Infection-induced apoptosis deletes bystander CD4+ T cells: a mechanism for suppression of autoimmunity during BCG infection

Structural Variability of Lipoarabinomannan Modulates Innate Immune Responses within Infected Alveolar Epithelial Cells

Mycobacterium tuberculosis (M. tb) is an intracellular pathogen persisting in phagosomes that has the ability to escape host immune surveillance causing tuberculosis (TB). Lipoarabinomannan (LAM), as a glycolipid, is one of the complex outermost components of the mycobacterial cell envelope and plays a critical role in modulating host responses during M. tb infection. Different species within the Mycobacterium genus exhibit distinct LAM structures and elicit diverse innate immune responses. However, little is known about the mechanisms. In this study, we first constructed a LAM-truncated mutant with fewer arabinofuranose (Araf) residues named M. sm-ΔM_6387 (Mycobacterium smegmatis arabinosyltransferase EmbC gene knockout strain). It exhibited some prominent cell wall defects, including tardiness of mycobacterial migration, loss of acid-fast staining, and increased cell wall permeability. Within alveolar epithelial cells (A549) infected by M. sm-ΔM_6387, the uptake rate was lower, phagosomes with bacterial degradation appeared, and microtubule-associated protein light chain 3 (LC3) recruitment was enhanced compared to wild type Mycobacterium smegmatis (M. smegmatis). We further confirmed that the variability in the removal capability of M. sm-ΔM_6387 resulted from host cell responses rather than the changes in the mycobacterial cell envelope. Moreover, we found that M. sm-ΔM_6387 or its glycolipid extracts significantly induced expression changes in some genes related to innate immune responses, including Toll-like receptor 2 (TLR2), class A scavenger receptor (SR-A), Rubicon, LC3, tumor necrosis factor alpha (TNF-α), Bcl-2, and Bax. Therefore, our studies suggest that nonpathogenic M. smegmatis can deposit LC3 on phagosomal membranes, and the decrease in the quantity of Araf residues for LAM molecules not only impacts mycobacterial cell wall integrity but also enhances host defense responses against the intracellular pathogens and decreases phagocytosis of host cells.

Efficacy of BCG vaccine in animal models of neurological disorders

The Bacillus Calmette-Guerin (BCG) vaccine can modulate the immune response via antigen-specific immune response, but also it can confer nonspecific protection and therapeutic benefits in several neurological conditions through different heterologous effects of vaccination. However, the precise mechanism of action of BCG remains unclear. In this review, different mechanisms underlying BCG-mediated immunity will be explained in animal models that reflects characteristic feature of neuroinflammatory and neurodegenerative disorders such as multiple sclerosis, Alzheimer's and Parkinson's diseases. Furthermore, evidence for a beneficial effect of the BCG on neuropsychiatric disorders, will be also discussed.

Mycobacterium bovis BCG-mediated suppression of Th17 response in mouse experimental autoimmune encephalomyelitis

INTRODUCTION

Multiple sclerosis (MS) is an autoimmune disease mediated by a pro-inflammatory immune response. Experimental autoimmune encephalomyelitis (EAE) induced by immunization of mice with a myelin oligodendrocyte glycoprotein (MOG) peptide emulsified in killed Mycobacterium tuberculosis-containing complete Freund's adjuvant (CFA-EAE) is used as a model of MS. Mycobacterium bovis BCG has been reported to ameliorate clinical symptoms of CFA-EAE, although the precise mechanism has not yet been documented. Since CFA-EAE uses adjuvant with mycobacterial antigens, mycobacterial antigen-specific T cells induced by CFA may cross-react with BCG and modulate EAE.

METHODS

To exclude the influence of cross-reactivity, a modified murine EAE model (cell wall skeleton (CWS)-EAE) that does not induce mycobacterial antigen-specific T cells was established and used to reevaluate the therapeutic effects of BCG on EAE.

RESULTS

Inoculation with BCG 6 d after CWS-EAE induction successfully ameliorated EAE symptoms, suggesting that the therapeutic effects of BCG are independent of the mycobacterial antigen-specific T cells induced by the CFA-EAE protocol. BCG inoculation into the CWS-EAE mice resulted in reduced levels of MOG-specific Th17 in the central nervous system (CNS) with reduced demyelinated lesions of the spinal cord. In the draining lymph nodes of the MOG-immunized sites, BCG inoculation resulted in an increase in MOG-specific Th17 and Th1 cells at an early stage of immune response.

CONCLUSION

The results suggest that BCG inoculation suppresses the Th17 response in the CNS of EAE mice via a mechanism that may involve the suppression of egress of encephalitogenic T cells from lymphoid organs.

BCG and protection against inflammatory and auto-immune diseases

INTRODUCTION

Bacillus Calmette-Guérin (BCG) is the only available vaccine against tuberculosis. Although its protective efficacy against pulmonary tuberculosis is still under debate, it provides protection against other mycobacterial diseases. BCG is also an effective therapy against superficial bladder cancer and potentially decreases overall childhood mortality. Areas covered: The purpose of this paper is to provide a state-of-the-art summary of the beneficial effects of BCG in inflammatory and auto-immune diseases. As a strong inducer of Th1 type immunity, BCG has been reported to protect against atopic conditions, such as allergic asthma, a Th2-driven disorder. Its protective effect has been well documented in mice, but still awaits definitive evidence in humans. Similarly, murine studies have shown a protective effect of BCG against auto-immune diseases, such as multiple sclerosis and insulin-dependent diabetes, but studies in humans have come to conflicting conclusions. Expert commentary: Studies in mice have shown a beneficial effect of the BCG vaccine against allergic asthma, multiple sclerosis and diabetes. However, the understanding of its mechanism is still fragmentary and requires further in depth research. Some observational or intervention studies in humans have also suggested a beneficial effect, but definitive evidence for this requires confirmation in carefully conducted prospective studies.

BCG and BCG/DNAhsp65 vaccinations promote protective effects without deleterious consequences for experimental autoimmune encephalomyelitis

A prime-boost strategy conserving BCG is considered the most promising vaccine to control tuberculosis. A boost with a DNA vaccine containing the mycobacterial gene of a heat shock protein (pVAXhsp65) after BCG priming protected mice against experimental tuberculosis. However, anti-hsp65 immunity could worsen an autoimmune disease due to molecular mimicry. In this investigation, we evaluated the effect of a previous BCG or BCG/pVAXhsp65 immunization on experimental autoimmune encephalomyelitis (EAE) development. Female Lewis rats were immunized with BCG or BCG followed by pVAXhsp65 boosters. The animals underwent EAE induction and were daily evaluated for weight loss and clinical score. They were euthanized during recovery phase to assess immune response and inflammatory infiltration at the central nervous system. Previous immunization did not aggravate or accelerate clinical score or weight loss. In addition, this procedure clearly decreased inflammation in the brain. BCG immunization modulated the host immune response by triggering a significant reduction in IL-10 and IFN-γ levels induced by myelin basic protein. These data indicated that vaccination protocols with BCG or BCG followed by boosters with pVAXhsp65 did not trigger a deleterious effect on EAE evolution.

[Diagnosis and management of adverse events occuring during BCG therapy for non-muscle invasive bladder cancer (NMIBC): review of the Cancer Committee of the French Association of Urology]

INTRODUCTION

Intravesical BCG immuno-therapy with maintenance therapy is considered as the standard treatment for non-muscle invasive bladder cancer with high risk of recurrence and progression. In practice, adverse events (AEs) of BCG therapy could restrict its prescription by urologists. The aim of this article was to present a review of these AEs and of their management.

MATERIALS AND METHODS

A bibliographic research in French and English using Medline(®) and Embase(®) with the keywords "BCG", "bladder", "complication", "toxicity", "adverse reaction", "prevention" and "treatment" was performed.

RESULTS

The main mechanism of AEs of BCG are infectious (cystitis, fever), immuno-allergic (granulomatous prostatitis, epididymo-orchitis, and granulomatous reactions) and auto-immune (arthralgies, rash). Management of AEs is based on their pathophysiological mechanisms. Classifications of BCG therapy AEs based on clinical features allow to adapt their treatments.

CONCLUSION

The combination of antibiotics directed against BCG, steroid or non-steroidal anti-inflammatory medication and symptomatic treatment is currently the triad on which is set up the appropriate treatment of severe AEs. Reductions of BCG doses and ofloxacin medication after instillation decrease the frequency and severity of minor and moderate AEs. Severe or more than 7 days long infectious AEs, immuno-allergic AEs or auto-immune during more than 7 days impose cessation of BCG immuno-therapy.

Adjuvant immunotherapy of experimental autoimmune encephalomyelitis: immature myeloid cells expressing CXCL10 and CXCL16 attract CXCR3+CXCR6+ and myelin-specific T cells to the draining lymph nodes rather than the central nervous system

CFA is a strong adjuvant capable of stimulating cellular immune responses. Paradoxically, adjuvant immunotherapy by prior exposure to CFA or live mycobacteria suppresses the severity of experimental autoimmune encephalomyelitis (EAE) and spontaneous diabetes in rodents. In this study, we investigated immune responses during adjuvant immunotherapy of EAE. Induction of EAE in CFA-pretreated mice resulted in a rapid influx into the draining lymph nodes (dLNs) of large numbers of CD11b(+)Gr-1(+) myeloid cells, consisting of immature cells with ring-shaped nuclei, macrophages, and neutrophils. Concurrently, a population of mycobacteria-specific IFN-γ-producing T cells appeared in the dLNs. Immature myeloid cells in dLNs expressed the chemokines CXCL10 and CXCL16 in an IFN-γ-dependent manner. Subsequently, CD4(+) T cells coexpressing the cognate chemokine receptors CXCR3 and CXCR6 and myelin oligodendrocyte glycoprotein (MOG)-specific CD4(+) T cells accumulated within the chemokine-expressing dLNs, rather than within the CNS. Migration of CD4(+) T cells toward dLN cells was abolished by depleting the CD11b(+) cells and was also mediated by the CD11b(+) cells alone. In addition to altering the distribution of MOG-specific T cells, adjuvant treatment suppressed development of MOG-specific IL-17. Thus, adjuvant immunotherapy of EAE requires IFN-γ, which suppresses development of the Th17 response, and diverts autoreactive T cells away from the CNS toward immature myeloid cells expressing CXCL10 and CXCL16 in the lymph nodes.

Th17 polarized cells from nonobese diabetic mice following mycobacterial adjuvant immunotherapy delay type 1 diabetes

IL-17-producing T cells are regarded as potential pathogenic T cells in the induction of autoimmune diseases. Previously, we have shown that injection of adjuvants containing Mycobacterium, such as CFA or bacillus Calmette-Guérin, can prevent type 1 diabetes in NOD mice. We injected NOD mice with mycobacterial products s.c. and analyzed the IL-17-producing cells from the draining lymph nodes and spleen by restimulating whole-cell populations or CD4(+) T cells in vitro with or without IL-17-polarizing cytokines. Mice receiving CFA had a concomitant rise in the level of IL-17, IL-22, IL-10, and IFN-gamma in the draining lymph node and spleen. Adoptive transfer of splenocytes from CFA-injected NOD mice polarized with TGF-beta plus IL-6 or IL-23 delayed the development of diabetes in recipient mice. IL-17-producing cells induced by CFA maintained their IL-17-producing ability in the recipient mice. Injection of CFA also changed the cytokine profile of cells in pancreatic tissue by increasing IL-17, IL-10, and IFN-gamma cytokine gene expression. We suggest that the rise in the level of IL-17 after adjuvant therapy in NOD mice has a protective effect on type 1 diabetes development.

Mycobacteria-induced suppression of autoimmunity in the central nervous system

Mycobacterial suppression of central nervous system (CNS) autoimmunity has been demonstrated in various experimental models, epidemiological studies, and clinical trials. Recent studies have led to an increased understanding of the cellular and molecular interactions involved in the pathogenesis of autoimmune diseases and of mycobacterial immunity. Here, we review some of the mechanisms by which mycobacterial infection might modulate the clinical course of CNS autoimmunity. A more complete understanding of these mechanisms may lead to the development of novel immunotherapeutic tools for treating autoimmune diseases.

Genetic deficiency of Irgm1 (LRG-47) suppresses induction of experimental autoimmune encephalomyelitis by promoting apoptosis of activated CD4+ T cells

The immunity-related GTPase Irgm1, also called LRG-47, is known to regulate host resistance to intracellular pathogens through multiple mechanisms that include controlling the survival of T lymphocytes. Here, we address whether Irgm1 also plays a role in the pathogenesis of experimental autoimmune encephalitis (EAE). We find that Irgm1/LRG-47 is a significant factor in the progression of EAE and multiple sclerosis (MS). Expression of Irgm1 was robustly elevated in MS-affected lesions and in the central nervous system (CNS) of myelin basic protein (MBP)-induced EAE mice, especially in cells of lymphoid and mononuclear phagocyte origin. Homozygous Irgm1 null mice were resistant to MBP-induced EAE, and CD4(+) T cells in spleen and CNS of these mice displayed decreased proliferative capacity, increased apoptosis, and up-regulated interferon (IFN)-gamma induction. Therefore, Irgm1-induced survival of autoreactive CD4(+) T cells contributes significantly to the pathogenesis of EAE. Blockade of Irgm1 may be a potential therapeutic strategy for halting multiple sclerosis.

Mycobacterium bovis bacille Calmette-Guérin infection in the CNS suppresses experimental autoimmune encephalomyelitis and Th17 responses in an IFN-gamma-independent manner

Multiple sclerosis and an animal model resembling multiple sclerosis, experimental autoimmune encephalomyelitis (EAE), are inflammatory demyelinating diseases of the CNS that are suppressed by systemic mycobacterial infection in mice and BCG vaccination in humans. Host defense responses against Mycobacterium in mice are influenced by T lymphocytes and their cytokine products, particularly IFN-gamma, which plays a protective regulatory role in EAE. To analyze the counter-regulatory role of mycobacterial infection-induced IFN-gamma in the CNS on the function of the pathological Th17 cells and the clinical outcome of EAE, we induced EAE in mice that were intracerebrally infected with Mycobacterium bovis bacille Calmette-Guerin (BCG). In this study, we demonstrate that intracerebral (i.c.) BCG infection prevented inflammatory cell recruitment to the spinal cord and suppressed the development of EAE. Concomitantly, there was a significant decrease in the frequency of myelin oligodendrocyte glycoprotein-specific IFN-gamma-producing CD4(+) T cells in the CNS. IL-17(+)CD4(+) T cell responses were significantly suppressed in i.c. BCG-infected mice following EAE induction regardless of T cell specificity. The frequency of Foxp3(+)CD4(+) T cells in these mice was equivalent to that of control mice. Intracerebral BCG infection-induced protection of EAE and suppression of myelin oligodendrocyte glycoprotein-specific IL-17(+)CD4(+) T cell responses were similar in both wild-type and IFN-gamma-deficient mice. These data show that live BCG infection in the brain suppresses CNS autoimmunity. These findings also reveal that the regulation of Th17-mediated autoimmunity in the CNS can be independent of IFN-gamma-mediated mechanisms.

Autoimmune Processes in the Central Nervous System

In this chapter we discuss the factors that contribute to the unique immunological environment of the central nervous system and the mechanisms that may account for the development of autoimmunity within the CNS, including infectious agents as inducers of autoimmune disease. Consideration is given to a variety of human neurological diseases of autoimmune or presumed autoimmune etiology: autism, neuromyelitis optica, neuromyotonia, schizophrenia, lethargic encephalitis and stiff‐man syndrome. Also, we discuss autoimmunity as a possible mediator of CNS repair and examples of the protective effects of bacterial and helminth infections on CNS disease. Multiple sclerosis and models of multiple sclerosis are discussed with special attention given to the Theiler's virus‐induced demyelination model.

Bystander macrophage apoptosis after Mycobacterium tuberculosis H37Ra infection

Human macrophages infected with Mycobacterium tuberculosis may undergo apoptosis. Macrophage apoptosis contributes to the innate immune response against M. tuberculosis by containing and limiting the growth of mycobacteria and also by depriving the bacillus of its niche cell. Apoptosis of infected macrophages is well documented; however, bystander apoptosis of uninfected macrophages has not been described in the setting of M. tuberculosis. We observed that uninfected human macrophages underwent significant bystander apoptosis 48 and 96 h after they came into contact with macrophages infected with avirulent M. tuberculosis. The bystander apoptosis was significantly greater than the background apoptosis observed in uninfected control cells cultured for the same length of time. There was no evidence of the involvement of tumor necrosis factor alpha, Fas, tumor necrosis factor-related apoptosis-inducing ligand, transforming growth factor beta, Toll-like receptor 2, or MyD88 in contact-mediated bystander apoptosis. This newly described phenomenon may further limit the spread of M. tuberculosis by eliminating the niche cells on which the bacillus relies.

Cutting edge: Complement (C3d)-linked antigens break B cell anergy

C3dg adducts of Ag can coligate complement receptor type 2 (CR2; CD21) and the B cell Ag receptor. This interaction significantly amplifies BCR-mediated signals in Ag-naive wild-type mice, lowering the threshold for B cell activation and the generation of humoral immune responses as much as 1000-fold. In this study we demonstrate that CR2-mediated complementation of BCR signals can also overcome B cell anergy. Unlike Ag alone, BCR/CR2 costimulation (Ars-CCG/C3dg complexes) of anergic Ars/A1 B cells led to Ca(2+) mobilization in vitro and the production of autoantibodies in vivo. Interestingly, the in vivo immune response of anergic cells occurs without the formation of germinal centers. These results suggest that the Ag unresponsiveness of anergic B cells can be overcome by cross-reactive (self-mimicking) Ags that have been complement-opsonized. This mechanism may place individuals exposed to complement-fixing bacteria at risk for autoimmunity.

CD1d expression on hemopoietic cells promotes CD4+ Th1 response in coxsackievirus B3 induced myocarditis

Coxsackievirus B3 induced murine myocarditis depends upon CD1d expression and upon a population of CD1d-restricted Vgamma4+ T cells. Infection upregulates CD1d expression in CD4+ T cells. Bone marrow chimeras were made between BALB/c and BALB/c CD1d-/- mice and showed that CD1d expression in either hemopoietic and non-hemopoietic cells induces myocarditis, although CD1d expression on hemopoietic cells was more effective in increasing Vgamma4+ cell numbers and activation, and CD4+ IFNgamma+ cell response than CD1d expression on non-hemopoietic cells. Co-culture of enriched CD4+ cells from infected CD1d-/- and BALB/c mice with Vgamma4+ T cells demonstrated that the Vgamma4+ cells bias the CD4+ cell response to the Th1 phenotype through CD1d. Anti-CD1d antibody effectively blocked promotion of IFNgamma expression by the CD4+ cell population. These results show that Vgamma4+ cells modulate developing adaptive immunity through recognition of CD1d on CD4+ T cells, and that this interaction, more than Vgamma4+ cell interaction with infected cardiocytes, determines pathogenicity.