Preferred SLA class I/class II haplotype combinations in German Landrace pigs.

Major histocompatibility complex (MHC) molecules are responsible for the antigen presentation to T lymphocytes. High recombination rates in the MHC genes, as observed in humans, are believed to serve the evolutionary goal to achieve a high genetic diversity, allowing for a broad and efficient immune response. In a cohort of 155 pedigreed German Landrace pigs (65 founders and 90 piglets), we found that MHC genes occur in particular class I and class II haplotype combinations. This phenomenon has not been described before, probably because most of the earlier MHC studies in pigs were not pedigree-based. After comparing our data with published genotypes of different European pig breeds and Asian pigs, we hypothesise that the combination of particular but different haplotypes in different geographical regions may have developed under the evolutionary pressure of regionally endemic pathogens. This proposed mechanism ensures an efficient immune response despite low recombination rates.