During human diamine oxidase (DAO) ELISA development we noticed that in serum DAO concentrations appear to be higher when compared to plasma. Neutrophils contain DAO in the specific granules and we hypothesized that DAO is released from neutrophils during serum coagulation. If activation of neutrophils can release DAO, its concentrations might be elevated in vivo after lipopolysaccharide (LPS) administration and in bacteremic patients. Using blood from healthy volunteers DAO concentrations were measured ex vivo in serum, citrate, EDTA and heparin plasma over several hours and after activation of neutrophils. Lipopolysaccharide and granulocyte-colony stimulating factor (G-CSF) were administered to 15 and 8 healthy volunteers, respectively and DAO concentrations were measured at different timepoints. DAO antigen levels were also determined in three different subcohorts of patients with culture-proven bacteremia and high C-reactive protein (CRP) levels. DAO concentrations were elevated in a time-dependent manner in serum but not in EDTA or citrate plasma (P < 0.01). Neutrophil activation using phorbol myristate acetate (PMA) and zymosan dose-dependently caused DAO concentrations to be elevated more than 10-fold at both 22°C and 37°C (both P-values <0.001). Administration of LPS to healthy volunteers released DAO from neutrophils (P < 0.001). Of the 55 different bacteremic patients selected from three independent cohorts only 3 (5.4%) showed highly elevated DAO concentrations. Serum DAO concentrations do not accurately reflect circulating enzyme levels but coagulation-induced neutrophil activation and consequently DAO release. Only a few bacteremic patients show high DAO concentrations able to degrade histamine rapidly.

在人二胺氧化酶（DAO）ELISA的开发过程中，我们注意到与血浆相比，血清DAO浓度似乎更高。中性粒细胞在特定颗粒中含有DAO，我们假设DAO在血清凝结过程中从中性粒细胞中释放出来。如果中性粒细胞的活化可以释放DAO，则在脂多糖（LPS）给药后和细菌性患者体内，其DAO浓度可能会升高。使用健康志愿者的血液，在嗜中性粒细胞活化后数小时内，在血清，柠檬酸盐，EDTA和肝素血浆中离体测量DAO浓度。分别向15名和8名健康志愿者施用脂多糖和粒细胞集落刺激因子（G-CSF），并在不同时间点测量DAO浓度。在三个经过文化验证的菌血症和高C反应蛋白（CRP）水平的亚人群中，还确定了DAO抗原水平。血清中DAO的浓度呈时间依赖性升高，但EDTA或柠檬酸盐血浆中的DAO浓度却没有升高（P  <0.01）。使用佛波肉豆蔻酸酯乙酸酯（PMA）和酵母聚糖的嗜中性粒细胞活化剂量依赖性地导致DAO浓度在22°C和37°C时都升高了10倍以上（均为P值<0.001）。对健康志愿者进行LPS给药可从中性粒细胞释放DAO（P  <0.001）。从三个独立的队列中选出的55名不同的细菌患者中，只有3名（5.4％）的DAO浓度高。血清DAO浓度不能准确反映循环酶水平，但会引起凝血诱导的中性粒细胞活化，进而导致DAO释放。只有少数细菌患者表现出能够迅速降解组胺的高DAO浓度。