Our immune system is critically important in eliminating pathogens that invade our body, including bacteria, viruses and parasites. To effectively challenge various classes of pathogens, the development of specific types of antigen-specific T cells is required, which activate different pathogen-tailored effector mechanisms. Protection against endosomal pathogens requires type 1 T helper (Th1) cells, protection against helminths Th2 cells, protection against bacteria Th17 cells and protection against viruses cytotoxic T (Tc) cells. Importantly, the function of these effector T cells is inhibited by T regulatory (Tr) cells, that prevent in this way excessive host tissue damage, autoimmunity and allergy. These different effector T cells develop from multipotent naive T cells. Our work has contributed to the concept that dendritic cells (DCs) are specialized antigen-presenting cells that orchestrate the development of protective type of effector T cell responses by their ability to sense different pathogen classes. An important research theme in my group is the question to what extent there are specialized DC subsets and by what mechanism DCs promote the development of Th1, Th2, Th17 or Treg cells. Secondly, this knowledge is applied in the development of novel therapies for immunological, inflammatory diseases such as allergic disorders.