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Reactive lymphocytes or variant lymphocytes are lymphocytes that become large as a result of antigen stimulation. Typically they can be more than 30 µm in diameter with varying size and shape. The nucleus of a reactive lymphocyte can be round, elliptic, indented, cleft or folded. The cytoplasm is often abundant and can be basophilic. Vacuoles and/or azurophilic granules are also sometimes present. Most often the cytoplasm is gray, pale blue or deep blue in colour. The distinctive cell associated with EBV or CMV is known as a "Downey cell", after Hal Downey, who contributed to the characterization of it in 1923.〔Downey H, McKinlay CA. Acute Lymphadenosis Compared with Acute Lymphatic Leukemia. Arch Intern Med. 1923;32:82-112〕 It is sometimes erroneously called a "Downy cell". ==Causes== Reactive lymphocytes are usually associated with viral illnesses, however, they can also be present as a result of drug reactions (such as phenytoin), immunisations, radiation, hormonal causes (such as stress and Addison's disease) as well as some auto-immune disorders (such as rheumatoid arthritis). Some pathogen-related causes include: * Epstein-Barr virus * Cytomegalovirus * Toxoplasma gondi * Treponema pallidum (Syphilis) * Streptococcus agalactiae (Group B Streptococci), * Hepatitis C * Hantavirus 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Reactive lymphocyte」の詳細全文を読む スポンサード リンク
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