Characterization of the adaptive immune system in fish

Accessibility of tools to monitor immune responses in fish, and knowledge on how the immune system works in different species, is important in vaccine development and other prophylactic measurements in the aquaculture industry.

As in mamals, the adaptive immune system in fish is based on molecules corresponding to MHC antigens, T-cell receptors, B-cell receptors, antibodies, and a large number of accessory molecules. However, the term “fish” encompasses a very heterogenous group of organisms, and the immune system of different species of for instance teleosts show distinct characteristics. Our studies have mostly been focused on Atlantic salmon, but other species like trout, char and wrasses (“cleaner fish”) are also studied.

The major systemic antibody in teleost fish is IgM, whereas a more recently discovered class of immunoglobulins, IgT, might be specialized to mucosal immune responses. As a result of ancestral tetraploidy (i.e. a whole genome duplication event), there are two paralogous Ig heavy chain gene complexes (A and B) in Atlantic salmon. Consequently, there are two IgM genes, two IgD genes, three intact IgT genes and five IgT pseudogenes in this species. Serum IgM in teleost fish is regarded to be a tetramer. In other vertebrates, IgM is a pentamer and a J-chain is involved in the polymer formation. A homolog of the polymeric Ig receptor (pIgR) has been identified in teleost fish, but is quite different from the counterpart in mammals.

A long term goal of our studies is to characterize and systematize all relevant immune genes in fish, and develop tools to monitor key components involved in the adaptive immune responses. In collaboration with other research groups, we study cell populations and tissues of the immune system in fish, and host-pathogen interactions.