Posttranslational Modification of HLA-DQ Binding Islet Autoantigens in Type 1 Diabetes

Abstract

Posttranslational modification (PTM) of islet autoantigens can cause lack of central tolerance in type 1 diabetes (T1D). Tissue transglutaminase (tTG), involved in PTM of gluten antigens in celiac disease, creates negatively charged peptides favored by T1D-predisposing HLA-DQ molecules, offering an attractive candidate modifying islet autoantigens in T1D. The highly predisposing HLA-DQ8cis/trans molecules share preferences for negatively charged peptides, as well as distinct peptide-binding characteristics that distinguish their peptide-binding repertoire. We screened islet autoantigens with the tTG substrate motif for candidate-modified epitopes binding to HLA-DQ8cis/trans and identified 31 candidate islet epitopes. Deamidation was confirmed for 28 peptides (90%). Two of these epitopes preferentially bound to HLA-DQ8cis and six to HLA-DQ8trans upon deamidation, whereas all other peptides bound equally to HLA-DQ8cis/trans. HLA-DQ8cis-restricted T cells from a new-onset T1D patient could only be generated against a deamidated proinsulin peptide, but cross-reacted with native proinsulin peptide upon restimulation. The rate of T-cell autoreactivity in recent-onset T1D patients extended from 42% to native insulin to 68% adding responses to modified proinsulin, versus 20% and 37% respectively, in healthy donors. Most patients responded by interferon-g, whereas most healthy donors produced interleukin-10 only. Thus, T-cell autoreactivity exists to modified islet epitopes that differs in quality and quantity between patients and healthy donors.

Autoreactive T cells in type 1 diabetes

“…Autoreactive T cells exhibit proinflammatory cytokine profiles in T1D patients and regulatory profiles in healthy subjects (85,110,111). T1D patients exhibit defects in peripheral tolerance, including impaired Treg function (112,113) and effector T cell (Teff) resistance to Treg suppression (114).…”

Antibodies to post-translationally modified insulin in type 1 diabetes

“…Although this mechanism is well established in other autoimmune diseases such as coeliac disease and rheumatoid arthritis [6,7], there is scant evidence available for type 1 diabetes [8][9][10][11][12]. We have previously shown that patients with type 1 diabetes had increased levels of autoantibodies against collagen type II modified by ROS, and that this response was under the genetic control of the HLA-DRB1*04 shared epitope alleles [13].…”

Dendritic Cells Guide Islet Autoimmunity through a Restricted and Uniquely Processed Peptidome Presented by High-Risk HLA-DR

“…PPI [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] , containing the WGPDPAAA core sequence, bound to HLA-DR4 (Fig. 6, Table I).…”

“…Table I). Two overlapping PPI peptides were eluted from HLA-DR4: PPI [14][15][16][17][18][19][20][21][22][23][24] and PPI [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] ( Fig. 2).…”

“…PBMC were freshly isolated by Ficoll centrifugation and resuspended in culture medium (IMDM (Life Technologies BRL, Paisely, U.K.) containing 10% heat-inactivated pooled human serum). PBMC were subsequently tested for the presence of autoreactive CD4 T cells using ELISPOT as described before (27).…”