SAT-LB036 Late Weaning Leads to Enrichment of Treg Cells Which Consequently Regulates Effector T Cell Responses in Peri-Pancreatic Lymph Nodes and Pancreas of Humanized Model T1D

The hallmark of type 1 diabetes (T1D) is immune-mediated destruction of insulin secreting β-cells in pancreatic islets. Children who progress to clinical T1D have detectable levels of islet-specific autoantibodies before age three. Early development of gut microbiota also has limited resilience and is vulnerable to perturbation. We recently developed humanized mice that spontaneously develop T1D. This mouse model mimics clinical human T1D, allowing us to carry out controlled studies where we investigated diabetes development and gut microbiota after normal weaning (NW) and late weaning (LW) stages. Our data revealed that the gut microbiota changes as weaning is delayed and that disease progression correlates with these changes. We hypothesized that a delay in T1D onset in our model might have been due to an enrichment of regulatory T (Treg) cells secondary to increased diversity of gut microbiome. We tested this hypothesis by setting up experiments where the breeder’s cages with larger litter sizes (8 pups) were separated into two groups. We allowed the breeder mice for a second-time pregnancy, and after birth, the second litters were sacrificed, and first litter (late weaning group) were allowed to stay with their mothers until day 45 as normal weaning group was separated at day 21. Late weaning was then separated from mothers and allowed to settle into new cages. At day 60 and 150, mice from both groups (n=10-12) were sacrificed. Organs (Peyer’s patches, peri-pancreatic lymph nodes (PLN), pancreas (PN) and spleen) were harvested and lymphocytes isolated. Flow cytometry of Peyer’s patches, a site of first immune cell interaction/activation with gut antigens, revealed that Tregs were significantly increased in late weaning group. In PLN, a site for islet antigen-specific T cell activation and recruitment in case of pancreas autoimmunity, flow cytometry data revealed that late weaning leads to enrichment of Tregs and consequently regulation of cytotoxic CD8 T lymphocytes (CTLs). Most interestingly, late weaning enriched the Treg population at the spleen level too. The enrichment of Tregs may have been due to a more diverse microbiome, which is known to increase immune tolerance, which might have regulated the diabetogenic Th1, Th17, and CTLs at PLN, PN, and spleen. Our data is the first to provide a scientific explanation for observed prolong nursing as affecting T1D outcomes in humans. We also investigated the possibility that induction of immune tolerance would protect pancreatic islet architecture. Newborn mice littermates were divided into late weaning and normal weaning groups. Pancreatic sections were stained with hematoxylin/eosin (H&E) for histological identification and localization of islets and lymphocytic infiltrates. Late weaning group, preserved the pancreatic islet architecture with fewer lymphocytic infiltrates and a significantly higher number of islet per H&E section. Unless otherwise noted, all abstracts presented at ENDO are embargoed until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. Abstracts presented at a news conference are embargoed until the date and time of the news conference. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.