The 281-2 antibody reacts with an extracellular epitope on the core protein of mouse CD138 (Syndecan-1), a ~60 – 100 kDa type 1 transmembrane glycoprotein expressed on the surface of pre-B cells, immature B cells, and normal and malignant plasma cells (but not mature circulating B cells). CD138 is also expressed on non-hematopoietic cells such as embryonic mesenchymal cells, endothelial, epithelial and neural cells. CD138 is thought to act primarily as a receptor that modulates cell proliferation, cell migration and cell-matrix associations by linking the extracellular matrix to the cytoskeleton. Heparin sulfate and chondroitin sulfate moieties attached to CD138 associate with several proteins, including collagens, fibronectin, tenascin, thrombospondin and certain cytokines.