POS0369 IN RHEUMATOID ARTHRITIS, IgA AUTOANTIBODIES ARE PRESENT IN A POLYMERIC STATE; CLUES FOR A MUCOSAL ORIGIN OF THE AUTOIMMUNE RESPONSE?

Background:

Rheumatoid arthritis (RA) is a prevalent autoimmune disease characterized by B-cells that produce autoantibodies against post translationally modified proteins, such as anti-citrullinated protein antibodies (ACPA), anti-acetylated protein antibodies (AAPA) and anti-carbamylated protein antibodies (a-CarP), together called anti-modified protein antibodies (AMPA). What initially leads to the breach in tolerance and eventually causes rheumatoid arthritis is still unknown, but there are indications, such as changes in the fecal microbiome composition of RA patients, that this tolerance breach takes place in the intestines.

Objectives:

Since antibody responses in the intestines are dominated by IgA, particularly in dimeric form, we set out to characterize the AMPA IgA response in detail.

Methods:

Sera from ACPA-positive RA, ACPA-negative RA and healthy donors were fractionated using size exclusion chromatography, separating proteins on size. Next, all fractions were tested by ELISA for ACPA IgA, AAPA IgA and anti-CarP IgA, as well as total IgM, IgA and IgG. Additionally, AMPA were purified from serum to determine their size by IgA western blot and to investigate the IgA tailpiece by tandem mass spectrometry (MS/MS). Lastly, monoclonal IgA was produced with both tailpiece variants, after which its ability to polymerize was analyzed.

Results:

Intriguingly, of all AMPA IgA, ~70% was found to be polymeric, while total IgA contained only ~20% polymeric IgA. MS/MS analysis furthermore showed a difference in the AMPA IgA tailpiece: in the dimeric fraction ~60% had the complete tailpiece, while in the monomeric fraction this was ~20%. Recombinant IgA with such a complete tailpiece formed up to ~90% polymers, while this was ~40% in IgA with a truncated tailpiece.

Conclusion:

These data indicate that AMPA IgA responses are differently regulated compared to the total IgA antibody response and that the tailpiece might be related to a difference in polymer formation. Moreover, the high abundance of polymeric AMPA IgA suggests a mucosal origin.

REFERENCES:

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Acknowledgements:

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Disclosure of Interests:

Anouk G. van Mourik: None declared, Sanne Reijm: None declared, Alice Bacon: None declared, Myrthe A.M van Delft: None declared, Nivine Levarht: None declared, Rayman Tjokrodirijo: None declared, Peter van Veelen: None declared, Leendert A Trouw Research funding from INOVA diagnostics, part of Werfen, Rene E.M. Toes Research funding from INOVA diagnostics, part of Werfen, Karin A. van Schie: None declared, Diane van der Woude Galapagos, Galapagos.