APOPTOSIS IS THE MODE OF BETA-CELL DEATH RESPONSIBLE FOR THE DEVELOPMENT OF IDDM IN THE NONOBESE DIABETIC (NOD) MOUSE

The NOD/Lt mouse, a widely used model of human autoimmune IDDM, was us ed to establish the mode of beta-cell death responsible for the develo pment of IDDM. Apoptotic cells were present within the islets of Lange rhans in hematoxylin and eosin-stained sections of pancreases harveste d from 3- to 18-week-old female NOD/Lt mice (a range of 11-50 apoptoti c cells per 100 islets). Immunohistochemical localization of insulin t o the dying cells confirmed the beta-cell origin of the apoptosis. Alt hough some islets from age-matched control female NOD/scid mice contai ned apoptotic cells, virtually all of these cells were insulin negativ e as determined by immunohistochemistry. The small number of apoptotic insulin-positive cells identified in islets from NOD/scid mice (a ran ge of 0-1 apoptotic cells per 100 islets) was not statistically signif icant, compared with the numbers recorded in NOD/Lt mice. All dying ce lls showed the morphological changes characteristic of cell death by a poptosis and stained positively with the TUNEL method for end-labeling DNA strand breaks. The maximum mean amount of beta-cell apoptosis occ urring in NOD/Lt mice was at week 15 (50 apoptotic cells per 100 islet s), which coincided with the earliest onset of diabetes as determined by blood glucose, urine glucose, and pancreatic immunoreactive insulin measurements. While there was no peak incidence of beta-cell apoptosi s throughout the time period studied (weeks 3-18), the incidence of ap optosis decreased at week 18, by which time 50% of the animals had ove rt diabetes. The low levels of beta-cell apoptosis observed is indicat ive of a gradual deletion of the beta-cell population throughout the e xtensive preclinical period seen in this model and would be sufficient to account for the beta-cell loss resulting in IDDM. Apoptosis of bet a-cells preceded the appearance of T-cells (CD3-positive by immunohist ochemistry) in islets. Lymphocytic infiltration of islets (insulitis) was not detected until week 6. The results show that beta-cell apoptos is is responsible for the development of IDDM in the NOD/Lt mouse and that its onset precedes lymphocytic infiltration of the islets.