B cell lines induce apoptosis selectively in transformed fibroblasts. Apoptosis induction is independent of direct cell contact. It seems to be based on superoxide anion production by transformed cells, subsequent spontaneous dismutation to hydrogen peroxide and utilization of the hydrogen peroxide by a peroxidase released by effector cells. The peroxidase then generates hypochlorous acid which may interact with target cell derived superoxide anions, yielding apoptosis-inducing hydroxyl radicals. In parallel, NO released by effector cells may interact with target cell derived superoxide anions and generate the apoptosis inducer peroxynitrite. Therefore, in parallel to their specific functions in humoral immunity, B cells seem to have the potential to contribute to those signalling pathways directed against transformed cells that have been recently shown to be established by TGF-β treated fibroblasts. This intercellular signalling system seems to represent an evolutionary ancient system for the control of cells that potentially endanger the survival of multicellular organisms.

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