DISTRIBUTION OF THE ALPHA-2-MACROGLOBULIN RECEPTOR LOW-DENSITY-LIPOPROTEIN RECEPTOR-RELATED PROTEIN IN HUMAN TISSUES

The hepatic alpha-2-macroglobulin receptor (alpha-2MR)/low density lipoprotein receptor-related protein (LRP) binds and endocytoses alpha-2-macroglobulin-proteinase complexes in plasma. In addition, it binds lipoproteins, a novel 40 kDa protein, and complexes between plasminogen activators and plasminogen activator inhibitor type-1. This study shows, for the first time, the tissue distribution of alpha-2MR/LRP as determined by immunohistochemistry with specific monoclonal antibodies. The analysis revealed alpha-2MR/LRP-expression in a restricted spectrum of cell types, including neurons and astrocytes in the central nervous system, epithelial cells of the gastrointestinal tract, smooth muscle cells, fibroblasts, Leydig cells in testis, granulosa cells in ovary, and dendritic interstitial cells of kidney. Monocyte-derived cells displayed marked alpha-2MR/LRP expression in the phagocytes of liver, lung and lymphoid tissues, but no or low expression in antigen-presenting cells including Langerhans' cells of the skin. The high abundance of alpha-2MR/LRP in certain cell types of most organs suggests two main routes for alpha-2MR/LRP-mediated ligand clearance: (1) systemic removal in liver of circulating ligands, and (2) non-hepatic interstitial removal in different organs, including the brain.