Granulocytes are innate immune cells that contain specialized granules to provide the first line of immune defense. Upon arrival at the site of infection, they participate in the inflammatory reaction by phagocytosis and intracellular killing of bacteria, the production of inflammatory mediators and the release of cytotoxic enzymes and proteins.
There are three basic types of granulocytes: neutrophils, basophils, and eosinophils.
Neutrophils, which constitute 50-70% of the circulating white blood cells are much more numberous than eosinophils (1-3%) or basophils (<1%).
Types of Granulocytes
1: Neutrophils are the ost abundant WBC in blood. They leave the blood and enter tissues to phaogcytize foreign material. An increase in neutrophils in the blood is indicative of a systemic bacterial infection. Because of the variation in nuclear appearance, they are also called polymorphonuclear neutrophils (PMNs). Neutrophile granuloctyes contain myeloperoxidase-rich azurophil granules.
2. Eosinophils are also phagocytic and can migrate from the blood into the tissue spaces. Eosionphil granuloctyes contain the peroxidase, the eosinophil peroxide with sahres about 70% DNA homology with myeloperoxidase.
3. Basophils secrete histamine to help mediate inflammatory reactions and are closely related in function to mast cells. As with mast cells (see immune cells), each mast cell carries 30-100k cell receptors which trigger the release of inflammatory cytokines from cytoplasmic granules (secretory vesicles) when bound by IgE that has been stimulated by the allergen.
The primary chemical mediators produces by mast cells and basophils are histamine (potent stimulatory of secretory glands and smooth muscle, which constricts smooth muscle layers of the small bronchi and intestine but actually relaxes vascular smooth muscle and dialates arterioles and ventules), serotonin, leuktriene (slow-reacting substance of anaphylaxis for its proeprty of inducing gradual contraction of smooth muscle), platelet-activating factor, prostaglandins (group of inflmmatory agents responsible for vasodilation, increased vascular permeability and sensitivity to pain as well as bronchoconstriction –nonsteroidal anti-inflammatory durgs (NSAIDS) such as aspirin and ibuprofen work by preventing the actions of protaglandins), and bradykinin (causes prolonged smooth muscle contraction of the bronchioles, dilation of peripheral arterioles, increased capillary permeability and increased muscus secretion. These inflammatory cytokines, acting alone or in combination account for allergy symptoms.
Identification of the different Granulocytes
The granulocytes are classified as neutrophils, eosinophils, or basophils on the basis of cellular morphology and cytoplasmic staining characteristics. The different pattern of peroxidase contained in the white blood cell fraction is the basis for leukocyte differentiation by an automatic blood cell counter, the Bayer/Technicon H3.
Goumenlouk (US6,046,019) discloses a method for detecting granulocytes where a blodo sample is dran, components that might interfere with the assay are remove/neutralized, the granulocytes present int he sample are disrupted to release intracellular myleoperoxidase and then the sample is contacted with a peroxide and a chromogenic donor dye. The MPO enzyme catalyzes hydrogen peroxide involved reactions which result in the dye changing color ir, and to the extent that, granulocytes are present in the blood sample.