Mast cells and mastocytosis.

Mast cells (MCs) typically reside at barrier sites of the body, including the intestinal mucosa, and play a vital role in innate host defence. Activated MCs release a wide variety of bioactive mediators. These include preformed mediators stored in the granules (e.g. histamine and tryptase) and newly synthesised mediators (e.g. prostaglandins, leukotrienes and cytokines). MCs are present in all layers throughout the gastrointestinal (GI) tract and there is a close bi-directional connection between MCs and enteric nerves that is of vital importance in the regulation of GI functions. Some gain-of-function mutations in c-kit, encoding the tyrosine kinase- receptor for stem cell factor, are associated with the rare disease entity, systemic mastocytosis. These patients present symptoms arising from MC mediator release or infiltration. GI manifestations are common in this patient group, mainly abdominal pain and diarrhoea. Endoscopy with biopsies reveals MC infiltration in the mucosa. Other diagnostic tools include bone marrow biopsy and serum tryptase. Treatment is symptomatic with antihistamines or cromoglycate in mild cases, whereas severe cases need cytoreductive therapy that should be managed with expert haematologists. From a day-to-day clinical perspective, the important role of MCs in neuroimmune interaction has been implicated in the intestinal response to stress, in alterations of mucosal and neuromuscular function in irritable bowel syndrome or inflammatory bowel disease, and in the pathogenesis of non-erosive oesophageal reflux disease. Thus, MCs have important regulatory and protective roles in innate defence, in addition to being a potential mediator of mucosal pathophysiology in GI diseases. We need to learn how to balance the response of these volatile cells to be able to benefit from their versatility.