ACTIVATION AND ACTIVATION-INDUCED DEATH OF HUMAN TONSILLAR B-CELLS AND BURKITT-LYMPHOMA CELLS - LACK OF CD95 (FAS APO-1) LIGAND EXPRESSION AND FUNCTION/

Activation of T cells was shown to up-regulate the Fas ligand (Fast) w hich binds to the CD95 (APO-1/Fas) antigen and mediates activation-ind uced cell death (AICD) of activated T cells and T lymphoma cells. A re cent report showed that mouse B cells express the Fast upon activation with lipopolysaccharide (LPS). We therefore asked whether activation of human B cells induces expression of Fast and whether AICD is mediat ed, as in T cells, through autocrine production of the Fast. We used h uman tonsillar B cells and Burkitt lymphoma cell lines which were acti vated by CD40 ligand, surface (s)IgM cross-linking, or LPS. Northern a nd Western blot analysis failed to detect Fast during B cell activatio n or AICD of both normal and malignant B cells. Low-level expression o f Fast was detected by reverse transcriptase-polymerase chain reaction . Functional experiments, however, showed that Fast is not functionall y expressed upon activation. IgM-mediated AICD in the tonsillar or Bur kitt lymphoma B cells could not be inhibited by Fast blocking. Thus, o ur data show that, in contrast to T cells, activation of normal or mal ignant human B cells does not lead to functional Fast expression.