This low selleck kinase inhibitor level of infection may be related to inefficient viral entry due to low-level surface expression of receptors for HIV. We were unable to detect expression of CD4, CCR5, or CXCR4 on the surfaces of multiple hepatic cell lines, although we clearly showed using flow cytometry that HIV used both CCR5 and CXCR4 to enter these cell lines. Previous studies using slot blot hybridization have shown that CD4 was not expressed on any of the hepatic cell lines tested (8). Other studies using more sensitive methods such as confocal microscopy and semiquantitative reverse transcriptase PCR have reported the presence of HIV coreceptors CXCR4 and CCR5 on hepatic cell lines where flow cytometry was negative (22). Increased apoptosis in Huh7 cells in the presence of soluble gp120 was blocked by pretreatment with AMD3100, consistent with expression of CXCR4 on Huh7 cells (1).

Taking these results together with our findings that HIV infection of AD38 cells could be blocked with either the CXCR4 antagonist AMD3100 or the CCR5 antagonist maraviroc, it is likely that hepatic cell lines express both HIV coreceptors but at levels below or at the limit of detection using flow cytometry. These in vitro data, together with previous in vivo studies demonstrating HIV in liver tissue, imply that HIV and HBV could replicate together in hepatocytes. Potential limitations of this study include the use of hepatic cell lines which are widely used as a convenient alternative to primary hepatocytes for in vitro studies. It is highly likely that after multiple passages, expression of both surface receptors and other cellular genes is altered.

We favored AD38 cells over HepG2.2.15 cells because HepG2.2.15 cells contain a retroviral LTR promoter instead of a cytomegalovirus promoter and therefore would not be an appropriate model for understanding intracellular interactions between HIV and HBV. Both AD38 and HepG2.2.15 cells mirror the HBV life cycle more closely than Hep3B cells, which do not produce infectious virions. Inclusion of EGFP in the VSV-NLNE was helpful in identifying efficiency of infection, although it is possible that the EGFP itself may have interfered with HBV replication. However, to our knowledge there have been no reports of the effect of EGFP on HBV replication, although there have been reports of cell toxicity related to EGFP in some circumstances (20).

In addition, pseudotyped HIV may not represent what happens in vivo, given the likely low level of HIV infection of hepatocytes. However, VSV-pseudotyped viruses have been used previously to understand the pathological effects in other cell types subject to low-level HIV infection, such as astrocytes (13). In Brefeldin_A summary, we demonstrated that HIV clearly infects hepatic cell lines but at low levels and that infection is noncytopathic and short lived.