The influence of insulin on local amyloidosis of the islets of Langerhans and insulinoma.

Amyloid-containing islets of Langerhans from the pancreas of 75 diabetics and one case of an amyloid-containing insulinoma were investigated. By light and electron microscopy, amyloid deposits were observed between the B cells and adjacent capillaries. The cytoplasm of B cells and extracellular amyloid display immunohistological binding of anti-insulin antibody. Correspondingly, ferritin-labeled anti-insulin antibody was found by electron microscopy on and between the amyloid fibrils. Insulin or proinsulin (or a protein closely related to insulin) thus appears to be a component of the protein which constitutes the amyloid. The molecular weight and mode of deposition of this form of amyloid are in agreement with other amyloidoses of the hormonal type (AH-type).