Abstract
IntroductionThis study examines the expression of IL-17A-secreting cells within the inflamed synovium and the relationship to in vivo joint hypoxia measurements.MethodsIL-17A expression was quantified in synovial tissue (ST), serum and synovial fluid (SF) by immunohistochemistry and MSD-plex assays. IL-6 SF and serum levels were measured by MSD-plex assays. Dual immunofluorescence for IL-17A was quantified in ST CD15+ cells (neutrophils), Tryptase+ (mast cells) and CD4+ (T cells). Synovial tissue oxygen (tpO2) levels were measured under direct visualisation at arthroscopy. Synovial infiltration was assessed using immunohistochemistry for cell specific markers. Peripheral blood mononuclear and polymorphonuclear cells were isolated and exposed to normoxic or 3% hypoxic conditions. IL-17A and IL-6 were quantified as above in culture supernatants.ResultsIL-17A expression was localised to mononuclear and polymorphonuclear (PMN) cells in inflamed ST. Dual immunoflourescent staining co-localised IL-17A expression with CD15+ neutrophils Tryptase+ mast cells and CD4+T cells. % IL-17A positivity was highest on CD15+ neutrophils, followed by mast cells and then CD4+T-cells. The number of IL-17A-secreting PMN cells significantly correlated with sublining CD68 expression (r = 0.618, p<0.01). IL-17A SF levels correlated with IL-6 SF levels (r = 0.675, p<0.01). Patients categorized according to tp02< or >20mmHg, showed those with low tp02<20mmHg had significantly higher IL-17A+ mononuclear cells with no difference observed for PMNs. Exposure of mononuclear and polymorphonuclear cells to 3% hypoxia, significantly induced IL-6 in mononuclear cells, but had no effect on IL-17A expression in mononuclear and polymorphonuclear cells.ConclusionThis study demonstrates IL-17A expression is localised to several immune cell subtypes within the inflamed synovial tissue, further supporting the concept that IL-17A is a key mediator in inflammatory arthritis. The association of hypoxia with Il-17A expression appears to be indirect, probably through hypoxia-induced pro-inflammatory pathways and leukocyte influx within the joint microenvironment.
Highlights
This study examines the expression of IL-17A-secreting cells within the inflamed synovium and the relationship to in vivo joint hypoxia measurements
The synovial lining layer thickens and the sublining is infiltrated with Tryptase+ (mast cells) and CD4+ (T cells), B cells, mast cells, neutrophils, monocytes and macrophages which secrete a wide range of mediators which further exacerbate the inflammatory response [4,5], little is known about the role of mast cells in driving the inflammatory response
When we compared matched serum and synovial fluid (SF) levels, we demonstrated that SF IL-17A levels [6.9pg/ml (0.9–156)] were significantly higher than serum IL-17A levels [1.5pg/ml (0.8–2.8)] (p,0.001) (Figure 1A)
Summary
This study examines the expression of IL-17A-secreting cells within the inflamed synovium and the relationship to in vivo joint hypoxia measurements. Recent studies in the K/BxN mouse model have firmly established mast cells as having a critical role in the pathogenesis of inflammatory arthritis [8,9]. These findings have renewed interest in previous histological studies demonstrating a marked increase in mast cell expression in the human RA synovial sublining, in particular at sites of cartilage erosion, and their relationship to increased joint inflammation [7,10]. Mast cell derived mediators such as tryptase have been implicated in the activation of synovial fibroblasts and proteoglycan depletion [11]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
