The Role of Mast Cells in Bacterial Enteritis

Abstract

Considering that the intestinal lumen is home to greater than 400 commensal bacterial species, it is curious that the mucosal immune system can detect the presence of pathogens among benign flora. The rapid and potent response of the innate immune cells ensures that virulent organisms are contained to the intestine, although this reaction can also damage surrounding tissue if not kept in balance. The work by Feng et al1 in this issue of The American Journal of Pathology demonstrates that mast cells are involved in the inflammatory reaction to intestinal pathogens and that mast cell products released during degranulation may be the cause of intestinal damage due to infection. Several innate immune cell types reside in the intestinal lamina propria, including mast cells, dendritic cells, and macrophages. Within the intestine, mast cells are found in the mucosal and submucosal layer and can release a variety of bioactive proteins that can directly affect ion secretion (leading to diarrhea) and epithelial barrier function (leading to bacterial translocation). Although it is well documented that mast cell activation contributes to secretory diarrhea and colitis, it is still unclear how mast cells are triggered by microbial products to cause pathology. The observations presented here by Feng et al1 demonstrate that Toll-like receptor (TLR)2 on mast cells is responsible for diarrhea caused by Staphylococcus aureus. This work is a culmination of past studies demonstrating that mast cell products affect intestinal physiology and that mast cells are an important part of the innate immune response to bacterial infection.