Natural Killer cells contribute to hepatic injury and help in viral persistence during progression of HBeAg-negative chronic HBV infection.

Abstract Hepatitis B e-antigen negative [e(-)] chronic HBV infection (CHI) encompasses a heterogeneous clinical spectrum ranging from inactive carrier (IC) state to e(-) chronic hepatitis B (CHB), cirrhosis and hepatic decompensation. In the backdrop of dysfunctional virus-specific T-cells, natural killer (NK) cells are emerging as innate effectors in CHI. We characterized CD3(-)CD56(+)NK cells in clinically well-defined, treatment-naive e(-) patients in IC, (e-)CHB or decompensated liver cirrhosis (LC) phase to appraise their role in disease progression. NK cell frequencies increased progressively with disease severity [IC (8.2%), e(-)CHB (13.2%) and LC (14.4%)]. Higher proportion of NK cells from LC/e(-)CHB expressed CD69, NKp46, NKp44, TRAIL and perforin, last two being prominent features of CD56(bright) and CD56(dim)NK subsets respectively. The frequencies of CD3(-)CD56(+)NK cells together with TRAIL(+)CD56(bright) and Perforin(+)CD56(dim)NK cells correlated positively with serum ALT levels in e(-)CHB/LC. K562 cell-stimulated NK cells from e(-)CHB/LC exhibited significantly greater degranulation but diminished IFN-γ production than IC. Further, Perforin(+)NK cell frequency inversely correlated with autologous CD4(+)T-cell count in e(-) patients and ligands of NK-receptors were over-expressed in CD4(+)T-cells from e(-)CHB/LC relative to IC. Co-culture of sorted CD56(dim)NK cells and CD4(+)T-cells from e(-)CHB showed enhanced CD4(+)T-cell apoptosis, which was reduced by perforin inhibitor, concanamycin A, suggesting a possible perforin-dependant NK cell-mediated CD4(+)T-cell depletion. Moreover, greater incidence of perforin-expressing NK cells and decline in CD4(+)T-cells were noticed intrahepatically in e(-)CHB than IC. Collectively, NK cells by enhanced TRAIL and perforin-dependent cytolytic activity and by restraining anti-viral immunity through reduced IFN-γ secretion and perforin-mediated CD4(+)T-cell lysis contribute to progression of e(-)CHI.