Fig. 2. Cholesterol efflux from J774-A1 macrophages in the presence of native and tyrosylated HDL₃ (A) or total HDL (B). J774-A1 cells were [³H]cholesterol-loaded with [³H]cholesteryl oleate-labeled AcLDL (50 µg apo B/ml, 7.6x10⁵ DPM/ml) as described in Materials and Methods. After an 18 hour equilibration period, the cells were incubated for 24 hours at 37°C with the indicated final concentrations of native (•) or tyrosylated () HDL₃ (A) or total HDL (B). After extensive washing with PBS, cellular and medium lipids were extracted, separated by TLC and counted to determine the [³H]cholesteryl ester and the [³H]free cholesterol fractions. Cholesterol efflux was calculated as the amount of [³H]cholesterol (free and esterified) released to the medium relative to total label in each well. Each value is the mean±s.e.m. of three determinations. ^*P<0.03, ^**P<0.02, ^***P<0.01.