Mucosal immunology

Mucosal immunology is the study of immune system responses that occur at mucosal membranes of the intestines, the urogenital tract and the respiratory system, i.e., surfaces that are in contact with the external environment.[1] In healthy states, the mucosal immune system provides protection against pathogens but maintains a tolerance towards non-harmful commensal microbes and benign environmental substances.[1] For example, in the oral and gut mucosa, the secretion of IgA provides an immune response to potential antigens in food without a large and unnecessary systemic immune response.[2] Since the mucosal membranes are the primary contact point between a host and its environment, a large amount of secondary lymphoid tissue is found here. The mucosa-associated lymphoid tissue, or MALT, provides the organism with an important first line of defense. Along with the spleen and lymph nodes, the tonsils and MALT are also considered to be secondary lymphoid tissue.[3] The mucosal immune system provides three main functions: serving as the body's first line defense from antigens and infection, preventing systemic immune responses to commensal bacteria and food antigens (primarily food proteins in the Gut-associated lymphoid tissue, so-called oral tolerance), and regulating appropriate immune responses to pathogens encountered on a daily basis.[4]

At birth, the neonate's mucosal immune system is relatively undeveloped, but the colonization of intestinal flora promotes its development.[5]

Because of its front-line status within the immune system, the mucosal immune system is being investigated for use in vaccines for various afflictions,[6] including AIDS[7][8][9][10] and allergies.[11]