Lymphoepithelial interactions in the mucosal immune system.

The efferent limb of secretory immunity depends on local production and selective epithelial transport of polymeric immunoglobulins (pIg). To this end there is a fascinating cooperation of the B-cell system and the epithelium with their production of two key factors, the J chain and the secretory component (SC), respectively. Interactions between activated leucocytes for example, T cells and macrophages, and the secretory epithelium may contribute to modulation of the SC-dependent plg transport. Indirect evidence is accumulating, moreover, that lymphoepithelial interactions may also be involved in regulation of the mucosal B-cell system and in T cellmediated mucosal induction of systemic tolerance to luminal antigens.