Marek's disease resistant/susceptible MHC haplotypes in Xiayan chickens identified on the basis of BLB2 PCR-RFLP and BLB2/BF2 sequence analyses.

1. The aim was to analyse the variability of the BLB2/BF2 genes of Xiayan chickens to identify homozygous birds with resistance or susceptibility to Marek's disease (MD). 2. The experiment used two lines: birds from a common line were divided into Group A (unvaccinated) and Group B (vaccinated with herpesvirus of turkeys (HVT)); and birds from an MD-resistant line were divided into Group C (unvaccinated) and Group D (vaccinated with HVT). They were challenged intra-abdominally with Marek's disease virus (MDV) and genomic DNA extracted from peripheral blood lymphocytes so that polymorphism of the BLB2/BF2 genes could be analysed using polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) and nucleotide sequence analysis. 3. A 374-bp fragment of the BLB2 gene was amplified from the samples and, after digesting with restriction enzymes Alu I, Cai I, Cfr I, Hin1 I, Hinf I and Rsa I for RFLP analysis, the 6 electrophoretic patterns were analysed. Seven homozygous genotypes were found and used tentatively to identify alleles of the BLB2 gene. 4. A 765-bp fragment of the BF2 gene was amplified from the 7 samples for cloning and sequencing. 5. Six homozygous birds were confirmed from the sequenced BLB2/BF2 gene. Four birds were resistant to MD. Three birds had identical nucleotide sequences and were highly homologous with MHC haplotype B⁶, which is MD resistant. One bird had high homology with the highly MD-resistant B²¹ haplotype, and two birds were susceptible and highly homologous to the B¹⁹ haplotype, which is highly MD susceptible.