Recent studies indicate that IL-1␣ functions intracellularly in pathways independent of its cell surface receptors by translocating to the nucleus and regulating transcription. Similarly, the chromatinassociated protein HMGB1 acts as both a nuclear factor and a secreted proinflammatory cytokine. Here, we show that IL-33, an IL-1-like cytokine that signals via the IL-1 receptor-related protein ST2 and induces T helper type 2-associated cytokines, is an endothelium-derived, chromatin-associated nuclear factor with transcriptional repressor properties. We found that IL-33 is identical to NF-HEV, a nuclear factor preferentially expressed in high endothelial venules (HEV), that we previously characterized. Accordingly, in situ hybridization demonstrated that endothelial cells constitute a major source of IL-33 mRNA in chronically inflamed tissues from patients with rheumatoid arthritis and Crohn's disease. Immunostaining with three distinct antisera, directed against the N-terminal part and IL-1-like C-terminal domain, revealed that IL-33 is a heterochromatin-associated nuclear factor in HEV endothelial cells in vivo. Association of IL-33 with heterochromatin was also observed in human and mouse cells under living conditions. In addition, colocalization of IL-33 with mitotic chromatin was noted. Nuclear localization, heterochromatin-association, and targeting to mitotic chromosomes were all found to be mediated by an evolutionarily conserved homeodomain-like helix-turn-helix motif within the IL-33 N-terminal part. Finally, IL-33 was found to possess transcriptional repressor properties, associated with the homeodomain-like helix-turn-helix motif. Together, these data suggest that, similarly to IL1␣ and HMGB1, IL-33 is a dual function protein that may function as both a proinflammatory cytokine and an intracellular nuclear factor with transcriptional regulatory properties.heterochromatin ͉ nucleus ͉ endothelium ͉ HMGB1 C ytokines of the IL-1 family play a major role in a wide range of inflammatory, infectious, and autoimmune diseases (1). The three best known members of this family, IL-1␣, IL-1␤, and IL-18, are highly inflammatory cytokines, and dysregulation of their production or activity can lead to severe pathological events (1, 2). IL-33 is the most recent addition to the IL-1 family (3). IL-33 has been shown to induce T helper (Th) type 2 responses (3) by signaling through the IL-1 receptor-related protein ST2 (IL-1 R4), an orphan member of the IL-1 receptor family (4, 5). Treatment of mice with recombinant IL-33 resulted in blood eosinophilia, splenomegaly, and increased serum levels of IgE, IgA, IL-5, and IL-13 (3). Exposure to IL-33 also caused severe pathological changes in the lungs and gastrointestinal tract, including eosinophilic and mononuclear infiltrates, increased mucus production, and epithelial cell hyperplasia and hypertrophy (3).IL-33 shares with the other members of the IL-1 family a single structural domain formed from 12 ␤ strands, arranged in a so-called IL-1/FGF ␤-trefoil fold (6, 7). Simila...

Endothelial cells play a central role in chronic inflammation: for example, they express adhesion molecules and present chemokines leading to enhanced leukocyte recruitment into tissues. Numerous markers of endothelial cells have been reported but there has been a lack of comparative data on their specificity. The present study compared the specificity of seven endothelial cell markers in the rheumatoid synovium and the colon of patients with Crohn's disease. These markers were: the sulphated epitope MECA-79, the Duffy antigen receptor for chemokines (DARC), von Willebrand factor, CD31 (PECAM-1), CD34, CD105 (endoglin) and CD146. MECA-79, DARC and von Willebrand factor showed a specific endothelial cell distribution. MECA-79, which recognizes sulphated ligands for leukocyte adhesion receptor L-selectin (CD62L), was selective for a subset of venules in highly inflamed tissue and was present in rheumatoid but not control osteoarthritic synovia. DARC was also specific for venules but had a more widespread distribution than MECA-79, and was present in rheumatoid and control synovia. The other markers all labelled endothelial cells in venules, arterioles and capillaries. However, they also localized to other cell types. For example, CD34 stained fibroblasts, CD146 was expressed by the pericytes and smooth muscle cells of vessel walls and CD31 and CD105 labelled a broad range of cell types.

60 COX = cyclooxygenase; CRH = corticotropin-releasing hormone; FGF = fibroblast growth factor; HEV = high endothelial venules; HGF = hepatocyte growth factor; ICAM = intercellular adhesion molecule; IL = interleukin; IFN = interferon; MCP-1 = monocyte chemoattractant protein-1; MHC = major histocompatibility complex; MMP = matrix metalloproteinase; OA = osteoarthritic; RA = rheumatoid arthritis; TIMP = tissue inhibitor of metalloproteinase; TNF = tumour necrosis factor; VCAM = vascular cell adhesion molecule; VEGF = vascular endothelial growth factor. Arthritis Research & TherapyVol 6 No 2 Middleton et al. IntroductionRheumatoid arthritis (RA) is a chronic, systemic inflammatory disease affecting the joints, and is associated with increased morbidity and mortality [1][2][3]. The synovium or synovial membrane, which surrounds the joint cavity, becomes massively hypertrophied in RA. This tissue, known as pannus, can become invasive, penetrating and degrading the cartilage and bone, resulting in joint deformities, in functional deterioration and in profound disability.The lining layer, or intima, of the synovium is normally one to three cells thick and it comprises macrophage-like cells and fibroblast-like cells [4]. This layer undergoes thickening and hypertrophy in RA, largely due to the increased recruitment of monocytes from the blood supply in the deeper layer, or subintima, of the tissue [5,6]. Other inflammatory cells such as T cells (mainly CD45RO) and B lymphocytes migrate from the blood into the synovium and can form ectopic lymphoid follicles around blood vessels. These structures resemble the lymphoid follicles of lymph nodes. In addition, neutrophils migrate into the synovium and end up in large numbers in the synovial joint fluid. The role of endothelial cells in RA AbstractEndothelial cells are active participants in chronic inflammatory diseases. These cells undergo phenotypic changes that can be characterised as activated, angiogenic, apoptotic and leaky. In the present review, these phenotypes are described in the context of human rheumatoid arthritis as the disease example. Endothelial cells become activated in rheumatoid arthritis pathophysiology, expressing adhesion molecules and presenting chemokines, leading to leukocyte migration from the blood into the tissue. Endothelial cell permeability increases, leading to oedema formation and swelling of the joints. These cells proliferate as part of the angiogenic response and there is also a net increase in the turnover of endothelial cells since the number of apoptotic endothelial cells increases. The endothelium expresses various cytokines, cytokine receptors and proteases that are involved in angiogenesis, proliferation and tissue degradation. Associated with these mechanisms is a change in the spectrum of genes expressed, some of which are relatively endothelial specific and others are widely expressed by other cells in the synovium. Better knowledge of molecular and functional changes occurring in endothelial cells during chronic inflammation...