The variability and immunological importance of the genes in the major histocompatibility complex (MHC) are ideal for identifying breeding lineages, evaluating immunologic vigor and identifying emergence of new genotypes that reflect ecosystem pressures. MHC genes encode a set of transmembrane proteins critical to the generation of immune responses. The variety of MHC-encoded proteins in an individual ultimately determines the repertoire of foreign peptides to which that animal is capable of responding and, at the population level, reflects the historic influence of pathogen pressures and the ability to adapt to future insults.
Since infectious disease is an important cause of morbidity and mortality in any mammalian population, the ability of an individual to adapt to changing pathogen pressures is critical to its survival and, ultimately, therefore, to population health. The relative degree of MHC polymorphism is an excellent measure of immune potential in a population. Based upon previous studies in California sea lions that demonstrated the majority of MHC class II polymorphism was in DRB, this gene complex was examined in Steller sea lions. MHC DRB genes were cloned and sequenced using peripheral blood mononuclear leukocytes derived from ten animals from Southeast Alaska, Prince William Sound and the Aleutian Islands. Nine unique DRB gene sequences were identified; all ten animals had all nine DRB genes. While MHC genotyping can be used to measure the potential immunologic vigor of a population, ecosystem-induced changes to MHC genotype can be slow to emerge. However, identification and quantification of differential MHC gene expression has the potential to provide evidence of real-time immunologic perturbations in a population. A quantitative PCR system was developed to examine MHC class II DRB gene expression in Steller sea lions. A Quantitect SYBR Green PCR Master Mix system was used in combination with icycler technology to quantify the level of expression of each MHC DRB gene in a subset of 6 sea lions. Although DRB in genomic DNA was consistent across all individuals, relative levels of expressed DRB mRNA was found to be highly variable, indicating differential immune potential between individuals. Application of this technique to a cross-section of the Steller sea lion population has the potential to contribute to an assessment of population health; decreased immune potential has been implicated as an underlying factor contributing to disease emergence in both human and wildlife populations.
Funded in part by the Alaskan Department of Fish & Game and a University of California Faculty Research Grant