Ultrastructural Localization of Endogenous Albumin in Human Aortic Tissue by Protein A-gold Immunocytochemistry

The presence of endogenous plasma albumin in human aortas was demonstrated by immunocytochemical procedures. The protein A-gold approach, combining high resolution and specificity, was applied at the light and electron microscope levels to determine the in situ cellular and extracellular localization of albumin on tissue sections derived from normal and atherosclerotic human aortas. The distribution of albumin across the aortic wall interstitium was found to be uneven, with low to moderate staining intensities in the aortic subendothelial space, low intensities in the media, and high intensities around the vasa vasorum in the adventitia. Albumin was associated with collagen fibers as well as with the electron-dense material bordering the elastic laminae in both normal and pathologic tissues. Extracellular multilamellar structures were found to be characteristic of the necrotic areas of atherosclerotic aortas. These structures were intensely labeled for albumin, with the labeling being closely associated with the membranes. Numerous smooth muscle cell-derived and monocyte-derived foam cells were present in pathologic tissues, and some of their lysosomal compartments were labeled for albumin, suggesting an internalization and degradation of interstitial albumin by these cells.