Eosinophile granulocytes are a type of blood cell belonging to the family of leukocytes, or white blood cells. They are involved in the immune system, notable in defending the body against parasites or allergic reactions. On average, they are found in very small quantities in comparison to the white blood cells, and can be entirely absent. Given this, a low eosinophile granulocyte count is common, and in no way constitutes a pathological abnormality. It is only when their count increases that the underlying cause should be investigated, as this is frequently caused by allergies or parasitic infestations.