Apolipoprotein localization and quantitation in the human intestine

Apolipoproteins B, A-I, and A-IV were localized in human intestinal epithelium using immunoperoxidase techniques. Staining was most obvious in villus tip cells. Lipid absorption resulted in an increase in intraepithelial staining for each apoprotein. The pattern for apo-B in the biopsy specimens taken after lipid absorption revealed a marked redistribution of staining to the intercellular spaces and an increase in the supranuclear staining of apo-A-I and apo-A-IV. After lipid absorption, staining appeared to extend further down the villus than in the fasting biopsy specimens. Quantitation of apo-A-I and apo-A-IV in isolated epithelial cells confirmed that the mass of these apoproteins increases in response to lipid absorption. Apolipoprotein B and apo-A-I were absent in the epithelium of 3 patients with abetalipoproteinemia while apo-A-IV was present in 2 patients. These studies demonstrate differences in the localization and quantitation of apoproteins in the villus-crypt unit as well as differences in the localization pattern of the different apoproteins.