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An exotoxin is a toxin secreted by bacteria. An exotoxin can cause damage to the host by destroying cells or disrupting normal cellular metabolism. They are highly potent and can cause major damage to the host. Exotoxins may be secreted, or, similar to endotoxins, may be released during lysis of the cell. Gram negative pathogens may secrete outer membrane vesicles containing lipopolysaccharide endotoxin and some virulence proteins in the bounding membrane along with some other toxins as intra-vesicular contents, thus adding a previously unforeseen dimension to the well-known eukaryote process of membrane vesicle trafficking, which is quite active at the host-pathogen interface. They may exert their effect locally or produce systemic effects. Well-known exotoxins include: botulinum toxin produced by ''Clostridium botulinum''; ''Corynebacterium diphtheriae'' toxin, produced during life-threatening symptoms of diphtheria; tetanospasmin produced by Clostridium tetani. The toxic properties of most exotoxins can be inactivated by heat or chemical treatment to produce a toxoid. These retain their antigenic specificity and can be used to produce antitoxins and, in the case of diphtheria and tetanus toxoids, are used as vaccines. Exotoxins are susceptible to antibodies produced by the immune system, but many exotoxins are so toxic that they may be fatal to the host before the immune system has a chance to mount defenses against them. For this reason antitoxin, anti-serum containing antibodies, is injected to provide passive immunity. == Types == Many exotoxins have been categorized.〔(【引用サイトリンク】title=Bacterial Pathogenesis: Bacterial Factors that Damage the Host - Producing Exotoxins )〕 This classification, while fairly exhaustive, is not the only system used. Other systems for classifying or identifying toxins include: * By organism generating the toxin * By organism susceptible to the toxin * By tissue target type susceptible to the toxin (neurotoxins affect the nervous system, cardiotoxins affect the heart, etc.) * By structure (for example, AB5 toxin) * By the ability of the toxin to endure in hostile environments, such as heat, dryness, radiation, or salinity. In this context, "labile" implies susceptibility, and "stable" implies a lack of susceptibility. * By a letter, such as "A", "B", or "C", to communicate the order in which they were identified. The same exotoxin may have different names, depending of the field of research. 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「Exotoxin」の詳細全文を読む スポンサード リンク
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