Neutrophilia is a term used to describe a condition where there are too many neutrophils circulating in the blood. Between forty and sixty percent of all white blood cells in the body are neutrophils. Neutrophils are the first to respond to foreign pathogens that invade into the body. When cells around the body become damaged, chemokines are released and attract neutrophils to the site. Neutrophils mediate foreign pathogens by undergoing the processes of endocytosis and phagocytosis or engulfing the pathogens. Once engulfed, specialized enzymes in neutrophils induce the destruction of the pathogen. A healthy individual typically has between 2500 and 7500 neutrophils per microliter of blood. Neutrophilia has numerous causes that can be classified into three groups. Reactive neutrophilia is an active response to stress or infection. Proliferative neutrophilia happens when some mechanism causes the bone marrow to overproduce neutrophils. Demargination occurs when specific neutrophils detach from the blood vessel lining and remain circulating in the blood.
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Individuals affected by arthritis may develop neutrophilia as a result of their inflammatory condition. Neutrophils are the main type of white blood cell that contributes to the trigger and progression of arthritis in affected individuals. Neutrophils play this role by their release of molecules that are toxic to other living cells in the body and molecules that mediate responses between macrophages and lymphocytes. Neutrophils in individuals who have arthritis have different cellular properties than those in healthy individuals. Rheumatoid arthritis patients have neutrophils with delayed cellular death and a more sophisticated ability to generate reactive oxygen species, activate and deactivate certain genes, and expression of high-affinity FcY receptors on the cell membrane. Arthritis patients also have an immune system that exhibits a defect in their function of neutrophil clearance due to the autoimmunity nature of arthritis. In some cases of autoimmune disorders such as arthritis, neutrophils may be the point of supply of the specific autoantigens or antibodies that propel the underlying mechanisms that result in the autoimmune disease. It is a combination of neutrophil apoptosis delay, clearance defects of neutrophils, and other abnormal properties of neutrophils that can cause an individual with arthritis to also be affected by neutrophilia.
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