Mast cells play a central role in inflammatory and immediate allergic reactions and are necessary for allergic reactions. Mast cells play a role in the pathophysiology of autoimmune diseases and appear to be especially important in inflamed tissues, because they infiltrate tissues and produce a variety of cytokines. Mast cells are important for both innate and adaptive immunity in tissues that are in close contact with the environment, i.e. the skin, the airways and the lung, and the lining of the intestine. However, there are still many unsolved issues of mast cell functions, including their regulatory mechanism on cell differentiation in bone marrow; for example, the cytokines and transcription factors necessary for their differentiation and expansion, as well as the molecular mechanism underlying basophil migration from the bloodstream to peripheral tissues such as lymph nodes still need to be clarified.