CDw40 and BLCa‐specific monoclonal antibodies detect two distinct molecules which transmit progression signals to human B lymphocytes

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Abstract
Two monoclonal antibodies (mAb), MA6 and G28‐5, have the common property of detecting markers expressed on both B lymphocytes and carcinomas: BLCa (B lymphocyte carcinoma cross‐reacting antigen) and CDw40 (Bp50). A comparison of the reactivity of these mAb revealed that MA6 and G28‐5 detect distinct epitopes with different cell line and tissue distributions. L cell transfectants expressing CDw40 were not bound by MA6 anti‐BLCa, but were bound by G28‐5 anti‐CDw40. G28‐5 or a CDw40‐specific heterantiserum could not block the migration of BLCa, while MA6 antibody could. These results indicate that CDw40 and BLCa are distinct surface molecules. Both G28‐5 anti‐CDw40 and MA6 anti‐BLCa mAb could provide progression signals for B cells activated by appropriate B cell activators such as phorbol esters or anti‐immunoglobulin; however, only G28‐5 anti‐CDw4O and not MA6 was co‐stimulatory with the anti‐CD20 competence signal, demonstrating a clear difference in the CDw40 and BLCa‐mediated progression signals. Apparently, these molecules, although structurally distinct, have related functions in B cell activation.