Figure 1.

A, Distribution of radiolabeled choles terol found in various cholesterol acceptor serum fractions, RAW264.7 macrophages were incubated in the absence (basal) or presence (ATP-binding cassette transporter A1 [ABCA1] stimulated) of 8-Br-cAMP as indicated with media containing apoB-depleted serum (1.4% vol/vol) in cholesterol efflux assays, as described in Methods in the online-only Data Supplement. Radiolabeled cholesterol in the indicated lipoprotein and lipoprotein-depleted fractions (densities are indicated) after stepwise buoyant density ultracentrifugation was quantified as described in Methods in the online-only Data Supplement. The distribution of radiolabeled-cho-lesterol in lipoprotein-depleted media as assessed after immunoprecipitation (IP) of apolipoprotein A1 (apoA1) and albumin using anti-apoA1 mouse monoclonal antibodies and antialbumin antibodies as described in Methods in the online-only Data Supplement. Results represent mean±SD for 4 separate experiments. B, (Left) Dose–response curves of various sources of albumin (bovine and human albumin from Sigma; fast performance liquid chro-matography (FPLC) -isolated human serum albumin [HSA] and FPLC-isolated and delipidated HSA) on total cholesterol efflux in [³H]-cholesterol-loaded RAW cells, and (right) isolated human apoA1. HDL indicates high-density lipoprotein; LDL, low-density lipoprotein; and VLDL, very low–density lipoprotein.