The genome sequence of Atlantic cod reveals a unique immune system

The genome of the Atlantic cod has been sequenced, and genomic analysis reveals an immune system that differs significantly from that in other vertebrates. The major histocompatibility complex (MHC) II has been lost, as have some other genes that are essential for MHC II function. But there is an expansion in the number of MHC I genes and a unique composition for its toll-like receptor family. These compensatory changes in both adaptive and innate immunity mean that cod is no more susceptible to disease than most other vertebrates. These findings challenge current models of vertebrate immune evolution, and may facilitate the development of targeted vaccines for disease management in aquaculture.