An aberrant immune tolerance towards exogenous or endogenous antigens can be observed in several mast cell-mediated diseases, such as, allergies, anaphylaxis, or chronic urticaria. Our main goal is to understand the immunological mechanisms that lead to breakage, development, or maintenance of immune tolerance in these diseases. We especially focus on the impact of UV light exposure on mast cell reactivity, immune tolerance, and clinical disease outcome. The projects in this research theme comprise the establishment and characterization of novel in vivo disease models to study different aspects of immune tolerance, as well as, immunological monitoring of patients undergoing therapy.