Background/Purpose: In spondyloarthritis (SpA) Th17 cells play a critical role in activating the pathogenic chain leading to manifestations related to skin, joints and entheses. Elevated levels of both Th17 cells and IL-17A have been detected in skin lesions, blood, and synovial fluid from patients with psoriatic arthritis (PsA) and ankylosing spondylitis (AS). The important role of IL-17A in SpA manifestations is reflected by the suppression of disease activity seen with IL-17A inhibitors in psoriasis, PsA and AS. However, it is still not well understood how IL-17A affects the extracellular matrix (ECM) of the joint. The aim of this study is to establish a cartilage model co-cultured with conditioned medium from Th17 cells to explore the effect of IL-17A on joint tissue remodeling.

Methods: CD4⁺ T cells were isolated from healthy human buffy coat and differentiated into Th17 cells. After 5 days of incubation conditioned medium from Th17 cells was harvested. The Th17 differentiation was confirmed by flow cytometry. Cytokine concentrations were quantified in conditioned medium by ELISA. Bovine cartilage explants (BEX) were cultured for 21 days with 7 different treatments; 1) Culture medium, 2) IL-17A [9.25 ng/mL], 3) IL-17A + TNF-α [9.25 + 20 ng/mL], 4-10) 2-fold titration of Th17 supernatant from 1:2 to 1:16 [9.25 to 0.58 ng/mL]. Each group comprised of 6 replicates. The BEX supernatant-harvest and addition of new treatment were repeated 3 times a week. Metabolic activity was measured by AlamarBlue. Neo-epitope biomarkers of type II collagen formation (PRO-C2) and degradation (T2CM, C2M), together with aggrecan degradation (AGNx1) were quantified in BEX supernatant by ELISA. Differences between groups were compared by two-way RM ANOVA with Dunnett’s multiple comparisons test.

Results: The cytokine concentrations of IL-17A/F/AF, IL-22 and TNF-α were quantified to 18.57, 0.05, 2.82, 1.58 and 12.8 ng/mL. In the BEX model, the metabolic activity was stable throughout study. T2CM and C2M were significantly upregulated in groups treated with Th17 conditioned medium at day 21 (Fig.1A-B), while PRO-C2 was downregulated in all groups compared to untreated (Fig.1C). Furthermore, on day 21 the AGNx1 release was significantly increased in all groups compared to untreated (Fig.1D).

Conclusion: The conditioned medium from Th17 cells showed to significantly increase the degradation of type II collagen and aggrecan, while type II collagen formation was decreased. Translational ECM biomarkers combined with ex vivo models can have great potential as output for describing joint disease mechanisms and predicting structural effect of treatment on bone and cartilage. Thus, this model may provide early indications of structural treatment efficacy in a clinical setting.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/development-of-a-novel-cartilage-model-co-cultured-with-conditioned-medium-from-th17-cells-to-explore-the-effect-of-il-17a-on-joint-tissue-remodeling/