Julie C. Antvorskov

Dietary gluten and the development of type 1 diabetes

Gluten proteins differ from other cereal proteins as they are partly resistant to enzymatic processing in the intestine, resulting in a continuous exposure of the proteins to the intestinal immune system. In addition to being a disease-initiating factor in coeliac disease (CD), gluten intake might affect type 1 diabetes development. Studies in animal models of type 1 diabetes have documented that the pathogenesis is influenced by diet. Thus, a gluten-free diet largely prevents diabetes in NOD mice while a cereal-based diet promotes diabetes development. In infants, amount, timing and mode of introduction have been shown to affect the diabetogenic potential of gluten, and some studies now suggest that a gluten-free diet may preserve beta cell function. Other studies have not found this effect. There is evidence that the intestinal immune system plays a primary role in the pathogenesis of type 1 diabetes, as diabetogenic T cells are initially primed in the gut, islet-infiltrating T cells express gut-associated homing receptors, and mesenteric lymphocytes transfer diabetes from NOD mice to NOD/severe combined immunodeficiency (SCID) mice. Thus, gluten may affect diabetes development by influencing proportional changes in immune cell populations or by modifying the cytokine/chemokine pattern towards an inflammatory profile. This supports an important role for gluten intake in the pathogenesis of type 1 diabetes and further studies should be initiated to clarify whether a gluten-free diet could prevent disease in susceptible individuals or be used with newly diagnosed patients to stop disease progression.

Dietary gluten alters the balance of pro-inflammatory and anti-inflammatory cytokines in T cells of BALB/c mice

Several studies have documented that dietary modifications influence the development of type 1 diabetes. However, little is known about the interplay of dietary components and the penetration of diabetes incidence. In this study we tested if wheat gluten is able to induce differences in the cytokine pattern of Foxp3+ regulatory T cells, as well as Foxp3− T cells, isolated from intestinal mucosal lymphoid tissue and non‐mucosal lymphoid compartments in BALB/c mice. The gluten‐containing standard diet markedly changed the cytokine expression within Foxp3− T cells, in all lymphoid organs tested, towards a higher expression of pro‐inflammatory interferon‐γ (IFN‐γ), interleukin‐17 (IL‐17) and IL‐2. In Foxp3+ regulatory T cells, gluten ingestion resulted in a mucosal increase in IL‐17 and IL‐2 and an overall increase in IFN‐γ and IL‐4. The gluten‐free diet induced an anti‐inflammatory cytokine profile with higher proportion of transforming growth factor‐β (TGF‐β)+ Foxp3− T cells in all tested lymphoid tissues and higher IL‐10 expression within non‐T cells in spleen, and a tendency towards a mucosal increase in TGF‐β+ Foxp3+ regulatory T cells. Our data shows that the gluten‐containing standard diet modifies the cytokine pattern of both Foxp3− T cells and Foxp3+ regulatory T cells towards a more inflammatory cytokine profile. This immune profile may contribute to the higher type 1 diabetes incidence associated with gluten intake.

Impact of dietary gluten on regulatory T cells and Th17 cells in BALB/c mice.

Dietary gluten influences the development of type 1 diabetes (T1D) and a gluten-free (GF) diet has a protective effect on the development of T1D. Gluten may influence T1D due to its direct effect on intestinal immunity; however, these mechanisms have not been adequately studied. We studied the effect of a GF diet compared to a gluten-containing standard (STD) diet on selected T cell subsets, associated with regulatory functions as well as proinflammatory Th17 cells, in BALB/c mice. Furthermore, we assessed diet-induced changes in the expression of various T cell markers, and determined if changes were confined to intestinal or non-intestinal lymphoid compartments. The gluten-containing STD diet led to a significantly decreased proportion of γδ T cells in all lymphoid compartments studied, although an increase was detected in some γδ T cell subsets (CD8+, CD103+). Further, it decreased the proportion of CD4+CD62L+ T cells in Peyers patches. Interestingly, no diet-induced changes were found among CD4+Foxp3+ T cells or CD3+CD49b+cells (NKT cells) and CD3−CD49b+ (NK) cells. Mice fed the STD diet showed increased proportions of CD4+CD45RBhigh+ and CD103+ T cells and a lower proportion of CD4+CD45RBlow+ T cells in both mucosal and non-mucosal compartments. The Th17 cell population, associated with the development of autoimmunity, was substantially increased in pancreatic lymph nodes of mice fed the STD diet. Collectively, our data indicate that dietary gluten influences multiple regulatory T cell subsets as well as Th17 cells in mucosal lymphoid tissue while fewer differences were observed in non-mucosal lymphoid compartments.

Dietary gluten increases natural killer cell cytotoxicity and cytokine secretion

Dietary gluten influences the development of type 1 diabetes in nonobese diabetic (NOD) mice and biobreeding rats, and has been shown to influence a wide range of immunological factors in the pancreas and gut. In the present study, the effects of gluten on NK cells were studied in vitro and in vivo. We demonstrated that gliadin increased direct cytotoxicity and IFN‐γ secretion from murine splenocytes and NK cells toward the pancreatic beta‐cell line MIN6 cells. Additionally, stimulation of MIN6 cells led to a significantly increased proportion of degranulating C57BL/6 CD107a+ NK cells. Stimulation of C57BL/6 pancreatic islets with gliadin significantly increased secretion of IL‐6 more than ninefold. In vivo, the gluten‐containing diet led to a higher expression of NKG2D and CD71 on NKp46+ cells in all lymphoid organs in BALB/c and NOD mice compared with the gluten‐free diet. Collectively, our data suggest that dietary gluten increases murine NK‐cell activity against pancreatic beta cells. This mechanism may contribute to development of type 1 diabetes and explain the higher disease incidence associated with gluten intake in NOD mice.

Effect of Dietary Gluten on Dendritic Cells and Innate Immune Subsets in BALB/c and NOD Mice

The innate immune system is known to play an important role in oral tolerance to dietary antigens. This is important in development of celiac disease (CD) but may also be important in type 1 diabetes (T1D), and could potentially explain the reduced incidence of T1D in mice receiving a gluten-free (GF) diet. The direct in vivo effect of gluten on innate cells, and particularly dendritic cells (DC) is not sufficiently clarified. Therefore, we wished to investigate the innate cell populations of spontaneous diabetic NOD mice and healthy BALB/c mice kept on a GF or a standard (STD) gluten containing diet. We studied, by flow cytometry and reverse transcription-quantitative polymerase chain reaction (qRT-PCR), if dietary gluten induces changes in the activation of DCs and distribution of selected innate cells in lymphoid, pancreatic and intestinal tissues in BALB/c and NOD mice. We found that a GF diet increased the percentage of macrophages in BALB/c spleen and of CD11c+ DCs in BALB/c and NOD spleen. Strictly gluten-free (SGF) diet increased the percentage of CD103+ DCs in BALB/c mice and decreased percentages of CD11b+ DCs in mesenteric and pancreatic lymph nodes in BALB/c mice. SGF diet in BALB/c mice also decreased DC expression of CD40, CCR7 and MHC-II in pancreatic lymph nodes. In conclusion, GF diet changes the composition of the innate immune system in BALB/c and NOD mice and increases expression of DC activation markers in NOD mice. These results contribute to the explanation of the low diabetes incidence in GF NOD mice. This mechanism may be important in development of type 1 diabetes, celiac disease and non-celiac gluten sensitivity.

A gluten-free diet lowers NKG2D and ligand expression in BALB/c and non-obese diabetic (NOD) mice

The interplay between diet and immune parameters which could affect type 1 diabetes (T1D) pathogenesis is not sufficiently clarified. Intestinal up‐regulation of the activating receptor natural killer group 2D (NKG2D) (CD314) and its ligands is a hallmark of coeliac disease. However, the direct effect of gluten on NKG2D expression is not known. We studied, by fluorescence activated cell sorter (lymphoid tissues) and reverse transcription–quantitative polymerase chain reaction (intestine and pancreatic islets), if a gluten‐free diet (GF diet) from 4 weeks of age or a gluten‐free diet introduced in breeding pairs (SGF diet), induced changes in NKG2D expression on DX5+(CD49b) natural killer (NK) cells, CD8+ T cells and in intestinal and islet levels of NKG2D and ligands in BALB/c and non‐obese diabetic (NOD) mice. Gluten‐free NOD mice had lower insulitis (P < 0·0001); reduced expression of NKG2D on DX5+ NK cells in spleen and auricular lymph nodes (P < 0·05); and on CD8+ T cells in pancreas‐associated lymph nodes (P = 0·04). Moreover, the level of CD71 on DX5+ NK cells and CD8+ T cells (P < 0·005) was markedly reduced. GF and SGF mice had reduced expression of NKG2D and DX5 mRNA in intestine (P < 0·05). Differences in intestinal mRNA expression were found in mice at 8, 13 and 20 weeks. Intestinal expression of NKG2D ligands was reduced in SGF mice with lower expression of all ligands. In isolated islets, a SGF diet induced a higher expression of specific NKG2D ligands. Our data show that a gluten‐free diet reduces the level of NKG2D and the expression of NKG2D ligands. These immunological changes may contribute to the lower T1D incidence associated with a gluten‐free diet.

Large Gliadin Peptides Detected in the Pancreas of NOD and Healthy Mice following Oral Administration

Gluten promotes type 1 diabetes in nonobese diabetic (NOD) mice and likely also in humans. In NOD mice and in non-diabetes-prone mice, it induces inflammation in the pancreatic lymph nodes, suggesting that gluten can initiate inflammation locally. Further, gliadin fragments stimulate insulin secretion from beta cells directly. We hypothesized that gluten fragments may cross the intestinal barrier to be distributed to organs other than the gut. If present in pancreas, gliadin could interact directly with the immune system and the beta cells to initiate diabetes development. We orally and intravenously administered 33-mer and 19-mer gliadin peptide to NOD, BALB/c, and C57BL/6 mice and found that the peptides readily crossed the intestinal barrier in all strains. Several degradation products were found in the pancreas by mass spectroscopy. Notably, the exocrine pancreas incorporated large amounts of radioactive label shortly after administration of the peptides. The study demonstrates that, even in normal animals, large gliadin fragments can reach the pancreas. If applicable to humans, the increased gut permeability in prediabetes and type 1 diabetes patients could expose beta cells directly to gliadin fragments. Here they could initiate inflammation and induce beta cell stress and thus contribute to the development of type 1 diabetes.

Gluten-Free Diet Only during Pregnancy Efficiently Prevents Diabetes in NOD Mouse Offspring

Studies have documented that the pathogenesis of autoimmune diabetes is influenced by the intake of gluten. Aims. To investigate the importance of gluten exposure during pregnancy and the subsequent development of autoimmune diabetes in offspring. Methods. Nonobese diabetic mice were divided into 7 groups to receive combinations of gluten-free and standard diet before, during, or after pregnancy. Diabetes incidence in offspring was followed in each group (n = 16–27) for 310 days. Insulitis score and intestinal expression of T-cell transcription factors (RT-QPCR) were evaluated in animals from the different diet groups. Results. If mothers were fed a gluten-free diet only during pregnancy, the development of autoimmune diabetes in offspring was almost completely prevented with an incidence reduction from 62.5% in gluten-consuming mice to 8.3% (p < 0.0001) in the gluten-free group. The islets of Langerhans were less infiltrated (p < 0.001) and the intestinal expression of RORγt (Th17) (p < 0.0001) reduced in mice whose mothers were Gluten-free during pregnancy. Conclusion. A gluten-free diet exclusively during pregnancy efficiently prevents autoimmune diabetes development in offspring and reduces insulitis and intestinal expression of RORγt (Th17).

CD1d knockout mice exhibit aggravated contact hypersensitivity responses due to reduced interleukin‐10 production predominantly by regulatory B cells

Conflicting observations have been reported concerning the role of CD1d‐dependent natural killer T (NKT) cells in contact hypersensitivity (CHS), supporting either a disease‐promoting or downregulatory function. We studied the role of NKT cells in CHS by comparing the immune response in CD1d knockout (CD1d KO) and wild‐type (Wt) mice after contact allergen exposure. For induction of CHS, C57BL/6 CD1d KO mice (n = 6) and C57BL/6 Wt mice (n = 6) were sensitised with 1% (w/v) dinitrochlorobenzene (DNCB) or vehicle for three consecutive days and subsequently challenged with a single dose of 0.5% DNCB (w/v) on the ears fifteen days later. We demonstrate that CD1d KO mice, as compared with Wt littermates, have more pronounced infiltration of mononuclear cells in the skin (29.1% increase; P < 0.001), lower frequencies of interleukin‐10+ B cells (Bregs) in the spleen (53.2% decrease; P < 0.05) and peritoneal cavity (80.8% decrease; P < 0.05) and increased production of interferon‐γ (3‐fold; P < 0.05) after DNCB sensitisation and challenge, which suggests an important regulatory and protective role of CD1d‐dependent NKT cells in CHS in our model, at least in part via regulation of IL‐10 producing Bregs.

Childhood body mass index in relation to subsequent risk of type 1 diabetes—A Danish cohort study

The incidence of type 1 diabetes (T1D) is increasing, and obesity may be a contributing factor by increasing the risk and accelerating the onset. We investigated the relation between childhood body mass index z‐scores (BMIz) and the later risk of T1D, including association with age at onset of T1D. The study included 238 cases and 10 147 controls selected from the Copenhagen School Health Record Register (CSHRR). Cases of T1D were identified in the Danish Registry of Childhood and Adolescent Diabetes and 2 regional studies and linked to CSHRR. Using conditional logistic regression models, the association of childhood prediagnostic BMIz at 7 and 13 years of age and changes between these ages with subsequent risk (odds ratio, OR) of T1D was estimated. A greater BMIz at 7 and 13 years of age was associated with increased risk of T1D with OR of 1.23 (confidence interval, CI 1.09‐1.37; P = .0001) and 1.20 (CI 1.04‐1.40; P = .016), respectively. The risk was increased by upward changes in z‐scores from birth to 7 years (OR=1.21, P = .003) and from 7 to 13 years of age (OR=1.95, P = .023), but in the latter age interval also by a decline in BMIz (OR = 1.91, P = .034). There were no associations between BMIz at 7 and 13 years of age and the age of onset (P = .34 and P = .42, respectively). Increased BMIz is associated with a moderate increase in risk of T1D, but with no relation to age at onset within the analyzed age range. Increased BMIz over time is unlikely to explain the rising incidence of T1D.