Opposing roles of CD95 (Fas/APO-1) and CD40 in the death and rescue of human low density tonsillar B cells.
The regulation of B cell death plays roles in the selection of Ag-specific B cells in humoral immune responses, controlling B cell homeostasis and perhaps limiting transformation. The present work addresses whether CD95 induces tonsillar B cells to undergo apoptosis and, if so, whether contact-dependent CD40-L:CD40 signaling can rescue tonsillar B cells from CD95-induced apoptosis. CD95 triggering by anti-CD95 mAb (APO-1) was studied in human tonsillar B cell populations that were separated by density centrifugation into fractions enriched for either low density, CD38+ B cells or high density, resting B cells. Low density tonsillar B cells express CD95 and undergo anti-CD95-mediated apoptosis by analysis of cellular morphology or DNA fragmentation by TUNEL assay. The induction of apoptosis in low density tonsillar B cells by anti-CD95 mAb is inhibited by CD40 signals provided by stably transfected CD40-L+ 293 cells, but not by control transfected 293 cells (expressing CD8). In addition, the rescuing effect of CD40-L+ cells is inhibited specifically by anti-CD40-L (mAb 5c8). The counteracting effects of CD95 and CD40 signaling were also studied in Ramos 2G6, a homogeneous B cell tumor line of germinal center phenotype that expresses CD95 and CD40. Similar to the behavior of low density tonsillar B cells, Ramos 2G6 undergoes anti-CD95-mediated apoptosis, which is prevented by CD40-mediated rescue. These data show that CD95 induces apoptosis in low density tonsillar B cells and that CD40-L:CD40 interactions rescue low density tonsillar B cells or the B cell tumor Ramos 2G6 from CD95-induced apoptosis, and suggest roles for CD95 and CD40 in B cell death and selection, respectively.
Cleary
A M
AM
Department of Medicine, Columbia University College of Physicians and Surgeons, New York, NY 10032, USA.
Fortune
S M
SM
Yellin
M J
MJ
Chess
L
L
Lederman
S
S
D017209:Apoptosis / Q000276:immunology*; D001402:B-Lymphocytes / Q000276:immunology* / Q000473:pathology; D001483:Base Sequence; D019013:CD40 Antigens / Q000276:immunology*; D002478:Cells, Cultured; D004247:DNA / Q000032:analysis; D004249:DNA Damage; D006801:Humans; D008969:Molecular Sequence Data; D014066:Palatine Tonsil / Q000276:immunology*; D019014:fas Receptor / Q000276:immunology*
D019013:CD40 Antigens; D019014:fas Receptor; D004247:DNA