Polymorphism and peptide-binding specificities of porcine major histocompatibility complex (MHC) class I molecules

The swine lymphocyte antigen class I (SLA I) is a highly polymorphic gene superfamily that plays an important role in swine anti-viral immune responses. However, an understanding of the highly variable sites and peptide-binding specificities of SLA I molecule is limited. In this study, a total of 27 SLA I alleles were identified from 3 Tibetan wild boars and 3 Heishan pigs. The phylogenetic relationship between the Tibetan wild boar and other breeds was analyzed using bioinformatics methods, and the highly variable sites were noted in the three dimensional structures of SLA I. Peptides from the porcine reproductive and respiratory syndrome virus (PRRSV) and influenza A virus (IAV) were screened with a bioinformatic method and refolding assay in vitro. The superior SLA I molecules, which have the ability to combine with more peptides, were selected from the Tibetan wild boars and Heishan pigs. The results showed that the SLA I of the Tibetan wild boars was not divergent from other pig breeds and that high-variation sites were mostly located in the peptide binding groove (PBG), suggesting that high variation sites could determines the peptide-binding characteristics and would possibly influences peptide-specific CD8⁺ T cell recognition. The SLA I allele SLA-1*0302 (known as KY113114) of the Tibetan wild boar formed stable complexes with three PRRSV peptides, and the SLA-3*hs0202 (KJ555032) from Heishan pigs was able to bind with four IAV peptides. The results from this study may benefit vaccine development and may help control IAV and PRRSV in swine.