POS0069 INCREASED T CELL RESPONSES, METABOLIC ACTIVITY AND FIBROBLAST INVASIVE CAPACITY IN CHILDREN WITH DOWN’S SYNDROME-ASSOCIATED ARTHRITIS COMPARED TO JUVENILE IDIOPATHIC ARTHRITIS
Authors: S. Foo, A. Floudas, S. Wade, A. O’ Brien, S. Ansboro, R. Mullan, D. Veale, E. MacDermott, D. Deely, C. Foley, O. Killeen, U. Fearon
Journal: Annals of the Rheumatic Diseases (2021)

Background: Juvenile idiopathic arthritis (JIA) was thought to be the most common inflammatory arthritis in children (Shih et al. , 2019). However an aggressive, erosive arthritis of little-known immunologic mechanism occurs 20 times more frequently in children with Down’s syndrome (Foley et al. , 2019). Objectives: This study was undertaken to characterize immune cell responses and synovial fibroblast invasiveness in children with Down’s syndrome-associated arthritis (DA). Methods: Multiparametric flow cytometric analysis was used to examine peripheral blood T cell, B cell and monocyte populations. In addition, T cell cytokine responses and their metabolic profile in children with DA, JIA, Down’s Syndrome (trisomy 21 [T21]), and in healthy controls were assessed. The function of DA primary synovial fibroblasts (FLS) was assessed in response to stimulation with pro-inflammatory mediators alone and in combination (TNF-α, IL-17a, IFN-γ, GM-CSF). The two major energy pathways glycolysis (ECAR) and oxidative phosphorylation (OCR) were quantified by the Seahorse XFe96 Analyser. Migration, adhesion, invasion and cytokine/chemokine secretion were quantified by wound repair scratch assays, Transwell collagen invasion chambers, adhesion binding assays, and ELISAs. Results: T cell frequencies were higher in DA compared to JIA and T21 in contrast to B cell frequencies which were decreased. T cell responses in DA were characterized by increased frequencies of CD4 + and CD8 + TNF- α, IFN- γ and GM-CSF producing T cells. The frequency of T peripheral helper (Tph) cells were elevated in children with DA compared to all other groups. In parallel, an increase in their metabolic profile evident by higher phosphorylation of mTOR pathway components AKT, mTOR and S6. Comparison of DA and JIA FLS demonstrated that DA FLS display a more invasive/migratory capacity and are more metabolically active. Based on the increased cytokine responses in DA T cells, we next examined the effect T cell derived cytokines TNF-α, IL-17A, IFN-γ and GM-CSF alone and in combination on DA FLS function. TNF-α, IL-17a and IFN-γ induced IL-6, RANTES and MCP-1 secretion, with no effect observed for GM-CSF. Furthermore, TNF-α and IL-17A induced DA FLS migration and PBMC adhesion to DA FLS. Finally IL17A and IFN-γ potentiated the effect of TNF-α on IL-6 and MCP-1 secretion compared to stimulations alone. Conclusion: DA is a more common and aggressive form of arthritis compared to JIA. It is characterized by increased T cell responses and a more invasive FLS phenotype compared to that of JIA, with T cell derived cytokine alone and in combination further inducing DA FLS pathogenic mechanisms. These effects mirror the increased erosive disease observed clinically. References: [1]Foley, C. et al. (2019) ‘Increased T cell plasticity with dysregulation of T follicular helper, T peripheral helper and T regulatory cell responses in children with JIA and Down syndrome-associated arthritis’, Arthritis &amp; Rheumatology , pp. 0–1. doi: 10.1002/art.41150. [2]Shih, Y. J. et al. (2019) ‘Enthesitis-related arthritis is the most common category of juvenile idiopathic arthritis in Taiwan and presents persistent active disease’, Pediatric Rheumatology . Pediatric Rheumatology. doi: 10.1186/s12969-019-0363-0. Disclosure of Interests: None declared.