8B8 specifically reacts with the 85 kD b-chain of humanLRP/a2MR which is expressed in a restricted spectrum ofcell types (for a recent review cf. Herz & Strickland). Astrong immunohistochemical reaction is seen in hepatocytes,tissue macrophages, subsets of neurones and astrocytesin the central nervous system, fibroblasts,smooth muscle cells, and monocyte-derived foam cells inatherosclerotic lesions in the arterial wall. The antibodycan also be used for the characterization of a subset ofmyelo-monocytic subtypes of chronic and acute leukemia(CD 91).