Talactac Melbourne Rio, Yoshii Kentaro, Maeda Hiroki, Kusakisako Kodai, Hernandez Emmanuel Pacia, Tsuji Naotoshi, Fujisaki Kozo, Galay Remil Linggatong, Tanaka Tetsuya, Mochizuki Masami
Department of Pathological and Preventive Veterinary Science, The United Graduate School of Veterinary Science, Yamaguchi University, Yoshida, Yamaguchi, 753-8515, Japan.
Laboratory of Infectious Diseases, Joint Faculty of Veterinary Medicine, Kagoshima University, 1-21-24 Korimoto, Kagoshima, 890-0065, Japan.
Parasit Vectors. 2016 Feb 2;9:59. doi: 10.1186/s13071-016-1344-5.
Longicin is a defensin-like peptide, identified from the midgut epithelium of hard tick Haemaphysalis longicornis. Several studies have already shown the antimicrobial and parasiticidal activities of longicin peptide and one of its synthetic partial analogs, longicin P4. In this study, longicin peptides were tested for potential antiviral activity against Langat virus (LGTV), a tick-borne flavivirus.
Longicin P1 and P4 peptides were chemically synthesized. Antiviral activity of the longicin peptides against LGTV was evaluated through in vitro virucidal assays, wherein the antiviral efficacy was determined by reduction in number of viral foci and virus yield. Additionally, longicin P4 was also tested for its activity against human adenovirus, a non-enveloped virus. Lastly, to assess the importance of longicin on the innate antiviral immunity of H. longicornis ticks, gene silencing through RNAi was performed.
Longicin P4 produced significant viral foci reduction and lower virus yield against LGTV, while longicin P1 failed to demonstrate the same results. Conversely, both longicin partial analogs (P1 and P4) did not show significant antiviral activity when tested on adenovirus. In addition, longicin-silenced ticks showed significantly higher virus titer after 7 days post-infection but a significantly lower titer was detected after an additional 14 days of observation as compared to the Luc dsRNA-injected ticks. Mortality in both groups did not show any significant difference.
Our results suggest that longicin P4 has in vitro antiviral activity against LGTV but not against a non-enveloped virus such as adenovirus. Likewise, though most cationic antimicrobial peptides like longicin act directly on target membranes, the exact mechanism of membrane targeting of longicin P4 in enveloped viruses, such as LGTV, requires further investigation. Lastly, while the in vitro virucidal capacity of longicin P4 was confirmed in this study, the role of the endogenous tick longicin in the antiviral defense of H. longicornis against LGTV still remains to be demonstrated.
长角血蜱防御素样肽（longicin）是从长角血蜱中肠上皮细胞中鉴定出的一种肽。多项研究已表明longicin肽及其一种合成部分类似物longicin P4具有抗菌和杀寄生虫活性。在本研究中，检测了longicin肽对蜱传黄病毒——兰加特病毒（LGTV）的潜在抗病毒活性。
化学合成了longicin P1和P4肽。通过体外杀病毒试验评估longicin肽对LGTV的抗病毒活性，其中抗病毒效力通过病毒蚀斑数量和病毒产量的减少来确定。此外，还检测了longicin P4对人腺病毒（一种无包膜病毒）的活性。最后，为评估longicin对长角血蜱先天抗病毒免疫的重要性，通过RNA干扰进行基因沉默。
longicin P4对LGTV产生了显著的病毒蚀斑减少和较低的病毒产量，而longicin P1未显示出相同结果。相反，当对腺病毒进行测试时，两种longicin部分类似物（P1和P4）均未显示出显著的抗病毒活性。此外，与注射Luc双链RNA的蜱相比，longicin基因沉默的蜱在感染后7天病毒滴度显著更高，但在额外观察14天后检测到的滴度显著更低。两组的死亡率没有显著差异。
我们的结果表明，longicin P4对LGTV具有体外抗病毒活性，但对腺病毒等无包膜病毒没有活性。同样，尽管大多数像longicin这样的阳离子抗菌肽直接作用于靶膜，但longicin P4在包膜病毒（如LGTV）中靶向膜的确切机制仍需进一步研究。最后，虽然本研究证实了longicin P4的体外杀病毒能力，但内源性蜱longicin在长角血蜱对LGTV的抗病毒防御中的作用仍有待证明。
