Franta Zdeněk, Frantová Helena, Konvičková Jitka, Horn Martin, Sojka Daniel, Mareš Michael, Kopáček Petr
Institute of Parasitology, Biology Centre, Academy of Sciences of the Czech Republic, Branišovská 31, České Budějovice, CZ-370 05, Czech Republic.
Parasit Vectors. 2010 Dec 14;3:119. doi: 10.1186/1756-3305-3-119.
Ticks are vectors of a wide variety of pathogens causing severe diseases in humans and domestic animals. Intestinal digestion of the host blood is an essential process of tick physiology and also a limiting factor for pathogen transmission since the tick gut represents the primary site for pathogen infection and proliferation. Using the model tick Ixodes ricinus, the European Lyme disease vector, we have previously demonstrated by genetic and biochemical analyses that host blood is degraded in the tick gut by a network of acidic peptidases of the aspartic and cysteine classes.
This study reveals the digestive machinery of the I. ricinus during the course of blood-feeding on the host. The dynamic profiling of concentrations, activities and mRNA expressions of the major digestive enzymes demonstrates that the de novo synthesis of peptidases triggers the dramatic increase of the hemoglobinolytic activity along the feeding period. Overall hemoglobinolysis, as well as the activity of digestive peptidases are negligible at the early stage of feeding, but increase dramatically towards the end of the slow feeding period, reaching maxima in fully fed ticks. This finding contradicts the established opinion that blood digestion is reduced at the end of engorgement. Furthermore, we show that the digestive proteolysis is localized intracellularly throughout the whole duration of feeding.
Results suggest that the egressing proteolytic system in the early stage of feeding and digestion is a potential target for efficient impairment, most likely by blocking its components via antibodies present in the host blood. Therefore, digestive enzymes are promising candidates for development of novel 'anti-tick' vaccines capable of tick control and even transmission of tick-borne pathogens.
蜱是多种病原体的传播媒介，可导致人类和家畜患上严重疾病。宿主血液的肠道消化是蜱生理过程的一个重要环节，也是病原体传播的一个限制因素，因为蜱的肠道是病原体感染和增殖的主要部位。利用欧洲莱姆病传播媒介蓖麻硬蜱作为模型蜱，我们先前通过遗传和生化分析证明，宿主血液在蜱的肠道中被天冬氨酸和半胱氨酸类酸性肽酶网络降解。
本研究揭示了蓖麻硬蜱在吸食宿主血液过程中的消化机制。主要消化酶的浓度、活性和mRNA表达的动态分析表明，肽酶的从头合成引发了整个进食期血红蛋白分解活性的急剧增加。总体而言，血红蛋白分解以及消化肽酶的活性在进食初期可忽略不计，但在缓慢进食期结束时急剧增加，在饱血蜱中达到最大值。这一发现与已有的观点相悖，即饱血末期血液消化会减少。此外，我们表明整个进食期间消化性蛋白水解作用都定位于细胞内。
结果表明，进食和消化早期出现的蛋白水解系统是有效破坏的潜在靶点，最有可能是通过宿主血液中存在的抗体阻断其成分来实现。因此，消化酶是开发新型“抗蜱”疫苗的有希望的候选物，这种疫苗能够控制蜱甚至传播蜱传病原体。
