Abstract : FcgammaRIIB the low affinity inhibitory receptor for IgG plas a key role in the negative regulation of immune responses. FcgammaRIIB inhibits BCR-dependent B cell functions, as well as it induces a cellular death process which is poorly characterized. Lately, a potential role of FcgammaRIIB in the tumorigenesis has been identified. In particular, the deregulated expression of FcgammaRIIB as a consequence of the chromosomal translocations in follicular lymphomas has been described. Thus, we have studied the consequences of the homoaggregation of FcgammaRIIB in human B lymphoma cell lines. We show that FcgammaRIIB homoaggregation with anti FcgammaRIIB antibody (FLI 8.26) induced the cellular death of B lymphoma cells, but did not induce the death of normal human B lymphocytes. This cell death pathway in B tumoral cells is caspase dependent (cytochrome c release, caspase-9 cleavage, caspase-3 activation) and independent (AIF release). FcgammaRIIB receptor phosphorylation was found to be an early signalling event in this cell death pathway. Interestingly, FLI 8.26 antibody treatment also induced the expression of HSP27. This report constitutes the first investigation of this cell death pathway in human B cells. We propose that this novel cell death pathway offers potential for therapeutic exploitation in lymphoma treatment.