MHC Class â…¡A Genes (DAA)Polymorphisms Are Associated With IHN Disease In Rainbow Trout (Oncorhynchus Mykiss)

Infectious hematopoietic necrosis (IHN) is a rhabdoviral disease of salmonid species andwich can cause losses of up to70%~90%in rainbow trout fry and fingerlings and hugeeconomic expenses result from this disease. Genes of the major histocompatibility complex(MHC) are crucial elements of adaptive immunity in vertebrate organisms and have beenlinked to resistance to numerous pathogenic diseases. In this study, polymerase chainreaction-single strand conformation polymorphism (PCR-SSCP) and cloning sequencing wereused to detect the polymorphism of DAA (MHC class II alpha) gene of104resistantindividuls and91susceptibility individuals. In addition, association between polymorphism ofDAA (MHC class II alpha) gene and IHN resistance of rainbow trout was identified. In thisstudy,17alleles were resolved, of which13were novel. The new sequences reported weredeposited into the GenBank database under the accession numbers JX136674, JX136675, andJX145651-JX145661. A maximum of five alleles were amplified per individual in this locus,indicating that a minimum of three loci or copies of the DAA exon2in rainbow trout.Pairwise comparisons of the17Onmy-DAA alleles revealed that the variation percentages ofnucleotide substitutions and amino acid mutations were22.09%and36.84%, respectively.And most of the mutations happened in PBR region. The non-synonymous (dN) in the PBRwas significantly higher than synonymous (dS)(P <0.001) and dNwas also large higher thandSin the total sequece (P <0.01), this result might suggest that the polymorphism of DAAgene seems to be maintained by a positive selection. Alleles potentially associated withresistance or susceptibility were identified, the alleles DAA*0301, DAA*0304, DAA*1301andDAA*1701was highly associated with resistance to IHN (P <0.001) and the DAA*0603,DAA*0802and DAA*1602was related to susceptibility to IHN (P≦0.001).