Cytokine and Chemokine Responses in the Acute Phase of Hepatitis B Virus Replication in Naive and Previously Vaccinated Blood and Plasma Donors

Despite reduced transmission following implementation of an effective vaccine, hepatitis B virus (HBV) remains a significant global health problem. According to World Health Organization (WHO) statistics, 2 billion people have been infected with HBV, 350 million currently have chronic infections, and 4 million new clinical cases occur annually [1]. The kinetics of acute viremia, the subsequent detection of hepatitis B surface antigen (HBsAg) and then development of antibodies to core proteins (anti-HBc) and HBsAg (anti-HBs) during infection have been well described [2–5]. The initial immune recognition of HBV replication has a 10–12 week delay from the point of infectious exposure to detection of HBsAg in plasma and subsequent suppression of viral replication by adaptive immune responses [6]. During this time there are no clinically overt signs or symptoms, nor are there manifestations of viral or immune mediated hepatocyte damage, such as elevated transaminase levels in plasma. This prolonged “eclipse” period may be due to initial infection of a low number of hepatocytes, to early innate immunological control of viral spread, or to ineffective priming of an early immune response within the liver [7–9]. It is not until the accelerated ramp-up of viremia occurs weeks after infection that the adaptive immune response is triggered and detectable systemically, often associated with clinical acute hepatitis [10, 11]. The induction of an early immune response may be required for effective viral control and for preventing chronic infection. Recent studies have investigated this early period by using longitudinal panels of specimens from individuals with known dates of infection. This makes it possible to observe viral kinetics and circulating cytokine and cellular responses in an attempt to identify immunological profiles during subclinical infections [10, 11]. Shortly after the acute phase of infection, the virus is usually eradicated, but in a subset of patients HBV persists, leading to chronic infection and subsequent development of cirrhosis or hepatocellular carcinoma [12]. The viral and host mechanisms underlying differences between infections that resolve and those that become chronic are not well understood. Since the 1980s, a prophylactic HBV vaccine has been available that induces strong humoral responses against the surface antigen after a 3-dose regimen. The HBV vaccine has been very successful at preventing infection when a protective antibody titer of 10 mIU/mL or greater is achieved, with >90% decreases of infection rates in infants and children [13], and consequent declines in late-stage complications of HBV infection, including cirrhosis and hepatocellular carcinoma. Nevertheless, HBV infection still does occur in vaccinated individuals following high-risk exposures, as evidenced by anti-HBc seroconversion in long-term follow-up studies [14–18]. More recently, vaccine breakthrough infections have been documented in blood donors with histories of previous vaccination and low levels of vaccine-induced anti-HBs who are detected as HBV DNA positive by screening using sensitive nucleic acid amplification technology (NAT) tests in parallel with HBV serological screening [4, 14, 19]. We hypothesized that previous vaccination would lead to suppression of viral replication kinetics by earlier induction of the innate and adaptive immune responses compared to infections in unvaccinated individuals. To investigate this hypothesis, vaccinated, previously uninfected individuals were identified by the presence of anti-HBs and lack of anti-HBc in index donation samples that tested positive for HBV DNA. Levels of viral DNA, HBsAg, anti-HBs, and anti-HBc, and a panel of cytokines were measured to demonstrate the evolution of HBV DNA, serological and immunological markers during acute infection in vaccinated compared to unvaccinated individuals. Our study extends the current understanding of early immune responses to HBV in unvaccinated individuals while providing insight into which cytokines/chemokines are induced during a virological challenge in individuals who had already been vaccinated, thereby providing a model for an effective, albeit nonsterilizing, vaccine-induced immune response [20].