A dendritic cell population responsible for transglutaminase 2–mediated gluten antigen presentation in celiac disease
Fu-Chen Yang, Harrison A. Besser, Hye Rin Chun, Megan Albertelli, Nielsen Q. Fernandez-Becker, Bana Jabri, Chaitan Khosla
Fu-Chen Yang, Harrison A. Besser, Hye Rin Chun, Megan Albertelli, Nielsen Q. Fernandez-Becker, Bana Jabri, Chaitan Khosla
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Research Article Gastroenterology

A dendritic cell population responsible for transglutaminase 2–mediated gluten antigen presentation in celiac disease

Abstract

In celiac disease (CeD), a gluten-dependent autoimmune disorder, transglutaminase 2 (TG2), deamidates selected glutamine residues in gluten peptides, while HLA-DQ2 presents deamidated antigens to inflammatory T cells. The cellular sources of pathogenic TG2 and DQ2 are unclear. Using chemical biology tools, we show that intestinal CD103+ dendritic cells (DCs) couple cell-surface TG2 to the endocytic LRP1 receptor to simultaneously deamidate gluten antigens and concentrate them in lysosomes. In DQ2-transgenic mice, CD103+ DCs loaded with deamidated antigens migrate from intestinal lamina propria and Peyer’s patches into mesenteric lymph nodes, where they engage T cells. In turn, gluten antigen presentation upregulates intestinal TG2 activity. The tool (HB-230) used to establish a role of CD103+ DCs in gluten antigen presentation and TG2 activation in mice also revealed that the TG2/LRP1 pathway is active in human CD14+ monocytes. Within this population of circulating monocytes, a DC subset with the gut-homing β7-integrin marker is elevated in patients with CeD with active disease compared with nonceliac controls or patients on a gluten-free diet. Our findings not only inform the cellular basis for gluten toxicity in CeD, but they also highlight the immunologic role of an enigmatic protein of growing therapeutic relevance in CeD and other immune disorders.

Authors

Fu-Chen Yang, Harrison A. Besser, Hye Rin Chun, Megan Albertelli, Nielsen Q. Fernandez-Becker, Bana Jabri, Chaitan Khosla

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Figure 2

Detection of different active forms of TG2 by HB-230.

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Detection of different active forms of TG2 by HB-230. (A) Bone marrow–de...
(A) Bone marrow–derived dendritic cells (BMDCs) from WT and TG2 knockout (TG2-KO) mice were treated with increasing concentrations of HB-230 for 90 minutes. WT BMDCs showed prominent HB-230 puncta, corresponding to lysosomes, which were absent in TG2-KO cells. (B) WT BMDCs pretreated with the LRP1 antagonist RAP (5 μM of HB-230 and 3 μM of RAP, 30 minutes) exhibited reduced HB-230 puncta formation following 90 minutes of probe treatment, indicating LRP1 is required for lysosomal delivery of TG2. (C) WT BMDCs were incubated with HB-230 (2 μM) for 5–90 minutes and costained with anti-TG2 antibody (green) and DAPI (blue), with or without cell permeabilization to detect surface or intracellular TG2, respectively. Early time points showed low red/green signal at the surface, suggesting limited catalytic activity of TG2. In permeabilized cells, HB-230 and TG2 colocalized at intermediate time points, consistent with lysosomal processing of TG2. A ~90-minute movie of the entire uptake process by a representative BMDC is available as Supplemental Video 1. (D) WT mice were orally dosed with HB-230 (10 mg/kg), and tissues were collected 2 hours later. Ileal cryosections showed four HB-230 labeling patterns: (no. 1) lysosomal puncta in lamina propria, (no. 2) subepithelial extracellular matrix (ECM) colocalization with TG2 at villus tips, (no. 3) sporadic ECM labeling in the muscularis, and (no. 4) basement membrane of villi. (E and F) Additional HB-230–labeled cells were observed in the lamina propria (E) and Peyer’s patches and mesenteric lymph nodes (MLN) (F), with perinuclear puncta (white arrows) suggestive of lysosomal localization. All images were acquired at 40× magnification.