Serine protease inhibitors (serpins) in ticks are implicated in the modulation of the vertebrate host response to the tick bite. Experimentally, it has been demonstrated that serpins interfere with tick-borne pathogen transmission. However, knowledge on serpins in the tick Haemaphysalis doenitzi is lacking. In this study, the expression of two serpin genes, named HDS1 and HDS2, were assessed in H. doenitzi, and their roles in immune regulation were further investigated. The expression of HDS1 and HDS2 showed no tissue specificity, with maximum expression levels detected in the hemolymph and salivary gland, respectively. Among the developmental stages, the highest expression of HDS1 and HDS2 were detected in larvae and adults, respectively. The recombinant protein rHDS1 displayed obvious inhibitory effects on trypsin and thrombin, whereas rHDS2 clearly inhibited thrombin only. In addition, rHDS1 and rHDS2 showed certain inhibitory activities against bacteria and fungi. The female engorgement body weight, female engorgement rate, and egg hatchability were significantly decreased after injection of double-stranded RNA (dsRNA) of HDS1 gene, whereas no significant effects were observed concerning the feeding period or attachment rate at 24 h after introduction via rabbit ears. When injected with dsRNA of HDS2 gene, no significant effect was observed on the attachment rate at 24 h after introduction into the rabbit ears, but the engorgement body weight and engorgement rate of female ticks were significantly decreased, and no egg hatchment occurred. The above results contribute to better understanding the function of serpins in the development and innate immunity of H. doenitzi.

壁虱中的丝氨酸蛋白酶抑制剂（serpins）与脊椎动物宿主对壁虱叮咬反应的调节有关。在实验上，已经证明丝氨酸蛋白酶抑制剂干扰tick传播的病原体传播。然而，就在滴答丝氨酸蛋白酶抑制剂知识长角血蛛是缺乏。在这项研究中，在H. doenitzi中评估了两个丝氨酸蛋白酶抑制蛋白基因（HDS1和HDS2）的表达，并进一步研究了它们在免疫调节中的作用。HDS1和HDS2的表达没有组织特异性，在淋巴和唾液腺中分别检测到最大表达水平。在发育阶段中，分别在幼虫和成虫中检测到HDS1和HDS2的最高表达。重组蛋白rHDS1对胰蛋白酶和凝血酶表现出明显的抑制作用，而rHDS2仅明显抑制凝血酶。此外，rHDS1和rHDS2对细菌和真菌显示出一定的抑制活性。注射HDS1基因的双链RNA（dsRNA）后，雌性发胖体重，雌性发胖率和卵孵化率显着降低，通过兔子的耳朵。注射HDS2基因的dsRNA后，引入兔耳后24 h对附着率无明显影响，但雌性s的充实体重和充血率明显降低，没有孵化卵。上述研究结果有助于更好地理解在发展和先天免疫丝氨酸蛋白酶的功能H.蛛。