High frequency of circulating HBcAg‐specific CD8 T cells in hepatitis B infection: a flow cytometric analysis
Viral antigen‐specific T cells are important for virus elimination. We studied the hepatitis B virus (HBV)‐specific T cell response using flow cytometry. Three phases of HBV infection were studied: Group A, HBeAg (+) chronic hepatitis; Group B, HBeAb (+) HBV carrier after seroconversion; and Group C, HBsAb (+) phase. Peripheral T cells were incubated with recombinant HB core antigen (HBcAg), and intracytoplasmic cytokines were analysed by flow cytometry. HBcAg‐specific CD4 and CD8 T cells were identified in all three groups and the number of IFN‐γ‐positive T cells was greater than TNF‐α‐positive T cells. The frequency of IFN‐γ‐positive CD4 and CD8 T cells was highest in Group C, compared with Groups A and B. No significant difference in the HBcAg‐specific T cell response was observed between Group A and Group B. The HBcAg‐specific CD8 T cell response was diminished by CD4 depletion, addition of antibody against human leucocyte antigen (HLA) class I, class II or CD40L. Cytokine‐positive CD8 T cells without HBcAg stimulation were present at a high frequency (7 of 13 cases) in Group B, but were rare in other groups. HBcAg‐specific T cells can be detected at high frequency by a sensitive flow cytometric analysis, and these cells are important for controlling HBV replication.