Pigment-producing granulomatous myopathy in Atlantic salmon: a novel inflammatory response

Fish Shellfish Immunol. 2012 Aug;33(2):277-85. doi: 10.1016/j.fsi.2012.05.012. Epub 2012 May 14.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Fish Diseases / immunology
  • Fish Diseases / pathology*
  • Gene Expression Profiling
  • Genes, MHC Class II / genetics
  • Genes, MHC Class II / immunology
  • Immunohistochemistry
  • Inflammation
  • Melanins / immunology*
  • Monophenol Monooxygenase / immunology
  • Muscle, Skeletal / enzymology
  • Muscle, Skeletal / immunology
  • Muscle, Skeletal / pathology*
  • Muscular Diseases / immunology
  • Muscular Diseases / pathology*
  • T-Lymphocytes / enzymology
  • T-Lymphocytes / immunology


  • Melanins
  • Monophenol Monooxygenase