Sequence variations of the MHC class I gene exon 2 and exon 3 between infected and uninfected chickens challenged with Marek's disease virus

- Morbidity of broilers after MDV injection concentrated during 21 and 35 dpc.
- Particular variable sites were found between infected and uninfected chickens.
- Balance selection was found in Mhc class I exon 3.
- No specific pathogen-driven selection were observed in exon 2 and exon 3.
- Exon 3 plays a more crucial role than exon 2 in MDV induced infection.

The major histocompatibility complex (MHC) among chickens has been well established as being associated with disease resistance and pathogens infection, but the genetic differences in MHC between chickens susceptible to certain infections and those chickens that remain uninfected have not been sufficiently determined. In this study, we sought the genetic basis that may underlie differences in susceptibility to infection among chickens by challenging four groups of broilers with Marek's disease virus (MDV). Over the course of the experiment, lesions began to appear between 21 and 35 days post challenge (dpc), and commercial broilers were not necessarily better than indigenous chickens in terms of disease resistance. The four groups showed neutral resistance to MDV infection validated by challenge results and evolutionary analysis of exons 2 and 3 of the MHC class I region. Several variable sites in exon 2 and exon 3 were exclusively appeared in infected chickens. Exon 3 was likely more crucial than exon 2 in disease resistance. Our observations offered a support for a potential association between promiscuous pathogens and conspicuous genetic diversity in the MHC class I region.