HIV-1 provirus expression in resting and activated conditions. (A) Histograms show average of HIV-1 transcripts per cell in resting (blue) and activated (red) conditions for the indicated clones and CD4⁺ T cells infected with HIV-1_YU2 for comparison (black). Copies of LTR, gag, and env transcripts were determined based on a standard curve. Average copy number per cell was calculated by dividing the estimated number of transcripts by the number of HIV-1⁺ cells in the assay (corrected based on culture enrichment). (B) Graphic representation of the limiting dilution assay. (C) Frequency of cells expressing HIV-1 LTR, gag, and env transcripts in resting (blue) and activated (red) conditions. The number of expressing cells was estimated by Poisson distribution, based on limiting dilution data, calculated using the MPN method. (D) Average number of transcripts per expressing cell in resting (blue) and activated (red) conditions, estimated based on the frequency of cells expressing HIV-1 transcripts as shown in C. Average transcripts per cell of an active infection by HIV-1_YU2 are shown for comparison (black). All experiments were performed in triplicates. Frequency of cells expressing and copies of transcripts could not be calculated for 603 due to the low number of transcripts.