Molecular Mimicry at the Gut–Immune Interface: A Mechanistic Link to Type 1 Diabetes

Type 1 diabetes (T1D) arises from T cell-mediated destruction of pancreatic β-cells. However, genetic susceptibility alone cannot account for the increasing incidence and earlier onset of T1D, suggesting a substantial contribution from environmental factors, particularly the gut microbiota. This review synthesises recent human, multiomics and experimental evidence linking gut microbiota dysbiosis and microbial metabolites to β-cell autoimmunity. We focus on two converging mechanisms: (1) metabolite-driven disruption of intestinal barrier integrity and immune regulation, and (2) molecular mimicry between microbial peptides and islet autoantigens that activate autoreactive T cells. Across human cohorts and animal models, T1D-associated dysbiosis features reduced short-chain fatty acid (SCFA)-producing bacteria (e.g., Faecalibacterium, Roseburia) and increased pro-inflammatory taxa (e.g., Bacteroides, Streptococcus spp.). SCFA deficiency compromises Treg induction and gut barrier stability, facilitating antigen translocation. Several gut-derived peptides, such as the Parabacteroides distasonis hprt4-18 peptide, share sequence homology with insulin and other islet antigens, activate insulin-reactive T cells and accelerate diabetes in NOD mice, supporting a role for molecular mimicry. Interventional approaches including FMT, probiotics and prebiotics show promise but remain heterogeneous; their efficacy is highly strain-, timing- and context-dependent and translation from animal studies to humans is still limited. Therapeutically targeting the gut-islet axis, through modulation of microbiota, microbial metabolites or cross-reactive antigens, offers potential for disease prevention or adjunctive treatment. We highlight emerging biomarkers, including MAIT-cell phenotypes, antimicrobial peptide reactivity and microbiome-derived functional signatures, and emphasise the need for stratified clinical trial designs based on age, genotype and baseline microbiota composition to address current variability. The microbiota-metabolite-molecular mimicry axis provides a coherent mechanistic framework linking gut dysbiosis to T1D pathogenesis. Advancing these insights into clinical application will require rigorous, genotype-stratified human studies and standardised, transparent methodological approaches.