Nuffield Department of Surgical Sciences, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom.
PLoS Pathog. 2013;9(6):e1003450. doi: 10.1371/journal.ppat.1003450. Epub 2013 Jun 27.
Hard ticks subvert the immune responses of their vertebrate hosts in order to feed for much longer periods than other blood-feeding ectoparasites; this may be one reason why they transmit perhaps the greatest diversity of pathogens of any arthropod vector. Tick-induced immunomodulation is mediated by salivary components, some of which neutralise elements of innate immunity or inhibit the development of adaptive immunity. As dendritic cells (DC) trigger and help to regulate adaptive immunity, they are an ideal target for immunomodulation. However, previously described immunoactive components of tick saliva are either highly promiscuous in their cellular and molecular targets or have limited effects on DC. Here we address the question of whether the largest and globally most important group of ticks (the ixodid metastriates) produce salivary molecules that specifically modulate DC activity. We used chromatography to isolate a salivary gland protein (Japanin) from Rhipicephalus appendiculatus ticks. Japanin was cloned, and recombinant protein was produced in a baculoviral expression system. We found that Japanin specifically reprogrammes DC responses to a wide variety of stimuli in vitro, radically altering their expression of co-stimulatory and co-inhibitory transmembrane molecules (measured by flow cytometry) and their secretion of pro-inflammatory, anti-inflammatory and T cell polarising cytokines (assessed by Luminex multiplex assays); it also inhibits the differentiation of DC from monocytes. Sequence alignments and enzymatic deglycosylation revealed Japanin to be a 17.7 kDa, N-glycosylated lipocalin. Using molecular cloning and database searches, we have identified a group of homologous proteins in R. appendiculatus and related species, three of which we have expressed and shown to possess DC-modulatory activity. All data were obtained using DC generated from at least four human blood donors, with rigorous statistical analysis. Our results suggest a previously unknown mechanism for parasite-induced subversion of adaptive immunity, one which may also facilitate pathogen transmission.
硬蜱通过唾液成分来调节宿主的免疫反应，从而延长其吸血时间，比其他吸血外寄生虫吸血时间更长；这可能是硬蜱作为节肢动物传播者传播最多样化的病原体的原因之一。蜱诱导的免疫调节是由唾液成分介导的，其中一些成分中和先天免疫的成分或抑制适应性免疫的发展。由于树突状细胞 (DC) 触发并有助于调节适应性免疫，因此它们是免疫调节的理想目标。然而，以前描述的蜱唾液中的免疫活性成分在其细胞和分子靶标上要么高度混杂，要么对 DC 的影响有限。在这里，我们提出了这样一个问题，即最大和全球最重要的蜱类（硬蜱亚目）是否产生专门调节 DC 活性的唾液分子。我们使用色谱法从 Rhipicephalus appendiculatus 蜱中分离出一种唾液腺蛋白（Japanin）。Japanin 被克隆，并在杆状病毒表达系统中产生重组蛋白。我们发现 Japanin 可特异性地重新编程 DC 对各种体外刺激的反应，从根本上改变其共刺激和共抑制跨膜分子的表达（通过流式细胞术测量）及其促炎、抗炎和 T 细胞极化细胞因子的分泌（通过 Luminex 多重分析评估）；它还抑制单核细胞向 DC 的分化。序列比对和酶糖基化降解表明 Japanin 是一种 17.7 kDa 的 N-糖基化脂联素。使用分子克隆和数据库搜索，我们在 R. appendiculatus 和相关物种中鉴定出一组同源蛋白，其中三种我们已表达并证明具有 DC 调节活性。所有数据均使用至少来自四个供体的 DC 获得，并进行了严格的统计分析。我们的结果表明了寄生虫诱导适应性免疫逃避的一种未知机制，这也可能有助于病原体的传播。
