Specialization of Cells Involved in Mucosal Immunity

An intricate network of innate and immune cells and their derived mediators protect us from toxic elements and infectious microbial diseases. Higher mammals have evolved a unique mucosal immune system in order to protect the vast surfaces bathed by external secretions that are exposed to a rather harsh environment. Mucosal immune system is comprised of anatomically defined lymphoid micro compartments such as the Peyer's patches, the mesenteric lymph nodes, the appendix and solitary follicles in the intestine. The mucosal immune system prevent the uptake of undegraded antigens including foreign proteins derived from ingested food, airborne matter and commensal microorganisms and it also protect the mucous membranes against colonization and invasion by potentially dangerous microbes that may be encountered and inhibit the development of potentially harmful immune responses to these antigens if they do reach the body interior. Mucosal epithelial cells are of central importance in host defence by providing both a physical barrier and innate immunity. Goblet cells secrete mucus, which forms a dense, protective covering for the entire epithelium. Mucosa-associated lymphoid tissue (MALT) is the highly specialized immune system which protects mucosal surfaces. It is the largest mammalian lymphoid organ system and in an adult it comprises approximately 80% of all lymphocytes. The lymphoid elements associated with different mucosal sites share organizational as well as functional similarities. MALT is populated by phenotypically and functionally distinct B cell, T cell and accessory cell subpopulations as compared with systemic lymphoid tissues, and has also developed strong restrictions upon lymphoid cell recirculation between mucosal sites.