IL-1R Family Research Articles

Chronic Pseudomonas aeruginosa Lung Infection Is IL-1R Independent, but Relies on MyD88 Signaling.

Cystic fibrosis is associated with chronic Pseudomonas aeruginosa colonization and inflammation. The role of MyD88, the shared adapter protein of the proinflammatory TLR and IL-1R families, in chronic P. aeruginosa biofilm lung infection is unknown. We report that chronic lung infection with the clinical P. aeruginosa RP73 strain is associated with uncontrolled lung infection in complete MyD88-deficient mice with epithelial damage, inflammation, and rapid death. Then, we investigated whether alveolar or myeloid cells contribute to heightened sensitivity to infection. Using cell-specific, MyD88-deficient mice, we uncover that the MyD88 pathway in myeloid or alveolar epithelial cells is dispensable, suggesting that other cell types may control the high sensitivity of MyD88-deficient mice. By contrast, IL-1R1-deficient mice control chronic P. aeruginosa RP73 infection and IL-1β Ab blockade did not reduce host resistance. Therefore, the IL-1R1/MyD88 pathway is not involved, but other IL-1R or TLR family members need to be investigated. Our data strongly suggest that IL-1 targeted neutralizing therapies used to treat inflammatory diseases in patients unlikely reduce host resistance to chronic P. aeruginosa infection.

Evolutionary conserved sequence patterns that determine functional specialization of metazoan TIR domains

Abstract Toll-Interleukin-1R Resistance (TIR) domains represent a type of protein fold ubiquitously present in all forms of cellular life. The TIR domains are present in functionally and architecturally diverse proteins. A large subgroup of metazoan TIRs is involved in signaling that initiate and regulate the immune response elicited by infection or damaged self. This study applies Bayesian partitioning with pattern selection (BPPS) to classify the TIR domains based on sequence patterns that best distinguish individual groups. The algorithm was applied to >26000 phylogenetically diverse TIR domain sequences selected for non-redundancy from publicly available protein sequence banks. The analysis has revealed 10 metazoan groups, nine of which comprise either orthologous proteins or a protein family. Available structural data suggest that the identified groups may be uniquely characterized by regional backbone fold variants, which can be associated with a corresponding group-specific sequence motif. In addition to these fold-defining motifs, the BPPS also identified groups of surface-exposed residues conserved in TIRAP and MyD88 orthologs, which correspond to predicted sites that mediate the signal-dependent TIR oligomerization. This analysis also has clarified the functional significance of locally conserved sequence motifs, named Box 2 and Box 3, as each of these motifs is a part of a larger block of conserved, intramolecularly interacting residues. Finally, this study has identified the sequence patterns that differentiate TIRs of different classes, such TIRs of TLRs, from TIRs of the IL-1R family, or their adapter proteins, and highlights the differences between metazoan, plant, and bacterial TIRs.

Induction of IκBζ Augments Cytokine and Chemokine Production by IL-33 in Mast Cells.

IκBζ (encoded by the Nfkbiz) is a member of the nuclear IκB family, which is involved in the expression of secondary response genes based on signals from TLR or IL-1R. ST2L, an IL-33R, is a member of the IL-1R family and abundantly expressed in tissue-resident immune cells, such as mast cells and innate lymphoid cells; however, its downstream signaling pathway remains unelucidated. In this study, we examined the role of IκBζ in ST2L-mediated cytokine and chemokine production in mast cells. Murine bone marrow cells were differentiated ex vivo into bone marrow-derived mast cells (BMMCs). The treatment of BMMCs with IL-33 transiently induced robust IκBζ expression. Of the 40 cytokines and chemokines examined using a cytokine and chemokine array, the concentrations of IL-6, IL-13, CCL2, CCL3, and TNF-α in the supernatant were augmented by IL-33. The deletion of IκBζ in BMMCs resulted in a significant reduction of the production of these mediators and the expression of their mRNA. NF-κB p50 but not p65 translocated to the nucleus by IL-33 and was not affected by the deletion of IκBζ. However, induction of IκBζ and the resultant cytokine and chemokine productions were significantly inhibited by pretreatment with an NF-κB inhibitor. The deletion of IκBζ did not affect the phosphorylation of ERK, p38 MAPK, or JNK by IL-33, and the treatment with inhibitors of these mitogen-activated kinases failed to abolish the expression of Nfkbiz Our findings suggest that IκBζ augments IL-33-dependent cytokine and chemokine production in BMMCs through the action of NF-κB.

IL1R8 Deficiency Drives Autoimmunity-Associated Lymphoma Development.

Chronic inflammation, including that driven by autoimmunity, is associated with the development of B-cell lymphomas. IL1R8 is a regulatory receptor belonging to the IL1R family, which negatively regulates NF-κB activation following stimulation of IL1R or Toll-like receptor family members. IL1R8 deficiency is associated with the development of severe autoimmune lupus-like disease in lpr mice. We herein investigated whether concomitant exacerbated inflammation and autoimmunity caused by the deficiency of IL1R8 could recapitulate autoimmunity-associated lymphomagenesis. We thus monitored B-cell lymphoma development during the aging of IL1R8-deficient lpr mice, observing an increased lymphoid cell expansion that evolved to diffuse large B-cell lymphoma (DLBCL). Molecular and gene-expression analyses showed that the NF-κB pathway was constitutively activated in Il1r8 -/-/lpr B splenocytes. In human DLBCL, IL1R8 had reduced expression compared with normal B cells, and higher IL1R8 expression was associated with a better outcome. Thus, IL1R8 silencing is associated with increased lymphoproliferation and transformation in the pathogenesis of B-cell lymphomas associated with autoimmunity.

Phase 1 study of CA-4948, a novel inhibitor of interleukin-1 receptor-associated kinase 4 (IRAK4) in patients (pts) with r/r non-Hodgkin lymphoma.

e19055 Background: IRAK4 is a signaling modulator of Toll-like receptors (TLRs) and members of the IL-1R family. TLR/IL-1R activity is frequently dysregulated in NHL, including DLBCL and Waldenström macroglobulinemia (WM). CA-4948, an oral inhibitor of IRAK4, has demonstrated anti-tumor activity in preclinical models. Methods: Dose finding cohorts (3+3 design) will test QD or BID dosing schedule in pts with R/R NHL. Dose expansion will occur in 2 cohorts of R/R NHL with or without MYD88 mutation at the RP2D or MTD. Key eligibility criteria: age ≥ 18 years, ECOG ≤1, and adequate organ function. Objectives: safety, MTD and RP2D (primary); PK and anti-tumor activity (secondary); exploratory biomarkers and PD effects. Plasma cytokine levels are being evaluated post ex-vivo TLR stimulation in whole blood. Results: 13 pts have been treated (6 at 50 mg QD; 3 at 100 mg QD; 4 at 50 mg BID). Tumor types included DLBCL (7), FL (5), WM (1). The most frequent treatment-emergent AEs (≥10% of pts) were fatigue (23%), conjunctivitis, constipation, neutrophil count decrease, white blood cell count decrease (each 15%). One pt treated at 100 mg QD experienced Gr 3 rash which resolved following oral steroid treatment; dose reduction to 50 mg QD was tolerated without flare up. One SAE of disease progression occurred. 9 pts completed the DLT evaluation period thru Cycle 2 including 2 ongoing in Cycle 4 and 6. Preliminary PK showed that CA-4948 is rapidly absorbed with maximum plasma concentration observed 1.0 to 4.0 hrs post administration. T1/2 in plasma was about 6 hrs. Minimal to no accumulation was observed following multiple doses. Plasma exposures were dose proportional. Preliminary PD data showed, similar to murine studies, on target reduction of NF-kB-associated factors such as IL-6 post-treatment from pts with complete sample sets (N = 8). Conclusions: Current dose/schedule is well tolerated with preliminary PK and PD effects at the initial dose level. MTD has not been reached. Clinical trial information: NCT03328078.

Synthetic human monoclonal antibody targets hIL1 receptor accessory protein chain with therapeutic potential in triple-negative breast cancer

High expression of Interluekin-1 receptor accessory protein chain (IL-1RAcP) and activated IL-1 signaling were found in some tumor types. IL-1RAcP is considered as the common accessory chain in the IL-1R family, and it is essential for the initiation of IL-1 signaling of all the receptor complexes that encompass it. Thus, the selection and characterization of human anti- IL-1RAcP single-chain antibody fragments variable (scFv) is the first step toward the construction of new anticancer monoclonal antibodies designed for optimal cancer therapy. Here, we found that IL-1RAcP expression was increased in both triple-negative breast cancer (TNBC) cell line cells and TNBC patient cohort, and correlated with shorter recurrence-free survival (RFS). In this study, we employed a human scFv–displaying phage library for the first establishment an antagonistic anti–IL-1RAcP human antibody, scFv 12H7. scFv 12H7 was found a high affinity and specificity binder of IL-1RAcP by a series assays, including EC50, IC50,KD values test and cell binding determination by flow cytometry and immunofluorescence. Also, scFv 12H7 was demonstrated bearing growth inhibitory activity of TNBC cells in vitro and in vivo. Mechanisms study showed that IL-1-activated-NF-κB pathway was significantly inhibited in TNBC cells by incubation with scFv 7H12 for 24 h. Crystal structure analysis, mutations introduction, and yeast two-hybrid assay showed that scFv 12H7 interacted with residues in the D1-D2 domain of IL-1RAcP, which further indicated that scFv 12H7 was a functional binding to IL-1RAcP and uncovered its structure mechanism. In conclusion, scFv 12H7 represent excellent therapeutic candidates for further preclinical and clinical development of TNBC therapy.

Crucial role for T cell-intrinsic IL-18R-MyD88 signaling in cognate immune response to intracellular parasite infection.

MyD88 is the main adaptor molecule for TLR and IL-1R family members. Here, we demonstrated that T-cell intrinsic MyD88 signaling is required for proliferation, protection from apoptosis and expression of activation/memory genes during infection with the intracellular parasite Trypanosoma cruzi, as evidenced by transcriptome and cytometry analyses in mixed bone-marrow (BM) chimeras. The lack of direct IL-18R signaling in T cells, but not of IL-1R, phenocopied the absence of the MyD88 pathway, indicating that IL-18R is a critical MyD88-upstream pathway involved in the establishment of the Th1 response against an in vivo infection, a presently controvert subject. Accordingly, Il18r1-/- mice display lower levels of Th1 cells and are highly susceptible to infection, but can be rescued from mortality by the adoptive transfer of WT CD4+ T cells. Our findings establish the T-cell intrinsic IL-18R/MyD88 pathway as a crucial element for induction of cognate Th1 responses against an important human pathogen.

IL1R9 Is Evolutionarily Related to IL18BP and May Function as an IL-18 Receptor.

The IL-1 families of ligands and receptors exhibit similarity of coding sequences, protein structures, and chromosomal positions, suggesting that they have arisen via duplication of ancestral genes. Within these families there is selectivity in ligand-receptor interactions as well as promiscuity. IL-18 and its receptor are members of these families. IL-18 is recognized as binding to the protein products of the IL18R1 and IL18RAP genes, and with high affinity to a separate IL-18 binding protein (IL-18BP). However, IL-18BP is anomalous, as it exhibits little resemblance to IL-18R proteins. Additionally, IL-18 is produced in the brain in medial habenula neurons, which project IL-18-containing axons to the interpeduncular nucleus. However, there is a lack of focal IL-18R expression in their terminal field. Given these anomalies, we hypothesized that another receptor for IL-18 may exist, and that IL18BP is evolutionarily related to this receptor. We examined Ensembl and National Center for Biotechnology Information databases to identify available IL18BP records (n = 86 species) and show through bioinformatics approaches that across mammalian species with IL18BP genes, IL-18BP is consistently most similar to IL-1R9 (IL-1R accessory protein-like 2), another member of the IL-1R family. IL-1R9 and the related IL-1R8, but not other IL-1R family members, exhibit an amino acid sequence similar to binding site A of human and viral IL-18BPs. Conserved intron/exon boundaries, protein structure, and key binding site amino acids suggest that IL18BP and IL1R9 are evolutionarily related, and that IL-1R9 and IL-1R8 may bind IL-18.

MK2/3 Are Pivotal for IL-33–Induced and Mast Cell–Dependent Leukocyte Recruitment and the Resulting Skin Inflammation

The IL-1R family member IL-33R mediates Fcε-receptor-I (FcεRI)-independent activation of mast cells leading to NF-κB activation and consequently the production of cytokines. IL-33 also induces the activation of MAPKs, such as p38. We aimed to define the relevance of the p38-targets, the MAPK-activated protein kinases 2 and 3 (MK2 and MK3) in IL-33-induced signaling and the resulting mast cell effector functions in vitro and in vivo. We demonstrate that the IL-33-induced IL-6 and IL-13 production strongly depends on the MK2/3-mediated activation of ERK1/2 and PI3K signaling. Furthermore, in the presence of the stem cell factors, IL-33 did induce an MK2/3-, ERK1/2- and PI3K-dependent production of TNF-α. In vivo, the loss of MK2/3 in mast cells decreased the IL-33-induced leukocyte recruitment and the resulting skin inflammation. Therefore, the MK2/3-dependent signaling in mast cells is essential to mediate IL-33-induced inflammatory responses. Thus, MK2/3 are potential therapeutic targets for suppression of IL-33-induced inflammation skin diseases such as psoriasis.

Expression and function of IL-1R8 (TIR8/SIGIRR): a regulatory member of the IL-1 receptor family in platelets.

Platelets express functional interleukin-1 receptor-1 (IL-1R1) as well as a repertoire of toll-like receptors (TLRs) involved in platelet activation, platelet-leucocyte reciprocal activation, and immunopathology. IL-1R8, also known as single Ig IL-1-related receptor (SIGIRR) or TIR8, is a member of the IL-1R family that negatively regulates responses to IL-1R family members and TLRs. In the present study, we addressed the expression of IL-1R8 in platelets and megakaryocytes and its role in the control of platelet activation during inflammatory conditions and thromboembolism. Here, we show by flow cytometry analysis, western blot, confocal microscopy, and quantitative real-time polymerase chain reaction that IL-1R8 is expressed on human and mouse platelets at high levels and on megakaryocytes. IL-1R8-deficient mice show normal levels of circulating platelets. Homotypic and heterotypic (platelet-neutrophil) aggregation triggered by Adenosine DiPhosphate (ADP) and IL-1 or lipopolysaccharide (LPS) was increased in IL-1R8-deficient platelets. IL-1R8-deficient mice showed increased soluble P-selectin levels and increased platelet-neutrophil aggregates after systemic LPS administration. Commensal flora depletion and IL-1R1 deficiency abated platelet hyperactivity and the increased platelet/neutrophil aggregation observed in Il1r8(-/-) mice in vitro and in vivo, suggesting a key role of IL-1R8 in regulating platelet TLR and IL-1R1 function. In a mouse model of platelet-dependent pulmonary thromboembolism induced by ADP administration, IL-1R8-deficient mice showed an increased frequency of blood vessel complete obstruction. These results show that platelets, which have a large repertoire of TLRs and IL-1 receptors, express high levels of IL-1R8, which plays a non-redundant function as a regulator of thrombocyte activity in vitro and in vivo.

IL-1R/TLR2 through MyD88 Divergently Modulates Osteoclastogenesis through Regulation of Nuclear Factor of Activated T Cells c1 (NFATc1) and B Lymphocyte-induced Maturation Protein-1 (Blimp1)

Toll-like receptors (TLR) and the receptor for interleukin-1 (IL-1R) signaling play an important role in bacteria-mediated bone loss diseases including periodontitis, rheumatoid arthritis, and osteomyelitis. Recent studies have shown that TLR ligands inhibit the receptor activator of NF-κB ligand (RANKL)-induced osteoclast differentiation from un-committed osteoclast precursors, whereas IL-1 potentiates RANKL-induced osteoclast formation. However, IL-1R and TLR belong to the same IL-1R/TLR superfamily, and activate similar intracellular signaling pathways. Here, we investigate the molecular mechanisms underlying the distinct effects of IL-1 and Porphyromonas gingivalis lipopolysaccharide (LPS-PG) on RANKL-induced osteoclast formation. Our results show that LPS-PG and IL-1 differentially regulate RANKL-induced activation of osteoclast genes encoding Car2, Ctsk, MMP9, and TRAP, as well as expression of NFATc1, a master transcription factor of osteoclastogenesis. Regulation of osteoclast genes and NFATc1 by LPS-PG and IL-1 is dependent on MyD88, an important signaling adaptor for both TLR and IL-1R family members. Furthermore, LPS-PG and IL-1 differentially regulate RANKL-costimulatory receptor OSCAR (osteoclast-associated receptor) expression and Ca(2+) oscillations induced by RANKL. Moreover, LPS-PG completely abrogates RANKL-induced gene expression of B lymphocyte-induced maturation protein-1 (Blimp1), a global transcriptional repressor of anti-osteoclastogenic genes encoding Bcl6, IRF8, and MafB. However, IL-1 enhances RANKL-induced blimp1 gene expression but suppresses the gene expression of bcl6, irf8, and mafb. Our study reveals the involvement of multiple signaling molecules in the differential regulation of RANKL-induced osteoclastogenesis by TLR2 and IL-1 signaling. Understanding the signaling cross-talk among TLR, IL-1R, and RANK is critical for identifying therapeutic strategies to control bacteria-mediated bone loss.

Alarmin' Immunologists: IL-33 as a Putative Target for Modulating T Cell-Dependent Responses.

IL-33 is a known member of the IL-1 cytokine superfamily classically named “atypical” due to its diverse functions. The receptor for this cytokine is the ST2 chain (or IL-1RL1), part of the IL-1R family, and the accessory chain IL-1R. ST2 can be found as both soluble and membrane-bound forms, property that explains, at least in part, its wide range of functions. IL-33 has increasingly gained our attention as a potential target to modulate immune responses. At the beginning, it was known as one of the participants during the development of allergic states and other Th2-mediated responses and it is now accepted that IL-33 contributes to Th1-driven pathologies as demonstrated in animal models of experimental autoimmune encephalomyelitis (EAE), collagen-induced arthritis, and trinitrobenzene sulfonic acid-induced experimental colitis, among others. Interestingly, current data are placing IL-33 as a novel regulator of immune tolerance by affecting regulatory T cells (Tregs); although the mechanism is not fully understood, it seems that dendritic cells and myeloid suppressor-derived cells may be cooperating in the generation and/or establishment of IL-33-mediated tolerance. Here, we review the most updated literature on IL-33, its role on T cell biology, and its impact in immune tolerance.

The potential role of IL-33/ST2 signaling in fibrotic diseases.

IL-33, a new member of the IL-1F, is widely expressed throughout the body and can be up-regulated by stimulation with proinflammatory factors. It has been identified as a functional ligand for the plasma membrane receptor complex that is a heterodimer consisting of membrane-bound ST2L, which is a member of the IL-1R family, and IL-1RAcP. IL-33 is crucial for the induction of Th2 immune responses. Additionally, under other circumstances, it can also act as an endogenous danger signal. Recently, many studies have demonstrated that IL-33 may be related to the development and progression of fibrotic diseases. It has proinflammatory effects in some fibrotic diseases but has anti-inflammatory effects in others. In this review, the biologic characteristics of IL-33 and the role of the IL-33/ST2 signaling pathway in various fibrotic diseases will be discussed. We hope this overview will provide new insights for the treatment of these diseases.

The structural basis for receptor recognition of human interleukin-18.

Interleukin (IL)-18 is a proinflammatory cytokine that belongs to the IL-1 family and plays an important role in inflammation. The uncontrolled release of this cytokine is associated with severe chronic inflammatory disease. IL-18 forms a signalling complex with the IL-18 receptor α (Rα) and β (Rβ) chains at the plasma membrane, which induces multiple inflammatory cytokines. Here, we present a crystal structure of human IL-18 bound to the two receptor extracellular domains. Generally, the receptors’ recognition mode for IL-18 is similar to IL-1β; however, certain notable differences were observed. The architecture of the IL-18 receptor second domain (D2) is unique among the other IL-1R family members, which presumably distinguishes them from the IL-1 receptors that exhibit a more promiscuous ligand recognition mode. The structures and associated biochemical and cellular data should aid in developing novel drugs to neutralize IL-18 activity.

The decreased frequency of SIGIRR-positive CD4+ T cells in peripheral blood of patients with SLE and its correlation with disease activity.

Recently, many studies have shown that Single immunoglobulin interleukin-1 receptor related protein (SIGIRR), a member of the IL-1R family acting as a negative regulator of TLR/IL-1R signaling, affects autoimmune responses in animal model of systemic lupus erythematosus (SLE). However, the role of SIGIRR in the pathogenesis of human SLE has not been widely explored. In this study, we analyzed the frequency of SIGIRR-positive CD4+ T cells in peripheral blood mononuclear cells (PBMCs) of SLE patients and its correlation with disease activity as well as the clinical data. Circulating SIGIRR-positive CD4+ T cells were quantified in 51 SLE patients and 38 healthy controls by using flow cytometer. Results showed that the percentages of SIGIRR-positive CD4+ T cells were decreased in the PBMCs of SLE patients compared with healthy controls (Z = -5.49, P < 0.001). The frequency of SIGIRR-positive CD4 + T cells were also significantly decreased in SLE patients with nephritis than those without nephritis (Z = -3.71, P < 0.001). In addition, there was significant correlation between the percentages of SIGIRR-positive CD4+ T cells and SLEDAI score (r s = -0.74, P < 0.001), 24-hour urine protein (r s = -0.62, P < 0.001), Scr (r s = -0.65, P < 0.001), ESR (r s = -0.60, P < 0.001), C3 (r s = 0.53, P < 0.001) as well as C4 (r s = 0.52, P < 0.001). However, there was no correlation between the proportion of SIGIRR-positive CD4+ T cells and glucocorticoid dose (P = 0.59). In summary, decreased numbers of SIGIRR-positive CD4+ T cells in SLE patients and its correlation with SLEDAI score as well as the clinical data suggest that SIGIRR may be involved in the pathogenesis of SLE.

187: Interleukin 37 employs the IL-1 family inhibitory receptor SIGIRR and the alpha chain of the IL-18 receptor to suppress innate immunity

IL-1 family member IL-37 inhibits a broad spectrum of inflammatory assaults in cell lines and primary PBMC; in vivo, mice transgenic for IL-37 (IL-37tg) exhibit markedly reduced manifestations of LPS-induced shock, DSS colitis, antigen-specific immune responses and ischemia–reperfusion injury. Although previous studies reported that recombinant IL-37 associates with the IL-18 receptor alpha chain (IL-18Rα), no biological activity was observed. Here, we reveal a functional role of IL-18Rα for the anti-inflammatory properties of IL-37. We also identify that the inhibitory IL-1R family member, SIGIRR, associates with IL-37 and is required by IL-37tg mice for protection from LPS-induced shock. In IL-37-transfected THP-1 macrophages, we observed an 83% reduction in IL-1β, but only a 34% reduction when endogenous SIGIRR was silenced. A similar attenuation of the anti-inflammatory effects was demonstrated in LPS-stimulated human PBMC and by silencing of IL-18Rα. By immunofluorescence, we observed that IL-37 associates with SIGIRR and IL-18Rα in LPS-stimulated RAW macrophages and in IL-1β-treated A549 cells, both transfected with IL-37. Using proximity ligation assays and FRET in PBMC, thus exploring interactions of the naturally occurring pairs IL-37-SIGIRR, IL-37-IL-18Rα and SIGIRR-IL-18Rα, we demonstrated sub-40 nm co-localization of each complex. The interactions were hardly detectable at steady-state, reached maximal association 15 min after LPS stimulation, and decreased to background by 6 h. We next generated a strain of SIGIRR-KO mice that are also transgenic for IL-37 (IL-37tg-SIGIRR-KO). As expected, the systemic response to LPS was markedly reduced in IL-37tg mice; however, there was no reduction in IL-37tg-SIGIRR-KO mice. For example, LPS induced severe hypothermia (trough at 25 °C) and acidosis (pH 7.16) in wild-type mice; however, disease severity was markedly ameliorated in IL-37tg mice (29 °C, pH 7.32). In IL-37tg-SIGIRR-KO mice, this protection was considerably weaker. We conclude that IL-37 limits the severity of inflammation by exploiting the inhibitory properties of SIGIRR and by associating with IL-18Rα.

Interleukin 37 employs the IL-1 family orphan receptor SIGIRR and the alpha chain of the IL-18 receptor to inhibit innate immunity (P6293)

Abstract IL-37 is a powerful anti-inflammatory IL-1 family member with activity against a broad spectrum of inflammatory assaults. One mechanism by which this beneficial effect is mediated is via intracellular association with Smad3; however, the cell surface receptor for IL-37 remains unknown. Here, we show that to block inflammation, IL-37 requires IL-18Rα and SIGIRR, a so-far orphaned member of the IL-1R family. In PBMC, which naturally express IL-37, knockdown of SIGIRR increased IL-1β and IL-6 threefold. Silencing of SIGIRR in THP-1 cells significantly attenuated the anti-inflammation of IL-37 (83% less IL-1β with IL-37 and SIGIRR, only 34% less without SIGIRR). Similar effects were observed when IL-18Rα was depleted. To study SIGIRR’s contribution to IL-37 function in vivo, we created a strain of SIGIRR-/- mice that express IL-37. The protective effect imparted by IL-37 was markedly reduced in these crossbred mice when they (and wild-type, IL-37-transgenic and SIGIRR-/- animals) were injected with LPS. Using proximity ligation assays and FRET in PBMC, thus exploring interactions of the naturally occurring pairs IL-37-SIGIRR, IL-37-IL-18Rα and SIGIRR-IL-18Rα, we showed sub-40nm colocalization of each complex. The association peaked 30min after LPS stimulation and decreased to background by 4h. Thus, IL-37 limits inflammation by employing the properties of SIGIRR and by associating with IL-18Rα, suggesting that SIGIRR-IL-18Rα functions as the cell surface receptor for IL-37.

BCAP, a TLR/IL1R signaling adapter, intrinsically regulates differentiation of T helper cells (P1159)

Abstract T helper cells utilize IL18 and IL1 signals provided by myeloid cells to achieve optimal Th1 and Th17 effector capacities. The IL1 and IL18 receptors belong to a family of receptors including Toll-like receptors (TLRs). The TLR/IL1R family share signaling components and (with the exception of TLR3) depend on the adapter MyD88 for engagement of downstream pathways. Signals from the receptor to the adapter are transmitted through homotypic interaction of TIR (Toll-Interleukin-1 receptor) homology domains found in all TLR/IL1R family members and their adapters. We have previously shown that BCAP (B-cell adapter for PI3K) contains a functional TIR domain enabling its participation in the TLR signaling pathway. Importantly, BCAP plays an obligate role in linking TLRs to activation of phosphoinositide 3-kinase (PI3K). Because the TLR/IL1R family share signaling components, we hypothesized that BCAP may regulate T cell differentiation through IL1R family signaling. Indeed, we found that BCAP intrinsically regulated differentiation of naïve T cells towards Th1 and Th17 effector lineages by participation in the IL1R family signaling pathways. Further, BCAP intrinsically regulated T cell proliferation and survival. Our continued efforts will further explore the molecular and transcriptional mechanisms by which BCAP regulates T cell activation. Significantly, this work will increase the understanding of key signaling pathways involved in disease and inflammation.

The GOLD Domain-containing Protein TMED1 Is Involved in Interleukin-33 Signaling*

The proinflammatory danger signal IL-33, which is released from damaged or dying cells, achieves its effects via the IL-1R family member ST2L. The detection of IL-33 by ST2L initiates downstream signaling pathways that result in the activation of MAPKs and NF-κB. Here, we show that TMED1 associates with ST2L. Using a series of mutation and deletion constructs, we demonstrate that this interaction is mediated by the GOLD domain of TMED1 and the TIR domain of ST2L. Our findings also demonstrate that TMED1 is required for optimal IL-33-induced IL-8 and IL-6 production. This discovery provides additional support to the concept that the TMED family members are important players in innate immune signaling.

Ligands and Receptors of the Interleukin-1 Family in Immunity and Disease

Ligands and Receptors of the Interleukin-1 Family in Immunity and Disease