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We are exposed to millions of microbial and dietary antigens via the gastrointestinal tract, which likely play a key role in type 1 diabetes (T1D). We differentiated the effects of these two major environmental factors on gut immunity and T1D. Diabetes-prone BioBreeding (BBdp) rats were housed in specific pathogen-free (SPF) or germ-free (GF) conditions and weaned onto diabetes-promoting cereal diets or a protective low-antigen hydrolyzed casein (HC) diet, and T1D incidence was monitored. Fecal microbiota 16S rRNA genes, immune cell distribution, and gene expression in the jejunum were analyzed. T1D was highest in cereal-SPF (65%) and cereal-GF rats (53%) but inhibited and delayed in HC-fed counterparts. Nearly all HC-GF rats remained diabetes-free, whereas HC-fed SPF rats were less protected (7 vs. 29%). Bacterial communities differed in SPF rats fed cereal compared with HC. Cereal-SPF rats displayed increased gut CD3+ and CD8α+ lymphocytes, ratio of Ifng to Il4 mRNA, and Lck expression, indicating T-cell activation. The ratio of CD3+ T cells expressing the Treg marker Foxp3+ was highest in HC-GF and lowest in cereal-SPF rats. Resident CD163+ M2 macrophages were increased in HC-protected rats. The cathelicidin antimicrobial peptide (Camp) gene was upregulated in the jejunum of HC diet–protected rats, and CAMP+ cells colocalized with CD163. A cereal diet was a stronger promoter of T1D than gut microbes in association with impaired gut immune homeostasis.

OBJECTIVEThere is evidence of gut barrier and immune system dysfunction in some patients with type 1 diabetes, possibly linked with exposure to dietary wheat polypeptides (WP). However, questions arise regarding the frequency of abnormal immune responses to wheat and their nature, and it remains unclear whether such responses are diabetes specific.RESEARCH DESIGN AND METHODSIn type 1 diabetic patients and healthy control subjects, the immune response of peripheral CD3+ T-cells to WPs, ovalbumin, gliadin, α-gliadin 33-mer peptide, tetanus toxoid, and phytohemagglutinin was measured using a carboxyfluorescein diacetate succinimidyl ester (CFSE) proliferation assay. T–helper cell type 1 (Th1), Th2, and Th17 cytokines were analyzed in WP-stimulated peripheral blood mononuclear cell (PBMNC) supernatants, and HLA was analyzed by PCR.RESULTSOf 42 patients, 20 displayed increased CD3+ T-cell proliferation to WPs and were classified as responders; proliferative responses to other dietary antigens were less pronounced. WP-stimulated PBMNCs from patients showed a mixed proinflammatory cytokine response with large amounts of IFN-γ, IL-17A, and increased TNF. HLA-DQ2, the major celiac disease risk gene, was not significantly different. Nearly all responders carried the diabetes risk gene HLA-DR4. Anti-DR antibodies blocked the WP response and inhibited secretion of Th1 and Th17 cytokines. High amounts of WP-stimulated IL-6 were not blocked.CONCLUSIONST-cell reactivity to WPs was frequently present in type 1 diabetic patients and associated with HLA-DR4 but not HLA-DQ2. The presence of an HLA-DR–restricted Th1 and Th17 response to WPs in a subset of patients indicates a diabetes-related inflammatory state in the gut immune tissues associated with defective oral tolerance and possibly gut barrier dysfunction.

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