Kumas Kaan, Andersen Maja Hauptmann, Jaafar Rzgar, Henard Cyril, Kania Per Walter, Buchmann Kurt
Laboratory of Aquatic Pathobiology, Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg, Denmark.
Front Immunol. 2025 Aug 20;16:1646450. doi: 10.3389/fimmu.2025.1646450. eCollection 2025.
Parasitic nematodes are prevalent in fish populations. The parasites are pathogenic but depress host responses, which limit clearance of the pathogens from the invasion sites. We hypothesized that one of several control strategies, which could augment protection, is immunization of the fish host with parasite antigens prior to live pathogen exposure.
We used rainbow trout as a host model and third stage larvae (L3) (Nematoda, Ascaridoidea, Anisakidae) as pathogen model. We used a total of 120 fish and immunized 40 of the fish with a homogenate (adjuvanted) of parasite larvae (i.p. injection), 40 fish received adjuvant only and 40 PBS. Following 38 days (d) half of the fish in each group were exposed to infection with live worms (oral administration), and after an additional 25 d the infection success was evaluated together with antibody responses in the different groups.
Injection of L3 antigens induced a series of adaptive and innate host responses. ELISA and Western blot analyses indicated specific IgM reactions in immunized trout against worm antigens with molecular weights (MW) of approximately 39, 103 and 119 kilodalton (kDa). Fish immunized and subsequently infected with live larvae reacted to those three and six additional antigens with MW approximately 61, 73, 84, 152, 186 and 277 kDa. The immunized fish showed a significantly lower worm burden following exposure to live parasite larvae (when compared to naïve fish), but no full protection was achieved. Expression analyses of both adaptive and innate immune genes in fish showed a general down-regulation following infection.
Prior immunization with L3 homogenate induced a strong antibody response, but the protection was incomplete. It was noteworthy that an infection period (25 d) with live parasites merely induced an insignificant antibody response. It may be explained by the immunosuppressive compounds released by live worm larvae. With the aim of increasing the protective response, we suggest in future immunization experiments to target immunosuppressive worm antigens by immunizing the host organisms with excretory/secretory (ES) proteins and extracellular particles from L3.
寄生线虫在鱼类种群中普遍存在。这些寄生虫具有致病性，但会抑制宿主反应，这限制了病原体从入侵部位的清除。我们假设，几种可增强保护作用的控制策略之一是在鱼类宿主接触活病原体之前用寄生虫抗原进行免疫。
我们使用虹鳟作为宿主模型，第三期幼虫（L3）（线虫纲，蛔目，异尖科）作为病原体模型。我们总共使用了120条鱼，其中40条鱼用寄生虫幼虫的匀浆（添加佐剂）进行免疫（腹腔注射），40条鱼仅接受佐剂，40条鱼接受磷酸盐缓冲盐水。38天后，每组中的一半鱼暴露于活虫感染（口服给药），再过25天后，评估不同组中的感染成功率以及抗体反应。
注射L3抗原诱导了一系列适应性和先天性宿主反应。酶联免疫吸附测定（ELISA）和蛋白质印迹分析表明，免疫后的虹鳟针对分子量（MW）约为39、103和119千道尔顿（kDa）的蠕虫抗原产生了特异性IgM反应。免疫后再感染活幼虫的鱼对这三种以及另外六种分子量约为61、73、84、152、186和277 kDa的抗原产生反应。与未免疫的鱼相比，免疫后的鱼在接触活寄生虫幼虫后虫负荷显著降低，但未实现完全保护。对鱼体内适应性和先天性免疫基因的表达分析表明，感染后这些基因普遍下调。
用L3匀浆预先免疫诱导了强烈的抗体反应，但保护作用并不完全。值得注意的是，活寄生虫感染期（25天）仅诱导了微不足道的抗体反应。这可能是由活虫幼虫释放的免疫抑制化合物所解释。为了增强保护反应，我们建议在未来的免疫实验中，通过用L3的排泄/分泌（ES）蛋白和细胞外颗粒免疫宿主生物体来靶向免疫抑制性蠕虫抗原。
