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-homozygous Kenya Boran cattle (Bos indicus). DQB second exon fragments were amplified by reverse transcription-polymerase chain reaction of total mononuclear cell RNA, cloned and sequenced. While a single DQB sequence was obtained from some animals, two DQB exon 2 sequences were found in others, implying expression of duplicated DQB genes. Two pairs of duplicated DQB genes were found in this group of homozygotes, and sequence analysis showed that both pairs contained distinct DQB alleles. One DQB duplication was observed in two related animals with the same MHC haplotype (F100 and F188), while the second was detected in three animals (F187, G166 and G277) that expressed the same class II DRB3 and DQB alleles but had different class I (BoLA-A) types, suggesting that this DR/DQ haplotype may be widespread in Boran cattle.