Mast Cells and Anaphylaxis

For half a century, it has been known that the mast cell is the cell responsible for the majority of anaphylactic events. Its mediators, taken as a whole, are capable of producing all of the clinical manifestations of these events. With the discovery of immunoglobulin E (IgE), it was originally felt that the vast majority of anaphylactic episodes were due to antigen coupling with two cell-bound IgE molecules. More recently it has been learned that many episodes are produced by direct activation of mast cells, not involving antigen binding to IgE, and that monomeric IgE under certain conditions can also cause degranulation. Of note—in regard to antigen independent degranulation—are recent reports that the human G-protein-coupled receptor, MRGPRX2, may be the receptor for many drugs and cationic proteins capable of producing direct mast cell degranulation and anaphylactic events.