During the course of evolution, the immune system had to continuously shape and refine its mechanisms of defense against pathogens. In response to different microorganisms, specialized types of specific responses allow the recognition and elimination of infectious agents. All individuals harbor autoreactive T cells that need activation and critical expansion in order to start active autoimmune disease. In a number of human diseases and in their corresponding experimental animal models, it has been suggested that pathogens can induce disease through autoimmune mechanisms. In this chapter, we will focus our attention to the basis of the host immune response, the mechanisms of autoimmunity, and to the link between Helicobacter pylori infection and gastric autoimmunity, the relevance of Chlamydophila pneumoniae and inflammation in atherosclerosis, the role of Th17 responses in Lyme arthritis, as well as the link between Behçet’s syndrome and infections.
