E-Mail The immune system can be a mixed blessing: Usually it is highly effective in protecting the human organism against bacteria, viruses and mycosis and even cancer. But these defense cells can also turn against the body's own tissues and trigger autoimmune diseases, including for example rheumatoid arthritis and systemic lupus erythematosus, an illness involving chronic dermatitis and inflammation of the joints, the nervous system and internal organs or even become cancer cells themselves and develop into leukemias or lymphomas. But what causes these destructive immune system attacks? "The question has yet to be finally resolved," says Prof. Juergen Ruland, Director of the TUM Institute for Clinical Chemistry and Pathobiochemistry. "B cells, a subgroup of white blood corpuscles produced in the bone marrow, play a central role in regulating immune responses. During a normal immune response, activated B cells produce antibodies which attack foreign substances. Defective activation can result in formation of antibodies which attack the body itself, triggering an autoimmune disease. The activity of B cells is controlled by a variety of signals, some of which we have yet to understand," observes Ruland. The immunologist and physician is also the winner of the 2021 German Research Foundation (DFG) Leibniz Prize, the most important German research award.