Mast cells and the power of local RAS activation.

More than 100 years ago, mast cells were discovered and named by Paul Ehrlich who was the first to recognize this well-fed appearing cell loaded with huge cytoplasmic granules in various tissues [1]. Mast cells derive from CD34þ multipotent bone marrow progenitor cells which circulate in small numbers in the blood as basophilic leucocytes, and enter the mucosal surfaces and connective tissue compartments of multiple organs [2]. This distinct cell type is today best known for its key role in immunoglobulinE-mediated allergic reactions such as bronchial asthma and anaphylactic reactions. More recently, however, mast cells have been found to be important modulators and mediators of innate immunity, chronic inflammation, tissue remodelling and organ fibrosis [3–5].