Effects of NOD-like receptors in human B lymphocytes and crosstalk between NOD1/NOD2 and Toll-like receptors

Control of adaptive immunity by pattern recognition receptors

One of the most significant conceptual advances in immunology in recent history is the recognition that signals from the innate immune system are required for induction of adaptive immune responses. Two breakthroughs were critical in establishing this paradigm: the identification of dendritic cells (DCs) as the cellular link between innate and adaptive immunity and the discovery of pattern recognition receptors (PRRs) as a molecular link that controls innate immune activation as well as DC function. Here, we recount the key events leading to these discoveries and discuss our current understanding of how PRRs shape adaptive immune responses, both indirectly through control of DC function and directly through control of lymphocyte function. In this context, we provide a conceptual framework for how variation in the signals generated by PRR activation, in DCs or other cell types, can influence T cell differentiation and shape the ensuing adaptive immune response.

Contribution of Nucleotide-Binding Oligomerization Domain-like (NOD) Receptors to the Immune and Metabolic Health

Nucleotide-binding oligomerization domain-like (NOD) receptors rely on the interface between immunity and metabolism. Dietary factors constitute critical players in the activation of innate immunity and modulation of the gut microbiota. The latter have been involved in worsening or improving the control and promotion of diseases such as obesity, type 2 diabetes, metabolic syndrome, diseases known as non-communicable metabolic diseases (NCDs), and the risk of developing cancer. Intracellular NODs play key coordinated actions with innate immune 'Toll-like' receptors leading to a diverse array of gene expressions that initiate inflammatory and immune responses. There has been an improvement in the understanding of the molecular and genetic implications of these receptors in, among others, such aspects as resting energy expenditure, insulin resistance, and cell proliferation. Genetic factors and polymorphisms of the receptors are determinants of the risk and severity of NCDs and cancer, and it is conceivable that dietary factors may have significant differential consequences depending on them. Host factors are difficult to influence, while environmental factors are predominant and approachable with a preventive and/or therapeutic intention in obesity, T2D, and cancer. However, beyond the recognition of the activation of NODs by peptidoglycan as its prototypical agonist, the underlying molecular response(s) and its consequences on these diseases remain ill-defined. Metabolic (re)programming is a hallmark of NCDs and cancer in which nutritional strategies might play a key role in preventing the unprecedented expansion of these diseases. A better understanding of the participation and effects of immunonutritional dietary ingredients can boost integrative knowledge fostering interdisciplinary science between nutritional precision and personalized medicine against cancer. This review summarizes the current evidence concerning the relationship(s) and consequences of NODs on immune and metabolic health.

The effects of NOD-like receptors on adaptive immune responses

It has long been appreciated that cues from the innate immune system orchestrate downstream adaptive immune responses. Although previous work has focused on the roles of Toll-like receptors in this regard, relatively little is known about how Nod-like receptors instruct adaptive immunity. Here we review the functions of different members of the Nod-like receptor family in orchestrating effector and anamnestic adaptive immune responses. In particular, we address the ways in which inflammasome and non-inflammasome members of this family affect adaptive immunity under various infectious and environmental contexts. Furthermore, we identify several key mechanistic questions that studies in this field have left unaddressed. Our aim is to provide a framework through which immunologists in the adaptive immune field may view their questions through an innate-immune lens and vice-versa.

Multifaceted roles and regulation of nucleotide-binding oligomerization domain containing proteins

Nucleotide-binding oligomerization domain-containing proteins, NOD1 and NOD2, are cytosolic receptors that recognize dipeptides and tripeptides derived from the bacterial cell wall component peptidoglycan (PGN). During the past two decades, studies have revealed several roles for NODs beyond detecting PGN fragments, including activation of an innate immune anti-viral response, NOD-mediated autophagy, and ER stress induced inflammation. Recent studies have also clarified the dynamic regulation of NODs at cellular membranes to generate specific and balanced immune responses. This review will describe how NOD1 and NOD2 detect microbes and cellular stress and detail the molecular mechanisms that regulate activation and signaling while highlighting new evidence and the impact on inflammatory disease pathogenesis.

B-cell capacity for expansion and differentiation into plasma cells are altered in osteoarthritis

OBJECTIVE

Autoantibody (autoAbs) production in osteoarthritis (OA), coupled with evidence of disturbed B-cell homoeostasis, suggest a potential role for B-cells in OA. B-cells can differentiate with T-cell help (T-dep) or using alternative Toll like recptor (TLR) co-stimulation (TLR-dep). We analysed the capacity for differentiation of B-cells in OA versus age-matched healthy controls (HCs) and compared the capacity of OA synovitis-derived stromal cells to provide support for plasma cell (PC) maturation.

METHODS

B-cells were isolated from OA and HC. Standardised in vitro models of B-cell differentiation were used comparing T-dep (CD40 (cluster of differentiation-40/BCR (B-cell receptor)-ligation) versus TLR-dep (TLR7/BCR-activation). Differentiation marker expression was analysed by flow-cytometry; antibody secretion (immunnoglobulins IgM/IgA/IgG) by ELISA (enzyme-linked immunosorbent assay), gene expression by qPCR (quantitative polymerase chain reaction).

RESULTS

Compared to HC, circulating OA B-cells showed an overall more mature phenotype. The gene expression profile of synovial OA B-cells resembled that of PCs. Circulating B-cells differentiated under both TLR-dep and T-dep, however OA B-cells executed differentiation faster in terms of change in surface marker and secreted more antibody at Day 6, while resulting in similar PC numbers at Day 13, with an altered phenotype at Day 13 in OA. The main difference was reduced early B-cells expansion in OA (notably in TLR-dep) and reduced cell death. Stromal cells support from OA-synovitis allowed better PC survival compared to bone marrow, with an additional population of cells and higher Ig-secretion.

CONCLUSION

Our findings suggest that OA B-cells present an altered capacity for proliferation and differentiation while remaining able to produce antibodies, notably in synovium. These findings may partly contribute to autoAbs development as recently observed in OA synovial fluids.

IL-6 effector function of group 2 innate lymphoid cells (ILC2) is NOD2 dependent

Cutaneous group 2 innate lymphoid cells (ILC2) are spatially and epigenetically poised to respond to barrier compromise and associated immunological threats. ILC2, lacking rearranged antigen-specific receptors, are primarily activated by damage-associated cytokines and respond with type 2 cytokine production. To investigate ILC2 potential for direct sensing of skin pathogens and allergens, we performed RNA sequencing of ILC2 derived from in vivo challenged human skin or blood. We detected expression of NOD2 and TLR2 by skin and blood ILC2. Stimulation of ILC2 with TLR2 agonist alone not only induced interleukin-5 (IL-5) and IL-13 expression but also elicited IL-6 expression in combination with Staphylococcus aureus muramyl dipeptide (MDP). Heat-killed skin-resident bacteria provoked an IL-6 profile in ILC2 in vitro that was notably impaired in ILC2 derived from patients with nucleotide-binding oligomerization domain-containing protein 2 (NOD2) mutations. In addition, we show that NOD2 signaling can stimulate autophagy in ILC2, which was also impaired in patients with NOD2 mutations. Here, we have identified a role for ILC2 NOD2 signaling in the differential regulation of ILC2-derived IL-6 and have reported a previously unrecognized pathway of direct ILC2 bacterial sensing.

Adenosine-Induced NLRP11 in B Lymphoblasts Suppresses Human CD4+ T Helper Cell Responses

NLRP11 is a member of the PYD domain-containing, nucleotide-binding oligomerization-domain (NOD-) like receptor (NLR) family. The true stimulus of NLRP11 is still unclear to date, so the current study is built upon NLRP11 induction via adenosine stimulation and that activation can shape adaptive immune responses in a caspase-1-independent manner. We examined the regulation and mechanism of adenosine responsiveness via NLRP11 in human Daudi Burkitt's B lymphoma cells and their effects on human peripheral CD4⁺ T lymphocytes from healthy individuals. NLRP11 was significantly upregulated after induction with adenosine at both the mRNA and protein levels, which led to the interaction of endogenous NLRP11 with the ASC adaptor protein; however, this interaction did not result in the activation of the caspase-1 enzyme. Furthermore, cocultures of NLRP11-expressing Burkitt's lymphoma cells and naïve human peripheral CD4⁺ T lymphocytes had reduced IFN-γ and IL-17A production, whereas IL-13 and IL-10 cytokines did not change. Interestingly, IFN-γ and IL-17A were recovered after transfection of Burkitt's lymphoma cells with siRNAs targeting NLRP11. Concomitant with NLRP11 upregulation, we also exhibited that adenosine A_2B receptor signaling induced two phosphorylated downstream effectors, pErk1/2 and pAkt (Ser473), but not pAkt (Thr308). Taken together, our data indicate that adenosine is a negative regulator of Th1 and Th17 responses via NLRP11 in an inflammasome-independent manner.

NOD1 and NOD2 in inflammatory and infectious diseases

It has been long recognized that NOD1 and NOD2 are critical players in the host immune response, primarily by their sensing bacterial peptidoglycan-conserved motifs. Significant advances have been made from efforts that characterize their upstream activators, assembly of signaling complexes, and activation of downstream signaling pathways. Disruption in NOD1 and NOD2 signaling has also been associated with impaired host defense and resistance to the development of inflammatory diseases. In this review, we will describe how NOD1 and NOD2 sense microbes and cellular stress to regulate host responses that can affect disease pathogenesis and outcomes.

Immune disruption occurs through altered gut microbiome and NOD2 in arsenic induced mice: Correlation with colon cancer markers

The gut microbial compositions are easily affected by the environmental chemicals like arsenic (As) leading to dysbiosis. The dysbiosis of gut microbiome has associated with numerous diseases; among which cancer is one of the major diseases. The meticulous mechanism underlying As- altered gut microbiome, Nucleotide domine containing protein 2 (NOD2) and how altered gut microbiome disturbs the intestinal homeostasis to regulate colon cancer markers remains unclear. For this, one hundred twenty 8-week old age male mice were divided into two exposure periods (3 and 6 months), and each exposure group animals were further divided into four groups as control (received only distilled H₂O), low (0.15 mg As₂O₃/L), medium (1.5 mg As₂O₃/L) and high (15 mg As₂O₃/L) dose (each group containing 15 mice) administrated for 3 and 6 months. The results showed that As exposure highly altered gut microbiome with a significant depletion in NOD2 in contrast to control groups. Moreover, the dendritic cells (CD11a, CD103, CX3CR1) and macrophages (F4/80) were significantly increased by As exposure. Interestingly, increased trend of inflammatory cytokines (TNF-α, IFN-γ, IL-17) and depleted anti-inflammatory cytokines (IL-10) was observed in As exposed mice. Furthermore, the colon cancer markers β-catenin has increased while APC was arrested by As both in 3 and 6 months treated animals. Many studies reported that As altered gut microbial compositions, in this study, our results suggested that altered gut microbiome indirectly regulates colon cancer marker through immune system destruction mediated by inflammatory cytokines.

NOD2 signaling pathway is involved in fibronectin fragment-induced pro-catabolic factor expressions in human articular chondrocytes

The nucleotide-binding and oligomerization domain (NOD) is an innate pattern recognition receptor that recognizes pathogen- and damage-associated molecular patterns. The 29-kDa amino-terminal fibronectin fragment (29-kDa FN-f) is a matrix degradation product found in the synovial fluids of patients with osteoarthritis (OA). We investigated whether NOD2 was involved in 29-kDa FN-f-induced pro-catabolic gene expression in human chondrocytes. The expression of mRNA and protein was measured using quantitative real-time polymerase chain reaction (qrt-PCR) and Western blot analysis. Small interfering RNAs were used for knockdown of NOD2 and toll-like receptor 2 (TLR-2). An immunoprecipitation assay was performed to examine protein interactions. The NOD2 levels in human OA cartilage were much higher than in normal cartilage. NOD1 and NOD2 expression, as well as pro-inflammatory cytokines, including interleukin-1beta (IL-1β) and tumor necrosis factor-alpha (TNF-α), were upregulated by 29-kDa FN-f in human chondrocytes. NOD2 silencing showed that NOD2 was involved in the 29-kDa FN-f-induced expression of TLR-2. Expressions of IL-6, IL-8, matrix metalloproteinase (MMP)-1, -3, and -13 were also suppressed by TLR-2 knockdown. Furthermore, NOD2 and TLR-2 knockdown data demonstrated that both NOD2 and TLR-2 modulated the expressions of their adaptors, receptor-interacting protein 2 (RIP2) and myeloid differentiation 88, in 29-kDa FN-f-treated chondrocytes. 29-kDa FN-f enhanced the interaction of NOD2, RIP2 and transforming growth factor beta-activated kinase 1 (TAK1), an indispensable signaling intermediate in the TLR-2 signaling pathway, and activated nuclear factor-κB (NF-κB), subsequently leading to increased expressions of pro-inflammatory cytokines and cartilage-degrading enzymes. These results demonstrate that 29-kDa FN-f modulated pro-catabolic responses via cross-regulation of NOD2 and TLR-2 signaling pathways.

B Cell Immunophenotyping and Transcriptional Profiles of Memory B Cells in Patients with Myasthenia Gravis

Myasthenia gravis (MG) is an autoimmune neuromuscular junction disorders mediated by various autoantibodies. Although most patients with MG require chronic immunosuppressive treatment to control disease activity, appropriate surveillance biomarkers that monitor disease activity or potential toxicity of immunosuppressants are yet to be developed. Herein, we investigated quantitative distribution of peripheral blood B cell subsets and transcriptional profiles of memory B cells (CD19+ CD27+) in several subgroups of MG patients classified according to the Myasthenia Gravis Foundation of America (MGFA) Clinical Classification. This study suggests potential immunologic B-cell markers that may guide treatment decision in future clinical settings.

The Nod2 Agonist Muramyl Dipeptide Cooperates with the TLR4 Agonist Lipopolysaccharide to Enhance IgG2b Production in Mouse B Cells

Many studies have shown that Toll-like receptors (TLRs) and Nod-like receptors (NLRs) were expressed in B cells and their signaling affects B cell functions. Nonetheless, the roles played by these receptors in B cell antibody (Ab) production have not been completely elucidated. In the present study, we examined the effect of the Nod2 agonist muramyl dipeptide (MDP) in combination with the TLR4 agonist lipopolysaccharide (LPS), a well-known B cell mitogen, on B cell viability, proliferation, and activation, and Ab production by in vitro culture of purified mouse spleen resting B cells. MDP combined with LPS to reinforce B cell viability, proliferation, and activation. Moreover, MDP enhanced LPS-induced IgG2b production, germline γ2b transcript (GLTγ2b) expression, and surface IgG2b expression. In an experiment with Nod2- and TLR4-deficient mouse B cells, we observed that the combined effect of MDP and LPS is dependent on Nod2 and TLR4 receptors. Furthermore, the combined effect on B cell viability and IgG2b switching was not observed in Rip2-deficient mouse cells. Collectively, this study suggests that Nod2 signaling enhances TLR4-activated B cell proliferation, IgG2b switching, and IgG2b production.

NOD Signaling and Cell Death

Innate immune signaling and programmed cell death are intimately linked, and many signaling pathways can regulate and induce both, transcription of inflammatory mediators or autonomous cell death. The best-characterized examples for these dual outcomes are members of the TNF superfamily, the inflammasome receptors, and the toll-like receptors. Signaling via the intracellular peptidoglycan receptors NOD1 and NOD2, however, does not appear to follow this trend, despite involving signaling proteins, or proteins with domains that are linked to programmed cell death, such as RIP kinases, inhibitors of apoptosis (IAP) proteins or the CARD domains on NOD1/2. To better understand the connections between NOD signaling and cell death induction, we here review the latest findings on the molecular regulation of signaling downstream of the NOD receptors and explore the links between this immune signaling pathway and the regulation of cell death.

The Multifaceted B Cell Response to Influenza Virus

Protection from yearly recurring, highly acute infections with a pathogen that rapidly and continuously evades previously induced protective neutralizing Abs, as seen during seasonal influenza virus infections, can be expected to require a B cell response that is too highly variable, able to adapt rapidly, and able to reduce morbidity and death when sterile immunity cannot be garnered quickly enough. As we outline in this Brief Review, the influenza-specific B cell response is exactly that: it is multifaceted, involves both innate-like and conventional B cells, provides early and later immune protection, employs B cells with distinct BCR repertoires and distinct modes of activation, and continuously adapts to the ever-changing virus while enhancing overall protection. A formidable response to a formidable pathogen.

The interplay between microbes and the immune response in inflammatory bowel disease

The aetiology and pathogenesis of inflammatory bowel disease (IBD) remains unclear but involves a complex interplay between genetic risk, environmental exposures, the immune system and the gut microbiota. Nearly two decades ago, the first susceptibility gene for Crohn's disease, NOD2, was identified within the IBD 1 locus. Since then, over 230 genetic risk loci have been associated with IBD and yet NOD2 remains the strongest association to date. As an intracellular innate immune sensor of bacteria, investigations into host-microbe interactions, involving both innate and adaptive immune responses, have become of particular interest in understanding the pathogenesis of IBD. Advancements in sequencing technology have lead to the groundbreaking characterization of the gut microbiota and its role in health and disease. While an altered microbiome has been described for IBD, whether it is a cause or an effect of the intestinal inflammation has yet to be determined. Moreover, the bidirectional relationship between the gut microbiota and the mucosal immune system adds to the multifaceted complexity of intestinal homeostasis. A better understanding of how host genetics, including NOD2, influence immune-microbe interactions and alter susceptibility to IBD is necessary in order to develop therapeutic and preventative treatments.

Nod2 is required for antigen-specific humoral responses against antigens orally delivered using a recombinant Lactobacillus vaccine platform

Safe and efficacious orally-delivered mucosal vaccine platforms are desperately needed to combat the plethora of mucosally transmitted pathogens. Lactobacillus spp. have emerged as attractive candidates to meet this need and are known to activate the host innate immune response in a species- and strain-specific manner. For selected bacterial isolates and mutants, we investigated the role of key innate immune pathways required for induction of innate and subsequent adaptive immune responses. Co-culture of murine macrophages with L. gasseri (strain NCK1785), L. acidophilus (strain NCFM), or NCFM-derived mutants—NCK2025 and NCK2031—elicited an M2b-like phenotype associated with TH2 skewing and immune regulatory function. For NCFM, this M2b phenotype was dependent on expression of lipoteichoic acid and S layer proteins. Through the use of macrophage genetic knockouts, we identified Toll-like receptor 2 (TLR2), the cytosolic nucleotide-binding oligomerization domain containing 2 (NOD2) receptor, and the inflammasome-associated caspase-1 as contributors to macrophage activation, with NOD2 cooperating with caspase-1 to induce inflammasome derived interleukin (IL)-1β in a pyroptosis-independent fashion. Finally, utilizing an NCFM-based mucosal vaccine platform with surface expression of human immunodeficiency virus type 1 (HIV-1) Gag or membrane proximal external region (MPER), we demonstrated that NOD2 signaling is required for antigen-specific mucosal and systemic humoral responses. We show that lactobacilli differentially utilize innate immune pathways and highlight NOD2 as a key mediator of macrophage function and antigen-specific humoral responses to a Lactobacillus acidophilus mucosal vaccine platform.

Toll-like Receptor 1/2 Agonist Pam3CSK4 Suppresses Lipopolysaccharide-driven IgG1 Production while Enhancing IgG2a Production by B Cells

Interaction between pathogen-associated molecular patterns and pattern recognition receptors triggers innate and adaptive immune responses. Several studies have reported that toll-like receptors (TLRs) are involved in B cell proliferation, differentiation, and Ig class switch recombination (CSR). However, roles of TLRs in B cell activation and differentiation are not completely understood. In this study, we investigated the direct effect of stimulation of TLR1/2 agonist Pam3CSK4 on mouse B cell viability, proliferation, activation, Ig production, and Ig CSR in vitro. Treatment with 0.5 µg/ml of Pam3CSK4 only barely induced IgG1 production although it enhanced B cell viability. In addition, high-dosage Pam3CSK4 diminished IgG1 production in a dose-dependent manner, whereas the production of other Igs, cell viability, and proliferation increased. Pam3CSK4 additively increased TLR4 agonist lipopolysaccharide (LPS)-induced mouse B cell growth and activation. However, interestingly, Pam3CSK4 abrogated LPS-induced IgG1 production but enhanced LPS-induced IgG2a production. Further, Pam3CSK4 decreased LPS-induced germline γ1 transcripts (GLTγ1)/GLTε expression but increased GLTγ2a expression. On the other hand, Pam3CSK4 had no effect on LPS-induced plasma cell differentiation. Taken together, these results suggest that TLR1/2 agonist Pam3CSK4 acts as a potent mouse B cell mitogen in combination with TLR4 agonist LPS, but these 2 different TLR agonists play diverse roles in regulating the Ig CSR of each isotype, particularly IgG1/IgE and IgG2a.

NOD1 and NOD2: Molecular targets in prevention and treatment of infectious diseases

Nucleotide-binding oligomerization domain (NOD) 1 and NOD2 are pattern-recognition receptors responsible for sensing fragments of bacterial peptidoglycan known as muropeptides. Stimulation of innate immunity by systemic or local administration of NOD1 and NOD2 agonists is an attractive means to prevent and treat infectious diseases. In this review, we discuss novel data concerning structural features of selective and non-selective (dual) NOD1 and NOD2 agonists, main signaling pathways and biological effects induced by NOD1 and NOD2 stimulation, including induction of pro-inflammatory cytokines, type I interferons and antimicrobial peptides, induction of autophagy, alterations of metabolism. We also discuss interactions between NOD1/NOD2 and Toll-like receptor agonists in terms of synergy and cross-tolerance. Finally, we review available animal data on the role of NOD1 and NOD2 in protection against infections, and discuss how these data could be applied in human infectious diseases.

TLRs/NLRs: Shaping the landscape of host immunity

Innate immune system provides the first line of defense against pathogenic organisms. It has a varied and large collection of molecules known as pattern recognition receptors (PRRs) which can tackle the pathogens promptly and effectively. Toll-like receptors (TLRs) and NOD-like receptors (NLRs) are members of the PRR family that recognize pathogen associated molecular patterns (PAMPs) and play pivotal roles to mediate defense against infections from bacteria, fungi, virus and various other pathogens. In this review, we discuss the critical roles of TLRs and NLRs in the regulation of host immune-effector functions such as cytokine production, phagosome-lysosome fusion, inflammasome activation, autophagy, antigen presentation, and B and T cell immune responses that are known to be essential for mounting a protective immune response against the pathogens. This review may be helpful to design TLRs/NLRs based immunotherapeutics to control various infections and pathophysiological disorders.

Hepatitis B core antigen based novel vaccine against porcine epidemic diarrhea virus

Porcine epidemic diarrhea Virus (PEDV) is the causative agent of porcine epidemic diarrhea, which is a devastating viral disease and causes severe economic loss to the swine industry. Current vaccine options for PEDV include modified live viruses and killed live viruses. Though these vaccines have shown efficacy, some have side effects including viral shedding. This report details an E. coli based expression and purification process of multiple vaccine candidates for PEDV using Hepatitis B Core Antigen (HBcAg) as a backbone protein. Short linear peptide sequences from PEDV were inserted into the immunodominant region of HBcAg in a novel recombinant vaccine design against PEDV. These peptide sequences were successfully inserted individually as well as all together in a multivalent strategy. Each vaccine candidate was tested in vivo in an intranasal as well as an intraperitoneal administration. Although each candidate was able to elicit a strong immunogenic response specific for the inserted peptide sequences, only two out of five of the test candidates demonstrated an ability to elicit an immune response capable of virus neutralization when delivered via intraperitoneal administration in mice.

Internal driving factors leading to extrahepatic manifestation of the hepatitis C virus infection

The hepatitis C virus (HCV) infection is associated with various extrahepatic manifestations, which are correlated with poor outcomes, and thus increase the morbidity and mortality of chronic hepatitis C (CHC). Therefore, understanding the internal linkages between systemic manifestations and HCV infection is helpful for treatment of CHC. Yet, the mechanism by which the virus evokes the systemic diseases remains to be elucidated. In the present study, using gene set enrichment analysis (GSEA) and signaling pathway impact analysis (SPIA), a comprehensive analysis of microarray data of mRNAs was conducted in HCV-infected and -uninfected Huh7.5 cells, and signaling pathways (which are significantly activated or inhibited) and certain molecules (which are commonly important in those signaling pathways) were selected. Forty signaling pathways were selected using GSEA, and eight signaling pathways were selected with SPIA. These pathways are associated with cancer, metabolism, environmental information processing and organismal systems, which provide important information for further clarifying the intrinsic associations between syndromes of HCV infection, of which seven pathways were not previously reported, including basal transcription factors, pathogenic Escherichia coli infection, shigellosis, gastric acid secretion, dorso-ventral axis formation, amoebiasis and cholinergic synapse. Ten genes, SOS1, RAF1, IFNA2, IFNG, MTHFR, IGF1, CALM3, UBE2B, TP53 and BMP7 whose expression may be the key internal driving molecules, were selected using the online tool Anni 2.1. Furthermore, the present study demonstrated the internal linkages between systemic manifestations and HCV infection, and presented the potential molecules that are key to those linkages.

CD11c+ T-bet+ memory B cells: Immune maintenance during chronic infection and inflammation?

CD11c+ T-bet+ B cells have now been detected and characterized in different experimental and clinical settings, in both mice and humans. Whether such cells are monolithic, or define subsets of B cells with different functions is not yet known. Our studies have identified CD11c+ IgM+ CD19^hi splenic IgM memory B cells that appear at approximately three weeks post-ehrlichial infection, and persist indefinitely, during low-level chronic infection. Although the CD11c+ T-bet+ B cells we have described are distinct, they appear to share many features with similar cells detected under diverse conditions, including viral infections, aging, and autoimmunity. We propose that CD11c+ T-bet+ B cells as a group share characteristics of memory B cells that are maintained under conditions of inflammation and/or low-level chronic antigen stimulation. In some cases, these cells may be advantageous, by providing immunity to re-infection, but in others may be deleterious, by contributing to aged-associated autoimmune responses.

Nod2: The intestinal gate keeper

Nucleotide-binding oligomerization domain 2 (NOD2) is an intracellular pattern recognition receptor that senses bacterial peptidoglycan (PGN)-conserved motifs in cytosol and stimulates host immune response. The association of NOD2 mutations with a number of inflammatory pathologies, including Crohn disease (CD), Graft-versus-host disease (GVHD), and Blau syndrome, highlights its pivotal role in host–pathogen interactions and inflammatory response. Stimulation of NOD2 by its ligand (muramyl dipeptide) activates pro-inflammatory pathways such as nuclear factor-κB (NF-κB), mitogen-activated protein kinases (MAPKs), and Caspase-1. A loss of NOD2 function may result in a failure in the control of microbial infection, thereby initiating systemic responses and aberrant inflammation. Because the ligand of Nod2 is conserved in both gram-positive and gram-negative bacteria, NOD2 detects a wide variety of microorganisms. Furthermore, current literature evidences that NOD2 is also able to control viruses’ and parasites’ infections. In this review, we present and discuss recent developments about the role of NOD2 in shaping the gut commensal microbiota and pathogens, including bacteria, viruses, and parasites, and the mechanisms by which Nod2 mutations participate in disease occurrence.

Role of NOD2 and RIP2 in host-microbe interactions with Gram-negative bacteria: insights from the periodontal disease model

NOD2 is a member of the NLR family of proteins that participate in the activation of the innate immune response. RIP2 is a downstream kinase activated by both NOD1 and NOD2. There is scarcity of information regarding the relevance of NOD2 in periodontitis, a chronic inflammatory condition characterized by inflammatory bone resorption. We used NOD2-KO and RIP2-KO mice in a model of microbial-induced periodontitis. Heat-killed Aggregatibacter actinomycetemcomitans was injected in the gingival tissues three times/wk for 4 wk. Bone resorption was assessed by μCT analysis; osteoclasts were identified by immunohistochemical staining for TRAP and inflammation was assessed using a severity score system in H/E-stained sections. In vitro studies using primary macrophages assessed the response macrophages using qPCR-based array and multi-ligand ELISA. Bone resorption and osteoclastogenesis were significantly reduced in NOD2-KO mice. Severity of inflammation was not affected. qPCR-focused arrays and multi-ligand ELISA showed that expression of pro-inflammatory mediators was reduced in NOD2- and RIP2-deficient cells. RANKL-induced osteoclastogenesis was impaired in NOD2- and RIP2-deficient macrophages. We conclude that NOD2 is important for osteoclast differentiation and inflammatory bone resorption in vivo and also for the macrophage response to Gram-negative bacteria.

PAX5 interacts with RIP2 to promote NF-κB activation and drug-resistance of B-lymphoproliferative disorders

Paired box protein 5 (PAX5) plays a lineage determination role in B-cell development. However, high expression of PAX5 has been also found in various malignant diseases including B-lymphoproliferative disorders (B-LPDs), but its functions and mechanisms in these diseases are still unclear. Here, we show that PAX5 induces drug-resistance through association and activation of receptor-interacting serine/threonine-protein kinase2 (RIP2) and subsequent activation of NF-κB signaling and anti-apoptosis genes expression in B-lymphoproliferative cells. Furthermore, PAX5 is able to interact with RIP1-3, modulating both RIP1- mediated TNFR and RIP2-mediated NOD1 and NOD2 pathways. Our findings describe a novel function of PAX5 in regulating RIP1 and RIP2 activation, which is at least involved in chemo drug-resistance in B-LPDs.

Nanocarriers for DNA Vaccines: Co-Delivery of TLR-9 and NLR-2 Ligands Leads to Synergistic Enhancement of Proinflammatory Cytokine Release

Adjuvants enhance immunogenicity of vaccines through either targeted antigen delivery or stimulation of immune receptors. Three cationic nanoparticle formulations were evaluated for their potential as carriers for a DNA vaccine, and muramyl dipeptide (MDP) as immunostimulatory agent, to induce and increase immunogenicity of Mycobacterium tuberculosis antigen encoding plasmid DNA (pDNA). The formulations included (1) trimethyl chitosan (TMC) nanoparticles, (2) a squalene-in-water nanoemulsion, and (3) a mineral oil-in-water nanoemulsion. The adjuvant effect of the pDNA-nanocomplexes was evaluated by serum antibody analysis in immunized mice. All three carriers display a strong adjuvant effect, however, only TMC nanoparticles were capable to bias immune responses towards Th1. pDNA naturally contains immunostimulatory unmethylated CpG motifs that are recognized by Toll-like receptor 9 (TLR-9). In mechanistic in vitro studies, activation of TLR-9 and the ability to enhance immunogenicity by simultaneously targeting TLR-9 and NOD-like receptor 2 (NLR-2) was determined by proinflammatory cytokine release in RAW264.7 macrophages. pDNA in combination with MDP was shown to significantly increase proinflammatory cytokine release in a synergistic manner, dependent on NLR-2 activation. In summary, novel pDNA-Ag85A loaded nanoparticle formulations, which induce antigen specific immune responses in mice were developed, taking advantage of the synergistic combinations of TLR and NLR agonists to increase the adjuvanticity of the carriers used.

Comparative genomic analysis of buffalo (Bubalus bubalis) NOD1 and NOD2 receptors and their functional role in in-vitro cellular immune response

Nucleotide binding and oligomerization domain (NOD)-like receptors (NLRs) are innate immune receptors that recognize bacterial cell wall components and initiate host immune response. Structure and function of NLRs have been well studied in human and mice, but little information exists on genetic composition and role of these receptors in innate immune system of water buffalo—a species known for its exceptional disease resistance. Here, a comparative study on the functional domains of NOD1 and NOD2 was performed across different species. The NOD mediated in-vitro cellular responses were studied in buffalo peripheral blood mononuclear cells, resident macrophages, mammary epithelial, and fibroblast cells. Buffalo NOD1 (buNOD1) and buNOD2 showed conserved domain architectures as found in other mammals. The domains of buNOD1 and buNOD2 showed analogy in secondary and tertiary conformations. Constitutive expressions of NODs were ubiquitous in different tissues. Following treatment with NOD agonists, peripheral lymphocytes showed an IFN-γ response along-with production of pro-inflammatory cytokines. Alveolar macrophages and mammary epithelial cells showed NOD mediated in-vitro immune response through NF-κB dependent pathway. Fibroblasts showed pro-inflammatory cytokine response following agonist treatment. Our study demonstrates that both immune and non-immune cells could generate NOD-mediated responses to pathogens though the type and magnitude of response depend on the cell types. The structural basis of ligand recognition by buffalo NODs and knowledge of immune response by different cell types could be useful for development of non-infective innate immune modulators and next generation anti-inflammatory compounds.

Aberrant expression of the CHFR prophase checkpoint gene in human B-cell non-Hodgkin lymphoma

Checkpoint with FHA and Ring Finger (CHFR) is a checkpoint protein that reportedly initiates a cell cycle delay in response to microtubule stress during prophase in mitosis, which has become an interesting target for understanding cancer pathogenesis. Recently, aberrant methylation of the CHFR gene associated with gene silencing has been reported in several cancers. In the present study, we examined the expression of CHFR in B-cell non-Hodgkin lymphoma (B-NHL) in vitro and in vivo. Our results showed that the expression level of CHFR mRNA and protein was reduced in B-NHL tissue samples and B cell lines. Furthermore, CHFR methylation was detected in 39 of 122 B-NHL patients, which was not found in noncancerous reactive hyperplasia of lymph node (RH) tissues. CHFR methylation correlated with the reduced expression of CHFR, high International Prognostic Index (IPI) scores and later pathologic Ann Arbor stages of B-NHL. Treatment with demethylation reagent, 5-Aza-dC, could eliminate the hypermethylation of CHFR, enhance CHFR expression and cell apoptosis and inhibit the cell proliferation of Raji cells, which could be induced by high expression of CHFR in Raji cells. Our results indicated that aberrant methylation of CHFR may be associated with the pathogenesis, progression for B-NHL, which might be a novel molecular marker as prognosis and treatment for B-NHL.

Genome-wide comparison of PU.1 and Spi-B binding sites in a mouse B lymphoma cell line

Background

Spi-B and PU.1 are highly related members of the E26-transformation-specific (ETS) family of transcription factors that have similar, but not identical, roles in B cell development. PU.1 and Spi-B are both expressed in B cells, and have been demonstrated to redundantly activate transcription of genes required for B cell differentiation and function. It was hypothesized that Spi-B and PU.1 occupy a similar set of regions within the genome of a B lymphoma cell line.

Results

To compare binding regions of Spi-B and PU.1, murine WEHI-279 lymphoma cells were infected with retroviral vectors encoding 3XFLAG-tagged PU.1 or Spi-B. Anti-FLAG chromatin immunoprecipitation followed by next generation sequencing (ChIP-seq) was performed. Analysis for high-stringency enriched genomic regions demonstrated that PU.1 occupied 4528 regions and Spi-B occupied 3360 regions. The majority of regions occupied by Spi-B were also occupied by PU.1. Regions bound by Spi-B and PU.1 were frequently located immediately upstream of genes associated with immune response and activation of B cells. Motif-finding revealed that both transcription factors were predominantly located at the ETS core domain (GGAA), however, other unique motifs were identified when examining regions associated with only one of the two factors. Motifs associated with unique PU.1 binding included POU2F2, while unique motifs in the Spi-B regions contained a combined ETS-IRF motif.

Conclusions

Our results suggest that complementary biological functions of PU.1 and Spi-B may be explained by their interaction with a similar set of regions in the genome of B cells. However, sites uniquely occupied by PU.1 or Spi-B provide insight into their unique functions.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1303-0) contains supplementary material, which is available to authorized users.

Network representations of immune system complexity

The mammalian immune system is a dynamic multiscale system composed of a hierarchically organized set of molecular, cellular, and organismal networks that act in concert to promote effective host defense. These networks range from those involving gene regulatory and protein–protein interactions underlying intracellular signaling pathways and single‐cell responses to increasingly complex networks of in vivo cellular interaction, positioning, and migration that determine the overall immune response of an organism. Immunity is thus not the product of simple signaling events but rather nonlinear behaviors arising from dynamic, feedback‐regulated interactions among many components. One of the major goals of systems immunology is to quantitatively measure these complex multiscale spatial and temporal interactions, permitting development of computational models that can be used to predict responses to perturbation. Recent technological advances permit collection of comprehensive datasets at multiple molecular and cellular levels, while advances in network biology support representation of the relationships of components at each level as physical or functional interaction networks. The latter facilitate effective visualization of patterns and recognition of emergent properties arising from the many interactions of genes, molecules, and cells of the immune system. We illustrate the power of integrating ‘omics’ and network modeling approaches for unbiased reconstruction of signaling and transcriptional networks with a focus on applications involving the innate immune system. We further discuss future possibilities for reconstruction of increasingly complex cellular‐ and organism‐level networks and development of sophisticated computational tools for prediction of emergent immune behavior arising from the concerted action of these networks. WIREs Syst Biol Med 2015, 7:13–38. doi: 10.1002/wsbm.1288

This article is categorized under: 1

Analytical and Computational Methods > Computational Methods

2

Laboratory Methods and Technologies > Macromolecular Interactions, Methods

Self DNA from lymphocytes that have undergone activation-induced cell death enhances murine B cell proliferation and antibody production

Systemic lupus erythematosus (SLE) is characterized by prominent autoinflammatory tissue damage associated with impaired removal of dying cells and DNA. Self DNA-containing immune complexes are able to activate both innate and adaptive immune responses and play an important role in the maintenance and exacerbation of autoimmunity in SLE. In this study, we used DNA from lymphocytes that have undergone activation-induced cell death (ALD-DNA) and analyzed its role on the activation and differentiation of B cells from normal BALB/c mice as well as lupus-prone MRL^+/+ and MRL/lpr mice. We found that ALD-DNA directly increased the expression of costimulatory molecules and the survival of naïve B cells in vitro. Although ALD-DNA alone had little effect on the proliferation of naïve B cells, it enhanced LPS-activated B cell proliferation in vitro and in vivo. In addition, ALD-DNA increased plasma cell numbers and IgG production in LPS-stimulated cultures of naïve B cells, in part via enhancing IL-6 production. Importantly, B cells from lupus mice were hyperresponsive to ALD-DNA and/or LPS relative to normal control B cells in terminal plasma cell differentiation, as evidenced by increases in CD138⁺ cell numbers, IgM production, and mRNA levels of B lymphocyte-induced maturation protein-1 (Blimp-1) and the X-box binding protein 1 (XBP1). Furthermore, ALD-DNA enhanced CD40-activated naïve B cell proliferation. Collectively, these data indicate that self DNA can serve as a DAMP (damage-associated molecular pattern) that cooperates with signals from both innate and adaptive immunity to promote polyclonal B cell activation, a common characteristic of autoimmune diseases.

The multifaceted nature of NLRP12

NLRs are a class of cytoplasmic PRRs with various functions, ranging from pathogen/damage sensing to the modulation of inflammatory signaling and transcriptional control of MHC and related genes. In addition, some NLRs have been implicated in preimplantation and prenatal development. NLRP12 (also known as RNO, PYPAF7, and Monarch-1), a member of the family containing an N-terminal PYD, a NBD, and a C-terminal LRR region, is one of the first described NLR proteins whose role remains controversial. The interest toward NLRP12 has been boosted by its recent involvement in colon cancer, as well as in the protection against some severe infections, such as that induced by Yersinia pestis, the causative agent of plague. As NLRP12 is mainly expressed by the immune cells, and its expression is down-regulated in response to pathogen products and inflammatory cytokines, it has been predicted to play a role as a negative regulator of the inflammatory response. Herein, we present an overview of the NLR family and summarize recent insights on NLRP12 addressing its contribution to inflammatory signaling, host defense, and carcinogenesis.

Nod2 activates NF-kB in CD4+ T cells but its expression is dispensable for T cell-induced colitis

Although the etiology of Crohn's disease (CD) remains elusive this disease is characterized by T cell activation that leads to chronic inflammation and mucosal damage. A potential role for maladaptation between the intestinal microbiota and the mucosal immune response is suggested by the fact that mutations in the pattern recognition receptor Nod2 are associated with higher risks for developing CD. Although Nod2 deletion in CD4⁺ T cells has been shown to impair the induction of colitis in the murine T cell transfer model, the analysis of T cell intrinsic Nod2 function in T cell differentiation and T cell-mediated immunity is inconsistent between several studies. In addition, the role of T cell intrinsic Nod2 in regulatory T cell (Treg) development and function during colitis remain to be analyzed. In this study, we show that Nod2 expression is higher in activated/memory CD4⁺ T cells and its expression was inducible after T cell receptor (TCR) ligation. Nod2 stimulation with muramyl dipeptide (MDP) led to a nuclear accumulation of c-Rel NF-kB subunit. Although functionally active in CD4⁺ T cells, the deletion of Nod2 did not impair the induction and the prevention of colitis in the T cell transfer model. Moreover, Nod2 deletion did not affect the development of Foxp3⁺ Treg cells in the spleen of recipient mice and Nod2 deficient CD4 T cells expressing the OVA specific transgenic TCR were able to differentiate in Foxp3⁺ Treg cells after OVA feeding. In vitro, CD25⁺ Nod2 deficient T cells suppressed T cell proliferation as well as wild type counter parts and T cell stimulation with MDP did not affect the proliferation and the cytokine secretion of T cells. In conclusion, our data indicate that Nod2 is functional in murine CD4⁺ T cells but its expression is dispensable for the T cell regulation of colitis.

NOD2 mutations affect muramyl dipeptide stimulation of human B lymphocytes and interact with other IBD-associated genes

BACKGROUND

Genetic and functional studies have associated variants in the NOD2/CARD15 gene with Crohn's disease.

AIMS

This study aims to replicate the association of three common NOD2 mutations with Crohn's disease, study its effect on NOD2 expression in B cells and its interaction with other IBD-associated genes.

METHODS

A total of 294 IBD patients (179 familial IBD, 115 sporadic IBD) and 298 unrelated healthy controls were from central Pennsylvania. NOD2 mutations were analyzed by primer-specific amplification, PCR based-RFLP, and validated with the ABI SNPlexM genotyping system. Gene-gene interaction was studied using a statistical model for epistasis analysis.

RESULTS

Three common NOD2 mutations are associated with Crohn's disease (p=5.08×10(-7), 1.67×10(-6), and 1.87×10(-2) for 1007fs, R720W, and G908R, respectively), but not with ulcerative colitis (p=0.1046, 0.1269, and 0.8929, respectively). For IBD overall, 1007finsC (p=4.4×10(-5)) and R720W (p=9.24×10(-5)) were associated with IBD, but not G908R (p=0.1198). We revealed significant interactions of NOD2 with other IBD susceptibility genes IL23R, DLG5, and OCTN1. We discovered that NOD2 was expressed in both normal human peripheral blood B cells and in EBV-transformed B cell lines. Moreover, we further demonstrated that muramyl dipeptide (MDP) stimulation of B lymphocytes up-regulated expression of NF-κB-p50 mRNA.

CONCLUSION

NOD2 is expressed in peripheral B cells, and the up-regulation of NOD2 expression by MDP was significantly impaired by NOD2 mutations. The finding suggests a possible role of NOD2 in the immunological response in IBD pathogenesis.

Innate immune receptors in human airway smooth muscle cells: activation by TLR1/2, TLR3, TLR4, TLR7 and NOD1 agonists

Background

Pattern-recognition receptors (PRRs), including Toll-like receptors (TLRs), NOD-like receptors (NLRs) and RIG-I-like receptors (RLRs), recognize microbial components and trigger a host defense response. Respiratory tract infections are common causes of asthma exacerbations, suggesting a role for PRRs in this process. The present study aimed to examine the expression and function of PRRs on human airway smooth muscle cells (HASMCs).

Methods

Expression of TLR, NLR and RLR mRNA and proteins was determined using real-time RT-PCR, flow cytometry and immunocytochemistry. The functional responses to ligand stimulation were investigated in terms of cytokine and chemokine release, cell surface marker expression, proliferation and proteins regulating the contractile state.

Results

HASMCs expressed functional TLR2, TLR3, TLR4, TLR7 and NOD1. Stimulation with the corresponding agonists Pam₃CSK₄, poly(I:C), LPS, R-837 and iE-DAP, respectively, induced IL-6, IL-8 and GM-CSF release and up-regulation of ICAM-1 and HLA-DR, while poly(I:C) also affected the release of eotaxin and RANTES. The proliferative response was slightly increased by LPS. Stimulation, most prominently with poly(I:C), down-regulated myosin light chain kinase and cysteinyl leukotriene 1 receptor expression and up-regulated β₂-adrenoceptor expression. No effects were seen for agonist to TLR2/6, TLR5, TLR8, TLR9, NOD2 or RIG-I/MDA-5.

Conclusion

Activation of TLR2, TLR3, TLR4, TLR7 and NOD1 favors a synthetic phenotype, characterized by an increased ability to release inflammatory mediators, acquire immunomodulatory properties by recruiting and interacting with other cells, and reduce the contractile state. The PRRs might therefore be of therapeutic use in the management of asthma and infection-induced disease exacerbations.

Innate receptors for adaptive immunity

Pattern recognition receptors (PRRs) are commonly known as sensor proteins crucial for the early detection of microbial or host-derived stress signals by innate immune cells. Interestingly, some PRRs are also expressed and functional in cells of the adaptive immune system. These receptors provide lymphocytes with innate sensing abilities; for example, B cells express Toll-like receptors, which are important for the humoral response. Strikingly, certain other NOD-like receptors are not only highly expressed in adaptive immune cells, but also exert functions related specifically to adaptive immune system pathways, such as regulating antigen presentation. In this review, we will focus particularly on the current understanding of PRR functions intrinsic to B and T lymphocytes; a developing aspect of PRR biology.

Evaluation of an intranasal virosomal vaccine against respiratory syncytial virus in mice: effect of TLR2 and NOD2 ligands on induction of systemic and mucosal immune responses

Introduction

RSV infection remains a serious threat to newborns and the elderly. Currently, there is no vaccine available to prevent RSV infection. A mucosal RSV vaccine would be attractive as it could induce mucosal as well as systemic antibodies, capable of protecting both the upper and lower respiratory tract. Previously, we reported on a virosomal RSV vaccine for intramuscular injection with intrinsic adjuvant properties mediated by an incorporated lipophilic Toll-like receptor 2 (TLR2) ligand. However, it has not been investigated whether this virosomal RSV vaccine candidate would be suitable for use in mucosal immunization strategies and if additional incorporation of other innate receptor ligands, like NOD2-ligand, could further enhance the immunogenicity and protective efficacy of the vaccine.

Objective

To explore if intranasal (IN) immunization with a virosomal RSV vaccine, supplemented with TLR2 and/or NOD2-ligands, is an effective strategy to induce RSV-specific immunity.

Methods

We produced RSV-virosomes carrying TLR2 (Pam₃CSK₄) and/or NOD2 (L18-MDP) ligands. We tested the immunopotentiating properties of these virosomes in vitro, using TLR2- and/or NOD2-ligand-responsive murine and human cell lines, and in vivo by assessing induction of protective antibody and cellular responses upon IN immunization of BALB/c mice.

Results

Incorporation of Pam₃CSK₄ and/or L18-MDP potentiates the capacity of virosomes to activate (antigen-presenting) cells in vitro, as demonstrated by NF-κB induction. In vivo, incorporation of Pam₃CSK₄ in virosomes boosted serum IgG antibody responses and mucosal antibody responses after IN immunization. While L18-MDP alone was ineffective, incorporation of L18-MDP in Pam₃CSK₄-carrying virosomes further boosted mucosal antibody responses. Finally, IN immunization with adjuvanted virosomes, particularly Pam₃CSK₄/L18-MDP-adjuvanted-virosomes, protected mice against infection with RSV, without priming for enhanced disease.

Conclusion

Mucosal immunization with RSV-virosomes, supplemented with incorporated TLR2- and/or NOD2-ligands, represents a promising approach to induce effective and safe RSV-specific immunity.

The CARD8 p.C10X mutation associates with a low anti-glycans antibody response in patients with Crohn's disease

BACKGROUND

Crohn's disease (CD) is associated with elevated anti-glycans antibody response in 60% of CD patients, and 25% of healthy first-degree relatives (HFDRs), suggesting a genetic influence for this humoral response. In mice, anti-glucan antibody response depends on the NLRP3 inflammasome. Here, we explored the effect of mutated CARD8, a component of the inflammasome, on anti-glycans antibody response in human.

METHODS

The association between p.C10X mutation (rs2043211) of the CARD8 gene and the levels of anti-glycans antibody response was examined in 39 CD families. The family-based QTDT association test was used to test for the genetic association between CARD8 p.C10X mutation and anti-glycan antibodies in the pedigrees. The difference in antibody responses determined by ELISA was tested in a subgroup of CD probands (one per family) and in a subgroup of HFDRs using the Wilcoxon Kruskal Wallis non-parametric test.

RESULTS

The QTDT familial transmission tests showed that the p.C10X mutation of CARD8 was significantly associated with lower levels of antibody to mannans and glucans but not chitin (p=0.024, p=0.0028 and p=0.577, for ASCA, ALCA and ACCA, respectively). These associations were independent of NOD2 and NOD1 genetic backgrounds. The p.C10X mutation significantly associated or displayed a trend toward lower ASCA and ALCA levels (p=0.038 and p=0.08, respectively) only in the subgroup of CD probands. Such associations were not significant for ACCA levels in both subgroups of CD probands and of HFDRs.

CONCLUSION

Our results show that ASCA and ALCA but not ACCA levels are under the influence of CARD8 genotype. Alteration of CARD8, a component of inflammasome, is associated with lower levels of antibodies directed to mannans and glucans at least in CD patients.

Moraxella catarrhalis: from interactions with the host immune system to vaccine development

Moraxella catarrhalis is a human-restricted commensal that over the last two decades has developed into an emerging respiratory tract pathogen. The bacterial species is equipped with various adhesins to facilitate its colonization. Successful evasion of the human immune system is a prerequisite for Moraxella infection. This strategy involves induction of an excessive proinflammatory response, intervention of granulocyte recruitment to the infection site, activation of selected pattern recognition receptors and cellular adhesion molecules to counteract the host bacteriolytic attack, as well as, finally, reprogramming of antigen presenting cells. Host immunomodulator molecules are also exploited by Moraxella to aid in resistance against complement killing and host bactericidal molecules. Thus, breaking the basis of Moraxella immune evasion mechanisms is fundamental for future invention of effective therapy in controlling Moraxella infection.

Distinct innate immunity pathways to activation and tolerance in subgroups of chronic lymphocytic leukemia with distinct immunoglobulin receptors

Subgroups of patients with chronic lymphocytic leukemia (CLL) have distinct expression profiles of Toll-like receptor (TLR) pathway-associated genes. To test the hypothesis that signaling through innate immunity receptors may influence the behavior of the malignant clone, we investigated the functional response triggered by the stimulation of TLRs and NOD2 in 67 CLL cases assigned to different subgroups on the basis of immunoglobulin heavy variable (IGHV ) gene usage, IGHV gene mutational status or B-cell receptor (BcR) stereotypy. Differences in the induction of costimulatory molecules and/or apoptosis were observed in mutated versus unmutated CLL. Different responses were also identified in subsets with stereotyped BcRs, underscoring the idea that "subset-biased" innate immunity responses may occur independently of mutational status. Additionally, differential modulation of kinase activities was induced by TLR stimulation of different CLL subgroups, revealing a TLR7-tolerant state for cases belonging to stereotyped subset #4. The distinct patterns of TLR/NOD2 functional activity in cells from CLL subgroups defined by the molecular features of the clonotypic BcRs might prove relevant for elucidating the immune mechanisms underlying CLL natural history and for defining subgroups of patients who might benefit from treatment with specific TLR ligands.

Toll-like Receptors in Chronic Lymphocytic Leukemia

Toll-like receptors belong to the pattern recognition receptors family present on a variety of immune cells including normal and malignant B-cells. They act as immediate molecular sentinels of innate immunity but also act as a molecular bridge between the innate and the adaptive immune response; distinct Toll-like receptors are able to bind specific pattern molecules of bacteria, viruses and autoantigens. In this review we will briefly introduce the Toll-like receptor family and their expression pattern, signaling and function in the B cell context; following we will summarize the published data on TLR in chronic lymphocytic leukemia, and we will discuss their emerging role in the modulation of leukemia pathobiology.

TLR ligand-peptide conjugate vaccines: toward clinical application

Approaches to treat cancer with therapeutic vaccination have made significant progress. In order to induce efficient antitumor immunity, a vaccine should target and activate antigen-presenting cells, such as the dendritic cell, while delivering the tumor-derived antigen of choice. Conjugates of synthetic peptides and ligands of pattern-recognition receptors (PRRs) combine these features and, given their synthetic nature, can be produced under GMP conditions. Therefore, conjugation of antigenic peptides to potent PRR ligands is a promising vaccination approach for the treatment of cancer. This review focuses on the different PRR families that can be exploited for the design of conjugates and explores the results obtained so far with PRR ligands conjugated to antigen. The uptake and processing of Toll-like receptor ligand-peptide conjugates are discussed in more detail, as well as future directions that may further enhance the immunogenicity of conjugates.

NOD1 and NOD2 stimulation triggers innate immune responses of human periodontal ligament cells

Nod-like receptors (NLRs) are cytosolic sensors for microbial molecules. Nucleotide-binding oligomerization domain (NOD)1 and NOD2 recognize the peptidoglycan derivatives, meso-diaminopimelic acid (meso-DAP) and muramyl dipeptide (MDP), respectively, and trigger host innate immune responses. In the present study, we examined the function of NOD1 and NOD2 on innate immune responses in human periodontal ligament (PDL) cells. The gene expression of NOD1 and NOD2 was examined by RT-PCR. IL-6 and IL-8 production in culture supernatants was measured by ELISA. Western blot analysis was performed to determine the activation of NF-κB and MAPK in response to Tri-DAP and MDP. The genes of NOD1 and NOD2 appeared to be expressed in PDL cells. Although the levels of NOD2 expression were weak in intact cells, MDP stimulation increased the gene expression of NOD2 in PDL cells. Tri-DAP and MDP led to the production of IL-6 and IL-8 and the activation of NF-κB and MAPK in PDL cells. Toll-like receptor (TLR) stimulation led to increased gene expression of NOD1 and NOD2 in PDL cells. Pam₃CSK₄ (a TLR2 agonist) and IFN-γ synergized with Tri-DAP and MDP to produce IL-8 and IL-6 in PDL cells. Our results indicate that NOD1 and NOD2 are functionally expressed in human PDL cells and can trigger innate immune responses.

Induction of mucosal and systemic immunity against respiratory syncytial virus by inactivated virus supplemented with TLR9 and NOD2 ligands

Respiratory syncytial virus (RSV) infection is the most important viral cause of severe respiratory disease in infants and children worldwide and also forms a serious threat in the elderly. The development of RSV vaccine, however, has been hampered by the disastrous outcome of an earlier trial using an inactivated and parenterally administered RSV vaccine which did not confer protection but rather primed for enhanced disease upon natural infection. Mucosal administration does not seem to prime for enhanced disease, but non-replicating RSV antigen does not induce a strong mucosal immune response. We therefore investigated if mucosal immunization with inactivated RSV supplemented with innate receptor ligands, TLR9 (CpG ODN) and NOD2 (L18-MDP) through the upper or total respiratory tract is an effective and safe approach to induce RSV-specific immunity. Our data show that beta-propiolactone (BPL) inactivated RSV (BPL-RSV) supplemented with CpG ODN and L18-MDP potentiates activation of antigen-presenting cells (APC) in vitro, as demonstrated by NF-κB induction in a model APC cell line. In vivo, BPL-RSV supplemented with CpG ODN/L18-MDP ligands induces local IgA responses and augments Th1-signature IgG2a subtype responses after total respiratory tract (TRT), but less efficient after upper respiratory tract (intranasal, IN) immunization. Addition of TLR9/NOD2 ligands to the inactivated RSV also promoted affinity maturation of RSV-specific IgG antibodies and shifted T cell responses from mainly IL-5-secreting cells to predominantly IFN-γ-producing cells, indicating a Th1-skewed response. This effect was seen for both IN and TRT immunization. Finally, BPL-RSV supplemented with TLR9/NOD2 ligands significantly improved the protection efficacy against a challenge with infectious virus, without stimulating enhanced disease as evidenced by lack of eotaxin mRNA expression and eosinophil infiltration in the lung. We conclude that mucosal immunization with inactivated RSV antigen supplemented with TLR9/NOD2 ligands is a promising approach to induce effective RSV-specific immunity without priming for enhanced disease.

Retinoic acid-inducible gene 1-like receptors in the upper respiratory tract

BACKGROUND

Retinoic acid-inducible gene 1-like receptors (RLRs) are a novel family of pattern recognition receptors that include retinoic acid-inducible gene 1 (RIG-1), melanoma differentiation-associated gene 5 (MDA-5), and laboratory of genomics and physiology 2 (LGP-2). The knowledge of RLRs and their function in the human airway is limited. This study explores the role of RLRs in the upper respiratory tract.

METHODS

Tonsils, adenoids, nasal polyps, and biopsy specimens from the nasal mucosa were examined for the occurrence of the RIG-1, MDA-5, and LGP-2 using real-time reverse-transcription polymerase chain reaction and immunohistochemistry. The nasopharyngeal epithelial cell line FaDu was cultured with the RIG-1/MDA-5 ligand poly(I:C)/LyoVec (Invivogen, San Diego, CA) and analyzed for cytokine release using ELISA.

RESULTS

RIG-1, MDA-5, and LGP-2 mRNA were found in all tissues tested. The airway epithelium appeared to be their most prominent location. The RIG-1 and MDA-5 mRNA levels were higher in nasal polyps than in normal nasal mucosa, a state that seemed to be reversed by local steroid treatment. Culture of FaDu with poly(I:C)/LyoVec resulted in IL-6 and IL-8 release. No alteration in RLR expression in tonsils was seen on infection.

CONCLUSION

This study shows the presence and functional activity of RLRs in the human upper airways. It also suggests a role for RLRs in nasal polyposis.

NOD-like receptors and RIG-I-like receptors in human eosinophils: activation by NOD1 and NOD2 agonists

NOD-like receptors (NLRs) and RIG-I-like receptors (RLRs) are newly discovered pattern-recognition receptors. They detect substructures of bacterial peptidoglycan and viral RNA, respectively, thereby initiating an immune response. However, their role in eosinophil activation remains to be explored. The aim of this study was to characterize the expression of a range of NLRs and RLRs in purified human eosinophils and assess their functional importance. Expression of NOD1, NOD2, NLRP3, RIG-I and MDA-5 was investigated using real-time reverse transcription PCR, flow cytometry and immunohistochemistry. The effects of the corresponding agonists iE-DAP (NOD1), MDP (NOD2), alum (NLRP3) and poly(I:C)/LyoVec (RIG-I/MDA-5) were studied in terms of cytokine secretion, degranulation, survival, expression of adhesion molecules and activation markers, and chemotactic migration. Eosinophils expressed NOD1 and NOD2 mRNA and protein. Low levels of RIG-I and MDA-5 were found, whereas expression of NLRP3 was completely absent. In accordance, stimulation with iE-DAP and MDP was found to induce secretion of interleukin-8, up-regulate expression of CD11b, conversely down-regulate CD62 ligand, increase expression of CD69 and induce migration. The MDP also promoted release of eosinophil-derived neurotoxin, whereas iE-DAP failed to do so. No effects were seen upon stimulation with alum or poly(I:C)/LyoVec. Moreover, the NOD1-induced and NOD2-induced activation was mediated via the nuclear factor-κB signalling pathway and augmented by interleukin-5 and granulocyte-macrophage colony-stimulating factor, but not interferon-γ. Taken together, the NLR system represents a novel pathway for eosinophil activation. The responses are enhanced in the presence of cytokines that regulate T helper type 2 immunity, suggesting that the NLRs constitute a link between respiratory infections and exacerbations of allergic disease.