IMMUNOBIOLOGY Tumor protein D52 (TPD52): a novel B-cell/plasma-cell molecule with unique expression pattern and Ca2-dependent association with annexin VI

We generated a murine monoclonal antibody (B28p) detecting an antigenic determinant shared by the immunoglobu-lin superfamily receptor translocation-associated 1 (IRTA1) receptor (the im-munogen used to raise B28p) and an unrelated 28-kDa protein that was subse-quently subjected to extensive character-ization. The expression of the 28-kDa protein in normal lymphohematopoietic tissues was restricted to B cells and plasma cells and clearly differed from that expected for IRTA1 (selectively ex-pressed by mucosa-associated lymphoid tissue [MALT] marginal zone B cells). Two-dimensional polyacrylamide gel elec-trophoresis (2D-PAGE)/mass-spectrom-etry analysis identified the 28-kDa protein as human tumor protein D52 (TPD52), whose expression had been previously described only in normal and neoplastic epithelia. Specific B28p reactivity with TPD52 was confirmed by immunostaining/ immunoblotting of TPD52-transfected cells. TPD52 expression pattern in normal and neoplastic B cells was unique. In fact, unlike other B-cell molecules (paired box 5 [PAX5], CD19, CD79a, CD20, CD22), which are down-regulated during differ-entiation from B cells to plasma cells, TPD52 expression reached its maximum levels at the plasma cell stage. In the Thiel myeloma cell line, TPD52 bound to annexin VI in a Ca2-dependent manner, suggesting that these molecules may act in concert to regulate secretory pro-cesses in plasma cells, similarly to what was observed in pancreatic acinar cells. Finally, the anti-TPD52 monoclonal anti-body served as a valuable tool for the diagnosis of B-cell malignancies. (Blood