Inherited disorders of human Toll-like receptor signaling: immunological implications

Heterozygous N-terminal deletion of IkappaBalpha results in functional nuclear factor kappaB haploinsufficiency, ectodermal dysplasia, and immune deficiency

BACKGROUND

Nuclear factor kappaB (NF-kappaB) is a master transcriptional regulator critical for ectodermal development and normal innate and adaptive immune function. Mutations in the IkappaB kinase gamma/NF-kappaB essential modifier have been described in male subjects with the syndrome of X-linked ectodermal dysplasia with immune deficiency that results from impaired activation of NF-kappaB.

OBJECTIVES

We sought to determine the genetic cause of ectodermal dysplasia with immune deficiency in a female patient.

METHODS

Toll-like receptor-induced production of the NF-kappaB-dependent cytokines TNF-alpha and IFN-alpha was examined by means of ELISA, the patient's IkappaBalpha gene was sequenced, and NF-kappaB activation was evaluated by means of electrophoretic mobility shift assay and NF-kappaB-luciferase assays in transfectants.

RESULTS

Toll-like receptor function was impaired in the patient. Sequencing of the patient's IkappaBalpha gene revealed a novel heterozygous mutation at amino acid 11 (W11X). The mutant IkappaBalphaW11X protein did not undergo ligand-induced phosphorylation or degradation and retained NF-kappaB in the cytoplasm. This led to roughly a 50% decrease in NF-kappaB DNA-binding activity, leading to functional haploinsufficiency of NF-kappaB activation. Unlike the only other reported IkappaBalpha mutant associated with ectodermal dysplasia associated with immune deficiency (ED-ID), S32I, IkappaBalphaW11X exerted no dominant-negative effect.

CONCLUSIONS

Functional NF-kappaB haploinsufficiency was associated with ED-ID, and this strongly suggests that normal ectodermal development and immune function are stringently dependent on NF-kappaB in that they might require more than half of normal NF-kappaB activity.

CLINICAL IMPLICATIONS

Although ED-ID is well described in male subjects, female subjects can present with a similar syndrome of ectodermal dysplasia with immune deficiency resulting from mutations in autosomal genes within the NF-kappaB pathway.

Inflammasomes in inflammatory disorders: the role of TLRs and their interactions with NLRs

The innate immune system relies on a variety of pattern recognition receptors (PRRs) such as Toll-like receptors (TLRs) and NOD-like receptors (NLRs) to sense microbial structures that are present in pathogens. Various levels of crosstalk between the TLR and NLR pathways have been described, most notably the description of a molecular scaffold complex, termed the inflammasome, which requires input from both pathways and leads to the activation of the proinflammatory cytokines interleukin (IL)-1beta and IL-18. In certain cases, the inflammatory process becomes dysregulated and chronic inflammatory diseases may develop. Understanding the interactions of the TLR and NLR pathways will provide further clues to the pathogeneses of these diseases and to the development of efficient therapies to combat them.

Innate immunogenetics: a tool for exploring new frontiers of host defence

The discovery of innate immune genes, such as those encoding Toll-like receptors (TLRs), nucleotide-binding oligomerisation domain-like receptors (NLRs), and related signal-transducing molecules, has led to a substantial improvement of our understanding of innate immunity. Recent immunogenetic studies have associated polymorphisms of the genes encoding TLRs, NLRs, and key signal-transducing molecules, such as interleukin-1 receptor-associated kinase 4 (IRAK4), with increased susceptibility to, or outcome of, infectious diseases. With the availability of high-throughput genotyping techniques, it is becoming increasingly evident that analyses of genetic polymorphisms of innate immune genes will further improve our knowledge of the host antimicrobial defence response and help in identifying individuals who are at increased risk of life-threatening infections. This is likely to open new perspectives for the development of diagnostic, predictive, and preventive management strategies to combat infectious diseases.

How important are Toll-like receptors for antimicrobial responses?

The innate immune system is the primary line of defence against invading pathogenic microbes. Toll-like receptors (TLRs) are a family of membrane receptors which play a pivotal role in sensing a wide range of invading pathogens including bacteria, fungi and viruses. TLR-deficient mice have provided us with immense knowledge on the functioning of individual TLRs. Dysregulation of TLR signalling is linked with a number of disease conditions. Disease models have helped show that targeting components of TLR signalling cascades could lead to novel therapies in the treatment of infectious diseases. In this review we focus on the evidence provided to date to explain just how important TLRs are in host defence against microbial pathogens.

Structure, function and regulation of the Toll/IL-1 receptor adaptor proteins

The Toll/IL-1 receptor (TIR) domain plays a central role in Toll-like receptor (TLR) signalling. All TLRs contain a cytoplasmic TIR domain, which, upon activation, acts as a scaffold to recruit adaptor proteins. The adaptor proteins MyD88, Mal, TRIF, TRAM and SARM are also characterized by the presence of a TIR domain. MyD88, Mal, TRIF and TRAM associate with the TLRs via homophilic TIR domain interactions whereas SARM utilizes its TIR domain to negatively regulate TRIF. It is well established that the differential recruitment of adaptors to TLRs provides a significant amount of specificity to the TLR-signalling pathways. Despite this, the TIR-TIR interface has not been well defined. However, structural studies have indicated the importance of TIR domain surfaces in mediating specific TIR-TIR interactions. Furthermore, recent findings regarding the regulation of adaptors provide further insight into the crucial role of the TIR domain in TLR signalling.

Epstein-Barr virus induces MCP-1 secretion by human monocytes via TLR2

Epstein-Barr virus (EBV) is a gammaherpesvirus infecting the majority of the human adult population in the world. TLR2, a member of the Toll-like receptor (TLR) family, has been implicated in the immune responses to different viruses including members of the herpesvirus family, such as human cytomegalovirus, herpes simplex virus type 1, and varicella-zoster virus. In this report, we demonstrate that infectious and UV-inactivated EBV virions lead to the activation of NF-kappaB through TLR2 using HEK293 cells cotransfected with TLR2-expressing vector along with NF-kappaB-Luc reporter plasmid. NF-kappaB activation in HEK293-TLR2 cells (HEK293 cells transfected with TLR2) by EBV was not enhanced by the presence of CD14. The effect of EBV was abrogated by pretreating HEK293-TLR2 cells with blocking anti-TLR2 antibodies or by preincubating viral particles with neutralizing anti-EBV antibodies 72A1. In addition, EBV infection of primary human monocytes induced the release of MCP-1 (monocyte chemotactic protein 1), and the use of small interfering RNA targeting TLR2 significantly reduced such a chemokine response to EBV. Taken together, these results indicate that TLR2 may be an important pattern recognition receptor in the immune response directed against EBV infection.

Cooperation of Toll-like receptor signals in innate immune defence

The mechanisms by which the recognition of Toll-like receptor (TLR) ligands leads to host immunity remain poorly defined. It is now thought that to induce an effective immune response, microorganisms must stimulate complex sets of pattern-recognition receptors, both within and outside of the TLR family. The combined activation of these different receptors can result in complementary, synergistic or antagonistic effects that modulate innate and adaptive immunity. Therefore, a complete understanding of the role of TLRs in host resistance to infection requires 'decoding' of these multiple receptor interactions. This Review highlights recent advances in the newly emerging field of TLR cooperation and discusses their implications for the development of adjuvants and immunotherapies.

Marketing in Heterozygous Advantage

As the rapidly advancing possibilities of biotechnology have outstripped the adaptive capacity of current legal and ethical institutions, a vigorous debate has arisen that considers the boundaries of appropriate use of this technology, particularly when applied to humans. This article examines ethical concerns surrounding the development of markets in a particular form of human genetic engineering in which heterozygotes are fitter than both homozygotes, a condition known as heterozygous advantage. To begin, we present a generalized model of the condition, illuminated by the application to sickle-cell anemia. Next, we propose a typology of related markets, some of which are currently functioning with available products and services, and others that are widely viewed as imminent. We suggest the manner in which perverse incentives may arise for firms that market genetic intervention in circumstances where heterozygous advantage is possible. Finally, we propose that this misalignment of incentives with social welfare has arisen from both ill-conceived market intervention where markets are capable of achieving efficient outcomes and the lack of market intervention where markets have failed. We offer specific legal and regulatory approaches for reform.

Toll like receptor-3 ligand poly-ICLC promotes the efficacy of peripheral vaccinations with tumor antigen-derived peptide epitopes in murine CNS tumor models

Background

Toll-like receptor (TLR)3 ligands serve as natural inducers of pro-inflammatory cytokines capable of promoting Type-1 adaptive immunity, and TLR3 is abundantly expressed by cells within the central nervous system (CNS). To improve the efficacy of vaccine strategies directed against CNS tumors, we evaluated whether administration of a TLR3 ligand, polyinosinic-polycytidylic (poly-IC) stabilized with poly-lysine and carboxymethylcellulose (poly-ICLC) would enhance the anti-CNS tumor effectiveness of tumor peptide-based vaccinations.

Methods

C57BL/6 mice bearing syngeneic CNS GL261 glioma or M05 melanoma received subcutaneous (s.c.) vaccinations with synthetic peptides encoding CTL epitopes- mEphA2 (671–679), hgp100 (25–33) and mTRP-2 (180–188) for GL261, or ovalbumin (OVA: 257–264) for M05. The mice also received intramuscular (i.m.) injections with poly-ICLC.

Results

The combination of subcutaneous (s.c.) peptide-based vaccination and i.m. poly-ICLC administration promoted systemic induction of antigen (Ag)-specific Type-1 CTLs expressing very late activation antigen (VLA)-4, which confers efficient CNS-tumor homing of vaccine-induced CTLs based on experiments with monoclonal antibody (mAb)-mediated blockade of VLA-4. In addition, the combination treatment allowed expression of IFN-γ by CNS tumor-infiltrating CTLs, and improved the survival of tumor bearing mice in the absence of detectable autoimmunity.

Conclusion

These data suggest that poly-ICLC, which has been previously evaluated in clinical trials, can be effectively combined with tumor Ag-specific vaccine strategies, thereby providing a greater index of therapeutic efficacy.

A novel X-linked recessive form of Mendelian susceptibility to mycobaterial disease

BACKGROUND

Mendelian susceptibility to mycobacterial disease (MSMD) is associated with infection caused by weakly virulent mycobacteria in otherwise healthy people. Causal germline mutations in five autosomal genes (IFNGR1, IFNGR2, STAT1, IL12RB1, IL12B) and one X-linked (NEMO) gene have been described. The gene products are physiologically related, as they are involved in interleukin 12/23-dependent, interferon gamma-mediated immunity. However, no genetic aetiology has yet been identified for about half the patients with MSMD.

METHODS

A large kindred was studied, including four male maternal relatives with recurrent mycobacterial disease, suggesting X-linked recessive inheritance. Three patients had recurrent disease caused by the bacille Calmette-Guérin vaccine, and the fourth had recurrent tuberculosis. The infections showed tropism for the peripheral lymph nodes.

RESULTS

Known autosomal and X-linked genetic aetiologies of MSMD were excluded through genetic and immunological investigations. Genetic linkage analysis of the X-chromosome identified two candidate regions, on Xp11.4-Xp21.2 and Xq25-Xq26.3, with a maximum LOD score of 2.

CONCLUSION

A new X-linked recessive form of MSMD is reported, paving the way for the identification of a new MSMD-causing gene.

Human genetics of infectious diseases: a unified theory

Since the early 1950s, the dominant paradigm in the human genetics of infectious diseases postulates that rare monogenic immunodeficiencies confer vulnerability to multiple infectious diseases (one gene, multiple infections), whereas common infections are associated with the polygenic inheritance of multiple susceptibility genes (one infection, multiple genes). Recent studies, since 1996 in particular, have challenged this view. A newly recognised group of primary immunodeficiencies predisposing the individual to a principal or single type of infection is emerging. In parallel, several common infections have been shown to reflect the inheritance of one major susceptibility gene, at least in some populations. This novel causal relationship (one gene, one infection) blurs the distinction between patient-based Mendelian genetics and population-based complex genetics, and provides a unified conceptual frame for exploring the molecular genetic basis of infectious diseases in humans.

IRAK-4 mutation (Q293X): rapid detection and characterization of defective post-transcriptional TLR/IL-1R responses in human myeloid and non-myeloid cells

Innate immunodeficiency has recently been reported as resulting from the Q293X IRAK-4 mutation with consequent defective TLR/IL-1R signaling. In this study we report a method for the rapid allele-specific detection of this mutation and demonstrate both cell type specificity and ligand specificity in defective IL-1R-associated kinase (IRAK)-4-deficient cellular responses, indicating differential roles for this protein in human PBMCs and primary dermal fibroblasts and in LPS, IL-1beta, and TNF-alpha signaling. We demonstrate transcriptional and post-transcriptional defects despite NF-kappaB signaling and intact MyD88-independent signaling and propose that dysfunctional complex 1 (IRAK1/TRAF6/TAK1) signaling, as a consequence of IRAK-4 deficiency, generates specific defects in MAPK activation that could underpin this patient's innate immunodeficiency. These studies demonstrate the importance of studying primary human cells bearing a clinically relevant mutation; they underscore the complexity of innate immune signaling and illuminate novel roles for IRAK-4 and the fundamental importance of accessory proinflammatory signaling to normal human innate immune responses and immunodeficiencies.

Evaluation of suspected immunodeficiency

The clinical utility and capacity to evaluate immunologic function has evolved significantly over the past few decades. This chapter summarizes screening methods and more sophisticated approaches to assess the immune system when there is a suspicion of an immune deficiency.

Immunodeficiency in childhood

Primary immunodeficiency disorders (PIDs) continue to illuminate mechanisms of human immunity and hypersensitivity. New discoveries in common variable immunodeficiency, the most enigmatic of PID syndromes, reveal molecular pathways of importance in human antibody production. FOXP3 mutations demonstrate the essential role that T-regulatory cells play in controlling autoantibody formation and disease. Interleukin-1 receptor-associated kinase 4 deficiency emphasizes the key role that innate immunity plays in the defense of bacterial disease occurring early in life. With respect to therapy, subcutaneous immunoglobulin treatment may indeed be a better treatment than intravenous immunoglobulin for many patients with antibody deficiency. Finally, PIDs remain in the vanguard for the treatment of inherited disorders by gene therapy. Gene therapy has cured patients with chronic granulomatous disease and severe combined immunodeficiency, but not without morbidity and mortality. Into the 21st century, PIDs continue to instruct us in human health and disease.

NF-kappaB and cytokines

Cytokines represent a heterogeneous group of soluble mediators which are involved in almost any physiological and pathological process. The release of many cytokines and numerous of their biological activities are mediated by nuclear factor-kappaB (NF-kappaB). NF-kappaB is a ubiquitous transcription factor which is crucially involved in many biological processes, including tissue development and maintenance of tissue homeostasis. NF-kappaB also controls apoptotic cell death of both normal and malignant cells. Thus, it is a challenging target for anticancer and anti-inflammatory strategies. However, it has been recognized that NF-kappaB does not only influence many biological processes but also under certain conditions the activities of NF-kappaB can be altered as well, for example, by cytokines. This cross talk needs to be taken into account when developing strategies targeting NF-kappaB for anticancer therapy.

A fast procedure for the detection of defects in Toll-like receptor signaling

OBJECTIVES

Inborn defects in Toll-like receptor signaling are recently described primary immunodeficiencies that predispose affected children to life-threatening infections. Patients with interleukin-1 receptor-associated kinase-4 deficiency are prone to invasive pneumococcal disease, and patients with UNC-93B deficiency are prone to herpes simplex virus encephalitis. These genetic disorders are underdiagnosed, partly because diagnosis currently requires expensive and time-consuming techniques available at only a few specialized centers worldwide. We, therefore, aimed to develop a cheap and fast test for the detection of defects in Toll-like receptor signaling.

PATIENTS AND METHODS

We used flow cytometry to evaluate the cleavage of membrane-bound L-selectin on granulocytes in 38 healthy controls and in 7 patients with genetically defined Toll-like receptor signaling defects (5 patients with interleukin-1 receptor-associated kinase-4 deficiency and 2 patients with UNC-93B deficiency), on activation with various Toll-like receptor agonists.

RESULTS

Impaired L-selectin shedding was observed with granulocytes from all of the interleukin-1 receptor-associated kinase-4-deficient patients on activation with agonists of Toll-like receptors 1/2, 2/6, 4, 7, and 8 and with granulocytes from all of the UNC-93B-deficient patients on activation with agonists of Toll-like receptors 7 and 8. All of the healthy controls responded to these stimuli.

CONCLUSIONS

The assessment of membrane-bound L-selectin cleavage on granulocytes by flow cytometry may prove useful for the detection of primary immunodeficiencies in the Toll-like receptor pathway, such as interleukin-1 receptor-associated kinase-4 deficiency and UNC-93B deficiency. This procedure is cheap and rapid. It may, therefore, be suitable for routine testing worldwide in children with invasive pneumococcal disease and in patients with herpes simplex encephalitis.

Impaired Toll-like receptor 8–mediated IL-6 and TNF-α production in antigen-presenting cells from patients with X-linked agammaglobulinemia

The critical role of Bruton tyrosine kinase (Btk) in B cells has been documented by the block of B-cell development in X-linked agammaglobulinemia (XLA). Less is known about Btk function in myeloid cells. Several pieces of evidence indicate that Btk is a component of Toll-like receptor (TLR) signaling. We analyzed whether Btk deficiency in XLA is associated with an impaired dendritic cell (DC) compartment or defective TLR signaling. We analyzed the expression of TLRs 1 to 9 on myeloid DCs generated from XLA patients and evaluated their response to activation by specific TLR agonists. We show that XLA patients have normal numbers of circulating DCs. Btk-deficient DCs have no defect in response to stimulation of TLRs 1/2, 2/6, 3, 4, and 5 but display a profound impairment of IL-6 and TNF-α production in response to stimulation by TLR-8 cognate agonist, ssRNA. These findings may provide an explanation for the susceptibility to enteroviral infections in XLA patients.

IRAK4 and NEMO mutations in otherwise healthy children with recurrent invasive pneumococcal disease

BACKGROUND

About 2% of childhood episodes of invasive pneumococcal disease (IPD) are recurrent, and most remain unexplained.

OBJECTIVE

To report two cases of otherwise healthy, unrelated children with recurrent IPD as the only clinical infectious manifestation of an inherited disorder in nuclear factor-kappaB(NF-kappaB)-dependent immunity.

RESULTS

One child carried two germline mutations in IRAK4, and had impaired cellular responses to interleukin (IL)1 receptor and toll-like receptor (TLR) stimulation. The other child carried a hemizygous mutation in NEMO, associated with a broader impairment of NF-kappaB activation, with an impaired cellular response to IL-1R, TLR and tumour necrosis factor receptor stimulation. The two patients shared a narrow clinical phenotype, associated with two related but different genotypes.

CONCLUSIONS

Otherwise healthy children with recurrent IPD should be explored for underlying primary immunodeficiencies affecting the IRAK4-dependent and NEMO-dependent signalling pathways.

TIR, CARD and PYRIN: three domains for an antimicrobial triad

Innate immunity to microorganisms in mammals has gained a substantial interest during the last decade. The discovery of the Toll-like receptor (TLR) family has allowed the identification of a class of membrane-spanning receptors dedicated to microbial sensing. TLRs transduce downstream signaling via their intracellular Toll-interleukin-1 receptor (TIR) domain. More recently, the role of intracellular microbial sensors has been uncovered. These molecules include the Nod-like receptors Nod1, Nod2, Ipaf and Nalps, together with the helicase domain-containing antiviral proteins RIG-I and Mda-5. The intracellular microbial sensors lack the TIR domain, but instead transduce downstream signals via two domains also implicated in homophilic protein-protein interactions, the caspase activation and recruitment domain (CARD) and PYRIN domains. In light with these recent findings, we propose that TIR, CARD and PYRIN domains represent the three arms of innate immune detection of microorganisms in mammals.

Peripheral blood neutrophil activation patterns are associated with pulmonary inflammatory responses to lipopolysaccharide in humans

Increased nuclear accumulation of NF-kappaB in LPS-stimulated peripheral blood neutrophils has been shown to be associated with more severe clinical course in patients with infection associated acute lung injury. Such observations suggest that differences in neutrophil response may contribute to the pulmonary inflammation induced by bacterial infection. To examine this question, we sequentially measured LPS-induced DNA binding of NF-kappaB in neutrophils collected from healthy humans on at least three occasions, each separated by at least 2 wk, and then determined pulmonary inflammatory responses after instillation of LPS into the lungs. Consistent patterns of peripheral blood neutrophil responses, as determined by LPS-induced NF-kappaB DNA binding, were present in volunteers, with a >80-fold difference between individuals in the mean area under the curve for NF-kappaB activation. The number of neutrophils recovered from bronchoalveolar lavage after exposure to pulmonary LPS was significantly correlated with NF-kappaB activation in peripheral blood neutrophils obtained over the pre-LPS exposure period (r = 0.65, p = 0.009). DNA binding of NF-kappaB in pulmonary neutrophils also was associated with the mean NF-kappaB area under the curve for LPS-stimulated peripheral blood neutrophils (r = 0.63, p = 0.01). Bronchoalveolar lavage levels of IL-6 and TNFRII were significantly correlated with peripheral blood neutrophil activation patterns (r = 0.75, p = 0.001 for IL-6; and r = 0.48, p = 0.049 for TNFRII. These results demonstrate that stable patterns in the response of peripheral blood neutrophils to LPS exist in the human population and correlate with inflammatory response following direct exposure to LPS in the lung.

The role of Toll-like receptors in immune disorders

Toll-like receptors (TLRs) play an important role in innate immunity. Individual TLRs recognise microbial components that are conserved among pathogens. Such recognition initiates necessary inflammatory immune responses and induces subsequent activation of adaptive immunity. Studies in people with polymorphisms in genes encoding TLR signalling can elucidate the relationship between TLRs and human diseases, such as infectious diseases, atherosclerosis and immunodeficiency. Indeed, accumulating data in respect to TLR signalling suggest that TLRs are closely related with the pathogenesis of autoimmune diseases. This review looks at the role of TLRs in various immune disorders, and discusses the pathogenesis of diseases.

The oligopeptide transporter hPepT1: gateway to the innate immune response

Bacterial products that are normally present in the lumen of the colon, such as N-formylated peptides and muramyl-dipeptide, are important for inducing the development of mucosal inflammation. The intestinal dipeptide transporter, hPepT1, which is expressed in inflamed but not in noninflamed colonic epithelial cells, mediates the transport of these bacterial products into the cytosol of colonic epithelial cells. The small bacterial peptides subsequently induce an inflammatory response, including the induction of MHC class I molecules expression and cytokines secretion, via the activation of nucleotide-binding site and leucine-rich repeat (NBS-LRR) proteins, for example NOD2, and activation of NF-kappaB. Subsequent secretion of chemoattractants by colonic epithelial cells induces the movement of neutrophils through the underlying matrix, as well as across the epithelium. These bacterial products can also reach the lamina propria through the paracellular pathway and across the basolateral membrane of epithelial cells. As a consequence, small formylated peptides can interact directly with immune cells through specific membrane receptors. Since immune cells, including macrophages, also express hPepT1, they can transport small bacterial peptides into the cytosol where these may interact with the NBS-LRR family of intracellular receptors. As in intestinal epithelial cells, the presence of these small bacterial peptides in immune cells may trigger immune response activation.

hPepT1 mediates bacterial tripeptide fMLP uptake in human monocytes

Here, we examined hPepT1 expression in the monocytic cell line, KG-1. Reverse transcription polymerase chain reaction (RT-PCR) analysis revealed that hPepT1 is expressed in KG-1 cells, while cDNA cloning and direct sequencing confirmed the sequence of KG-1 hPepT1 (accession number, AY634368). Immunoblotting of cell lysates from KG-1 cells or macrophages isolated from human peripheral blood revealed a approximately 100 kDa immunoreactive band mainly present in the membrane fraction. Uptake experiments showed that the transport of 20 microM radiolabeled Gly-Sarcosine ([14C]Gly-Sar) in KG-1 cells was Na+, Cl- dependent and disodium 4,4'-diisothiocyanatostilbene-2,2'-disulfonate (DIDS)-sensitive. In addition, hPepT1 activity was likely to be coupled to a Na+/H+ exchanger, as evidenced by the fact that [14C]Gly-Sar uptake was not affected by the absence of Na+ when cells were incubated at low pH (5.2). Interestingly, hPepT1-mediated transport was reduced in KG-1 cells incubated at low pH as it was also observed in nonpolarized Caco2-BBE cells. This pattern of pH-dependence is due to a disruption of the driving force of hPepT1-mediated transport events. This was supported by our finding that nonpolarized cells, Caco2-BBE cells and KG-1 cells, have an increased permeability to H+ when compared to polarized Caco2-BBE cells. Finally, we showed that hPepT1 is responsible for transporting fMLP into undifferentiated and differentiated (macrophage-like) KG-1 cells. Together, these results show that hPepT1 is expressed in nonpolarized immune cells, such as macrophages, where the transporter functions best at the physiological pH 7.2. Furthermore, we provide evidence for hPepT1-mediated fMLP transport, which might constitute a novel immune cell activation pathway during intestinal inflammation.

The NEMO mutation creating the most-upstream premature stop codon is hypomorphic because of a reinitiation of translation

Amorphic mutations in the NF- kappa B essential modulator (NEMO) cause X-dominant incontinentia pigmenti, which is lethal in males in utero, whereas hypomorphic mutations cause X-recessive anhidrotic ectodermal dysplasia with immunodeficiency, a complex developmental disorder and life-threatening primary immunodeficiency. We characterized the NEMO mutation 110_111insC, which creates the most-upstream premature translation termination codon (at codon position 49) of any known NEMO mutation. Surprisingly, this mutation is associated with a pure immunodeficiency. We solve this paradox by showing that a Kozakian methionine codon located immediately downstream from the insertion allows the reinitiation of translation. The residual production of an NH(2)-truncated NEMO protein was sufficient for normal fetal development and for the subsequent normal development of skin appendages but was insufficient for the development of protective immune responses.

TLR9 activation is defective in common variable immune deficiency

Common variable immune deficiency (CVID) is a primary immune deficiency characterized by low levels of serum immune globulins, lack of Ab, and reduced numbers of CD27+ memory B cells. Although T, B, and dendritic cell defects have been described, for the great majority, genetic causes have not been identified. In these experiments, we investigated B cell and plasmacytoid dendritic cell activation induced via TLR9, an intracellular recognition receptor that detects DNA-containing CpG motifs from viruses and bacteria. CpG-DNA activates normal B cells by the constitutively expressed TLR9, resulting in cytokine secretion, IgG class switch, immune globulin production, and potentially, the preservation of long-lived memory B cells. We found that CpG-DNA did not up-regulate expression of CD86 on CVID B cells, even when costimulated by the BCR, or induce production of IL-6 or IL-10 as it does for normal B cells. TLR9, found intracytoplasmically and on the surface of oligodeoxynucleotide-activated normal B cells, was deficient in CVID B cells, as was TLR9 mRNA. TLR9 B cell defects were not related to proportions of CD27+ memory B cells. CpG-activated CVID plasmacytoid dendritic cells did not produce IFN-alpha in normal amounts, even though these cells contained abundant intracytoplasmic TLR9. No mutations or polymorphisms of TLR9 were found. These data show that there are broad TLR9 activation defects in CVID which would prevent CpG-DNA-initiated innate immune responses; these defects may lead to impaired responses of plasmacytoid dendritic cells and loss of B cell function.

Targeting Toll-like receptor signaling in plasmacytoid dendritic cells and autoreactive B cells as a therapy for lupus

This review focuses on the role of Toll-like receptors (TLRs) in lupus and on possibilities to treat lupus using TLR modulating inhibitory oligodeoxynucleotides (INH-ODNs). TLRs bridge innate and adaptive immune responses and may play an important role in the pathogenesis of systemic lupus erythematosus. Of particular interest are TLR3, -7, -8, and -9, which are localized intracellularly. These TLRs recognize single-stranded or double-stranded RNA or hypomethylated CpG-DNA. Exposure to higher order CpG-DNA ligands or to immune complexed self-RNA triggers activation of autoreactive B cells and plasmacytoid dendritic cells. INH-ODNs were recently developed that block all downstream signaling events in TLR9-responsive cells. Some of these INH-ODNs can also target TLR7 signaling pathways. Based on their preferential cell reactivity, we classify INH-ODNs into class B and class R. Class B ('broadly reactive') INH-ODNs target a broad range of TLR-expressing cells. Class R ('restricted') INH-ODNs easily form DNA duplexes or higher order structures, and are preferentially recognized by autoreactive B cells and plasmacytoid dendritic cells, rather than by non-DNA specific follicular B cells. Both classes of INH-ODNs can block animal lupus. Hence, therapeutic application of these novel INH-ODNs in human lupus, particularly class R INH-ODNs, may result in more selective and disease-specific immunosuppression.

Innate cellular immune responses in newborns

Innate immunity assures the first line of defense against pathogenic microorganisms. Innate immune responses induced by bacteria, fungi, or viral replication are triggered by granulocytes, monocytes, macrophages, dentritic cells, and natural killer cells. Neonatal deficiency of innate cellular immunity includes a decreased production of interferons, IL-12/IL-23, and IL-18, and other proinflammatory cytokines, an impaired type-1 response of macrophages to IFN-gamma, the most potent macrophage-activating agent in vivo, and to lipopolysaccharide, the primary constituent of the outer membrane of Gram-negative bacteria. An increasing body of evidence suggests impaired responses of neonatal monocytes and macrophages to multiple TLR ligands. This review will discuss recent advances in understanding innate cellular immunity in human neonates, with respect to selected aspects of immune functions that may be related to increased susceptibility to infections. Components of TLR signaling and the immune consequence that may result from neonatal deficiencies will be highlighted. A better understanding of innate immunity can make the development of techniques possible by which physicians more accurately tailor prevention and treatment of neonatal infections.

Triggering TLR signaling in vaccination

Toll-like receptors (TLRs) are a family of pattern-recognition receptors that are an important link between innate and adaptive immunity. Many established, as well as experimental, vaccines incorporate ligands for TLRs, not only to protect against infectious diseases but also in therapeutic immunization against noninfectious diseases, such as cancer. We review the underlying mechanisms by which engagement of TLR signaling pathways might trigger an adaptive immune response after immunization. Although the engagement of TLR signaling pathways is a promising mechanism for boosting vaccine responses, questions of efficacy, feasibility and safety remain the subject of active investigation.

Syndrome de susceptibilite mendélienne aux infections mycobacteriennes : défauts de l’axe Interleukine-12 - Interféron

INTRODUCTION

Environmental non tuberculous mycobacteria and Bacillus Calmette-Guerin vaccines are weakly virulent mycobacteria. Nevertheless they may cause severe diseases in otherwise healthy children with no overt immunodeficiency. Parental consanguinity and familial forms are frequently observed among these patients, therefore this syndrome was named "Mendelian Susceptibility to Mycobacterial Disease".

STATE OF THE ART

In the last nine years, fife genes have been found to be mutated in patients with this syndrome: IFNGR1, IFNGR2, STAT1, IL12B, IL12RB1. Allelic heterogeneity accounts for ten distinct genetic disorders. Clinical phenotype differs between patients. The spectrum of disease extends from early-onset overwhelming mycobacterial infection to adult-onset localized disease and tuberculosis. Impaired IFN-gamma-mediated immunity is the common mechanism of the disease, outlining its major role in mycobacterial immunity.

PERSPECTIVES AND CONCLUSIONS

Better understanding of these disorders reveals an expanding clinical phenotype which justifies studying adult patients with pulmonary non tuberculous mycobacterial infection without known risk factors, severe BCGitis and recurrent tuberculosis. Molecular diagnosis makes it possible to introduce a specific regimen based on physiopathology.

Human TLR-7-, -8-, and -9-mediated induction of IFN-alpha/beta and -lambda Is IRAK-4 dependent and redundant for protective immunity to viruses

Five TLRs are thought to play an important role in antiviral immunity, sensing viral products and inducing IFN-alpha/beta and -lambda. Surprisingly, patients with a defect of IRAK-4, a critical kinase downstream from TLRs, are resistant to common viruses. We show here that IFN-alpha/beta and -lambda induction via TLR-7, TLR-8, and TLR-9 was abolished in IRAK-4-deficient blood cells. In contrast, IFN-alpha/beta and -lambda were induced normally by TLR-3 and TLR-4 agonists. Moreover, IFN-beta and -lambda were normally induced by TLR-3 agonists and viruses in IRAK-4-deficient fibroblasts. We further show that IFN-alpha/beta and -lambda production in response to 9 of 11 viruses tested was normal or weakly affected in IRAK-4-deficient blood cells. Thus, IRAK-4-deficient patients may control viral infections by TLR-3- and TLR-4-dependent and/or TLR-independent production of IFNs. The TLR-7-, TLR-8-, and TLR-9-dependent induction of IFN-alpha/beta and -lambda is strictly IRAK-4 dependent and paradoxically redundant for protective immunity to most viruses in humans.

Molecular mechanisms of autoimmunity triggered by microbial infection

Autoimmunity can be triggered by microbial infection. In this context, the discovery of Toll-like receptors (TLRs) provides new insights and research perspectives. TLRs induce innate and adaptive antimicrobial immune responses upon exposure to common pathogen-associated molecules, including lipopeptides, lipopolysaccharides, and nucleic acids. They also have the potential, however, to trigger autoimmune disease, as has been revealed by an increasing number of experimental reports. This review summarizes important facts about TLR biology, available data on their role in autoimmunity, and potential consequences for the management of patients with autoimmune disease.