Inactivated Parapoxvirus ovis as inducer of immunity in silver catfish (Rhamdia quelen)

ABSTRACT Molecules with immune modulating activity are ubiquitously distributed in nature and their impact on aquaculture has been exploited in order to increase fish resistance to pathogens. Here, we investigated the effect of inactivated Parapoxvirus ovis (iPPVO) on blood cells and innate and acquired immune response of silver catfish (Rhamdia quelen). iPPVO inoculation had no effect on respiratory burst activity; however, following iPPVO inoculation, we observed a significant decrease on circulating monocytes concomitantly with an increased number of heterophilic granulocytes and thrombocytes, which are the main cells involved in innate immunity and provide connection with acquired immunity. Fish inoculated with a combination of bovine serum albumin (BSA) + iPPVO had significantly higher levels of antibodies to BSA compared to fish inoculated with BSA alone, but lower than fish inoculated with BSA + Freund's incomplete adjuvant (FIA). These findings points to the potential usefulness of iPPVO as immunomodulator in fish and instigate further research to identify its component that interact with immune cells and that could be exploited as adjuvants in fish.

摘要 具有免疫调节活性的分子广泛分布于自然界，其对水产养殖的有益作用已被开发利用，以提升鱼类抵御病原体的能力。本研究探究了灭活绵羊副痘病毒（inactivated Parapoxvirus ovis, iPPVO）对银鲶（Rhamdia quelen）血细胞以及先天与适应性免疫应答的影响。接种iPPVO对鱼类的呼吸爆发活性无显著影响；但接种iPPVO后，我们观察到循环单核细胞数量显著减少，同时嗜异粒细胞与血栓细胞的数量增加——这两类细胞是先天免疫的核心细胞，且可介导先天免疫与适应性免疫的衔接。相较于仅接种牛血清白蛋白（bovine serum albumin, BSA）的实验组，联合接种BSA与iPPVO的银鲶其抗BSA抗体水平显著更高，但仍低于接种BSA与弗氏不完全佐剂（Freund's incomplete adjuvant, FIA）的实验组。本研究结果提示，iPPVO作为鱼类免疫调节剂具备潜在应用价值，同时也为后续研究指明方向：即鉴定其与免疫细胞相互作用的活性组分，进而开发可应用于水产养殖的鱼类疫苗佐剂。