Detection of hepatitis B virus DNA in the liver of children with chronic hepatitis B by in situ hybridization and its relation to other viral markers

G1 phase dependent nuclear localization of relaxed-circular hepatitis B virus DNA and aphidicolin-induced accumulation of covalently closed circular DNA

During chronic hepatitis B virus (HBV) infection, virus persistence relies on the maintenance of a pool of covalently closed circular DNA (cccDNA) in the nuclei of infected hepatocytes. To achieve this, HBV DNA has to be transported from the cytoplasm to the nucleus. By carrying out subcellular fractionation experiment, both of the relaxed-circular (RC) and single-stranded (SS) HBV DNA were found in the cytoplasm whereas only RC form could be detected in the nucleus of a hepatoblastoma cell line (HepG2) stably producing HBV. This fraction of nuclear RC viral DNA was clearly demonstrated in the G1 but not S phase of synchronized HepG2 cells. Conversely, the relative amount of cytoplasmic RC viral DNA in the S phase was larger than that in the G1 phase. Although no cccDNA could be detected in HepG2 cells without synchronization, an increasing amount of cccDNA in the nucleus was demonstrated after prolonged incubation of the cells in aphidicolin. Finally, by undertaking in situ hybridization using a probe specific to plus-strand HBV DNA, nuclear viral DNA was detected predominantly in the G1 phase of HepG2 cells. In summary, the results indicated that only RC but not SS form of HBV DNA was localized to the nuclei of HepG2 cells. The nuclear localization occurred preferentially in the G1 but not S phase and prolonged treatment with aphidicolin resulted in accumulation of nuclear cccDNA.

Low level virus replication in infants with vertically transmitted fulminant hepatitis and their anti-HBe positive mothers

Perinatal transmission of hepatitis B virus (HBV) occurs in about 10%-20% of anti-HBe seropositive mothers. The babies are at risk of developing fulminant hepatitis. In most cases no viral DNA has been detected in the sera of mothers and children by conventional hybridisation techniques. Thus, the aim of our investigation was to demonstrate HBV DNA in three children with liver failure and their anti-HBe positive mothers by more sensitive molecular hybridisation techniques. The babies were healthy at birth and did not receive vaccination. At 3 months of age they developed acute liver failure and died from liver insufficiency. Only in one child serum HBV DNA was detected by dot blot hybridisation, but polymerase chain reaction (PCR)-detectable HBV DNA was present in all sera. The liver specimen was negative for HBV DNA by Southern blot hybridisation, but showed a focal distribution of viral sequences as determined by in situ hybridisation. This finding was confirmed by PCR. Our results prove that chronic anti-HBe positive HBsAg carrier mothers and their babies show a low level virus replication. Fulminant hepatitis is due to vertical transmission of very small amounts of viral DNA, only detectable by most sensitive techniques like PCR and in situ hybridisation. Our findings underline the necessity to vaccinate all babies of HBsAg positive mothers regardless of HBeAg/anti-HBe status.