The role of Interleukin-21 in the pathogenesis of autoimmune diabetes

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T cells are a component of our blood (white blood cells) and a major component of the body's defense system against infection, known as immunity. Without T cells, we would fail to resist infection by foreign agents, such as viruses, bacteria and fungi. Autoimmune (type 1) diabetes is a disease in which T cells attack our own pancreatic islet self tissues as if they were foreign. T cells that react against the islets of the pancreas cause destruction of the insulin producing beta cells so that the pancreas can no longer make insulin. Diabetes is a life-threatening disease because insulin is a hormone that enables people to get energy from food. Type 1 diabetes is usually diagnosed in childhood and insulin must be administered daily by injection or through a pump in order to survive. Unfortunately, taking insulin doesn t cure diabetes and people continue to suffer from an extensive list of complications affecting most vital organs. Interleukin-21 (IL-21) is a soluble protein that is produced by cells enabling them to communicate with other cells. IL-21 helps cells to produce factors that cause inflammation and assist in clearance of viruses and bacteria from the body. However, our studies show that IL-21 is a major factor in the development of the T cells that destroy beta cells and cause diabetes. Our studies show that IL-21 is over-expressed in an important murine model of spontaneous type-1 diabetes. We have isolated the T cells that cause diabetes and show that they are distinguished from other T cells by very high levels of the receptor for IL-21. This project focuses on the IL-21-responsive T cells that cause diabetes and aims to determine the mechanisms by which the cytokine IL-21 causes destructive immune responses and ways to modulate its production. This project applies basic science to the important public health issue of type 1 diabetes for the development of therapeutic intervention strategies.