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Bjørgen H, Brimsholm M, Asserson CF, Skaar K, Knutsen GM, Oaland Ø, Haldorsen R, Fjelldal PG, Hansen T, Rimstad E, Kleist BA, Lund-Iversen M, Kowalewski MP, Koppang EO. Deciphering the pathogenesis of melanized focal changes in the white skeletal muscle of farmed Atlantic salmon (Salmo salar). JOURNAL OF FISH DISEASES 2024:e13988. [PMID: 38943363 DOI: 10.1111/jfd.13988] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/08/2024] [Revised: 06/04/2024] [Accepted: 06/06/2024] [Indexed: 07/01/2024]
Abstract
Melanized focal changes (MFCs) in the fillet of farmed Atlantic salmon is a major quality concern. The changes are thought to initially appear as acute red focal changes (RFCs) that progress into chronic MFCs. Recent findings have indicated that hypoxia may be important in their development, possibly leading to necrosis affecting not only myocytes but also adipocytes. Thus, the aim of this study was to investigate possible hypoxic conditions in RFCs and the subsequent inflammatory responses and lesions in the adipose tissue in RFCs and MFCs. A collection of RFCs, MFCs and control muscle samples from several groups of farmed salmon was studied. Using immunohistochemistry, we found induction of the hypoxia-inducible factor 1 pathway in RFCs. Histological investigations of RFCs and MFCs revealed different stages of fat necrosis, including necrotic adipocytes, a myospherulosis-like reaction and the formation of pseudocystic spaces. Accumulations of foamy macrophages were detected in MFCs, indicating degradation and phagocytosis of lipids. Using in situ hybridization, we showed the presence of tyrosinase- and tyrosinase-related protein-1-expressing amelanotic cells in RFCs, which in turn became melanized in MFCs. In conclusion, we propose a sequence of events leading to the formation of MFCs, highlighting the pivotal role of adiposity, hypoxia and fat necrosis.
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Affiliation(s)
- Håvard Bjørgen
- Unit of Anatomy, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
| | - Malin Brimsholm
- Unit of Anatomy, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
| | | | - Kirstin Skaar
- Institute of Veterinary Anatomy, Vetsuisse Faculty, University of Zurich (UZH), Zurich, Switzerland
| | | | | | | | | | - Tom Hansen
- Matre Research Station, Institute of Marine Research, Matredal, Norway
| | - Espen Rimstad
- Unit of Virology, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
| | | | | | - Mariusz Pawel Kowalewski
- Institute of Veterinary Anatomy, Vetsuisse Faculty, University of Zurich (UZH), Zurich, Switzerland
| | - Erling Olaf Koppang
- Unit of Anatomy, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
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Bjørgen H, Brimsholm M, Lund M, Dahle MK, Rimstad E, Koppang EO. Red and melanized focal changes in the white skeletal muscle of farmed rainbow trout Oncorhynchus mykiss. DISEASES OF AQUATIC ORGANISMS 2024; 158:201-213. [PMID: 38934260 DOI: 10.3354/dao03797] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/28/2024]
Abstract
Fillet discoloration by red and melanized focal changes (RFCs and MFCs) is common in farmed Atlantic salmon Salmo salar. In farmed rainbow trout Oncorhynchus mykiss, similar changes have been noted, but their prevalence and histological characteristics have not been investigated. Thus, we conducted a study encompassing 1293 rainbow trout from 3 different farm sites in Norway, all examined at the time of slaughter. Both macroscopic and histological assessments of the changes were performed. Reverse transcription (RT)-qPCR analyses and in situ hybridization (ISH) were used to detect the presence and location, respectively, of potential viruses. Only 1 RFC was detected in a single fillet, while the prevalence of MFCs ranged from 1.46 to 6.47% between populations. The changes were predominantly localized in the cranioventral region of the fillet. Histological examinations unveiled necrotic myocytes, fibrosis, and regeneration of myocytes. Melano-macrophages were found in the affected areas and in myoseptal adipose tissue. Organized granulomas were observed in only 1 fish. Notably, the presence of inflammatory cells, including melano-macrophages, appeared lower compared to what has been previously documented in Atlantic salmon MFCs. Instead, fibrosis and regeneration dominated. RT-qPCR and ISH revealed the presence of piscine orthoreovirus 1 (PRV-1) and salmonid alphavirus (SAV) in skeletal muscle. However, these viruses were not consistently associated with lesioned areas, contrasting previous findings in Atlantic salmon. In conclusion, rainbow trout develop MFCs of a different character than farmed Atlantic salmon, and we speculate whether the observed pathological differences are contributing to their reduced occurrence in farmed rainbow trout.
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Affiliation(s)
- Håvard Bjørgen
- Unit of Anatomy, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, 1433 Ås, Norway
| | - Malin Brimsholm
- Unit of Anatomy, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, 1433 Ås, Norway
| | - Morten Lund
- Pure Salmon Kaldnes, 3241 Sandefjord, Norway
| | | | - Espen Rimstad
- Unit of Virology, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, 1433 Ås, Norway
| | - Erling Olaf Koppang
- Unit of Anatomy, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, 1433 Ås, Norway
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3
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Bjørgen H, Koppang EO. The melano-macrophage: The black leukocyte of fish immunity. FISH & SHELLFISH IMMUNOLOGY 2024; 148:109523. [PMID: 38522495 DOI: 10.1016/j.fsi.2024.109523] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/04/2024] [Revised: 03/20/2024] [Accepted: 03/21/2024] [Indexed: 03/26/2024]
Abstract
Melanin and the process of melanin synthesis or melanogenesis have central roles in the immune system of insects, and production of melanin-synthesizing enzymes from their haemocytes may be induced following activation through danger signals. Melanin-containing macrophage-like cells have been extensively studied in amphibians and they are also present in reptiles. In fish, melano-macrophages are especially recognized with respect to melano-macrophage centres (MMCs), hypothesized to be analogues of germinal centres in secondary lymphoid organs of mammals and some birds. Melano-macrophages are in addition present in several inflammatory conditions, in particular melanised focal changes, or black spots, in the musculature of farmed Atlantic salmon, Salmo salar. Melanins are complex compounds that may be divided into different forms which all have the ability to absorb and scatter light. Other functions include the quenching of free radicals and a direct effect on the immune system. According to the common view held in the pigment cell community, vertebrate melanin synthesis with melanosome formation may only occur in cells of ectodermal origin. However, abundant information suggests that also myeloid cells of ectothermic vertebrates may be classified as melanocytes. Here, we discuss these opposing views and review relevant literature. Finally, we review the current status on the research concerning melanised focal muscle changes that represent the most severe quality problem in Norwegian salmon production, but also other diseases where melano-macrophages play important roles.
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Affiliation(s)
- Håvard Bjørgen
- Unit of Anatomy, Veterinary Faculty, Norwegian University of Life Sciences (NMBU), Ås, Norway
| | - Erling Olaf Koppang
- Unit of Anatomy, Veterinary Faculty, Norwegian University of Life Sciences (NMBU), Ås, Norway.
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Bjørgen H, Malik S, Rimstad E, Vaadal M, Nyman IB, Koppang EO, Tengs T. Cellular heterogeneity in red and melanized focal muscle changes in farmed Atlantic salmon (Salmo salar) visualized by spatial transcriptomics. Cell Tissue Res 2024; 395:199-210. [PMID: 38087072 PMCID: PMC10837230 DOI: 10.1007/s00441-023-03850-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2023] [Accepted: 11/24/2023] [Indexed: 12/31/2023]
Abstract
Spatial transcriptomics is a technique that provides insight into gene expression profiles in tissue sections while retaining structural information. We have employed this method to study the pathological conditions related to red and melanized focal changes in farmed Atlantic salmon (Salmo salar). Our findings support a model where similar molecular mechanisms are involved in both red and melanized filet discolorations and genes associated with several relevant pathways show distinct expression patterns in both sample types. Interestingly, there appears to be significant cellular heterogeneity in the foci investigated when looking at gene expression patterns. Some of the genes that show differential spatial expression are involved in cellular processes such as hypoxia and immune responses, providing new insight into the nature of muscle melanization in Atlantic salmon.
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Affiliation(s)
- H Bjørgen
- Unit of Anatomy, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, 1433, Ås, Norway
| | - S Malik
- Department of Breeding and Genetics, Nofima, 1433, Ås, Norway
| | - E Rimstad
- Unit of Virology, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, 1433, Ås, Norway
| | - M Vaadal
- Department of Breeding and Genetics, Nofima, 1433, Ås, Norway
| | - I B Nyman
- Unit of Virology, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, 1433, Ås, Norway
| | - E O Koppang
- Unit of Anatomy, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, 1433, Ås, Norway
| | - T Tengs
- Department of Breeding and Genetics, Nofima, 1433, Ås, Norway.
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Brimsholm M, Fjelldal PG, Hansen T, Fraser TKW, Solberg M, Glover K, Koppang EO, Bjørgen H. Red and melanized focal changes in white skeletal muscle in Atlantic salmon (Salmo salar): Comparative analysis of farmed, wild and hybrid fish reared under identical conditions. JOURNAL OF FISH DISEASES 2023; 46:1377-1389. [PMID: 37675872 DOI: 10.1111/jfd.13856] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/12/2023] [Revised: 08/16/2023] [Accepted: 08/22/2023] [Indexed: 09/08/2023]
Abstract
Selective breeding plays a vital role in the production of farmed Atlantic salmon and has shown success in many aspects. Still, challenges related to fish health and welfare continue to result in significant economic losses. One such challenge is red and melanized focal changes (RFC/MFC), which result from acute and chronic inflammation, respectively, in the skeletal muscle. Importantly, RFC/MFC has not been observed in wild Atlantic salmon, suggesting that both external and genetic factors may contribute to the development of inflammation. To investigate the underlying cause of RFC/MFC, we conducted a study involving 1854 Atlantic salmon of farmed, wild and hybrid origin. All fish were reared under identical conditions to minimize the influence of external factors. Throughout the production cycle, the fish was monitored for growth parameters and examined for RFC/MFC using macroscopic and histological analysis. We found no association between the experimental groups and the presence of RFC/MFC. Histological investigations revealed melano-macrophages in the soft tissue in freshwater smolt, although no macroscopic discoloration was observed. MFC showed granulomas in various stages, suggesting a complex progression of the condition. In summary, we conclude that RFC/MFC is primarily caused by external factors found in the rearing facilities of farmed Atlantic salmon.
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Affiliation(s)
- Malin Brimsholm
- Unit of Anatomy, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
| | | | - Tom Hansen
- Matre Research Station, Institute of Marine Research, Matredal, Norway
| | | | - Monica Solberg
- Population Genetics Research Group, Institute of Marine Research, Bergen, Norway
| | - Kevin Glover
- Population Genetics Research Group, Institute of Marine Research, Bergen, Norway
| | - Erling Olaf Koppang
- Unit of Anatomy, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
| | - Håvard Bjørgen
- Unit of Anatomy, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
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Wakamatsu K, Dijkstra JM, Mørkøre T, Ito S. Eumelanin Detection in Melanized Focal Changes but Not in Red Focal Changes on Atlantic Salmon ( Salmo salar) Fillets. Int J Mol Sci 2023; 24:16797. [PMID: 38069120 PMCID: PMC10706398 DOI: 10.3390/ijms242316797] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2023] [Revised: 11/16/2023] [Accepted: 11/22/2023] [Indexed: 12/18/2023] Open
Abstract
Superficial discolored spots on Atlantic salmon (Salmo salar) fillets are a serious quality problem for commercial seafood farming. Previous reports have proposed that the black spots (called melanized focal changes (MFCs)) may be melanin, but no convincing evidence has been reported. In this study, we performed chemical characterization of MFCs and of red pigment (called red focal changes (RFCs)) from salmon fillets using alkaline hydrogen peroxide oxidation and hydroiodic acid hydrolysis. This revealed that the MFCs contain 3,4-dihydroxyphenylalanine (DOPA)-derived eumelanin, whereas the RFCs contain only trace amounts of eumelanin. Therefore, it is probable that the black color of the MFCs can be explained by the presence of eumelanin from accumulated melanomacrophages. For the red pigment, we could not find a significant signature of either eumelanin or pheomelanin; the red color is probably predominantly hemorrhagic in nature. However, we found that the level of pigmentation in RFCs increased together with some melanogenic metabolites. Comparison with a "mimicking experiment", in which a mixture of a salmon homogenate + DOPA was oxidized with tyrosinase, suggested that the RFCs include conjugations of DOPAquinone and/or DOPAchrome with salmon muscle tissue proteins. In short, the results suggest that melanogenic metabolites in MFCs and RFCs derive from different chemical pathways, which would agree with the two different colorations deriving from distinct cellular origins, namely melanomacrophages and red blood cells, respectively.
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Affiliation(s)
- Kazumasa Wakamatsu
- Institute for Melanin Chemistry, Fujita Health University, Toyoake 470-1192, Japan;
| | | | - Turid Mørkøre
- Department of Animal and Aquaculture Sciences, Norwegian University of Life Sciences, NO 1432 Ås, Norway;
| | - Shosuke Ito
- Institute for Melanin Chemistry, Fujita Health University, Toyoake 470-1192, Japan;
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Ouyang P, Tao Y, Wei W, Li Q, Liu S, Ren Y, Huang X, Chen D, Geng Y. Spring Viremia of Carp Virus Infection Induces Carp IL-10 Expression, Both In Vitro and In Vivo. Microorganisms 2023; 11:2812. [PMID: 38004823 PMCID: PMC10673272 DOI: 10.3390/microorganisms11112812] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2023] [Revised: 10/28/2023] [Accepted: 11/10/2023] [Indexed: 11/26/2023] Open
Abstract
Interleukin-10 (IL-10) is a pleiotropic cytokine with both immune enhancement and immunosuppression activities, but the main role is immunosuppression and anti-inflammatory ability. In order to use the immunosuppressive function of IL-10, many viruses, such as SARS-CoV-2, hepatitis B virus and EB virus, can evade the host's immune surveillance and clearance by increasing the expression of host IL-10. However, it has not been reported whether the aquatic animal infection virus can upregulate the expression of host IL-10 and the mechanisms are still unknown. Spring viremia of carp (SVC) is a fatal viral disease for many fish species and is caused by spring viremia of carp virus (SVCV). This disease has caused significant economic losses in the aquaculture industry worldwide. In this study, the expression of carp IL-10 with or without infection of SVCV in epithelioma papulosum cyprinid (EPC) cells, carp head kidney (cHK) primary cells and common carp tissues were analyzed using RT-PCR and ELISA. The results show that SVCV infection induced carp IL-10 mRNA and protein expression, both in vitro and in vivo. However, the upregulation of carp IL-10 by SVCV was hindered by specific inhibitors of the JAK inhibitor (CP-690550), STAT3 inhibitor (STA-21), NF-κB inhibitor (BAY11-7082) and p38 MAPK (mitogen-activated protein kinase) inhibitor (SB202190), but not JNK inhibitor (SP600125). Furthermore, the results demonstrated that JAK1, JAK2, JAK3, TYK2 and STAT5 played important roles in carp IL-10 production induced by SVCV infection. Taken together, SVCV infection significantly induced carp IL-10 expression and the upregulation trigged in JAK-STAT, NF-κB and p38MAPK pathways. To our knowledge, this is the first time that a fish infection virus upregulated the host IL-10 expression through the JAK-STAT, NF-κB and p38MAPK pathways. Altogether, fish viruses may have a similar mechanism as human or other mammalian viruses to escape host immune surveillance and clearance.
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Affiliation(s)
- Ping Ouyang
- Department of Basic Veterinary, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu 611130, China; (Y.T.); (Q.L.); (S.L.); (Y.R.); (Y.G.)
| | - Yu Tao
- Department of Basic Veterinary, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu 611130, China; (Y.T.); (Q.L.); (S.L.); (Y.R.); (Y.G.)
| | - Wenyan Wei
- Chengdu Academy of Agriculture and Forestry Sciences, Chengdu 611130, China;
| | - Qiunan Li
- Department of Basic Veterinary, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu 611130, China; (Y.T.); (Q.L.); (S.L.); (Y.R.); (Y.G.)
| | - Shuya Liu
- Department of Basic Veterinary, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu 611130, China; (Y.T.); (Q.L.); (S.L.); (Y.R.); (Y.G.)
| | - Yongqiang Ren
- Department of Basic Veterinary, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu 611130, China; (Y.T.); (Q.L.); (S.L.); (Y.R.); (Y.G.)
| | - Xiaoli Huang
- Department of Aquaculture, College of Animal Science and Technology, Sichuan Agricultural University, Chengdu 611130, China; (X.H.); (D.C.)
| | - Defang Chen
- Department of Aquaculture, College of Animal Science and Technology, Sichuan Agricultural University, Chengdu 611130, China; (X.H.); (D.C.)
| | - Yi Geng
- Department of Basic Veterinary, College of Veterinary Medicine, Sichuan Agricultural University, Chengdu 611130, China; (Y.T.); (Q.L.); (S.L.); (Y.R.); (Y.G.)
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Brimsholm M, Rønning L, Rimstad E, Koppang EO, Bjørgen H. Diffuse melanization of the red skeletal musculature in farmed Atlantic salmon (Salmo salar L.). JOURNAL OF FISH DISEASES 2023; 46:453-458. [PMID: 36353756 DOI: 10.1111/jfd.13729] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/09/2022] [Revised: 10/14/2022] [Accepted: 10/18/2022] [Indexed: 06/16/2023]
Affiliation(s)
- Malin Brimsholm
- Unit of Anatomy, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
| | | | - Espen Rimstad
- Unit of Virology, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
| | - Erling Olaf Koppang
- Unit of Anatomy, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
| | - Håvard Bjørgen
- Unit of Anatomy, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
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Brimsholm M, Fjelldal PG, Hansen T, Trangerud C, Knutsen GM, Asserson CF, Koppang EO, Bjørgen H. Anatomical and pathological characteristics of ribs in the Atlantic salmon (Salmo salar L.) and its relevance to soft tissue changes. Anat Histol Embryol 2023; 52:421-436. [PMID: 36637047 DOI: 10.1111/ahe.12900] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2022] [Accepted: 12/21/2022] [Indexed: 01/14/2023]
Abstract
Studies on the anatomical and pathological characteristics of ribs in farmed Atlantic salmon (Salmo salar L.) are warranted due to their possible association with red and melanized focal changes (RFC and MFC) in the fillet, a major quality and animal welfare concern. In this work, we provide an anatomical description of ribs based on radiographical and histological analyses. We also address various pathological rib changes and their association to RFC and MFC. In total, 129 fish were investigated; captured wild (n = 10) and hatchery reared (n = 119) Atlantic salmon (3.5-6.1 kg). The fish were selected based on the macroscopic presence of RFC, MFC or no changes (controls). Radiographic results revealed costal abnormalities in all fish groups. By histological investigations of the variations herein, our results provide new insight into the anatomical characteristics including vascularization within the ribs; a potential site for haemorrhage following costal fractures. Costal fractures were detected by radiology in 40 of 129 samples (RFC: 38.4%, MFC: 47.2%, controls: 9.5 %). A statistically significant association was found between costal fractures and red (p = 0.007) and melanized changes (p = 0.000). However, red and melanized changes were also observed in samples with no costal fractures (n = 45), indicating that also other factors influence the development of RFC/MFC.
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Affiliation(s)
- Malin Brimsholm
- Unit of Anatomy, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
| | | | - Tom Hansen
- Matre Research Station, Institute of Marine Research, Matredal, Norway
| | - Cathrine Trangerud
- Unit of Radiology, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
| | | | | | - Erling Olaf Koppang
- Unit of Anatomy, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
| | - Håvard Bjørgen
- Unit of Anatomy, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
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Malik MS, Bjørgen H, Nyman IB, Wessel Ø, Koppang EO, Dahle MK, Rimstad E. PRV-1 Infected Macrophages in Melanized Focal Changes in White Muscle of Atlantic Salmon ( Salmo salar) Correlates With a Pro-Inflammatory Environment. Front Immunol 2021; 12:664624. [PMID: 33995395 PMCID: PMC8116804 DOI: 10.3389/fimmu.2021.664624] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2021] [Accepted: 04/13/2021] [Indexed: 12/27/2022] Open
Abstract
Melanized focal changes in white skeletal muscle of farmed Atlantic salmon, "black spots", is a quality problem affecting on average 20% of slaughtered fish. The spots appear initially as "red spots" characterized by hemorrhages and acute inflammation and progress into black spots characterized by chronic inflammation and abundant pigmented cells. Piscine orthoreovirus 1 (PRV-1) was previously found to be associated with macrophages and melano-macrophages in red and black spots. Here we have addressed the inflammatory microenvironment of red and black spots by studying the polarization status of the macrophages and cell mediated immune responses in spots, in both PRV-1 infected and non-infected fish. Samples that had been collected at regular intervals through the seawater production phase in a commercial farm were analyzed by multiplex fluorescent in situ hybridization (FISH) and RT-qPCR methods. Detection of abundant inducible nitric oxide synthase (iNOS2) expressing M1-polarized macrophages in red spots demonstrated a pro-inflammatory microenvironment. There was an almost perfect co-localization with the iNOS2 expression and PRV-1 infection. Black spots, on the other side, had few iNOS2 expressing cells, but a relatively high number of arginase-2 expressing anti-inflammatory M2-polarized macrophages containing melanin. The numerous M2-polarized melano-macrophages in black spots indicate an ongoing healing phase. Co-localization of PRV-1 and cells expressing CD8+ and MHC-I suggests a targeted immune response taking place in the spots. Altogether, this study indicates that PRV-1 induces a pro-inflammatory environment that is important for the pathogenesis of the spots. We do not have indication that infection of PRV-1 is the initial causative agent of this condition.
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Affiliation(s)
- Muhammad Salman Malik
- Section of Virology, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
| | - Håvard Bjørgen
- Section of Anatomy, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
| | - Ingvild Berg Nyman
- Section of Virology, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
| | - Øystein Wessel
- Section of Virology, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
| | - Erling Olaf Koppang
- Section of Anatomy, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
| | - Maria K. Dahle
- Department of Fish Health, Norwegian Veterinary Institute, Oslo, Norway
| | - Espen Rimstad
- Section of Virology, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, Ås, Norway
- *Correspondence: Espen Rimstad,
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