B－CELL APOPTOSIS INDUCED BY ANTIGEN RECEPTOR CROSSLINKING IS BLOCKED BY A T－CELL SIGNAL THROUGH CD40

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B-CELL APOPTOSIS INDUCED BY ANTIGEN RECEPTOR CROSSLINKING IS BLOCKED BY A T-CELL SIGNAL THROUGH CD40

in mice transgenic for an autoantibody,self-reactive B cells have been shown to be eliminated upon interaction with membranebound self-antigens in the periphery as well as in the bone marrow, suggesting that both immature and mature B cells are eliminated by multimerization of surface immunoglobulins(0Ig).Activation B cells by antigens may thus require a second signal that inhibits sIg-mediated apoptosis.Such a second signal is likely to be provided by T helper cells,because B-cell tolerance is more easily induced in the absence of T helper cells.To assess the molecular nature of the signal that inhibits sIg-mediated apoptosis,we used anti-IgM--induced apoptotic death of WEHI-231B lymphoma cells as a model system.Here we report that the signal for abrogating sIg-mediated apoptosis is generated by association of the CD401 molecule on T-cells with the CD40molecule on WEHI-231 cells.T-cells help through CD50 may thus determine whether B cells are eliminated or activated upon interaction with antigens.