The innervation of mast cells

In this chapter we hope to persuade the reader that many, if not all mast cells are innervated, i.e., mast cells are closely apposed to varicose axons and that the interchange of chemical messengers occurs at these sites. This may not be surprising to anatomists and morphologists who have documented the microanatomical association of numerous mast cells with nerve bundles for many years. 1,2 In spite of this well described relationship, the potential for direct “neurocrine” communication between individual axons and mast cells has not received much attention, although an “axon-reflex” pathway involving mast cells has been proposed in the skin. 3,4. This chapter persuades the reader that many, if not all mast cells are innervated, that is, mast cells are closely apposed to varicose axons and that the interchange of chemical messengers occurs at these sites. It demonstrates an intimate microanatomical association of the presumably bone-marrow-derived mucosal mast cell with subepithelial nerves in the gastrointestinal lamina propria, and suggests an axon-reflex pathway similar to that proposed in the skin. The chapter presents some of morphological and physiological evidence to support the suggestion in both the gastrointestinal and respiratory tracts. It describes experiments involving co-culture of mast cells and explanted nerves, and discusses some experiments with nerve-growth factor, which has been found to cause both mast-cell degranulation and proliferation. The chapter investigates the effects of antigen on epithelial function using in vitro studies in an Ussing chamber. It presents the regarding changes in epithelial transport and permeability support the interaction of mast cells and nerves and their involvement in homeostasis.