Interest of the Immunohistological Analysis of Architecture and Cells Distribution of the Synovial Membrane in Rheumatoid Arthritis

Introduction: Rheumatoid arthritis (RA) is an immune-mediated disease in which synovial inflammatory lesions resemble those found in secondary lymphoid organs. The histopathological characteristics of several synovial tissue specimens from RA patients were compared to the characteristics of synovial samples from patients with osteoarthritis (OA) in order to highlight histological features of RA synovium that could be associated with clinical phenotypes. Methods: Synovial tissue specimens obtained from 17 patients with RA were compared to synovial samples from 9 patients with OA. Krenn’s synovitis score and synovial microarchitecture were analysed. Immuno-histological analysis of synovium tissue was performed to observe the cells distribution in the inflammatory infiltrates, using CD3, CD20 and CD68 markers. Results: Synovitis scores were of high-grade synovitis in 76.4% of the RA tissue specimens against 55.5% in the OA samples but the median synovitis score was higher in the RA group (p=0.05). The synovial tissue architecture in the RA group was characterised by the presence of lymphocyte aggregates in 70.5% of tissue specimens and diffuse infiltration in all others. Significant differences between the RA and OA samples were also observed with respect to the distribution of macrophages in the stroma. Conclusion: This study highlights the importance of inflammatory infiltrates in the RA synovium and suggests that histopathological analysis of RA synovium can still bring data on the pathophysiological mechanisms and potential therapeutic targets in RA.