A Novel Technique for the In Vivo Imaging of Autoimmune Diabetes Development in the Pancreas by Two-Photon Microscopy

Type 1 diabetes (T1D) is characterized by the immune-mediated destruction of beta cells in the pancreas. Little is known about the in vivo dynamic interactions between T cells and beta cells or the kinetic behavior of other immune cell subsets in the pancreatic islets. Utilizing multiphoton microscopy we have designed a technique that allows for the real-time visualization of diabetogenic T cells and dendritic cells in pancreatic islets in a live animal, including their interplay with beta cells and the vasculature. Using a custom designed stage, the pancreas was surgically exposed under live conditions so that imaging of islets under intact blood pressure and oxygen supply became possible. We demonstrate here that this approach allows for the tracking of diabetogenic leukocytes as well as vascularization phenotype of islets and accumulation of dendritic cells in islets during diabetes pathogenesis. This technique should be useful in mapping crucial kinetic events in T1D pathogenesis and in testing the impact of immune based interventions on T cell migration, extravasation and islet destruction

Intravital imaging of CTLs killing islet cells in diabetic mice

Type 1 diabetes (T1D) is caused by autoimmune destruction of the insulin-producing β cells in the pancreatic islets, which are essentially mini-organs embedded in exocrine tissue. CTLs are considered to have a predominant role in the autoimmune destruction underlying T1D. Visualization of CTL-mediated killing of β cells would provide new insight into the pathogenesis of T1D, but has been technically challenging to achieve. Here, we report our use of intravital 2-photon imaging in mice to visualize the dynamic behavior of a virally expanded, diabetogenic CTL population in the pancreas at cellular resolution. Following vascular arrest and extravasation, CTLs adopted a random motility pattern throughout the compact exocrine tissue and displayed unimpeded yet nonlinear migration between anatomically nearby islets. Upon antigen encounter within islets, a confined motility pattern was acquired that allowed the CTLs to scan the target cell surface. A minority of infiltrating CTLs subsequently arrested at the β cell junction, while duration of stable CTL–target cell contact was on the order of hours. Slow-rate killing occurred in the sustained local presence of substantial numbers of effector cells. Collectively, these data portray the kinetics of CTL homing to and between antigenic target sites as a stochastic process at the sub-organ level and argue against a dominant influence of chemotactic gradients

Increase in pancreatic proinsulin and preservation of β-cell mass in autoantibody-positive donors prior to type 1 diabetes onset

Type 1 diabetes is characterized by the loss of insulin production caused by β-cell dysfunction and/or destruction. The hypothesis that β-cell loss occurs early during the prediabetic phase has recently been challenged. Here we show, for the first time in situ, that in pancreas sections from autoantibody-positive (Ab+) donors, insulin area and β-cell mass are maintained before disease onset and that production of proinsulin increases. This suggests that β-cell destruction occurs more precipitously than previously assumed. Indeed, the pancreatic proinsulin-to-insulin area ratio was also increased in these donors with prediabetes. Using high-resolution confocal microscopy, we found a high accumulation of vesicles containing proinsulin in β-cells from Ab+ donors, suggesting a defect in proinsulin conversion or an accumulation of immature vesicles caused by an increase in insulin demand and/or a dysfunction in vesicular trafficking. In addition, islets from Ab+ donors were larger and contained a higher number of β-cells per islet. Our data indicate that β-cell mass (and function) is maintained until shortly before diagnosis and declines rapidly at the time of clinical onset of disease. This suggests that secondary prevention before onset, when β-cell mass is still intact, could be a successful therapeutic strategy. © 2017 American Diabetes Associatio

Heterogeneity and Lobularity of Pancreatic Pathology in Type 1 Diabetes during the Prediabetic Phase

Type 1 diabetes (T1D) is an autoimmune disease in which insulin-producing beta cells are destroyed in the islets of Langerhans. One of its main pathological manifestations is the hyper-expression of Major Histocompatibility Complex I (MHC-I) by beta cells, which was first described over 3 decades ago yet its cause remains unknown. It might not only be a sign of beta cell dysfunction but could also render the cells susceptible to autoimmune destruction; for example, by islet-infiltrating CD8 T cells. In this report, we studied pancreas tissue from a 22-year-old non-diabetic male cadaveric organ donor who had been at high risk of developing T1D, in which autoantibodies against GAD and IA-2 were detected. Pancreas sections were analyzed for signs of inflammation. Multiple insulin-containing islets were identified, which hyper-expressed MHC-I. However, islet density and MHC-I expression exhibited a highly lobular and heterogeneous pattern even within the same section. In addition, many islets with high expression of MHC-I presented higher levels of CD8 T cell infiltration than normal islets. These results demonstrate the heterogeneity of human pathology that occurs early during the pre-diabetic, autoantibody positive phase, and should contribute to the understanding of human T1D

Demonstration of islet-autoreactive CD8 T cells in insulitic lesions from recent onset and long-term type 1 diabetes patients

A direct association of islet-autoreactive T cells with. cell destruction in human pancreatic islets from type 1 diabetes (T1D) patients has never been demonstrated, and little is known about disease progression after diagnosis. Frozen pancreas samples were obtained from 45 cadaveric T1D donors with disease durations ranging from 1 wk to >50 yr, 14 nondiabetic controls, 5 nondiabetics with islet autoantibodies, 2 cases of gestational diabetes, and 6 T2D patients. Sections were systematically analyzed for the presence of insulin-sufficient beta cells, CD8(+) insulitic lesions, and HLA class I hyperexpression. Finally, consecutive sections from HLA-A2-expressing individuals were probed for CD8 T cell reactivity against six defined islet autoantigens associated with T1D by in situ tetramer staining. Both single and multiple CD8 T cell autoreactivities were detected within individual islets in a subset of patients up to 8 yr after clinical diagnosis. Pathological features such as HLA class I hyperexpression and insulitis were specific for T1D and persisted in a small portion of the patients with longstanding disease. Insulitic lesions consistently presented in a multifocal pattern with varying degrees of infiltration and. cell loss across affected organs. Our observations provide the first direct proof for islet autoreactivity within human islets and underscore the heterogeneous and chronic disease course