Institute of Animal Physiology, University of Münster, Germany.
Acta Trop. 2012 Oct;124(1):15-26. doi: 10.1016/j.actatropica.2012.05.013. Epub 2012 Jun 4.
Onchocerca volvulus is a human pathogenic filarial nematode causing chronic onchocerciasis, a disease characterized by chronic skin and eye lesions. Despite attempts to control this infection from many perspectives, it still remains a threat to public health because of adverse effects of available drugs and recent reports of drug resistance. Under control of an intact immune system, O. volvulus survives for a long time in the host by employing a variety of strategies including the utility of antioxidant enzymes. In the present study, we focus on the extracellular superoxide dismutase from O. volvulus (OvEC-SOD) found in the excretory/secretory products of adult worms. Contrary to previous studies, the OvEC-SOD was found to have a 19 amino acid long signal peptide that is cleaved off during the process of maturation. To validate this result, we designed a novel method based on Caenorhabditis elegans cup5(ar465) mutants to specifically evaluate signal peptide-mediated secretion of nematodal proteins. Following purification, the recombinant OvEC-SOD was active as a dimer. Site-directed mutagenesis of the three cysteines present in the OvEC-SOD shows that enzyme activity is markedly reduced in the Cys-192 mutant. A homology model of the OvEC-SOD underlines the importance of Cys-192 for the stabilization of the adjacent active site channel. The generation of a humoral immune response to secretory OvEC-SOD was indicated by demonstrating IgG reactivity in sera from patients infected with O. volvulus while the cross-reactivity of IgG in plasma samples from cows, infected with the most closely related parasite Onchocerca ochengi, occurred only marginally. High IgG1 and IgM titres were recorded in sera from mice infected with the filaria Litomosoides sigmodontis, however, low or no cellular proliferative responses were observed. Thus, the present data suggest that secretory OvEC-SOD is a target of the humoral immune response in human onchocerciasis and induced strongest IgG responses in hyperreactive onchocerciasis. Furthermore, humoral response during murine infection induced SOD-specific IgG that cross-reacted with OvEC-SOD.
旋毛虫是一种人类致病性的丝虫，会引起慢性旋毛虫病，这是一种以慢性皮肤和眼部损伤为特征的疾病。尽管从多个角度尝试控制这种感染，但由于现有药物的不良反应和最近报道的耐药性，它仍然对公共卫生构成威胁。在完整的免疫系统的控制下，旋毛虫通过利用抗氧化酶等各种策略在宿主体内存活很长时间。在本研究中，我们专注于从成虫排泄/分泌产物中发现的旋毛虫细胞外超氧化物歧化酶（OvEC-SOD）。与之前的研究不同，我们发现 OvEC-SOD 有一个 19 个氨基酸长的信号肽，在成熟过程中被切割掉。为了验证这一结果，我们设计了一种基于秀丽隐杆线虫 cup5(ar465)突变体的新方法，专门评估线虫蛋白的信号肽介导分泌。经过纯化后，重组 OvEC-SOD 作为二聚体发挥活性。对 OvEC-SOD 中存在的三个半胱氨酸进行定点突变表明，Cys-192 突变会显著降低酶活性。OvEC-SOD 的同源模型强调了 Cys-192 对稳定相邻活性位点通道的重要性。在感染旋毛虫的患者血清中证明了针对分泌 OvEC-SOD 的体液免疫反应，而在感染最密切相关寄生虫盘尾丝虫的牛血浆样本中的 IgG 交叉反应仅略有发生。在感染旋毛虫的小鼠血清中记录到高 IgG1 和 IgM 滴度，但观察到低或无细胞增殖反应。因此，目前的数据表明，分泌 OvEC-SOD 是人类旋毛虫病体液免疫反应的靶标，并在超反应性旋毛虫病中引起最强的 IgG 反应。此外，在感染期间诱导的体液反应产生了与 OvEC-SOD 发生交叉反应的 SOD 特异性 IgG。
