Differential effects of TNF and LTalpha in the host defense against M. bovis BCG

Mycobacterium tuberculosis PE17 (Rv1646) promotes host cell apoptosis via host chromatin remodeling mediated by reduced H3K9me3 occupancy

Tuberculosis caused by Mycobacterium tuberculosis remains a serious global public health threat. M. tuberculosis PE and PPE proteins are closely involved in pathogen-host interaction. To explore the predicted function of the M. tuberculosis PE17 (Rv1646), we heterologously expressed PE17 in a non-pathogenic Mycobacterium smegmatis strain (Ms_PE17). PE17 can reduce the survival of M. smegmatis within macrophages associated with altering the transcription levels of inflammatory cytokines IL1β, IL6, TNFα, and IL10 in Ms_PE17 infected macrophages through JNK signaling. Furthermore, macrophages apoptosis was increased upon Ms_PE17 infection in a caspases-dependent manner, accompanied by the activation of the Endoplasmic Reticulum stress IRE1α/ASK1/JNK signaling pathway. This can be largely interpreted by the epigenetic changes through reduced H3K9me3 chromatin occupancy post Ms_PE17 infection. To our knowledge, this is the first report that PE17 altered the macrophages apoptosis via H3K9me3 mediated chromatin remodeling.

TNF-α antagonists differentially induce TGF-β1-dependent resuscitation of dormant-like Mycobacterium tuberculosis

TNF-α- as well as non-TNF-α-targeting biologics are prescribed to treat a variety of immune-mediated inflammatory disorders. The well-documented risk of tuberculosis progression associated with anti-TNF-α treatment highlighted the central role of TNF-α for the maintenance of protective immunity, although the rate of tuberculosis detected among patients varies with the nature of the drug. Using a human, in-vitro granuloma model, we reproduce the increased reactivation rate of tuberculosis following exposure to Adalimumab compared to Etanercept, two TNF-α-neutralizing biologics. We show that Adalimumab, because of its bivalence, specifically induces TGF-β1-dependent Mycobacterium tuberculosis (Mtb) resuscitation which can be prevented by concomitant TGF-β1 neutralization. Moreover, our data suggest an additional role of lymphotoxin-α–neutralized by Etanercept but not Adalimumab–in the control of latent tuberculosis infection. Furthermore, we show that, while Secukinumab, an anti-IL-17A antibody, does not revert Mtb dormancy, the anti-IL-12-p40 antibody Ustekinumab and the recombinant IL-1RA Anakinra promote Mtb resuscitation, in line with the importance of these pathways in tuberculosis immunity.

Mycobacterium tuberculosis (Mtb) is the world’s leading infectious killer. Multi-cellular immune structures called granulomas may constitute a latent form of Mtb infection and a potential reservoir for future cases. Post-marketing surveillance data suggested that Mtb protective immunity is unequally impacted by different TNF-α-targeting drugs used to treat inflammatory disorders. We used an in-vitro granuloma model to reproduce these clinical observations and gain mechanistic insights and, in addition, to assess the risk of tuberculosis reactivation associated with the use of other immunomodulatory drugs. These results may inspire pharmacologists to design future drug-development strategies of biologics in particular, while immunologists and microbiologists will find a relevant experimental approach to disentangle the complex interactions involved in Mtb protective immunity and immunopathogenesis.

Insights into ligand binding by a viral tumor necrosis factor (TNF) decoy receptor yield a selective soluble human type 2 TNF receptor

Etanercept is a soluble form of the tumor necrosis factor receptor 2 (TNFR2) that inhibits pathological tumor necrosis factor (TNF) responses in rheumatoid arthritis and other inflammatory diseases. However, besides TNF, etanercept also blocks lymphotoxin-α (LTα), which has no clear therapeutic value and might aggravate some of the adverse effects associated with etanercept. Poxviruses encode soluble TNFR2 homologs, termed viral TNF decoy receptors (vTNFRs), that display unique specificity properties. For instance, cytokine response modifier D (CrmD) inhibits mouse and human TNF and mouse LTα, but it is inactive against human LTα. Here, we analyzed the molecular basis of these immunomodulatory activities in the ectromelia virus-encoded CrmD. We found that the overall molecular mechanism to bind TNF and LTα from mouse and human origin is fairly conserved in CrmD and dominated by a groove under its 50s loop. However, other ligand-specific binding determinants optimize CrmD for the inhibition of mouse ligands, especially mouse TNF. Moreover, we show that the inability of CrmD to inhibit human LTα is caused by a Glu-Phe-Glu motif in its 90s loop. Importantly, transfer of this motif to etanercept diminished its anti-LTα activity in >60-fold while weakening its TNF-inhibitory capacity in 3-fold. This new etanercept variant could potentially be used in the clinic as a safer alternative to conventional etanercept. This work is the most detailed study of the vTNFR-ligand interactions to date and illustrates that a better knowledge of vTNFRs can provide valuable information to improve current anti-TNF therapies.

Mycobacterium tuberculosis PE_PGRS41 Enhances the Intracellular Survival of M. smegmatis within Macrophages Via Blocking Innate Immunity and Inhibition of Host Defense

The success of Mycobacterium tuberculosis (M. tuberculosis) as a pathogen is largely contributes to its ability to manipulate the host immune responses. The genome of M. tuberculosis encodes multiple immune-modulatory proteins, including several members of the multi-genic PE_PPE family. Despite of intense research, the roles of PE_PGRS proteins in mycobacterial pathogenesis remain elusive. The function of M. tuberculosis PE_PGRS41, characterized by an extended and unique C-terminal domain, was studied. Expression of PE_PGRS41 in Mycobacterium smegmatis, a non-pathogenic species intrinsically deficient of PE_PGRS, severely impaired the resistance of the recombinant to multiple stresses via altering the cell wall integrity. Macrophages infected by M. smegmatis harboring PE_PGRS41 decreased the production of TNF-α, IL-1β and IL-6. In addition, PE_PGRS41 boosted the survival of M. smegmatis within macrophage accompanied with enhanced cytotoxic cell death through inhibiting the cell apoptosis and autophagy. Taken together, these results implicate that PE_PGRS41 is a virulence factor of M. tuberculosis and sufficient to confer pathogenic properties to M. smegmatis.

Tumor Necrosis Factor and Its Receptors Are Crucial to Control Mycobacterium bovis Bacillus Calmette-Guerin Pleural Infection in a Murine Model

Tumor necrosis factor (TNF) is crucial to control Mycobacterium tuberculosis infection, which remains a leading cause of morbidity and mortality worldwide. TNF blockade compromises host immunity and may cause reactivation of latent infection, resulting in overt pulmonary, pleural, and extrapulmonary tuberculosis. Herein, we investigate the roles of TNF and TNF receptors in the control of Mycobacterium bovis bacillus Calmette-Guerin (BCG) pleural infection in a murine model. As controls, wild-type mice and those with a defective CCR5, a receptor that is crucial for control of viral infection but not for tuberculosis, were used. BCG-induced pleural infection was uncontrolled and progressive in absence of TNF or TNF receptor 1 (TNFR1)/TNFR2 (TNFR1R2) with increased inflammatory cell recruitment and bacterial load in the pleural cavity, and heightened levels of pleural and serum proinflammatory cytokines and chemokines, compared to wild-type control mice. The visceral pleura was thickened with chronic inflammation, which was prominent in TNF(-/-) and TNFR1R2(-/-) mice. The parietal pleural of TNF(-/-) and TNFR1R2(-/-) mice exhibited abundant inflammatory nodules containing mycobacteria, and these mice developed nonresolving inflammation and succumbed from disseminated BCG infection. By contrast, CCR5(-/-) mice survived and controlled pleural BCG infection as wild-type control mice. In conclusion, BCG-induced pleurisy was uncontrolled in the absence of TNF or TNF receptors with exacerbated inflammatory response, impaired bacterial clearance, and defective mesothelium repair, suggesting a critical role of TNF to control mycobacterial pleurisy.

Immunity against Mycobacterium tuberculosis and the risk of biologic anti-TNF-α reagents

A third of the world's population is exposed to Mycobacterium tuberculosis in their lifetime. Over eight million people develop a tuberculosis (TB) illness and 1.3 million people die from the disease every year. Acquired immunity (cytotoxic CD8+ T cells (CBT), Th1 CD4+ helper T cells) macrophages, and dendritic cells all play important roles in TB infection. Recently, it is well established that innate immunity as well plays a definitive role in the development of TB immunity under the effects of several cytokines, microbicidal proteins and Toll-like receptors. Meanwhile, the introduction and widespread use of biological disease-modifying anti-rheumatic reagents over the last 15 years worldwide has dramatically advanced and improved the standard care and prognosis of patients with rheumatoid arthritis (RA) and juvenile idiopathic arthritis (JIA). However, as clinical experience with these drugs has grown, the risk of granulomatous infections, especially disseminated TB and fungal infections, has become apparent, especially because having RA or JIA may innately increase the risk of infection (bacterial, viral and fungal). The knowledge of basic immunology has also advanced over the past 10 years and adult and pediatric rheumatologists should increase their understanding of this dynamic between arthritis diseases, anti-TNF-α medications, and TB. This review will provide an up-to-date discussion of both the immunology of the TB organism in the human host and the pathophysiologic mechanisms of the TNF-α blockers in the development of secondary (disseminated) tuberculosis.

Prominent role for T cell-derived tumour necrosis factor for sustained control of Mycobacterium tuberculosis infection

Tumour Necrosis Factor (TNF) is critical for host control of M. tuberculosis, but the relative contribution of TNF from innate and adaptive immune responses during tuberculosis infection is unclear. Myeloid versus T-cell-derived TNF function in tuberculosis was investigated using cell type-specific TNF deletion. Mice deficient for TNF expression in macrophages/neutrophils displayed early, transient susceptibility to M. tuberculosis but recruited activated, TNF-producing CD4⁺ and CD8⁺ T-cells and controlled chronic infection. Strikingly, deficient TNF expression in T-cells resulted in early control but susceptibility and eventual mortality during chronic infection with increased pulmonary pathology. TNF inactivation in both myeloid and T-cells rendered mice critically susceptible to infection with a phenotype resembling complete TNF deficient mice, indicating that myeloid and T-cells are the primary TNF sources collaborating for host control of tuberculosis. Thus, while TNF from myeloid cells mediates early immune function, T-cell derived TNF is essential to sustain protection during chronic tuberculosis infection.

T Cell Activation and Proinflammatory Cytokine Production in Clinically Cured Tuberculosis Are Time-Dependent and Accompanied by Upregulation of IL-10

Background

Th1 cytokines are essential for the control of M. tuberculosis infection. The role of IL-10 in tuberculosis is controversial and there is an increasing body of evidence suggesting that the relationship between Th1 cytokines and IL-10 is not as antagonistic as it was first believed, and that these cytokines may complement each other in infectious diseases.

Methods

The present study evaluated the activating capacity of CD4+ and CD8+ T cell repertoire in response to antigen stimulation through the expression of CD69 using Flow Cytometry, as well as the functionality of PBMCs by determining the cytokine profile in patients with active tuberculosis and in clinically cured patients after in vitro stimulation using ELISA. Treated patients were subdivided according to time after clinical cure (<12 months or >12 months post-treatment).

Results

We observed that T cell activation was higher in TB-treated patients, especially CD8+ T cell activation in TB-Treated >1 year. Th1 cytokines were significantly higher in TB-Treated, and the levels of IFN-γ and TNF-α increased continuously after clinical cure. Moreover, IL-10 production was significantly higher in cured patients and it was also enhanced in cured patients over time after treatment. Th17, Th2 and Th22 cytokines showed no statistically significant differences between Healthy Donors, Active-TB and TB-Treated.

Conclusions

This study describes a scenario in which potentiation of CD4+ and CD8+ T cell activation and increased Th1 cytokine production are associated with the clinical cure of tuberculosis in the absence of significant changes in Th2 cytokine production and is accompanied by increased production of IL-10. In contrast to other infections with intracellular microorganisms, this response occurs later after the end of treatment.

Mycobacteria and biological response modifiers: two sides of the relationship

With increasing use of biological response modifiers (BRMs) for various systemic inflammatory diseases there is a need to be vigilant about complications with the use of these therapies. It is important to have appropriate screening for the infections in patients requiring BRMs. However, many studies have reported benefits of certain BRMs in the treatment of infections such as tuberculosis as adjuncts. Continued research and technical advances in immunogenetics helps understand complex mechanisms in the usage of the BRMs. This article summarizes the different aspects of the relationship between mycobacterial infections and the use of various BRMs for inflammatory conditions.

Leprosy and the human genome

Despite the availability of effective treatment for several decades, leprosy remains an important medical problem in many regions of the world. Infection with Mycobacterium leprae can produce paucibacillary disease, characterized by well-formed granulomas and a Th1 T-cell response, or multibacillary disease, characterized by poorly organized cellular infiltrates and Th2 cytokines. These diametric immune responses confer states of relative resistance or susceptibility to leprosy, respectively, and have well-defined clinical manifestations. As a result, leprosy provides a unique opportunity to dissect the genetic basis of human in vivo immunity. A series of studies over the past 40 years suggests that host genes influence the risk of leprosy acquisition and the predilection for different clinical forms of the disease. However, a comprehensive, cellular, and molecular view of the genes and variants involved is still being assembled. In this article, we review several decades of human genetic studies of leprosy, including a number of recent investigations. We emphasize genetic analyses that are validated by the replication of the same phenotype in independent studies or supported by functional experiments demonstrating biological mechanisms of action for specific polymorphisms. Identifying and functionally exploring the genetic and immunological factors that underlie human susceptibility to leprosy have yielded important insights into M. leprae pathogenesis and are likely to advance our understanding of the immune response to other pathogenic mycobacteria. This knowledge may inform new treatment or vaccine strategies for leprosy or tuberculosis.

Limited role for lymphotoxin α in the host immune response to Mycobacterium tuberculosis

The contribution of lymphotoxin (LT)α in the host immune response to virulent Mycobacterium tuberculosis and Mycobacterium bovis bacillus Calmette-Guérin infections was investigated. Despite their ability to induce Th1 cytokine, IFN-γ, and IL-12 pulmonary response, "conventional" LTα(-/-) mice succumb rapidly to virulent M. tuberculosis aerosol infection, with uncontrolled bacilli growth, defective granuloma formation, necrosis, and reduced pulmonary inducible NO synthase expression, similar to TNF(-/-) mice. Contributions from developmental lymphoid abnormalities in LTα(-/-) mice were excluded because hematopoietic reconstitution with conventional LTα(-/-) bone marrow conferred enhanced susceptibility to wild-type mice, comparable to conventional LTα(-/-) control mice. However, conventional LTα(-/-) mice produced reduced levels of TNF after M. bovis bacillus Calmette-Guérin infection, and their lack of control of mycobacterial infection could be due to a defective contribution of either LTα or TNF, or both, to the host immune response. To address this point, the response of "neo-free" LTα(-/-) mice with unperturbed intrinsic TNF expression to M. tuberculosis infection was investigated in a direct comparative study with conventional LTα(-/-) mice. Strikingly, although conventional LTα(-/-) mice were highly sensitive, similar to TNF(-/-) mice, neo-free LTα(-/-) mice controlled acute M. tuberculosis infection essentially as wild-type mice. Pulmonary bacterial burden and inflammation was, however, slightly increased in neo-free LTα(-/-) mice 4-5 mo postinfection, but importantly, they did not succumb to infection. Our findings revise the notion that LTα might have a critical role in host defense to acute mycobacterial infection, independent of TNF, but suggest a contribution of LTα in the control of chronic M. tuberculosis infection.

Accelerated thymic atrophy as a result of elevated homeostatic expression of the genes encoded by the TNF/lymphotoxin cytokine locus

TNF, lymphotoxin (LT)-alpha, LT-beta and LIGHT are members of a larger superfamily of TNF-related cytokines that can cross-utilize several receptors. Although LIGHT has been implicated in thymic development and function, the role of TNF and LT remains incompletely defined. To address this, we created a model of modest homeostatic overexpression of TNF/LT cytokines using the genomic human TNF/LT locus as a low copy number Tg. Strikingly, expression of Tg TNF/LT gene products led to profound early thymic atrophy characterized by decreased numbers of thymocytes and cortical thymic epithelial cells, partial block of thymocyte proliferation at double negative (DN) 1 stage, increased apoptosis of DN2 thymocytes and severe decline of T-cell numbers in the periphery. Results of backcrossing to TNFR1-, LTbetaR- or TNF/LT-deficient backgrounds and of reciprocal bone marrow transfers implicated both LT-alpha/LT-beta to LTbetaR and TNF/LT-alpha to TNFR1 signaling in accelerated thymus degeneration. We hypothesize that chronic infections can promote thymic atrophy by upregulating LT and TNF production.

An ENU-induced mutation in the lymphotoxin alpha gene impairs organogenesis of lymphoid tissues in C57BL/6 mice

The TNF family is critical for development of lymphoid organs and plays significant roles in regulation of innate and adoptive immune responses. Here, we describe a novel N-ethyl-N-nitrosourea (ENU)-induced mutant strain, HLB382, with a point mutation in the Lta gene, which encodes lymphotoxin (LT) alpha, a member of the TNF family. Mutant mice had no lymph nodes and no Peyer's patches. Microscopically, the spleens had disordered follicles and no germinal centers or discernible marginal zones (MZ). While the development of T cells and follicular B cells was normal, the numbers of NK and MZ B cells were significantly reduced. Interestingly, the numbers of peritoneal B1b cells were significantly increased. Genomic DNA sequences revealed a single base pair insertion in the coding region of Lta resulting in a frame shift and a premature stop codon. This new strain provides opportunities for understanding the full range of Lta gene function on a pure C57BL/6 background.

Differential effects of pyrrolidine dithiocarbamate on TNF-alpha-mediated liver injury in two different models of fulminant hepatitis

BACKGROUND/AIMS

Pyrrolidine dithiocarbamate (PDTC) is an inhibitor of nuclear factor kappa B (NF-kappaB) activation. The present study aimed to investigate the effects of PDTC on lipopolysaccharide (LPS)-induced liver injury in two different models of fulminant hepatitis.

METHODS

Mice infected with Bacillus Calmette Guerin (BCG) were challenged with LPS (0.2 mg/kg) to induce the model of inflammatory liver injury. Mice were injected with D-galactosamine (GalN, 600 mg/kg) and LPS (20 microg/kg) to induce the model of apoptotic liver injury. In the treatment groups, mice were pre-treated with PDTC (100 mg/kg), initiated 24 h prior to LPS.

RESULTS

PDTC pretreatment reduced the infiltration of inflammatory cells, inhibited NF-kappaB activation and the expression of tumor necrosis factor alpha (TNF-alpha), attenuated nitric oxide production, and alleviated hepatic glutathione depletion. Correspondingly, PDTC reduced serum alanine aminotransferase, improved hepatic necrosis, and prolonged the survival in the BCG/LPS model. Conversely, PDTC accelerated death and aggravated liver apoptosis in the GalN/LPS model, although it reduced nitric oxide production, attenuated glutathione depletion, and inhibited the expression of TNF-alpha in liver.

CONCLUSIONS

PDTC protects mice against BCG/LPS-induced inflammatory liver injury through the repression of NF-kappaB-mediated TNF-alpha release, while it seems to be detrimental in GalN/LPS-induced apoptotic liver damage.

Bovine TB and the development of new vaccines

Bovine tuberculosis (bTB) is caused by Mycobacterium bovis. The incidence of bTB is increasing in cattle herds of developed countries that have a wild life reservoir of M. bovis, such as the UK, New Zealand and the USA. The increase in the incidence of bTB is thought to be due, at least in part, to a wildlife reservoir of M. bovis. M. bovis is also capable of infecting humans and on a worldwide basis, M. bovis is thought to account for up to 10% of cases of human TB [Cosivi O, Grange JM, Daborn CJ et al. Zoonotic tuberculosis due to Mycobacterium bovis in developing countries. Emerg Infect Dis 1998;4(1):59-70]. Thus, the increased incidence of bTB, besides being a major economic problem, poses an increased risk to human health. In the UK, the incidence of bTB continues to rise despite the use of the tuberculin test and slaughter control policy, highlighting the need for improved control strategies. Vaccination of cattle, in combination with more specific and sensitive diagnostic tests, is suggested as the most effective strategy for bovine TB control. The only vaccine currently available for human and bovine TB is the live attenuated Bacille Calmette Guerin (BCG). BCG is thought to confer protection through the induction of Th1 responses against mycobacteria. However, protection against TB conferred by BCG is variable and to this date the reasons for the successes and failures of BCG are not clear. Therefore, there is a need to develop vaccines that confer greater and more consistent protection against bTB than that afforded by BCG. Given that BCG is currently the only licensed vaccine against human TB, it is likely that any new vaccine or vaccination strategy will be based around BCG. In this review we discuss immune responses elicited by mycobacteria in cattle and the novel approaches emerging for the control of bovine TB based on our increasing knowledge of protective immune responses.

Characterization of the deregulated immune activation occurring at late stages of mycobacterial infection in TNF-deficient mice

In the absence of TNF, mice infected with Mycobacterium avium suffer a peculiar disintegration of the granulomas, with extensive apoptosis and necrosis of their cells, occurring during the course of the infection and leading to the death of the animals within a few days of its onset. The survival time depends on the virulence of the infecting strain as well as on the dose and route of infection. Intravenously infected mice developed the typical lesions in hepatic granulomas whereas aerosol-infected animals developed them in the lung granulomas. At the onset of the development of pulmonary granuloma disintegration, extensive expansion of T cells, with intense up-regulation of activation markers, massive exacerbation of their ability to secrete IFN-gamma, and increased cytotoxic activity of both CD4(+) and CD8(+) T cells were observed. Forced expression of Bcl2 did not prevent the early death of infected TNF-deficient mice leading merely to a modest increase in survival times. The expression of the FasL on T cells was not affected but there was an intense up-regulation of the TRAIL in T cells and, in particular, myeloid cells. We thus show that an exacerbated immune response occurs in TNF-deficient hosts during M. avium infections that leads to enhanced IFN-gamma production and late up-regulation of TRAIL which may contribute to granuloma disintegration.

Reactivation of latent tuberculosis by TNF blockade: the role of interferon gamma

Tumor necrosis factor (TNF) plays a pathogenic role in psoriasis and rheumatoid arthritis but is essential for host defenses against mycobacteria and other granulomatous pathogens. The risk of reactivation of latent Mycobacterium tuberculosis infection is significantly greater with the TNF monoclonal antibody infliximab than with the soluble TNF-receptor etanercept. We have examined the biologic basis of this difference using whole blood culture. Infliximab and adalimumab reduced the proportion of T buciclate-responsive cells by 70 and 50%, respectively, and suppressed antigen-induced IFN-gamma production by 70 and 64%. In contrast, etanercept produced no significant effect. The difference between infliximab and etanercept remained whether one compared equal or peak therapeutic drug concentrations, suggesting a relationship to mechanism of action rather than pharmacokinetics. Adalimumab and etanercept caused divergent, concentration dependent effects on control of intracellular growth of M. tuberculosis. None of the drugs induced significant levels of apoptosis or necrosis in monocytes or T cells, excluding T-cell death as a mechanism for suppression of antigen-induced responses. IL-10 production was equally suppressed by all three drugs, excluding excess IL-10 as a regulatory mechanism. The tuberculosis risk posed by infliximab may reflect its combined effects on TNF and IFNgamma.

Stepwise replication identifies a low-producing lymphotoxin-alpha allele as a major risk factor for early-onset leprosy

Host genetics has an important role in leprosy, and variants in the shared promoter region of PARK2 and PACRG were the first major susceptibility factors identified by positional cloning. Here we report the linkage disequilibrium mapping of the second linkage peak of our previous genome-wide scan, located close to the HLA complex. In both a Vietnamese familial sample and an Indian case-control sample, the low-producing lymphotoxin-alpha (LTA)+80 A allele was significantly associated with an increase in leprosy risk (P = 0.007 and P = 0.01, respectively). Analysis of an additional case-control sample from Brazil and an additional familial sample from Vietnam showed that the LTA+80 effect was much stronger in young individuals. In the combined sample of 298 Vietnamese familial trios, the odds ratio of leprosy for LTA+80 AA/AC versus CC subjects was 2.11 (P = 0.000024), which increased to 5.63 (P = 0.0000004) in the subsample of 121 trios of affected individuals diagnosed before 16 years of age. In addition to identifying LTA as a major gene associated with early-onset leprosy, our study highlights the critical role of case- and population-specific factors in the dissection of susceptibility variants in complex diseases.

Mycobacterium tuberculosis subverts innate immunity to evade specific effectors

The macrophage is the niche of the intracellular pathogen Mycobacterium tuberculosis. Induction of macrophage apoptosis by CD4(+) or CD8(+) T cells is accompanied by reduced bacterial counts, potentially defining a host defense mechanism. We have already established that M. tuberculosis-infected primary human macrophages have a reduced susceptibility to Fas ligand (FasL)-induced apoptosis. To study the mechanisms by which M. tuberculosis prevents apoptotic signaling, we have generated a cell culture system based on PMA- and IFN-gamma-differentiated THP-1 cells recapitulating the properties of primary macrophages. In these cells, nucleotide-binding oligomerization domain 2 or TLR2 agonists and mycobacterial infection protected macrophages from apoptosis and resulted in NF-kappaB nuclear translocation associated with up-regulation of the antiapoptotic cellular FLIP. Transduction of a receptor-interacting protein-2 dominant-negative construct showed that nucleotide-binding oligomerization domain 2 is not involved in protection in the mycobacterial infection system. In contrast, both a dominant-negative construct of the MyD88 adaptor and an NF-kappaB inhibitor abrogated the protection against FasL-mediated apoptosis, showing the implication of TLR2-mediated activation of NF-kappaB in apoptosis protection in infected macrophages. The apoptosis resistance of infected macrophages might be considered as an immune escape mechanism, whereby M. tuberculosis subverts innate immunity signaling to protect its host cell against FasL(+)-specific cytotoxic lymphocytes.

Activation of mouse natural killer T cells accelerates liver regeneration after partial hepatectomy

BACKGROUND & AIMS

Activation of natural killer T cells with the synthetic ligand alpha-galactosylceramide (alpha-GalCer) induced hepatotoxicity through the tumor necrosis factor (TNF) and Fas-ligand-mediated pathway in aged mice. The aim of this study was to elucidate how alpha-GalCer-activated natural killer T cells function in hepatocyte proliferation and liver regeneration in partially hepatectomized (PHx) mice.

METHODS

Mice were injected with alpha-GalCer at 36 hours after 70% PHx. Hepatocyte mitosis was evaluated by either mitotic figures or proliferating cell nuclear antigen staining. The role of TNF and Fas-ligand in hepatocyte mitosis also was assessed.

RESULTS

In PHx mice injected with alpha-GalCer, hepatocyte mitosis was greatly enhanced at 44 hours after surgery and the increase was more obvious in aged mice than in young mice. The expression of both TNF receptor 1 and Fas-ligand in liver natural killer T cells tended to increase after alpha-GalCer injection in PHx mice. Treatment of mice with anti-NK1.1 Ab 3 days before and just after hepatectomy greatly inhibited the effect of alpha-GalCer on hepatocyte mitosis and liver regeneration. Furthermore, pretreatment of PHx mice with either anti-TNF Ab or anti-FasL Ab 1 hour before alpha-GalCer injection mostly abrogated the increase in hepatocyte proliferation. alpha-GalCer injection did not accelerate hepatocyte proliferation in Fas-mutated lpr mice after PHx. CD1d-/- mice without alpha-GalCer injection showed decreased hepatocyte mitosis after PHx.

CONCLUSIONS

Activated natural killer T cells help hepatocyte proliferation and liver regeneration after PHx via the TNF and Fas/Fas-ligand-mediated pathway.

Novel lymphotoxin alpha (LTalpha) knockout mice with unperturbed tumor necrosis factor expression: reassessing LTalpha biological functions

Lymphotoxin alpha (LTalpha) can exist in soluble form and exert tumor necrosis factor (TNF)-like activity through TNF receptors. Based on the phenotypes of knockout (KO) mice, the physiological functions of LTalpha and TNF are considered partly redundant, in particular, in supporting the microarchitecture of the spleen and in host defense. We exploited Cre-LoxP technology to generate a novel neomycin resistance gene (neo) cassette-free LTalpha-deficient mouse strain (neo-free LTalpha KO [LTalphaDelta/Delta]). Unlike the "conventional" LTalpha-/- mice, new LTalphaDelta/Delta animals were capable of producing normal levels of systemic TNF upon lipopolysaccharide (LPS) challenge and were susceptible to LPS/D-galactosamine (D-GalN) toxicity. Activated neutrophils, monocytes, and macrophages from LTalphaDelta/Delta mice expressed TNF normally at both the mRNA and protein levels as opposed to conventional LTalpha KO mice, which showed substantial decreases in TNF. Additionally, the spleens of the neo-free LTalpha KO mice displayed several features resembling those of LTbeta KO mice rather than conventional LTalpha KO animals. The phenotype of the new LTalphaDelta/Delta mice indicates that LTalpha plays a smaller role in lymphoid organ maintenance than previously thought and has no direct role in the regulation of TNF expression.

Independent protective effects for tumor necrosis factor and lymphotoxin alpha in the host response to Listeria monocytogenes infection

Although the essential role of tumor necrosis factor (TNF) in resistance to Listeria monocytogenes infection is well established, the roles of the related cytokines lymphotoxin alpha (LTalpha) and lymphotoxin beta (LTbeta) are unknown. Using C57BL/6 mice in which the genes for these cytokines were disrupted, we examined the contributions of TNF, LTalpha, and LTbeta in the host response to Listeria. To overcome the lack of peripheral lymph nodes in LTalpha(-/-) and LTbeta(-/-) mice, bone marrow chimeras were constructed. TNF(-/-) and LTalpha(-/-) chimeras that lacked both secreted LTalpha(3) and membrane-bound LTalpha(1)beta(2) and LTalpha(2)beta(1) were highly susceptible and succumbed 4.5 and 6 days, respectively, after a low-dose infection (200 CFU). LTbeta(-/-) chimeras, which lacked only membrane-bound LT, controlled the infection in a manner comparable to wild-type (WT) chimeras. The Listeria-specific proliferative and gamma interferon T-cell responses were equivalent in all five groups of infected mice (LTalpha(-/-) and LTbeta(-/-) chimeras, WT chimeras, and TNF(-/-) and WT mice). TNF(-/-) mice and LTalpha(-/-) chimeras, however, failed to generate the discrete foci of lymphocytes and macrophages that are essential for bacterial elimination. Rather, aberrant necrotic lesions comprised predominantly of neutrophils with relatively few lymphocytes and macrophages were observed in the livers and spleens of TNF(-/-) and LTalpha(-/-) chimeras. Therefore, in addition to TNF, soluble LTalpha(3) plays a separate essential role in control of listerial infection through control of leukocyte accumulation and organization in infected organs.

Differential effects of total and partial neutralization of tumor necrosis factor on cell-mediated immunity to Mycobacterium bovis BCG infection

The effects of total and partial inhibition of tumor necrosis factor (TNF) on sensitivity to Mycobacterium bovis BCG infection were investigated by using transgenic mice in which hepatocytes produced different amounts of human soluble TNF receptor 1 (sTNFR1) fused to the Fc fragment of human immunoglobulin G3 that could be detected in the serum. Transgenic mice expressing high serum levels of sTNFR1, neutralizing all circulating TNF, failed to develop differentiated granulomas and bactericidal mechanisms, and they succumbed to BCG infection. sTNFR1 transgenic mice did not activate BCG-induced Th1-type cytokines early in infection, but uncontrolled cytokine release was found late in infection. In this work we also evaluated the effect of partial inhibition of TNF on resistance to BCG infection. Transgenic mice expressing low levels of sTNFR1 were protected against BCG infection, and they developed increased bactericidal mechanisms, such as enhanced inducible nitric oxide synthase activity, increased macrophage activation, and showed higher numbers of liver granulomas early in infection compared to their negative littermates. Our data suggest that while total inhibition of TNF prevented BCG-induced cell-mediated immune responses, partial inhibition of TNF could contribute to macrophage activation, induction of bactericidal mechanisms, and granuloma formation in the early phase of BCG infection.

Contribution of transmembrane tumor necrosis factor to host defense against Mycobacterium bovis bacillus Calmette-guerin and Mycobacterium tuberculosis infections

To study the specific role of transmembrane tumor necrosis factor (TmTNF) in host defense mechanisms against bacillus Calmette-Guerin (BCG) and Mycobacterium tuberculosis infections, we compared the immune responses of TNF/lymphotoxin (LT)-alpha(-/-) mice expressing a noncleavable transgenic TmTNF (TmTNF tg) to those of TNF/LT-alpha(-/-) and wild-type mice. Susceptibility of TNF/LT-alpha(-/-) mice to BCG infection was associated with impaired induction of systemic RANTES but not of monocyte chemoattractant protein 1 (MCP-1), the development of excessive local and systemic Th1-type immune responses, and a substantially reduced inducible nitric oxide synthase (iNOS) activity. Resistance of TmTNF tg mice to BCG infection was associated with efficient activation of iNOS in granulomas and with the regulated release of local and systemic chemokines and Th1-type cytokines. However, M. tuberculosis infection of TmTNF tg mice resulted in longer survival and enhanced resistance compared to TNF/LT-alpha(-/-) mice but higher sensitivity than wild-type mice. TmTNF tg mice exhibited reduced pulmonary iNOS expression and showed an exacerbated cellular infiltration in the lungs despite a modest bacillary content. Our data thus indicate a role for TmTNF in host defense against mycobacteria by contributing to induction and regulation of Th1-type cytokine and chemokine expression leading to development of bactericidal granulomas expressing iNOS, which critically determines susceptibility versus resistance of the host to mycobacterial infections.

The immunopathology of experimental visceral leishmaniasis

Experimental murine infection with the parasites that cause human visceral leishmaniasis (VL) results in the establishment of infection in the liver, spleen, and bone marrow. In most strains of mice, parasites are eventually cleared from the liver, and hepatic resistance to infection results from a coordinated host response involving a broad range of effector and regulatory pathways targeted within defined tissue structures called granulomas. In contrast, parasites persist in the spleen and bone marrow by mechanisms that are less well understood. Parasite persistence is accompanied by the failure of granuloma formation and by a variety of pathologic changes, including splenomegaly, disruption of lymphoid tissue microarchitecture, and enhanced hematopoietic activity. Here, we review the salient features of these distinct tissue responses and highlight the varied roles that cytokines of the tumor necrosis factor family play in immunity to this infection. In addition, we also discuss recent studies aimed at understanding how splenomegaly affects the survival and function of memory cells specific for heterologous antigens, an issue of considerable importance for our understanding of the disease-associated increase in secondary infections characteristic of human VL.

Signal transduction by the lipopolysaccharide receptor, Toll-like receptor-4

An understanding of lipopolysaccharide (LPS) signal transduction is a key goal in the effort to provide a molecular basis for the lethal effect of LPS during septic shock and point the way to novel therapies. Rapid progress in this field during the last 6 years has resulted in the discovery of not only the receptor for LPS - Toll-like receptor 4 (TLR4) - but also in a better appreciation of the complexity of the signalling pathways activated by LPS. Soon after the discovery of TLR4, the formation of a receptor complex in response to LPS, consisting of dimerized TLR4 and MD-2, was described. Intracellular events following the formation of this receptor complex depend on different sets of adapters. An early response, which is dependent on MyD88 and MyD88-like adapter (Mal), leads to the activation of nuclear factor-kappaB (NF-kappaB). A later response to LPS makes use of TIR-domain-containing adapter-inducing interferon-beta (TRIF) and TRIF-related adapter molecule (TRAM), and leads to the late activation of NF-kappaB and IRF3, and to the induction of cytokines, chemokines, and other transcription factors. As LPS signal transduction is an area of intense research and rapid progress, this review is intended to sum up our present understanding of the events following LPS binding to TLR4, and we also attempt to create a model of the signalling pathways activated by LPS.

Inhibition of inducible nitric oxide synthase protects against liver injury induced by mycobacterial infection and endotoxins

BACKGROUND/AIMS

Bacillus Calmette Guerin (BCG) infection causes hepatic injury following granuloma formation and secretion of cytokines which render mice highly sensitive to endotoxin-mediated hepatotoxicity. This work investigates the role of inducible nitric oxide synthase (iNOS) in liver damage induced by BCG and endotoxins in BCG-infected mice.

METHODS

Liver injury and cytokine activation induced by BCG and by LPS upon BCG infection (BCG/LPS) were compared in wild-type and iNOS-/- mice.

RESULTS

iNOS-/- mice infected with living BCG are protected from hepatic injury when compared to wild-type mice which express iNOS protein in macrophages forming hepatic granulomas. In addition, iNOS-/- mice show a decrease in BCG-induced IFN-gamma serum levels. LPS challenge in BCG-infected mice strongly activates iNOS in the liver and spleen of wild-type mice which show important liver damage associated with a dramatic increase in TNF and IL-6 and also Th1 type cytokines. In contrast, iNOS-/- mice are protected from liver injury after BCG/LPS challenge and their TNF, IL-6 and Th1 type cytokine serum levels raise moderately.

CONCLUSIONS

These results demonstrate that nitric oxide (NO) from iNOS is involved in hepatotoxicity induced by both mycobacterial infection and endotoxin effects upon BCG infection and that inhibition of NO from iNOS protects from liver injuries.

T cell-derived tumour necrosis factor is essential, but not sufficient, for protection against Mycobacterium tuberculosis infection

Tumour necrosis factor (TNF) is critical for sustained protective immunity against Mycobacterium tuberculosis infection. To investigate the relative contributions of macrophage- and T cell-derived TNF towards this immunity T cells from wild-type (WT) or TNF-/- mice were transferred into RAG-/- or TNF-/- mice which were then infected with M. tuberculosis. Infected RAG-/- mice and RAG-/- recipients of TNF deficient T cells developed overwhelming infection, with extensive pulmonary and hepatic necrosis and succumbed with a median of only 16 days infection. By contrast, RAG-/- recipients of WT T cells showed a significant increase in survival with a median of 32 days. Although initial bacterial growth was similar in all groups of RAG-/- mice, the transfer of WT, but not TNF-/-, T cells led to the formation of discrete foci of leucocytes and macrophages and delayed the development of necrotizing pathology. To determine requirements for macrophage-derived TNF, WT or TNF-/- T cells were transferred into TNF-/- mice at the time of M. tuberculosis infection. Transfer of WT T cells significantly prolonged survival and reduced the early tissue necrosis evident in the TNF-/- mice, however, these mice eventually succumbed indicating that T cell-derived TNF alone is insufficient to control the infection. Therefore, both T cell- and macrophage-derived TNF play distinct roles in orchestrating the protective inflammatory response and enhancing survival during M. tuberculosis infection.

Contribution of CD30/CD153 but not of CD27/CD70, CD134/OX40L, or CD137/4-1BBL to the optimal induction of protective immunity toMycobacterium avium

A panel of monoclonal antibodies specific for CD27 ligand (CD70), CD30 ligand (CD153), CD134 ligand (OX40L), and CD137 ligand (4-1BBL) were screened in vivo for their ability to affect the control of Mycobacterium avium infection in C57Bl/6 mice. Only the blocking of CD153 led to increased mycobacterial burdens. We then used CD30-deficient mice and found an increase in the proliferation of two strains of M. avium in these mice as compared with control animals. The increased mycobacterial growth was associated with decreased T cell expansion and reduced interferon-gamma (IFN-gamma) responses as a result of reduced polarization of the antigen-specific, IFN-gamma-producing T cells. At late times but not early in infection, the lymphoid cuff surrounding granulomas was depleted in the CD30-deficient animals. This report expands our knowledge about tumor necrosis factor superfamily members involved in the immune responses to mycobacterial infection by identifying CD30-CD153 interactions as required for optimal immune control of M. avium infection.

Consideration of the risk and treatment of tuberculosis in patients who have rheumatoid arthritis and receive biologic treatments

Evidence supports the association of tuberculosis (TB) with tumor necrosis factor inhibitor therapy in patients who have rheumatoid arthritis. There seem to be differential risks of TB with the currently available inhibitors. Screening for latent TB infection with purified protein derivative is indicated for patients who are being considered for treatment; it seems to be effective in reducing the occurrence of TB in treated patients.

T cell contributions to the different phases of granuloma formation

Granulomatous inflammation is a form of delayed type hypersensitivity reaction that is involved in protection against chronic infections. Granulomatous inflammation can also occur without any clear inciting stimulus such as in sarcoidosis. An in depth knowledge of granuloma formation is essential to our understanding of protection against chronic infection as well as the dysregulation which occurs in granulomatous diseases of unknown origin. Granuloma formation is a complex and dynamic process involving the recruitment and coordination of diverse cell types. This review is focused on the important roles that T cells play in initiating and building the granuloma as well as in mediating effector functions and eventually resolving granulomatous inflammation. CD4(+) T cells emerge as the central mediators of this process, with T cells from other subsets also participating in the later phases of granuloma formation.

Astroglial-derived lymphotoxin-? exacerbates inflammation and demyelination, but not remyelination

Tumor necrosis factoralpha (TNFalpha) and lymphotoxin-alpha (Ltalpha) are upregulated in and around multiple sclerosis plaques and are proposed to play a role during chronic inflammation in demyelinating disease. Despite the perceived detrimental role of these cytokines, human clinical trials inhibiting TNFalpha signaling has led to worsening of symptoms in multiple sclerosis (MS) patients. Our laboratory has verified a role for TNFalpha in the exacerbation of demyelination but, more importantly, has demonstrated a novel role for TNFalpha in reparative remyelination in a cuprizone-induced demyelination model. This may explain the worsening of symptoms experienced by MS patients. In view of the cross-talk in TNF family signaling, the aim of this study is to understand the role of Ltalpha in demyelination and remyelination in hopes of improving therapeutic strategies for MS. Using the same model, we show that mice lacking Ltalpha exhibit a delay in demyelination that is greater than that exhibited by TNFalpha null mice. In this model, Ltalpha is expressed primarily by astroglia. The delay in demyelination is accompanied by a delay in the loss of mature GSTpi-positive oligodendrocytes in Ltalpha-/- mice compared with wild-type mice. Ltalpha-/- mice have decreased numbers of microglia at the site of insult during demyelination, although the number of astrocytes present is similar between strains. In contrast to TNFalpha the lack of Ltalpha did not alter the time course of remyelination, or the number of mature oligodendrocytes during the remyelination phase. Since Ltalpha is detrimental in inflammation and demyelination, but not necessary for remyelination and repair, inhibiting Ltalpha signaling may represent a promising strategy to treat MS.

Tumor necrosis factors in a murine model of allergic peritonitis: effects on eosinophil accumulation and inflammatory mediators' release

In allergic disorders, the role of tumor necrosis factors (TNF) is not well established. We investigated the role of TNF in allergic peritonitis induced by ovalbumin (OVA) challenge in double TNF (TNF-alpha(-/-)/lymphotoxin-alpha(-/-)) knock out (TNF-KO) mice. In the peritoneal lavage of TNF-KO mice, mast cell number and histamine level (radioenzymatic assay) were similar to that in wild type (WT) mice. TNF-alpha (ELISA) and histamine were increased 1 h after challenge in WT mice. However, three days later eosinophil number and eosinophil peroxidase (EPO) levels (colorimetric-enzymatic assay) were found to be lower in TNF-KO mice. A second challenge three days after the first, increased EPO, histamine and IL-6 (ELISA) but did not alter eosinophil and mast cell numbers in both types of mice. On the other hand histamine and IL-6 were higher, while EPO was lower in TNF-KO mice. In conclusion, our findings show that TNF is involved in eosinophil accumulation and inflammatory mediators' release in a murine model of allergy.

TNF regulates chemokine induction essential for cell recruitment, granuloma formation, and clearance of mycobacterial infection

Host immunity to mycobacterial infection is dependent on the activation of T lymphocytes and their recruitment with monocytes to form granulomas. These discrete foci of activated macrophages and lymphocytes provide a microenvironment for containing the infection. The cytokine, TNF, is essential for the formation and maintenance of granulomas, but the mechanisms by which TNF regulates these processes are unclear. We have compared the responses of TNF-deficient (TNF(-/-)) and wild-type C57BL/6 mice to infection with Mycobacterium smegmatis, a potent inducer of TNF, and virulent Mycobacterium tuberculosis to delineate the TNF-dependent and -independent components of the process. The initial clearance of M. smegmatis was TNF independent, but TNF was required for the early expression of mRNA encoding C-C and C-X-C chemokines and the initial recruitment of CD11b(+) macrophages and CD4(+) T cells to the liver during the second week of infection. Late chemokine expression and cell recruitment developed in TNF(-/-) mice associated with enhanced Th1-like T cell responses and mycobacterial clearance, but recruited leukocytes did not form tight granulomas. Infection of TNF(-/-) mice with M. tuberculosis also resulted in an initial delay in chemokine induction and cellular recruitment to the liver. Subsequently, increased mRNA expression was evident in TNF(-/-) mice, but the loosely associated lymphocytes and macrophages failed to form granulomas and prevent progressive infection. Therefore, TNF orchestrates early induction of chemokines and initial leukocyte recruitment, but has an additional role in the aggregation of leukocytes into functional granulomas capable of controlling virulent mycobacterial infection.

Transmembrane TNF induces an efficient cell-mediated immunity and resistance to Mycobacterium bovis bacillus Calmette-Guérin infection in the absence of secreted TNF and lymphotoxin-alpha

The contribution of a transmembrane (Tm) form of TNF to protective immunity against Mycobacterium bovis bacillus Calmette-Guérin (BCG) was studied in transgenic (tg) mice expressing a noncleavable Tm TNF but lacking the TNF/lymphotoxin-alpha (LT-alpha) locus (Tm TNF tg mice). These mice were as resistant to BCG infection as wild-type mice, whereas TNF/LT-alpha(-/-), TNF(-/-), and LT-alpha(-/-) mice succumbed. Tm TNF tg mice developed granulomas of smaller size but at 2- to 4-fold increased frequencies compared with wild-type mice. Granulomas were mainly formed by monocytes and activated macrophages expressing Tm TNF mRNA and accumulating acid phosphatase. NO synthase 2 activation as a key macrophage bactericidal mechanism was low during the acute phase of infection in Tm TNF tg mice but was still sufficient to limit bacterial growth and increased in late infection. While infection with virulent Mycobacterium tuberculosis resulted in very rapid death of TNF/LT-alpha(-/-) mice, it also resulted in survival of Tm TNF tg mice which presented an increase in the number of CFU in spleen (5-fold) and lungs (10-fold) as compared with bacterial load of wild-type mice. In conclusion, the Tm form of TNF induces an efficient cell-mediated immunity and total resistance against BCG even in the absence of LT-alpha and secreted TNF. However, Tm TNF-mediated protection against virulent M. tuberculosis infection can also be efficient but not as strong as in BCG infection, in which cognate cellular interactions may play a more predominant role in providing long-term surveillance and containment of BCG-infected macrophages.