Transcriptional profiling of MHC class I genes in rainbow trout infected with infectious hematopoietic necrosis virus

Major histocompatibility complex (MHC) molecules are important mediators of cell-mediated immunity in vertebrates. MHC class IA molecules are important for host anti-viral immunity as they present intracellular antigens and regulate natural killer cell (NK) activity. MHC class Ib molecules on the other hand are less understood and have demonstrated diverse immune and non-immune functions in mammals. Rainbow trout possess a single classical MHC IA locus (Onmy-UBA) that is believed to function similar to that of mammalian MHC class Ia. Numerous MHC class Ib genes with undetermined functions have also been described in trout. Here we utilize quantitative reverse transcriptase PCR (qRT-PCR) techniques to survey the levels of basal and inducible transcription for selected trout MHC class Ib genes, sIgM and sentinels of IFN induction in response to viral infection. Basal transcription of all the class Ib genes examined in this study was lower than Onmy-UBA in naïve fish. UBA, along with all of the non-classical genes were induced in fish infected with virus but not in control fish. Our results support a non-classical designation for the majority of the class IB genes surveyed in this study based upon expression levels while also indicating that they may play an important role in anti-viral immunity in trout.