October 03, 2010

USMLE 2 Question 2

A young man with anorexia, nausea, and brown urine is thought to have acute viral hepatitis following hepatitis B infection.

Screening serologic studies show that IgM anti-HBV core AB is positive.

Which of the following mechanisms is likely to explain the hepatic injury in this patient?

a) Direct injury by viral surface antigen
b) hepatocyte lysis by IgM antibody to viral core antigen
c) obstruction of the microcirculation of the liver by B lymphocytes
d) disruption of the hepatocyte membrane by the hepatitis B virus
e) T lymphocyte-mediated lysis of infected hepatic cells


The correct answer is E


The symptoms (anorexia, nausea, and brown urine) are typical of hepatitis. The body fights viral infections by CD8+ T cell-mediated lysis of infected cells that present viral antigens on their surface. The viral surface antigen does not directly injure hepatocyte membranes.

The role of the host immune response in determining clinical outcome following hepatitis B virus (HBV) infection is well recognized. In patients infected with hepatitis B, therapies, diseases, or conditions that impair specific lymphocyte responses lead to a high rate of chronic infection; in addition, the vigor of the host T-cell response to HBV-encoded antigenic peptides appears to correlate directly with the degree of acute hepatocellular injury and inversely with levels of HBV viremia. IgM directed against core antigen does not cause the hepatocytes to lyse

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