Role for basophils in systemic anaphylaxis.

For more than 100 years since the discovery of basophils by Paul Ehrlich, the functional significance of this rare leukocyte as compared to mast cells has remained an enigma. Studies on basophils have long been hampered by their rarity (less than 1% of peripheral blood leukocytes) and the lack of useful analytical tools such as model animals deficient only in basophils. Recent studies have now defined previously-unrecognized roles for basophils in both allergic responses and immune regulation, and markedly changed our image of basophils, from a neglected minority to a key player in the immune system. We have recently demonstrated that basophils and mast cells play distinct roles in systemic anaphylaxis in mice. Basophils are dispensable for IgE-mediated systemic anaphylaxis unlike mast cells. Instead, basophils play the major role in IgG-mediated systemic anaphylaxis. In vivo depletion of basophils protects mice from anaphylactic death. Upon capture of IgG-allergen complexes, basophils release platelet-activating factor that increases vascular permeability, leading to anaphylactic shock. Thus, there are two major, distinct pathways to allergen-induced systemic anaphylaxis: one mediated by basophils, IgG and platelet-activating factor, and the other 'classical' pathway mediated by mast cells, IgE and histamine.