An apparent deficiency of lymphatic capillaries in the islet of Langerhans in the human pancreas

The lymphatic system is crucial for efficient immune surveillance and for maintenance of a physiological pressure in the interstitial space. Even so, almost no information is available concerning the lymph drainage of the islets of Langerhans in the human pancreas. Immunohistochemical staining allowed us to distinguish lymphatic capillaries from blood capillaries. Almost no lymphatic capillaries were found within the islets in pancreatic biopsies from non-diabetic subjects, or from subjects with either T1D or T2D. Lymphatic capillaries were, however, found at the islet-exocrine interface, frequently located along blood capillaries and other fibrotic structures within or close to the islet capsule. Lymphatic capillaries were regularly found in the exocrine pancreas, with small lymphatic vessels located close to and around acini. Larger collecting lymphatic vessels were located in fibrotic septa between the exocrine lobules and adjacent to the ductal system of pancreas. In summary, we report a pronounced deficiency of lymphatic capillaries in human islets, a finding with implications for both immune surveillance and the regulation of interstitial fluid transport in the endocrine pancreas, as well as for the pathophysiology of both type 1 and type 2 diabetes.