Endocrine cells in pancreatic islets are embedded in a network of microvessels that regulate islet blood flow and hormone secretion. It is still unknown what happens to the islet microvasculature in type 1 diabetes (T1D), despite being the site of immune cell recruitment and infiltration. The microvasculature consists of capillary tubes made of a thin layer of endothelial cells covered by pericytes. Pericytes are the mural cells of the microcirculation. They are crucial for proper microvascular function, by giving structural stability, participating in angiogenesis, controlling vascular permeability and blood flow. While a wide body of literature exists on islet endothelial cells, the function of the islet pericyte is largely unknown. The aim of this research project is to look at pericytes in islets from non-diabetic donors as well as in individuals at different stages of type 1 diabetes. My hypothesis is that loss of pericyte coverage of capillaries leads to microvascular dysfunction and immune cell infiltration, contributing to the development of T1D. I also plan to assess whether pericytes control human islet capillary diameter, similarly to their role in mouse islets.