Effects of type II collagen epitope carbamylation and citrullination in HLA-DR4+ monozygotic twins discordant for rheumatoid arthritis

The aim of the study is to investigate the effect of the native, citrullinated or carbamylated type II-human collagen T cell- and B cell-epitopes on the adaptive immune response in rheumatoid arthritis (RA). Peripheral blood T and B cells obtained from an HLA-DR4+ woman with early RA, her healthy monozygotic twin, and an unrelated HLA-DR3+ woman with early RA were analyzed for activation (CD154/CD69), apoptosis (annexin/7-AAD), cytokine production (INFγ/IL-17/IL-4/IL-10/IL-6), and functional phenotype (CD45Ra/CCR7) after stimulation with the collagen native T cell-epitope (T261-273), the K264 carbamylated T cell-epitope (carT261-273), the native B cell-epitope (B359-369), or the R360 citrullinated B cell-epitope (citB359-369), and the combinations of these. The T cell memory compartment was activated by T cell-epitopes in both discordant DR4+ twins, but not in the DR3+ RA. The collagen-specific activation of CD4+ T cells was induced with both the native and carbamylated T cell-epitopes only in the RA twin. Both T cell-epitopes also induced IL-17 production in the RA twin, but a greater IL-4 and IL-10 response in the healthy twin. The citrullinated B cell-epitope, particularly when combined with the carbamylated T cell-epitope, induced B cell activation and an increased IL-6/IL-10 ratio in the RA twin compared to a greater IL-10 production in the healthy twin. Our data suggest that circulating collagen-specific T and B cells are found in HLA-DR4+ subjects, but only in RA activated cells express costimulatory molecules and produce pro-inflammatory cytokines. Carbamylation and citrullination further modulate the activation and cytokine polarization of T and B cells. This article is protected by copyright. All rights reserved.