The Atlantic cod genome has been surveyed to improve farmed cod immune system. (Photo: cees.uio.no)
Immune system discovery could lead to better vaccines for cod
Thursday, August 11, 2011, 23:40 (GMT + 9)
Researchers at the University of Oslo have sequenced the Atlantic cod (Gadus morhua) genome and discovered an immune system that could lead to better vaccines and better disease management in farmed cod. This immune system has never before been observed in jawed vertebrates.
Kjetill Jakobsen and colleagues, from the university, saw that, by losing the genes for three important components of the adaptive immune system, Atlantic cod have partly lost their ability to fight off pathogens and develop the immune memory that combats infection.
The findings were published this week in Nature.
One of the missing components, the major histocompatibility complex (MHC) II, shows fragments of bacteria and other pathogens to cells in the immune system to set off a broader response. Another gene lacking is one for the proteins CD4, which interacts with the former, and invariant chain, which works to make and transport MHC II.
Jakobsen noted that mice genetically engineered to lack MHC II suffer from immune defects.
"MHC II is something that you can't really lose without suffering from some severe illnesses", said Jakobsen.
"Our findings affect fundamental assumptions about the immune system evolution," he commented, Science Mag reports.
Sebastian Fugmann, a molecular immunologist at the National Institute on Aging in Baltimore, Maryland, called the announcement "quite unexpected."
"This is the most dramatic example reported thus far of the plasticity of the adaptive immune system in jawed vertebrates on an evolutionary timescale," he stated.
Cod compensate for their missing MHC II, for example, by possessing 10 times more genes than other vertebrates for another component of the immune system, called MHC I. MHC I displays proteins from within the cell on the cell surface, letting the immune system detect and destroy the foreign bodies.
Further, cod rely more heavily than other vertebrates on molecules called Toll-like receptors, which recognize bacterial and viral invaders.
The team’s findings could allow targeted vaccine development, helping in the disease management and domestication of Atlantic cod in aquaculture.
Cod may have developed their unusual immune system due to having evolved in deep waters with a very specific variety of pathogens. This is particularly important, Jakobsen said, because cod’s unique immune system may leave it particularly vulnerable to disease if they are raised outside their natural habitat.
The findings might also defy the current understanding of the evolution and flexibility of the vertebrate immune system.
"The fact that we see cod lacking MHC class II and actually doing well without it opens our eyes towards understanding human immunity", says Jakobsen.
Also, the sequencing of related species may reveal parallel adaptations.
"It would be really interesting to look at the comparative genomics of those species closest to cod," said Jakobsen.
By Natalia Real