Modification and Immune Function of Porcine PD-1 and PD-L1 Interaction Epitope Peptides

Abstract Background The programmed death-1/programmed death-ligand-1 (PD-1/PD-L1) pathway transmits the negative immunoregulatory signals, leading to immunosuppression. Blocking the PD-1/PD-L1 pathway with peptides or antibodies can reverse the function of exhausted T cells, which can be a reference for developing studies on treating viral immunosuppressive diseases. Therefore, this work was developed to analyze the immune function of epitope peptides interacting with porcine PD-1 and PD-L1. Results After optimization, the proliferation percentages of PD-L14QN-GF and PD-L14QN-AF on PBMCS were 45.33%±6.16% and 56.20%±4.94%, respectively, which were increased by 14.7% and 25.8%. The inhibition rates of PD-L14QN-AF on PRRSV and PD-1 were 56.1.8% and 74.8%, which were increased by 35.0% and 29.4% compared with PD-L14, respectively. The inhibition rates of PD-L14QN-GF on PRRSV and PD-1 were 43.8% and 65.3%, which were 22.7% and 20.4% higher than those of PD-L14, respectively. The expression levels of IL-2 and IFN-γ in the PD-L14QN-GF group were 2.1 times and 2.8 times higher than those in the PD-L14 group and 1.2 times and 1.5 times higher than those in the PD-L14QN-AF group, respectively. The protein secretion levels of IL-2 and IFN-γ in the PD-L14QN-GF group were 2.5 times and 1.7 times higher than those in the PD-L14 group and 1.5 times and 1.2 times higher than those in the PD-L14QN-AF group, respectively. Furthermore, the PD-L14QN-GF and PD-L14QN-AF exhibited better immune effects than PD-L14. At 14 days after immunization, the antibody-positive rate in the PD-L14QN-GF group reached 80%, which was 30% and 50% higher than that in the PD-L14 group and normal group, respectively. The antibody titer in the PD-L14QN-GF group was 1.5 and 2 times higher than that in the PD-L14 and the normal groups, respectively. Conclusion PD-L14QN-GF was proved to be of high potential to develop immune-enhancing adjuvant.