In vitro IFN-γ production from PBMCs in subjects and controls. PBMC secretion of IFN-γ after a 72-h incubation with PHA (a), HBcAg (b) and HBsAg (c) from 23 neonatal subjects born to HBsAg+ mothers (•) and 24 neonatal controls (○) at birth, 1 and 6 months of age. The data were compared by Mann–Whitney test: no significant differences were found between the two groups (P>0. 005). Each dot represents a single donor and horizontal bars represent the mean values. HBcAg, hepatitis B core antigen; HBsAg, hepatitis B surface antigen; IFN, interferon; PBMC, peripheral blood mononuclear cell; PHA, phytohemagglutinin.