van Dam G J, Seino J, Rotmans J P, Daha M R, Deelder A M
Laboratory of Parasitology, University of Leiden, The Netherlands.
Eur J Immunol. 1993 Nov;23(11):2807-12. doi: 10.1002/eji.1830231113.
Adult schistosome parasites, living in the blood vessels of their mammalian hosts, protect themselves against immune damage in a variety of ways. In addition to the tegument, the intestinal epithelium of the blood-feeding worms is permanently exposed to both the innate and the acquired immune system. In this study, we investigated whether the Schistosoma gut-associated antigens CAA and CCA (circulating anodic antigen and circulating cathodic antigen, respectively), which are excreted in relatively large quantities into the host's circulation, might play a role in evading complement attack. Of several complement components tested, only purified C1q showed significant binding to CAA, a negatively charged highly glycosylated glycoprotein. CCA, also highly glycosylated, but neutral or slightly positively charged, did not bind to C1q. CAA bound only to the collagen-like stalks of C1q and not to the globular heads. No detectable interaction of CAA with precursor human C1 was found and CAA did not induce activation of C1 in whole human serum as assessed by consumption of hemolytic C4 activity. Also CAA could not induce activation of precursor C1 in vitro. These results suggest that CAA behaves like a receptor for C1q, and might be involved in protecting the vulnerable schistosome gut against complement-mediated attack.
成年血吸虫寄生于哺乳动物宿主的血管中，通过多种方式保护自身免受免疫损伤。除了体表外，吸血虫的肠上皮还长期暴露于固有免疫系统和获得性免疫系统。在本研究中，我们调查了在宿主循环系统中大量排泄的血吸虫肠道相关抗原CAA和CCA（分别为循环阳极抗原和循环阴极抗原）是否可能在逃避补体攻击中发挥作用。在测试的几种补体成分中，只有纯化的C1q与CAA（一种带负电荷的高度糖基化糖蛋白）有显著结合。CCA同样高度糖基化，但呈中性或略带正电荷，不与C1q结合。CAA仅与C1q的胶原样柄结合，而不与球形头部结合。未发现CAA与前体人C1有可检测到的相互作用，并且通过溶血C4活性的消耗评估，CAA在全人血清中未诱导C1的激活。此外，CAA在体外也不能诱导前体C1的激活。这些结果表明，CAA的行为类似于C1q的受体，可能参与保护脆弱的血吸虫肠道免受补体介导的攻击。
