Hepatitis delta virus heterogeneity: a study by immunofluorescence.

Hepatitis delta virus (HDV)-RNA shows a microheterogeneity at nucleotide 1015 resulting in the production of two co-terminal forms of the HDV-associated antigen (HDAg), referred to as p24 and p27. In vitro experiments have shown that p24 is localized within the nucleolus, while p27 expression is probably confined to the nucleoplasm. The sequential appearance of these two proteins may play a role in the HDV-induced cell damage. We have examined 12 formalin-fixed human liver biopsies taken at different phases of the natural course of HDV infection. Specimens were assayed for HDAg by direct immunofluorescence with a human IgG reactive towards both p24 and p27. Positive cells were then examined for cytopathological features after hematoxylin/eosin staining. All biopsies contained intranuclear HDAg. However, three different patterns of fluorescence were seen: (1) nucleolar with weak nucleoplasmic; (2) homogeneous nucleoplasmic with negative nucleolus; (3) intense fluorescence diffuse to the whole nucleus. Pattern 1 was found in 15-50% of positive nuclei of all samples, irrespective of the phase of infection, while the remaining positive nuclei mostly showed another pattern (2) of fluorescence. Neither pattern was associated with cytoplasmic eosinophilia. Degenerated hepatocytes, when infected (5%), showed pattern 3 of HDAg fluorescence but were mostly negative for HDV. Therefore, the intranuclear distribution of HDAg, as assayed in vivo, does not seem to correlate with peculiar phases of HDV infection. Different phases of the viral life style, instead, are asynchronously represented within each liver sample.(ABSTRACT TRUNCATED AT 250 WORDS)