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Temporal patterns of human immunodeficiency virus type 1 transcripts in human fetal astrocytes

Human immunodeficiency virus type 1 (HIV-1) infection of the developing central nervous system results in a dementing process in children, termed HIV-1-associated encephalopathy. Infection of astroglial elements of the pediatric nervous system has been demonstrated and suggests that direct infection of some astrocytes may contribute to the neurologic deficit. In this model, HIV-1 establishes a persistent state of infection in astrocytes, which can be reactivated by the cytokines tumor necrosis factor alpha (TNF-alpha) and interleukin 1 beta (IL-1 beta). To better understand the natural history of viral persistence in astroglial cells, we characterized infection at the transcriptional level. The most abundant viral transcript during the establishment of persistence was the subgenomic multiply spliced 2-kb message, similar to mononuclear cell models of HIV-1 latency. Following reactivation with TNF-alpha or IL-1 beta the multiply spliced 2-kb message remained the most abundant viral transcript, in contrast to infected mononuclear cells in which reactivation leads to the reemergence of the 9- and 4-kb transcripts. Further characterization of the persistent 2-kb transcript by PCR amplification of in vitro-synthesized viral cDNA showed that, in the absence of cytokine stimulation, the most abundant multiply spliced transcripts were the Nef- and Rev-specific messages. However, following cytokine stimulation, double- and triple-spliced Tat-, Rev-, and Nef-specific messages could be identified. Immunohistochemical staining demonstrated that, during viral persistence, astrocytes expressed Nef protein but few or no viral structural proteins. These results demonstrate that viral persistence in astrocytes at the transcriptional level is fundamentally different from that seen in mononuclear cells and could account for the virtual absence of astroglial expression of viral structural antigens in vivo.