Differences in chicken major histocompatibility complex (MHC) class Ialpha gene expression between Marek's disease-resistant and -susceptible MHC haplotypes.

The expression of chicken major histocompatibility complex (MHC) class Ialpha genes was investigated in spleen cells from a panel of chickens with well-defined MHC haplotypes, and two class Ialpha transcripts of 1.9 and 1.5 kb were detected in various amounts. In BW1, B130 and B21, the two transcripts were almost equally expressed. In B2, B6, B12 and B19, the ratio between the two transcripts was 4 : 1, with the 1.9 kb transcript having the strongest expression. In B14 and B15, the 1.5 kb transcript was undetectable and the 1.9 kb transcript appeared to be exclusively expressed. Thus, haplotypes considered to have an MHC-determined resistance to Marek's disease (MD) had the highest relative amount of the 1.5 kb transcript, whereas haplotypes considered to be MD-susceptible had the lowest. In order to address a possible correlation between MHC-Ialpha transcriptional patterns and MD resistance, a larger animal material experimentally infected with MD virus (MDV) was examined. The expression of MHC class Ialpha genes was investigated in spleens as well as in other organs, 9 weeks post-infection (p.i.), from animals of the two MD-resistant haplotypes B21 and BW1 as well as from the MD-susceptible haplotype B19. In the spleen cells of infected animals, the relative amount of the 1.5 kb transcript in the haplotypes BW1 and B21 was shown to be significantly higher than that in B19. Interestingly, in infected BW1 and B21 animals, the relative amount of the 1.5 kb transcript was also significantly higher than that in healthy MHC-matched controls. In B19, no differences were detected between uninfected and infected animals. Furthermore, it was shown in BW1 and B21 that the two classical MHC-Ialpha genes located in the MHC region were both able to produce both mRNA transcripts. Hybridization experiments, using specific probes upstream and downstream of the polyadenylation signals in the 3' end of the MHC-Ialpha genes, demonstrated that alternate use of these signals is probably involved in the production of the two mRNA transcripts.