Objective: Serum anti-citrullinated protein/peptides antibodies (ACPA) are a valuable diagnostic parameter that might be involved in rheumatoid arthritis (RA) pathogenesis. CD95-dependent apoptosis is defective in RA synovium. The present study explores the occurrence of ACPA IgG, and the CD95-mediated control of ACPA IgG-secreting plasma cells (PC) in RA patients.
Methods: Mononuclear cells (MC) were purified from synovial fluid (SF) and peripheral blood (PB) of 15 RA patients. PC capable of secreting ACPA IgG were detected in MC cultures. ACPA IgG present in serum and SF, and PB and SF MC culture supernatant was measured by ELISA. CD95, CD27 and CD138 expression was examined on RA PC identified as CD19(low) CD38(high) cells by flow cytometry. CD95-ligation was obtained by treatment of cultured MC with the anti-CD95 Ab CH11. Apoptotic PC were identified as Annexin-V+.
Results: ACPA IgG level was found higher in patients' SF than in their serum. PC were detectable in SF and PB, and exhibited high CD95 and CD27 expression. In contrast, SF, but not PB, PC expressed elevated levels of CD138. SF, but not PB, PC actively secreted ACPA IgG in cultures, in a linear fashion for at least 14 days, and CD95-ligation markedly reduced this activity and provoked PC apoptosis.
Conclusions: The results suggest that RA synovium is a prominent site for ACPA IgG formation and for the accumulation of ACPA IgG-secreting PC exhibiting prolonged survival, probably due to RA defective CD95-mediated control.