CD138 (syndecan 1) is a transmembrane proteoglycan that can bind a variety of cytokines and modulate their activity, as well as the activity of extracellular matrix components and influence many developmental processes. CD138 is expressed mainly in differentiating keratinocytes and is transiently upregulated in all layers of the epidermis upon tissue injury. It is also highly expressed on plasma cells and can be detected even on fibroblasts, vascular smooth muscle cells and endothelial cells. Up-regulation and down-regulation of CD138 on the cell surface often correlates with the gain of cancerous characteristics. Serum levels of the shedded soluble sCD138 are used as a prognostic factor of cancerogenesis.Purified by protein-A affinity chromatography. The mouse monoclonal antibody MI15 recognizes an extracellular epitope of CD138 (syndecan 1), a 65-70 kDa heparan sulfate proteoglycan expressed mainly in the epidermis and plasma cells, but also in growth factor-stimulated lymphocytes.