Mast cells in innate immunity

Masts cells are known to be the main effector cells in the elicitation of t he IgE-mediated allergic response. The specific location of mast cells with in tissues that interface the external environment, and the extent of their functional capacity, including the ability to phagocytose and to produce a nd secrete a wide spectrum of mediators, have led investigators to propose a potential role for mast cells in innate immune responses. Certain microor ganisms have been found to interact either directly or indirectly with mast cells. This interaction results in mast cell activation and mediator relea se which elicit an inflammatory response or direct killing leading to bacte rial clearance. The in vivo relevance of these in vitro observations has be en demonstrated by the use of complement-deficient and/or mast cell-deficie nt and mast cell-reconstituted mice. It thus has been shown that both C3 an d mast cell- and tumor necrosis factor-alpha-dependent recruitment of circu lating leukocytes with bactericidal properties are crucial to a full respon se in certain models of acute infection. Modulation of mast cell numbers in vivo was also found to affect the host response against bacterial infectio n. Thus, mast cells do have a role in innate immunity in defined animal mod els of bacterial infection. Whether mast cells participate in innate immune responses in the protection of the human host against bacteria remains to be determined.