Amplification of HIV-1 from viral-exposed human and murine stromal layers. Primary human stromal layers (○) or layers of the murine S17 stromal cell line (X's) were infected with HIV-1_JR-FL at MOI = 1.0. On day 8 after infection, human monocytic cells were added to each culture to amplify low levels of HIV-1 present. Samples of the culture supernatants were then sampled daily and analyzed for p24 gag protein by ELISA.