Specificity: Recognizes a heparan sulfate rich membrane glycoprotein of 200kD known as Syndecan-1 (CD138). Syndecan functions as a receptor for collagen, fibronectin and thrombospondin. Stains all plasma cells and plasma cell lines. No staining of other leucocytes is seen in peripheral blood or bone marrow, although some ALL cell lines express the antigen weakly. Some staining of epithelial and endothelial cells may be seen in immunohistology.