Detection and Characterization of Small and Large HDV Antigens

Hepatitis delta virus antigen (HDV Ag) was discovered by Rizzetto and associates in 1977 following the detection of a novel nuclear antigen in the hepatocytes of some hepatitis B virus carriers (1 ). HDV Ag is the nucleocapsid protein of a small RNA virus known as HDV. In infected liver tissue, HDV Ag is generally localized to the nucleo-plasm of the nucleus but has also been detected in the cytoplasm in patients with acute HDV infection (2 ). In cell cultures transfected with HDV cDNA, three different patterns of nuclear staining of HDV Ag have been reported: nucleolar, mixed nucleolar and nucleoplasmic, and exclusively nucleoplasmic (3 ). Although the reason for these differences is unknown, we have noted that the nucleolar pattern is more commonly seen when only the HDV Ag gene is expressed (4 ).