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.
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.