Wang Xuting, Clark Theodore G, Noe Jane, Dickerson Harry W
Department of Medical Microbiology, University of Georgia, Athens, GA 30602-7371, USA.
Fish Shellfish Immunol. 2002 Nov;13(5):337-50. doi: 10.1006/fsim.2001.0410.
Surface immobilisation antigens (i-antigens) were purified from two strains of Ichthyophthirius multifiliis (NY1 and G5) that represent different i-antigen serotypes, namely A and D, respectively. The efficacy of the purified antigens as subunit vaccines was then tested in challenge studies using parasites of the homologous or heterologous serotype. Three groups of juvenile channel catfish (70 animals per group) were immunised with i-antigens from either the G5 or NY1 isolates, or with bovine serum albumin (BSA) as a control. Proteins were injected intraperitoneally (i.p.) at a dose of 10 microg/fish with complete Freund's adjuvant on day 1, followed by a second injection in incomplete Freund's adjuvant on day 15. Fish immunised with the purified i-antigens developed high titres of serum immobilising antibodies whereas sera from BSA-injected control fish did not. Fish antisera immobilised parasites of the homologous, but not the heterologous strain, and recognised the corresponding i-antigens on Western blots run under non-reducing conditions. On day 36, each group was divided into two subgroups (n=30). One subgroup was challenged with G5 parasites, and the other was challenged with NY1 parasites. When challenged with G5 parasites, 70% of fish immunised with the G5 i-antigens survived. When challenged with NY1 parasites, 33.3% of fish immunised with the NY1 i-antigens survived. All BSA-injected control fish died, as did all fish injected with the purified antigens and challenged with the non-homologous parasite strain. Statistical analyses indicated significant differences among test and control groups with regard to the mean days to death (MDD). While the results of these studies clearly support a role for i-antigens in protection, active immunity in response to natural infection is not serotype-specific. The utility of i-antigens, as well as the existence of other potential vaccine candidates for the prevention of 'white-spot' disease, are discussed.
从多子小瓜虫的两个菌株（NY1和G5）中纯化了表面固定抗原（i抗原），这两个菌株分别代表不同的i抗原血清型，即A和D。然后在使用同源或异源血清型寄生虫的攻毒研究中测试纯化抗原作为亚单位疫苗的效力。三组幼鲶（每组70只）分别用G5或NY1分离株的i抗原免疫，或用牛血清白蛋白（BSA）作为对照。第1天，蛋白质以10μg/鱼的剂量与完全弗氏佐剂一起腹腔注射（i.p.），第15天在不完全弗氏佐剂中进行第二次注射。用纯化的i抗原免疫的鱼产生了高滴度的血清固定抗体，而注射BSA的对照鱼血清则没有。鱼抗血清能固定同源菌株的寄生虫，但不能固定异源菌株的寄生虫，并且在非还原条件下运行的Western印迹中识别相应的i抗原。在第36天，每组分为两个亚组（n = 30）。一个亚组用G5寄生虫攻毒，另一个亚组用NY1寄生虫攻毒。当用G寄生虫攻毒时，用G5 i抗原免疫的鱼中有70%存活。当用NY1寄生虫攻毒时，用NY1 i抗原免疫的鱼中有33.3%存活。所有注射BSA的对照鱼都死亡，所有注射纯化抗原并用非同源寄生虫菌株攻毒的鱼也都死亡。统计分析表明，试验组和对照组在平均死亡天数（MDD）方面存在显著差异。虽然这些研究结果清楚地支持了i抗原在保护中的作用，但对自然感染的主动免疫不是血清型特异性的。文中讨论了i抗原的效用以及预防“白点”病的其他潜在疫苗候选物的存在。
