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) which binds to the CD95 (APO-1/Fas) antigen and mediates activation-induced cell death (AICD) of activated T cells and T lymphoma cells. A recent 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 mediated, as in T cells, through autocrine production of the Fast. We used human tonsillar B cells and Burkitt lymphoma cell lines which were activated by CD40 ligand, surface (s)IgM cross-linking, or LPS. Northern and Western blot analysis failed to detect Fast during B cell activation or AICD of both normal and malignant B cells. Low-level expression of Fast was detected by reverse transcriptase-polymerase chain reaction. Functional experiments, however, showed that Fast is not functionally expressed upon activation. IgM-mediated AICD in the tonsillar or Burkitt lymphoma B cells could not be inhibited by Fast blocking. Thus, our data show that, in contrast to T cells, activation of normal or malignant human B cells does not lead to functional Fast expression.