NEUTROPHILS, (also called segmented neutrophils, segs, polymorphonuclear cells, polys, or PMNs) are about 12 microns in diameter, whose function is to engulf and destroy invading organisms. They make up about 50 to 70% of the total WBC count in the peripheral blood and may have two to five nuclear lobes connected by a thin strand of nuclear material. This WBC may be seen in greater numbers during infections, malignancies or extreme stress situations. Using a standard Romanowsky dye, the blood slides are stained to better visualize the various cell types. The cytoplasm of neutrophils is pale and often contains small pink to purple granules. These granules (specific granules and azurophilic granules) contain certain enzymes and proteins that neutralize or destroy microorganisms.

Anomalies of WBCs may include:

• Toxic Granulation: large dark blue granules in the cytoplasm, associated with severe infection, chemical poisoning, and other toxic states.
• Vacuolization: vacuoles appear as holes in the cytoplasm and are frequently found in association with toxic granulation.
• Döhle bodies: irregular grayish or greenish inclusions in the peripheral cytoplasm of neutrophils. They are nuclear remnants that are often seen in association with toxic granules and vacuoles. They may be present in association with burns, trauma, acute or systemic infections, and may be present with exposure to cytotoxic agents (ie, chemotherapy). They may also be seen during a normal pregnancy.
• Auer Bodies (Auer Rods): unique, pink or red rod-shaped inclusions that are seen in very immature granulocytes ("blasts") in patients with acute non-lymphocytic leukemias (i.e., Acute Myeloid leukemia; AML).
• Bands: immature neutrophils with a “U” shaped nucleus. Bands are normal in the circulation in small numbers but if there is a percentage increase of them, there is said to be a “left shift.” This may happen when an acute infection stimulates increased neutrophil production causing the bone marrow to prematurely release some WBCs before they have matured to the neutrophil stage.
• Hypersegmentation: neutrophils with 6 or more nuclear segments. This is mainly associated with B12 and Folate deficiency.
• Pelger-Huët: hereditary anomaly where neutrophils appear with fewer than two lobes. The nucleus is often in the shape of a peanut or dumbbell, or may consist of two lobes connected with an obvious filament. They may also appear in certain disease states and is referred to a "pseudo- Pelger-Huët".
• Alder-Reilly granules: large, dark leukocyte granules that stain purple. They are indicative of mucopolysaccharidosis (an inherited enzyme deficiency disorder, Hurler's and Hunter's syndromes).
• Chédiak-Higashi syndrome: an inherited anomaly characterized by the presence of big red, blue, or greenish granules of variable size that are peroxidase positive and indicate a lethal metabolic disorder, they may be found in granulocytes, lymphocytes, and monocytes. Patients with this syndrome may exhibit neurological problems as well as a compromised immune system and photophobia. Death often ensues.

EOSINOPHILS have 2 or 3 lobes to their nucleus and contain characteristic reddish/orange granules in their cytoplasm. They are most often involved in allergic responses and parasitic infections. About 1 – 4% of WBCs are eosinophils.

BASOPHILS have a multi-lobed nucleus and have many dark blue granules (which contain histamines) in their cytoplasm. Only about 1% of WBCs are basophils. A sight elevation in number may be seen during an allergic response, ulcerative colitis, chronic sinusitis, chicken pox and immunizations. A significant increase is not uncommon in certain myeloid leukemias.

LYMPHOCYTES are relatively small (7-10 µm) and round in shape. The nucleus is generally large in relation to the amount of cytoplasm. The cytoplasm is pale blue and generally does not contain any granules. The nucleus of most lymphocytes is smooth in appearance and is dark blue. There are two major types of lymphocytes, B cell and T-cell, but they cannot be distinguished when viewed under the microscope using standard staining techniques. B cells can be differentiated from T cells using specific fluorescent-labeled antibody stains in conjunction with a special instrument called a flow cytometer. B cells create specific antibodies while T-cells can activate B cells as well as recognize and destroy invading organisms. Lymphocytes make up about 20% to 40% of the total WBC count.

• Reactive Lymphocyte (atypical, activated, Downey cells): these cells are large lymphocytes that contain a greater amount of cytoplasm and can vary in size and shape. Often a characteristic bluish tinge of cytoplasm is seen where the cell abuts with surrounding RBCs. Increase numbers of atypical lymphocytes are found in viral illnesses such as infectious mononucleosis.
• Hairy Cells: these lymphocytes have tiny projections that make them appear hairy under the microscope. They are found in hairy cell leukemia.

MONOCYTES are the largest of the WBCs and comprise less than 6% in normal blood. They are characterized by their abundant blue-grey cytoplasm that is irregular in shape and have a folded nucleus. The main function of Monocytes is to ingest microorganisms and respond to infection and inflammation by releasing certain proteins (monokines) that can inactivate bacteria. When stimulated by cytokines, monocytes can move out of the bloodstream and become tissue macrophages.