Department of Biological Sciences, University of Bergen, P.O. Box 7803, NO-5020, Bergen, Norway.
Department of Biological Sciences, University of Bergen, P.O. Box 7803, NO-5020, Bergen, Norway.
Fish Shellfish Immunol. 2024 Nov;154:109992. doi: 10.1016/j.fsi.2024.109992. Epub 2024 Oct 30.
The salmon louse (Lepeophtheirus salmonis) is an ectoparasite feeding on mucus, skin, and blood of salmonids. On parasitised fish erosions and, at later lice stages, ulcerations appear at the louse feeding site. In susceptible species like Atlantic salmon (Salmo salar) with a limited rejection of lice, only a mild inflammatory response with minor influx of immune cells is seen at these lesions, as the salmon louse secrete proteins that can dampen immune responses. In a previous study, Lepeophtheirus salmonis labial gland protein 3 (LsLGP3) was suggested to dampen cellular responses, and the present study aimed at increasing our understanding of its mode of action. LsLGP3 was found to be secreted on to the host skin, and both in vivo and in vitro experiments were performed to elucidate its function. Histological analysis of the louse attachment site revealed an epidermal and dermal influx of mainly macrophages and granulocytes after 5 days post infestation. The immune cell influx was deeper in the dermis throughout the louse infestation, and LsLGP3 may be involved in dampening this response. Enriched populations of Atlantic salmon B-cells, T-cells, granulocytes, and monocytes were exposed to recombinant LsLGP3 (recLGP3) in vitro, resulting in a significant decrease in cell viability compared to non-exposed controls. An apoptotic cell morphology with "beads-on-a-string" like protrusions was seen in all leukocyte cell fractions after recLGP3 exposure, but not in erythrocytes or keratocytes. A decreased viability was also detected in pink salmon leucocytes, which was not in leucocytes from non-salmonid species. These functional insights suggest that LsLGP3 specifically induces apoptosis of salmonid leukocytes and is likely a key protein secreted by the lice that disables the Atlantic salmon ability to mount an adequate immune response towards the salmon louse. In vivo LsLGP3 knock down studies indicated that the effect is localised primarily at the lice feeding site, without affecting immune cells that are not situated adjacent to the lice-inflicted lesion. The findings from this study could significantly aid in the development of new immune based anti-salmon louse prophylactic measures and treatments.
鲑鱼虱（Lepeophtheirus salmonis）是一种外寄生虫，以鲑鱼的黏液、皮肤和血液为食。在被寄生虫感染的鱼身上，在寄生虫吸食的部位会出现侵蚀和溃疡，而在像大西洋鲑鱼（Salmo salar）这样对寄生虫容忍度较低的易感物种身上，只有轻微的炎症反应和少量免疫细胞浸润，因为鲑鱼虱会分泌可以抑制免疫反应的蛋白质。在之前的研究中，Lepeophtheirus salmonis 唇腺蛋白 3（LsLGP3）被认为可以抑制细胞反应，本研究旨在进一步了解其作用模式。研究发现 LsLGP3 被分泌到宿主皮肤上，进行了体内和体外实验来阐明其功能。感染后 5 天，对寄生虫附着部位进行组织学分析显示表皮和真皮中主要有巨噬细胞和粒细胞浸润。在整个寄生虫感染过程中，真皮中的免疫细胞浸润更深，LsLGP3 可能参与了这种反应的抑制。从大西洋鲑鱼中富集 B 细胞、T 细胞、粒细胞和单核细胞，将其暴露于重组 LsLGP3（recLGP3）中，与未暴露对照相比，细胞活力显著下降。在所有白细胞细胞群中，暴露于 recLGP3 后都出现了凋亡细胞形态，具有“串珠状”突起，但在红细胞或角质细胞中没有。在粉鲑鱼白细胞中也检测到活力下降，但在非鲑鱼物种的白细胞中没有。这些功能研究表明，LsLGP3 特异性诱导鲑鱼白细胞凋亡，可能是寄生虫分泌的关键蛋白，使大西洋鲑鱼无法对鲑鱼虱产生足够的免疫反应。体内 LsLGP3 敲低研究表明，这种效应主要局限于寄生虫吸食部位，而不会影响不位于寄生虫损伤部位附近的免疫细胞。这项研究的结果可以显著帮助开发新的基于免疫的预防和治疗鲑鱼虱的措施。
