiently produced T cells responsive to in vitro secondary stimulation with HSP70, MMP-II, and M. tuberculosis-derived cytosolic protein and inhibited the multiplication of subsequently aerosol-challenged M. tuberculosis more efficiently than did vector control BCG. These results indicate that the introduction of MMP-II and HSP70 into urease-deficient BCG may be useful for improving BCG for control of tuberculosis.

An in vitro model of Mycobacterium leprae induced granuloma formation

Background

Leprosy is a contagious and chronic systemic granulomatous disease caused by Mycobacterium leprae. In the pathogenesis of leprosy, granulomas play a key role, however, the mechanisms of the formation and maintenance of M. leprae granulomas are still not clearly understood.

Methods

To better understand the molecular physiology of M. leprae granulomas and the interaction between the bacilli and human host cells, we developed an in vitro model of human granulomas, which mimicked the in vivo granulomas of leprosy. Macrophages were differentiated from human monocytes, and infected with M. leprae, and then cultured with autologous human peripheral blood mononuclear cells (PBMCs).

Results

Robust granuloma-like aggregates were obtained only when the M. leprae infected macrophages were co-cultured with PBMCs. Histological examination showed M. leprae within the cytoplasmic center of the multinucleated giant cells, and these bacilli were metabolically active. Macrophages of both M1 and M2 types co-existed in the granuloma like aggregates. There was a strong relationship between the formation of granulomas and changes in the expression levels of cell surface antigens on macrophages, cytokine production and the macrophage polarization. The viability of M. leprae isolated from granulomas indicated that the formation of host cell aggregates benefited the host, but the bacilli also remained metabolically active.

Conclusions

A simple in vitro model of human M. leprae granulomas was established using human monocyte-derived macrophages and PBMCs. This system may be useful to unravel the mechanisms of disease progression, and subsequently develop methods to control leprosy.

PARK2 mediates interleukin 6 and monocyte chemoattractant protein 1 production by human macrophages

Leprosy is a persistent infectious disease caused by Mycobacterium leprae that still affects over 200,000 new patients annually. The host genetic background is an important risk factor for leprosy susceptibility and the PARK2 gene is a replicated leprosy susceptibility candidate gene. The protein product of PARK2, Parkin, is an E3 ubiquitin ligase that is involved in the development of various forms of Parkinsonism. The human macrophage is both a natural host cell of M. leprae as well as a primary mediator of natural immune defenses, in part by secreting important pro-inflammatory cytokines and chemokines. Here, we report that down-regulation of Parkin in THP-1 macrophages, human monocyte-derived macrophages and human Schwann cells resulted in a consistent and specific decrease in interleukin-6 (IL-6) and monocyte chemoattractant protein 1 (MCP-1/CCL2) production in response to mycobacteria or LPS. Interestingly, production of IL-6 at 6 hours by THP-1 cells stimulated with live M. leprae and M. bovis BCG was dependent on pretreatment with 1,25-dihydroxyvitamin D₃ (VD). Parkin knockdown in VD-treated cells blocked IL-6 induction by mycobacteria. However, IκB-α phosphorylation and levels of IκB-ξ, a nuclear protein required for IL-6 expression, were not affected by Parkin silencing. Phosphorylation of MAPK ERK1/2 and p38 was unaffected by Parkin silencing while JNK activation was promoted but did not explain the altered cytokine production. In a final set of experiments we found that genetic risk factors of leprosy located in the PARK2 promoter region were significantly correlated with M. leprae sonicate triggered CCL2 and IL6 transcript levels in whole blood assays. These results associated genetically controlled changes in the production of MCP-1/CCL2 and IL-6 with known leprosy susceptibility factors.

Leprosy is an infectious disease with a strong host genetic component. The identification of host genetic lesions predisposing to disease is a powerful approach for mapping key junctions in the host pathogen interplay. Genetic variants located in the promoter region of the PARK2 gene are replicated leprosy susceptibility factors. To better understand a possible contribution of PARK2 to host effector mechanisms in leprosy patients, we developed a cellular model to test the contribution of the PARK2 encoded parkin protein to host responses to mycobacterial antigens. We observed that parkin was a mediator of IL-6 production in response to mycobacterial antigen in both THP-1 macrophages and human Schwann cells while human monocyte-derived macrophages needed to be pre-activated with VitD to show the same impact. Parkin also impacted on the constitutive production of MCP-1. The regulatory activity of parkin on cytokine production was found to be independent of the canonical TLR-NFκB signalling pathway. We also tested association of IL6 and CCL2 gene expression levels in whole blood assays with PARK2 polymorphisms. For both cytokines, we found significant associations with those PARK2 variants that were established leprosy susceptibility factors. Hence, our results show that genetic PARK2 variants that are correlated with leprosy susceptibility are also correlated with production of these cytokines following stimulation with M. leprae sonicate.

A lipopeptide facilitate induction of Mycobacterium leprae killing in host cells

Little is known of the direct microbicidal activity of T cells in leprosy, so a lipopeptide consisting of the N-terminal 13 amino acids lipopeptide (LipoK) of a 33-kD lipoprotein of Mycobacterium leprae, was synthesized. LipoK activated M. leprae infected human dendritic cells (DCs) to induce the production of IL-12. These activated DCs stimulated autologous CD4+ or CD8+ T cells towards type 1 immune response by inducing interferon-gamma secretion. T cell proliferation was also evident from the CFSE labeling of target CD4+ or CD8+ T cells. The direct microbicidal activity of T cells in the control of M. leprae multiplication is not well understood. The present study showed significant production of granulysin, granzyme B and perforin from these activated CD4+ and CD8+ T cells when stimulated with LipoK activated, M. leprae infected DCs. Assessment of the viability of M. leprae in DCs indicated LipoK mediated T cell-dependent killing of M. leprae. Remarkably, granulysin as well as granzyme B could directly kill M. leprae in vitro. Our results provide evidence that LipoK could facilitate M. leprae killing through the production of effector molecules granulysin and granzyme B in T cells.

Modulation of the cytokine response in human monocytes by mycobacterium leprae phenolic glycolipid-1

Leprosy is a chronic but treatable infectious disease caused by the intracellular pathogen Mycobacterium leprae. M. leprae cell wall is characterized by a unique phenolic glycolipid-1 (PGL-1) reported to have several immune functions. We have examined the role of PGL-1 in the modulation of monocyte cytokine/chemokine production in naive human monocytes. PGL-1 in its purified form or expressed in a recombinant Mycobacterium bovis Bacillus Colmette-Guérin (BCG) background (rBCG-PGL-1) was tested. We found that PGL-1 selectively modulated the induction of specific monocyte cytokines and chemokines and, when used as prestimulus, exerted priming and/or inhibitory effects on the induction of selected cytokines/chemokines in response to a second stimulus. Taken together, the results of this study support a modulatory role for PGL-1 in the innate immune response to M. leprae. Thus, PGL-1 may play an important role in the development of the anergic clinical forms of disease and in tissue damage seen in lepromatous patients and during the reactional states of leprosy.

Serum metabolomics reveals higher levels of polyunsaturated fatty acids in lepromatous leprosy: potential markers for susceptibility and pathogenesis

BACKGROUND

Leprosy is a disease of the skin and peripheral nervous system caused by the obligate intracellular bacterium Mycobacterium leprae. The clinical presentations of leprosy are spectral, with the severity of disease determined by the balance between the cellular and humoral immune response of the host. The exact mechanisms that facilitate disease susceptibility, onset and progression to certain clinical phenotypes are presently unclear. Various studies have examined lipid metabolism in leprosy, but there has been limited work using whole metabolite profiles to distinguish the clinical forms of leprosy.

METHODOLOGY AND PRINCIPAL FINDINGS

In this study we adopted a metabolomics approach using high mass accuracy ultrahigh pressure liquid chromatography mass spectrometry (UPLC-MS) to investigate the circulatory biomarkers in newly diagnosed untreated leprosy patients. Sera from patients having bacterial indices (BI) below 1 or above 4 were selected, subjected to UPLC-MS, and then analyzed for biomarkers which distinguish the polar presentations of leprosy. We found significant increases in the abundance of certain polyunsaturated fatty acids (PUFAs) and phospholipids in the high-BI patients, when contrasted with the levels in the low-BI patients. In particular, the median values of arachidonic acid (2-fold increase), eicosapentaenoic acid (2.6-fold increase) and docosahexaenoic acid (1.6-fold increase) were found to be greater in the high-BI patients.

SIGNIFICANCE

Eicosapentaenoic acid and docosahexaenoic acid are known to exert anti-inflammatory properties, while arachidonic acid has been reported to have both pro- and anti-inflammatory activities. The observed increase in the levels of several lipids in high-BI patients may provide novel clues regarding the biological pathways involved in the immunomodulation of leprosy. Furthermore, these results may lead to the discovery of biomarkers that can be used to investigate susceptibility to infection, facilitate early diagnosis and monitor the progression of disease.

Immunostimulatory activity of major membrane protein II from Mycobacterium tuberculosis

Previously, we observed that both major membrane protein II of Mycobacterium leprae (MMP-ML) and its fusion with M. bovis BCG (BCG)-derived heat shock protein 70 (HSP70) (Fusion-ML) are immunogenic and that recombinant BCG secreting either of these proteins effectively inhibits the multiplication of M. leprae in mice. Here, we purified M. tuberculosis-derived major membrane protein II (MMP-MTB) and its fusion with HSP70 (Fusion-MTB) in a lipopolysaccharide-free condition and evaluated their immunostimulatory abilities. Both MMP-MTB and Fusion-MTB activated monocyte-derived dendritic cells (DC) in terms of phenotype and interleukin-12 (IL-12) production, but Fusion-MTB more efficiently activated them than MMP-MTB did. The IL-12 production was a consequence of the ligation of those recombinant proteins with Toll-like receptor 2. The M. tuberculosis-derived and M. leprae-derived recombinant proteins activated naïve T cells of both CD4 and CD8 subsets, but M. tuberculosis-derived proteins were superior to M. leprae-derived proteins and fusion proteins were superior to MMP, regardless of the origin of the protein. Memory-type CD4(+) T cells obtained from BCG-vaccinated healthy individuals seem to be primed with MMP-MTB by the vaccination, and both M. tuberculosis-derived recombinant proteins produced perforin-producing CD8(+) T cells from memory-type CD8(+) T cells. Further, infection of DC and macrophages with M. tuberculosis H37Ra and H37Rv induced the expression of MMP on their surface. These results indicate that M. tuberculosis-derived MMP, as a sole protein or as part of a fusion protein, may be useful for developing new vaccinating agents against tuberculosis.

Mycobacterium leprae phenolglycolipid-1 expressed by engineered M. bovis BCG modulates early interaction with human phagocytes

The species-specific phenolic glycolipid 1 (PGL-1) is suspected to play a critical role in the pathogenesis of leprosy, a chronic disease of the skin and peripheral nerves caused by Mycobacterium leprae. Based on studies using the purified compound, PGL-1 was proposed to mediate the tropism of M. leprae for the nervous system and to modulate host immune responses. However, deciphering the biological function of this glycolipid has been hampered by the inability to grow M. leprae in vitro and to genetically engineer this bacterium. Here, we identified the M. leprae genes required for the biosynthesis of the species-specific saccharidic domain of PGL-1 and reprogrammed seven enzymatic steps in M. bovis BCG to make it synthesize and display PGL-1 in the context of an M. leprae-like cell envelope. This recombinant strain provides us with a unique tool to address the key questions of the contribution of PGL-1 in the infection process and to study the underlying molecular mechanisms. We found that PGL-1 production endowed recombinant BCG with an increased capacity to exploit complement receptor 3 (CR3) for efficient invasion of human macrophages and evasion of inflammatory responses. PGL-1 production also promoted bacterial uptake by human dendritic cells and dampened their infection-induced maturation. Our results therefore suggest that M. leprae produces PGL-1 for immune-silent invasion of host phagocytic cells.

Disparity in circulating peripheral blood dendritic cell subsets and cytokine profile of pulmonary tuberculosis patients compared with healthy family contacts

Dendritic cell (DC) subsets, myeloid DCs (mDCs), and plasmacytoid DCs (pDCs) play a fundamental role in immune response to Mycobacterium tuberculosis (M. tuberculosis). Flow-cytometric estimation of DC subsets showed differences in the ratio of these subsets in untreated, smear-positive pulmonary tuberculosis patients compared with healthy family contacts (HFC, p < 0.05). The percentage of pDCs (0.14 +/- 0.01) was higher than mDCs (0.12 +/- 0.01) in patients, whereas in HFC, mDCs (0.15 +/- 0.01) was higher than pDCs (0.1 +/- 0.01). The percentage of mDCs (0.15 +/- 0.01) and pDCs (0.11 +/- 0.01) was restored in treated patients. Alteration in the DC subsets before and after chemotherapy was confirmed in the follow-up of acid-fast bacilli (AFB)-positive patients. This reversal in the percentage of mDC vs pDCs implicates the influence of active disease on circulating DC subsets. The cytokine bead array revealed an inverse relationship in the circulating levels of IL-12 and IFN-gamma. High IL-12 (37.9 +/- 15.2) and low IFN-gamma (11.09 +/- 3.6) was seen in HFCs derived serum samples compared with that of patients (p < 0.05). The higher percentage of mDCs and elevated IL-12 levels was found to be associated with high risk HFCs investigated. Furthermore CpG/LPS-stimulated whole-blood culture of untreated patients expressed high IFN-alpha in pDCs and less IL-12 in mDCs compared with those of treated patients.

The role of dendritic cells in mycobacterium-induced granulomas

The presence of dendritic cells (DCs) in mycobacterium-containing granulomas, as well as in other granuloma-inducing diseases, is beginning to be appreciated. This review will summarize what is known about DCs with regards to the granuloma and discuss the potential roles DCs may be playing during mycobacterial infection. Potential functions may include mycobacterial dissemination from lesions or sampling of granuloma-containing mycobacterial antigens and migration to the draining lymph nodes to maintain continuous T cell priming. Additionally, the review will discuss the potential outcomes of DC-T cell cross-talk within the granuloma and whether it results in boosting the effector functions of newly arrived T cells or anergizing systemic T cells locally. Understanding the DCs complex and changing role during this critical stage may help explain how latency is achieved and maintained. Such knowledge might also lead to improved vaccination strategies.

How do mycobacteria activate CD8+ T cells?

CD8(+) T cells are activated upon presentation of antigens from the cytosol. Therefore, it was unclear how pathogenic mycobacteria could prime this type of lymphocyte, given that these microbes were thought to remain in phagosomes and, hence, be shielded from the host cytosol. Recently, it was shown that some mycobacteria can enter the cytosol through translocation from phagolysosomes, providing a direct mechanism for CD8(+) T cell priming. However, this mechanism might not apply to other mycobacteria, which do not appear to be able to enter the cytosol. Here, we discuss the different hypotheses to explain the induction of CD8(+) T cell responses in mycobacterial infections.

Induction of cross-priming of naive CD8+ T lymphocytes by recombinant bacillus Calmette-Guerin that secretes heat shock protein 70-major membrane protein-II fusion protein

Because Mycobacterium bovis bacillus Calmette-Guérin (BCG) unconvincingly activates human naive CD8(+) T cells, a rBCG (BCG-70M) that secretes a fusion protein comprising BCG-derived heat shock protein (HSP)70 and Mycobacterium leprae-derived major membrane protein (MMP)-II, one of the immunodominant Ags of M. leprae, was newly constructed to potentiate the ability of activating naive CD8(+) T cells through dendritic cells (DC). BCG-70M secreted HSP70-MMP-II fusion protein in vitro, which stimulated DC to produce IL-12p70 through TLR2. BCG-70M-infected DC activated not only memory and naive CD8(+) T cells, but also CD4(+) T cells of both types to produce IFN-gamma. The activation of these naive T cells by BCG-70M was dependent on the MHC and CD86 molecules on BCG-70M-infected DC, and was significantly inhibited by pretreatment of DC with chloroquine. Both brefeldin A and lactacystin significantly inhibited the activation of naive CD8(+) T cells by BCG-70M through DC. Thus, the CD8(+) T cell activation may be induced by cross-presentation of Ags through a TAP- and proteosome-dependent cytosolic pathway. When naive CD8(+) T cells were stimulated by BCG-70M-infected DC in the presence of naive CD4(+) T cells, CD62L(low)CD8(+) T cells and perforin-producing CD8(+) T cells were efficiently produced. MMP-II-reactive CD4(+) and CD8(+) memory T cells were efficiently produced in C57BL/6 mice by infection with BCG-70M. These results indicate that BCG-70M activated DC, CD4(+) T cells, and CD8(+) T cells, and the combination of HSP70 and MMP-II may be useful for inducing better T cell activation.

Mycobacterium leprae actively modulates the cytokine response in naive human monocytes

Leprosy is a chronic but treatable infectious disease caused by the intracellular pathogen Mycobacterium leprae. Host immunity to M. leprae determines the diversity of clinical manifestations seen in patients, from tuberculoid leprosy with robust production of Th1-type cytokines to lepromatous disease, characterized by elevated levels of Th2-type cytokines and a suboptimal proinflammatory response. Previous reports have indicated that M. leprae is a poor activator of macrophages and dendritic cells in vitro. To understand whether M. leprae fails to elicit an optimal Th1 immune response or actively interferes with its induction, we have examined the early interactions between M. leprae and monocytes from healthy human donors. We found that, in naïve monocytes, M. leprae induced high levels of the negative regulatory molecules MCP-1 and interleukin-1 (IL-1) receptor antagonist (IL-1Ra), while suppressing IL-6 production through phosphoinositide-3 kinase (PI3K)-dependent mechanisms. In addition, low levels of proinflammatory cytokines were observed in association with reduced activation of nuclear factor-kappaB (NF-kappaB) and delayed activation of IL-1beta-converting enzyme, ICE (caspase-1), in monocytes stimulated with M. leprae compared with Mycobacterium bovis BCG stimulation. Interestingly, although in itself a weak stimulator of cytokines, M. leprae primed the cells for increased production of tumor necrosis factor alpha and IL-10 in response to a strongly inducing secondary stimulus. Taken together, our results suggest that M. leprae plays an active role to control the release of cytokines from monocytes by providing both positive and negative regulatory signals via multiple signaling pathways involving PI3K, NF-kappaB, and caspase-1.

Tryptophan aspartate-containing coat protein (CORO1A) suppresses Toll-like receptor signalling in Mycobacterium leprae infection

Mycobacterium leprae is an intracellular pathogen that survives within the phagosome of host macrophages. Several host factors are involved in producing tolerance, while others are responsible for killing the mycobacterium. Tryptophan aspartate-containing coat protein (TACO; also known as CORO1A or coronin-1) inhibits the phagosome maturation that allows intracellular parasitization. In addition, the Toll-like receptor (TLR) activates the innate immune response. Both CORO1A and TLR-2 co-localize on the phagosomal membrane in the dermal lesions of patients with lepromatous leprosy. Therefore, we hypothesized that CORO1A and TLR-2 might interact functionally. This hypothesis was tested by investigating the effect of CORO1A in TLR-2-mediated signalling and, inversely, the effect of TLR-2-mediated signalling on CORO1A expression. We found that CORO1A suppresses TLR-mediated signal activation in human macrophages, and that TLR2-mediated activation of the innate immune response resulted in suppression of CORO1A expression. However, M. leprae infection inhibited the TLR-2-mediated CORO1A suppression and nuclear factor-kappaB activation. These results suggest that the balance between TLR-2-mediated signalling and CORO1A expression will be key in determining the fate of M. leprae following infection.

GM-CSF-mediated T-cell activation by macrophages infected with recombinant BCG that secretes major membrane protein-II of Mycobacterium leprae

The potential of Mycobacterium bovis Bacillus Calmette-Guerin (BCG) needs to be augmented to efficiently activate CD4(+) T cells through macrophages. Mycobacterium leprae-derived recombinant major membrane protein (MMP)-II induced GM-CSF production from macrophages. A recombinant BCG-SM that secretes MMP-II more efficiently produced GM-CSF and activated interferon (IFN)-gamma-producing CD4(+) T cells than did vector control BCG when infected with macrophages. The T-cell activation by BCG-SM was dependent on the GM-CSF production by macrophages. Interleukin (IL)-10 production by macrophages stimulated with M. leprae was inhibited in a GM-CSF-dependent manner when the precursor monocytes were infected with BCG-SM. BCG inducing GM-CSF production was effective in macrophage-mediated T-cell activation partially through IL-10 inhibition.

Mycobacterium abscessus and M. avium trigger Toll-like receptor 2 and distinct cytokine response in human cells

Mycobacterium avium (MAV) and M. abscessus (MAB) are ubiquitous environmental organisms increasingly recognized to cause chronic lung disease in patients with apparently normal immune function. Little is yet known about their human pathophysiology. Our objective was to examine cytokine and chemokine responses (protein and gene expression) and signaling pathways triggered by reference and clinical isolates of MAB and MAV in human peripheral blood mononuclear cells, monocytes, and murine bone marrow-derived macrophages in vitro. MAB-induced TNF-alpha production was higher than that induced by MAV. IFN-gamma, IL-1beta, and the chemokines macrophage inflammatory protein-1alpha and regulated on activation, normal T cell expressed and secreted were equally up-regulated. Differences between MAB and MAV do not require replication and are heat stable. We found no differential effect due to rough or smooth colonies within the same species. Similar to MAV, MAB triggered mitogen-activated protein kinase (MAPK) signaling and nuclear factor-kappaB translocation. Induction of TNF-alpha was dependent on MAPK pathways, since pre-incubation of cells with signaling inhibitors led to more than 85% reduction in cytokine secretion. MAB also triggered a Toll-like receptor 2 (TLR2)-mediated response that led to TNF-alpha production by human monocytes. Accordingly, stimulation of murine TLR2- or myeloid differentiation factor 88-deficient bone marrow-derived macrophages did not elicit TNF-alpha, reinforcing a critical role for TLR2 in MAB-induced cell activation. We concluded that MAB signals human cells through MAPK and TLR2 pathways and triggers more pronounced pro-inflammatory cytokines and chemokines than MAV.

Haemophilus ducreyi partially activates human myeloid dendritic cells

Dendritic cells (DC) orchestrate innate and adaptive immune responses to bacteria. How Haemophilus ducreyi, which causes genital ulcers and regional lymphadenitis, interacts with DC is unknown. H. ducreyi evades uptake by polymorphonuclear leukocyte and macrophage-like cell lines by secreting LspA1 and LspA2. Many H. ducreyi strains express cytolethal distending toxin (CDT), and recombinant CDT causes apoptosis of DC in vitro. Here, we examined interactions between DC and H. ducreyi 35000HP, which produces LspA1, LspA2, and CDT. In human volunteers infected with 35000HP, the ratio of myeloid DC to plasmacytoid DC was 2.8:1 in lesions, compared to a ratio of 1:1 in peripheral blood. Using myeloid DC derived from monocytes as surrogates for lesional DC, we found that DC infected with 35000HP remained as viable as uninfected DC for up to 48 h. Gentamicin protection and confocal microscopy assays demonstrated that DC ingested and killed 35000HP, but killing was incomplete at 48 h. The expression of LspA1 and LspA2 did not inhibit the uptake of H. ducreyi, despite inactivating Src kinases. Infection of DC with live 35000HP caused less cell surface marker activation than infection with heat-killed 35000HP and lipopolysaccharide (LPS) and inhibited maturation by LPS. However, infection of DC with live bacteria caused the secretion of significantly higher levels of interleukin-6 and tumor necrosis factor alpha than infection with heat-killed bacteria and LPS. The survival of H. ducreyi in DC may provide a mechanism by which the organism traffics to lymph nodes. Partial activation of DC may abrogate the establishment of a full Th1 response and an environment that promotes phagocytosis.

Expression of B7-1 costimulatory molecules in patients with multibacillary leprosy and reactional states

BACKGROUND

The expression of B7 as a costimulatory molecule on the surface of antigen-presenting cells such as macrophages and on dendritic cells characterizes the efficiency of the cell-mediated immune response.

AIMS

Our purpose was to evaluate B7-1 expression in peripheral blood mononuclear cells (PBMCs) immediately after cell isolation ('spontaneous' B7 expression), and in inflammatory cells from cutaneous lesions of patients with multibacillary leprosy (MB-L) without and during the reactional states of erythema nodosum leprosum (ENL) or reversal reaction (RR).

METHODS

Peripheral blood samples and skin biopsies of eight patients without (MB-L) and with reactional episodes (ENL and RR) were studied using antibodies against B7-1, CD1b, DR and CD14 in flow-cytometry and immunohistochemistry experiments.

RESULTS

The flow-cytometry studies (mean +/- SD% of fluorescent cells) revealed significant B7-1 expression on PBMCs isolated from patients with ENL (8.0 +/- 0.6%) and RR (15.0 +/- 1.4%) compared with that observed for patients with MB-L (0.4 +/- 0.2%). Similar results were observed for cutaneous lesions of these patients by immunohistochemical assays. One patient studied before and during ENL revealed weak B7 expression before the reactional episode (0.3% of cells) compared with the marked level of B7-expressing cells detected during ENL (8.5% fluorescent cells). Interestingly, an even higher B7 expression (15% of cells) was observed in patients with RR.

CONCLUSIONS

Our results strongly suggest that B7 expression precedes reactional episodes in MB-L, which could be related to the acquisition of effective immunity to Mycobacterium leprae during reactional episodes in leprosy. We propose B7 expression as a marker of CMI response in reactional episodes in leprosy.

Mycobacterium leprae inhibits dendritic cell activation and maturation

Leprosy presents with a clinical spectrum of skin lesions that span from strong Th1-mediated cellular immunity and control of bacillary growth at one pole to poor Ag-specific T cell immunity with extensive bacillary load and Th2 cytokine-expressing lesions at the other. To understand how the immune response to Mycobacterium leprae is regulated, human dendritic cells (DC), potent inducers of adaptive immune responses, exposed to M. leprae, Mycobacterium tuberculosis (Mtb), and Mycobacterium bovis bacillus Calmette-Guerin (BCG) were studied for their ability to be activated and to prime T cell proliferation. In contrast with Mtb and BCG, M. leprae did not induce DC activation/maturation as measured by the expression of selected surface markers and proinflammatory cytokine production. In MLR, T cells did not proliferate in response to M. leprae-stimulated DC. Interestingly, M. leprae-exposed MLR cells secreted increased Th2 cytokines as well as similar Th1 cytokine levels as compared with Mtb- and BCG-exposed cells. Gene expression analysis revealed a reduction in levels of mRNA of DC activation and maturation markers following exposure to M. leprae. Our data suggest that M. leprae does not induce and probably suppresses in vitro DC maturation/activation, whereas Mtb and BCG are stimulatory.

Immunostimulatory activity of recombinant Mycobacterium bovis BCG that secretes major membrane protein II of Mycobacterium leprae

We previously demonstrated that major membrane protein II (MMP-II) is one of the immunodominant antigens (Ags) of Mycobacterium leprae capable of activating T cells through Toll-like receptor 2. Based on the observation that Mycobacterium bovis BCG secreting a 30-kDa protein offered better protection against tuberculosis, we constructed a recombinant BCG strain (BCG-SM) that secretes MMP-II to improve the potency of BCG against leprosy. The secreted MMP-II protein from BCG-SM stimulated monocyte-derived dendritic cells (DC) to produce interleukin-12. DC infected with BCG-SM expressed MMP-II on their surfaces, and MMP-II expression was suppressed by the pretreatment of DC with chloroquine. These results indicated that secreted MMP-II was processed by DC for higher expression levels on their surfaces. In addition, BCG-SM phenotypically activated DC and induced higher expression levels of major histocompatibility complex, CD86, and CD83 Ags on DC than did vector control BCG (BCG-pMV). The DC infected with BCG-SM more efficiently stimulated naïve and memory CD4+ T cells and memory CD8+ T cells to produce gamma interferon than did those infected with BCG-pMV. However, naïve CD8+ T cells were significantly activated only when they were stimulated with BCG-SM-infected DC. When CD8+ T cells were cocultured with BCG-SM-infected DC, the proportion of perforin-producing T cells was significantly higher than that in cells cocultured with BCG-pMV-infected DC. Moreover, MMP-II-specific memory T cells were more efficiently produced in mice inoculated with BCG-SM than in mice inoculated with BCG-pMV. Taken together, these results indicate that BCG capable of secreting the immunodominant Ag is more potent in the stimulation of T cells.

Contribution of GM-CSF on the enhancement of the T cell-stimulating activity of macrophages

Mycobacterium leprae is an intracellular parasitic organism that multiplies in macrophages (MØ). It inhibits the fusion of mycobacterial phagosome with lysosome and induces interleukin (IL)-10 production from macrophages. However, macrophages are heterogenous in various aspects. We examined macrophages that differentiated from monocytes using either recombinant (r) granulocyte-MØ colony-stimulating factor (GM-CSF) (these MØ are named as GM-MØ) or rMØ colony-stimulating factor (M-CSF) (cells named as M-MØ) in terms of the T cell-stimulating activity. Although both macrophages phagocytosed the mycobacteria equally, GM-MØ infected with M. leprae and subsequently treated with IFN-gamma- and CD40 ligand (L) stimulated T cells to produce interferon-gamma (IFN-gamma), but M-MØ lacked the ability to stimulate T cells. While M-MØ mounted a massive IL-10 production, GM-MØ did not produce the cytokine on infection with M. leprae. M. leprae-infected, IFN-gamma- and CD40L-treated GM-MØ expressed a higher level of HLA-DR and CD86 Ags than those of M-MØ, and expressed one of the dominant antigenic molecules of M. leprae, Major Membrane Protein-II on their surface. These results indicate that GM-CSF, but not M-CSF, contributes to the up-regulation of the T cell-stimulating activity of M. leprae-infected macrophages.

High-level expression of pseudogenes in Mycobacterium leprae

Recent studies have revealed that some RNAs are transcribed from noncoding DNA regions, including pseudogenes, and are functional as riboregulators. We have attempted to assess the gene expression profile throughout the Mycobacterium leprae genome using an array technique. Twelve highly expressed gene regions were identified that show an alteration in expression levels upon infection. Six of these were pseudogenes. Although M. leprae has an exceptional number and proportion of pseudogenes among species, our results suggest that some of the M. leprae pseudogenes are not just 'decayed' genes, but may have a functional role.

Impaired maturation and function of dendritic cells by mycobacteria through IL-1beta

Dendritic cells (DC) are pivotal for initiation and regulation of innate and adaptive immune responses evoked by vaccination and natural infection. After infection, mycobacterial pathogens first encounter monocytes, which produce pro-inflammatory cytokines, including IL-1beta, TNF-alpha and IL-6. The role of these cytokines in DC maturation remains incompletely understood. Here, we show that maturation of DC from monocytes was impaired by pretreatment of monocytes with low doses of IL-1beta. Under these conditions, Mycobacterium leprae-infected DC failed to stimulate antigen-specific T cell responses. Expression of CD86 and CD83 and production of IL-12 in response to lipopolysaccharide and peptidoglycan were diminished. In contrast, these DC functions were not impaired by pretreatment with TNF-alpha, IL-6 or IL-10. When monocytes were infected with M. bovis Bacillus Calmette-Guérin, and subsequently differentiated to DC, the activity of these DC was suppressed as well. Thus, IL-1beta acts at early stages of differentiation of DC and impairs biological functions of DC at later stages. Therefore, production of IL-1beta by mycobacteria-infected antigen-presenting cells counteracts effective stimulation of innate and adaptive immune responses.

The continuing challenges of leprosy

Leprosy is best understood as two conjoined diseases. The first is a chronic mycobacterial infection that elicits an extraordinary range of cellular immune responses in humans. The second is a peripheral neuropathy that is initiated by the infection and the accompanying immunological events. The infection is curable but not preventable, and leprosy remains a major global health problem, especially in the developing world, publicity to the contrary notwithstanding. Mycobacterium leprae remains noncultivable, and for over a century leprosy has presented major challenges in the fields of microbiology, pathology, immunology, and genetics; it continues to do so today. This review focuses on recent advances in our understanding of M. leprae and the host response to it, especially concerning molecular identification of M. leprae, knowledge of its genome, transcriptome, and proteome, its mechanisms of microbial resistance, and recognition of strains by variable-number tandem repeat analysis. Advances in experimental models include studies in gene knockout mice and the development of molecular techniques to explore the armadillo model. In clinical studies, notable progress has been made concerning the immunology and immunopathology of leprosy, the genetics of human resistance, mechanisms of nerve injury, and chemotherapy. In nearly all of these areas, however, leprosy remains poorly understood compared to other major bacterial diseases.

Identification of an Immunomodulating Agent from Mycobacterium leprae

A search for an immunomodulating agent from mycobacteria was carried out using Mycobacterium leprae. The antigenicity of each fraction of the bacterial membrane, which contains the most antigenic components of M. leprae, was assessed by using sera from paucibacillary leprosy. N-terminal sequencing of the serum-reactive protein and functional assessment of the membrane fractions using monocyte-derived dendritic cells (DCs) identified major membrane protein II (MMP-II) as one of the efficient T-cell-activating candidates. Purified MMP-II stimulated DCs from healthy individuals to produce interleukin-12 p70 and up-regulated the surface expression of major histocompatibility complex class I and II, CD86, and CD83 molecules. Also, there was an increase in the percentage of CD83(+) cells in the DC population. Furthermore, MMP-II-pulsed DCs expressed their derivatives on their surfaces. Using Toll-like receptor 2 (TLR-2)-dependent receptor constructs, we found that TLR-2 signaling was involved in DC maturation induced by MMP-II. Taken together, MMP-II can be recognized as an immunomodulating protein in terms of activation of antigen-presenting cells and innate immunity.

Human monocytes infected with Yersinia pestis express cell surface TLR9 and differentiate into dendritic cells

TLR9 recognizes DNA sequences containing hypomethylated CpG motifs and is a component of the innate immune system highly conserved during eukaryotic evolution. Previous reports suggested that the expression of TLR9 is restricted to plasmacytoid dendritic cells and B lymphocytes. Our results indicate that low levels of TLR9 are present on the cell surface of freshly isolated human monocytes, and expression is greatly increased by infection with Yersinia pestis. Enhanced cell surface TLR9 coincided with elevated levels of cytoplasmic TLR9 and recruitment of MyD88. Infected monocytes differentiated into mature dendritic cells, expressed IFN-alpha, and stimulated proliferative and cytotoxic T cell responses specific to Y. pestis. Furthermore, uninfected B cells and monocytes both increased cell surface TLR9, CD86, and HLA-DR in response to treatment with CpG-containing oligonucleotides, whereas cell surface TLR9 was down-modulated on infected dendritic cells by the addition of agonist oligonucleotide. Our results suggest that increased expression of TLR9 on the surface of infected cells may serve a role as an activation signal to other cells of the immune system.

Immunostimulatory activity of major membrane protein-II from Mycobacterium leprae

We examined the antigenicity of an immunomodulatory protein, major membrane protein (MMP)-II, from Mycobacterium leprae, since host defense against M. leprae largely depends on adaptive immunity. Both unprimed and memory T cells from healthy individuals were stimulated by autologous MMP-II-pulsed monocyte-derived dendritic cells (DCs) to produce IFN-gamma. The DC-mediated IFN-gamma production was dependent on the expression of MHC, CD86, and MMP-II antigens. Memory T cells from paucibacillary (PB) leprosy more extensively responded to MMP-II-pulsed DCs than T cells from healthy individuals, while comparable IFN-gamma was produced by unprimed T cells. Memory T cells from multibacillary leprosy, which are normally believed to be anergic, were activated similarly to those from healthy individuals by MMP-II-pulsed DCs. These results suggest that memory T cells from PB leprosy are primed with MMP-II prior to the manifestation of the disease, and MMP-II is highly antigenic in terms of activation of adaptive immunity.