Novel Immune biomarkers for the early stratification of oligoarthritis patients at risk of developing polyarticular extension.

Introduction: Oligoarthritis, the most common form of Juvenile Idiopathic Arthritis in Western countries and a leading cause of disability, exhibits a variable clinical course. Early identification of children at risk of polyarticular extension is critical for guiding targeted therapy, but requires new biomarkers. This study aimed at profiling T cell and monocyte/macrophage (MM) subset composition and activation/maturation state combined with extracellular vesicle (EV) surface markers in synovial fluid (SF) and peripheral blood (PB) from new-onset Oligoarthritis patients to prospectively evaluate their correlation with clinical course over a two-year follow-up period and identify potential prognostic biomarkers. Methods: SF and PB samples were collected from 42 untreated patients at disease onset. Immune cell subsets were analyzed by flow cytometry, EV marker expression profiles by bead-based multiplex assays, and soluble TREM1 (sTREM1) levels by ELLA. Differences between patients exhibiting oligoarticular course (Group 1) or polyarticular extension (Group 2) over two years of follow-up were assessed. Results: Group 2 patients showed significantly higher CD3:CD14 ratio (AUC = 0.831,p<0.005) and HLA-DR+ CD4+ T cell percentages (64.8%vs52.5%,p=0.02) in SF compared to Group 1 patients. In PB, both HLA-DR+CD4+ and HLA-DR+CD8+ cells were significantly increased (AUC = 0.946,p<0.001) in Group 2. Group 2 patients also exhibited significantly higher proportions of effector memory (EM) CD4+ (AUC = 0.911, p<0.001) and CD8+ (AUC:0.929, p<0.001) subsets, along with lower proportions of naïve CD4+ (AUC = 0.929, p<0.001) and CD8+ (AUC = 0.893, p<0.001) subsets in the circulation, that was reflected in a significantly higher EM:naïve ratios for both CD4+ (AUC = 0.893,p<0.001) and CD8+ (AUC = 0.946;p<0.001) populations. TREM1+ CD14+ cell percentages in both SF and PB were significantly (p<0.05) lower (SF: 83.6%vs90.47%; PB:40.16%vs53.21%), while sTREM1 levels higher (SF: 8926vs5822 pg/ml; PB:298.8vs232 pg/ml), in Group 2 compared to Group 1. Finally, SF-derived EVs from Group 2 showed significantly reduced HLA-ABC (AUC = 0.857,p=0.012) and CD3 (AUC = 0.949,p<0.001) expression. Combining these markers further improved the discriminatory performance of the models (AUC = 1,p<0.001). Discussion: This exploratory study identifies novel immune classifiers combining T lymphocytes and MM subsets with EV markers which stratify, at onset, Oligoarthritis patients who will develop polyarticular extension and provide important mechanistic insights into arthritis progression.