Leukocyte Responses to Endotoxin

描述（由申请方提供）：血小板活化因子（PAF）是一种磷脂类自凝物，最初定义为将过敏性休克动物的休克转移至未处理动物的原理。它是迄今为止定义的最强大的炎性脂质介质：注射合成PAF会导致休克伴外周血融合不足和血管舒张、肺血管收缩、心脏功能受损，并诱导血液浓缩伴组织水肿。急性炎症/先天性免疫系统的所有细胞组分表达PAF受体。PAF募集、引发和激活组织并引发巨噬细胞、单核细胞和血小板。 PAF在脓毒症和对内毒素的反应中起主要作用。在实验性内毒素血症的研究中，PAF的血清水平增加，并且PAF受体的阻断完全阻断LPS诱导的死亡。PAF是吸入细菌内毒素和注射PAF乙酰水解酶（一种特异性灭活PAF的磷脂酶）后释放的主要损伤促进介质，可预防过敏性休克动物模型的死亡。PAF乙酰水解酶活性降低与临床脓毒症相关。 然而，与模型相反，PAF的单一受体的阻断在人类中并不有效，最有可能是因为PAF受体拮抗剂相对于PAF较弱。一个更有效的方法，抑制PAF的合成，不能完成，因为PAF合成的限速酶尚未被分子表征。我们不了解内毒素如何诱导PAF合成，因为我们不知道有哪种细胞能产生PAF并在内毒素刺激下释放PAF。存在通过对循环脂质的不受调节的氧化攻击形成的生物活性PAF类似物，并且我们不知道在内毒素暴露后在血液和肺灌洗液中检测到的PAF活性是生物合成的PAF还是也激活PAF受体的化学产生的氧化磷脂。 我们建议纯化和分子克隆合成PAF的酶，建立白细胞中连接内毒素受体和PAF产生的信号转导通路，确定PAF合成是否促进PAF样脂质结构模拟物的形成，并确定PAF如何影响合成它的细胞，我们预计这项工作将导致一类新的抗炎剂。

DESCRIPTION (provided by applicant): Platelet-activating factor (PAF), a phospholipid autocoid, was originally defined as a principle that transferred shock from an animal in anaphylactic shock to a naive animal. It is the most powerful inflammatory lipid mediator yet defined: injection of synthetic PAF causes shock with peripheral hypofusion and vasodilation, pulmonary vasoconstriction, compromises cardiac function, and it induces hemoconcentration with tissue edema. All cellular components of the acute inflammatory/innate immune system express the receptor for PAF. PAF recruits, primes, and activates tissue and elicited macrophages, monocytes, and platelets. PAF has a major role in sepsis and the response to endotoxins. Serum levels of PAF are increased in studies of experimental endotoxemia, and blockade of the PAF receptor completely blocks LPS-induced death. PAF is the major injury-promoting mediator released after inhalation of bacterial endotoxin and injection of PAF acetylhydrolase--a phospholipase that specifically inactivates PAF--prevents death in animal models of anaphylactic shock. Decreased PAF acetylhydrolase activity is associated with clinical sepsis. However, models to the contrary, blockade of the single receptor for PAF has not been efficacious in humans, most likely because PAF receptor antagonists are weak relative to PAF. A more efficacious approach, suppression of PAF synthesis, cannot be accomplished because the rate-limiting enzyme for PAF synthesis has not been molecularly characterized. We do not understand how endotoxin might induce PAF synthesis because we do not know of a cell that makes PAF and releases in response to endotoxin stimulation. There are biologically-active PAF analogs formed by unregulated oxidative attack on circulating lipid, and we do not know whether the PAF activity detected in blood and lung lavage after endotoxin exposure is biosynthetic PAF or a chemically produced oxidized phospholipid that also activates the PAF receptor. We propose to purify and molecularly clone the enzyme that synthesizes PAF, to establish the signal transduction path in leukocytes that connects endotoxin receptors to PAF production, determine if PAF synthesis promotes the formation of PAF-like lipid structural mimetics, and to determine how PAF might affect the cell that synthesizes it. We anticipate this work will lead to a new class of anti-inflammatory agents.