eosinofily

Eosinophils are a type of white blood cell, part of the immune system. They belong to the granulocyte family and are characterized by a bilobed nucleus and granules that stain with eosin, giving the cell its name. In healthy individuals, eosinophils constitute about 1–6% of circulating leukocytes, with an absolute count typically below roughly 500–600 cells per microliter.

Eosinophils originate in the bone marrow from hematopoietic stem cells and mature under signals such as interleukin-5 (IL-5). They circulate briefly in the blood and migrate into tissues, where they reside in mucosal surfaces of the respiratory and gastrointestinal tracts, among others. The granules contain cytotoxic proteins and enzymes, including major basic protein (MBP), eosinophil cationic protein (ECP), eosinophil-derived neurotoxin (EDN) and eosinophil peroxidase (EPO). They can release these mediators via degranulation in response to parasites or allergens.

Functions of eosinophils include defense against helminth parasites, modulation of inflammatory responses, and participation in allergic reactions. They interact with mast cells, T cells and antigen-presenting cells, and can secrete cytokines, chemokines and growth factors that influence other immune cells. In excess, eosinophils can contribute to tissue damage and fibrosis, as seen in conditions such as eosinophilic asthma, eosinophilic esophagitis, and certain hypereosinophilic syndromes.

Clinical relevance: eosinophilia refers to an elevated eosinophil count and can result from parasitic infections, allergic diseases, drug reactions, and some malignancies or autoimmune disorders. Diagnosis relies on blood counts and clinical context; management targets the underlying cause, with newer options including anti-IL-5 therapies for selected severe eosinophilic diseases.