After hepatitis B virus (HBV) infection, liver injury and viral control hav
e been thought to result from lysis of infected hepatocytes by virus-specif
ic cytotoxic T cells. Patients are usually studied only after developing si
gnificant liver injury, and so the viral and immune events during the incub
ation phase of disease have not been defined. During a single-source outbre
ak of HBV infection, we identified patients before the onset of symptomatic
hepatitis. The dynamics of HBV replication, liver injury, and HBV-specific
CD8+ and CD4+ cell responses were investigated from incubation to recovery
. Although a rise in alanine transaminase (ALT) levels was present at the t
ime of the initial fall in HBV-DNA levels, maximal reduction in virus level
occurred before significant liver injury, Direct ex vivo quantification of
HBV-specific CD4+ and CD8+ cells, by using human leukocyte antigen (HLA) c
lass I tetramers and intracellular cytokine staining, showed that adaptive
immune mechanisms are present during the incubation phase, at least 4 weeks
before symptoms. The results suggest that the pattern of reduction in HBV
replication is not directly proportional to tissue injury during acute hepa
titis B in humans. Furthermore, because virus-specific immune responses and
significant reductions in viral replication are seen during the incubation
phase, it is likely that the immune events central to viral control occur
before synptomatic disease.