Camila Ruz guardian.co.uk, Wednesday 10 August 2011 18.58 BST
The cod genome lacks a set of genes that were thought to be indispensable for immunity against bacteria and other parasites.
Atlantic cod have evolved to survive without a set of genes that scientists thought were essential to the immune system, according to an analysis of the fish's genome. Researchers hope the finding will lead to better vaccines for farmed cod-protecting declining fish stocks-and may even open new avenues of medical research for human disease.
“Pathogens are a major challenge to fish farming, particularly under the dense stocking conditions that are typical of aquaculture, and vaccination is a major approach to protect from diseases,” said Prof Christopher Secombe, head of the Scottish Fish Immunology Research Centre. The new research will help them to target vaccine research more effectively.
Cod is one of the five fish species most commonly eaten in the UK. British consumers spent more than £313.3m on cod last year.
The research team discovered that Atlantic cod do not have a set of immunity-related genes called MHC Class II that are found in almost all backboned animals. In other species, these genes contribute to the immune system's ability to recognise invading bacteria and parasites. “We could not find MHC Class II and also two other genes that are essential for protection against pathogenic bacteria and other parasites coming from the outside,” said Professor Kjetill Jakobsen from the University of Oslo in Norway, who led the study.
The MHC molecules coded by the genes latch onto pieces of pathogens and present them on the surface of the infected cell, so that the cells can be recognised and destroyed by the immune system. There are two kinds of MHC molecules: MHC Class I molecules specialise in finding viruses within cells and MHC II molecules police the outside of the cell looking for bacteria and parasites. It was thought that both types of MHC molecule were crucial for survival.
But it appears that over evolutionary time, as the MHC Class II genes have been lost in cod, other genes have stepped in to compensate for the loss. “It is one of the most striking examples to date of the amazing plasticity of the immune system over evolutionary time,” said Professor Jim Kaufman, an immunologist from the University of Cambridge.
“From a traditional point of view MHC Class I cannot fight bacterial infections but maybe it can in cod because they have 10 times more gene copies of the MHC Class I than other fishes and humans do,” he said.
Their results, published on Wednesday in the journal Nature, could present new possibilities for the treatment of human disease. “This has some implications for medical research. I can tell you that I had a talk at the main hospital here in Oslo and there were hundreds of doctors sitting there listening to me talking about cod," said Jakobsen. "Maybe we can regulate the human immune system differently and maybe that could be treatment against certain diseases, multiple sclerosis for example.”Scientists hope that the finding will also lead to improved vaccines for farmed Atlantic Cod. Prof Secombe said the discovery that Atlantic cod don't have MHC II would prevent vaccine developers wasting time trying “to trigger something that is actually missing”.