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

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 degrees 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.