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.

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.

In conclusion, IL-33 may play a protective role in the development of adipose tissue inflammation during obesity.

Material

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. Note added after publication: For an update on this topic, please see the latest https://doi.org/10.1002/eji.201746938