Overview of the mucosal immune system structure

Abstract

Pioneering experiments in the early 1960s showed that the large lymphocytes that enter the bloodstream from the thoracic duct migrate into the intestinal lamina propria and undergo terminal differentiation into plasmablasts and plasma cells. The inductive sites are the organized mucosa-associated lymphoid tissue (MALT) structures together with mucosa-draining lymph nodes, whereas the effector sites are the mucosal epithelia and underlying lamina propria, which contains stromal cells and associated connective tissue stroma. The MALT concept was introduced to emphasize that solitary organized mucosa-associated lymphoid follicles and larger follicle aggregates have common features and are the origin of T and B cells that traffic to secretory effector sites. MALT is subdivided according to anatomical regions, and cellular content of these lymphoid structures depends on whether the tissue is normal or chronically inflamed, superimposed upon striking age and species differences. MALT resembles lymph nodes with B-cell follicles, interfollicular T-cell areas, and a variety of antigen-presenting cells but lacks afferent lymphatics and a capsule.