New insights into the roles for basophils in acute and chronic allergy

Basophils represent less than 1% of peripheral blood leukocytes. They are often recruited to the site of allergic inflammation, albeit in small numbers. However, it remained uncertain whether basophils play any significant role in allergic reactions or act as minor and redundant 'circulating mast cells'. We have recently demonstrated that basophils play critical roles in systemic anaphylaxis and chronic allergic inflammation, distinctively from mast cells. Basophils are one of the major players in the IgG- but not IgE-mediated systemic anaphylaxis, in contrast to mast cells. In response to the allergen-IgG immune complexes, basophils release the platelet-activating factor rather than histamine as the major chemical mediator to induce the systemic anaphylaxis. The depletion of basophils protects mice from death due to anaphylactic shock. Basophils also play a crucial role in the development of the IgE-mediated chronic allergic inflammation with massive eosinophil infiltration in the skin, independently of T cells and mast cells, even though basophils account for only approximately 2% of the infiltrates. The basophil depletion shows a therapeutic effect on on-going allergic inflammation. Accumulating evidence suggests that basophils function as initiators rather than effectors of the chronic allergic inflammation. Thus, basophils and their products seem to be promising therapeutic targets for allergic disorders.