Eosinophils, along with the rest of the myeloid blood cell lineages, develop in the bone marrow microenvironment from multipotent hematopoietic stem cells.
Normal numbers of circulating eosinophils range from 0–500 per μL in human blood (1–5% of all circulating leukocytes) , but in certain conditions can increase by 20-fold or more.
Eosinophil participate in innate immunity to parasites, especially to helminths.
Peripheral blood eosinophilia is generally defined as an absolute eosinophil count (AEC) ≥500/μL and is associated with allergic conditions like asthma and atopic dermatitis, to eosinophilic gastrointestinal disorders (EGID) and others.
(Source: Klion, 2020)