Synovial fluid in ankylosing spondylitis

HIF-1α and MIF enhance neutrophil-driven type 3 immunity and chondrogenesis in a murine spondyloarthritis model

The hallmarks of spondyloarthritis (SpA) are type 3 immunity-driven inflammation and new bone formation (NBF). Macrophage migration inhibitory factor (MIF) was found to be a key driver of the pathogenesis of SpA by amplifying type 3 immunity, yet MIF-interacting molecules and networks remain elusive. Herein, we identified hypoxia-inducible factor-1 alpha (HIF1A) as an interacting partner molecule of MIF that drives SpA pathologies, including inflammation and NBF. HIF1A expression was increased in the joint tissues and synovial fluid of SpA patients and curdlan-injected SKG (curdlan-SKG) mice compared to the respective controls. Under hypoxic conditions in which HIF1A was stabilized, human and mouse neutrophils exhibited substantially increased expression of MIF and IL-23, an upstream type 3 immunity-related cytokine. Similar to MIF, systemic overexpression of IL-23 induced SpA pathology in SKG mice, while the injection of a HIF1A-selective inhibitor (PX-478) into curdlan-SKG mice prevented or attenuated SpA pathology, as indicated by a marked reduction in the expression of MIF and IL-23. Furthermore, genetic deletion of MIF or HIF1A inhibition with PX-478 in IL-23-overexpressing SKG mice did not induce evident arthritis or NBF, despite the presence of psoriasis-like dermatitis and blepharitis. We also found that MIF- and IL-23-expressing neutrophils infiltrated areas of the NBF in curdlan-SKG mice. These neutrophils potentially increased chondrogenesis and cell proliferation via the upregulation of STAT3 in periosteal cells and ligamental cells during endochondral ossification. Together, these results provide supporting evidence for an MIF/HIF1A regulatory network, and inhibition of HIF1A may be a novel therapeutic approach for SpA by suppressing type 3 immunity-mediated inflammation and NBF.

The Role of Neutrophils in Spondyloarthritis: A Journey across the Spectrum of Disease Manifestations

Spondyloarthritis (SpA) contemplates the inflammatory involvement of the musculoskeletal system, gut, skin, and eyes, delineating heterogeneous diseases with a common pathogenetic background. In the framework of innate and adaptive immune disruption in SpA, neutrophils are arising, across different clinical domains, as pivotal cells crucial in orchestrating the pro-inflammatory response, both at systemic and tissue levels. It has been suggested they act as key players along multiple stages of disease trajectory fueling type 3 immunity, with a significant impact in the initiation and amplification of inflammation as well as in structural damage occurrence, typical of long-standing disease. The aim of our review is to focus on neutrophils' role within the spectrum of SpA, dissecting their functions and abnormalities in each of the relevant disease domains to understand their rising appeal as potential biomarkers and therapeutic targets.

Macrophage migration inhibitory factor drives pathology in a mouse model of spondyloarthritis and is associated with human disease

[Figure: see text].

IL-17A expressed on neutrophil extracellular traps promotes mesenchymal stem cell differentiation toward bone-forming cells in ankylosing spondylitis

Ankylosing spondylitis (AS) is an inflammatory disease characterized by excessive bone formation. We investigated the presence of neutrophil extracellular traps (NETs) in AS and how they are involved in the osteogenic capacity of bone marrow mesenchymal stem cells (MSCs) through interleukin-17A (IL-17A). Peripheral neutrophils and sera were obtained from patients with active AS and healthy controls. NET formation and neutrophil/NET-associated proteins were studied using immunofluorescence, immunoblotting, qPCR, and ELISA. In vitro co-culture systems of AS NET structures and MSCs isolated from controls were deployed to examine the role of NETs in the differentiation of MSCs toward osteogenic cells. Analysis was performed using specific staining and qPCR. Neutrophils from patients with AS were characterized by enhanced formation of NETs carrying bioactive IL-17A and IL-1β. IL-17A-enriched AS NETs mediated the differentiation of MSCs toward bone-forming cells. The neutrophil expression of IL-17A was positively regulated by IL-1β. Blocking IL-1β signaling on neutrophils with anakinra or dismantling NETs using DNase-I disrupted osteogenesis driven by IL-17A-bearing NETs. These findings propose a novel role of neutrophils in AS-related inflammation, linking IL-17A-decorated NETs with the differentiation of MSCs toward bone-forming cells. Moreover, IL-1β triggers the expression of IL-17A on NETs offering an additional therapeutic target in AS.

Multiomic blood correlates of genetic risk identify presymptomatic disease alterations

Transitions from health to disease are characterized by dysregulation of biological networks under the influence of genetic and environmental factors, often over the course of years to decades before clinical symptoms appear. Understanding these dynamics has important implications for preventive medicine. However, progress has been hindered both by the difficulty of identifying individuals who will eventually go on to develop a particular disease and by the inaccessibility of most disease-relevant tissues in living individuals. Here we developed an alternative approach using polygenic risk scores (PRSs) based on genome-wide association studies (GWAS) for 54 diseases and complex traits coupled with multiomic profiling and found that these PRSs were associated with 766 detectable alterations in proteomic, metabolomic, and standard clinical laboratory measurements (clinical labs) from blood plasma across several thousand mostly healthy individuals. We recapitulated a variety of known relationships (e.g., glutamatergic neurotransmission and inflammation with depression, IL-33 with asthma) and found associations directly suggesting therapeutic strategies (e.g., Ω-6 supplementation and IL-13 inhibition for amyotrophic lateral sclerosis) and influences on longevity (leukemia inhibitory factor, ceramides). Analytes altered in high-genetic-risk individuals showed concordant changes in disease cases, supporting the notion that PRS-associated analytes represent presymptomatic disease alterations. Our results provide insights into the molecular pathophysiology of a range of traits and suggest avenues for the prevention of health-to-disease transitions.

Immune checkpoint inhibitor-induced inflammatory arthritis as a model of autoimmune arthritis

The development of inflammatory arthritis in patients receiving immune checkpoint inhibitor therapy is increasingly recognized due to the growing use of these drugs for the treatment of cancer. This represents an important opportunity not only to define the mechanisms responsible for the development of this immune-related adverse event and to ultimately predict or prevent its development, but also to provide a unique window into early events in the development of inflammatory arthritis. Knowledge gained through the study of this patient population, for which the inciting event is known, could shed light into the pathogenesis of autoimmune arthritis. This review will highlight the clinical and immunologic features of these entities to define common elements for future study.

Light and electron microscopic observations on the synovitis of ankylosing spondylitis

Light microscopic studies on synovium obtained from seven knees and three hips of patients with ankylosing spondylitis and peripheral arthritis showed surface fibrin, proliferation of synovial lining cells, moderate infiltration with lymphocytes, and sometimes striking numbers of plasma cells. There was some vascular congestion and obliteration, occasional bone and cartilage debris, and a tendency toward increased fibrous tissue. Although the intensity of some findings varies from those in rheumatoid arthritis, there were no consistent distinguishing features. Electron microscopy of eight synovial tissue specimens showed increased type B or synthetic lining cells. Structures that could possibly have been organisms were seen among synovial cells in two patients. Immune complex-like deposits were not seen in vessel walls, although there were other vascular alterations. Synovial fluid studies showed 2,200 to 16,500 white blood cells/mm3 (mean, 8,236), 29% to 93% polymorphonuclear leukocytes (mean, 66%), and 0.5 to 32% lymphocytes (mean, 18%). The presence of at least some activated lymphocytes (lymphoblasts) in seven of nine patients in addition to the above findings in synovium suggest an immunological component to the driven process. No more than 32% lymphocytes was found in any synovial fluid despite the use of nonsteroidal antiinflammatory drugs. Thus no support for synovial fluid lymphocytosis, such as has been described in rheumatoid arthritis patients treated with nonsteroidal antiinflammatory drugs alone, is provided.

The absence of circulating immune complexes in patients with ankylosing spondylitis

Sera from 50 patients with well-defined ankylosing spondylitis were examined for circulating immune complexes using both a Clq binding (fluid phase) assay and a Raji cell assay. No more than five of the patients assessed had circulating immune complexes by either one of these techniques and none were positive in both. This result is in contrast to the high prevalence in sera from unselected patients with rheumatoid arthritis and systemic lupus used as positive controls.

Immunoblasts in synovial fluid and blood in the rheumatic diseases

Synovial fluid studies have been made on 43 patients with rheumatic disease. Lymphocytes separated by a 2-stage procedure were examined for the presence of activated large lymphoid cells or immunoblasts. Such immunoblasts were found in 19 of 21 patients with classical rheumatoid arthritis and 7 of 10 patients with seronegative polyarthritis, including patients with Still's disease, psoriatic arthritis, and ankylosing spondylitis. No immunoblasts were seen in synovial fluid from osteoarthrosis or in the inflammatory but nonimmune synovial fluid from crystal-induced arthritis. The presence of immunoblasts showed a correlation with the lymphocyte count in the synovial fluid but not with the total white cell count. Preliminary studies confirm the spontaneous metabolic activity of these cells by autoradiography and show them by scanning electron microscopy to have a villous surface membrane. Simultaneous peripheral blood studies showed a lower incidence of immunoblasts than in the synovial fluid. It is suggested that these cells originate in the synovial membrane. In view of the known migration characteristic of immunoblasts these cells may be important in the spread of immune arthritis as well as being markers of disease activity.

Diminished mixed lymphocyte response in ankylosing spondylitis

A diminished mixed lymphocyte response was reported by Nikbin et al. (1976) among patients with ankylosing spondylitis, their asymptomatic relatives and also normal controls carrying the B27 antigen. In the present communication, the responses in 48 ankylosing spondylitis patients and 45 controls were examined in mixed lymphocyte cultures tested against a 'standard stimulator' made up of pooled lymphocytes. A significantly diminished response is confirmed among the ankylosing spondylitis patients, but not in the control group carrying the B27 antigen. The diminished mixed lymphocyte response therefore appears to be more directly associated with the disease than with the B27 antigen, and possibly represents a specific T-cell defect associated with the pathogenesis of the disease.

HLA-B27 and frozen shoulder

Histocompatibility antigens were determined in 38 patients with frozen shoulder and 216 normal blood-donors. HLA-B27 was significantly more common in patients with frozen shoulder (42%) than in the controls (10%). The distribution of the other 19 histocompatibility antigens was similar in the patient and control groups. This result may be associated with the suggested immunological pathogenesis of the condition.

Immunological reactivity in ankylosing spondylitis. Circulating immunoblasts, autoantibodies, and immunoglobulins

Circulating immunoblasts were studied in 39 cases of ankylosing spondylitis. The results were compared with 20 normal subjects and a group of 39 patients with rheumatoid arthritis, Immunoblasts were found to be increased in 11 patients with ankylosing spondylitis and in 22 patients with rheumatoid arthritis in contrast to the controls who were found to have a normal lymphoid cell population in the peripheral blood. Fifteen patients showed raised levels of one or more class of immunoglobulin. Autoantibodies, including antinuclear factors, were negative in all cases. There was a correlation between raised immunoblasts and plasma viscosity but not with clinical assessment of activity. The increase of immunoblasts in the peripheral blood, together with the raised immunoglobulins supports the suggestion of an immunological basis for ankylosing spondylitis.