ACTIVATED B-CELLS EXPRESS FUNCTIONAL FAS LIGAND

Fas ligand (FasL, Apo-1L) is a member of the tumor necrosis factor pro tein family and binding to its receptor (Fas, Apo-1, CD95) triggers ce ll death through apoptosis. Ligand expression is restricted to cells w ith known cytolytic activity and found on hematopoietic cells of the T cell and natural killer lineage. Here we provide evidence that B lymp hocytes can express FasL. Flow cytometric analysis revealed that FasL is expressed on the surface of B cells upon stimulation with either li popolysaccharide or phorbol 12-myristute 13-acetate/ionomycin. FasL ex pression on activated B cells was confirmed by Western blot and revers e transcriptase polymerase chain reaction analysis. FasL on B cells is functional since lipopolysaccharide-activated B lymphocytes derived f rom wild type. but not fron gld mutant mice, were able to kill Fas-sen sitive target cells. Our data suggest that the Fas system may contribu te to the control of B cell homeostasis.