Cupp M S, Zhang D, Cupp E W
Department of Entomology, Auburn University, Auburn University, AL 36849-5413, USA.
J Med Entomol. 2000 May;37(3):416-21. doi: 10.1093/jmedent/37.3.416.
The horn fly, Hematobia irritans (L.), is an important pest of livestock because the adult stage of both sexes are aggressive blood-feeders. Remarkably, even though horn fly adults feed recurrently on their hosts as ectoparasites, these flies lack the ADP-responsive antiplatelet aggregation and vasodilatory antihemostatic systems described for other blood-feeding Diptera. Horn fly salivary gland extracts do interfere with the normal coagulation process as demonstrated by the recalcification time assay. Using this as a baseline, the effects of saliva on recalcification time, activated partial thromboplastin time, prothrombin time, and thrombin time were measured to determine which arm(s) of the coagulation cascade might be impacted. Factor-deficient plasma assays also were used to measure possible perturbations in clotting. Gland-free saliva delayed the recalcification time as well as the activated partial thromboplastin time, prothrombin time, and thrombin time. Saliva also further delayed clotting times of plasmas deficient in factor V, factor VIII, and factor XIII, indicating that other factors in the coagulation cascade were inhibited. Although horn fly saliva did not alter the ability of deficient plasma reconstituted with factor X to clot, it did inhibit deficient plasma reconstituted with factor II (thrombin). Antithrombin activity in saliva was confirmed by its ability to interfere with thrombin hydrolysis of fibrinogen, its normal substrate, and by its inhibition of thrombin action on a chromagenic substrate that mimics the hydrolytic site of fibrinogen. Thus, horn fly saliva contains a factor that specifically targets thrombin, a key component in the coagulation cascade. While the biochemical mechanisms of inhibition may vary, this antihemostatic characteristic is shared with other zoophilic Diptera such as black flies, Simulium spp., and tsetse, Glossina morsitans morsitans Westwood, that feed on ungulates.
角蝇，即血吸蝇（Hematobia irritans (L.)），是家畜的一种重要害虫，因为其雌雄成虫均为攻击性吸血者。值得注意的是，尽管角蝇成虫作为外寄生虫反复吸食宿主血液，但这些苍蝇缺乏其他吸血双翅目昆虫所具有的ADP反应性抗血小板聚集和血管舒张性抗止血系统。角蝇唾液腺提取物确实会干扰正常的凝血过程，这在复钙时间测定中得到了证实。以此为基线，测量唾液对复钙时间、活化部分凝血活酶时间、凝血酶原时间和凝血酶时间的影响，以确定凝血级联反应的哪些环节可能受到影响。还使用了缺乏因子的血浆测定法来测量凝血过程中可能的扰动。无腺体唾液延迟了复钙时间以及活化部分凝血活酶时间、凝血酶原时间和凝血酶时间。唾液还进一步延迟了缺乏因子V、因子VIII和因子XIII的血浆的凝血时间，表明凝血级联反应中的其他因子也受到了抑制。尽管角蝇唾液不会改变用因子X重构的缺乏血浆的凝血能力，但它确实抑制了用因子II（凝血酶）重构的缺乏血浆的凝血能力。唾液中的抗凝血酶活性通过其干扰纤维蛋白原（其正常底物）的凝血酶水解的能力以及其对模拟纤维蛋白原水解位点的发色底物上凝血酶作用的抑制作用得到了证实。因此，角蝇唾液含有一种特异性靶向凝血酶的因子，凝血酶是凝血级联反应中的关键成分。虽然抑制的生化机制可能不同，但这种抗止血特性与其他以有蹄类动物为食的嗜动物双翅目昆虫如蚋（Simulium spp.）和采采蝇（Glossina morsitans morsitans Westwood）相同。
