Our main research focus is to understand the mechanisms of protective immunity against human-pathogenic viruses. We study the virus-specific immune responses with a special emphasis on the fine-specificities of CD4 T helper cells that recognize epitopes in the viral structural proteins and thus can provide direct help to B cells producing neutralizing and protective antibodies. Based on the known crystallographic structures of viral proteins, immunodominant regions of T cell epitopes have been mapped to specific structural domains in the context of human infections as well as vaccination. The results will provide insights into incompletely understood aspects of human T cell responses that contribute to protective immunity against emerging virus pathogens.