Up-regulated expression of PD-1 and its ligands during acute Classical Swine Fever virus infection in swine

• The roles of the PD-1/PD-Ls pathway during CSFV infection in swine are poorly understood.
• The levels of PD-1 and its ligands mRNA were significantly increased in PBMCs during CSFV acute infection in swine.
• Elevation of PD-1 and its ligands probably correlated with host immunosuppression during acute CSFV infection.
• A novel mechanism of immunocompromised resulted by CSFV infection has been discovered.

In order to investigate the relationship between the PD-1 pathway and impairment of immune responses with the CSFV infection, the mRNA expression of PD-1 and its ligands were evaluated by quantitative polymerase chain reaction (qPCR) during artificial CSFV infection. Simultaneously, expression of IL-2 and IL-10 mRNA were detected. The T cell proliferation and CSFV load in plasma were also measured. Results showed that the expression of PD-1 and its ligands mRNA were significantly increased (p < 0.01) in PBMC from 3 to 7 days post infection (dpi). Meanwhile the level of IL-10 was up-regulated (p < 0.01). The IL-2 mRNA was not obviously changed but it is significantly increased from 14 dpi. The T cell proliferation was notably decreased at 7 dpi. The CSFV load was also increased in plasma. Overall, our results suggest that the expression of PD-1 and its ligands were up-regulated and probably correlated with immune inhibition during acute CSFV infection.