Basophils: historical reflections and perspectives.

Basophils were discovered by Paul Ehrlich in 1879 and account for less than 1% of blood leukocytes, which suggests a tightly controlled regulation of basopoiesis. The conservation of basophils in a wide spectrum of the animal kingdom suggests a non-redundant role in innate and adaptive immunity. In the early 1990s, it was demonstrated that murine and human basophils synthesize interleukin (IL)-4 and IL-13, thereby suggesting that these cells are important for Th2 polarization and IgE synthesis. Human basophils also synthesize IL-3, VEGFs and other pro-angiogenic molecules. Recently, various groups have introduced the use of basophil-depleting antibodies or have developed transgenic mice that constitutively lack basophils by more than 90%. These models have highlighted previously unrecognized roles of basophils, distinct from those played by mast cells, in innate and adaptive immunity. Although the physiologic role of basophils remains unknown, there is now compelling evidence that basophils, despite their small numbers in peripheral blood and inflamed tissues, are critically involved in a wide spectrum of immunologic disorders (allergic, autoimmune and infectious diseases, immunodeficiencies and cancer). It is not inconceivable that basophils and/or their products could be promising therapeutic targets for such disorders.