Circulating level of sPD-1 and PD-1 genetic variants are associated with hepatitis B infection and related liver disease progression.

Background: Programmed cell death-1 (PD-1) variants and circulating level of soluble PD-1 are associated with susceptibility to malignant and infectious disease. This study aimed to examine the association of PD-1.5 and PD-1.9 variants, and plasma sPD-1 level with hepatitis B virus (HBV) infection and disease progression.

Methods: The study cohort consisted of adults infected with HBV (n=513) - stratified by clinical course, including chronic hepatitis B (CHB, n=173), liver cirrhosis (LC, n=134) and hepatocellular carcinoma (HCC, n=206) - and matched healthy controls (HC, n=196). The PD-1.5 (rs2227981 C/T) and PD-1.9 (rs2227982 C/T) genetic variants were genotyped by Sanger sequencing, and plasma sPD-1 levels were quantified by enzyme immunoassay.

Results: Plasma sPD-1 levels were significantly higher among patients infected with HBV. The highest plasma sPD-1 levels were observed in patients with CHB, followed by patients with LC and HCC. In addition, the plasma sPD-1 levels correlated positively with liver inflammation [aspartate transaminase (AST): rho=0.57, P<0.0001; alanine aminotransferase: rho=0.57, P<0.0001], and were positively correlated with liver fibrosis [AST to platelet ratio index score: rho=0.53, P<0.0001). The PD-1.9 TT genotype was less common in patients with CHB compared with patients with LC, HCC, and HCC+LC in both codominant and recessive models (P<0.01), and was found to be a risk factor for HCC predisposition {HCC vs non-HCC: odds ratio (OR) 2.0 [95% confidence interval (CI) 1.13-3.7], P=0.017}. The PD-1.5 CT genotype was associated with reduced risk of acquiring HCC [OR 0.6 (95% CI 0.4-0.9), P=0.031].

Conclusion: sPD-1 level was associated with liver inflammation and progression of liver fibrosis, and the PD-1.5 and PD-1.9 variants were associated with HBV infection and progression of liver disease.