Soluble programmed death-1 is a useful indicator for inflammatory and fibrosis severity in chronic hepatitis B

Elevated programmed death-1 (PD-1) has been found in immune cells in viral infections and plays an important role in infection persistence. The soluble form of PD-1 (sPD-1) is involved in tumours and viral infections. The aim of this study was to investigate the role of sPD-1 in chronic hepatitis B (CHB). A total of two hundred and eighteen CHB patients and sixty healthy controls (HC) were enrolled. Demographic data and clinical parameters were collected. An ELISA assay was used to measure serum sPD-1 levels, and the relationships between sPD-1 and clinical/virological characteristics was analysed. sPD-1 levels in CHB patients were higher (median 4.409 IQR 3.435-5.306 pg/mL) than those of HC individuals (median 0.3665 IQR 0.2425-0.5010 pg/mL). Among patients at various disease stages, patients with immune activity showed the highest sPD-1 levels (median 5.138 IQR 4.329-5.406 pg/mL). sPD-1 concentration was associated with HBV markers (HBsAg, HBV DNA and HBeAg) and biochemical parameters (serum aspartate aminotransferase [AST], alanine aminotransferase [ALT], total bilirubin [TBil] and gamma glutamyl transferase [γ-GT] levels) (all P < 0.05). sPD-1 levels were higher in CHB patients with moderate-to-severe inflammation or fibrosis than in those with mild inflammation or fibrosis, regardless of ALT levels. The association between sPD-1 and disease progression of CHB suggests that sPD-1 could serve as a new indicator in assessing liver fibrosis. These findings may further aid in determining the initiation of antiviral treatment in patients with normal ALT levels.