Epitopes exposed on hepatitis delta virus ribonucleoproteins.

A total of 17 antibodies, raised in several nonhuman species and specific for different regions on the delta antigen (delta Ag), were used to map, via immunoprecipitation, those domains exposed on the surface of the viral ribonucleoprotein (RNP). These studies showed that the domains for the nuclear localization signal and the C-terminal extension, unique to the large form of delta Ag, are exposed. Also exposed is the C-terminal region of the small form of delta Ag. In contrast, reactivity was not found with the coiled-coil domain needed for protein dimerization. When the hepatitis delta virus (HDV) RNA was released by treatment of viral RNP with vanadyl ribonucleoside complexes, no change in the pattern of delta Ag epitope presentation was detected, consistent with the interpretation that a multimeric protein structure persists in the absence of RNA. These RNP studies have implications not only for understanding of the process of HDV assembly but also for evaluation of the immune responses of an infected host to HDV replication.