Figure 1.

X4 but not R5 HIV-1 infects and crosses Caco-2 or M cell monolayers. PCR analysis, with gag-specific primers, of DNA extracted from Caco-2 or M cell monolayers at day 9 and from CD4⁺ T cells (X4 targets) or monocytes (R5 targets) in the lower chamber of the Transwell devices. Target cells have been further cultivated for 7 days after exposure of the monolayers to HIV-1. An HIV-1 gag amplicon (115 bp) was detected in epithelial cells, whether or not converted, and in target CD4⁺ T cells as soon as 30 min after apical addition of X4 HIV-1 (a and b). No transcripts were detected in the Caco-2 or M cells and the target monocytes when exposed to R5 HIV-1 strains (c and d). The X4 HIV-1 amplicon observed in Caco-2 cells was not the result of de novo reverse transcription, because the virus was detected in the presence of 1 μg/ml zidovudine (e). A similar TCID₅₀ for X4 and R5 HIV-1 was applied. CD4⁺ T cells infected with X4 or R5 HIV-1 and monocytes infected with R5 HIV-1 served as positive control. The first two lanes in the right panel and the four lanes in the left panel are controls. One representative result of four independent experiments is shown.