Nyarko K A, Coomber B L, Mellors A, Gentry P A
Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, Canada.
Vet Microbiol. 1998 Mar 15;61(1-2):81-91. doi: 10.1016/s0378-1135(98)00171-0.
Platelet and fibrin deposits are among characteristic changes observed in lung alveoli of cattle with pasteurellosis induced by Pasteurella haemolytica (biotype A, serotype 1). To determine whether the platelet function could be directly affected by protein products produced by the bacterium, the effects of leukotoxin and O-sialoglycoprotease, culture supernatant antigen secreted by Pasteurella haemolytica A1, on bovine platelet activation were examined by evaluating the enhancement of platelet adhesion to a negatively charged surface relative to untreated control samples. The glycoprotease, or the leukotoxin, was added to plasma free suspensions of bovine platelets and platelet adhesion assessed by two parameters: (i) the number of 3H-adenine-labeled adherent platelets and (ii) the morphology of unlabeled platelets adhering to the charged surface under scanning electron microscopy (SEM). In the presence of calcium, the glycoprotease produced a dose-dependent increase in adhesion. At a concentration of 4.0 micrograms glycoprotease extract protein per 10(7) platelets, a 2-fold increase in adhesion was observed which was similar to the increase in adhesion induced by 0.10 units of thrombin, a known platelet agonist. Both increased platelet adhesion and platelet aggregation were observed with 0.8 microgram glycoprotease extract protein in the presence of calcium. The response of the bovine platelet suspensions to leukotoxin extract protein was dependent on the dosage of the leukotoxin. Adhesion was enhanced at dosages of 25 micrograms leukotoxin protein per 10(7) platelets and below, while at dosages of 50 micrograms and above adhesion was suppressed. Thus, the two proteins secreted by P. haemolytica may interact directly with bovine platelets to initiate platelet aggregation and fibrin formation in alveolar tissue in pneumonic pasteurellosis.
血小板和纤维蛋白沉积是由溶血巴斯德氏菌（生物型A，血清型1）引起的牛巴氏杆菌病的牛肺泡中观察到的特征性变化之一。为了确定血小板功能是否会受到该细菌产生的蛋白质产物的直接影响，通过评估相对于未处理的对照样品，血小板对带负电荷表面的粘附增强情况，研究了溶血巴斯德氏菌A1分泌的白细胞毒素和O-唾液酸糖蛋白酶（培养上清液抗原）对牛血小板活化的影响。将糖蛋白酶或白细胞毒素添加到牛血小板的无血浆悬浮液中，并通过两个参数评估血小板粘附：（i）3H-腺嘌呤标记的粘附血小板数量，以及（ii）扫描电子显微镜（SEM）下粘附在带电表面的未标记血小板的形态。在有钙的情况下，糖蛋白酶使粘附呈剂量依赖性增加。在每10^7个血小板中加入4.0微克糖蛋白酶提取物蛋白时，观察到粘附增加了2倍，这与已知的血小板激动剂0.10单位凝血酶诱导的粘附增加相似。在有钙的情况下，0.8微克糖蛋白酶提取物蛋白同时增加了血小板粘附和血小板聚集。牛血小板悬浮液对白细胞毒素提取物蛋白的反应取决于白细胞毒素的剂量。在每10^7个血小板中加入25微克及以下白细胞毒素蛋白时，粘附增强，而在50微克及以上剂量时，粘附受到抑制。因此，溶血巴斯德氏菌分泌的这两种蛋白质可能直接与牛血小板相互作用，从而在肺炎巴氏杆菌病的肺泡组织中引发血小板聚集和纤维蛋白形成。
