Defective interleukin (IL)-18-mediated natural killer and T helper cell type 1 responses in IL-1 receptor-associated kinase (IRAK)-deficient mice

Combined delivery of IL12 and an IL18 mutant without IL18BP-binding activity by an adenoviral vector enhances tumor specific immunity

Cytokines play pivotal roles in anticancer immune response. We previously reported that adenovirus armed with an IL18 variant (DR18) that overcomes IL18BP neutralizing effect displayed powerful therapeutic effects in local and distant tumors when delivered intratumorally. Here, we tested a combined delivery of IL12 and DR18 in tumor models since IL12 and IL18 are known to act synergistically in potentiating IFNγ production and antitumor immunity. To minimize adverse effects associated with systemic delivery, we constructed oncolytic adenoviruses (oAd) harboring DR18 and IL12 (oAd.DR18/IL12). IL12 was expressed as a single chain IL12 (scIL12) peptide composed of the IL12/p40 and IL12/p35 subunits. Intratumoral administration of oAd.DR18/IL12, oAd-expressing DR18 (oAd.DR18), or oAd-expressing IL12 (oAd.IL12) showed antitumor effect in syngeneic colorectal tumor models. Compared to oAd.DR18 or oAd.IL12, administration of oAd.DR18/IL12 improved the antitumor effects as well as increased survival rate in these models. We detected enhanced tumor infiltrating T lymphocytes and NK cells in oAd.DR18/IL12-treated mice than those from mock-treated or individually treated groups. Moreover, mice received oAd.DR18/IL12 had more robust tumor-specific cytotoxicity. Importantly, mice that had tumor regression after oAd.DR18/IL12 treatment established anti-tumor specific immune memory. These results show that adenovirus armed with engineered cytokines boosts tumor specific immunity and antitumor effect.

A Narrative Review of the IL-18 and IL-37 Implications in the Pathogenesis of Atopic Dermatitis and Psoriasis: Prospective Treatment Targets

Atopic dermatitis and psoriasis are prevalent inflammatory skin conditions that significantly impact the quality of life of patients, with diverse treatment options available. Despite advances in understanding their underlying mechanisms, recent research highlights the significance of interleukins IL-18 and IL-37, in Th1, Th2, and Th17 inflammatory responses, closely associated with the pathogenesis of psoriasis and atopic dermatitis. Hence, IL-18 and IL-37 could potentially become therapeutic targets. This narrative review synthesizes knowledge on these interleukins, their roles in atopic dermatitis and psoriasis, and emerging treatment strategies. Findings of a literature search up to 30 May 2024, underscore a research gap in IL-37-targeted therapies. Conversely, IL-18-focused treatments have demonstrated promise in adult-onset Still's Disease, warranting further exploration for their potential efficacy in psoriasis and atopic dermatitis.

An antibody to IL-1 receptor 7 protects mice from LPS-induced tissue and systemic inflammation

Introduction

Interleukin-18 (IL-18), a pro-inflammatory cytokine belonging to the IL-1 Family, is a key mediator ofautoinflammatory diseases associated with the development of macrophage activation syndrome (MAS).High levels of IL-18 correlate with MAS and COVID-19 severity and mortality, particularly in COVID-19patients with MAS. As an inflammation inducer, IL-18 binds its receptor IL-1 Receptor 5 (IL-1R5), leadingto the recruitment of the co-receptor, IL-1 Receptor 7 (IL-1R7). This heterotrimeric complex subsequentlyinitiates downstream signaling, resulting in local and systemic inflammation.

Methods

We reported earlier the development of a novel humanized monoclonal anti-human IL-1R7 antibody whichspecifically blocks the activity of human IL-18 and its inflammatory signaling in human cell and wholeblood cultures. In the current study, we further explored the strategy of blocking IL-1R7 inhyperinflammation in vivo using animal models.

Results

We first identified an anti-mouse IL-1R7 antibody that significantly suppressed mouse IL-18 andlipopolysaccharide (LPS)-induced IFNg production in mouse splenocyte and peritoneal cell cultures. Whenapplied in vivo, the antibody reduced Propionibacterium acnes and LPS-induced liver injury and protectedmice from tissue and systemic hyperinflammation. Importantly, anti-IL-1R7 significantly inhibited plasma,liver cell and spleen cell IFNg production. Also, anti-IL-1R7 downregulated plasma TNFa, IL-6, IL-1b,MIP-2 production and the production of the liver enzyme ALT. In parallel, anti-IL-1R7 suppressed LPSinducedinflammatory cell infiltration in lungs and inhibited the subsequent IFNg production andinflammation in mice when assessed using an acute lung injury model.

Discussion

Altogether, our data suggest that blocking IL-1R7 represents a potential therapeutic strategy to specificallymodulate IL-18-mediated hyperinflammation, warranting further investigation of its clinical application intreating IL-18-mediated diseases, including MAS and COVID-19.

Expanded ILC2s in human infant intestines promote tissue growth

Early life is characterized by extraordinary challenges, including rapid tissue growth and immune adaptation to foreign antigens after birth. During this developmental stage, infants have an increased risk of immune-mediated diseases. Here, we demonstrate that tissue-resident, interleukin (IL)-13- and IL-4-producing group 2 innate lymphoid cells (ILC2s) are enriched in human infant intestines compared to adult intestines. Organoid systems were employed to assess the role of infant intestinal ILC2s in intestinal development and showed that IL-13 and IL-4 increased epithelial cell proliferation and skewed cell differentiation toward secretory cells. IL-13 furthermore upregulated the production of mediators of type-2 immunity by infant intestinal epithelial cells, including vascular endothelial growth factor-A and IL-26, a chemoattractant for eosinophils. In line with these in vitro findings increased numbers of eosinophils were detected in vivo in infant intestines. Taken together, ILC2s are enriched in infant intestines and can support intestinal development while inducing an epithelial secretory response associated with type 2 immune-mediated diseases.

Functional characterization of IL-18 receptor subunits, IL-18Rα and IL-18Rβ, and its natural inhibitor, IL-18 binding protein (IL-18BP) in rainbow trout Oncorhynchus mykiss

As an important proinflammation and immunomodulatory cytokine, IL-18 has been reported in several species of fish, but its receptor subunits, IL-18Rα and IL-18Rβ, and its decoy receptor, IL-18BP, have not been functionally characterized in fish. In the present study, IL-18Rα, IL-18Rβ and IL-18BP were cloned from rainbow trout Oncorhynchus mykiss, and they possess common conserved domains with their mammalian orthologues. In tested organs/tissues, IL-18Rα and IL-18Rβ exhibit basal expression levels, and IL-18BP has a pattern of constitutive expression. When transfected with different combinations of chimeric receptors in HEK293T cells, recombinant IL-18 (rIL-18) can induce the activation of NF-κB only when pcDNA3.1-IL-18Rα/IL-1R1 and pcDNA3.1-IL-18Rβ/IL-1RAP were both expressed. On the other hand, recombinant receptors, including rIL-18BP, rIL-18Rα-ECD-Fc and rIL-18Rβ-ECD-Fc can down-regulate significantly the activity of NF-κB, suggesting the participation of IL-18Rα, IL-18Rβ and IL-18BP in rainbow trout IL-18 signal transduction. Co-IP assays indicated that IL-18Rβ may form a complex with MyD88, IRAK4, IRAK1, TRAF6 and TAB2 in HEK293T cells, indicating that IL-18Rβ, in IL-18 signalling pathway, is associated with these signalling molecules. In conclusion, IL-18Rα, IL-18Rβ and IL-18BP in rainbow trout are conserved in function and signalling pathway with their mammalian orthologues.

Interleukin-18 and IL-18BP in inflammatory dermatological diseases

Interleukin (IL)-18, an interferon-γ inducer, belongs to the IL-1 family of pleiotropic pro-inflammatory factors, and IL-18 binding protein (IL-18BP) is a native antagonist of IL-18 in vivo, regulating its activity. Moreover, IL-18 exerts an influential function in host innate and adaptive immunity, and IL-18BP has elevated levels of interferon-γ in diverse cells, suggesting that IL-18BP is a negative feedback inhibitor of IL-18-mediated immunity. Similar to IL-1β, the IL-18 cytokine is produced as an indolent precursor that requires further processing into an active cytokine by caspase-1 and mediating downstream signaling pathways through MyD88. IL-18 has been implicated to play a role in psoriasis, atopic dermatitis, rosacea, and bullous pemphigoid in human inflammatory skin diseases. Currently, IL-18BP is less explored in treating inflammatory skin diseases, while IL-18BP is being tested in clinical trials for other diseases. Thereby, IL-18BP is a prospective therapeutic target.

Interleukin-18 in metabolism: From mice physiology to human diseases

Interleukin-18 (IL-18) is a classical member of the IL-1 superfamily of cytokines. As IL-1β, IL-18 precursor is processed by inflammasome/caspase-1 into a mature and biologically active form. IL-18 binds to its specific receptor composed of two chains (IL-18Rα and IL-18Rβ) to trigger a similar intracellular signaling pathway as IL-1, ultimately leading to activation of NF-κB and inflammatory processes. Independently of this IL-1-like signaling, IL-18 also specifically induces IFN-γ production, driving the Th1 immune response. In circulation, IL-18 binds to the IL-18 binding protein (IL-18BP) with high affinity, letting only a small fraction of free IL-18 able to trigger receptor-mediated signaling. In contrast to other IL-1 family members, IL-18 is produced constitutively by different cell types, suggesting implications in normal physiology. If the roles of IL-18 in inflammatory processes and infectious diseases are well described, recent experimental studies in mice have highlighted the action of IL-18 signaling in the control of energy homeostasis, pancreatic islet immunity and liver integrity during nutritional stress. At the same time, clinical observations implicate IL-18 in various metabolic diseases including obesity, type 1 and 2 diabetes and nonalcoholic fatty liver disease (NAFLD)/nonalcoholic steatohepatitis (NASH). In the present review, we summarize and discuss both the physiological actions of IL-18 in metabolism and its potential roles in pathophysiological mechanisms leading to the most common human metabolic disorders, such as obesity, diabetes and NAFLD/NASH.

Immune response against toxoplasmosis-some recent updates RH: Toxoplasma gondii immune response

AIMS

Cytokines, soluble mediators of immunity, are key factors of the innate and adaptive immune system. They are secreted from and interact with various types of immune cells to manipulate host body's immune cell physiology for a counter-attack on the foreign body. A study was designed to explore the mechanism of Toxoplasma gondii (T. gondii) resistance from host immune response.

METHODS AND RESULTS

The published data on aspect of host (murine and human) immune response against T. gondii was taken from Google scholar and PubMed. Most relevant literature was included in this study. The basic mechanism of immune response starts from the interactions of antigens with host immune cells to trigger the production of cytokines (pro-inflammatory and anti-inflammatory) which then act by forming a cytokinome (network of cytokine). Their secretory equilibrium is essential for endowing resistance to the host against infectious diseases, particularly toxoplasmosis. A narrow balance lying between Th1, Th2, and Th17 cytokines (as demonstrated until now) is essential for the development of resistance against T. gondii as well as for the survival of host. Excessive production of pro-inflammatory cytokines leads to tissue damage resulting in the production of anti-inflammatory cytokines which enhances the proliferation of Toxoplasma. Stress and other infectious diseases (human immunodeficiency virus (HIV)) that weaken the host immunity particularly the cellular component, make the host susceptible to toxoplasmosis especially in pregnant women.

CONCLUSION

The current review findings state that in vitro harvesting of IL12 from DCs, Np and MΦ upon exposure with T. gondii might be a source for therapeutic use in toxoplasmosis. Current review also suggests that therapeutic interventions leading to up-regulation/supplementation of SOCS-3, IL12, and IFNγ to the infected host could be a solution to sterile immunity against T. gondii infection. This would be of interest particularly in patients passing through immunosuppression owing to any reason like the ones receiving anti-cancer therapy, the ones undergoing immunosuppressive therapy for graft/transplantation, the ones suffering from immunodeficiency virus (HIV) or having AIDS. Another imortant suggestion is to launch the efforts for a vaccine based on GRA6Nt or other similar antigens of T. gondii as a probable tool to destroy tissue cysts.

A novel anti-human IL-1R7 antibody reduces IL-18-mediated inflammatory signaling

Unchecked inflammation can result in severe diseases with high mortality, such as macrophage activation syndrome (MAS). MAS and associated cytokine storms have been observed in COVID-19 patients exhibiting systemic hyperinflammation. Interleukin-18 (IL-18), a proinflammatory cytokine belonging to the IL-1 family, is elevated in both MAS and COVID-19 patients, and its level is known to correlate with the severity of COVID-19 symptoms. IL-18 binds its specific receptor IL-1 receptor 5 (IL-1R5, also known as IL-18 receptor alpha chain), leading to the recruitment of the coreceptor, IL-1 receptor 7 (IL-1R7, also known as IL-18 receptor beta chain). This heterotrimeric complex then initiates downstream signaling, resulting in systemic and local inflammation. Here, we developed a novel humanized monoclonal anti-IL-1R7 antibody to specifically block the activity of IL-18 and its inflammatory signaling. We characterized the function of this antibody in human cell lines, in freshly obtained peripheral blood mononuclear cells (PBMCs) and in human whole blood cultures. We found that the anti-IL-1R7 antibody significantly suppressed IL-18-mediated NFκB activation, reduced IL-18-stimulated IFNγ and IL-6 production in human cell lines, and reduced IL-18-induced IFNγ, IL-6, and TNFα production in PBMCs. Moreover, the anti-IL-1R7 antibody significantly inhibited LPS- and Candida albicans–induced IFNγ production in PBMCs, as well as LPS-induced IFNγ production in whole blood cultures. Our data suggest that blocking IL-1R7 could represent a potential therapeutic strategy to specifically modulate IL-18 signaling and may warrant further investigation into its clinical potential for treating IL-18-mediated diseases, including MAS and COVID-19.

Interleukin-18 in Inflammatory Kidney Disease

Interleukin (IL)-18, a member of the IL-1 superfamily, is a pro-inflammatory cytokine that is structurally similar to IL-1β. IL-18 promotes the production of interferon gamma (IFN-γ) and strongly induces a Th1 response. IL-18 drives the same myeloid differentiation factor 88 (MyD88)/nuclear factor kappa B (NF-κB) signaling pathway as IL-1β. In physiological conditions, IL-18 is regulated by the endogenous inhibitor IL-18 binding protein (IL-18BP), and the activity of IL-18 is balanced. It is reported that in several inflammatory diseases, the IL-18 activity is unbalanced, and IL-18 neutralization by IL-18BP is insufficient. IL-18 acts synergistically with IL-12 to induce the production of IFN-γ as a Th1 cytokine, and IL-18 acts alone to induce the production of Th2 cytokines such as IL-4 and IL-13. In addition, IL-18 alone enhances natural killer (NK) cell activity and FAS ligand expression. The biological and pathological roles of IL-18 have been studied in many diseases. Here we review the knowledge regarding IL-18 signaling and the role of IL-18 in inflammatory kidney diseases. Findings on renal injury in coronavirus disease 2019 (COVID-19) and its association with IL-18 will also be presented.

Molecular characterization, expression and functional analysis of IRAK1 and IRAK4 in Nile tilapia (Oreochromis niloticus)

Interleukin-1 receptor-associated kinase 1 (IRAK1) and IRAK4 are critical signalling mediators and play pivotal roles in the innate immune and inflammatory responses mediated by TLR/IL-1R. In the present study, two IRAK family members, OnIRAK1 and OnIRAK4, were identified in the Nile tilapia Oreochromis niloticus with a conserved N-terminal death domain and a protein kinase domain, similar to those of other fishes and mammals. The gene structures of OnIRAK1 and OnIRAK4 are organized into fifteen exons split by fourteen introns and ten exons split by nine introns. OnIRAK1 and OnIRAK4 were broadly expressed in all of the tissues tested, with the highest expression levels being observed in the blood and the lowest expression levels being observed in the liver. Both genes could be detected from 2 d post-fertilization (dpf) to 8 dpf during embryonic development. Moreover, the expression levels of OnIRAK1 and OnIRAK4 were clearly altered in all five tissues after Streptococcus agalactiae infection in vivo and could be induced by LPS, Poly I: C, S. agalactiae WC1535 and △CPS in Nile tilapia macrophages. The overexpression of OnIRAK1 and OnIRAK4 in 293T cells showed that they were both distributed in the cytoplasm and could significantly increase NF-κB activation. Interestingly, after transfection, OnIRAK1 significantly upregulated OnMyd88-induced NF-κB activation, while OnIRAK4 had no effect on OnMyd88-induced NF-κB activation. Co-immunoprecipitation (Co-IP) assays showed that OnMyd88 did not interact with either OnIRAK1 or OnIRAK4 and that OnIRAK1 did not interact with OnIRAK4. Taken together, these findings suggest that OnIRAK1 and OnIRAK4 could play important roles in TLR/IL-1R signalling pathways and the immune response to pathogen invasion.

Emerging Roles for Interleukin-18 in the Gastrointestinal Tumor Microenvironment

Interleukin (IL)-18, a member of the IL-1 family of cytokines, has emerged as a key regulator of mucosal homeostasis within the gastrointestinal tract. Like other members of this family, IL-18 is secreted as an inactive protein and is processed into its active form by caspase-1, although other contributors to precursor processing are emerging.Numerous studies have evaluated the role of IL-18 within the gastrointestinal tract using genetic or complementary pharmacological tools and have revealed multiple roles in tumorigenesis. Most striking among these are the divergent roles for IL-18 in colon and gastric cancers. Here, we review our current understanding of IL-18 biology and how this applies to colorectal and gastric cancers.

Interleukin-18 in Health and Disease

Interleukin (IL)-18 was originally discovered as a factor that enhanced IFN-γ production from anti-CD3-stimulated Th1 cells, especially in the presence of IL-12. Upon stimulation with Ag plus IL-12, naïve T cells develop into IL-18 receptor (IL-18R) expressing Th1 cells, which increase IFN-γ production in response to IL-18 stimulation. Therefore, IL-12 is a commitment factor that induces the development of Th1 cells. In contrast, IL-18 is a proinflammatory cytokine that facilitates type 1 responses. However, IL-18 without IL-12 but with IL-2, stimulates NK cells, CD4⁺ NKT cells, and established Th1 cells, to produce IL-3, IL-9, and IL-13. Furthermore, together with IL-3, IL-18 stimulates mast cells and basophils to produce IL-4, IL-13, and chemical mediators such as histamine. Therefore, IL-18 is a cytokine that stimulates various cell types and has pleiotropic functions. IL-18 is a member of the IL-1 family of cytokines. IL-18 demonstrates a unique function by binding to a specific receptor expressed on various types of cells. In this review article, we will focus on the unique features of IL-18 in health and disease in experimental animals and humans.

Interleukin 18 binding protein ameliorates ischemia/reperfusion-induced hepatic injury in mice

Inflammation-associated oxidative stress contributes to hepatic ischemia/reperfusion injury (IRI). Detrimental inflammatory event cascades largely depend on activated Kupffer cells (KCs) and neutrophils, as well as proinflammatory cytokines, including tumor necrosis factor α (TNF-α) and interleukin (IL) 18. The aim of our study was to evaluate the effects of IL 18 binding protein (IL 18Bp) in hepatic IRI of mice. Thirty C57BL/6 mice were allocated into 3 groups: sham operation, ischemia/reperfusion (I/R), and I/R with intravenous administration of IL 18Bp. Hepatic ischemia was induced for 30 minutes by Pringle's maneuver. After 120 minutes of reperfusion, mice were euthanized, and the liver and blood samples were collected for histological, immunohistochemical, molecular, and biochemical analyses. I/R injury induced the typical liver pathology and upregulated IL-18 expression in the liver of mice. Binding of IL 18 with IL 18Bp significantly reduced the histopathological indices of I/R liver injury and KC apoptosis. The I/R-induced increase of TNF-α, malondialdehyde, aspartate aminotransferase, and alanine aminotransferase levels was prevented in statistically significant levels because of the pretreatment with IL 18Bp. Likewise, blocking of IL 18 ablated the I/R-associated elevation of nuclear factor kappa B, c-Jun, myeloperoxidase, and IL 32 and the up-regulation of neutrophils and T-helper lymphocytes. Administration of IL 18Bp protects the mice liver from I/R injury by intervening in critical inflammation-associated pathways and KC apoptosis.

Expression of Interleukin-1 and Interleukin-1 Receptors Type 1 and Type 2 in Hodgkin Lymphoma

Signaling through the IL-1-receptor type 1 (IL-1R1), IL-1 is required for initiation and maintenance of diverse activities of the immune system. A second receptor, IL-1R2, blocks IL-1 signal transduction. We studied expression of IL-1beta, IL-1R1, and IL-1R2 in 17 Hodgkin lymphomas (HL) by in situ hybridization (ISH). IL-1beta expressing cells, morphologically consistent with endothelial cells and fibroblasts, occurred in all HL tissues with elevated transcript levels in areas of active fibrosis. Hodgkin and Reed-Sternberg (HRS) cells of all cases expressed low IL-1R1 transcript levels in some tumor cells, and high levels of IL-1R2 in large proportions of HRS cells. Only few bystander cells showed low levels of IL-1R1 and IL-1R2 RNA. Supernatants of 4 out of 7 HL-derived cell lines contained soluble IL-1R2 protein at high levels. HL patient sera carried variably amounts of IL-1R2 protein with significantly increased titers in patients with active disease compared to patients in complete remission and control individuals without HL. Western blots and co-immunoprecipitations showed binding of the IL-1R2 to the intracellular IL-1R-accessory protein (IL-1IRAcP). These data suggest functions of the IL-1R2 as a „decoy-receptor” sequestrating paracrine IL-1 extracellularly and intracellularly by engaging IL-1IRAcP, thus depriving IL1-R1 molecules of their extracellular and intracellular ligands. Expression of IL1-R2 by HRS cells seems to contribute to local and systemic modulation of immune function in HL.

The pathological role of IL-18Rα in renal ischemia/reperfusion injury

Interleukin (IL)-18 is a proinflammatory cytokine produced by leukocytes and parenchymal cells (eg, tubular epithelial cells (TECs), mesangial cells, and podocytes). IL-18 receptor (IL-18R) is expressed on these cells in the kidney during ischemia/reperfusion injury (IRI), but its role in this injury is unknown. Fas/Fas ligand (FasL) is also involved in the pathogenesis of renal IRI via tubular apoptosis. In addition, IL-18 enhances the expression of FasL on TECs, but the mechanism underlying this enhancement is not known. Here we used IL-18Rα-deficient mice to explore the pathological role of IL-18Rα in renal IRI. We found that compared to wild-type (WT) mice with renal IRI as an acute kidney injury (AKI), the IL-18Rα-deficient mice demonstrated decreased renal function (as represented by blood urea nitrogen), tubular damage, an increased accumulation of leukocytes (CD4+ T cells, neutrophils, and macrophages), upregulated early AKI biomarkers (ie, urinary kidney injury molecule-1 levels), and increased mRNA expressions of proinflammatory cytokines (IL-1β, IL-12p40, and IL-18) and chemokines (intercellular adhesion molecule-1 and CCL2/monocyte chemoattractant protein-1). The mRNA expression of FasL in the kidney was increased in the IL-18Rα-deficient mice compared to the WT mice. The adoptive transfer of splenocytes by WT mice led to decreased renal IRI compared to the IL-18Rα-deficient mice. In vitro, the mRNA expression of FasL on TECs was promoted in the presence of recombinant IL-18. These data reveal that IL-18Rα has an anti-inflammatory effect in IRI-induced AKI. Above all, IL-18 enhanced the inflammatory mechanisms and the apoptosis of TECs through the Fas/FasL pathway by blocking IL-18Rα.

Increased expression of the interleukin-1 receptor-associated kinase (IRAK)-1 is associated with adipose tissue inflammatory state in obesity

BACKGROUND

The emerging role of TLR2/4 as immuno-metabolic receptors points to key involvement of TLR/IL-1R/MyD88 pathway in obesity/type-2 diabetes (T2D). IL1R-associated kinase (IRAK)-1 is a critical adapter protein (serine/threonine kinase) of this signaling pathway. The changes in adipose tissue expression of IRAK-1 in obesity/T2D remain unclear. We determined modulations in IRAK-1 gene/protein expression in the subcutaneous adipose tissues from lean, overweight and obese individuals with or without T2D.

METHODS

A total of 49 non-diabetic (22 obese, 19 overweight and 8 lean) and 42 T2D (31 obese, 9 overweight and 2 lean) adipose tissue samples were obtained by abdominal subcutaneous fat pad biopsy and IRAK-1 expression was determined using real-time RT-PCR, immunohistochemistry, and confocal microscopy. IRAK-1 mRNA expression was compared with adipose tissue proinflammatory mediators (TNF-α, IL-6, IL-18), macrophage markers (CD68, CD11c, CD163), and plasma markers (CCL-5, C-reactive protein, adiponectin, and triglycerides). The data were analyzed using t test, Pearson's correlation, and multiple stepwise linear regression test.

RESULTS

In non-diabetics, IRAK-1 gene expression was elevated in obese (P = 0.01) and overweight (P = 0.04) as compared with lean individuals and this increase correlated with body mass index (r = 0.45; P = 0.001) and fat percentage (r = 0.36; P = 0.01). In diabetics, IRAK-1 mRNA expression was also higher in obese as compared with lean subjects (P = 0.012). As also shown by immunohistochemistry/confocal microscopy in non-diabetics and by immunohistochemistry in diabetics, IRAK-1 protein expression was higher in obese than overweight and lean adipose tissues. IRAK-1 gene expression correlated positively/significantly with mRNAs of TNF-α (r = 0.46; P = 0.0008), IL-6 (r = 0.30; P = 0.03) and IL-18 (r = 0.31; P = 0.028) in non-diabetics; and only with TNF-α (r = 0.32; P = 0.03) in diabetics. IRAK-1 expression also correlated positively/significantly with CD68 (r = 0.32; P = 0.02), CD11c (r = 0.30; P = 0.03), and CD163 (r = 0.43; P = 0.001) in non-diabetics; and only with CD163 (r = 0.34; P = 0.02) in diabetics. IRAK-1 mRNA levels also correlated with plasma markers including CCL-5 (r = 0.39; P = 0.02), C-reactive protein (r = 0.48; P = 0.005), adiponectin (r = -0.36; P = 0.04), and triglycerides (r = 0.40; P = 0.02) in non-diabetics; and only with triglycerides (r = -0.36; P = 0.04) in diabetics. IRAK-1 expression related with TLR2 (r = 0.39; P = 0.007) and MyD88 (r = 0.36; P = 0.01) in non-diabetics; and MyD88 (r = 0.52; P = 0.0003) in diabetics.

CONCLUSIONS

The elevated IRAK-1 expression in obese adipose tissue showed consensus with local/circulatory inflammatory signatures and represented as a tissue marker for metabolic inflammation. The data have clinical significance as interventions causing IRAK-1 suppression may alleviate meta-inflammation in obesity/T2D.

Interleukin-18 as a therapeutic target in acute myocardial infarction and heart failure

Interleukin 18 (IL-18) is a proinflammatory cytokine in the IL-1 family that has been implicated in a number of disease states. In animal models of acute myocardial infarction (AMI), pressure overload, and LPS-induced dysfunction, IL-18 regulates cardiomyocyte hypertrophy and induces cardiac contractile dysfunction and extracellular matrix remodeling. In patients, high IL-18 levels correlate with increased risk of developing cardiovascular disease (CVD) and with a worse prognosis in patients with established CVD. Two strategies have been used to counter the effects of IL-18:IL-18 binding protein (IL-18BP), a naturally occurring protein, and a neutralizing IL-18 antibody. Recombinant human IL-18BP (r-hIL-18BP) has been investigated in animal studies and in phase I/II clinical trials for psoriasis and rheumatoid arthritis. A phase II clinical trial using a humanized monoclonal IL-18 antibody for type 2 diabetes is ongoing. Here we review the literature regarding the role of IL-18 in AMI and heart failure and the evidence and challenges of using IL-18BP and blocking IL-18 antibodies as a therapeutic strategy in patients with heart disease.

IL-18 in inflammatory and autoimmune disease

Inflammation serves as the first line of defense in response to tissue injury, guiding the immune system to ensure preservation of the host. The inflammatory response can be divided into a quick initial phase mediated mainly by innate immune cells including neutrophils and macrophages, followed by a late phase that is dominated by lymphocytes. Early in the new millennium, a key component of the inflammatory reaction was discovered with the identification of a number of cytosolic sensor proteins (Nod-like receptors) that assembled into a common structure, the 'inflammasome'. This structure includes an enzyme, caspase-1, which upon activation cleaves pro-forms of cytokines leading to subsequent release of active IL-1 and IL-18. This review focuses on the role of IL-18 in inflammatory responses with emphasis on autoimmune diseases.

Simultaneous targeting of TNF and Ang2 with a novel bispecific antibody enhances efficacy in an in vivo model of arthritis

Despite the clinical success of anti-tumor necrosis factor (TNF) therapies in the treatment of inflammatory conditions such as rheumatoid arthritis, Crohn disease and psoriasis, full control of the diseases only occurs in a subset of patients and there is a need for new therapeutics with improved efficacy against broader patient populations. One possible approach is to combine biological therapeutics, but both the cost of the therapeutics and the potential for additional toxicities needs to be considered. In addition to the various mediators of immune and inflammatory pathways, angiogenesis is reported to contribute substantially to the overall pathogenesis of inflammatory diseases. The combination of an anti-angiogenic agent with anti-TNF into one molecule could be more efficacious without the risk of severe immunosuppression. To evaluate this approach with our Zybody technology, we generated bispecific antibodies that contain an Ang2 targeting peptide genetically fused to the anti-TNF antibody adalimumab (Humira®). The bispecific molecules retain the binding and functional characteristics of the anti-TNF antibody, but with additional activity that neutralizes Ang2. In a TNF transgenic mouse model of arthritis, the bispecific anti-TNF-Ang2 molecules showed a dose-dependent reduction in both clinical symptoms and histological scores that were significantly better than that achieved by adalimumab alone.

DICER1 loss and Alu RNA induce age-related macular degeneration via the NLRP3 inflammasome and MyD88

Alu RNA accumulation due to DICER1 deficiency in the retinal pigmented epithelium (RPE) is implicated in geographic atrophy (GA), an advanced form of age-related macular degeneration that causes blindness in millions of individuals. The mechanism of Alu RNA-induced cytotoxicity is unknown. Here we show that DICER1 deficit or Alu RNA exposure activates the NLRP3 inflammasome and triggers TLR-independent MyD88 signaling via IL18 in the RPE. Genetic or pharmacological inhibition of inflammasome components (NLRP3, Pycard, Caspase-1), MyD88, or IL18 prevents RPE degeneration induced by DICER1 loss or Alu RNA exposure. These findings, coupled with our observation that human GA RPE contains elevated amounts of NLRP3, PYCARD, and IL18 and evidence of increased Caspase-1 and MyD88 activation, provide a rationale for targeting this pathway in GA. Our findings also reveal a function of the inflammasome outside the immune system and an immunomodulatory action of mobile elements.

miR-155 regulates IFN-γ production in natural killer cells

MicroRNAs (miRs) are small, noncoding RNA molecules with important regulatory functions whose role in regulating natural killer (NK) cell biology is not well defined. Here, we show that miR-155 is synergistically induced in primary human NK cells after costimulation with IL-12 and IL-18, or with IL-12 and CD16 clustering. Over-expression of miR-155 enhanced induction of IFN-γ by IL-12 and IL-18 or CD16 stimulation, whereas knockdown of miR-155 or its disruption suppressed IFN-γ induction in monokine and/or CD16-stimulated NK cells. These effects on the regulation of NK cell IFN-γ expression were found to be mediated at least in part via miR-155's direct effects on the inositol phosphatase SHIP1. Consistent with this, we observed that modulation of miR-155 overrides IL-12 and IL-18-mediated regulation of SHIP1 expression in NK cells. Collectively, our data indicate that miR-155 expression is regulated by stimuli that strongly induce IFN-γ in NK cells such as IL-12, IL-18, and CD16 activation, and that miR-155 functions as a positive regulator of IFN-γ production in human NK cells, at least in part via down-regulating SHIP1. These findings may have clinical relevance for targeting miR-155 in neoplastic disease.

Interleukin-1 receptor-associated kinase 4 is essential for initial host control of Brucella abortus infection

Brucella abortus is a facultative intracellular bacterial pathogen that causes abortion in domestic animals and undulant fever in humans. Recent studies have revealed that Toll-like receptor (TLR)-initiated immune response to Brucella spp. depends on myeloid differentiation factor 88 (MyD88) signaling. Therefore, we decided to study the role of the interleukin-1 receptor-associated kinase 4 (IRAK-4) in host innate immune response against B. abortus. After Brucella infection, it was shown that the number of CFU in IRAK-4(-/-) mice was high compared to that in IRAK-4(+/-) animals only at 1 week postinfection. At 3 and 6 weeks postinfection, IRAK-4(-/-) mice were able to control the infection similarly to heterozygous animals. Furthermore, the type 1 cytokine profile was evaluated. IRAK-4(-/-) mice showed lower production of systemic interleukin-12 (IL-12) and gamma interferon (IFN-γ). Additionally, a reduced percentage of CD4(+) and CD8(+) T cells expressing IFN-γ was observed compared to IRAK-4(+/-). Further, the production of IL-12 and tumor necrosis factor alpha (TNF-α) by macrophages and dendritic cells from IRAK-4(-/-) mice was abolished at 24 h after stimulation with B. abortus. To investigate the role of IRAK-4 in mitogen-activated protein kinase (MAPK) and NF-κB signaling pathways, macrophages were stimulated with B. abortus, and the signaling components were analyzed by protein phosphorylation. Extracellular signal-regulated kinase 1 (ERK1) and ERK2 and p38 as well as p65 NF-κB phosphorylation was profoundly impaired in IRAK-4(-/-) and MyD88(-/-) macrophages activated by Brucella. In summary, the results shown in this study demonstrated that IRAK-4 is critical to trigger the initial immune response against B. abortus but not at later phases of infection.

Toll-like receptor signaling pathways and the evidence linking toll-like receptor signaling to cardiac ischemia/reperfusion injury

Toll-like receptors (TLRs) play a key role in innate immune defenses. After activation by foreign pathogens or host-derived molecules, TLRs signal via overlapping or distinct signaling cascades and eventually induce numerous genes involved in a variety of cellular responses. A growing body of evidence suggests that TLR signaling also plays an important role in cardiac ischemia/reperfusion injury. We review our current understanding of the TLR signaling pathways and their roles in the pathophysiology of cardiac ischemia/reperfusion injury, as well as discuss several mechanisms for TLR activation and regulation.

Immune complex-mediated cell activation from systemic lupus erythematosus and rheumatoid arthritis patients elaborate different requirements for IRAK1/4 kinase activity across human cell types

IL-1R-associated kinases (IRAKs) are important mediators of MyD88-dependent signaling by the TLR/IL-1R superfamily and facilitate inflammatory responses. IRAK4 and IRAK1 function as active kinases and as scaffolds for protein-protein interactions. We report that although IRAK1/4 kinase activity is essential for human plasmacytoid dendritic cell (pDC) activation, it is dispensable in B, T, dendritic, and monocytic cells, which is in contrast with an essential active kinase role in comparable mouse cell types. An IRAK1/4 kinase inhibitor abrogated TLR7/9-induced IFN-α responses in both mouse and human pDCs, but other human immune cell populations activated via TLR7/9 or IL-1R were refractory to IRAK4 kinase inhibition. Gene ablation experiments using small interfering RNA demonstrated an essential scaffolding role for IRAK1 and IRAK4 in MyD88-dependent signaling. Finally, we demonstrate that autoimmune patient (systemic lupus erythematosus and rheumatoid arthritis) serum activates both pDC and B cells, but IRAK1/4 kinase inhibition affects only the pDC response, underscoring the differential IRAK1/4 functional requirements in human immune cells. These data reveal important species differences and elaborate cell type requirements for IRAK1/4 kinase activity.

The inhibition of apoptosis by glycyrrhizin in hepatic injury induced by injection of lipopolysaccharide / D-galactosamine in mice

The inhibition of apoptosis by glycyrrhizin (GL) in hepatic injury induced by injection of lipopolysaccharide (LPS)/D-galactosamine (D-GalN) was examined in the present study. Morphological and biochemical analyses of LPS/D-GalN-induced mouse liver injury revealed that apoptosis occurred exclusively in injured hepatocytes of the centrilobular area. The degree of hepatic injury was associated with a substantial number of hepatocytes undergoing apoptosis. Transaminase levels were significantly increased at 6 to 8 h after the injection of LPS/D-GalN compared with controls. GL inhibited the elevation of serum transaminase levels when it was given to mice at 30 min before the administration of LPS/D-GalN. Morphological analyses using the TUNEL-method showed GL significantly reduced the number of TUNEL-labeled cells in acute hepatitis induced with LPS/D-GalN-treatment. Cells from the pericentral hepatic injury region were dissected out using a microdissection-method, and the DNA-ladder was clearly documented. Furthermore, results obtained through the TUNEL-method were confirmed with an oligonucleosome-bound DNA ELISA. From the current results, it seems reasonable to conclude that the protective role of GL in LPS/D-GalN-induced liver injury is performed through the inhibition of hepatic apoptosis.

Interleukin-18-related genes are induced during the contraction phase but do not play major roles in regulating the dynamics or function of the T-cell response to Listeria monocytogenes infection

Proinflammatory cytokines, such as gamma interferon (IFN-gamma), impact aspects of T-cell responses after infection, including expansion, contraction, and memory formation. Interleukin-18 (IL-18) functions as a proinflammatory cytokine by stimulating the production of IFN-gamma from multiple cell types and accentuating the development of Th1 CD4 T-cell responses. Focused microarray analyses revealed upregulation of IL-18 and IL-18 receptor genes in CD8 T cells during the contraction phase. Based on these findings we investigated if and how signaling through the IL-18 receptor influences the development and kinetics of antigen (Ag)-specific CD8 and CD4 T-cell responses following infection. IL-18Ralpha(-/-) and IL-18(-/-) mice developed frequencies and total numbers of Ag-specific CD8 T cells after Listeria monocytogenes infection that were similar to those of wild-type C57BL/6 mice. The kinetics of expansion, contraction, and memory CD8 T-cell maintenance were also similar. When IL-18Ralpha deficiency was isolated to Ag-specific CD8 T cells, the kinetics of the expansion and contraction phases were also normal. These basic findings were confirmed by examining the response to vaccinia virus infection. In contrast, the expansion of Ag-specific CD4 T cells was slightly curtailed by the absence of IL-18Ralpha; however, contraction and the maintenance of memory were not altered. Importantly, both memory Ag-specific CD8 and CD4 T cells generated in the absence of IL-18Ralpha expanded appropriately after secondary antigen exposure and were protective, indicating that signaling through the IL-18 receptor is not required for normal T-cell response kinetics and survival of immunized mice challenged with a lethal L. monocytogenes infection.

Helicobacter pylori infection upregulates interleukin-18 production from gastric epithelial cells

BACKGROUND

Helicobacter pylori infection induces a biased T helper type 1 (Th1) response that produces IFN-gamma and Fas ligand (FasL). Th1 cytokines are associated with apoptosis in the gastric epithelial cells.

AIM

We aimed to define the role of the recently cloned IL-18, a IFN-gamma inducing factor, in gastric mucosal injury induced by H. pylori infection.

METHODS

Twenty-seven gastric ulcer (GU) patients and 20 functional dyspepsia (FD) patients were enrolled in this study. Mucosal biopsy samples were obtained from the gastric antrum and GU site during endoscopy. Samples were used for histological examination, H. pylori culture and in-situ stimulation for 48 h in the presence of 10 microg/ml phytohemagglutinin-P. IL-18, IFN-gamma, and soluble FasL (sFasL) levels in culture supernatants were assayed by the enzyme-linked immunosorbent assay method. IL-18, IL-1beta-converting enzyme (ICE) and caspase-3 were evaluated by western blotting in gastric cancer cell lines (MKN45) cocultured with H. pylori.

RESULTS

All 27 GU patients and ten out of 20 FD patients were found to be H. pylori-positive, whereas ten FD patients were H. pylori-negative. Antral mucosal tissues from H. pylori-positive FD patients contained (P<0.01) higher levels of IL-18, IFN-gamma, and sFasL than those from uninfected FD patients. IL-18, IFN-gamma, and sFasL levels at the ulcer site were significantly (P<0.01) higher than those at distant sites in the antrum. A significant relationship was seen between IL-18 and IFN-gamma levels at the ulcer site (r=0.7, P<0.01). H. pylori eradication led to a significant decrease in the levels of IL-18, IFN-gamma, and sFasL at the ulcer site. Western blotting showed that IL-18, ICE, and caspase-3 were activated in gastric cancer cell lines cocultured with H. pylori.

CONCLUSION

This study suggests that H. pylori infection enhanced mucosal injury by stimulating a Th1 response, which was mediated by IL-18 upregulation as well as activation of ICE and caspase-3.

Interleukin 18 in the heart

IL-18, originally termed as interferon gamma (IFN-gamma) inducing factor, is a proinflammatory cytokine that belongs to the IL-1 cytokine superfamily. IL-18 plays an important role in immune, infectious, and inflammatory diseases due to its induction of IFN-gamma. However, accumulated evidence has demonstrated that other effects of IL-18 are independent of IFN-gamma. Here, we reviewed the current literatures regarding the role of IL-18 in the heart and cardiovascular system. Infiltrated neutrophils, resident macrophages, endothelial cells, smooth muscle cells, and cardiomyocytes in the heart are able to produce IL-18 in response to injury. IL-18 is produced as a biologically inactive precursor (pro-IL-18) that is activated by caspase 1 (the IL-1beta converting enzyme). Elevated IL-18 levels have been observed in cardiac tissue and circulation after myocardial I/R and sepsis. The possible cellular and molecular mechanisms concerning IL-18-induced myocardial injury include induction of inflammation, increased apoptosis, a cardiac hypertrophy effect, modulation of mitogen activated protein kinase activation, and changes in intracellular calcium. Finally, we briefly reviewed the therapeutic strategies for inhibiting IL-18's biological activity to protect cardiac tissue from injury.

IRAK1: A critical signaling mediator of innate immunity

The innate immune system is equipped with sensitive and efficient machineries to provide an immediate, first line defense against infections. Toll-like receptors (TLRs) detect pathogens and the IL-1 receptor (IL-1R) family enables cells to quickly respond to inflammatory cytokines by mounting an efficient protective response. Interleukin-1 receptor activated kinases (IRAKs) are key mediators in the signaling pathways of TLRs/IL-1Rs. By means of their kinase and adaptor functions, IRAKs initiate a cascade of signaling events eventually leading to induction of inflammatory target gene expression. Due to this pivotal role, IRAK function is also highly regulated via multiple mechanisms. In this review, we focus on IRAK1, the earliest known and yet the most interesting member of this family. An overview on its structure, function and biology is given, with emphasis on the different novel mechanisms that regulate IRAK1 function. We also highlight several unresolved questions in this field and evaluate the potential of IRAK1 as a target for therapeutic intervention.

Interleukin-18 induces angiogenic factors in rheumatoid arthritis synovial tissue fibroblasts via distinct signaling pathways

OBJECTIVE

Interleukin-18 (IL-18) is a proinflammatory cytokine implicated in the pathogenesis of rheumatoid arthritis (RA). This study was undertaken to examine the role of IL-18 in up-regulating secretion of the angiogenic factors stromal cell-derived factor 1alpha (SDF-1alpha)/CXCL12, monocyte chemoattractant protein 1 (MCP-1)/CCL2, and vascular endothelial growth factor (VEGF) in RA synovial tissue (ST) fibroblasts, and the underlying signaling mechanisms involved.

METHODS

We used enzyme-linked immunosorbent assays, Western blotting, and chemical inhibitors/antisense oligodeoxynucleotides to signaling intermediates to assess the role of IL-18.

RESULTS

IL-18 significantly enhanced the production of SDF-1alpha/CXCL12, MCP-1/CCL2, and VEGF in RA ST fibroblasts, in a time- and concentration-dependent manner. IL-18-induced SDF-1alpha/CXCL12 up-regulation was dependent on JNK, p38 MAPK, phosphatidylinositol 3-kinase (PI3K), and NFkappaB. While IL-18-induced production of SDF-1alpha/CXCL12 was also dependent on protein kinase Cdelta (PKCdelta), production of MCP-1/CCL2 was dependent on PKCalpha, not PKCdelta. Additionally, RA ST fibroblast IL-18-induced MCP-1/CCL2 production was mediated by JNK, PI3K, and NFkappaB. In contrast, IL-18 did not induce secretion of RA ST fibroblast MCP-1/CCL2 or VEGF via p38 MAPK. IL-18-induced RA ST fibroblast production of VEGF was mediated mainly by JNK-2, PKCalpha, and NFkappaB. IL-18 induced phosphorylation of JNK, PKCdelta, p38 MAPK, and activating transcription factor 2 (ATF-2) in RA ST fibroblasts in a time-dependent manner, with JNK-2 being upstream of PKCdelta, ATF-2, and NFkappaB.

CONCLUSION

These data support the notion that IL-18 has a unique role in inducing the secretion of angiogenic SDF-1alpha/CXCL12, MCP-1/CCL2, and VEGF in RA ST fibroblasts, via distinct signaling intermediates.

Natural killer cells play a key role in the antitumor immunity generated by chaperone-rich cell lysate vaccination

Tumor derived chaperone-rich cell lysate (CRCL) when isolated from tumor tissues is a potent vaccine that contains at least 4 of the highly immunogenic heat shock proteins (HSP) such as HSP70, HSP90, glucose related protein 94 and calreticulin. We have previously documented that CRCL provides both a source of tumor antigens and danger signals triggering dendritic cell (DC) activation. Immunization with tumor derived CRCL elicits tumor-specific T cell responses leading to tumor regression. In the current study, we further dissect the mechanisms by which CRCL simulates the immune system, and demonstrate that natural killer (NK) cells are required for effective antitumor effects to take place. Our results illustrate that CRCL directly stimulates proinflammatory cytokine and chemokine production by NK cells, which may lead to activation and recruitment of macrophages at the tumor site. Thus, this report provides further insight into the function of CRCL as an immunostimulant against cancer.

Pathophysiology of interleukin-1 receptor-associated kinase-M: implications in refractory state

PURPOSE OF REVIEW

The pseudo-kinase interleukin-1 receptor-associated kinase-M has emerged as a critical molecule in the down-regulation of inflammatory responses. Dysregulation of the toll-like receptor-interleukin-1 receptor-associated kinase system, and in particular interleukin-1 receptor-associated kinase-M up-regulation, are associated with a number of pathologies. This review highlights recent findings on interleukin-1 receptor-associated kinase-M reported in biomedical literature.

RECENT FINDINGS

Interleukin-1 receptor-associated kinase-M plays a critical role in generating a refractory state of the immune system following monocytes/macrophages encounter with bacteria or tumor cells. This state has been demonstrated so far in patients who suffer from sepsis, leukemia, and acute coronary syndrome, and seems to be associated with interleukin-1 receptor-associated kinase-M overexpression in their circulating monocytes. In addition, the pseudo-kinase represents a central regulator of osteoclast differentiation and activation, and might thus be related to the onset of osteoporosis.

SUMMARY

Interleukin-1 receptor-associated kinase-M is involved in the control of endotoxin tolerance in monocytes, in osteoporosis, as well as in the deactivation of tumor-infiltrating macrophages. Additionally, patients who suffer from several pathologies related to inflammatory responses express high levels of this molecule in their circulating monocytes. Human monocytes treated with a nitric oxide donor also express large amounts of interleukin-1 receptor-associated kinase-M, apparently under the control of tumor necrosis factor-alpha. This mechanism could explain the induction of interleukin-1 receptor-associated kinase-M in monocytes from patients who suffer from an inflammatory pathology.

Role for TLR2 in NK cell-mediated control of murine cytomegalovirus in vivo

Natural killer (NK) cells are essential for the early control of murine cytomegalovirus (MCMV) infection. Here, we demonstrate that toll-like receptor 2 (TLR2) plays a role in the NK cell-mediated control of MCMV. TLR2 knockout (KO) mice had elevated levels of MCMV in the spleen and liver on day 4 postinfection compared to C57BL/6 mice. In vivo depletion of NK cells with anti-NK1.1 antibodies, however, eliminated the differences in viral titers between the two groups, suggesting that the effect of TLR2 on MCMV clearance on day 4 was NK cell mediated. The defect in early antiviral control was associated with a decreased NK cell population in the spleen and liver and reduced amounts of interleukin-18 and alpha/beta interferon secreted in the TLR2 KO mice. Our studies suggest that in addition to the reported involvement of TLR9 and TLR3, TLR2 is also involved in innate immune responses to MCMV infection.

Postnatal acquisition of endotoxin tolerance in intestinal epithelial cells

The role of innate immune recognition by intestinal epithelial cells (IECs) in vivo is ill-defined. Here, we used highly enriched primary IECs to analyze Toll-like receptor (TLR) signaling and mechanisms that prevent inappropriate stimulation by the colonizing microflora. Although the lipopolysaccharide (LPS) receptor complex TLR4/MD-2 was present in fetal, neonatal, and adult IECs, LPS-induced nuclear factor κB (NF-κB) activation and chemokine (macrophage inflammatory protein 2 [MIP-2]) secretion was only detected in fetal IECs. Fetal intestinal macrophages, in contrast, were constitutively nonresponsive to LPS. Acquisition of LPS resistance was paralleled by a spontaneous activation of IECs shortly after birth as illustrated by phosphorylation of IκB-α and nuclear translocation of NF-κB p65 in situ as well as transcriptional activation of MIP-2. Importantly, the spontaneous IEC activation occurred in vaginally born mice but not in neonates delivered by Caesarean section or in TLR4-deficient mice, which together with local endotoxin measurements identified LPS as stimulatory agent. The postnatal loss of LPS responsiveness of IECs was associated with a posttranscriptional down-regulation of the interleukin 1 receptor–associated kinase 1, which was essential for epithelial TLR4 signaling in vitro. Thus, unlike intestinal macrophages, IECs acquire TLR tolerance immediately after birth by exposure to exogenous endotoxin to facilitate microbial colonization and the development of a stable intestinal host–microbe homeostasis.

A method for the generation of standardized qualitative dynamical systems of regulatory networks

BACKGROUND

Modeling of molecular networks is necessary to understand their dynamical properties. While a wealth of information on molecular connectivity is available, there are still relatively few data regarding the precise stoichiometry and kinetics of the biochemical reactions underlying most molecular networks. This imbalance has limited the development of dynamical models of biological networks to a small number of well-characterized systems. To overcome this problem, we wanted to develop a methodology that would systematically create dynamical models of regulatory networks where the flow of information is known but the biochemical reactions are not. There are already diverse methodologies for modeling regulatory networks, but we aimed to create a method that could be completely standardized, i.e. independent of the network under study, so as to use it systematically.

RESULTS

We developed a set of equations that can be used to translate the graph of any regulatory network into a continuous dynamical system. Furthermore, it is also possible to locate its stable steady states. The method is based on the construction of two dynamical systems for a given network, one discrete and one continuous. The stable steady states of the discrete system can be found analytically, so they are used to locate the stable steady states of the continuous system numerically. To provide an example of the applicability of the method, we used it to model the regulatory network controlling T helper cell differentiation.

CONCLUSION

The proposed equations have a form that permit any regulatory network to be translated into a continuous dynamical system, and also find its steady stable states. We showed that by applying the method to the T helper regulatory network it is possible to find its known states of activation, which correspond the molecular profiles observed in the precursor and effector cell types.

A method for the generation of standardized qualitative dynamical systems of regulatory networks

Background

Modeling of molecular networks is necessary to understand their dynamical properties. While a wealth of information on molecular connectivity is available, there are still relatively few data regarding the precise stoichiometry and kinetics of the biochemical reactions underlying most molecular networks. This imbalance has limited the development of dynamical models of biological networks to a small number of well-characterized systems. To overcome this problem, we wanted to develop a methodology that would systematically create dynamical models of regulatory networks where the flow of information is known but the biochemical reactions are not. There are already diverse methodologies for modeling regulatory networks, but we aimed to create a method that could be completely standardized, i.e. independent of the network under study, so as to use it systematically.

Results

We developed a set of equations that can be used to translate the graph of any regulatory network into a continuous dynamical system. Furthermore, it is also possible to locate its stable steady states. The method is based on the construction of two dynamical systems for a given network, one discrete and one continuous. The stable steady states of the discrete system can be found analytically, so they are used to locate the stable steady states of the continuous system numerically. To provide an example of the applicability of the method, we used it to model the regulatory network controlling T helper cell differentiation.

Conclusion

The proposed equations have a form that permit any regulatory network to be translated into a continuous dynamical system, and also find its steady stable states. We showed that by applying the method to the T helper regulatory network it is possible to find its known states of activation, which correspond the molecular profiles observed in the precursor and effector cell types.

Opposing roles of NF-kappaB family members in the regulation of NK cell proliferation and production of IFN-gamma

It is well established that the nuclear factor-kappaB (NF-kappaB) family of transcription factors participates in the regulation of many aspects of innate and adaptive immunity. The majority of these reports have focused on the role of NF-kappaB in accessory cell and T or B cell function, but less is known about the role of NF-kappaB in NK cells. However, several studies have demonstrated that these transcription factors are required for NK cell production of IFN-gamma and proliferation. The studies presented here examine the role of two NF-kappaB members, c-Rel and p50, in NK cell function. In vitro data revealed that in the absence of c-Rel, NK cells have a defect in their ability to secrete IFN-gamma, but remain unaffected in their capacity to proliferate. In contrast, p50-/- NK cells have enhanced proliferative and IFN-gamma responses compared with wild-type NK cells. The latter findings suggest a role for p50 as a negative regulator of NK cell production of IFN-gamma and chromatin immunoprecipitation assays demonstrated the association of p50 with the IFN-gamma promoter of resting NK cells. Consistent with the in vitro studies, in vivo studies with NF-kappaB gene-deficient mice infected with Toxoplasma gondii revealed that the absence of p50 leads to enhanced NK cell proliferation and production of IFN-gamma. Together, these studies define distinct roles for c-Rel and p50 in the function of NK cells.

MyD88-dependent and -independent murine cytomegalovirus sensing for IFN-alpha release and initiation of immune responses in vivo

Antiviral immunity requires early and late mechanisms in which IFN-alpha and IL-12 play major roles. However, the initial events leading to their production remain largely unclear. Given the crucial role of TLR in innate recognition, we investigated their role in antiviral immunity in vivo. Upon murine CMV (MCMV) infection, both MyD88-/- and TLR9-/- mice were more susceptible and presented increased viral loads compared with C57BL/6, TLR2-/-, TLR3-/-, or TLR4-/- mice. However, in terms of resistance to infection, IFN-alpha production and in many other parameters of early inflammatory responses, the MyD88-/- mice showed a more defective response than TLR9-/- mice. In the absence of the TLR9/MyD88 signaling pathway, cytokine production was dramatically impaired with a complete abolition of bioactive IL-12p70 serum release contrasting with a high flexibility for IFN-alpha release, which is initially (36 h) plasmacytoid dendritic cell- and MyD88-dependent, and subsequently (44 h) PDC-, MyD88-independent and, most likely, TLR-independent. NK cells from MCMV-infected MyD88-/- and TLR9-/- mice displayed a severely impaired IFN-gamma production, yet retained enhanced cytotoxic activity. In addition, dendritic cell activation and critical inflammatory cell trafficking toward the liver were still effective. In the long term, except for isotype switching to MCMV-specific IgG1, the establishment of Ab responses was not significantly altered. Thus, our results demonstrate a critical requirement of TLR9 in the process of MCMV sensing to assure rapid antiviral responses, coordinated with other TLR-dependent and -independent events that are sufficient to establish adaptive immunity.

A network model for the control of the differentiation process in Th cells

T helper cells differentiate from a precursor type, Th0, to either the Th1 or Th2 phenotypes. While a number of molecules are known to participate in this process, it is not completely understood how they regulate each other to ensure differentiation. This article presents the core regulatory network controlling the differentiation of Th cells, reconstructed from published molecular data. This network encompasses 17 nodes, namely IFN-gamma, IL-4, IL-12, IL-18, IFN-beta, IFN-gammaR, IL-4R, IL-12R, IL-18R, IFN-betaR, STAT-1, STAT-6, STAT-4, IRAK, SOCS-1, GATA-3, and T-bet, as well as their cross-regulatory interactions. The reconstructed network was modeled as a discrete dynamical system, and analyzed in terms of its constituent feedback loops. The stable steady states of the Th network model are consistent with the stable molecular patterns of activation observed in wild type and mutant Th0, Th1 and Th2 cells.

IL-18 Induces Monocyte Chemotactic Protein-1 Production in Macrophages through the Phosphatidylinositol 3-Kinase/Akt and MEK/ERK1/2 Pathways

Macrophages are activated during an inflammatory response and produce multiple inflammatory cytokines. IL-18 is one of the most important innate cytokines produced from macrophages in the early stages of the inflammatory immune response. Monocyte chemoattractant protein (MCP-1) is expressed in many inflammatory diseases such as multiple sclerosis and rheumatoid arthritis, and its expression is correlated with the severity of the disease. Both IL-18 and MCP-1 have been shown to be involved in inflammatory immune responses. However, it has been unclear whether IL-18 is involved in the induction of MCP-1. This investigation was initiated to determine whether IL-18 can induce MCP-1 production, and if so, by which signal transduction pathways. We found that IL-18 induced the production of MCP-1 in macrophages, which was IL-12-independent and was not mediated by autocrine cytokines such as IFN-gamma or TNF-alpha. We then examined signal transduction pathways involved in IL-18-induced MCP-1 production. We found that IL-18 did not activate the IkappaB kinase/NF-kappaB pathway, evidenced by no degradation of IkappaBalpha and no translocation of NF-kappaB p65 to the nucleus in IL-18-stimulated macrophages. Instead, IL-18 activated the PI3K/Akt and MEK/ERK1/2 pathways. Inhibition of either of these pathways attenuated MCP-1 production in macrophages, and inhibition of both signaling pathways resulted in the complete inhibition of MCP-1 production. On the basis of these observations, we conclude that IL-18 induces MCP-1 production through the PI3K/Akt and MEK/ERK1/2 pathways in macrophages.

Stage-dependent gene expression profiles during natural killer cell development

Natural killer (NK) cells develop from hematopoietic stem cells (HSCs) in the bone marrow. To understand the molecular regulation of NK cell development, serial analysis of gene expression (SAGE) was applied to HSCs, NK precursor (pNK) cells, and mature NK cells (mNK) cultured without or with OP9 stromal cells. From 170,464 total individual tags from four SAGE libraries, 35,385 unique genes were identified. A set of genes was expressed in a stage-specific manner: 15 genes in HSCs, 30 genes in pNK cells, and 27 genes in mNK cells. Among them, lipoprotein lipase induced NK cell maturation and cytotoxic activity. Identification of genome-wide profiles of gene expression in different stages of NK cell development affords us a fundamental basis for defining the molecular network during NK cell development.

A novel splice variant of interleukin-1 receptor (IL-1R)-associated kinase 1 plays a negative regulatory role in Toll/IL-1R-induced inflammatory signaling

The interleukin-1 (IL-1) receptor-associated kinase 1 (IRAK1) is a member of the IRAK kinase family that plays a pivotal role in the Toll/IL-1 receptor (TIR) family signaling cascade. We have identified a novel splice variant, IRAK1c, which lacks a region encoded by exon 11 of the IRAK1 gene. IRAK1c expression was confirmed by both RNA and protein detection. Although both IRAK1 and IRAK1c are expressed in most tissues tested, IRAK1c is the predominant form of IRAK1 expressed in the brain. Unlike IRAK1, IRAK1c lacks kinase activity and cannot be phosphorylated by IRAK4. However, IRAK1c retains the ability to strongly interact with IRAK2, MyD88, Tollip, and TRAF6. Overexpression of IRAK1c suppressed NF-kappaB activation and blocked IL-1beta-induced IL-6 as well as lipopolysaccharide- and CpG-induced tumor necrosis factor alpha production in multiple cellular systems. Mechanistically, we provide evidence that IRAK1c functions as a dominant negative by failing to be phosphorylated by IRAK4, thus remaining associated with Tollip and blocking NF-kappaB activation. The presence of a regulated, alternative splice variant of IRAK1 that functions as a kinase-dead, dominant-negative protein adds further complexity to the variety of mechanisms that regulate TIR signaling and the subsequent inflammatory response.