GBV-C Abs do not block HIV-1 entry following HIV-1 attachment to cells. Following attachment of HIV particles to MT-2 cells for 2 h at 4°C, rabbit anti–GBV-C E2 Ab or Fab fragments were added to cells for 1 h. Following washing, Abs were included in the media (maintain) or not (remove). Cells were warmed to 37°C, and HIV-1 p24 Ag release was measured 3 d later (A). HIV envelope pseudotyped defective HIV-1 particles were similarly analyzed in HOS cells. Following attachment at 4°C, pre- or postimmune rabbit GBV-C E2 IgG was added at the concentrations indicated (B). Cells were warmed to 37°C, and transduction (luciferase activity) was measured 72 h later and compared to the virus only control (B).