Membrane-bound TNF induces protective immune responses to M. bovis BCG infection: regulation of memTNF and TNF receptors comparing two memTNF molecules

Reducing brain TACE activity improves neuroinflammation and cardiac function in heart failure rats

Tumor necrosis factor (TNF)-α converting enzyme (TACE) is a key metalloprotease mediating ectodomain shedding of a variety of inflammatory mediators, substrates, and growth factors. We previously reported that TACE-mediated production of TNF-α in the hypothalamic paraventricular nucleus (PVN) contributes to sympathetic excitation in heart failure (HF). Here, we sought to determine whether central interventions in TACE activity attenuate neuroinflammation and improve cardiac function in heart failure. Myocardial infarction-induced HF or sham-operated (SHAM) rats were treated with bilateral paraventricular nucleus microinjection of a TACE siRNA or a 4-week intracerebroventricular (ICV) infusion of the TACE inhibitor TAPI-0. Compared with SHAM rats, scrambled siRNA-treated HF rats had higher TACE levels in the PVN along with increased mRNA levels of TNF-α, TNF-α receptor 1 and cyclooxygenase-2. The protein levels of TNF-α in cerebrospinal fluid and phosphorylated (p-) NF-κB p65 and extracellular signal-regulated protein kinase (ERK)1/2 in the PVN were also elevated in HF rats treated with scrambled siRNA. The expression of these inflammatory mediators and signaling molecules in the PVN of HF rats were significantly attenuated by TACE siRNA. Interestingly, the mRNA level of TNF-α receptor 2 in the PVN was increased in HF treated with TACE siRNA. Moreover, sympathetic excitation, left ventricular end-diastolic pressure, pulmonary congestion, and cardiac hypertrophy and fibrosis were reduced by PVN microinjection of TACE siRNA. A 4-week treatment with intracerebroventricular TAPI-0 had similar effects to ameliorate these variables in HF rats. These data indicate that interventions suppressing TACE activity in the brain mitigate neuroinflammation, sympathetic activation and cardiac dysfunction in HF rats.

Transmembrane TNF and Its Receptors TNFR1 and TNFR2 in Mycobacterial Infections

Tumor necrosis factor (TNF) is one of the main cytokines regulating a pro-inflammatory environment. It has been related to several cell functions, for instance, phagocytosis, apoptosis, proliferation, mitochondrial dynamic. Moreover, during mycobacterial infections, TNF plays an essential role to maintain granuloma formation. Several effector mechanisms have been implicated according to the interactions of the two active forms, soluble TNF (solTNF) and transmembrane TNF (tmTNF), with their receptors TNFR1 and TNFR2. We review the impact of these interactions in the context of mycobacterial infections. TNF is tightly regulated by binding to receptors, however, during mycobacterial infections, upstream activation signalling pathways may be influenced by key regulatory factors either at the membrane or cytosol level. Detailing the structure and activation pathways used by TNF and its receptors, such as its interaction with solTNF/TNFRs versus tmTNF/TNFRs, may bring a better understanding of the molecular mechanisms involved in activation pathways which can be helpful for the development of new therapies aimed at being more efficient against mycobacterial infections.

Vaccine targeting TNF epitope 1-14 do not suppress host defense against Mycobacterium bovis Bacillus Calmette-Guérin infection

Anti-TNF inhibitors are efficacious in the treatment of chronic inflammatory diseases such as rheumatoid arthritis (RA), Crohn's disease (CD), juvenile idiopathic arthritis (JIA), and ankylosing spondylitis (AS). However, more and more clinical case reports revealed that anti-TNF inhibitors could increase the risk of viral, fungal, and bacterial (especially intracellular) infection. In this study, based on Immune Epitope Database (IEDB) online B cell epitope prediction and the knowledge of TNF three dimensional (3D) structure we developed a novel vaccine (DTNF114-TNF114) that targeting TNF epitope 1-14, which produced antibodies only partially binding to trans-membrane TNF (tmTNF), therefore partially sparing tmTNF-TNFR1/2 interaction. Immunization with DTNF114-TNF114 significantly protected and prolonged the survival rate of mice challenged with lipopolysaccharide (LPS); and in the mCherry expressing Mycobacterium bovis Bacillus Calmette-Guérin (mCherry-BCG) infection model, DTNF114-TNF114 immunization significantly decreased soluble TNF (solTNF) level in serum, meanwhile did not suppress host immunity against infection. Thus, this novel and infection concern-free vaccine provides a potential alternative or supplement to currently clinically used anti-TNF inhibitors.

Myeloid cell TNFR1 signaling dependent liver injury and inflammation upon BCG infection

TNF plays a critical role in mononuclear cell recruitment during acute Bacillus Calmette-Guérin (BCG) infection leading to an effective immune response with granuloma formation, but may also cause tissue injury mediated by TNFR1 or TNFR2. Here we investigated the role of myeloid and T cell specific TNFR1 and R2 expression, and show that absence of TNFR1 in myeloid cells attenuated liver granuloma formation and liver injury in response to acute BCG infection, while TNFR2 expressed in myeloid cells contributed only to liver injury. TNFR1 was the main receptor controlling cytokine production by liver mononuclear cells after antigenic specific response, modified CD4/CD8 ratio and NK, NKT and regulatory T cell recruitment. Further analysis of CD11b⁺CD3⁺ phagocytic cells revealed a TCRαβ expressing subpopulation of unknown function, which increased in response to BCG infection dependent of TNFR1 expression on myeloid cells. In conclusion, TNFR1 expressed by myeloid cells plays a critical role in mononuclear cell recruitment and injury of the liver after BCG infection.

Transmembrane TNF and Partially TNFR1 Regulate TNFR2 Expression and Control Inflammation in Mycobacterial-Induced Pleurisy

Pleural tuberculosis is one of the most frequent forms of extra-pulmonary tuberculosis observed in patients infected with Mycobacterium tuberculosis. Tumor Necrosis Factor (TNF) is a crucial cytokine needed to control tuberculosis infection that remains a leading cause of morbidity and mortality worldwide. TNF blockade compromises host immunity and may increase the risk of reactivation of latent infection resulting in overt pulmonary, pleural and extra-pulmonary tuberculosis. While TNF signaling is mainly considered pro-inflammatory, its requirement for the anti-inflammation process involved in the resolution of infection and tissue repair is less explored. Our study analyzes the role of TNF and TNF receptors in the control of the inflammatory process associated with Bacillus Calmette-Guérin (BCG)-induced pleurisy. This study shows that the absence of TNF causes exacerbated inflammation in the pleural cavity of BCG-infected mice which is controlled by the transmembrane TNF (tmTNF) expression. The lack of TNF is associated with an impaired cellular expression and shedding of TNFR2 in the pleural cavity. The presence of tmTNF restores the normal expression of TNFR2 on myeloid cells during BCG-induced pleurisy. We also show that absence of TNFR1 affects the expression of TNFR2 on pleural cells and inflammation in the pleural cavity of BCG-infected mice. In conclusion, tmTNF but not soluble TNF prevents pleural cavity inflammation leading to attenuation and the resolution of the inflammatory process caused by mycobacterial pleurisy in association with the expression of TNFR2 on myeloid cells.

Transmembrane Tumor Necrosis Factor Controls Myeloid-Derived Suppressor Cell Activity via TNF Receptor 2 and Protects from Excessive Inflammation during BCG-Induced Pleurisy

Pleural tuberculosis (TB) is a form of extra-pulmonary TB observed in patients infected with Mycobacterium tuberculosis. Accumulation of myeloid-derived suppressor cells (MDSC) has been observed in animal models of TB and in human patients but their role remains to be fully elucidated. In this study, we analyzed the role of transmembrane TNF (tmTNF) in the accumulation and function of MDSC in the pleural cavity during an acute mycobacterial infection. Mycobacterium bovis BCG-induced pleurisy was resolved in mice expressing tmTNF, but lethal in the absence of tumor necrosis factor. Pleural infection induced MDSC accumulation in the pleural cavity and functional MDSC required tmTNF to suppress T cells as did pleural wild-type MDSC. Interaction of MDSC expressing tmTNF with CD4 T cells bearing TNF receptor 2 (TNFR2), but not TNFR1, was required for MDSC suppressive activity on CD4 T cells. Expression of tmTNF attenuated Th1 cell-mediated inflammatory responses generated by the acute pleural mycobacterial infection in association with effective MDSC expressing tmTNF and interacting with CD4 T cells expressing TNFR2. In conclusion, this study provides new insights into the crucial role played by the tmTNF/TNFR2 pathway in MDSC suppressive activity required during acute pleural infection to attenuate excessive inflammation generated by the infection.

Persistent p55TNFR expression impairs T cell responses during chronic tuberculosis and promotes reactivation

The pleiotropic activities of TNF are mediated by two structurally related but functionally distinct type I transmembrane receptors, p55TNFR and p75TNFR expressed in most cell types, that can be cleaved and act as TNF scavengers. Here, we investigated the effect of persistent p55TNFR cell surface expression during aerosol inhalation challenge with virulent M. tuberculosis H37Rv. We demonstrated that persistency of p55TNFR in macrophage cultures increased the synthesis of soluble TNF, p75TNFR and NO, however, had no effects on bacteria killing ability. Furthermore, it did not facilitate enhanced protection to primary acute M. tuberculosis infection in p55^∆NS mice. Without exacerbated lung inflammation, we found a compensatory increase in p75TNFR shedding and decrease in bioactive TNF in BAL of p55^∆NS mice after M. tuberculosis challenge. Defective expressions of CD44 and INFγ attributed to an impaired T cell response during persistent p55TNFR expression that caused marginal transient susceptibility during chronic infection. Moreover, persistent p55TNFR expression induced early reactivation during latent tuberculosis infection. These data indicate a prominent role of p55TNFR shedding in Th1 mediated protection against chronic and latent tuberculosis infection.

Low Dose BCG Infection as a Model for Macrophage Activation Maintaining Cell Viability

Mycobacterium bovis BCG, the current vaccine against tuberculosis, is ingested by macrophages promoting the development of effector functions including cell death and microbicidal mechanisms. Despite accumulating reports on M. tuberculosis, mechanisms of BCG/macrophage interaction remain relatively undefined. In vivo, few bacilli are sufficient to establish a mycobacterial infection; however, in vitro studies systematically use high mycobacterium doses. In this study, we analyze macrophage/BCG interactions and microenvironment upon infection with low BCG doses and propose an in vitro model to study cell activation without affecting viability. We show that RAW macrophages infected with BCG at MOI 1 activated higher and sustained levels of proinflammatory cytokines and transcription factors while MOI 0.1 was more efficient for early stimulation of IL-1β, MCP-1, and KC. Both BCG infection doses induced iNOS and NO in a dose-dependent manner and maintained nuclear and mitochondrial structures. Microenvironment generated by MOI 1 induced macrophage proliferation but not MOI 0.1 infection. In conclusion, BCG infection at low dose is an efficient in vitro model to study macrophage/BCG interactions that maintains macrophage viability and mitochondrial structures. This represents a novel model that can be applied to BCG research fields including mycobacterial infections, cancer immunotherapy, and prevention of autoimmunity and allergies.

Genetic ablation of soluble tumor necrosis factor with preservation of membrane tumor necrosis factor is associated with neuroprotection after focal cerebral ischemia

Microglia respond to focal cerebral ischemia by increasing their production of the neuromodulatory cytokine tumor necrosis factor, which exists both as membrane-anchored tumor necrosis factor and as cleaved soluble tumor necrosis factor forms. We previously demonstrated that tumor necrosis factor knockout mice display increased lesion volume after focal cerebral ischemia, suggesting that tumor necrosis factor is neuroprotective in experimental stroke. Here, we extend our studies to show that mice with intact membrane-anchored tumor necrosis factor, but no soluble tumor necrosis factor, display reduced infarct volumes at one and five days after stroke. This was associated with improved functional outcome after experimental stroke. No changes were found in the mRNA levels of tumor necrosis factor and tumor necrosis factor-related genes (TNFR1, TNFR2, TACE), pro-inflammatory cytokines (IL-1β, IL-6) or chemokines (CXCL1, CXCL10, CCL2); however, protein expression of TNF, IL-1β, IL-6 and CXCL1 was reduced in membrane-anchored tumor necrosis factor(Δ/Δ) compared to membrane-anchored tumor necrosis factor(wt/wt) mice one day after experimental stroke. This was paralleled by reduced MHCII expression and a reduction in macrophage infiltration in the ipsilateral cortex of membrane-anchored tumor necrosis factor(Δ/Δ) mice. Collectively, these findings indicate that membrane-anchored tumor necrosis factor mediates the protective effects of tumor necrosis factor signaling in experimental stroke, and therapeutic strategies specifically targeting soluble tumor necrosis factor could be beneficial in clinical stroke therapy.

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.

Neutrophil and Alveolar Macrophage-Mediated Innate Immune Control of Legionella pneumophila Lung Infection via TNF and ROS

Legionella pneumophila is a facultative intracellular bacterium that lives in aquatic environments where it parasitizes amoeba. However, upon inhalation of contaminated aerosols it can infect and replicate in human alveolar macrophages, which can result in Legionnaires' disease, a severe form of pneumonia. Upon experimental airway infection of mice, L. pneumophila is rapidly controlled by innate immune mechanisms. Here we identified, on a cell-type specific level, the key innate effector functions responsible for rapid control of infection. In addition to the well-characterized NLRC4-NAIP5 flagellin recognition pathway, tumor necrosis factor (TNF) and reactive oxygen species (ROS) are also essential for effective innate immune control of L. pneumophila. While ROS are essential for the bactericidal activity of neutrophils, alveolar macrophages (AM) rely on neutrophil and monocyte-derived TNF signaling via TNFR1 to restrict bacterial replication. This TNF-mediated antibacterial mechanism depends on the acidification of lysosomes and their fusion with L. pneumophila containing vacuoles (LCVs), as well as caspases with a minor contribution from cysteine-type cathepsins or calpains, and is independent of NLRC4, caspase-1, caspase-11 and NOX2. This study highlights the differential utilization of innate effector pathways to curtail intracellular bacterial replication in specific host cells upon L. pneumophila airway infection.

Innate myeloid cell TNFR1 mediates first line defence against primary Mycobacterium tuberculosis infection

TNF is crucial for controlling Mycobacterium tuberculosis infection and understanding how will help immunomodulating the host response. Here we assessed the contribution of TNFR1 pathway from innate myeloid versus T cells. We first established the prominent role of TNFR1 in haematopoietic cells for controlling M. tuberculosis in TNFR1 KO chimera mice. Further, absence of TNFR1 specifically on myeloid cells (M-TNFR1 KO) recapitulated the uncontrolled M. tuberculosis infection seen in fully TNFR1 deficient mice, with increased bacterial burden, exacerbated lung inflammation, and rapid death. Pulmonary IL-12p40 over-expression was attributed to a prominent CD11b⁺ Gr1^high cell population in infected M-TNFR1 KO mice. By contrast, absence of TNFR1 on T-cells did not compromise the control of M. tuberculosis infection over 6-months. Thus, the protective TNF/TNFR1 pathway essential for controlling primary M. tuberculosis infection depends on innate macrophage and neutrophil myeloid cells, while TNFR1 pathway in T cells is dispensable.

Exposure of Monocytes to Lipoarabinomannan Promotes Their Differentiation into Functionally and Phenotypically Immature Macrophages

Lipoarabinomannan (LAM) is a lipid virulence factor secreted by Mycobacterium tuberculosis (Mtb), the etiologic agent of tuberculosis. LAM can be measured in the urine or serum of tuberculosis patients (TB-patients). Circulating monocytes are the precursor cells of alveolar macrophages and might be exposed to LAM in patients with active TB. We speculated that exposing monocytes to LAM could produce phenotypically and functionally immature macrophages. To test our hypothesis, human monocytes were stimulated with LAM (24–120 hours) and various readouts were measured. The study showed that when monocytes were exposed to LAM, the frequency of CD68⁺, CD33⁺, and CD86⁺ macrophages decreased, suggesting that monocyte differentiation into mature macrophages was affected. Regarding functionality markers, TLR2⁺ and TLR4⁺ macrophages also decreased, but the percentage of MMR⁺ expression did not change. LAM-exposed monocytes generated macrophages that were less efficient in producing proinflammatory cytokines such as TNF-α and IFN-γ; however, their phagocytic capacity was not modified. Taken together, these data indicate that LAM exposure influenced monocyte differentiation and produced poorly functional macrophages with a different phenotype. These results may help us understand how mycobacteria can limit the quality of the innate and adaptive immune responses.

Peripheral administration of the selective inhibitor of soluble tumor necrosis factor (TNF) XPro®1595 attenuates nigral cell loss and glial activation in 6-OHDA hemiparkinsonian rats

BACKGROUND

Parkinson's disease (PD) is a complex multi-system age-related neurodegenerative disorder. Targeting the ongoing neuroinflammation in PD patients is one strategy postulated to slow down or halt disease progression. Proof-of-concept studies from our group demonstrated that selective inhibition of soluble Tumor Necrosis Factor (solTNF) by intranigral delivery of dominant negative TNF (DN-TNF) inhibitors reduced neuroinflammation and nigral dopamine (DA) neuron loss in endotoxin and neurotoxin rat models of nigral degeneration.

OBJECTIVE

As a next step toward human clinical trials, we aimed to determine the extent to which peripherally administered DN-TNF inhibitor XPro®1595 could: i) cross the blood-brain-barrier in therapeutically relevant concentrations, ii) attenuate neuroinflammation (microglia and astrocyte), and iii) mitigate loss of nigral DA neurons in rats receiving a unilateral 6-hydroxydopamine (6-OHDA) striatal lesion.

METHODS

Rats received unilateral 6-OHDA (20 μg into the right striatum). Three or 14 days after lesion, rats were dosed with XPro®1595 (10 mg/kg in saline, subcutaneous) every third day for 35 days. Forelimb asymmetry was used to assess motor deficits after the lesion; brains were harvested 35 days after the lesion for analysis of XPro®1595 levels, glial activation and nigral DA neuron number.

RESULTS

Peripheral subcutaneous dosing of XPro®1595 achieved plasma levels of 1-8 microgram/mL and CSF levels of 1-6 ng/mL depending on the time the rats were killed after final XPro®1595 injection. Irrespective of start date, XPro®1595 significantly reduced microglia and astrocyte number in SNpc whereas loss of nigral DA neurons was attenuated when drug was started 3, but not 14 days after the 6-OHDA lesion.

CONCLUSIONS

Our data suggest that systemically administered XPro®1595 may have disease-modifying potential in PD patients where inflammation is part of their pathology.

Control of Mycobacterial Infections in Mice Expressing Human Tumor Necrosis Factor (TNF) but Not Mouse TNF

Tumor necrosis factor (TNF) is an important cytokine for host defense against pathogens but is also associated with the development of human immunopathologies. TNF blockade effectively ameliorates many chronic inflammatory conditions but compromises host immunity to tuberculosis. The search for novel, more specific human TNF blockers requires the development of a reliable animal model. We used a novel mouse model with complete replacement of the mouse TNF gene by its human ortholog (human TNF [huTNF] knock-in [KI] mice) to determine resistance to Mycobacterium bovis BCG and M. tuberculosis infections and to investigate whether TNF inhibitors in clinical use reduce host immunity. Our results show that macrophages from huTNF KI mice responded to BCG and lipopolysaccharide similarly to wild-type macrophages by NF-κB activation and cytokine production. While TNF-deficient mice rapidly succumbed to mycobacterial infection, huTNF KI mice survived, controlling the bacterial burden and activating bactericidal mechanisms. Administration of TNF-neutralizing biologics disrupted the control of mycobacterial infection in huTNF KI mice, leading to an increased bacterial burden and hyperinflammation. Thus, our findings demonstrate that human TNF can functionally replace murine TNF in vivo, providing mycobacterial resistance that could be compromised by TNF neutralization. This new animal model will be helpful for the testing of specific biologics neutralizing human TNF.

Much More than M1 and M2 Macrophages, There are also CD169(+) and TCR(+) Macrophages

Monocytes are considered to be precursor cells of the mononuclear phagocytic system, and macrophages are one of the leading members of this cellular system. Macrophages play highly diverse roles in maintaining an organism's integrity by either directly participating in pathogen elimination or repairing tissue under sterile inflammatory conditions. There are different subpopulations of macrophages and each one has its own characteristics and functions. In this review, we summarize present knowledge on the polarization of macrophages that allows the generation of subpopulations called classically activated macrophages or M1 and alternative activated macrophages or M2. Furthermore, there are macrophages that their origin and characterization still remain unclear but have been involved as main players in some human pathologies. Thus, we also review three other categories of macrophages: tumor-associated macrophages, CD169(+) macrophages, and the recently named TCR(+) macrophages. Based on the literature, we provide information on the molecular characterization of these macrophage subpopulations and their specific involvement in several human pathologies such as cancer, infectious diseases, obesity, and asthma. The refined characterization of the macrophage subpopulations can be useful in designing new strategies, supplementing those already established for the treatment of diseases using macrophages as a therapeutic target.

Bacillus calmette-guerin infection in NADPH oxidase deficiency: defective mycobacterial sequestration and granuloma formation

Patients with chronic granulomatous disease (CGD) lack generation of reactive oxygen species (ROS) through the phagocyte NADPH oxidase NOX2. CGD is an immune deficiency that leads to frequent infections with certain pathogens; this is well documented for S. aureus and A. fumigatus, but less clear for mycobacteria. We therefore performed an extensive literature search which yielded 297 cases of CGD patients with mycobacterial infections; M. bovis BCG was most commonly described (74%). The relationship between NOX2 deficiency and BCG infection however has never been studied in a mouse model. We therefore investigated BCG infection in three different mouse models of CGD: Ncf1 mutants in two different genetic backgrounds and Cybb knock-out mice. In addition, we investigated a macrophage-specific rescue (transgenic expression of Ncf1 under the control of the CD68 promoter). Wild-type mice did not develop severe disease upon BCG injection. In contrast, all three types of CGD mice were highly susceptible to BCG, as witnessed by a severe weight loss, development of hemorrhagic pneumonia, and a high mortality (∼ 50%). Rescue of NOX2 activity in macrophages restored BCG resistance, similar as seen in wild-type mice. Granulomas from mycobacteria-infected wild-type mice generated ROS, while granulomas from CGD mice did not. Bacterial load in CGD mice was only moderately increased, suggesting that it was not crucial for the observed phenotype. CGD mice responded with massively enhanced cytokine release (TNF-α, IFN-γ, IL-17 and IL-12) early after BCG infection, which might account for severity of the disease. Finally, in wild-type mice, macrophages formed clusters and restricted mycobacteria to granulomas, while macrophages and mycobacteria were diffusely distributed in lung tissue from CGD mice. Our results demonstrate that lack of the NADPH oxidase leads to a markedly increased severity of BCG infection through mechanisms including increased cytokine production and impaired granuloma formation.

A TNFSF15 disease-risk polymorphism increases pattern-recognition receptor-induced signaling through caspase-8-induced IL-1

Inflammatory diseases are characterized by dysregulated cytokine production. Altered functions for most risk loci, including the inflammatory bowel disease and leprosy-associated tumor necrosis factor ligand superfamily member 15 (TNFSF15) region, are unclear. Regulation of pattern-recognition-receptor (PRR)-induced signaling and cytokines is crucial for immune homeostasis; TNFSF15:death receptor 3 (DR3) contributions to PRR responses have not been described. We found that human macrophages expressed DR3 and that TNFSF15:DR3 interactions were critical for amplifying PRR-initiated MAPK/NF-κB/PI3K signaling and cytokine secretion in macrophages. Mechanisms mediating TNFSF15:DR3 contributions to PRR outcomes included TACE-induced TNFSF15 cleavage to soluble TNFSF15; soluble TNFSF15 then led to TRADD/FADD/MALT-1- and caspase-8-mediated autocrine IL-1 secretion. Notably, TNFSF15 treatment also induced cytokine secretion through a caspase-8-dependent pathway in intestinal myeloid cells. Importantly, rs6478108 A disease risk-carrier macrophages demonstrated increased TNFSF15 expression and PRR-induced signaling and cytokines. Taken together, TNFSF15:DR3 interactions amplify PRR-induced signaling and cytokines, and the rs6478108 TNFSF15 disease-risk polymorphism results in a gain of function.

Relative contribution of IL-1α, IL-1β and TNF to the host response to Mycobacterium tuberculosis and attenuated M. bovis BCG

TNF and IL-1 are major mediators involved in severe inflammatory diseases against which therapeutic neutralizing antibodies are developed. However, both TNF and IL-1 receptor pathways are essential for the control of Mycobacterium tuberculosis infection, and it is critical to assess the respective role of IL-1α, IL-1β, and TNF. Using gene-targeted mice we show that absence of both IL-1α and IL-1β recapitulates the uncontrolled M. tuberculosis infection with increased bacterial burden, exacerbated lung inflammation, high IFNγ, reduced IL-23 p19 and rapid death seen in IL-1R1-deficient mice. However, presence of either IL-1α or IL-1β in single-deficient mice is sufficient to control acute M. tuberculosis infection, with restrained bacterial burden and lung pathology, in conditions where TNF deficient mice succumbed within 4 weeks with overwhelming infection. Systemic infection by attenuated M. bovis BCG was controlled in the absence of functional IL-1 pathway, but not in the absence of TNF. Therefore, although both IL-1α and IL-1β are required for a full host response to virulent M. tuberculosis, the presence of either IL-1α or IL-1β allows some control of acute M. tuberculosis infection, and IL-1 pathway is dispensable for controlling M. bovis BCG acute infection. This is in sharp contrast with TNF, which is essential for host response to both attenuated and virulent mycobacteria and may have implications for anti-inflammatory therapy with IL-1β neutralizing antibodies.

Tumour necrosis factor in infectious disease

TNF signals through two distinct receptors, designated TNFR1 and TNFR2, which initiate diverse cellular effects that include cell survival, activation, differentiation, and proliferation and cell death. These cellular responses can promote immunological and inflammatory responses that eradicate infectious agents, but can also lead to local tissue injury at sites of infection and harmful systemic effects. Defining the molecular mechanisms involved in TNF responses, the effects of natural and experimental genetic diversity in TNF signalling and the effects of therapeutic blockade of TNF has increased our understanding of the key role that TNF plays in infectious disease.

Pre-treatment with Mycobacterium avium-derived lipids reduces the macrophage response to interferon γ in BCG-vaccinated mice

Mycobacterium bovis Bacille Calmette-Guérin (BCG) is the current vaccine used against Mycobacterium tuberculosis (MTB) infection. However, exposure to environmental pathogens, such as Mycobacterium avium, interferes with the immune response induced by BCG vaccination. How M. avium affects the efficiency of BCG is unclear. In this study, BCG-vaccinated mice pre-treated with M. avium-derived lipids (MALs) showed a higher mycobacterial load and increased infiltration of inflammatory cells compared to control mice treated with Escherichia coli-derived lipids (ELs). Unexpectedly, there were no changes in cell proliferation or IFN-γ levels in spleen cells stimulated with protein purified derivatives (PPD) or heat-inactivated BCG in MALs-treated mice. However, pre-treatment with MALs decreased the bactericidal effect as well as the production of TNF-α and nitric oxide (NO) in murine macrophages from BCG-vaccinated mice stimulated with IFN-γ. These results suggest that MAL pre-treatment dampens the immune response against MTB and that this dampening is associated with a decreased response to IFN-γ stimulation in murine macrophages. T-lymphocyte responses, however, were unaffected.

IL-36 signaling amplifies Th1 responses by enhancing proliferation and Th1 polarization of naive CD4+ T cells

The interleukin-1 (IL-1) superfamily of cytokines comprises a set of pivotal mediators of inflammation. Among them, the action of IL-36 cytokines in immune responses has remained elusive. In a recent study, we demonstrated a direct effect of IL-36 on immune cells. Here we show that, among T cells, the IL-36 receptor is predominantly expressed on naive CD4(+) T cells and that IL-36 cytokines act directly on naive T cells by enhancing both cell proliferation and IL-2 secretion. IL-36β acts in synergy with IL-12 to promote Th1 polarization and IL-36 signaling is also involved in mediating Th1 immune responses to Bacillus Calmette-Guerin infection in vivo. Our findings point toward a critical function of IL-36 in the priming of Th1 cell responses in vitro, and in adaptive immunity in a model of mycobacterial infection in vivo.