29 Sep 2022


White Blood Cells: The Immune System's First Line of Defense

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White blood cells form part of the blood cellular components and are characterized by having irregular shapes, have nuclei, and lack hemoglobin. Leucocytes are formed from the stem cells found in the red bone marrow. Leukocytes normally circulate in lymph fluid as well as blood. Different types of white blood cells exist and play a critical role as far as the immune system is concerned. 

Different types of leukocytes exist, and each type is produced based on the regulation of a protein referred to as a Colony Stimulating Factor (CSF) ( Mader et al., 2006) . The classification of leukocytes is centered on the presence or absence of granules in their cytoplasm. The granular leukocytes, otherwise known as Polymorphonuclear (PMN), are three, namely, eosinophils, neutrophils, and basophils. Eosinophils have a bilobed nucleus and mediate immune responses by acting as the main inflammatory cells in both protein and allergic reactions. Additionally, eosinophils protect the body against large parasites through phagocytosis. 

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Neutrophils refer to the granulocytes that have a multilobed nucleus. Neutrophils defend the body against fungal and bacterial infections. Through phagocytosis, the neutrophils engulf the bacteria or fungus and eventually kills it. Basophils are the granulocytes that have a double-lobed nucleus that forms a U shape. The granules of the basophils contain heparin and histamine as part of its composition. Histamine plays the role of dilating blood vessels so that capillaries gain more permeability and increase blood flow. Increased blood flows ensures that more leukocytes reach the area of infection ( Mader et al., 2006) . Heparin, on the other hand, aid in inhibiting the formation of blood clots since they have anticoagulant properties. The role of basophils in mediating immune response is that they play the role of mediating the immune system's hypersensitivity reactions. 

Concerning the agranular leukocytes, they are the leukocytes that lack granules in their cytoplasm. The leukocytes are monocytes and lymphocytes. Lymphocytes are the white blood cells that perform a critical role in the immune system of the body. Lymphocytes mediate the immune system against infections by recognizing antigens, producing antibodies, and destroying the pathogenic cells ( Mader et al., 2006) . The antibodies produced by the lymphocytes also destroy the toxins produced by bacteria. Monocytes are the white blood cells that are the largest and can differentiate into myeloid lineage dendritic cells and macrophages. Monocytes act as tissue macrophages that respond to foreign organisms and remove them. Monocytes inhibit the invasion of pathogens that could not be killed effectively by the neutrophils. 


Mader, S. S., Windelspecht, M., & Cox, D. (2006).  Human biology . New York: McGraw-Hill. 

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