Overview of the Mucosal Immune System

Targeted disruption of the mouse transforming growth factor-β1 gene results in multifocal inflammatory disease

“…Mucosal or secretory immunity involves induction of precursor IgA-secreting cells in bronchial-associated and gut-associated lymphatic tissue, including Peyer's patches; migration of these cells to mucosal sites (including gut, respiratory tract, mammary gland, lacrimal gland and genitourinary system); and terminal differentiation to IgA-secreting cells in these tissues 42 . TGF-β1 specifically enhances IgA expression in stimulated Peyer's patch and splenic B cells 43,44 and seems to be involved in lymphocyte homing to mucosal sites, enhancing expression of human HML-l and murine β 7 α M290 integrins which are believed to mediate homing to the mucosa 45,46 .…”

Distribution of Monoclonal Antibodies in Intestinal and Urogenital Secretions of Mice Bearing Hybridoma ‘Backpack’ Tumours

“…Mucosal immunization results in the generation of IgA lymphoblasts in organized mucosal lymphoid tissues, the local inductive sites of the mucosal immune system [1,19,20]. The progeny of these cells, committed to synthesis of dimeric or polymeric IgA against a specific antigen, circulate systemically and ultimately migrate into mucosal and glandular sites throughout the body where they terminally differentiate into IgA-producing plasma cells [reviews 9,21].…”

“…The presence of immunoglobulin A (IgA) in secretions has been associated with protection of epithelial surfaces against foreign antigens and microbial pathogens [1][2][3]. It has been difficult to directly assess the contribution of secretory IgA to mucosal protection, however, because of the technical difficulties in collecting local mucosal secretions and the complexity of immune responses after oral immunization or microbial challenge.…”

“…Such studies have demonstrated that specific IgA antibodies can indeed protect against viral infection, bacterial invasion and toxin binding. However, passive application of antibodies to mucosal surfaces does not accurately reproduce the distribution of secretory IgA in secretions of immunized animals, where IgA is produced by plasma cells in mucosal tissues and transported continuously into glandular secretions and onto mucosal surfaces by epithelial cells [1,3,9].…”

Do most lymphocytes in humans really reside in the gut?

“…However, the above-stated estimate of the gut surface includes microvilli, which do not harbor any lymphocytes; the surface area of the gut excluding microvilli is much smaller, on the order of 2-10 m 2 [25,26]. Second, it has been estimated that up to 80% of all IgA-producing plasma B cells in mice and humans are located in the gut, arguing for a large population of lymphocytes at this site [27,28]. However, antibody-secreting cells constitute only a small fraction of all lymphocytes in the body [27,29].…”