Live Brugia malayi Microfilariae Inhibit Transendothelial Migration of Neutrophils and Monocytes

Lymphatic filariasis is a major tropical disease caused by the parasite Brugia malayi. Microfilariae (Mf) circulate in the peripheral blood for 2–3 hours in synchronisation with maximal feeding of the mosquito vector. When absent from the peripheral blood, Mf sequester in the capillaries of the lungs. Mf are therefore in close contact with vascular endothelial cells (EC) and may induce EC immune function and/or wound repair mechanisms such as angiogenesis. In this study, Mf were co-cultured with human umbilical vein EC (HUVEC) or human lung microvascular EC (HLMVEC) and the transendothelial migration of leukocyte subsets was analysed. In addition, the protein and/or mRNA expression of chemokine, cytokine and angiogenic mediators in endothelial cells in the presence of live microfilariae were measured by a combination of cDNA arrays, protein arrays, ELISA and fluorescence antibody tests. Surprisingly, our findings indicate that Mf presence partially blocked transendothelial migration of monocytes and neutrophils, but not lymphocytes. However, Mf exposure did not result in altered vascular EC expression of key mediators of the tethering stage of extravasation, such as ICAM-1, VCAM-1 and various chemokines. To further analyse the immunological function of vascular EC in the presence of Mf, we measured the mRNA and/or protein expression of a number of pro-inflammatory mediators. We found that expression levels of the mediators tested were predominantly unaltered upon B. malayi Mf exposure. In addition, a comparison of angiogenic mediators induced by intact Mf and Wolbachia-depleted Mf revealed that even intact Mf induce the expression of remarkably few angiogenic mediators in vascular EC. Our study suggests that live microfilariae are remarkably inert in their induction and/or activation of vascular cells in their immediate local environment. Overall, this work presents important insights into the immunological function of the vascular endothelium during an infection with B. malayi.

淋巴丝虫病（Lymphatic filariasis）是由寄生虫马来布鲁线虫（Brugia malayi）引发的一类主要热带疾病。微丝蚴（Microfilariae，简称Mf）会在外周血中循环2~3小时，其周期与传播媒介蚊子的最大吸血时段同步。当外周血中无Mf存在时，它们会藏匿于肺部毛细血管内。因此，Mf会与血管内皮细胞（vascular endothelial cells，简称EC）紧密接触，并可能诱导EC的免疫功能及血管生成等伤口修复机制。本研究中，研究人员将Mf与人脐静脉内皮细胞（human umbilical vein EC，简称HUVEC）或人肺微血管内皮细胞（human lung microvascular EC，简称HLMVEC）进行共培养，并分析了白细胞亚群的跨内皮迁移情况。此外，本研究通过cDNA芯片、蛋白质芯片、酶联免疫吸附试验（ELISA）及荧光抗体检测的组合方法，检测了活Mf存在时内皮细胞内趋化因子、细胞因子及血管生成介质的蛋白质和/或mRNA表达水平。令人意外的是，本研究结果显示，Mf的存在会部分阻断单核细胞与中性粒细胞的跨内皮迁移，但对淋巴细胞无此影响。然而，Mf暴露并未改变血管EC在渗出黏附阶段关键介质的表达，如细胞间黏附分子1（ICAM-1）、血管细胞黏附分子1（VCAM-1）及多种趋化因子。为进一步分析Mf存在时血管EC的免疫功能，本研究检测了多种促炎介质的mRNA和/或蛋白质表达水平。研究发现，在暴露于马来布鲁线虫Mf后，所检测的介质表达水平大多未发生改变。此外，对比完整Mf与去除沃尔巴克氏体（Wolbachia）的Mf所诱导的血管生成介质发现，即便完整Mf也仅能在血管EC中诱导极少的血管生成介质表达。本研究表明，活Mf在其局部微环境中对血管细胞的诱导及/或激活作用极为微弱。总体而言，本研究为马来布鲁线虫感染过程中血管内皮的免疫功能提供了重要的科学见解。