Apolipoprotein AIV of human interstitial fluid is associated with apolipoprotein AI-containing but not with AII-containing particles

Apolipoproteins and lipoprotein particles from human interstitial fluid and plasma were analyzed. The interstitial fluid was enriched in apolipoproteins AI, AII, and AIV compared with apo B, apo CIII, and apo E. LpAI was found to contain apo AIV which was absent from LpAI : AII. Moreover, the bulk of lecithin-cholesterol acyltransferase was present in LpAI. The concentration range of these particles was in agreement with those required in vitro for cholesterol efflux. Thus the interstitial fluid contains particles in which two agonists but no antagonists of cholesterol efflux are associated with lecithin-cholesterol acyltransferase activity. This supports apolipoprotein AI- and/or AIV-containing particles playing a critical role in the first step of reverse cholesterol transport.