A 24-year-old hospital phlebotomist comes to the occupational health clinic after sustaining a needlestick injury while drawing blood from a hepatitis B-positive patient. She has no medical history and received the complete hepatitis B vaccination series prior to her hospital employment a year ago. She is closely monitored over the next 6 months with repeat hepatitis B serologies and does not develop clinical or laboratory evidence of infection. Which of the following mechanisms most likely explains her immunity?

Question

A 24-year-old hospital phlebotomist comes to the occupational health clinic after sustaining a needlestick injury while drawing blood from a hepatitis B-positive patient.  She has no medical history and received the complete hepatitis B vaccination series prior to her hospital employment a year ago.  She is closely monitored over the next 6 months with repeat hepatitis B serologies and does not develop clinical or laboratory evidence of infection.  Which of the following mechanisms most likely explains her immunity?

Quizplus · Accepted Answer

Serologic evidence of hepatitis B virus (HBV) exposure is present in approximately 2 billion people worldwide. Nearly 250 million of these individuals have chronic infection and can transmit the virus to others. Perinatal transmission is most common in high prevalence countries (eg, sub-Saharan Africa); unprotected sex or intravenous drug use causes most infections in low-incidence countries (eg, United States). Health care providers are at high risk for infection due to potential exposure to the blood of infected patients. HBV vaccination is recommended for all health care providers and other high-risk individuals (eg, intravenous drug users). The vaccine utilizes recombinant HBsAg to generate protective immunity against the virus. HBsAg is a collection of envelope glycoproteins found on the surface of HBV; these glycoproteins mediate attachment of the virus to hepatocytes and subsequent viral entry. Patients who adequately respond to the HBV vaccine generate anti-HBs antibodies, which bind to circulating viral particles and prevent attachment to and penetration of hepatocytes. Patients who have been immunized against HBV as well as those who have cleared the virus after acute infection will have anti-HBs antibodies. These 2 populations are distinguished by the presence of anti-HBc antibodies, which are seen only in those who have been exposed to the virus (not in immunized patients). (Choice A) The immunity conferred by the hepatitis B vaccination is mediated by protective antibodies against HBsAg; the protective effects are not due to activation of cytotoxic T cells. However, in patients exposed to HBV, the resolution of acute infection is mediated primarily by a vigorous, polyclonal cytotoxic T-cell response that destroys infected hepatocytes. (Choice B) HIV treatment often includes nucleotide and non-nucleoside reverse transcriptase inhibitors, which disrupt viral genome replication. Hepatitis C virus is often treated with similar medications (eg, sofosbuvir) that target viral RNA-dependent RNA polymerase. Immunization against HBV does not interfere with replication of the HBV genome. (Choice C) HBV is considered a stealth virus because it possesses virulence factors that block portions of the innate immune system, including the release of interferon-gamma from infected cells. However, HBV immunization does not significantly affect the innate immune system. (Choice E) NS5A inhibitors (eg, ledipasvir) are thought to block hepatitis C virus replication and assembly. HBV immunization generates protective antibodies against the HBsAg; it does not affect viral assembly. Educational objective: Immunization against hepatitis B virus uses recombinant HBsAg to generate anti-HBs antibodies. These antibodies prevent infection by binding to the envelope of circulating virus and inhibiting viral entry. __________ References: Novel mechanism of antibodies to hepatitis B virus in blocking viral particle release from cells. (http://www.ncbi.nlm.nih.gov/pubmed/20593455) Hepatitis B: the virus and disease. (http://www.ncbi.nlm.nih.gov/pubmed/19399811) Pathogenesis of hepatitis B virus infection. (http://www.ncbi.nlm.nih.gov/pubmed/20116937)

A 24-Year-Old Hospital Phlebotomist Comes to the Occupational Health Clinic