My research group addresses the intercellular communication of innate immune cells and its impact on the onset, kinetic and amplitude of adaptive immunity. Here, we employ the innovative technique of multiphoton microscopy of transgenic mouse models in which one to three cell types express distinct fluorescent reporter proteins. In particular, the non-invasive intravital imaging of mouse ear skin allows us to monitor immune cells at work in real time and to follow immune responses during skin inflammation until regeneration of the tissue. One particular focus of our group is the function of mast cells (MCs) in immune responses and inflammation. MCs are well-known as effector cells of type I allergic reactions but their role in maintaining tissue integrity, and in the induction and regulation of innate and adaptive immunity is far less understood. Our recent work has shown that MCs exhibit a critical role as tissue resident sentinel cells that initiate innate immune responses and impact on adaptive immunity.