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FRI0354 Effects of Carbamylation and Citrullination of B and T Epitopes of Human Type II Collagen on Lymphocytes from Dr4+ Monozygotic Twins Discordant for Rheumatoid Arthritis
  1. M. De Santis1,2,
  2. F. Cavaciocchi1,2,
  3. A. Ceribelli1,2,
  4. M.S. Massarotti1,
  5. F. Meda1,
  6. E. Generali1,
  7. C.F. Selmi1,2
  1. 1Rheumatology and Clinical Immunology, Humanitas Research Hospital, Rozzano
  2. 2Biometra, University of Milan, Milan, Italy

Abstract

Background Rheumatoid arthritis (RA) susceptibility is linked to HLA DR4 and DR1. T cells in RA recognize the DR4/DR1-restricted epitope 261-273 of the human type II collagen, whereas B cells recognize the epitope 359-369. These epitopes can undergo post-translational modifications such as carbamylation and citrullination and both processes are involved in RA pathogenesis.

Objectives To investigate the role of B and T cell epitopes and their post-translational modifications on the adaptive immune response in the unique model of DR4 carrying monozygotic twins discordant for RA.

Methods PBMCs were obtained from a treatment-naïve HLA-DR4 positive woman with early RA (rheumatoid factor +, anti-CCP -, elevated CRP, bilateral wrist arthritis for 3 months) and from her healthy monozygotic twin sister (autoantibody-negative, normal CRP). Cells were cultured for 3 days with the native form of the collagen T epitope, its K264 carbamylated form (homocitT), the native form of the collagen B epitope, its R360 citrullinated form (citB) or a combination of the native and modified epitopes. After the stimulation, cells were analyzed by flow cytometry for activation, apoptosis, and cytokine polarization.

Results The activation of CD4 T cells was induced only with the modified B and T epitope stimulation in the RA twin (CD4+CD154+ in RA vs healthy; unstimulated: 1 vs 0.4%; T: 0.9 vs 1.6%; homocitT: 1.5 vs 0.7; B: 1 vs 0.6%; citB: 1.7 vs 0.1%, T + B: 0,5 vs 0,3%; homocitT + citB: 0,9 vs 0,4%). The antigen-activated CD4 T cells in the RA twin were significantly less apoptotic compared to unstimulated cells and the healthy twin (RA vs healthy; unstimulated: 37.5 vs 40%; T: 25 vs 24.1%; homocitT: 17 vs 50%; B: 30.8 vs 28%; citB: 13.9 vs 83.3%; T + B: 12.3 vs 63.6%; homocitT + citB: 19 vs 50%). Opposite from what observed in RA, the healthy twin manifested a higher increase in Th2 cells (CD4+CD154+IL4+ in RA vs healthy; unstimulated: 1.7 vs 2.1%; T: 2.9 vs 5.7%; homocitT: 3.6 vs 5.8%; T + B: 4 vs 4.9%; homocitT + citB: 3.9 vs 2.9%) compared to Th17 cells (CD4+CD154+IL17+ in RA vs healthy; unstimulated: 2.7 vs 1.7%; T: 4.1 vs 3.1%; homocitT: 4.5 vs 3.2%; T + B: 4.8 vs 3.5%; homocitT + citB: 5.5 vs 3%). In the healthy twin the Th2 increase was observed also in the antigen-activated CD8 T cells while B cell activation increased after different stimulations, but in all conditions activated B cells were apoptotic in 80% of the cases. Cytokine B cell production was not substantially altered with the epitope stimulations in the RA twin, while in the healthy twin there was a general increase in all cytokines.

Conclusions Our data obtained in the unique model of discordant monozygotic twins suggest that the exposure of collagen self-epitopes to lympocytes induces changes with pathogenic or protective effects that appear to be independent on DR4 and on post-translational antigen modifications. Further, this is associated with a greater Th17 shift in the antigen-activated CD4 T cells and with their enhanced resistance to spontaneous apoptosis in RA, while a greater Th2 shift is observed in the healthy twin. Carbamylation and citrullination of collagen epitopes may promote the activation of CD4 T cells.

Disclosure of Interest None declared

DOI 10.1136/annrheumdis-2014-eular.4278

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