- Mucosal-associated Lymphoid Tissue (MALT) refers to the unencapsulated lymphoid tissue distributed in association with mucosal tissues, primarily within their lamina propria.
- The key feature of MALT is its presence in the mucosal lamina propria and its unencapsulated nature. MALT can appear as aggregations of immune cells roughly similar in architecture to a section of a lymph node and may contain lymphoid follicles with germinal centers. Unlike lymph nodes, MALT aggregations are not penetrated by lymphatic vessels and are exposed to antigens directly from the mucosa they surround. In addition, MALT refers to the diffusely distributed immune cells, usually lymphocytes, found throughout the lamina propria of mucosa.
- Given the enormous microbial burden present at mucosal surfaces, MALT provides the immune system easy histological access to the organisms. Thus, MALT allows the immune system to sample microbial antigens for development of adaptive immune responses and provides a location for Plasma Cells to synthesize IgA.
- MALT is found in several prominent locations and the lymphoid collections at each anatomical location are given some unique identifiers as discussed below.
- Bronchial Associated Lymphoid Tissue (BALT): Found in Conducting Airways, specifically in the Respiratory Lamina Propria
- Gastric Associated Lymphoid Tissue (GALT): Found in the Stomach, specifically the Gastric Lamina Propria
- Peyer's Patches: Found in the Small Intestine, specifically the Small Intestine Lamina Propria
- Appendix: Contains abundant MALT in its lamina propria
- Tonsils: Tonsils are essentially MALT found mucosa of the pharynx