Expression of c-FLIP is primarily detected in diffuse large B-cell lymphoma and Hodgkin's lymphoma and correlates with lack of caspase 8 activation

Aims: Inhibition of apoptosis is important in the pathogenesis of lymphomas. c-FLIP, a regulator of caspase 8-mediated apoptosis, plays an important role in protecting normal B and T cells from apoptosis and possibly also in lymphomas. Because of contradictory reports about immunohistochemical detection of c-FLIP expression, the aim was to test the specificity of four antibodies in c-FLIP-transfected cells and subsequently to investigate expression of c-FLIP in different types of lymphoma. Methods and results: Two of four antibodies were specific. In primary lymphomas c-FLIP expression was restricted to Hodgkin's lymphomas (> 90%) and diffuse large B-cell lymphomas (44%). Burkitt lymphomas and indolent B-cell lymphomas were negative in all cases. No expression was detected in primary T-cell lymphomas, although expression was observed in one relapsed ALK+ anaplastic large cell lymphoma. Expression of c-FLIP was inversely correlated with caspase 8 activation. Conclusions: c-FLIP is important in escape of B cells from apoptosis during normal follicle centre cell reaction and may thus be an important early event in the development of B-cell-derived lymphomas. Moreover, non-specific staining of frequently used antibodies might explain discrepancies in different reports of c-FLIP expression.