No abstract

F12 human immunodeficiency virus type 1 (HIV-1

The expression of human immunodeficiency virus Nef increases the viral infectivity through mechanisms still not fully elucidated. Here we report that wild-type (wt) human immunodeficiency virus, type 1 (HIV-1), particles were neutralized by higher concentrations of either anti-Env glycoprotein (gp) 41 antibodies or recombinant soluble human CD4 compared with ⌬nef HIV-1. This appeared to be the result of a Nef-induced increase of virion incorporation of both gp41 (transmembrane (TM)) and surface gp120 Env products likely originating from enhanced steady-state levels of cell membrane-associated Env products. This, in turn, seemed to be the consequence of a reduced retention of the Env precursor. Most interesting, we found that both the Nef-directed increase of Env membrane expression and the Nef-induced enhancement of HIV-1 infectivity relied on the presence of the intracytoplasmic domain of TM, supporting the hypothesis of a functional correlation between these effects. Mutagenesis studies allowed us to establish that the two leucine residues at the TM C terminus, which are part of a sorting motif involved in the control of Env membrane expression, and the 181-210-residue Nef C-terminal region were critically involved in the Nef/Env functional interaction. In conclusion, we propose that Nef increases the infectivity of HIV-1 at least in part by enhancing the amounts of Env products incorporated into virus particles.

No abstract

Two different strains of HIV-1, the lymphotropic HIV-IIIB and the monocytotropic HIV-Ba-L, were able to infect tertiary cultures of astrocytes established from the human embryonic brain. The infection did not require contact with infected cells, as astrocytes were exposed to infectious cell-free supernatants. Except for an early transient peak of p24 consistently observed after infection with HIV-Ba-L, the infection of astrocytes appeared to be nonproductive. However, viral production was always observed when infected astrocytes were cocultured with permissive cells (CEM-SS or monocytes). To exclude the possibility that undetectable levels of virus are chronically produced by astrocytes, we exposed permissive cells to p24 negative supernatants taken from infected cultures. In such conditions permissive cells were never infected. Infection of astrocytes by HIV-1 was further supported by the finding that provirus persisted in these cells. Indeed, by a nested PCR, we detected HIV-1 DNA even one month after infection. Moreover, at the transcriptional level we observed expression of the multiply spliced RNA (tat and nef primers). Noteworthy, this pattern of HIV-1 expression did not change appreciably when astrocytes were pretreated and cultivated in the presence of IL-1 beta. Altogether, our data support the concept that astrocytes may play a role in the spread of HIV-1 infection within the brain and in the pathogenesis of neuro-AIDS.