Evaluation of the immunogenicity of Schistosoma mansoni egg surface

Abstract INTRODUCTION Immunogenicity of Schistosoma mansoni egg surface was examined to determine whether intact eggshells have lower antigenicity than ruptured eggs. METHODS: Swiss Webster mice were inoculated with intact or ultrasonicated S. mansoni eggs isolated from infected human feces. Mice were separated into four groups of six animals each and immunizations were performed approximately every 20 days during a 60-day period. Groups 1-4 were administered with saline solution, sonicated eggs with Freund’s adjuvant, sonicated eggs without Freund’s adjuvant, and intact eggs, respectively. IgG humoral immune response was assessed by ELISA using Soluble Egg Antigen produced from eggs isolated from the livers of infected mice. RESULTS Sonicated eggs co-administered with adjuvant induced the highest humoral response at 58 days, which was 11.9-fold (95% CI 6.2-17.5) greater than the response induced by saline solution. Sonicated eggs without adjuvant induced a 4.3-fold stronger response (95% CI 2.4-6.2) than normal saline. Intact eggs induced humoral response that was nominally twice stronger (95% CI 0.8-3.2) than that induced by normal saline but the effect did not reach statistical significance. CONCLUSIONS Soluble antigens are not abundant on the surface of S. mansoni eggs and/or are not secreted in sufficient quantities to induce a significant immune response to intact eggs. Assuming that isolation procedures had not damaged the eggs used for inoculation, our observations suggest that intact eggs either do not induce a significant immune response or, if they do, the mechanism involves insoluble antigens from the egg surface.【摘要】引言：本研究旨在探究曼氏血吸虫（Schistosoma mansoni）虫卵表面的免疫原性，以明确完整卵壳的抗原性是否低于破裂虫卵。方法：将从感染患者粪便中分离得到的完整或经超声处理的曼氏血吸虫虫卵接种至瑞士韦伯斯特小鼠体内。实验将小鼠分为4组，每组6只，在60天的周期内约每20天进行一次免疫接种。第1至第4组分别给予生理盐水、添加弗氏佐剂（Freund’s adjuvant）的超声处理虫卵、不含弗氏佐剂的超声处理虫卵以及完整虫卵。采用酶联免疫吸附试验（ELISA），以从感染小鼠肝脏中分离的虫卵制备的可溶性虫卵抗原（Soluble Egg Antigen）为检测底物，评估IgG体液免疫应答水平。结果：与佐剂联合使用的超声处理虫卵在第58天时诱导产生最高的体液免疫应答，其应答水平较生理盐水组高11.9倍（95%置信区间：6.2~17.5）。不含佐剂的超声处理虫卵的免疫应答水平较生理盐水组高4.3倍（95%置信区间：2.4~6.2）。完整虫卵诱导的体液免疫应答水平较生理盐水组仅名义上高出2倍（95%置信区间：0.8~3.2），但该差异未达到统计学显著性。结论：曼氏血吸虫虫卵表面的可溶性抗原含量较低，且/或分泌量不足以诱导针对完整虫卵的显著免疫应答。假设用于接种的虫卵未因分离操作受损，本研究结果提示，完整虫卵要么无法诱导显著免疫应答，要么其免疫应答机制源自虫卵表面的不溶性抗原。