Surface antigen is the earliest serologic marker of hepatitis B virus infection, appearing 1-12 weeks after infection and persisting for 5-20 weeks in acutely infected individuals. Several weeks after the disappearance of surface antigen, protective surface antibodies appear in the blood. E antigen appears slightly later than surface antigen and indicates active viral replication and strong infectiousness; E antibodies appear after E antigen has turned negative, mostly indicating reduced hepatitis B virus replication and infectiousness. Core antigen exists in the core of hepatitis B virus particles and in the nucleus of infected hepatocytes. Core antibody IgM appears 2-4 weeks after surface antigen positivity, which is a sign of acute hepatitis B virus infection and chronic infection activity.