Lymphocytes live int he immune rich tissues like the lymph nodes, spleen, tonsils, thymus, gastrointestinal lymphoid tissue, bronchial lymphoid tissue, bone marrow and in the blood.
There are many possible causes for an abnormally low (less than 15%) lymphocyte count. Since lymphocytes are made in the bone marrow (a tissue that fills the openings of bones), if not enough bone marrow is produced or the activity of the bone marrow decreases, an abnormally low lymphocyte count can occur. Bone marrow destruction occurs in aplastic anemia. Aplastic anemia is a condition in which the there is an abnormal decrease in the cells that make up blood (such as white blood cells) because the bone marrow is not working properly to make these cells. Aplastic anemia can cause an abnormally low lymphocyte count.
People with AIDS (Acquired Immune Deficiency Syndrome) often have an abnormally low lymphocyte count. AIDS is a decrease in the effectiveness of the body's immune (defense) system that is due to infection from a virus known as HIV (human immunodeficiency virus). Tumors (tissues that grow more rapidly than normal) can cause an abnormally low lymphocyte count.
Steroids can cause an abnormal decrease in the lymphocyte account. Steroids are any of a large number of hormone substances with a similar and basic chemical structure. Hormones are natural chemicals produced by the body and released into the blood that have a specific effect on tissues in the body. An overactive adrenal cortex can also cause an abnormal decrease in the lymphocyte count. The adrenal cortex is the outer part of an important organ (the adrenal gland) that produces hormones that are essential for the body to regulate itself.
Some disorders that affect the nerves in the body can cause the lymphocyte level to be too low. Examples are multiple sclerosis, myasthenia gravis, and Guillain-Barre syndrome. Multiple sclerosis is a condition in which people develop multiple areas of abnormal patches (also known as plaques or sclerosis) in the brain and/or spinal cord (depending on the stage of the illness). Myasthenia gravis is a type of disorder in which the muscles get weak and tire easily as a result of poor conduction (transmission) of nerve impulses. Guillain-Barre syndrome is a rare disorder that causes weakness in the arms and legs because of nerve damage
There are many possible causes for an abnormally high lymphocyte count. A lymphocyte level that is more than 40% is considered to be abnormally high. Some basic causes of a high lymphocyte count are the flu and the chickenpox. Other causes of a high lymphoocyte level include tuberculosis, mumps, rubella, varicella, whooping cough, brucellosis, and herpes simplex.
Acute lymphoblastic leukemia (ALL) and chronic lymphocytic leukemia (CLL) cause increases in lymphocytes. Leukemia is a type of cancer in the blood in which bone marrow (a tissue that fills the openings of bones) is replaced by early forms of white blood cells. Cancer is a group of disease in which symptoms are due to an abnormal and excessive growth of cells in one of the body organs or tissues. ALL is a type of leukemia in which there are too many immature (not fully developed) white blood cells called blasts that are produced by the bone marrow (a tissue that fills the openings of bones). One type of blast present in ALL is the lymphoblast, which is an immature lymphocyte. CLL is a type of leukemia characterized by the presence of too many mature lymphocytes.
Other conditions that can cause an abnormally high lymphocyte count include mononucleosis, hepatitis, toxoplasmosis, and cytomegalovirus. Mononucleosis is suddenly occurring virus infection that is characterized by an abnormal increase in a type of white blood cell in the blood. Hepatitis is an infection of the liver that causes liver inflammation. The liver is the largest organ in the body and is responsible for filtering (removing) harmful chemical substances, producing important chemicals for the body, and other important functions. Toxoplasmosis is a type of infection of birds, reptiles, and other animals that can also occur in humans. Cytomegalovirus is a type of virus that usually causes infections in the eye and the stomach area.
Certain medications can also lead to a high lymphocyte count. Two such medications are Dilantin and mephenytoin, which are both anti-seizure medications Seizures are involuntary muscle movements and/or decreased environmental awareness due to overexcitement of nerve cells in the brain. High lymphocyte levels also occur after blood transfusions. A blood transfusion is a procedure in medicine in which blood (usually from another person) is introduced into someone's bloodstream.
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