Bcl-2 
,^ Survival Pathway 
r 
Apoptotic 
Death 
Centrocytes 
r Light Zone 
I (). Basal 
^J^^^^Light Zone 
Bcl-2 
Dark^ 
Zonel 
B Blast <][ 
Plasma 
Cell 
Memory 
Centroblasts 
Distribution of the Bcl-2 protein that blocks cell death within the germinal center of the immune 
system. Bcl-2 is confined to survival zones. B cells in the follicular mantle are longer lived and 
recirculate. The growing centroblasts in the dark zone and the dying centrocytes in the basal light 
zone lack the protein. It returns in the apical light zone, where long-lived memory cells emerge to 
permit recall responses. 
Research of Stanley Korsmeyer. 
232 
