FIG. 2.
CD4 expression on astrocytes confers susceptibility to infection with HIV and SIV. (A) The activity of Ad-CD4 was tested by pretreating NP2/CCR5 cells with Ad-CD4 for 3 h, rinsing, and incubating overnight. Ad-CD4-pretreated and untreated NP2/CCR5 cells, as well as NP2 cells stably expressing CD4 and CCR5, were exposed to the R5-using HIV-1 strain SF162 for 3 h, and infected cells detected by p24 immunostaining were counted after 72 h. (B) Untransformed GFAP-positive adult astrocytes 001A and 004.2 were pretreated with Ad-CD4 before infection with the HIV-1, HIV-2, and SIV strains shown. After 72 h, cells were fixed and stained for intracellular viral antigens. (C and D) The titer of each HIV or SIV isolate was assessed on adult astrocytes 001A and 004.2 (C) and fetal astrocytes F01 (D). Cells were exposed to Ad-CD4 and infected as described above. All HIV and SIV isolates tested had titers of between 1 × 105 and 5 × 105 FFU/ml on NP2/CD4 coreceptor-expressing indicator cells (Table 1). Infected cells were detected by immunostaining for viral antigens and counted. All data are representative of those from at least three independent experiments.