Final answer:
Eosinophilia is defined as an absolute eosinophil count above 500 cells/µL. These cells play a role in immune responses against parasitic infections and allergies. Elevated or reduced counts indicate various medical conditions.
Step-by-step explanation:
Eosinophilia is defined as an absolute eosinophil count above 500 cells per microliter (µL) of blood. Eosinophils are a type of white blood cell that make up 2-4 percent of the total leukocyte count and are typically 10-12 µm in diameter. They play a role in combating parasitic infections and allergic reactions. High counts of eosinophils in the blood can indicate conditions such as allergies, parasitic infections, and certain autoimmune diseases. The granules of eosinophils contain antihistamines and substances toxic to parasites. Additionally, eosinophils can perform phagocytosis, especially when antibodies bind to a target, forming an antigen-antibody complex. Low eosinophil counts might be observed in cases of drug toxicity or stress.