LAUSR

Background Our group has recently described that the majority of polyarticular juvenile idiopathic arthritis (pJIA) and a large fraction of extended oligoarticular JIA (oJIA) patients fulfil classification criteria for rheumatoid arthritis (RA) in adulthood. B cells play several important roles in RA pathogenesis, but it is still unclear if the pattern of B cell involvement in pJIA and extended oJIA follows what has been described for adults with RA. Objectives The main goal of this study was to characterise peripheral blood B cell phenotype and cellular activation in pJIA and extended oJIA patients when compared to established RA. Methods Blood samples were collected from JIA patients (n=10; mean age 10±4 years), established RA patients treated with synthetic DMARDs (n=10; mean age 72±7 years) and two corresponding groups of age- and sex-matched healthy donors. B cell phenotype was characterised by flow cytometry and B cell apoptosis was assessed after 48 hour of in vitro cell culture. Results JIA patients recruited in this study were either classified as extended oJIA (n=6) or pJIA (n=4). Seven JIA patients (4 extended oJIA and 3 pJIA) were treated with methotrexate and three patients (2 extended oJIA and 1 pJIA) were untreated. We found that JIA patients had similar CD19 +B cell levels in circulation when compared to controls, but significantly higher CD19 +B cell frequencies in comparison to established RA. In addition, increased frequencies of transitional (IgD +CD38++) and naïve (IgD +CD27+) B cell subpopulations were observed in JIA patients when compared to RA. However, established RA patients had significantly higher levels of CD21lowCD38low, post-switch (IgD-CD27+) and IgD-CD27- memory B cell subsets when compared not only to controls, but also to JIA patients. No significant differences were detected in pre-switch (IgD +CD27+) memory and plasmablasts (IgD-CD38++) levels in JIA patients when compared to both controls and RA. Furthermore, the frequency of CD5 +B cells, CD5 median fluorescence intensity (MFI), CD40 MFI and CXCR5 MFI B cell expression levels were significantly increased in JIA patients when compared to established RA, but not to controls. No significant differences were observed between JIA and established RA patients in BAFF-R, FcgRIIB, CD21, CD23, CD38, CD86, CD95, HLA-DR, TLR9 and RANKL expression on B cells. After 48 hour of in vitro cell culture a significantly higher B cell death was found in JIA in comparison to RA patients. Conclusions The increased frequencies of transitional, naïve and CD5 +B cells in circulation and reduced levels of memory B cell subpopulations in JIA patients when compared to established RA are probably related to an immature immune system present in children when compared to adults. Nevertheless, the similarity in B cell phenotype found between extended oJIA, pJIA and established RA patients suggests an early B cell involvement in the pathogenesis of these two categories of JIA. Disclosure of Interest None declared