Background Anti-citrulline protein antibodies (ACPA) are a hallmark of HLA-associated RA, but it is still not established whether these antibodies represent a cause or a consequence of arthritis. It is however clear that such antibodies can enhance murine arthritis, but a corresponding effect in patients is difficult to prove.
Objectives We have approached this question by assessing the specificity and immunoglobulin gene characteristics of B cells derived from RA synovial fluid of RA.
Methods We have utilized a method that allows in vitro production of monoclonal antibodies derived from single human memory B cells. To this end we have cloned single flow cytometry purified CD19+IgG+ B cells from synovial fluid of four ACPA+ and three ACPA- RA patients and analyzed the seqences for mutational patterns. Moreover, we have expressed recombinant monoclonal antibodies from three of the ACPA+ and one ACPA- RA patient and tested, by ELISA, the generated antibodies for reactivity to different known citrullinated antigens.
Results On the molecular level, striking differences were found between ACPA+ and ACPA- patients taking into consideration the mutational pattern of the Ig genes. Indeed, based on DNA sequences, we could demonstrate that B cells from ACPA+ patients did not have more total mutations than ACPA- patients but when focusing on the CDR1, 2 and 3 regions of the Ig variable region, the ACPA+ clones clones displayed strikingly more replacement mutations than did the ACPA- clones.
Regarding the specificity of the generated monoclonal antibodies, our results so far show citrulline reactive antibodies could be found from the ACPA+ but not from the ACPA- RA patient. These recombinant antibodies demonstrated reactivity, to variable degrees, to CCP and different citrullinated antigens including citrullinated a-enolase, fibrinogen, and vimentin.
Conclusions In summary, our data suggest that citrulline-reactive B cells are common in synovial fluid and the Ig molecules bear clear signs of antigen-driven maturation.
Disclosure of Interest None Declared
Statistics from Altmetric.com
If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.