[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Endocrine system](https://durgical.com/en/general-pathology/areas/endocrine/) › Type 1 diabetes # Type 1 diabetes - Mechanism In type 1 diabetes, the immune system destroys the insulin-making cells. People need insulin for life. Updated Nov 12, 2026 ## Key points - Strongest genetic risk: HLA class II, DR3 and DR4 with DQ8; other genes include INS (VNTR in the promoter), PTPN22, CTLA4 and IL2RA. - Autoantibodies: insulin, GAD65, IA-2 and ZnT8; their number predicts progression. - Effector cells: CD8 cytotoxic T cells kill beta cells; CD4 Th1 cells and IFN-gamma activate macrophages. - Insulitis: lymphocytes in and around islets early; later islets lose beta cells (only alpha and delta cells remain). - Environmental triggers proposed: enteroviruses (coxsackie), molecular mimicry, diet and microbiome. - Classic triad: polyuria, polydipsia, polyphagia, with weight loss and ketoacidosis. ## What it is Type 1 diabetes is an autoimmune disease in which T cells destroy pancreatic beta cells. Autoantibodies appear years before symptoms, and the disease becomes overt when most beta cells are gone. It usually starts in childhood or adolescence, though it can begin at any age, and it shares HLA risk with other autoimmune diseases. ## Structure - Early: lymphocytic infiltrate (insulitis), mainly CD8 T cells, in and around islets. - Late: small islets made only of non-beta cells; insulin immunostaining is absent. - Exocrine pancreas: atrophy and a smaller organ. - Insulin-dependent childhood diabetes can also be seen in infants of diabetic mothers as beta-cell hyperplasia (a different, reactive change). ## Step by step - A genetically susceptible child (HLA-DR3/DR4-DQ8) has defective central and peripheral tolerance to beta-cell antigens. - An environmental trigger (perhaps a virus) injures beta cells and exposes antigens. - Autoreactive CD4 T cells are activated and help CD8 T cells and B cells; autoantibodies appear. - CD8 T cells and cytokines destroy beta cells progressively over years (insulitis). - When roughly most of the beta-cell mass is lost, hyperglycaemia appears; a brief honeymoon may follow insulin start. ## Markers - GAD65 antibody - IA-2 antibody - Insulin autoantibody - ZnT8 antibody - Low C-peptide ## Clinical notes - Onset is often with diabetic ketoacidosis. - Latent autoimmune diabetes of adults (LADA) is slow-onset type 1 that can be mistaken for type 2. - Associated autoimmunity: Hashimoto thyroiditis, coeliac disease, Addison disease (APS-2). ## Memory aid In type 1 the islet is a crime scene: CD8 detectives turned killers, and the antibody fingerprints appear long before the body is found. ## Test yourself Think of the answer, then tap the question to see it. ## Which HLA haplotypes carry the highest risk for type 1 diabetes? HLA-DR3 and DR4, especially with DQ8 (DR3/DR4 heterozygotes have the highest risk). ## What is insulitis? A lymphocytic, mainly CD8 T-cell, infiltrate in and around the islets during active beta-cell destruction. ## Which three islet autoantibodies are used in type 1 diabetes? Anti-GAD65, anti-IA-2, anti-insulin (also anti-ZnT8). [Add to my cards (3)](https://durgical.app/estudiar/?add=/en/general-pathology/type-1-diabetes/) [More Pathology questions →](https://durgical.com/en/practice/?f=pathology) ## Elsewhere in DurgiPedia - [HLA associations with disease](https://durgical.com/en/immunology/hla-associations-with-disease/) - [Immune tolerance and how autoimmunity begins](https://durgical.com/en/immunology/immune-tolerance-and-how-autoimmunity-begins/) - [Molecular mimicry and post-infectious autoimmunity](https://durgical.com/en/immunology/molecular-mimicry-and-post-infectious-autoimmunity/) - [CD8⁺ cytotoxic T cell](https://durgical.com/en/immunology/cd8-cytotoxic-t-cell/) - [Autoantibodies: the table to know](https://durgical.com/en/immunology/autoantibodies-the-table-to-know/) ## Connections ## Related 5 - [Diabetes mellitus: diagnosis and classification](https://durgical.com/en/general-pathology/diabetes-mellitus-diagnosis-and-classification/) - [Type 2 diabetes](https://durgical.com/en/general-pathology/type-2-diabetes/) - [Diabetes: acute complications (DKA, HHS)](https://durgical.com/en/general-pathology/diabetes-acute-complications/) - [Hashimoto thyroiditis](https://durgical.com/en/general-pathology/hashimoto-thyroiditis/) - [Coeliac disease](https://durgical.com/en/general-pathology/coeliac-disease/) ## Related conditions 6 - [Type 1 diabetes mellitus](https://durgical.com/en/conditions/type-1-diabetes-mellitus/) - [Autoimmune polyendocrine syndromes (APS-1, APS-2) and IPEX](https://durgical.com/en/conditions/autoimmune-polyendocrine-syndromes-and-ipex/) - [Coeliac disease](https://durgical.com/en/conditions/coeliac-disease/) - [Thyroiditis (subacute, painless and postpartum)](https://durgical.com/en/conditions/thyroiditis/) - [Hypothyroidism](https://durgical.com/en/conditions/hypothyroidism/) - [Diabetic ketoacidosis](https://durgical.com/en/conditions/diabetic-ketoacidosis/) [← All of general pathology](https://durgical.com/en/general-pathology/) Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given. Sources: [Diabetes Type 1](https://medlineplus.gov/diabetestype1.html) (MedlinePlus, US National Library of Medicine, 2025); [Type 1 diabetes](https://medlineplus.gov/genetics/condition/type-1-diabetes/) (MedlinePlus, US National Library of Medicine, 2025). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/general-pathology/type-1-diabetes/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/type-1-diabetes/