Diabetes is an autoimmune disease. This means that it is caused by your immune system accidentally destroying your own healthy cells.
Learn more about autoimmune diseases here >>

If you have Diabetes, your immune system destroys cells in your pancreas. Your pancreas is below your stomach and helps you digest food. Your pancreas makes insulin after you eat. Insulin helps your body use the sugar from your food for energy. Diabetics don't have the cells that make insulin, so they can't use the sugar in their blood. The sugar stays in the blood too long, making them very sick. Diabetics have to take insulin shots to make sure they can use their blood sugar and don't get sick.
Learn more about the pancreas and insulin here >>

Type 1 Diabetes affects approximately 5% to 10% of the general population, and it usually sets in during childhood. No one can say for sure what triggers Type 1 Diabetes, but scientists believe genetics and environmental factors play a role.  Similar to many other autoimmune disorders, if someone has family members that are diabetic, they have a greater chance of developing Diabetes than someone who has no family history of Diabetes.

Environmental factors, like certain chemicals and viral infections, are believed to initiate or exacerbate Type 1 Diabetes.  Also, there is evidence linking Type 1 Diabetes to other autoimmune diseases like anemia, thyroid disease, and Addison’s disease.

Pathogenesis:  What Actually Happens?

In Type 1 Diabetes, the special insulin-producing cells of the pancreas - the beta islet cells - are attacked and destroyed by the body’s T cells.  The immune system becomes intolerant to certain cells of its own body, the islet cells, and begins to produce antibodies against them.  This then is an auto (against the self) immune (immune response) disease.

It is very unusual for the body to mistake healthy cells for infected ones.  There are many steps taken to prevent this.  T cells are the mediators and regulators of the immune system.  They activate the antibody response and stimulate phagocytosis.  If they mistakenly recognize healthy body cells as infected, they activate other cells of the body to attack as well.  To prevent this, when T cells are maturing in the thymus, they are evaluated before they are released into the body. If they recognize and attack body cells, they are automatically destroyed—nearly 90% of T cells are destroyed in the thymus before traveling to the body! 

But, this system isn't perfect! Does the thymus release irregular T cells into the body?  The next page outlines some major theories behind the origin of Type 1 Diabetes.