AFTR: A fifth human B-cell-specific surface antigen

Abstract We report the identification and characterization of a fifth B-cell-specific surface antigen (AFTR) detected by three murine monoclonal antibodies. AFTR is present on all malignant human B-cell lines tested except those of plasma cells and on malignant B cells from 49/49 patients, including those with pre-B cell acute lymphoblastic leukemia. Similarly, AFTR is found on all CD19 + B cells from normal bone marrow, peripheral blood, and tonsil, although it is only weakly expressed on Epstein-Barr virus-transformed normal B cells. AFTR is not expressed on T lymphocytes, thymocytes, myelocytes, monocytes, granulocytes, or erythrocytes, or on endothelial or epithelial cells. Isolation of AFTR from surface-iodinated cells by immune precipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis reveals bands at 38 and 42 kd in the acute lymphoblastic leukemia cell lines Laz 221 and NALM-6. Molecular weights of these two bands vary slightly between different B-cell populations but change little under reducing and nonreducing conditions. In contrast, relative intensities of these bands vary considerably between different B-cell populations. Like the B-cell-specific surface immunoglobulin and CD19 antigens, but unlike CD20, expression of AFTR is specifically reduced or modulated when cells are incubated with monoclonal antibodies at 37°C. The molecular weight, behavior, and cellular distribution of AFTR are distinct from those of known B-cell surface antigens. One of these MoAbs (J3–109) is a prototype reagent for the CD72 antigen cluster.