Inappropriate Immune Activation Research Articles

Mitochondria, Microbiome and Their Potential Psychiatric Modulation

Pervasive developmental disorders, or autism spectrum disorders, are multifaceted and have a high rate of occurrence. Additionally, the origin of Autism appears to be multidimensional and largely unknown. Thus, it would appear novel approaches and concepts are needed in this area of scientific endeavor. In this regard, microbial cells harbored within the human gut and elsewhere are being studied to understand their multi-functional properties and their ability to affect physiological activities in their “host” organism. The communities of approximately 10 trillion microbial cells that live within the gut are involved in functions such as metabolism, nutrition and immune regulation. We and others surmise this microbiota can contribute to disruption of normal activities, causing harmful pathologies such as gastrointestinal complications, obesity, and diabetes and autism. They have the ability to trigger inappropriate immune activation, especially macrophages, which can travel from the gut and penetrate the blood brain barrier and communicate inappropriately with neural cells, altering behavior. Normally these immune cells can enter the brain and become microglia. However, being abnormally stimulated, many more can enter the brain, awakening the sentinel microglia and establishing a proinflammatory state, inducing hypoxia (altering mitochondrial performance). Thus, the microbiome has the potential to extend its influence into the brain, suggesting this may also take place within the parameters of normal activity. In part, the behavioral outcome of such an inappropriate invasion would depend on the region(s) penetrated, manifesting itself with a multidimensional behavioral profile such as occurs in autism.

Immunomodulation of antiretroviral drug-suppressed chronic HIV-1 infection in an oral probiotic double-blind placebo-controlled trial.

A putative source of inappropriate immune activation that drives human immunodeficiency virus (HIV)-1 immunopathogenesis is the gastrointestinal tract. Even with effective antiretroviral treatment, residual activation persists. We hypothesized that an oral probiotic could improve the residual immune activation in chronic treated HIV-1 infection, and tested a Bacillus coagulans GBI-30, 6086 capsule probiotic in HIV-1-infected persons with suppressed viremia on stable antiretroviral therapy in a 3-month double-blind placebo-controlled trial (10 probiotic, 7 placebo). The Gastrointestinal Symptom Rating Scale (GSRS) was administered monthly. Blood was tested at the start and end of placebo/probiotic administration for viremia, CD4(+) T cell percentage/concentration, soluble (s)CD14, soluble intestinal fatty acid binding protein, sCD163, D-dimer, C-reactive protein (CRP), interleukin-8, and tumor necrosis factor-α. All participants maintained viremia <40 RNA copies/ml. The probiotic was safe and well tolerated, and appeared to improve chronic gastrointestinal symptoms. Its administration was associated with a significant increase in the percentage of blood CD4(+) T cells compared to placebo (+2.8% versus -1.8%, p=0.018) although CD4(+) T cell concentrations were generally unchanged in both groups. None of the biomarkers showed significant changes on probiotic treatment or between-group differences in change (although significance was borderline for a greater sCD163 drop in the probiotic versus placebo group, p=0.05). Some biomarkers showed significant correlations to each other, particularly D-dimer with CRP and sCD14 with tumor necrosis factor (TNF)-α. These data demonstrate the safety and possible benefit of this probiotic for residual inflammation in treated HIV-1 infection, although further study will be required to determine the immune pathways involved.

Increased prevalence of autoimmune diseases in functional gastrointestinal disorders: case-control study of 23471 primary care patients.

There is increasing evidence that impaired mucosal defence mechanisms are implicated in the pathogenesis of the functional gastrointestinal disorders (FGIDs), allowing inappropriate immune activation. To test the hypothesis that an excess of autoimmune disorders among sufferers, using a large primary care database to examine this. Cases were diagnosed with FGIDs - irritable bowel syndrome (IBS), functional dyspepsia (FD), chronic idiopathic constipation (CIC), and multiple FGIDs. Controls were those without FGIDs. Prevalence of autoimmune disorders was compared between cases and controls using odds ratios (ORs) and 95% confidence intervals (CIs). We included 23,471 patients (mean age 51.4 years, 66.1% female). Prevalence of autoimmune disorders was greater among all FGIDs, compared with controls without. In those with FD (OR 1.35; 95% CI 1.12-1.63), CIC (OR 1.75; 95% CI 1.11-2.75), or multiple FGIDs (OR 1.49; 95% CI 1.25-1.77) this was statistically significant after controlling for age and gender. Rheumatological autoimmune disorders were significantly more frequent in those with FD (OR 1.44; 95% CI 1.15-1.80), CIC (OR 1.84; 95% CI 1.08-3.13), or multiple FGIDs (OR 1.53; 95% CI 1.24-1.88), after controlling for age and gender. However, endocrine autoimmune disorders were no more frequent in those with FGIDs, after controlling for age and gender. In a large sample of primary care patients, there was a significantly higher prevalence of autoimmune disorders among those with FD, CIC, or multiple FGIDs not explained by differences in age or gender. We were unable to control for concomitant drug use, which may partly explain this association.

Regulatory tone and mucosal immunity in asthma.

The lung is constantly exposed to a variety of inhaled foreign antigens, many of which are harmless to the body. Therefore, the mucosal immune system must not only have the capacity to distinguish self from non-self, but also harmless versus dangerous non-self. To address this, mucosal immune cells establish an anti-inflammatory steady state in the lung that must be overcome by inflammatory signals in order to mount an effector immune response. In the case of inhaled allergens, the false detection of dangerous non-self results in inappropriate immune activation and eventual allergic asthma. Both basic and clinical studies suggest that the balance between tolerogenic and inflammatory immune responses is a key feature in the outcome of health or disease. This review is focused on what we term 'regulatory tone': the immunosuppressive environment in the lung that must be overcome to induce inflammatory responses. We will summarize the current literature on this topic, with a particular focus on the role of regulatory T cells in preventing allergic disease of the lung. We propose that inter-individual differences in regulatory tone have the potential to not only establish the threshold for immune activation in the lung, but also shape the quality of resulting effector responses following tolerance breakdown.

The ribonucleotide reductase inhibitors didox and trimidox suppress IgE-stimulated mast cell cytokine secretion (HYP3P.350)

Abstract Ribonucleotide reductase is the enzyme responsible for catalyzing the production of deoxynucleotide triphosphates (dNTPs), essential for proper DNA synthesis and cell cycle progression. Inhibitors of ribonucleotide reductase have become attractive therapeutic agents for the treatment of conditions characterized by excessive cell proliferation or inappropriate immune cell activation, including myeloproliferative disorders, psoriasis and cancer. Late phase IgE-stimulated mast cell (MC) activation elicits sustained inflammation and is marked by synthesis and secretion of cytokines that have been implicated in the inflammatory responses associated with rheumatoid arthritis, multiple sclerosis and heart disease. Given the potential utility of ribonucleotide reductase inhibitors as cytostatic agents that may influence immune cell activation, we investigated the anti-inflammatory abilities of Didox and Trimidox as a therapeutic approach to attenuate the allergic response. Our results have found that Didox and Trimidox pre-treatment yields a dose-dependent reduction in IgE-stimulated bone marrow-derived mast cells (BMMC) cytokine secretion. These effects are not directly linked to an increase in cell death. Together this preliminary data could indicate a role for Didox and Trimidox in the treatment of MC-associated inflammatory and autoimmune diseases.

Transcription repressor Hes1 is a selective regulator of TLR-induced CXCL1 expression and neutrophil responses (IRM5P.708)

Abstract Chemokine-mediated neutrophil recruitment to sites of inflammation is a critical initial step in host defense and inflammatory responses. However, neutrophil recruitment must be tightly regulated to avoid inappropriate immune activation which may lead to autoimmune and inflammatory diseases. Here we show that transcription repressor hairy and enhancer of split 1 (Hes1) suppresses TLR-induced expression of CXCL1, a chemokine crucial for recruiting neutrophils. Interestingly, Hes1 deficiency does not affect expression of other pro-inflammatory cytokines such as Tnf and Il1b. Hes1 negatively regulates Cxcl1 expression and neutrophil recruitment in vivo in LPS-induced peritonitis. In addition, deficiency of Hes1 exacerbated severity of K/BxN serum-induced arthritis in which neutrophils play a key pathogenic role. Mechanistically, regulation of Cxcl1 expression by Hes1 is at the transcriptional level but not via modification of TLR-induced canonical signaling events. Instead, Hes1 represses Cxcl1 productive transcription by attenuating occupancy of a positive-transcription elongation complex P-TEFb at the Cxcl1 gene locus and thus preventing subsequent recruitment of serine 2-phosphorylated RNA polymerase II. In summary, our results identify Hes1 as a novel homeostatic regulator of CXCL1 expression and neutrophil responses and suggest that targeting Hes1-mediated repressive pathway may represent a new therapeutic approach to selectively curbing neutrophil-mediated inflammation.

The Arg-62 Residues of the TREX1 Exonuclease Act Across the Dimer Interface Contributing to Catalysis in the Opposing Protomers

TREX1 is a 3'-deoxyribonuclease that degrades single- and double-stranded DNA (ssDNA and dsDNA) to prevent inappropriate nucleic acid-mediated immune activation. More than 40 different disease-causing TREX1 mutations have been identified exhibiting dominant and recessive genetic phenotypes in a spectrum of autoimmune disorders. Mutations in TREX1 at positions Asp-18 and Asp-200 to His and Asn exhibit dominant autoimmune phenotypes associated with the clinical disorders familial chilblain lupus and Aicardi-Goutières syndrome. Our previous biochemical studies showed that the TREX1 dominant autoimmune disease phenotype depends upon an intact DNA-binding process coupled with dysfunctional active site chemistry. Studies here show that the TREX1 Arg-62 residues extend across the dimer interface into the active site of the opposing protomer to coordinate substrate DNA and to affect catalysis in the opposing protomer. The TREX1(R62A/R62A) homodimer exhibits ∼50-fold reduced ssDNA and dsDNA degradation activities relative to TREX1(WT). The TREX1 D18H, D18N, D200H, and D200N dominant mutant enzymes were prepared as compound heterodimers with the TREX1 R62A substitution in the opposing protomer. The TREX1(D18H/R62A), TREX1(D18N/R62A), TREX1(D200H/R62A), and TREX1(D200N/R62A) compound heterodimers exhibit higher levels of ss- and dsDNA degradation activities than the homodimers demonstrating the requirement for TREX1 Arg-62 residues to provide necessary structural elements for full catalytic activity in the opposing TREX1 protomer. This concept is further supported by the loss of dominant negative effects in the TREX1 D18H, D18N, D200H, and D200N compound heterodimers. These data provide compelling evidence for the required TREX1 dimeric structure for full catalytic function.

The role of indoleamine 2,3-dioxygenase (IDO) in immune tolerance: Focus on macrophage polarization of THP-1 cells

Macrophages can be divided into two groups as M1 and M2 phenotype. Our results and other groups revealed that IFN-γ can up-regulate the IDO expression and differentiate THP-1 cells to M1 phenotype. Therefore we hypothesized that IDO may play potential roles in macrophage differentiation. Interesting, our results indicated that the ectopic IDO increases the expression of M2 markers such as IL-10 and CXCR4 while decreases the M1 markers such as CCR7 and IL-12p35. In contrast, the knockdown of IDO expression in THP-1 cells resulted in increased M1 markers and lower M2 markers. Our results suggested that the expression intensity of IDO modulates macrophages differentiation. These finding support the counter-regulatory role for IDO with regarding to the polarization of macrophages to restrain excessive or inappropriate immune activation in inflammatory or tumor microenvironment. It throws new light on the mechanisms about the immunosuppressive effect of IDO in tumor or inflammatory diseases.

Antigen-specific expansion of human regulatory T cells as a major tolerance mechanism against mucosal fungi.

Foxp3(+) regulatory T cells (Treg) have a central role for keeping the balance between pro- and anti-inflammatory immune responses against chronically encountered antigens at mucosal sites. However, their antigen specificity especially in humans is largely unknown. Here we used a sensitive enrichment technology for antigen-reactive T cells to directly compare the conventional vs. regulatory CD4(+) T-cell response directed against two ubiquitous mucosal fungi, Aspergillus fumigatus and Candida albicans. In healthy humans, fungus-specific CD4(+)CD25(+)CD127(-)Foxp3(+) Treg are strongly expanded in peripheral blood and possess phenotypic, epigenetic and functional features of thymus-derived Treg. Intriguingly, for A. fumigatus, the strong Treg response contrasts with minimal conventional T-cell memory, indicating selective Treg expansion as an effective mechanism to prevent inappropriate immune activation in healthy individuals. By contrast, in subjects with A. fumigatus allergies, specific Th2 cells were strongly expanded despite the presence of specific Treg. Taken together, we demonstrate a largely expanded Treg population specific for mucosal fungi as part of the physiological human T-cell repertoire and identify a unique capacity of A. fumigatus to selectively generate Treg responses as a potentially important mechanism for the prevention of allergic reactions.

Anti-IL-6 Treatment for Inflammatory Bowel Diseases: Next Cytokine, Next Target

Inflammatory bowel diseases (IBD) are chronic, relapsing, and destructive inflammatory disorders of the gastrointestinal tract. Both Crohn's disease (CD) and ulcerative colitis (UC) seem to arise from an impaired dialog between the environment and gut microbiota in genetically susceptible hosts, leading to an inappropriate immune activation and resulting in the over-production of pro-inflammatory cytokines. IL-6 is a key modulator of inflammatory response. It is a phylogenetically important cytokine with relevance in IBD, as well as in other chronic inflammatory diseases and cancer. Influencing the production of this cytokine can change the balance of effector CD4+ T cell subsets and induce B cell antibody production. Moreover, given IL-6 is mostly produced from innate immune cells such as macrophages, neutrophils and mast cells, it is a strategic bridge between the innate and the adaptive system. Interestingly, IL-6 induced signaling can be primarily seen in a relatively small number of IL-6 responsive cells whereas in a chronic phase of inflammation it is able to activate almost all cells of the body through a process known as trans-signaling. In this review, we discuss the role of IL-6 in chronic inflammation, with particular emphasis on its role in CD and UC, and we explore the potential to develop anti-IL-6 agents for IBD treatment.

The TREX1 C-terminal Region Controls Cellular Localization through Ubiquitination

TREX1 is an autonomous 3'-exonuclease that degrades DNA to prevent inappropriate immune activation. The TREX1 protein is composed of 314 amino acids; the N-terminal 242 amino acids contain the catalytic domain, and the C-terminal region (CTR) localizes TREX1 to the cytosolic compartment. In this study, we show that TREX1 modification by ubiquitination is controlled by a highly conserved sequence in the CTR to affect cellular localization. Transfection of TREX1 deletion constructs into human cells demonstrated that this sequence is required for ubiquitination at multiple lysine residues through a "non-canonical" ubiquitin linkage. A proteomic approach identified ubiquilin 1 as a TREX1 CTR-interacting protein, and this interaction was verified in vitro and in vivo. Cotransfection studies indicated that ubiquilin 1 localizes TREX1 to cytosolic punctate structures dependent upon the TREX1 CTR and lysines within the TREX1 catalytic core. Several TREX1 mutants linked to the autoimmune diseases Aicardi-Goutières syndrome and systemic lupus erythematosus that exhibit full catalytic function were tested for altered ubiquitin modification and cellular localization. Our data show that these catalytically competent disease-causing TREX1 mutants exhibit differential levels of ubiquitination relative to WT TREX1, suggesting a novel mechanism of dysfunction. Furthermore, these differentially ubiquitinated disease-causing mutants also exhibit altered ubiquilin 1 co-localization. Thus, TREX1 post-translational modification indicates an additional mechanism by which mutations disrupt TREX1 biology, leading to human autoimmune disease.

234: Selective regulation of CXCL1 expression and neutrophil responses by transcription repressor Hes1

Recruitment of neutrophils to sites of inflammation is essential for eliciting competent immune responses. However, uncontrolled neutrophil responses contribute to inappropriate immune activation under a number of autoimmune and inflammatory conditions. Therefore, neutrophil responses must be tightly regulated to ensure strong activation while avoiding excessive inflammation. Here we show that transcription repressor hairy and enhancer of split 1 (Hes1) suppresses toll-like receptor 4 (TLR4)-induced expression of CXCL1, a chemokine crucial for recruitment of neutrophils to sites of inflammation. Interestingly, Hes1 deficiency specifically promotes Cxcl1 expression without affecting expression of other prototypical pro-inflammatory cytokine genes such as Tnf and Ilb . Hes1 negatively regulates Cxcl1 expression and neutrophil recruitment in vivo in a model of LPS-induced peritonitis. In addition, deficiency of Hes1 exacerbated severity of K/BxN serum-induced arthritis, a model of inflammatory arthritis in which neutrophil plays a key pathogenic role. Mechanistically, regulation of Cxcl1 expression by Hes1 is at the transcriptional level but not via modification of TLR4-induced canonical signaling events such as activation of NF-kB. Instead, Hes1 represses Cxcl1 expression by inhibiting occupancy of serine 2-phosphorylated RNA polymerase II, a hallmark of efficient transcription elongation, at the Cxcl1 gene locus. In summary, these results identify Hes1 as a homeostatic negative regulator of CXCL1 expression and neutrophil responses and suggest that targeting Hes1-mediated repressive pathway may represent a novel therapeutic approach that selectively curbs neutrophil-mediated inflammation while preserving other aspects of immunity.

Preferential depletion of gut CD4-expressing iNKT cells contributes to systemic immune activation in HIV-1 infection.

Chronic inappropriate immune activation is the central defect-driving loss of CD4(+) T helper cells and progression to AIDS in persons with HIV-1 infection, but the mechanisms remain controversial. We examined key regulatory invariant receptor natural killer T (iNKT) cells in the gut, the largest reservoir of lymphocytes and a key arena of HIV-1 pathogenesis. In healthy control persons, the anti-inflammatory CD4(+) iNKT-cell subset predominated over the pro-inflammatory CD4(-) iNKT-cell subset in the gut, but not in the blood, compartment. HIV-1 infection resulted in a preferential loss of this anti-inflammatory CD4(+) iNKT-cell subset within the gut. The degree of loss of the CD4(+) iNKT-cell subset in the gut, but not in the blood, correlated to the systemic immune activation and exhaustion that have been linked to disease progression. These results suggest a potentially important contribution of gut iNKT-cell imbalance in determining the systemic immune activation that is the hallmark of HIV-1 pathogenesis.

Can immunotherapy be useful as a "functional cure" for infection with Human Immunodeficiency Virus-1?

Immunotherapy aims to assist the natural immune system in achieving control over viral infection. Various immunotherapy formats have been evaluated in either therapy-naive or therapy-experienced HIV-infected patients over the last 20 years. These formats included non-antigen specific strategies such as cytokines that stimulate immunity or suppress the viral replication, as well as antibodies that block negative regulatory pathways. A number of HIV-specific therapeutic vaccinations have also been proposed, using in vivo injection of inactivated virus, plasmid DNA encoding HIV antigens, or recombinant viral vectors containing HIV genes. A specific format of therapeutic vaccines consists of ex vivo loading of autologous dendritic cells with one of the above mentioned antigenic formats or mRNA encoding HIV antigens.This review provides an extensive overview of the background and rationale of these different therapeutic attempts and discusses the results of trials in the SIV macaque model and in patients. To date success has been limited, which could be explained by insufficient quality or strength of the induced immune responses, incomplete coverage of HIV variability and/or inappropriate immune activation, with ensuing increased susceptibility of target cells.Future attempts at therapeutic vaccination should ideally be performed under the protection of highly active antiretroviral drugs in patients with a recovered immune system. Risks for immune escape should be limited by a better coverage of the HIV variability, using either conserved or mosaic sequences. Appropriate molecular adjuvants should be included to enhance the quality and strength of the responses, without inducing inappropriate immune activation. Finally, to achieve a long-lasting effect on viral control (i.e. a “functional cure”) it is likely that these immune interventions should be combined with anti-latency drugs and/or gene therapy.

The role and pathophysiological relevance of membrane transporter PepT1 in intestinal inflammation and inflammatory bowel disease.

Intestinal inflammation is characterized by epithelial disruption, leading to loss of barrier function and the recruitment of immune cells, including neutrophils. Although the mechanisms are not yet completely understood, interactions between environmental and immunological factors are thought to be critical in the initiation and progression of intestinal inflammation. In recent years, it has become apparent that the di/tripeptide transporter PepT1 may play an important role in the pathogenesis of such inflammation. In healthy individuals, PepT1 is primarily expressed in the small intestine and transports di/tripeptides for metabolic purposes. However, during chronic inflammation such as that associated with inflammatory bowel disease, PepT1 expression is upregulated in the colon, wherein the protein is normally expressed either minimally or not at all. Several recent studies have shown that PepT1 binds to and transports various bacterial di/tripeptides into colon cells, leading to activation of downstream proinflammatory responses via peptide interactions with innate immune receptors. In the present review, we examine the relationship between colonic PepT1-mediated peptide transport in the colon and activation of innate immune responses during disease. It is important to understand the mechanisms of PepT1 action during chronic intestinal inflammation to develop future therapies addressing inappropriate immune activation in the colon.

MHC Class II and T Cell Receptor Signals Are Dispensable for IL-2-Induced Regulatory T Cell Proliferation In Vivo

Abstract 2181Regulatory T cells (Tregs) protect the host from autoimmunity and inappropriate immune activation. Thus, to ensure immune tolerance in the steady state, an adequate number of peripheral Tregs must be constantly maintained. Prior work has suggested that major histocompatibility class II (MHC II) and interleukin-2 (IL-2) are both necessary to maintain peripheral Treg homeostasis and proliferation in vivo. However, we have recently reported that Treg proliferation may not strictly depend on MHC II, as the provision of IL-2 was sufficient to drive proliferation of Tregs in an MHC II-independent manner in vitro, as long as the Tregs interacted with dendritic cells (DC)s.Here, extending our previous in vitro observations, we tested the dependence of Treg proliferation on IL-2, DCs, and TCR signaling in vivo. Proliferation of adoptively transferred Tregs was detected in wildtype (WT) mice. This proliferation was markedly enhanced when the mice were injected with IL-2 immune complexes (IC)s but not when the IL-2 IC-injected mice lacked DCs, suggesting that IL-2-induced Treg proliferation was dependent on DCs in vivo. As previously reported, adoptively transferred Tregs did not proliferate in MHC II-deficient hosts. However, the injection of IL-2 ICs into these mice induced Treg proliferation comparable to those transferred into IL-2 IC-injected WT mice, suggesting that IL-2 signaling by Tregs obviated the need of MHC II for their proliferation. Furthermore, while the ablation of TCR signaling by conditional deletion of the adaptor protein SH2 domain-containing leukocyte phosphoprotein of 76 kDa (SLP-76) rendered Tregs unable to proliferate by themselves, IL-2 IC treatment partially rescued this deficiency.We next examined the signaling pathways involved in Treg proliferation downstream of the IL-2 receptor. Despite the importance of the Stat5 pathway in IL-2 receptor signaling during Treg development in the thymus, activation of Stat5b alone was insufficient to rescue proliferation of SLP-76-deficient Tregs, indicating that alternative pathways must also be activated for Treg proliferation. Additional studies investigating the role of other signaling molecules downstream of the IL-2 receptor are currently underway.In summary, we have demonstrated for the first time that Tregs do not require TCR signaling through interaction with MHC II for their proliferation in vivo. We propose that this MHC II-independent mode of Treg proliferation allows Tregs with multiple antigen specificities to proliferate, which ensures that a diverse TCR repertoire is continuously maintained in the Treg pool. Furthermore, we believe that exploitation of these pathways may be therapeutically beneficial in autoimmunity and in transplantation. Disclosures:No relevant conflicts of interest to declare.

The TREX1 Exonuclease R114H Mutation in Aicardi-Goutières Syndrome and Lupus Reveals Dimeric Structure Requirements for DNA Degradation Activity

Mutations in the TREX1 gene cause Aicardi-Goutières syndrome (AGS) and are linked to the autoimmune disease systemic lupus erythematosus. The TREX1 protein is a dimeric 3' DNA exonuclease that degrades DNA to prevent inappropriate immune activation. One of the most common TREX1 mutations, R114H, causes AGS as a homozygous and compound heterozygous mutation and is found as a heterozygous mutation in systemic lupus erythematosus. The TREX1 proteins containing R114H and the insertion mutations aspartate at position 201 (D201ins) and alanine at position 124 (A124ins), found in compound heterozygous AGS with R114H, were prepared and the DNA degradation activities were tested. The homodimer TREX1(R114H/R114H) exhibits a 23-fold reduced single-stranded DNA (ssDNA) exonuclease activity relative to TREX1(WT). The TREX1(D201ins/D201ins) and TREX1(A124ins/A124ins) exhibit more than 10,000-fold reduced ssDNA degradation activities. However, the TREX1(R114H/D201ins) and TREX1(R114H/A124ins) compound heterodimers exhibit activities 10-fold greater than the TREX1(R114H/R114H) homodimer during ssDNA and double-stranded DNA (dsDNA) degradation. These higher levels of activities measured in the TREX1(R114H/D201ins) and TREX1(R114H/A124ins) compound heterodimers are attributed to Arg-114 residues of TREX1(D201ins) and TREX1(A124ins) positioned at the dimer interface contributing to the active sites of the opposing TREX1(R114H) protomer. This interpretation is further supported by exonuclease activities measured for TREX1 enzymes containing R114A and R114K mutations. These biochemical data provide direct evidence for TREX1 residues in one protomer contributing to DNA degradation catalyzed in the opposing protomer and help to explain the dimeric TREX1 structure required for full catalytic competency.

Can immunotherapy be useful for a « functional cure » of HIV infection?

Highly active antiretroviral therapy (HAART) alone cannot eliminate HIV from the body and even in patients with undetectable viral load, full recovery of the system is not being obtained, with signs of inappropriate immune activation and immuno-senescence. Therapeutic strategies, complementary to HAART, aim at a cure i.e. control HIV in such a way that it no longer produces harm to the system. Anti-latency drugs, anti-inflammatory agents and/or measures to prevent or eliminate concomitant infections may contribute to a functional cure. Immunotherapy represents another possible strategy, which should reverse deficient T cell generation, aberrant differentiation, exhaustion and ineffective HlV-specific T cell responses. Four major pathways are being attempted: 1. Administration of so called common γ-chain cytokines, including inter-leukin (IL)-2, IL-7, IL-15 or IL-21, which are crucial in T cell generation, differentiation and function. Only IL-2 has been formally evaluated in a phase 3 trial: although it increased CD4 T counts, it failed to improve clinical outcome. 2. Blockade of negative regulator receptor-ligand interaction, including CTLA-4, PD-1, TIM-3 has been shown to improve HlV-specific T cell function in vitro, but seemingly discrepant results have been obtained in the SIV macaque model. PD-1 blockade lowered viral load and improved survival, whereas CTLA-4 blockade increased viral load, probably because of activation. 3. Therapeutic immunization with HIV antigens. Older trials with de-enveloped HIV particles (Remune®) failed to improve clinical outcome in HIV-infected subjects. More recent trials, using ALVAC®, a canarypox vaccine, containing HIV antigens-encoding genes, mitigated viral load rebound after HAART interruption in several trials, but had no effect or even increased rebound in other trials, the latter result being probably linked to inappropriate activation. 4. The most recent tendency is to target dendritic cells with either inactivated autologous virus or virus antigen-encoding RNA. Safety and immunogenicity of this strategy has been well established, but clinical results are equivocal as yet. In any case, this approach is amendable to further refinement, with regard to inclusion of RNA encoded patient-adapted viral sequences and co-stimulatory molecules, as well as improved targeting. In conclusion, several HIV immunotherapy strategies are being attempted, with varying success. The basic challenge remains to find a (combined) strategy, successfully activating effective HlV-specific T cell responses, while reducing inappropriate HIV-promoting activation.

Establishment of intestinal homeostasis during the neonatal period.

The intestinal mucosa faces the challenge of regulating the balance between immune tolerance towards commensal bacteria, environmental stimuli and food antigens on the one hand, and induction of efficient immune responses against invading pathogens on the other hand. This regulatory task is of critical importance to prevent inappropriate immune activation that may otherwise lead to chronic inflammation, tissue disruption and organ dysfunction. The most striking example for the efficacy of the adaptive nature of the intestinal mucosa is birth. Whereas the body surfaces are protected from environmental and microbial exposure during fetal life, bacterial colonization and contact with potent immunostimulatory substances start immediately after birth. In the present review, we summarize the current knowledge on the mechanisms underlying the transition of the intestinal mucosa during the neonatal period leading to the establishment of a stable, life-long host-microbial homeostasis. The environmental exposure and microbial colonization during the neonatal period, and also the influence of maternal milk on the immune protection of the mucosa and the role of antimicrobial peptides, are described. We further highlight the molecular mechanisms of innate immune tolerance in neonatal intestinal epithelium. Finally, we link the described immunoregulatory mechanisms to the increased susceptibility to inflammatory and infectious diseases during the neonatal period.

Immune system in the intestine and mucosal inflammation

The gastrointestinal tract is home to the largest accumulation of leukocytes in the body where they are constantly being exposed to a wide array of foreign antigens. Complex signalling networks between multiple cell types ensure that the appropriate balance is maintained between immune protection from infection and tolerance of harmless antigens, such as the resident bacterial flora and dietary antigens. Disturbance of this balance results in inappropriate immune activation, as observed in patients with Inflammatory Bowel Disease or food allergy. The intestine is highly adapted to facilitate immunological sampling of intestinal contents. Specialized epithelial cells, M cells, actively transport antigen to underlying lymphoid follicles for immunological processing while dendritic cells extend dendrites between epithelial cells in order to sample adherent bacterial species. We will focus on the mechanisms by which the intestinal immune system samples luminal antigen and the controlling features that determine immunological tolerance. In particular, the molecular mechanisms by which intestinal microbes induce tolerogenic responses within the gut and the relevance of intestinal T regulatory cell responses to protection from intestinal inflammation will be discussed.