Pathogen resistance and gene frequency stability of major histocompatibility complex class IIB alleles in the giant spiny frog Quasipaa spinosa

Abstract

The major histocompatibility complex (MHC) is a highly polymorphic genomic region, which widely exists in vertebrates and plays a pivotal role in immune response. As such, the association between MHC alleles and pathogen resistance has been investigated in many vertebrates. However, limited information is reported about the heredity of alleles associated with disease resistance, and the related research has not been reported in amphibians. In this study, PCR primers were developed for a portion of the second exon of the MHC class II B gene in the giant spiny frog Quasipaa spinosa, which is an important aquaculture species with high economical value in China. 31 MHC class II B alleles were identified from 100 individuals intraperitoneally injected with Aeromonas hydrophila. We selected six high-frequency alleles that exist in death and survival to investigate the association between MHC class II B alleles and disease resistance/susceptibility. Q. spinosa with qasp-DAB*h and qasp-DAB*l alleles exhibited a higher resistance to A. hydrophila than Q. spinosa with other alleles. By contrast, Q. spinosa with qasp-DAB*e alleles displayed a higher susceptibility to A. hydrophila than Q. spinosa with other alleles. We also determined an array of immunological and haematological parameters of Q. spinosa offspring after this organism was intraperitoneally injected with A. hydrophila, Acinetobacter baumannii and Citrobacter braakii. We found that the resistant offspring group showed higher immunity than the control offspring group. Twenty-six MHC class II B alleles were identified from 100 resistant offspring individuals. Two alleles qasp-DAB*0701 and qasp-DAB*1001 that is same to qasp-DAB*h and qasp-DAB*l of parents were also determined in the resistant offspring. The constant transmission of the qasp-DAB*h and qasp-DAB*l alleles were observed. This study confirmed the association between MHC class II B gene alleles and disease resistance. This study also detected the two alleles correlated with high resistance to bacterial infection in Q. spinosa parents and offspring. Statement of relevanceQ. spinosa is highly valued in Chinese markets because of its medicinal and nutritional values. The paper plays an important role on the selective breeding of resistant and genetically stable Q. spinosa strains.