Activated primary rat T-cells exhibit a profound block to HIV-1 replication at the level of early HIV-1 gene expression. (A) Representative FACS dot plots of T-cells from a human donor, a hCD4/hCCR5-transgenic rat, and a BALB/c mouse infected with the indicated HIV-1 GFP reporter viruses (50 ng p24 CA per 2–3 × 106 cells) and analyzed for GFP expression on day 6 after infection. Viable cells were identified by gating on the live lymphocyte population (gate R1) in the FSC/SSC plot (left vertical panels). Gate R2 defines the GFP-positive subpopulation of gate R1. Shown are results obtained from cells infected in the absence (middle vertical panels) and presence of efavirenz (EFV) (right vertical panels). (B) Percentage of GFP-positive cells obtained for T-cell cultures from four human donors, four hCD4/hCCR5-transgenic rats, and two BALB/c mice which had been infected as described in A (p = 0.77; n.s.) (C) MFI(GFP) of infected human and rat T-cell cultures shown in B (p = 0.02; * = significant).