From Proteopediaproteopedia link
Structure of the MHC class II molecule HLA-DQ8 bound with a deamidated gluten peptide
[DQA1_HUMAN] Binds peptides derived from antigens that access the endocytic route of antigen presenting cells (APC) and presents them on the cell surface for recognition by the CD4 T-cells. The peptide binding cleft accommodates peptides of 10-30 residues. The peptides presented by MHC class II molecules are generated mostly by degradation of proteins that access the endocytic route, where they are processed by lysosomal proteases and other hydrolases. Exogenous antigens that have been endocytosed by the APC are thus readily available for presentation via MHC II molecules, and for this reason this antigen presentation pathway is usually referred to as exogenous. As membrane proteins on their way to degradation in lysosomes as part of their normal turn-over are also contained in the endosomal/lysosomal compartments, exogenous antigens must compete with those derived from endogenous components. Autophagy is also a source of endogenous peptides, autophagosomes constitutively fuse with MHC class II loading compartments. In addition to APCs, other cells of the gastrointestinal tract, such as epithelial cells, express MHC class II molecules and CD74 and act as APCs, which is an unusual trait of the GI tract. To produce a MHC class II molecule that presents an antigen, three MHC class II molecules (heterodimers of an alpha and a beta chain) associate with a CD74 trimer in the ER to form a heterononamer. Soon after the entry of this complex into the endosomal/lysosomal system where antigen processing occurs, CD74 undergoes a sequential degradation by various proteases, including CTSS and CTSL, leaving a small fragment termed CLIP (class-II-associated invariant chain peptide). The removal of CLIP is facilitated by HLA-DM via direct binding to the alpha-beta-CLIP complex so that CLIP is released. HLA-DM stabilizes MHC class II molecules until primary high affinity antigenic peptides are bound. The MHC II molecule bound to a peptide is then transported to the cell membrane surface. In B-cells, the interaction between HLA-DM and MHC class II molecules is regulated by HLA-DO. Primary dendritic cells (DCs) also to express HLA-DO. Lysosomal miroenvironment has been implicated in the regulation of antigen loading into MHC II molecules, increased acidification produces increased proteolysis and efficient peptide loading. [GDA9_WHEAT] Gliadin is the major seed storage protein in wheat.
Publication Abstract from PubMed
The risk of celiac disease is strongly associated with human leukocyte antigen (HLA) DQ2 and to a lesser extent with HLA DQ8. Although the pathogenesis of HLA-DQ2-mediated celiac disease is established, the underlying basis for HLA-DQ8-mediated celiac disease remains unclear. We showed that T helper 1 (Th1) responses in HLA-DQ8-associated celiac pathology were indeed HLA DQ8 restricted and that multiple, mostly deamidated peptides derived from protease-sensitive sites of gliadin were recognized. This pattern of reactivity contrasted with the more absolute deamidation dependence and relative protease resistance of the dominant gliadin peptide in DQ2-mediated disease. We provided a structural basis for the selection of HLA-DQ8-restricted, deamidated gliadin peptides. The data established that the molecular mechanisms underlying HLA-DQ8-mediated celiac disease differed markedly from the HLA-DQ2-mediated form of the disease. Accordingly, nondietary therapeutic interventions in celiac disease might need to be tailored to the genotype of the individual.
A structural and immunological basis for the role of human leukocyte antigen DQ8 in celiac disease.,Henderson KN, Tye-Din JA, Reid HH, Chen Z, Borg NA, Beissbarth T, Tatham A, Mannering SI, Purcell AW, Dudek NL, van Heel DA, McCluskey J, Rossjohn J, Anderson RP Immunity. 2007 Jul;27(1):23-34. Epub 2007 Jul 12. PMID:17629515
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.