Infection with hepatitis B virus (HBV) can be prevented by vaccination with HB surface (HBs) antigen, which induces HBs-specific antibodies and T cells. However, the duration of vaccine-induced protective immunity is poorly defined for health care workers who were vaccinated as adults.
Dr Barbara Rehermann and colleagues from Maryland, USA investigated the immune mechanisms of long-term protection by the HBV vaccine in 90 health care workers with or without occupational exposure to HBV, 10−28 years after vaccination.
The researchers found that 65% of health care workers had levels of antibodies to HBs antigen above the cut-off, and 33% had HBs-specific T cells that produced interferon-gamma.
Titers of antibodies to HBs antigen correlated with numbers of HBs-specific interferon-gamma−producing T cells, but not with time after vaccination.
|65% of health care workers had levels of antibodies to HBs antigen above the cut-off|
Although occupational exposure to HBV after vaccination did not induce antibodies to the HBV core protein (HBcore), the standard biomarker for HBV infection, CD4+ and CD8+ T cells against HBcore and polymerase antigens were detected.
The research team noted that similar numbers of HBcore- and polymerase-specific CD4+ and CD8+ T cells were detected in health care workers with occupational exposure to HBV and in patients who acquired immunity via HBV infection.
Most of the HBcore- and polymerase-specific T cells were CD45RO+CCR7−CD127− effector memory cells in exposed health care workers, and in patients with acquired immunity.
In contrast, the team noted that most of the vaccine-induced HBs-specific T cells were CD45RO−CCR7−CD127− terminally differentiated cells.
Dr Rehermann's team commented, "HBs antigen vaccine-induced immunity protects against future infection but does not provide sterilizing immunity, as evidenced by HBcore- and polymerase-specific CD8+ T cells in vaccinated health care workers with occupational exposure to HBV."
"The presence of HBcore- and HBV polymerase-specific T-cell responses is a more sensitive indicator of HBV exposure than detection of HBcore-specific antibodies."