Abstract
Major histocompatibility complex (MHC) class I molecules play an essential role in the
defence against intracellular pathogens. CD8+ T cells recognise antigenic peptides in
association with self-MHC, a process known as MHC restriction. In this study we
examined bovine MHC class I genes using both molecular and cellular approaches.
There is evidence for the existence of five or six classical class I loci in cattle, with the
number of genes expressed varying between haplotypes. Most alleles are putatively
assigned to a locus according to their grouping following phylogenetic analysis. Here
we applied reference strand mediated conformational analysis (RSCA), a high resolution
typing method, to four of these groups: 1, 2, 3 and 6. Using group-specific primers and
two reference strands 22 potential new alleles were identified with one probable
pseudoallele in group 1. Based on the results obtained and previous phylogenetic
analysis, groups 1 and 3 appear to be the most polymorphic.
The need for a reliable typing method for MHC class I genes in cattle can be seen
through studies of CD8+ T cell responses to Theileria parva. T. parva is an intracellular
parasite against which CD8+ CTL have been shown to be the principal effector cells in
infected cattle. Previous studies identified a clear bias in class I restriction of CTL to
either the maternal or paternal haplotype, and showed that haplotypes differ in their
ability to restrict this response. We have extended these studies using animals with wellcharacterised haplotypes. We showed that the A14 and A18 haplotypes appear to be
dominant over the A10 and A31 haplotypes respectively. A14 expresses three class I
genes, D18.1, D18.4 and D18.5. Assays testing an A14-restricted CTL clone against
D18.1 and D18.4 transfected target cells proved inconclusive indicating a need for
further investigation and the inclusion of D 18.5 in any studies.
