Fig. 5. Incubation with U18666A causes intracellular accumulation of cholesterol. A431 cells (A,B) and HEp-2 cells (C,D) were incubated with or without 1 µg/ml U18666A for 48 hours prior to fixation. Cholesterol was labeled using filipin, as described in Materials and Methods. In untreated cells (A,C) filipin labeled mainly the plasma membrane. Upon treatment with U18666A (B,D) filipin labeling revealed accumulation of cholesterol in intracellular vesicles.