EXPRESSION OF MULTIPLE DQB GENES IN BOS-INDICUS CATTLE

Polymorphism of expressed bovine major histocompatibility complex (MHC ) class II DQB genes was investigated in a group of nine MHC-homozygou s Kenya Boran cattle (Bos indicus). DQB second exon fragments were amp lified by reverse transcription-polymerase chain reaction of total mon onuclear cell RNA, cloned and sequenced. While a single DQB sequence w as obtained from some animals, two DQB exon 2 sequences were found in others, implying expression of duplicated DQB genes. Two pairs of dupl icated DQB genes were found in this group of homozygotes, and sequence analysis showed that both pairs contained distinct DQB alleles. One D QB duplication was observed in two related animals with the same MHC h aplotype (F100 and F188), while the second was detected in three anima ls (F187, G166 and G277) that expressed the same class II DRB3 and DQB alleles but had different class I (BoLA-A) types, suggesting that thi s DR/DQ haplotype may be widespread in Boran cattle.