The danger from within: alarmins in arthritis Nefla, Meriam; Holzinger, Dirk; Berenbaum, Francis ...
Nature reviews. Rheumatology,
11/2016, Letnik:
12, Številka:
11
Journal Article
Recenzirano
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.
Abstract The cytoplasmic S100 proteins derived from cells of myeloid origin are promising new markers of (auto-)inflammation. S100A8/A9 and S100A12 are released from monocytes and granulocytes during ...activation of the innate immune system. Tissue and serum concentrations correlate to disease activity, both during local and systemic inflammation. In autoinflammatory diseases such as Familial Mediterranean Fever (FMF) and Systemic onset Juvenile Idiopathic Arthritis (SJIA), a dysregulation of alternative secretory pathways may be involved in pathogenesis and lead to hypersecretion of S100 proteins. Since autoinflammatory diseases can be difficult to diagnose, phagocyte-derived S100 proteins are valid tools in the diagnosis of autoinflammatory diseases. In addition, they may help achieve a better understanding of the pathophysiology of autoinflammatory disorders including SJIA and FMF, and even provide novel therapeutic targets in the future.
Hemophagocytic lymphohistiocytosis (HLH) and macrophage activation syndrome (MAS) are life-threatening hyperferritinemic systemic inflammatory disorders. Although profound cytotoxic impairment causes ...familial HLH (fHLH), the mechanisms driving non-fHLH and MAS are largely unknown. MAS occurs in patients with suspected rheumatic disease, but the mechanistic basis for its distinction is unclear. Recently, a syndrome of recurrent MAS with infantile enterocolitis caused by NLRC4 inflammasome hyperactivity highlighted the potential importance of interleukin-18 (IL-18). We tested this association in hyperferritinemic and autoinflammatory patients and found a dramatic correlation of MAS risk with chronic (sometimes lifelong) elevation of mature IL-18, particularly with IL-18 unbound by IL-18 binding protein, or free IL-18. In a mouse engineered to carry a disease-causing germ line NLRC4T337S mutation, we observed inflammasome-dependent, chronic IL-18 elevation. Surprisingly, this NLRC4T337S-induced systemic IL-18 elevation derived entirely from intestinal epithelia. NLRC4T337S intestines were histologically normal but showed increased epithelial turnover and upregulation of interferon-γ–induced genes. Assessing cellular and tissue expression, classical inflammasome components such as Il1b, Nlrp3, and Mefv predominated in neutrophils, whereas Nlrc4 and Il18 were distinctly epithelial. Demonstrating the importance of free IL-18, Il18 transgenic mice exhibited free IL-18 elevation and more severe experimental MAS. NLRC4T337S mice, whose free IL-18 levels were normal, did not. Thus, we describe a unique connection between MAS risk and chronic IL-18, identify epithelial inflammasome hyperactivity as a potential source, and demonstrate the pathogenicity of free IL-18. These data suggest an IL-18–driven pathway, complementary to the cytotoxic impairment of fHLH, with potential as a distinguishing biomarker and therapeutic target in MAS.
•IL-18 distinguishes susceptibility to MAS amongst hyperferritinemic and autoinflammatory diseases.•Excess IL-18 in NLRC4 gain-of-function mice derives from intestinal epithelia, and free IL-18 promotes experimental MAS.
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To give an overview about the expanding spectrum of autoinflammatory diseases due to mutations in proline-serine-threonine phosphatase-interacting protein 1 (PSTPIP1) and new insights into their ...pathogenesis.
In addition to classical pyogenic sterile arthritis, pyoderma gangrenosum, and acne (PAPA) syndrome, PSTPIP1-associated myeloid-related proteinemia inflammatory (PAMI) syndrome has been described as a distinct clinical phenotype of PSTPIP1-associated inflammatory diseases (PAID) and other entities are emerging. In addition to dysregulation of IL-1ß release from activated PAPA monocytes that requires NLR family, pyrin domain containing 3 (NLRP3), PSTPIP1 mutations have an general impact on cellular dynamics of cells of the innate immune system. In addition, overwhelming expression and release of the alarmins myeloid-related protein (MRP) 8 and 14 by activated phagocytes and keratinocytes, which promote innate immune mechanisms in a Toll like receptor (TLR) 4-dependent manner, are a characteristic feature of these diseases and form a positive feed-back mechanism with IL-1ß.
Autoinflammatory diseases due to PSTPIP1 mutations are not restricted to the classical PAPA phenotype but might present with other distinct clinical features. MRP8/14 serum levels are a hallmark of PAPA and PAMI and can be used as screening tool to initiate targeted genetic testing in suspected cases. The feedback mechanism of IL-1ß and MRP-alarmin release may offer novel targets for future therapeutic approaches.
Autoimmune and auto-inflammatory diseases in children are causing chronic inflammation, organ damage, and pain. Although several options for treatment are nowadays available a significant number of ...patients does not respond sufficiently to current therapies. In these diseases inflammatory processes are triggered by numerous exogenous and endogenous factors. There is now increasing evidence that especially a novel family of pro-inflammatory molecules, named alarmins, play a significant role in inflammatory processes underlying these diseases. Alarmins are endogenous proteins released during stress reactions that confer inflammatory signaling via Pattern Recognition Receptors (PRRs), like the Toll-like receptor 4 (TLR4). The most abundant alarmins in juvenile rheumatic diseases belong to the family of pro-inflammatory calcium-binding S100-proteins. In this review we will give a general introduction in S100-biology. We will demonstrate the functional relevance of these proteins in animal models of autoimmune and auto-inflammatory diseases. We will show the expression patterns of S100-alarmins and correlation to disease activity in different forms of juvenile idiopathic arthritis, auto-inflammatory diseases, and systemic autoimmune disorders. Finally, we will discuss the clinical use of S100-alarmins as biomarkers for diagnosis and monitoring of rheumatic diseases in children and will point out potential future therapeutic approaches targeting inflammatory effects mediated by S100-alarmins.
Objective
Systemic juvenile idiopathic arthritis (JIA) is a multifactorial autoinflammatory disease with a historically poor prognosis. With current treatment regimens, approximately half of patients ...still experience active disease after 1 year of therapy. This study was undertaken to evaluate a treat‐to‐target approach using recombinant interleukin‐1 receptor antagonist (rIL‐1Ra; anakinra) as first‐line monotherapy to achieve early inactive disease and prevent damage.
Methods
In this single‐center, prospective study, patients with new‐onset systemic JIA with an unsatisfactory response to nonsteroidal antiinflammatory drugs received rIL‐1Ra monotherapy according to a treat‐to‐target strategy. Patients with an incomplete response to 2 mg/kg rIL‐1Ra subsequently received 4 mg/kg rIL‐1Ra or additional prednisolone, or switched to alternative therapy. For patients in whom inactive disease was achieved, rIL‐1Ra was tapered after 3 months and subsequently stopped.
Results
Forty‐two patients, including 12 who had no arthritis at disease onset, were followed up for a median of 5.8 years. The median time to achieve inactive disease was 33 days. At 1 year, 76% had inactive disease, and 52% had inactive disease while not receiving medication. High neutrophil counts at baseline and a complete response after 1 month of rIL‐1Ra were highly associated with inactive disease at 1 year. After 5 years of follow‐up, 96% of the patients included had inactive disease, and 75% had inactive disease while not receiving medication. Articular or extraarticular damage was reported in <5%, and only 33% of the patients received glucocorticoids. Treatment with rIL‐1Ra was equally effective in systemic JIA patients without arthritis at disease onset.
Conclusion
Treatment to target, starting with first‐line, short‐course monotherapy with rIL‐1Ra, is a highly efficacious strategy to induce and sustain inactive disease and to prevent disease‐ and glucocorticoid‐related damage in systemic JIA.
Juvenile idiopathic arthritis-associated uveitis (JIAU) is the most common uveitis entity in childhood. As S100A8/A9 and S100A12 proteins are valuable biomarkers in childhood arthritis, we ...investigated the occurrence of these proteins in childhood uveitis.
Serum samples from patients with JIAU (n = 79) or idiopathic anterior uveitis (IAU, n = 24), as well as from nonuveitic controls (n = 24), were collected. Furthermore, aqueous humor samples (JIAU n = 17, nonuveitic controls n = 16, IAU n = 12) were obtained. Samples were analyzed for S100A8/A9 and S100A12 protein levels by ELISA. Intergroup comparisons were performed, involving patient data, clinical data, and S100 levels.
S100A8/A9 and S100A12 serum levels were elevated in IAU and JIAU patients as compared to nonuveitic controls (all P < 0.05). S100 serum levels in JIAU patients were higher in active arthritis (not significant; P = 0.289 for S100A8/A9 and P = 0.196 for S100A12) and active uveitis (P = 0.010 for S100A8/A9 and P = 0.026 for S100A12) than in controls. No significant differences in S100 levels were found in a subgroup analysis for sex, antinuclear antibody (ANA) status, disease duration, or presence of uveitis complications. In JIAU patients, S100 serum levels correlated with age and age at onset of uveitis. A longitudinal analysis in JIAU patients showed a correlation of serum S100A8/A9 and S100A12 levels with uveitis activity (both P = 0.03). S100A8/A9 levels in aqueous humor of patients with JIAU (P = 0.001) and IAU (P = 0.0002) were increased as compared to nonuveitic controls.
Increased S100A8/A9 and S100A12 levels are found in the serum and aqueous humor of patients with autoimmune uveitis. Serum levels reflect activity of joint and eye disease.
The role of the pore-forming Staphylococcus aureus toxin Panton-Valentine leukocidin (PVL) in severe necrotizing diseases is debated due to conflicting data from epidemiological studies of ...community-associated methicillin-resistant S. aureus (CA-MRSA) infections and various murine disease-models. In this study, we used neutrophils isolated from different species to evaluate the cytotoxic effect of PVL in comparison to other staphylococcal cytolytic components. Furthermore, to study the impact of PVL we expressed it heterologously in a non-virulent staphylococcal species and examined pvl-positive and pvl-negative clinical isolates as well as the strain USA300 and its pvl-negative mutant. We demonstrate that PVL induces rapid activation and cell death in human and rabbit neutrophils, but not in murine or simian cells. By contrast, the phenol-soluble modulins (PSMs), a newly identified group of cytolytic staphylococcal components, lack species-specificity. In general, after phagocytosis of bacteria different pvl-positive and pvl-negative staphylococcal strains, expressing a variety of other virulence factors (such as surface proteins), induced cell death in neutrophils, which is most likely associated with the physiological clearing function of these cells. However, the release of PVL by staphylococcal strains caused rapid and premature cell death, which is different from the physiological (and programmed) cell death of neutrophils following phagocytosis and degradation of virulent bacteria. Taken together, our results question the value of infection-models in mice and non-human primates to elucidate the impact of PVL. Our data clearly demonstrate that PVL acts differentially on neutrophils of various species and suggests that PVL has an important cytotoxic role in human neutrophils, which has major implications for the pathogenesis of CA-MRSA infections.
Staphylococcus aureus is a frequent cause for serious, chronic and therapy‐refractive infections in spite of susceptibility to antibiotics in vitro. In chronic infections, altered bacterial ...phenotypes, such as small colony variants (SCVs), have been found. Yet, it is largely unclear whether the ability to interconvert from the wild‐type to the SCV phenotype is only a rare clinical and/or just laboratory phenomenon or is essential to sustain an infection. Here, we performed different long‐term in vitro and in vivo infection models with S. aureus and we show that viable bacteria can persist within host cells and/or tissues for several weeks. Persistence induced bacterial phenotypic diversity, including SCV phenotypes, accompanied by changes in virulence factor expression and auxotrophism. However, the recovered SCV phenotypes were highly dynamic and rapidly reverted to the fully virulent wild‐type form when leaving the intracellular location and infecting new cells. Our findings demonstrate that bacterial phenotype switching is an integral part of the infection process that enables the bacteria to hide inside host cells, which can be a reservoir for chronic and therapy‐refractive infections.
→ See accompanying Closeup by Christian Garzoni and William Kelley DOI 10.1002/emmm.201100123.
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