Background/Purpose: B cells participate in the pathogenesis of rheumatoid arthritis (RA) through a mechanism still not fully understood. In RA, B cells are believed to plays roles in: 1) the production of autoantibodies, 2) the release of proinflammatory cytokines, and 3) T-cell activation by acting as antigen-presenting cells. Objective: To study the potential involvement of B cells as antigen-presenting cell in the arthritis synovial microenvironment

Methods: The presence of class II molecules (HLA-DR) and costimulatory molecules (CD86 and CD40) in CD20+ cells was studied by immunohistochemistry in biopsies of RA synovium. The surface-expression levels of CD27, class II molecules (HLA-DP, -DQ and -DR) and CD86 were analyzed by double-staining flow cytometry on CD20+ cells from peripheral blood (PB) and synovial fluid (SF) from 14 patients with RA and 12 with psoriatic arthritis (PA). The surface-expression levels of CD40 and CD20 on CD19+ and CD138- cells were studied in cells from both compartments by triple labeling. The expression of the interferon-induced protein, IFIT-4, which is involved in the differentiation into dendritic cells, was assessed by quantitative RT-PCR in immunoselected CD20+ cells from SF and PB of RA patients.

Results: Immunohistochemical studies showed that CD20+ B cells present in the RA synovial infiltrate express molecules involved in antigen presentation (HLA-DR) and costimulation (CD40 and CD86). In the patients included in this study the percentage of mononuclear CD20+ cells in SF (2.12±0.69%) was lower than in PB (7.44±0.62%). Flow cytometry analysis showed a significant increment in the expression levels of CD27 on B-cells from SF versus PB in both RA and PA patients, indicating that memory B cells are recruited into the inflamed synovium. CD20+ cells from SF showed an increased expression of HLA-DR and -DQ compared to PB in both RA and PA patients. HLA-DP was also elevated in SF with respect to PB in RA, although in PA, a significantly lower expression of HLA-DP was observed in SF with respect to PB. Surface expression of CD86 was higher in B cells from SF compared to those from PB in both pathologies. CD40 expression increased in SF compared to PB in PA patients; otherwise, a decrease was observed in SF with respect to PB in RA patients. Interestingly, a CD20 expression was lower in B cells (CD19+, CD138-) from SF in both RA (69.82±17.22%) and PA (54.44±15.66%) patients with respect to PB (considered 100%). Finally, qRT-PCR showed approximately a 5-fold increase in IFIT-4 mRNA content in B cells from SF compared to PB in RA patients

Conclusion:

These data show that the B cells present in the synovial microenvironment express an antigen-presenting cell phenotype, which suggests that this cell type may participate in RA pathogenesis via antigen presentation.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/role-of-cd20-b-cells-as-antigen-presenting-cells-in-arthritis/