Wen et al. show that there are gut microbial antigens sharing significant homology with the host pancreatic protein peptide IGRP and that can drive self-reactive T cell activation and accelerate diabetes in NOD mice.

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Type 1 diabetes (T1D) is a T cell-mediated autoimmune disease that involves the slow, progressive destruction of islet β-cells and loss of insulin production, as a result of interaction with environmental factors, in genetically susceptible individuals. The gut microbiome is established very early in life. Commensal microbiota establish mutualism with the host and form an important part of the environment to which individuals are exposed in the gut, providing nutrients and shaping immune responses. Here, we studied the impact of targeting most Gram-negative bacteria in the gut of Non obese diabetic (NOD) mice at different time points in their life, using a combination of three antibiotics - neomycin, polymyxin B and streptomycin (NPS), on diabetes development. We found that the prenatal period is a critical time for shaping the immune tolerance in the progeny, influencing development of autoimmune diabetes. Prenatal NPS treatment protected NOD mice from diabetes development through alterations in the gut microbiota, as well as induction of tolerogenic antigen-presenting cells (APCs), which led to reduced activation of diabetogenic CD8 T cells. Most importantly, we found that the protective effect was age-dependent and the most profound protection was found when the mice were treated before birth. This indicates the importance of the prenatal environment and early exposure to commensal bacteria in shaping the host immune system and health.

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