Mechanisms of CD23 hyperexpression on B cells from patients with rheumatoid arthritis

Objective. To analyze the mechanisms involved in the characteristic hyperex pression of CD23 on peripheral blood B cells from patients with rheumatoid arthritis (RA). Methods. Peripheral blood mononuclear cells (PBMC) were obtained from patie nts with active disease and activated during 18 h with an anti-CD3 monoclon al antibody in the presence or absence of blocking antibodies to CD154 or C D40. PBMC were further purified by rosetting and CD23 expression was assess ed on B cells by flow cytometry after double staining (CD19/CD23). Lymphocy tes were also isolated from synovial fluid (SF), CD154 expression was analy zed on PB or SF CD4+ T cells after double staining (CD4/CD154) by flow cyto metry at basal conditions and after different stimuli [anti-CD3 or phorbol myristic acetate (PMA) plus ionomycin], Go-culture experiments between SF a nd PB cells were performed to analyze the involvement of the CD40-CD154 int eraction on CD23 expression. CD154 and CD23 expression was also analyzed on synovial membrane by immunohistochemical techniques. Results. A high proportion of activated CD23 B cells was detected in patien ts with RA. Blocking experiments with both anti-CD40 and anti-CD154 Mab sho wed a significant reduction in the proportion of PB B cells expressing CD23 . Following activation with anti-CD3 Mab or PMA plus ionomycin, CD154 expre ssion was mainly induced on PB CD4+ T cells. In co-culture experiments, SF T cells were more efficient than PB T cells in inducing CD40 dependent CD23 expression on PB B cells. In addition, CD4+ T cells from synovial membrane clearly expressed CD154. Conclusion. Our results establish a link between CD154-CD40 pathway and CD2 3 expression on PB B cells from patients with RA. T cells from the synovial microenvironment were active participants in this CD23 expression, presuma bly in the context of cell recirculation.