Inhibition of HIV-1 infection of PBLs by Vif-derived peptides. HIV-1-infected PBLs were cultured with various additions and at the indicated times after infection, cell supernatants were harvested for measurement of viral core antigen p24 levels. (a) Culture with no additions to growth medium, 100 μg/ml Vif21–65 or Vif41–65, or 1 μM Ro 31–8959. (b) Cultured with no additions to growth medium, different concentrations of Vif41–65 or β endorphin peptide, or 1 μM Ro 31–8959. (c) p24 levels on day 7 after infection as shown in b presented relative to the p24 level in cells cultured with no additions to growth medium.