Electron microscopy of renal and ocular changes in virus-induced diabetes mellitus in mice

Viruses in type 1 diabetes: brief review

Type 1 diabetes results from the progressive destruction of insulin-producing pancreatic beta cells. Although the etiology of type 1 diabetes is believed to have a major genetic component, studies on the risk of developing type 1 diabetes suggest that environmental factors, such as viruses, may be important etiological determinants. Among the viruses, the most clear and unequivocal evidence that a virus induces type 1 diabetes in animals comes from studies on the D variant of encephalomyocarditis (EMC-D) virus in mice and Kilham rat virus (KRV) in rats. A high titer of EMC-D viral infection results in the development of diabetes within 3 days, primarily due to the rapid destruction of beta cells by viral replication within the cells. A low titer of EMC-D viral infection results in the recruitment of macrophages to the islets. Soluble mediators produced by the activated macrophages such as interleukin-1Beta, tumor necrosis factor-alpha, and nitric oxide play a critical role in the destruction of residual beta cells. KRV causes autoimmune type 1 diabetes in diabetes resistant-BioBreeding rats by breakdown of immune balance, including the preferential activation of effector T cells, such as Th1-like CD45RC+CD4+ T cells and CD8+ T cells, and down-regulation of Th2-like CD45RC-CD4+ and CD4+CD25+ T cells, rather than by direct infection of pancreatic beta cells.

Role of viruses in the pathogenesis of IDDM

Insulin-dependent diabetes mellitus (IDDM), also known as type I diabetes, results from the destruction of pancreatic beta cells. During the past few decades, genetic factors, autoimmunity and viral infections have been extensively studied as the possible cause of beta cell destruction. The evidence for virus-induced diabetes comes largely from experiments in animals, but several studies in humans also point to viruses as a trigger of this disease in some cases. There are at least two possible mechanisms for the involvement of viruses in the pathogenesis of IDDM: (a) cytolytic infection of beta cells may result in destruction of the cells without the induction of autoimmunity, or may be a final insult leading to the clinical onset of diabetes in individuals with an already decreased beta cell mass resulting from an autoimmune process; and (b) persistent viral infection (e.g. retrovirus, rubella virus, cytomegalovirus) may result in the triggering of autoimmune IDDM in certain circumstances. Regarding the latter possibility, viruses may insert, expose, or alter antigens in the plasma membrane of the beta cell, which may initiate autoimmunity leading to the destruction of the cells.

Pancreatic islet transplantation ameliorates the effect of diabetes on retinal capillary endothelial cell kinetics

Perturbations in capillary endothelial cell function are early events in the pathogenesis of diabetic retinopathy. We used tritiated thymidine autoradiography to study the turn-over rate of retinal capillary endothelial cells in retinovascular preparations from normal, untreated diabetic and diabetic mice treated with pancreatic islet-cell transplants. Capillary endothelial cell turnover was significantly increased in poorly controlled diabetes and this increase was reduced by islet-cell transplantation. The prevention of excessive endothelial cell replication by tight control of hyperglycemia may help prevent the characteristic structural changes of diabetic microangiopathy, such as basement membrane accumulation.

Morphologic evaluation of Descemet's membrane and corneal endothelium in diabetes mellitus

Diabetes mellitus is characterized by abnormally thickened basement membranes throughout the body and the eye. In addition, abnormal corneal endothelial cell morphology has been found in eyes of diabetics. The authors examined Descemet's membrane (the basement of the corneal endothelium) and the endothelial cells in 19 diabetic corneas and 19 age-matched nondiabetic normal corneas in a masked fashion by transmission electron microscopy and specular microscopy. No statistically significant quantitative or qualitative differences were found between the two groups.