Department of Biological Sciences, National University of Singapore, Singapore.
J Innate Immun. 2009;1(5):465-79. doi: 10.1159/000209224. Epub 2009 Mar 11.
Serine protease cascades boost immune responses while maintaining homeostasis. These crucial actions are intricately regulated by cognate serine protease inhibitors. However, the mechanism underlying such a dynamic immunomodulation during acute phase infection remains obscure, particularly where the pathogen's serine protease adds a new challenge to the host. Here, we found that infection of horseshoe crab, Carcinoscorpius rotundicauda, induced reciprocal profiles of CrSPI (serine protease inhibitor) and CrFurin (serine protease) with respect to their transcription and protein activities. Using recombinant rCrSPI, we explored its inhibitory activity against various microbial proteases and found it most efficacious against a model serine protease, subtilisin A. rCrSPI inhibited subtilisin at Ki 10(-9)M with a molar ratio of 1 rCrSPI:2 subtilisin. The rCrSPI also inhibited plasma CrFurin, suppressed subtilisin-mediated activation of prophenoloxidase (PPO) and interacted with complement C3. Taken together, CrSPI acts as a key immunomodulatory 'on-off' switch in a 2-way regulation of serine protease microbial subtilisin and host serine proteases (CrFurin and CrC3), thereby controlling immune responses involving the complements and the PPO-mediated antimicrobial activities, while maintaining homeostasis.
丝氨酸蛋白酶级联反应既能增强免疫应答，又能维持体内平衡。这种关键作用是由同源丝氨酸蛋白酶抑制剂精细调控的。然而，在急性感染期间，这种动态免疫调节的机制仍不清楚，特别是当病原体的丝氨酸蛋白酶给宿主带来新的挑战时。在这里，我们发现，圆尾蝎的感染诱导了 CrSPI（丝氨酸蛋白酶抑制剂）和 CrFurin（丝氨酸蛋白酶）在转录和蛋白活性方面的相互作用。使用重组 rCrSPI，我们研究了它对各种微生物蛋白酶的抑制活性，发现它对模型丝氨酸蛋白酶枯草杆菌蛋白酶 A 的抑制效果最佳。rCrSPI 以 10(-9)M 的 Ki 值抑制枯草杆菌蛋白酶 A，摩尔比为 1 rCrSPI:2 枯草杆菌蛋白酶 A。rCrSPI 还抑制血浆中的 CrFurin，抑制枯草杆菌蛋白酶介导的原酚氧化酶（PPO）的激活，并与补体 C3 相互作用。总之，CrSPI 作为一种关键的免疫调节“开-关”开关，在丝氨酸蛋白酶微生物枯草杆菌蛋白酶 A 和宿主丝氨酸蛋白酶（CrFurin 和 CrC3）的双向调控中发挥作用，从而控制涉及补体和 PPO 介导的抗菌活性的免疫反应，同时维持体内平衡。
