Eosinophilic Disorders

Eosinophils are primarily tissue leukocytes with a short circulatory half-life. They are involved in host defense against certain infections as well as in many other immunological responses. An increase in eosinophil count can be seen in peripheral blood, in various tissues, or both. When the increase in eosinophil level is secondary to an underlying infectious, allergic, endocrine, autoimmune, or malignant process or to consumption of a drug, it is known as a secondary eosinophilic disorder. When eosinophils are increased due to an aberrant or abnormal process in the bone marrow or the molecules which control the production and distribution of eosinophils, the condition is termed primary eosinophilia. Hypereosinophilic syndromes are a constellation of leukoproliferative disorders that fall in the latter category. Advances in immunohistochemical studies, molecular diagnosis, and targeted therapies related to the underlying pathophysiology have changed the outcomes of many of these conditions. It is essential for allergists-immunologists to have a solid knowledge of these conditions, whether on a daily practice or as consultants to other services and specialties.