Eosinophil leukocytes appear to participate in a bewildering array of disease processes that includes allergies, metazoan parasitic infestations, some neoplasms, a few vasculitides, and certain skin diseases. Eosinophilia generally occurs in the setting of repeated or persistent tissue inflammatory responses combined with a hypersensitivity reaction, usually involving immediate (reaginic) or delayed (granulomatous) hypersensitivity but often demonstrating combinations of all possible immune mechanisms. It is not known, however, why one host response (for example, to parasites) elicits eosinophilia while another seemingly similar response (for example, to tuberculin) does not. Further, eosinophilia may be an aberrant reaction, such as to ectopic release