Human immunodeficiency virus type 1 (HIV-1) replication is restricted partially in SK-N-MC and completely in SK-N-SH neuronal cells. To investigate the molecular mechanism of this differential restriction of HIV-1 replication, cells infected with HIV-1 were analysed for their steady-state levels of: total and unintegrated HIV-1 DNA by DNA PCR, different species of HIV-1 RNA by RT-PCR, and HIV-1 p24 protein production by an ELISA procedure. We found that the kinetics of the infection were slower and there was a lower level of accumulation of HIV-1 macromolecules (total and unintegrated circular DNA, unspliced and spliced RNAs and viral proteins) in the SK-N-MC cells than in the permissive CEM cells. In SK-N-SH cells, HIV-1 DNA was only transiently detected during the first 24 h post-infection, and the unspliced RNA was detected up to 1 week post-infection. However, the HIV-1 spliced RNAs and the 2-LTR circular DNA were not detected at all during the course of infection. Both SK-N-MC and SK-N-SH cells showed higher levels of HIV-1 DNA, RNA and p24 protein when infected with an HIV-1 (amphotropic retrovirus) pseudotype, HIV-1B. However, the level of HIV-1 replication was still lower in SK-N-SH than in SK-N-MC cells. Moreover, although the kinetics of viral protein production were comparable in SK-N-MC cells infected with HIV-1B and CEM cells infected with HIV-1, the overall level of virus replication was still much lower in HIV-1B-infected SK-N-MC cells. These data suggest that the restriction of HIV-1 replication in neuronal cell lines takes place at both virus-entry and post-entry levels, and cellular factors may be involved in the differential restriction of HIV-1 replication in these cells.

*HIV-1/PHYSIOLOGY *Nervous System/VIROLOGY *Virus Replication

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