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Celiac.com 12/12/2012 - In duodenal biopsy samples from people with active celiac disease, the transferrin receptor, CD71, is up-regulated, and promotes retro-transport of secretory immunoglobulin A (SIgA)-gliadin complexes. To better understand how interactions between SIgA and CD71 promote transepithelial transport of gliadin peptides, a team of researchers set out to determine if interactions among secretory immunoglobulin A, CD71, and transglutaminase-2 affect permeability of intestinal epithelial cells to gliadin peptides. The research team included C. Lebreton, S. Ménard, J. Abed, I.C. Moura, R. Coppo, C. Dugave, R.C. Monteiro, A. Fricot, M.G. Traore, M. Griffin, C. Cellier, G. Malamut, N. Cerf-Bensussan, and M. Heyman. They are affiliated with the Mixed Research Unit 989 of the National Institute of Health and Medical Research (INSERM UMR989) in Paris, France. For their study, the team evaluated duodenal biopsy specimens from 8 adults and 1 child with active celiac disease. The team used fluorescence-labeled small interfering RNAs against CD71 to transfect Caco-2 and HT29-19A epithelial cell lines. They used flow cytometry, immunoprecipitation, and confocal microscopy to assess interactions among IgA, CD71, and transglutaminase 2 (Tgase2). They then assessed transcytosis of SIgA-CD71 complexes and intestinal permeability to the gliadin 3H-p31-49 peptide in polarized monolayers of Caco-2 cells. To assess physical interplay between SIgA and CD71 or CD71 and Tgase2 at the apical surface of enterocytes in biopsy samples and monolayers of Caco-2 cells, the team used fluorescence resonance energy transfer and in situ proximity ligation assays. They co-precipitated CD71 and Tgase2 with SIgA, bound to the surface of Caco-2 cells. They found that SIgA-CD71 complexes were internalized and localized in early endosomes and recycling compartments, but not in lysosomes. In the presence of celiac IgA or SIgA against p31-49, transport of intact 3H-p31-49 increased significantly across Caco-2 monolayers, while soluble CD71 or Tgase2 inhibitors interfered with transport. Once it binds to apical CD71, SIgA (with or without gliadin peptides) enters a recycling pathway and avoids lysosomal degradation; this process allows apical-basal transcytosis of bound peptides. This mechanism is assisted by Tgase2 and might be involved in the pathogenesis of celiac disease. Source: Gastroenterology. 2012 Sep;143(3):698-707.e1-4. doi: 10.1053/j.gastro.2012.05.051.
Celiac.com 12/05/2011 - Class II major histocompatibility molecules are one of the main points of susceptibility for a number of autoimmune disorders, including type 1 diabetes. A team of researchers recently set out to investigate structure-based selection of small molecules to alter allele-specific MHC Class II antigen presentation The research team included Aaron W. Michels, David A. Ostrov, Li Zhang, Maki Nakayama, Masanori Fuse, Kristen McDaniel, Bart O. Roep, Peter A. Gottlieb, Mark A. Atkinson, and George S. Eisenbarth. They are variously affiliated with the Barbara Davis Center for Childhood Diabetes at the University of Colorado Denver, the Department of Pathology, Immunology and Laboratory Medicine, University of Florida College of Medicine, in Gainesville, FL, and with the Department of Immunohaematology and Blood Transfusion at Leiden University Medical Center in Leiden, The Netherlands. In the NOD mouse model of spontaneous autoimmune diabetes, Human DQ8 and I-Ag7 imparts diabetes risk by modulating presentation of specific islet peptides in the thymus and surrounding area. To define small molecules that could live in specific structural pockets along the I-Ag7 binding groove, the research team made use of an in-silico molecular docking program to review a vast “drug-like” chemical library. They were hoping to either promote or inhibit presentation to T cells of the autoantigen insulin B chain peptide, which consists of amino acids 9–23. By making use of both murine and human cells, the team's results show that small molecules can in fact influence specific TCR signals in the presence of cognate target peptides, based upon the targeted structural pocket. The effect of a compound on TCR response varied among targeted pockets, with pocket 1 and 6 compounds inhibiting TCR response, and molecules targeted at pocket 9 promoting peptide responses. It takes just nanomolar levels of the inhibitory molecules to block the insulin B chain peptide, which consists of amino acids 9–23, endogenous insulin, and islet-stimulated T cell responses. At concentrations as low as 10 nM, Glyphosine, a pocket 9 compound, enhances insulin peptide presentation to T cells, upregulates IL-10 secretion, and prevents diabetes in NOD mice. These studies offer a new way to identify small molecules that can both stimulate and inhibit T cell responses, thus offering a potential for future therapeutic treatment options. Source: Journal of Immunology doi: 10.4049/â€‹jimmunol.1100746