Pigment-producing granulomatous myopathy in Atlantic salmon: a novel inflammatory response.
Melanin comprises a complex group of pigmented polymers whose primary function is ascribed to dermal solar protection, but may also have an interesting role in innate immunity. In ectothermic vertebrates, melanogenesis is reported in leukocyte populations, but it is not known if this occurs in connection with inflammatory reactions. Melanin accumulations in ectopic locations, in particular muscle, represent a serious quality problem in salmon production. Here, we investigated such changes for the expression of dopachrome tautomerase and tyrosinase as well as some important immune genes and pathogens. Furthermore, the nature of the pathological changes was addressed by morphological methods. Gene transcripts encoding key enzymes in melanogenesis, suggesting a de novo melanin synthesis in pigmented muscle, were found. MHC class II transcripts were up-regulated and there was no indication of bacterial or viral infection. The histological examination revealed granulomatous inflammation with distribution of MHC class II positive cells and T cells, analogous to the pattern found in mammals. Importantly, in contrast to mammals pigmented cells were contributing in the inflammation. We demonstrate that melanin production occurs in granulomatous inflammation in salmon, revealing a close and hitherto unreported link between the pigmentary and immune systems.
Section of Anatomy and Pathology, Institute of Basic Science and Aquatic Medicine, Norwegian School of Veterinary Science, Oslo, Norway.
Hilde A S
HA
Larsen
Lars
L
Austbø
Turid
T
Mørkøre
Jim
J
Thorsen
Ivar
I
Hordvik
Uwe
U
Fischer
Emilio
E
Jirillo
Espen
E
Rimstad
Erling O
EO
Koppang
D000818:Animals; D005393:Fish Diseases / Q000276:immunology / Q000473:pathology*; D020869:Gene Expression Profiling; D005802:Genes, MHC Class II / Q000235:genetics / Q000276:immunology; D007150:Immunohistochemistry; D007249:Inflammation; D008543:Melanins / Q000276:immunology*; D014442:Monophenol Monooxygenase / Q000276:immunology; D018482:Muscle, Skeletal / Q000201:enzymology / Q000276:immunology / Q000473:pathology*; D009135:Muscular Diseases / Q000276:immunology / Q000473:pathology*; D013601:T-Lymphocytes / Q000201:enzymology / Q000276:immunology
D008543:Melanins; D014442:Monophenol Monooxygenase