Eosinophils basically go through the same maturation stages as neutrophils. However, they are only recognizable as eosinophils if the specific eosinophilic granules occur. This is the case only from the myelocyte stage on. Since nuclear maturation does not occur immediately, immature eosinophils are distinguished from mature eosinophils in bone marrow. Eosinophils constitute about of nucleated bone marrow cells (myelogram).
Immature eosinophils have a round to oval nucleus. The granules are relatively coarse and uniformly distributed. In the course of maturation, they change color form bluish to brownish orange to orange. The cytoplasm appears bluish between the granules.