Sp17 is expressed on the surface of B-lymphoid cell lines and primary tumor cells.

Sp17 is detected on the surface of ARP-1, ARH-77, and ARK cells by flow cytometry. The graph in the upper left panel demonstrates that the mean fluorescence intensity of staining with anti-Sp17 decreases in a dose-dependent manner as the concentration of rSp17 increases, thereby confirming antibody specificity. (Sp17 antiserum was incubated with 0, 47, 167, or 333 μg/mL rSp17 before it was used for immunostaining of ARP-1 cells as described in “Materials and methods.”) Data shown are representative of a minimum of 2 independent experiments. The lower panels show staining of freshly isolated tumor cells from the blood of a patient with plasma cell leukemia (patient L) and from a pleural effusion of a myeloma patient (patient H). Samples were dual stained with antiserum to Sp17 and antibody B-B4, a monoclonal antibody that recognizes the plasma cell marker CD138 (syndecan-1). The histograms shown are Sp17 staining of the CD138⁺tumor cells.