Granulocytes are a category of leokocytes characterized by the presence of granules in their cytoplasm. Granulocytes originate from stem cells in the bone marrow. There are three types of granulocytes: neutrophil granulocytes, eosinophil granulocytes, and basophil granulocytes. Names of different granulocytes are derived from their staining characteristics; for example, the most abundant granulocyte is the neutrophil granulocyte, which has neutrally-staining cytoplasmic granules. These include antibodies that serve as a pan marker of granulocytes that are considered immature (CD16, CD34) and activated (CD11b, CD18). CD15 and CD66b, also as a markers for the identification of granulocytes.
Basophils are a rare subset of granulocytes that contain large granules containing histamine, proteoglycans, proteolytic enzymes, lipid mediators (leukotrienes) and cytokines. These granules release their contects with activation by IgE or other stimuli. Basophils are involved in defense against parasites and play a role in allergic reactions. Basophils display a variety of Cluster of differentiation / CD antigens. Basophils express two subtypes of IgG receptors (CD32a and CD32b). Basophils display a number of growth-factor receptors, such as IL-2R (CD25, CD122, CD132), IL-3R (CD123), IL-4R (CD124), CD116, CD271, and CD181. Contrasting with c-kit (CD117) is displayed only feebly on basophils. It is interesting that basophils express different types of chemokine receptors such as CD191, CD192, CD193, CD195, CD181, CD182, CD184, and CD294. Basophils also display a number of adhesion molecules and myeloid markers, such as CD13, CD26, CD45, CD33, CD43, CD44, CD54, CD11b, CD17, CD31, and CD35. Typical myelomonocytic antigens, such as CD14, CD15, and CD16; natural killer (NK) cell markers (CD56, CD57); or Band T-cell antigens (CD19, CD20, CD21, CD3, CD4, and CD8, respectively), are not detected on normal basophils. Finally, basophils express ceramide monohexoside class I molecules and CD63, which is displayed on the surface of granules in resting cells but becomes detectable on the cell membrane after activation.
Eosinophilic granulocytes are mostly located in tissues, and not in the peripheral blood, which are a small subset of granulocytes that play a role in the innate immune defense against parasites and viruses, while also contributing to allergy and asthma. They differentiate from myeloid precursor cells in response to CD123, CD125, and CD116.
Neutrophils are the most common cell type found in the blood, constituting a major part of the innate immune system. Neutrophil migration from the circulation into an area of inflammation involves regulated expression of clusters of differentiation antigens. CD62L is important in the initial attachment of leucocytes to endothelium, and is rapidly shed after neutrophil activation. CD11b and CD18 are followed by tight adhesion and transendothelial migration. Neutrophil activation is associated with upregulation of CD11b and CD18 from intracellular storage pools, and shedding of CD62L. The other markers for the identification of Neutrophils by flow cytometry, example CD15, CD35, and CD68.