Two Broad Categories Overlapping With Rheumatoid Arthritis Observed in Synovial Biopsies from Patients With Juvenile Idiopathic Arthritis.

Objective: The objective is to characterize transcriptomic profiles and immune cell composition and distribution in juvenile idiopathic arthritis (JIA) synovial biopsies, assess for associations of these features with clinical parameters, and compare JIA and rheumatoid arthritis (RA) synovial features.

Methods: RNA sequencing (RNASeq) was performed on 24 samples, with pathway analysis and inference of relative abundance of immune cell subsets based on gene expression data. Two multiplex fluorescence immunohistochemistry (IHC) panels were performed on 28 samples (including 13 on which RNASeq was performed), staining for CD206 classical and CD206 nonclassical macrophages, and CD8 and CD4 T and B lymphocytes. Data were compared to a published series of early RA synovial biopsies.

Results: Pathway analysis of the most variably expressed genes (n = 339) identified a B and plasma cell signature as the main driver of heterogeneity in JIA synovia, with strong overlap between JIA and RA synovitis. Multiplex IHC confirmed heterogeneity of immune cell infiltration. M1-like macrophage-rich synovial lining was associated with greater lining hypertrophy and higher (CD45) pan-immune cell and CD8 T cell infiltration.

Conclusion: Our study indicates significant similarities between JIA and RA synovitis. Similar to RA, JIA synovia may be broadly categorized into two groups: (1) those with an inflammatory/adaptive immune transcriptomic signature, M1-like macrophage and CD8 T cell infiltration, and thicker, M1-like macrophage-rich synovial lining, and (2) those with an M2-like macrophage transcriptomic signature, greater M2/M1-like macrophage ratios, and thinner, M2-like macrophage-rich synovial lining. Synovial features were not significantly associated with clinical parameters, likely because of group size and heterogeneity.