Fine specificity of the autoimmune response to the Ro/SSA and La/SSB ribonucleoproteins

Increased non-canonical splicing of autoantigen transcripts provides the structural basis for expression of untolerized epitopes

“…Further evidence to support this concept comes from a study that showed a fine specificity of the autoimmune response to SSA and SSB ribonucleo-proteins. 7 These chimeric autoantigens may impose the endogenous danger signals for the host immune system to react, similar to that of exogenous danger signals elaborated by pathogens. Fifth, differential expression of autoantigen isoforms has been shown to occur in experimentally induced autoimmune myocarditis.…”

“…1 Because the length of peptides needed for antibody binding, MHC class I binding, and MHC class II binding is 8 to 15 amino acids, additional exons introduced by alternative splicing are long enough to produce novel antigenic epitopes. Because immune responses to autoantigen epitopes are highly specific, 7 alternative splicing of exons could provide the structural basis for expression of novel untolerized antigen epitopes with altered antigenic properties and hence create the potential to break existing immune tolerance. 8,9 Previously, 19 autoantigens were identified as having alternatively spliced isoforms, [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] suggesting that alternative splicing may indeed contribute to the regulated expression of autoantigens.…”

T cell epitopes of the La/SSB autoantigen in humanized transgenic mice expressing the hLa class II haplotype DRB1*0301/DQB1*0201

“…Paraformaldehyde-fixed, EpsteinBarr virus-transformed B cells (1 ϫ 10 6 /well) expressing DR3 and DQ2 were incubated with previously described mycobacterial peptides, MT65kDa [3][4][5][6][7][8][9][10][11][12][13] (DR3 specific) or MB65kDa 243-265 Y (DQ2 specific) (23), at concentrations calculated to give 50% maximal binding and unlabeled competitive hLa peptides at 100-fold molar excess. Samples were incubated for 24 hours at 37°C followed by lysis in PBS containing 50 mM Tris (pH 8.0), 0.5M NaCl, 0.5% Ipegal 630 (Sigma, St. Louis, MO), and protease inhibitors (Complete Cocktail Tablets; Roche, Basel, Switzerland).…”

“…An in vitro competitive binding assay was performed using biotinylated reporter peptides MT65kDa [3][4][5][6][7][8][9][10][11][12][13] (DR3 specific) or MB65kDa 243-255 Y (DQ2 specific) to identify HLA-DR3 or HLA-DQ binding peptides within hLa. The panel of 155 overlapping 15-mer hLa peptides with a 12-13-amino acid overlap was tested for binding to DR3 and DQ2.…”

“…Autoantibodies directed against La are a distinctive feature of Sjögren's syndrome (SS), are present at lower frequencies in systemic lupus erythematosus (SLE) (1), and are associated with neonatal lupus and complete congenital heart block (2). Mechanisms driving autoimmune responsiveness against La remain obscure, although the magnitude of antibody responses (3), recognition of multiple regions of targeted autoantigens (4), and evidence that these antibodies are class switched and somatically hypermutated (2,5) imply an autoantigen-driven, T cell-dependent process.…”