Human mast cells, bacteria, and intestinal immunity

Mast cells are versatile tissue regulator cells controlling major intestinal functions such as epithelial secretion, epithelial permeability, blood flow, neuroimmune interactions, and peristalsis. Most importantly, mast cells are key regulators of the integrity and function of the gastrointestinal barrier. At the same time, they can act as immunomodulatory cells by reacting to various exogenous signals from bacteria, viruses, and parasites through innate recognition receptors, such as Toll-like receptors (TLRs) or through receptors of the specific immune system, such as immunoglobulins (Igs) bound to their cell surface. This mast cell function is enhanced by an intensive cross talk of mast cells with other cells of the innate or adaptive immune systems. Finally, mast cells act as inflammatory cells mediating diseases such as allergy, once they become dysregulated because of excess of allergen, allergen-specific IgE and cytokines, or invading microbes. The present article focuses on the human mast cell functions in the intestine and compares the data with those derived from animal experiments. In particular, the role of bacteria and TLRs expression by mast cells for allergic reactions are discussed.