Cloning and identification of porcine programmed death 1

Programmed death 1 (PD-1) is a member of the immunoglobulin (Ig) superfamily, which is expressed on activated T cells, B cells and monocytes. Many researches have demonstrated that a high level of PD-1 expression is closely related to persistent infection and immune evasion in some human infections. In order to study the relationship between PD-1 expression and persistent infections caused by some porcine viruses, we first cloned the porcine PD-1 from porcine PBMCs based on the blast result in the EST database using the human PD-1 sequence. Sequence analysis showed that the cloned PD-1 molecule shares 63 and 54% amino acid sequence identity with human and murine PD-1, respectively. Its molecular structure is also similar to that of human and murine PD-1, containing an IgV-like domain in the extracellular region and two immune regulatory motifs in its cytoplasmic tail. The in vitro T cell proliferation assay showed that the cloned PD-1 could inhibit porcine T cell proliferation by 71% and secretion of IFN-γ and IL-2 by 64 and 53%, respectively. These data suggest that porcine PD-1 negatively regulates the porcine immune response in a similar manner to that of its counterpart in the human and mouse immune system.