Interactions Among Secretory Immunoglobulin A, CD71, and Transglutaminase-2 Affect Permeability of Intestinal Epithelial Cells to Gliadin Peptides
INSERM, UMR989, Paris, France. Gastroenterology
(Impact Factor: 16.72).
06/2012; 143(3):698-707.e1-4. DOI: 10.1053/j.gastro.2012.05.051
The transferrin receptor (CD71) is up-regulated in duodenal biopsy samples from patients with active celiac disease and promotes retrotransport of secretory immunoglobulin A (SIgA)-gliadin complexes. We studied intestinal epithelial cell lines that overexpress CD71 to determine how interactions between SIgA and CD71 promote transepithelial transport of gliadin peptides.
We analyzed duodenal biopsy specimens from 8 adults and 1 child with active celiac disease. Caco-2 and HT29-19A epithelial cell lines were transfected with fluorescence-labeled small interfering RNAs against CD71. Interactions among IgA, CD71, and transglutaminase 2 (Tgase2) were analyzed by flow cytometry, immunoprecipitation, and confocal microscopy. Transcytosis of SIgA-CD71 complexes and intestinal permeability to the gliadin 3H-p31-49 peptide were analyzed in polarized monolayers of Caco-2 cells.
Using fluorescence resonance energy transfer and in situ proximity ligation assays, we observed physical interactions between SIgA and CD71 or CD71 and Tgase2 at the apical surface of enterocytes in biopsy samples and monolayers of Caco-2 cells. CD71 and Tgase2 were co-precipitated with SIgA, bound to the surface of Caco-2 cells. 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; this transport was inhibited by soluble CD71 or Tgase2 inhibitors.
Upon binding 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 facilitated by Tgase2 and might be involved in the pathogenesis of celiac disease.
Available from: Constanza Bondar
- "In addition, since CD138+ plasma cells express CXCR3, the CXCL10/CXCR3 chemokine axis would take a relevant role in the recruitment of plasma cells into the LP. Interestingly, CD138+ plasma cells produce locally anti-gliadin and anti-TG2 antibodies which play important roles in CD pathogenesis , . "
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ABSTRACT: Lymphocytic infiltration in the lamina propria (LP), which is primarily composed of CD4(+) Th1 cells and plasma cells, and increased numbers of intraepithelial lymphocytes (IELs), is a characteristic finding in active celiac disease (CD). Signals for this selective cell recruitment have not been fully established. CXCR3 and its ligands, particularly CXCL10, have been suggested to be one of the most relevant pathways in the attraction of cells into inflamed tissues. In addition, CXCR3 is characteristically expressed by Th1 cells. The aim of this work was to investigate the participation of the chemokine CXCL10/CXCR3 axis in CD pathogenesis. A higher concentration of CXCL10 was found in the serum of untreated CD patients. The mRNA levels of CXCL10 and CXCL11 but not CXCL9 were significantly higher in duodenal biopsies from untreated CD patients compared with non-CD controls or treated patients. The results demonstrate that CXCL10 is abundantly produced in untreated CD and reduced in treated patients, and the expression of CXCL10 was found to be correlated with the IFNγ levels in the tissue. Plasma cells and enterocytes were identified as CXCL10-producing cells. Moreover, the CXCL10 expression in intestinal tissues was upregulated by poly I:C and IL-15. IELs, LP T lymphocytes, and plasma cells, which infiltrate the intestinal mucosa in untreated CD, express CXCR3. The CXCR3/CXCL10 signalling axis is overactivated in the small intestinal mucosa in untreated patients, and this finding explains the specific recruitment of the major cell populations that infiltrate the epithelium and the LP in CD.
Available from: Robert A Fenton
- "So far, in vivo studies have provided limited evidence for expression of the megalin/cubilin/amnionless receptor complex in the terminal ileum [13,14] (reviewed in 15, which plays a role in apical endocytosis of he intrinsic factor-vitamin B12 complex and possibly Tf . Moreover, the Tf receptor may mediate apical uptake and transcytosis of Tf though, in contrast to in vitro studies [11,17,18], evidence for apical expression of the Tf receptor in vivo is sparse . Here we focussed on the possibility that endo-/transcytosis of proteins, such as Tf, but also MT and PC3, may also be mediated by the r24p3-R/hNGAL-R in the intestine. "
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ABSTRACT: The lipocalin 2//NGAL/24p3 receptor (NGAL-R/24p3-R) is expressed in rodent distal nephron where it mediates protein endocytosis. The mechanisms of apical endocytosis and transcytosis of proteins and peptides in the intestine are poorly understood. In the present study, the expression and localization of rodent 24p3-R (r24p3-R) and human NGAL-R (hNGAL-R) was investigated in intestinal segments by immunofluorescence and confocal laser scanning microscopy, immunohistochemistry and immunoblotting. r24p3-R/hNGAL-R was also studied in human Caco-2 BBE cells and CHO cells transiently transfected with r24p3-R by immunofluorescence microscopy, RT-PCR and immunoblotting of plasma membrane enriched vesicles (PM). To assay function, endocytosis/transcytosis of putative ligands phytochelatin (PC3), metallothionein (MT) and transferrin (Tf) was assayed by measuring internalization of fluorescence-labelled ligands in Caco-2 BBE cells grown on plastic or as monolayers on Transwell inserts. The binding affinity of Alexa 488-PC3 to colon-like Caco-2 BBE PM was quantified by microscale thermophoresis (MST). r24p3-R/hNGAL-R expression was detected apically in all intestinal segments but showed the highest expression in ileum and colon. Colon-like, but not duodenum-like, Caco-2 BBE cells expressed hNGAL-R on their surface. Colon-like Caco-2 BBE cells or r24p3-R transfected CHO cells internalized fluorescence-labelled PC3 or MT with half-maximal saturation at submicromolar concentrations. Uptake of PC3 and MT (0.7 µM) by Caco-2 BBE cells was partially blocked by hNGAL (500 pM) and an EC 50 of 18.6 ± 12.2 nM was determined for binding of Alexa 488-PC3 to PM vesicles by MST. Transwell experiments showed rapid (0.5-2 h) apical uptake and basolateral delivery of fluorescent PC3/MT/Tf (0.7 µM). Apical uptake of ligands was significantly blocked by 500 pM hNGAL. hNGAL-R dependent uptake was more prominent with MT but transcytosis efficiency was reduced compared to PC3 and Tf. Hence, r24p3-R/hNGAL-R may represent a high-affinity multi-ligand receptor for apical internalization and transcytosis of intact proteins/peptides by the lower intestine.
Available from: Alessio Fasano
- "Further, persistent presence of inflammatory mediators such as TNF-α and interferon (IFN)-γ has been shown to increase the permeability across the endothelial and epithelial layers [19, 20], suggesting that the initial breach of the intestinal barrier function caused by zonulin can be perpetuated by the inflammatory process after the access of gliadin to the submucosa . Additionally, evidence exists suggesting also a transcellular passage of gliadin, particularly when the mucosal damage is already established and the transferrin receptor (CD71) that mediates this transport is expressed on the luminal side of enterocytes, so promoting retrotransport of secretory immunoglobulin (SIg) A-gliadin complexes [22, 23]. Direct evidence of the rapid activation of the innate immune system has been proven in organ culture studies. "
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ABSTRACT: Celiac disease (CD) is an immune-mediated enteropathy triggered by the ingestion of gluten in genetically susceptible individuals. Gluten is a protein component in wheat and other cereals like rye and barley. At present, the only available treatment is a strict gluten-free diet. Recent advances have increased our understanding of the molecular basis for this disorder. Last decade has seen new scientific developments in this disease and led to the formulation of new concepts of pathophysiology that offer possible targets for new treatments or interventions integrative to the gluten-free diet.
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