Mucosal Immunity and Immune Tolerance

The mucosa is in direct contact with the outside and is the first line of defense of the immune system, undertaking the complex immune task of both tolerance to beneficial commensal microorganisms and food and immunity to pathogenic microbial infection. The mucosal immune system recognizes pathogen-associated molecular patterns (PAMPs) through pattern recognition receptors (PRRs) to generate an immune response, clear pathogens, and maintain homeostasis in the organism. Immune tolerance is the unresponsiveness of the adaptive immune system to an antigen. Immune tolerance results from the clearance or suppression of antigen-specific lymphocytes or from their conversion to regulatory T cells (Treg). Immune tolerance ensures that the immune system does not produce an immune response to self-antigens, however if immune tolerance is broken, the immune system will attack self tissues, resulting in autoimmune disease. The digestive, respiratory, and genitourinary tracts all have mucosal tissues, and this chapter focuses on the basic principles of mucosal immunity and immune tolerance, using the intestinal mucosa as an example.