Type 1 diabetes (T1D) is an autoimmune disease where the insulin secreting beta cells are destroyed by immune cells, leading to increased blood glucose levels. Beta cells are located in the Islets of Langerhans within the pancreas and are responsible for the production of a vital hormone called insulin. Due to the lack of insulin, T1D patients experience hyperglycemia, which can cause severe complications such as heart disease, stroke, nerve damage, and kidney failure. T1D develops in childhood or adolescence but can also occur in adults, where the disease onset and progression are triggered by either environmental or immunological events (1).
T1D has a strong genetic component, with susceptibility largely linked to HLA class II genes (HLA-DR, HLA-DQ, and HLA-DP). Certain haplotypes, such as HLA-DR3/DR4, are associated with a higher risk, whereas other variants may confer protection (2). Additionally, non-HLA genes like INS (insulin gene), PTPN22, CTLA-4, and IL2RA play crucial roles in immune regulation and T1D susceptibility (3). In healthy individuals, central tolerance mechanisms in the thymus eliminate self-reactive T cells through negative selection. However, in genetically susceptible individuals, autoreactive CD4+ T helper cells (Th1 and Th17 subsets) escape deletion and become activated in peripheral lymphoid tissues. A key event in T1D pathogenesis is the presentation of beta cell antigens by antigen-presenting cells (APCs) (4). Dendritic cells and macrophages engulf beta cell-derived proteins (e.g., insulin, GAD65, IA-2, ZnT8) and present them to naive T cells via HLA class II molecules. This leads to the activation of: (i) CD4+ T cells, which orchestrate immune responses by secreting proinflammatory cytokines such as IFN-γ, IL-2, and IL-17; and (ii) CD8+ cytotoxic T lymphocytes (CTLs), which directly mediate beta cell destruction through the perforin/granzyme and Fas-FasL pathways. Regulatory T cells (Tregs), which normally suppress autoimmunity, are dysfunctional in T1D, allowing excessive immune activation ( Figure 1 ). Additionally, B cells contribute to autoimmunity by producing islet autoantibodies against insulin, GAD65, and IA-2, which serve as biomarkers for disease progression (5).
The pancreatic islets in T1D are infiltrated by immune cells in a process called insulitis. This inflammatory environment is enriched with TNF-α, IFN-γ, and IL-1β, which impair beta cell function and enhance apoptosis. In parallel, beta cells under attack initiate stress responses and secrete chemokines (e.g., CXCL10, CCL5) that further recruit immune cells, amplifying the autoimmune loop. Beta cell destruction occurs through multiple mechanisms: (i) direct killing by CD8+ T cells via granzyme B/perforin-mediated cytotoxicity, (ii) Fas — Fas ligand (FasL) signaling, where beta cells expressing Fas undergo apoptosis upon interaction with FasL-expressing T cells, (iii) cytokine-induced dysfunction, as TNF-α, IL-1β, and IFN-γ activate endoplasmic reticulum (ER) stress and the JAK-STAT and NF-κB pathways, leading to metabolic stress and apoptosis (6). The intricate interplay between T cells, B cells, APCs, and beta cells emphasizes the challenges in developing therapies to halt or reverse the disease. Understanding these mechanisms is crucial for designing targeted interventions, including immune modulation, beta cell replacement, and genetic engineering approaches to restore glucose homeostasis.
