Adaptive immunity in teleost fish is based on molecular components with overall similarity to the mammalian counterparts, i.e. T cell receptors, MHC antigens and immunoglobulins. However, significant differences have been introduced between homologous molecules in fish and mammals during evolution, and many new molecules have emerged as a result of gene duplications. Our main goal is to gain more insight into host – pathogen interactions in fish, and in the course of our studies, broaden the spectrum of well characterized components of the adaptive immune system in Atlantic salmon.
Teleost fish possess three classes of immunoglobulins; IgM, IgD and IgT. Furhermore, it has been reported that a possible counterpart of the polymeric immunoglobulin receptor (pIgR) is involved in the transport of immunoglobulins into mucosal sites of fish, but further investigations are needed to reveal whether the transport mechanisms are equivalent to those in mammals. As a key entry point for pathogens, studies of immune responses at mucosal sites are among the priorities in our laboratory. In this context, a newly discovered lymphoid tissue in the gills of fish, rich in T cells, is of particular interest. Another topic that we want to elucidate further is the biological significance of antibody diversity related to ancestral tetraploidy in salmonid fish. Atlantic salmon possess sub-variants of each immunoglobulin class as a result of the tetraploid event that occurred in the ancestor of the salmonid fish family.
Characterization of cells and molecules of the immune system, accompanied by developing tools to identify them, have been an essential driving force in immunological research in humans. Teleost fish comprise a very heterogenous group, which implicates that specific tools must be developed for each species of interest. Salmonid fish are among the most widely studied model fish species, and have been selected for several large scale projects. Although many putative CD (“clusters of differentiation”) markers are represented among the ESTs in the databanks, the list of well characterized cell markers and other immune related genes in teleost fish is still far from complete.