The image about shows morphology of cells of the neutrophilic series. The first cell to show commitment to a particular granulcoytic series (eosinophilic, basophilic or eosinophilic) is the promyelocyte. The promyelocytes of the three series can however only be differentiated by electron microscopy. The earliest cell showing features of neutrophilic differentiation on staining with Romanowsky staining is the myelocyte. Myelocytes may be neutrophilic, eosinophilic and basophilic. Myelocyte is a round cell with a round to oval nucleus that may be eccentrically placed. The cytoplasm shows two types of granules.
- Primary granules: The primary granules are azurophilic (reddish-purple or burgundy color) and are remnants of the granules of the promyelocyte stage. The myelocyte does not synthesize primary granules. As the cell matures the number of primary granules declines and they disappear by the cells matures to a polymorphonuclear neutrophil.
- Secondary granules: The the size and staining of secondary granules are specific to the type of granulocytes. In neutrophils these granules are fine and pink staining
As the myelocyte matures the nucleus becomes more indented and finally becomes lobed.
The image above captures these changes
- Cells labels (1) are myelocytes. These show a pink cytoplasm with few primary (azurophilic) and many secondary (fine pink) granules and have a oval eccentrically placed nucleus with clumped chromatin without a nucleolus.
- The myelocyte develops and indentation of the nucleus and matures to a metamyelocyte. The metamyelocyte matures to a band neutrophil (cells labeled 2). which is called so because the nucleus is band shaped. With maturation the nucleus develops lobulation. The differentiation between a band neutrophil and a two lobed neutrophil is arbitrary and of little practical importance. A band cell becomes a two lobed neutrophil when its nucleus develops a constriction that is more than half to two third of the nuclear width (cell labeled 3).
- A neutrophil usually has 2-5 nuclear lobes (cells labeled 4)