One of the more perplexing questions in biomedical research is—why does the body’s protective shield against infections, the immune system, attack its own vital cells, organs, and tissues? The answer to this question is central to understanding an array of autoimmune diseases, such as rheumatoid arthritis, type 1 diabetes, systemic lupus erythematosus, and Sjogren’s syndrome. When some of the body’s cellular proteins are recognized as “foreign” by immune cells called T lymphocytes, a destructive cascade of inflammation is set in place. Current therapies to combat these cases of cellular mistaken identity dampen the body’s immune response and leave patients vulnerable to life-threatening infections.

Research on stem cells is now providing new approaches to strategically remove the misguided immune cells and restore normal immune cells to the body. Presented here are some of the basic research investigations that are being guided by adult and embryonic stem cell discoveries. Introduction

The body’s main line of defense against invasion by infectious organisms is the immune system. To succeed, an immune system must distinguish the many cellular components of its own body (self) from the cells or components of invading organisms (nonself). “Nonself” should be attacked while “self” should not. Therefore, two general types of errors can be made by the immune system. If the immune system fails to quickly detect and destroy an invading organism, an infection will result. However, if the immune system fails to recognize self cells or components and mistakenly attacks them, the result is known as an autoimmune disease. Common autoimmune diseases include rheumatoid arthritis, systemic lupus erythematosis (lupus), type 1 diabe