Abstract
Vertically transmitted hepatitis B virus (HBV) usually causes chronic infection. While combined active-passive immunoprophylaxis in neonates of hepatitis B surface antigen-positive (HBsAg(+)) mothers at birth prevents vertical transmission, it is not yet clear whether neonates encounter the virus or its products in the absence of hepatitis B e antigen (HBeAg). This study was undertaken to investigate HBV antigen-specific T-cell responses in vaccinated neonates of HBsAg(+)/HBeAg(-) mothers. Blood was collected from 46 HBsAg(+) mothers and their neonates (subjects) as well as 24 age-matched controls. All neonates of HBsAg(+) mothers received appropriate immunoprophylaxis, and HBsAg and hepatitis B surface antibody (anti-HBs) antibody titers were determined after completion of the vaccination course. Peripheral blood mononuclear cells (PBMCs) from infants at birth, 1 and 6 months of age were stimulated with recombinant HBsAg, hepatitis B core antigen (HBcAg) and mitogen, and interferon (IFN)-γ concentrations were determined by ELISA. HBsAg-induced production of IL-2, IL-5, IL-6 and IL-10 was assessed using a cytometric bead array kit on cells from 6-month-old neonates post-vaccination. All neonates were HBsAg(-) and responded to vaccination. Increased IFN-γ production following HBcAg stimulation was seen in 30.4% of neonates born to HBsAg(+)/HBeAg(-) mothers. Subjects demonstrated significantly higher IL-2 production post-HBsAg stimulation, whereas IL-5, IL-6 and IL-10 cytokine responses were not significantly different. Almost one-third of uninfected neonates developed viral antigen-induced IFN-γ production, suggesting that they had been exposed to virions or viral derivatives. This encounter, however, did not impair their T-cell responses to vaccination.