Abstract

The phytohaemagglutinin (PHA) skin-swelling test is often used as an in vivo challenge in studies on immunoecology and ecotoxicology as it is useful to estimate the response and proliferation of several types of immune cells to a given effector.³ MHC class II genes encode cell surface glycoproteins involved in the presentation of foreign antigens, be these pathogen and nonpathogen-derived peptides, and they also participate in the activation and proliferation of effector lymphocytes.^1,4 To date, a few ecoimmunological studies have explored the role of MHC in terms of PHA, but the relationship between MHC diversity and PHA-induced inflammation remains mostly unknown for most vertebrate systems. In this preliminary study, we examined the importance of MHC class II DRB gene polymorphisms as an explanatory variable for PHA-induced swelling in 18 California sea lion pups sampled in October 2012. We used generalized linear models (GLMs) to analyze the potential effect of DRB gene polymorphisms, total number of circulating white blood cells (WBC, as a proxy for current infections), lymphocyte counts (as DRB molecules interact with T-cell receptors), and sex on the magnitude of PHA-induced swelling, and examined potential effects due to pup body condition. We found that the magnitude of PHA-induced inflammation is significantly explained by the interaction between DRB polymorphism, body condition, and circulating WBC (GLM, F = 4.23, df = 16, p < 0.05) and that the effect is different between sexes (p < 0.05). Previous results suggest that while PHA-induced swelling is mainly influenced by the body condition of pups, DRB gene polymorphism per se does not explain a significant amount of variation in inflammation.² Because our sample size is still modest, at this stage we cannot conclude unequivocally that DRB polymorphism influences PHA-induced skin swelling, but the observed trend warrants further investigation. Future work will examine potential association of specific DRB genotypes and synergistic gene effects related to PHA-induced swelling and other immune responses in California sea lion pups.

* Presenting author
+ Student presenter

Literature Cited

1.  Kennedy MW, Nager RG (2006) The perils and prospects of using phytohaemagglutinin in evolutionary ecology. Trends in Ecology and Evolution 21: 653–655.

2.  Bernatchez L, Landry C (2003) MHC studies in nonmodel vertebrates: what have we learned about natural selection in 15 years? Journal of Evolutionary Biology 16: 363–377.

3.  Kumanovics A, Takada T, Lindahl KF (2003) Genomic organization of the mammalian MHC. Annual Review of Immunology 21:629–657.

4.  Bonneaud C, Sinsheimer JS, Richard M, Chastel O, Sorci G (2009) MHC polymorphisms fail to explain the heritability of phytohaemagglutinin-induced skin swelling in a wild passerine. Biology Letters 5: 784–787.