Granulocytes have two types of granules primary and secondary. Primary granules are azurophilic, most numerous and prominent at the promyelocyte stage (see morphology of myeloid precursors) and diminish in number with further maturation. As the granulocyte matures the staining characters of the primary granules changes. They initially become violet and then became inapparent because they fail to take up stain. The secondary granules appear in the myelocytes and persist for the rest of the ice of the granulocyte. Neutrophils have fine pink secondary granules.
In conditions of intense stimulation of neutrophil maturation the primay granules may continue to take up stain in mature neutrophil because of a higher concentration of acid mucosubstances. These are called as toxic granules and the change called toxic change. The toxic granules are so called because they were first described in patients with gram negative sepsis and endotoxemia but may be found under conditions of intense stimulation of neutrophil production. The may be seen in
- Inflammatory diseases
- Use of haemopoietic growth factors (G-CSF or GM-CSF)
Neutrophilic Cells. The images shows myelocyte (1), band neutrophils (2), two lobed neutrophil (3) and neutrophils (4)
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)
The image above shows a lymphocyte (left) and a polymprphonuclear neutrophil (right) in the peripheral blood. The lymphocyte is a cell about 10μ in size with a dense purple nucleus and agranular, slightly basophilic (blue) cytoplasm. About 10% of the lymphocytes are larger and have more abundant cytoplasm which shows granules (large granular lymphocytes). This is a small lymphocyte. A polymorphonuelear neutrophil is 12-15μ a cell with a segmented nucleus (not visible in this picture because the nucleus is folded on itself) that has clumped chromatin and an eosinophilic (pink) cytoplasm and pink granules. The contrast between nuclear shape, chromatin, cytoplasmic staining and granulation of the two cells is evident.
One X chromosome of women is inactivated. In nrutrophils this may appear in one of three forms. Drumsticks are nuclear appendages 1.5μ in diameter. They are seen in 0.5-2.6% of neutrophils. The inactivated X chromosome may also appear as sessile nodules or as a condensation under the nuclear membrane. The frequency of drumsticks increases with nuclear segmentation. They may be seen in eosinophils but are uncommon as eosinophils have fewer lobes. Racquet forms have a central clearing and should not be confused with drumsticks. They are not inactivations of X chromosomes. The X chromosome is only inactivated in an individual with more than one chromosome. Drumsticks are not seen in individuals having only one X chromosomes [males (XY), Turner's syndrome (XO) and testicular feminization (XY)]. Contrary to expectations individuals who are XXX rarely have cells with two drumsticks. They have an increased incidence of sessile nodule. XXX is also characterized by fewer neutrophil segments. Drumsticks in XXX are less common than normal women. The incidence of drumsticks in patients with Klienfelter’s Syndrome (XXY) is lesser than normal women. Shift to left, CML and Down’s syndrome is characterized by a decreased drumstick count. It returns to normal in CML following treatment. Drumsticks are more frequent in women with isochromosome of the long are of X. Patients with megaloblastic anaemia and congenital hypersegmentation have a higher frequency of drumsticks in the peripheral smear.