Immunohistology of islet amyloid polypeptide in diabetes mellitus: semi-quantitative studies in a post-mortem series.

Immunoreactivity for islet amyloid polypeptide (IAPP) in the islets of Langerhans of non-insulin-dependent diabetic patients and non-diabetic patients of a non-selected post-mortem series was studied with a new polyclonal IAPP antibody. Out of 133 patients examined, 124 exhibited immunoreactivity for IAPP. Immunoreactivity was localized intra- and extracellularly and was limited to the islets of Langerhans. No extracellular immunoreactivity was observed in amyloid-negative cases. Co-localization of insulin and IAPP in the same islet-cells was verified by double staining with monoclonal insulin and polyclonal IAPP antibodies. Of 100 patients with non-insulin-dependent diabetes mellitus (NIDDM) and islet amyloid, 98 exhibited IAPP-positive deposits and 71 exhibited intracellular immunoreactivity. Evaluation of intracellular immunoreactivity and degree of islet amyloid deposition in cases of overt NIDDM revealed an inverse relationship, in that intracellular IAPP immunoreactivity were reduced in patients with developing islet amyloid deposition. Our data are consistent with the hypothesis of primary beta-cell dysfunction leading to amyloid formation, with subsequent disturbance of beta-cell homeostasis.