title: The danger from within: alarmins in arthritis.
abstract: Alarmins (also known as danger signals) are endogenous molecules that are released to the extracellular milieu after infection or tissue damage. Extracellular alarmins interact with specific receptors expressed by cells that are engaged in host defence to stimulate signalling pathways that result in initiation of innate and adaptive immune responses, triggering inflammation or tissue repair. Alarmins are considered to be markers of destructive processes that occur in degenerative joint diseases (primarily osteoarthritis (OA)) and chronic inflammatory joint diseases (such as rheumatoid arthritis, psoriatic arthritis and spondylarthropathy). In OA, high mobility group protein B1 (HMGB1) and S100 proteins, along with many other alarmins, are abundantly secreted by joint cells, promoting cartilage matrix catabolism, osteophyte formation, angiogenesis and hypertrophic differentiation. The involvement of alarmins in chronic inflammatory arthritides is suggested by their presence in serum at high levels in these conditions, and their expression within inflamed synovia and synovial fluid. S100 proteins, HMGB1, IL-33 and other endogenous molecules have deleterious effects on joints, and can recruit immune cells such as dendritic cells to inflamed synovia, initiating the adaptive immune response and perpetuating disease. Improving our understanding of the pathological mechanisms associated with these danger signals is important to enable the targeting of new therapeutic approaches for arthritis.
authors.affiliation: Sorbonne University, UPMC University Paris 06, UMR_S 938, 75005 Paris, France.|INSERM UMR_S938, UPMC University Paris 06, 75012 Paris, France.|Inflammation-Immunopathology-Biotherapy Department (DHU i2B), 184 rue du Faubourg Saint-Antoine, 75012 Paris, France.
authors.forename: Meriam
authors.initials: M
authors.lastname: Nefla
authors.affiliation: Department of Pediatric Rheumatology and Immunology, University Children's Hospital Münster, Domagkstr. 3, 48149 Münster, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Holzinger
authors.affiliation: Sorbonne University, UPMC University Paris 06, UMR_S 938, 75005 Paris, France.|INSERM UMR_S938, UPMC University Paris 06, 75012 Paris, France.|Inflammation-Immunopathology-Biotherapy Department (DHU i2B), 184 rue du Faubourg Saint-Antoine, 75012 Paris, France.|Department of Rheumatology, Assistance Publique-Hôpitaux de Paris, Saint-Antoine Hospital, 184 rue du Faubourg Saint-Antoine, 75012 Paris, France.
authors.forename: Francis
authors.initials: F
authors.lastname: Berenbaum
authors.affiliation: Sorbonne University, UPMC University Paris 06, UMR_S 938, 75005 Paris, France.|INSERM UMR_S938, UPMC University Paris 06, 75012 Paris, France.|Inflammation-Immunopathology-Biotherapy Department (DHU i2B), 184 rue du Faubourg Saint-Antoine, 75012 Paris, France.
authors.forename: Claire
authors.initials: C
authors.lastname: Jacques
mesh_terms: D056704:Adaptive Immunity / Q000276:immunology; D000067531:Alarmins / Q000097:blood*; D015535:Arthritis, Psoriatic / Q000276:immunology; D001172:Arthritis, Rheumatoid / Q000276:immunology; D015415:Biomarkers / Q000097:blood; D003713:Dendritic Cells / Q000276:immunology; D006801:Humans; D000067596:Interleukin-33 / Q000097:blood; D010003:Osteoarthritis / Q000097:blood / Q000276:immunology* / Q000473:pathology*; D011237:Predictive Value of Tests; D009418:S100 Proteins / Q000097:blood; D012680:Sensitivity and Specificity; D013582:Synovial Fluid / Q000276:immunology
chemical_list: D000067531:Alarmins; D015415:Biomarkers; D000067596:Interleukin-33; D009418:S100 Proteins