Interleukin (IL)-1 was first cloned in the 1980s, and rapidly emerged as a key player in the regulation of inflammatory processes. The term IL-1 refers to two cytokines, IL-1alpha and IL-1beta, which are encoded by two separate genes. The effects of IL-1 are tightly controlled by several naturally occurring inhibitors, such as IL-1 receptor antagonist (IL-1Ra), IL-1 receptor type II (IL-1RII), and other soluble receptors. Numerous IL-1 inhibitors have been developed and tested primarily in rheumatoid arthritis, with only modest effects. By contrast, the use of IL-1 antagonists has been uniformly associated with beneficial effects in patients with hereditary autoinflammatory conditions associated with excessive IL-1 signaling, such as cryopyrinopathies and IL-1Ra deficiency. Successful treatment with IL-1 blockers has also been reported in other hereditary autoinflammatory diseases, as well as in nonhereditary inflammatory diseases, such as Schnizler syndrome, systemic-onset juvenile idiopathic arthritis and adult Still disease. The role of microcrystals in the regulation of IL-1beta processing and release has provided the rationale for the use of IL-1 inhibitors in crystal-induced arthritis. Finally, preliminary results indicating that IL-1 targeting is efficacious in type 2 diabetes and smoldering myeloma have further broadened the spectrum of IL-1-driven diseases.

IL-36␣ (IL-1F6), IL-36␤ (IL-1F8

Objective. Interleukin-33 (IL-33; or, IL-1F11) was recently identified as the ligand of the IL-1 family receptor T1/ST2. The aim of this study was to examine IL-33 production in human and mouse joints and to investigate the role of IL-33 and T1/ST2 in experimental arthritis.Methods. IL-33 expression was examined in human synovial tissue, rheumatoid arthritis (RA) synovial fibroblasts, and arthritic mouse joints. Mice with collagen-induced arthritis (CIA) were treated with blocking anti-ST2 antibody or control antibody beginning at the onset of disease. Arthritis severity was assessed by clinical and histologic scoring. Draining lymph node (LN) cell responses were examined ex vivo, and joint messenger RNA (mRNA) was used for expression profiling.Results. IL-33 was highly expressed in human RA synovium. In cultured synovial fibroblasts, IL-33 expression was strongly induced by IL-1␤ and/or tumor necrosis factor ␣. Furthermore, IL-33 mRNA was detected in the joints of mice with CIA and increased during the early phase of the disease. Administration of a blocking anti-ST2 antibody at the onset of disease attenuated the severity of CIA and reduced joint destruction. Anti-ST2 antibody treatment was associated with a marked decrease in interferon-␥ production as well as with a more limited reduction in IL-17 production by ex vivo-stimulated draining LN cells. Finally, RANKL mRNA levels in the joint were reduced by anti-ST2 treatment.Conclusion. IL-33 is produced locally in inflamed joints, and neutralization of IL-33 signaling has a therapeutic effect on the course of arthritis. These observations suggest that locally produced IL-33 may contribute to the pathogenesis of joint inflammation and destruction.Interleukin-33 (IL-33; or, IL-1F11) was recently identified as a ligand for the orphan IL-1 family receptor T1/ST2. IL-33 is produced as a 30-kd propeptide and, like IL-1␤ and IL-18, is cleaved by caspase 1 to generate mature 18-kd IL-33, at least in vitro (1). Mature IL-33 has been reported to mediate its biologic effects via T1/ST2 binding by activating NF-B and MAP kinases (1). T1/ST2-dependent IL-33 responses resemble classic IL-1-like signaling, and several recent studies identified the IL-1 receptor accessory protein as the coreceptor involved in IL-33 signaling (2-4).A number of studies have established T1/ST2 (also referred to as ST2L) as a selective marker of both murine and human Th2 lymphocytes (for review, see ref.5). In addition, T1/ST2 is highly expressed on mast cells (6). Several recent reports describe a stimulatory effect of IL-33 on cytokine and chemokine secretion in mast cells (3,(7)(8)(9)(10), suggesting that, in addition to promoting Th2 responses, IL-33 exhibits proinflammatory potential by inducing the production of a number of inflammatory mediators in mast cells. T1/ST2 also exists as a soluble isoform (sST2) obtained by differential messenger RNA (mRNA) processing. Soluble ST2 is identical with the extracellular region of the long T1/ST2 isoform except

ObjectivesRheumatoid arthritis (RA) has been associated with a relative expansion of faecal Prevotellaceae. To determine the microbiome composition and prevalence of Prevotella spp. in a group of individuals at increased risk for RA, but prior to the development of the disease.MethodsIn an ongoing cohort study of first-degree relatives (FDRs) of patients with RA, we identified ‘FDR controls’, asymptomatic and without autoantibodies, and individuals in pre-clinical RA stages, who had either developed anticitrullinated peptide antibodies or rheumatoid factor positivity and/or symptoms and signs associated with possible RA. Stool sampling and culture-independent microbiota analyses were performed followed by descriptive statistics and statistical analyses of community structures.ResultsA total of 133 participants were included, of which 50 were categorised as ‘FDR controls’ and 83 in ‘pre-clinical RA stages’. The microbiota of individuals in ‘pre-clinical RA stages’ was significantly altered compared with FDR controls. We found a significant enrichment of the bacterial family Prevotellaceae, particularly Prevotella spp., in the ‘pre-clinical RA’ group (p=0.04).Conclusions Prevotella spp. enrichment in individuals in pre-clinical stages of RA, before the onset of RA, suggests a role of intestinal dysbiosis in the development of RA.

The new interleukin (IL)-1 family cytokine IL-33 is synthesized as a 30-kDa precursor. Like pro-IL-1␤, human pro-IL-33 was reported to be cleaved by caspase-1 to generate an 18-kDa fragment, which is sufficient to activate signaling by the IL-33 receptor T1/ST2. However, the proposed caspase-1 cleavage site is poorly conserved between species. In addition, it is not clear whether caspase-1 cleavage of pro-IL-33 occurs in vivo and whether, as for IL-1␤, this cleavage is a prerequisite for IL-33 secretion and bioactivity. In this study, we further investigated caspase-1 cleavage of mouse and human pro-IL-33 and assessed the potential bioactivity of the IL-33 precursor. We observed the generation of a 20-kDa IL-33 fragment in cell lysates, which was enhanced by incubation with caspase-1. However, in vitro assays of mouse and human pro-IL-33 indicated that IL-33 is not a direct substrate for this enzyme. Consistently, caspase-1 activation in THP-1 cells induced cleavage of pro-IL-1␤ but not of pro-IL-33, and activated THP-1 cells released full-length pro-IL-33 into culture supernatants. Finally, addition of full-length pro-IL-33 induced T1/ST2-dependent IL-6 secretion in mast cells. However, we observed in situ processing of pro-IL-33 in mast cell cultures, and it remains to be determined whether fulllength pro-IL-33 itself indeed represents the bioactive species. In conclusion, our data indicate that pro-IL-33 is not a direct substrate for caspase-1. In addition, our results clearly show that caspase-1 cleavage is not required for pro-IL-33 secretion and bioactivity, highlighting major differences between IL-1␤ and IL-33.

IntroductionThe interleukin-1 (IL-1) family of cytokines comprises 11 members, including IL-1␣, IL-1␤, IL-18, IL-33, and the recently renamed IL-36␣, ␤, ␥ (previously known as IL-1F6, IL-1F8, and IL-1F9). 1 All these cytokines use heterodimeric receptors for signaling. IL-1, IL-33, and IL-36 bind to specific receptor ␣-chains, which are IL-1RI for IL-1␣ and IL-1␤, T1/ST2 (also known as IL-33R) for IL-33, and IL-36R (previously termed IL-1Rrp2) for IL-36, and then recruit the same coreceptor IL-1R accessory protein (IL-1RAcP). IL-18 uses IL-18R␣ and the coreceptor IL-18R␤. On receptor binding, all IL-1 family cytokines activate similar intracellular signals, including NF-B and mitogenactivated protein kinase (MAPK) pathways. IL-1 receptor antagonist (IL-1Ra) and IL-36Ra (previously termed IL-1F5), 2 additional members of the IL-1 family, act as natural inhibitors for the biologic activities of IL-1 and IL-36, respectively. [2][3][4] IL-1␣, IL-1␤, IL-18, and IL-33 are produced by activated innate immune cells (neutrophils, monocytes, macrophages, and dendritic cells) and epithelial cells, and stimulate proinflammatory innate and adaptive immune responses. More specifically, these cytokines influence CD4 ϩ T-cell responses and their polarization into the different T helper (Th) subsets Th1, Th2, and Th17. IL-1 promotes the proliferation and survival of naive CD4 ϩ T cells and plays a critical role in Th17 differentiation. 5-9 IL-18 and IL-33 stimulate the polarization of CD4 ϩ T cells into Th1 and Th2, respectively,10 although the selectivity of these responses may be modulated by the cytokine environment. Consistently, Th1, Th2, and Th17 cells selectively express the IL-1 family cytokine receptors IL-18R␣, T1/ST2, and IL-1RI, respectively. 10 IL-36 cytokines and IL-36R are abundantly expressed by keratinocytes and other epithelial cell types. 4,[11][12][13] IL-36 plays a major role in mouse experimental skin inflammation and in human psoriasis both in the initiation and regulation of inflammatory responses. [14][15][16][17][18][19] Furthermore, the association of a form of generalized pustular psoriasis with genetic IL-36Ra deficiency in humans argues in favor of a significant role of IL-36 in inflammatory skin diseases. 20,21 Recently, we have shown that dendritic cells (DCs) express IL-36R and that IL-36 stimulates the production of several cytokines and enhances the expression of costimulatory molecules in bone marrow-derived DCs (BMDCs). The stimulatory effects of IL-36 were more robust than those of the other members of the IL-1 family. In addition, IL-36 stimulated the production of interferon ␥ (IFN-␥), IL-4, and to a lesser extent IL-17 by cultured splenocytes and activated CD4 ϩ T cells, and IL-36 was able to act as an adjuvant to stimulate Th1 responses in vivo. 22 In the results described herein we show that, among CD4 ϩ T-cell subsets, IL-36R is predominantly expressed by naive CD4 ϩ T (referred to also as naive Th) cells and that IL-36 stimulates activated naive CD4 ϩ T (referred to also as Th0) cell ...

The proinflammatory activities of IL-1 are tightly controlled at different levels. IL-1R2 acts as a decoy receptor and has been shown to regulate the biological effects of IL-1 in vitro and in vivo. However, little is known about its natural expression in the mouse in physiologic and pathologic conditions. In this study, we examined IL-1R2 mRNA and protein expression in isolated cells and tissues in response to different stimulatory conditions. Data obtained using ex vivo CD11b(+)Ly6G(+) peripheral blood cells and in vitro-differentiated CD11b(+)Ly6G(+) BMG indicated that neutrophils are the major source of constitutively expressed IL-1R2 in the mouse. The expression of IL-1R2 on BMG and ex vivo Ly6G(+) peripheral blood cells was highly up-regulated by HC. IL-1R2 pull-down experiments showed that mouse rIL-1β binds to BMG IL-1R2, whereas binding of IL-1Ra could not be detected. Furthermore, LPS treatment induced shedding of IL-1R2 from the neutrophil membrane in vitro and in vivo, executed mainly by ADAM17. Finally, in in vivo models of inflammation, including thioglycolate-induced acute peritonitis and acute lung injury, infiltrating Ly6G(+) neutrophils, expressed IL-1R2. Our data show that in the mouse, neutrophils mainly express the decoy receptor IL-1R2 under naïve and inflammatory conditions. These data suggest that neutrophils may contribute to the resolution of acute inflammation.

GenBank entries for mouse Il33 reveal the existence of two transcripts, Il33a and Il33b, with different 5'UTRs but coding for the same protein. We investigated expression of these transcripts in different mouse organs and cell types in basal and inflammatory conditions. Il33a and Il33b mRNAs start with different noncoding first exons, transcribed from different promoter regions, which both contain a consensus TATA-like sequence. Constitutive Il33a mRNA expression was detected in mouse stomach, lung, spleen, and brain, whereas basal Il33b mRNA expression was observed only in the stomach. Expression of both transcripts increased after systemic LPS administration. In vitro, we observed high constitutive expression of Il33 transcripts in MEFs. Constitutive Il33a mRNA expression was observed also in BMDCs, where it was preferentially increased in response to poly(I:C), whereas LPS increased levels of Il33a and Il33b mRNA. In contrast, BMMs and Raw 264.7 cells did not express Il33 mRNA constitutively, and LPS stimulation selectively induced expression of Il33b mRNA in these cells. Our data indicate that the Il33 gene is expressed from two alternative promoters in the mouse and that the relative expression of Il33a and Il33b transcripts is cell type- and stimulus-dependent.