USING THE GENOME TO UNDERSTAND IMMUNOGENETICS OF POULTRY
Location: Avian Disease and Oncology Laboratory
Title: Genetics and Vaccine Efficacy: Host Genetic Variation Affecting Marek's Disease Vaccine Efficacy in White Leghorn Chickens
Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 11, 2010
Publication Date: October 1, 2010
Citation: Chang, S., Dunn, J.R., Heidari, M., Lee, L.F., Song, J., Ernst, C.W., Ding, Z., Bacon, L.D., Zhang, H. 2010. Genetics and Vaccine Efficacy: Host Genetic Variation Affecting Marek's Disease Vaccine Efficacy in White Leghorn Chickens. Poultry Science. 89(10):2083-2091.
Interpretive Summary: The use of vaccines has been a very successful story in protecting human and animals from diseases induced by viruses. Use of vaccines against Marek’s disease (MD), an economically important virus induced cancer-like disease of chickens, has historically rescued and presently sustains the prosperity of the poultry industry. However, more virulent MD viruses, emerging from mutation or DNA recombination or both, evade vaccine efficacy and result in sporadic outbreaks of MD worldwide. Development of new MD vaccines often uses more virulent strains of MD viruses, which in turn escalates the evolvement of MD viruses toward more virulent strains. In order to study the role of genetics in response of chickens to MD vaccination, we used a series of specialized chicken lines developed and maintained at the USDA-ARS, Avian Disease and Oncology Laboratory, East Lansing, Michigan. Genetic differences among these lines are minor and constitute approximately 1/8 of total genes. The outcome of this study revealed that not all of the chicken lines were protected equally; some lines of chickens were protected much better compared to the other lines by a common MD vaccine, suggesting that host genetics plays an important role in how well a vaccine protects a particular genetic line of chickens. This finding should inspire considerations of host genetic differences in vaccine development and has significant implications in vaccine design, selection, and usage, a benefit to the poultry industry which may be applied to other livestock.
Marek’s disease (MD) is a T cell lymphoma disease of domestic chickens induced by Marek’s disease viruses (MDV), a naturally oncogenic and highly contagious cell-associated alpha-herpesvirus. Earlier reports have shown that the major histocompatibility complex (MHC) haplotype as well as non-MHC genes are responsible for genetic resistance to MD. The MHC was also shown to affect efficiency of vaccine response. Using specific pathogen-free chickens from a series of nineteen recombinant congenic strains (RCS) and their two progenitor lines (lines 63 and 72), vaccine challenge experiments were conducted to examine the effect of host genetic variation on vaccine efficacy. The 21 inbred lines of White Leghorns share the same B*2 MHC haplotype and the genome of each RCS differs by a random 1/8 sample of the susceptible donor line (72) genome. Chickens from each of the lines were divided into two groups. One was vaccinated with turkey herpesvirus (HVT) strain FC126 at the day of hatch and the other was treated as a non-vaccinated control. Chickens of both groups were inoculated with a very virulent plus strain of MDV on the 5th day post hatch. Analyses of the Marek’s disease data showed that the genetic line significantly influenced MD incidence and days of survival post MDV infection following vaccination of chickens (p < 0.01). The protective indices against MD varied greatly among the lines with a range of 0 up to 84 percent. This is the first evidence that non-MHC host genetic variation significantly affects Marek’s disease vaccine efficacy in chickens in a designed prospective study.