Darren L. Asquith

IL-33 reduces the development of atherosclerosis

Atherosclerosis is a chronic inflammatory disease of the vasculature commonly leading to myocardial infarction and stroke. We show that IL-33, which is a novel IL-1–like cytokine that signals via ST2, can reduce atherosclerosis development in ApoE−/− mice on a high-fat diet. IL-33 and ST2 are present in the normal and atherosclerotic vasculature of mice and humans. Although control PBS-treated mice developed severe and inflamed atherosclerotic plaques in the aortic sinus, lesion development was profoundly reduced in IL-33–treated animals. IL-33 also markedly increased levels of IL-4, -5, and -13, but decreased levels of IFNγ in serum and lymph node cells. IL-33 treatment also elevated levels of total serum IgA, IgE, and IgG1, but decreased IgG2a, which is consistent with a Th1-to-Th2 switch. IL-33–treated mice also produced significantly elevated antioxidized low-density lipoprotein (ox-LDL) antibodies. Conversely, mice treated with soluble ST2, a decoy receptor that neutralizes IL-33, developed significantly larger atherosclerotic plaques in the aortic sinus of the ApoE−/− mice compared with control IgG-treated mice. Furthermore, coadministration of an anti–IL-5 mAb with IL-33 prevented the reduction in plaque size and reduced the amount of ox-LDL antibodies induced by IL-33. In conclusion, IL-33 may play a protective role in the development of atherosclerosis via the induction of IL-5 and ox-LDL antibodies.

Cutting Edge: Mast Cells Express IL-17A in Rheumatoid Arthritis Synovium

The proinflammatory cytokine IL-17A is considered a crucial player in rheumatoid arthritis (RA) pathogenesis. In experimental models of autoimmune arthritis, it has been suggested that the cellular source of IL-17A is CD4+ T cells (Th17 cells). However, little is known about the source of IL-17 in human inflamed RA tissue. We explored the cellular sources of IL-17A in human RA synovium. Surprisingly, only a small proportion of IL-17–expressing cells were T cells, and these were CCR6 negative. Unexpectedly, the majority of IL-17A expression colocalized within mast cells. Furthermore, we demonstrated in vitro that mast cells produced RORC-dependent IL-17A upon stimulation with TNF-α, IgG complexes, C5a, and LPS. These data are consistent with a crucial role for IL-17A in RA pathogenesis but suggest that in addition to T cells innate immune pathways particularly mediated via mast cells may be an important component of the effector IL-17A response.

MicroRNA-155 as a proinflammatory regulator in clinical and experimental arthritis

MicroRNA (miRNA) species (miR) regulate mRNA translation and are implicated as mediators of disease pathology via coordinated regulation of molecular effector pathways. Unraveling miR disease-related activities will facilitate future therapeutic interventions. miR-155 recently has been identified with critical immune regulatory functions. Although detected in articular tissues, the functional role of miR-155 in inflammatory arthritis has not been defined. We report here that miR-155 is up-regulated in synovial membrane and synovial fluid (SF) macrophages from patients with rheumatoid arthritis (RA). The increased expression of miR-155 in SF CD14+ cells was associated with lower expression of the miR-155 target, Src homology 2-containing inositol phosphatase-1 (SHIP-1), an inhibitor of inflammation. Similarly, SHIP-1 expression was decreased in CD68+ cells in the synovial lining layer in RA patients as compared with osteoarthritis patients. Overexpression of miR-155 in PB CD14+ cells led to down-regulation of SHIP-1 and an increase in the production of proinflammatory cytokines. Conversely, inhibition of miR-155 in RA synovial CD14+ cells reduced TNF-α production. Finally, miR-155–deficient mice are resistant to collagen-induced arthritis, with profound suppression of antigen-specific Th17 cell and autoantibody responses and markedly reduced articular inflammation. Our data therefore identify a role of miR-155 in clinical and experimental arthritis and suggest that miR-155 may be an intriguing therapeutic target.

Animal models of rheumatoid arthritis

Animal models have been used extensively in studies of rheumatoid arthritis pathogenesis. Despite the inherent limitations of all animal models, several rodent models have significantly progressed our understanding of the fundamental mechanisms underpinning rheumatoid arthritis and contributed to several current major advances in treatment. These models include the induced arthritis models such as collagen‐induced arthritis, collagen‐antibody‐induced arthritis, zymosan‐induced arthritis, and the methylated BSA model, and the genetically manipulated or spontaneous arthritis models such as the TNF‐α‐transgenic mouse, K/BxN mouse, and the Skg mouse. Here, we describe these animal models and discuss their advantages and limitations.

Interleukin-33 Induces Protective Effects in Adipose Tissue Inflammation During Obesity in Mice

Rationale: Chronic low-grade inflammation involving adipose tissue likely contributes to the metabolic consequences of obesity. The cytokine interleukin (IL)-33 and its receptor ST2 are expressed in adipose tissue, but their role in adipose tissue inflammation during obesity is unclear. Objective: To examine the functional role of IL-33 in adipose tissues and investigate the effects on adipose tissue inflammation and obesity in vivo. Methods and Results: We demonstrate that treatment of adipose tissue cultures in vitro with IL-33 induced production of Th2 cytokines (IL-5, IL-13, IL-10) and reduced expression of adipogenic and metabolic genes. Administration of recombinant IL-33 to genetically obese diabetic (ob/ob) mice led to reduced adiposity, reduced fasting glucose and improved glucose and insulin tolerance. IL-33 also induced accumulation of Th2 cells in adipose tissue and polarization of adipose tissue macrophages toward an M2 alternatively activated phenotype (CD206+), a lineage associated with protection against obesity-related metabolic events. Furthermore, mice lacking endogenous ST2 fed high-fat diet had increased body weight and fat mass and impaired insulin secretion and glucose regulation compared to WT controls fed high-fat diet. Conclusions: In conclusion, IL-33 may play a protective role in the development of adipose tissue inflammation during obesity.

IL-33 induces skin inflammation with mast cell and neutrophil activation

Psoriasis is a common chronic autoimmune condition of the skin characterized by hyperplasia of epidermal keratinocytes associated with pro‐inflammatory cytokines. IL‐33 is a new member of the IL‐1 superfamily that signals through the ST2 receptor and was originally defined as an inducer of T helper 2 (Th2) cytokines. Recently, broader immune activatory potential has been defined for IL‐33 particularly via mast cell activation and neutrophil migration. Here, we show that ST2−/− mice exhibit reduced cutaneous inflammatory responses compared with WT mice in a phorbol ester‐induced model of skin inflammation. Furthermore, injections of IL‐33 into the ears of mice induce an inflammatory skin lesion. This inflammatory response was partially dependent on mast cells as mast cell‐deficient mice (KitW‐sh/W‐sh) showed delayed responses to IL‐33. IL‐33 also recruited neutrophils to the ear, an effect mediated in part by increased production of the chemokine KC (CXCL1). Finally, we show that IL‐33 expression is up‐regulated in the epidermis of clinical psoriatic lesions, compared with healthy skin. These results therefore demonstrate that IL‐33 may play a role in psoriasis‐like plaque inflammation. IL‐33 targeting may provide a new treatment strategy for psoriasis.

Emerging cytokine targets in rheumatoid arthritis.

Purpose of reviewThe utility of cytokines as therapeutic targets in rheumatoid arthritis has been unequivocally demonstrated by the success of tumour necrosis factor blockade in clinical practice. Partial and non-responses to tumour necrosis factor blocking agents, however, together with the increasing clinical drive to remission induction, requires that further therapeutic targets be identified. Recent findingsNumerous cytokine activities with pathogenetic potential have now been demonstrated in rheumatoid arthritis synovial membrane, including members of the IL-1 superfamily and the IL-12 superfamily. Continued efforts are ongoing to target IL-6 and IL-15 in clinical trials with promising data emerging. There is particular interest in the biology of IL-17 and of the recently described IL-32 as critical effector mediators. SummaryNovel cytokine activities are emerging on an ongoing basis. There remain difficulties in ascribing the optimal regulatory hierarchy for given moieties on the basis of existing preclinical model systems. This in turn poses novel challenges in determining which cytokines represent the best therapeutic targets.

Liver X receptor agonism promotes articular inflammation in murine collagen‐induced arthritis

OBJECTIVE Liver X receptors (LXRs) have previously been implicated in the regulation of inflammation and have, in general, been ascribed an antiinflammatory role. This study was therefore undertaken to explore the biologic mechanisms of LXRs in vivo and in vitro in an experimental inflammatory arthritis model. METHODS Male DBA/1 mice were immunized with type II collagen and treated from an early or established stage of arthritis with 2 different concentrations of the LXR agonists T1317 and GW3965 or vehicle control. The mice were monitored for articular inflammation and cartilage degradation by scoring for clinical signs of arthritis, histologic examination of the joints, and analysis of serum cytokine and antibody levels. In vitro, primary human monocytes and T cells were cultured in the presence of GW3965 or T1317, and the concentrations of proinflammatory cytokines were measured by multiplex assay. RESULTS Contrary to expectations, LXR agonism with the use of 2 discrete, specific molecular entities led to substantial exacerbation of articular inflammation and cartilage destruction in this murine collagen-induced arthritis model. This was associated ex vivo with elevated cytokine expression, with enhanced Th1 and Th17 cellular responses, and with elevated collagen-specific autoantibody production. In vitro, LXR agonists, in concert with lipopolysaccharide, promoted cytokine and chemokine release from human monocytes, and similar effects were observed in a T cell-macrophage coculture model that closely recapitulates the pathways that drive synovial cytokine release. CONCLUSION Since LXRs are present in rheumatoid arthritis (RA) synovium, these results suggest that LXR-mediated pathways could exacerbate the chronic inflammatory response typical of RA.

CCX-CKR deficiency alters thymic stroma impairing thymocyte development and promoting autoimmunity

The atypical chemokine receptor CCX-CKR regulates bioavailability of CCL19, CCL21, and CCL25, homeostatic chemokines that play crucial roles in thymic lymphopoiesis. Deletion of CCX-CKR results in accelerated experimental autoimmunity induced by immunization. Here we show that CCX-CKR deletion also increases incidence of a spontaneous Sjögrens syndrome-like pathology, characterized by lymphocytic infiltrates in salivary glands and liver of CCX-CKR(-/-) mice, suggestive of a defect in self-tolerance when CCX-CKR is deleted. This prompted detailed examination of the thymus in CCX-CKR(-/-) mice. Negatively selected mature SP cells were less abundant in CCX-CKR(-/-) thymi, yet expansion of both DP and immature SP cells was apparent. Deletion of CCX-CKR also profoundly reduced proportions of DN3 thymocyte precursors and caused DN2 cells to accumulate within the medulla. These effects are likely driven by alterations in thymic stroma as CCX-CKR(-/-) mice have fewer cTECs per thymocyte, and cTECs express the highest level of CCX-CKR in the thymus. A profound decrease in CCL25 within the thymic cortex was observed in CCX-CKR(-/-) thymi, likely accounting for their defects in thymocyte distribution and frequency. These findings identify a novel role for CCX-CKR in regulating cTEC biology, which promotes optimal thymocyte development and selection important for self-tolerant adaptive immunity.

Collagen-induced arthritis is not impaired in mast cell-deficient mice

Mast cells are recognised as important effectors in allergic disease. However, it is increasingly clear that mast cells may fulfil more diverse roles within the immune system and may be pathogenic in a number of diseases not typically associated with T-helper type 2 immune responses.1 Indeed, studies have described the presence of degranulated mast cells within inflamed rheumatoid arthritis (RA) synovium and as such implicate mast cells as potential mediators in the pathogenesis of RA.2 Consistent with these observations, the severity of arthritis, induced by antibody transfer, is reduced in mast cell-deficient strains of mice, W/Wv and Sl/Sld, and can be restored by adoptive transfer of mast cells.3 4 Murine collagen-induced arthritis is a well-characterised model of RA that combines adaptive and innate immune effector components. When complete Freunds adjuvant/collagen …