Differential MHC class I mRNA expression in three chicken haplotypes infected with Marek's disease virus

The expression of classical Major Histocompatibility Complex (MHC) class I genes was tested in spleen cells from chickens differing in resistance to Marek's disease (MD). A comparison was made between mRNA profiles from two MD resistant MHC haplotypes (B-W1 and B-21) and one MD susceptible MHC haplotype (B-19). Two class I mRNA transcripts of 1.5 kb and 1.9 kb were detected in spleen cells from healthy animals, however, the distribution of the transcripts differs between the haplotypes. In the B-19 haplotype, the 1.9 kb transcript was dominantly expressed whereas only very low levels of the 1.5 kb transcript were detected. In B-21 and B-W1, equal levels of both transcripts were detected. Nine weeks after infection with the MDV-Md5 strain of Marek's disease virus, an increase of the 1.5 kb transcript was observed exclusively in MD resistant animals. Two B-F genes (B-FIV21 and B-FI21) have been identified in the chicken MFIC region, and here we show that both genes express both MHC class I mRNA transcripts. Furthermore, hybridization with specific oligonucleotides present before and after the first polyadenylation signal in the class I genes indicates that both class I genes express both mRNA transcripts as a result of alternate polyadenylation.