The immune system is designed to protect us from infection, but when its regulation is impaired it can give rise to diseases in which normal tissues are damaged. Lupus (SLE) is the prototype of such a disease. The component of the immune system that regulates its activity is a type of white blood cell called a lymphocyte. Like all cells, a complex network of regulatory proteins controls the activation of a lymphocyte. Among the most important of these is one called Ras. Ras functions as a simple molecular switch (“on” versus “off”). Recently, a strain of mice that develop lupus was found to have defective control of Ras. Dr. Adam Mor developed novel tools to study when and where Ras becomes active in living cells. He will apply these tools to lymphocytes from normal and lupus mice to learn what aspects of Ras activation are relevant for the development of the disease. In order to prevent onset of the disease, we must understand the defects at the molecular level. Learning the basic pathways involved in the pathology of lupus is a crucial step in the development of drugs against the disease.