Abstract
Swine leukocyte antigen (SLA) class I molecules play a crucial role in generating specific cellular immune responses against viruses and other intracellular pathogens. They mainly bind and present antigens of intracellular origin to circulating MHC I-restricted cytotoxic T lymphocytes (CTLs). Binding of an appropriate epitope to an SLA class I molecule is the single most selective event in antigen presentation and the first step in the killing of infected cells by CD8+ CTLs. Moreover, the antigen epitopes are strictly restricted to specific SLA molecules. In this study, we constructed SLA class I complexes in vitro comprising viral epitope peptides, the extracellular region of the SLA-1 molecules, and β2-microglobulin (β2m) using splicing overlap extension polymerase chain reaction (SOE-PCR). The protein complexes were induced and expressed in an Escherichia coli prokaryotic expression system and subsequently purified and refolded. Specific binding of seven SLA-1 proteins to one classical swine fever virus (CSFV) and four porcine reproductive and respiratory syndrome virus (PRRSV) epitope peptides was detected by enzyme-linked immunosorbent assay (ELISA)-based method. The SLA-1∗13:01, SLA-1∗11:10, and SLA-1∗11:01:02 proteins were able to bind specifically to different CTL epitopes of CSFV and PRRSV and the MHC restrictions of the five epitopes were identified. The fixed combination of Asn151Val152 residues was identified as the potentially key amino acid residues influencing the binding of viral several CTL epitope peptides to SLA-1∗13:01 and SLA-1∗04:01:01 proteins. The more flexible pocket E in the SLA-1∗13:01 protein might have fewer steric limitations and therefore be able to accommodate more residues of viral CTL epitope peptides, and may thus play a critical biochemical role in determining the peptide-binding motif of SLA-1∗13:01. Characterization of the binding specificity of peptides to SLA class I molecules provides an important basis for epitope studies of infectious diseases in swine, and for the rational development of novel porcine vaccines, as well as for detailed studies of CTL responses in pigs used as animal models.
Highlights
The swine major histocompatibility complex (MHC), referred to as swine leukocyte antigen (SLA), has been associated with the porcine immune response to various infections and vaccinations (Lunney and Murrell, 1988; Lumsden et al, 1993; Lunney et al, 2009)
The sequencing results showed that the inserted genes were 1192 bp in length, and identical to the extracellular sequences of SLA1 and the mature peptide sequence of the β2m gene described above, with an insertion encoding a 15-amino acid glycine-rich linker
The current results showed that Swine leukocyte antigen (SLA)-1∗13:01, SLA-1∗11:10, and SLA-1∗11:01:02 proteins were able to bind to different cytotoxic T lymphocyte (CTL) epitopes of classical swine fever virus (CSFV) and porcine reproductive and respiratory syndrome virus (PRRSV)
Summary
The swine major histocompatibility complex (MHC), referred to as swine leukocyte antigen (SLA), has been associated with the porcine immune response to various infections and vaccinations (Lunney and Murrell, 1988; Lumsden et al, 1993; Lunney et al, 2009). SLA class I heavy chain, epitope peptide, and β2-microglobulin (β2m) have been shown to form a ternary complex, with the protein complexes being expressed constitutively on the surface of virtually all nucleated cells. These are crucially important for the normal growth of CD8+ cytotoxic T lymphocytes (CTLs), and play a pivotal role in the cell-mediated immune response against viral infections and cancer. CTLs kill the specific target cells directly, and induce host cell-mediated specific immune responses by simultaneously identifying the epitope peptides bound to SLA class I molecules and the SLA class I molecules (MHC restriction). The protein complexes interact with natural killer (NK)
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