In spite of the advent of antibiotics, antivirals and numerous successes in the combat of infectious diseases in the past century it has now become painfully clear that known and newly emerging infectious diseases will be a major challenge for the world at large in the coming decades. In main theme 4 the research focuses on the molecular regulation of the interactions between infectious pathogens and the host and on improvement in the diagnosis, therapy and prevention of infectious diseases and immunological disorders. This also includes the work on having control over the sometimes severe infectious problems that are inevitably linked to transplantation of organs that needs immune-suppresive treatments. The work within theme 4 happens with significant collaboration between the respective workgroups, taking advantage of complementary research activities and infrastructure of the other three themes. The long-term goal of main theme 4 is to limit the epidemiological, clinical and economic impact of infections, using state of the art technologies.