Bcl-2 expression on germinal center lymphocytes modulated by the emperipolesis of follicular dendritic cells

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Germinal center (GC) B cells are highly susceptible to apoptosis. The cellular mechanism regulating this sensitivity, however has not yet been fully delineated. To investigate whether follicular dendritic cells (FDC) are capable of regulating the susceptibility to apoptosis of GC B cells, we constructed a GC model in vitro : emperipolesis of tonsillar B cells by FDC. We then analyzed the expression of apoptosis-related proteins (Bcl-2 and Fas) on the cells by three-color flow cytometry. B cells nonentrapped B cells were rescued for at least 18h and showed peculiar regulation of Gfas and Bcl-2. GC founder cells (CD38ィイD1+ィエD1, IgDィイD1+ィエD1 ; GCFC) and GC B cells (CD38ィイD1+ィエD1, IgDィイD1-ィエD1) showed approximately a twofold increased expression of Fas ; in contrast, mantle zone B cells (CD38ィイD1-ィエD1, IgDィイD1+ィエD1) and memory B cells (CD38ィイD1-ィエD1, IgDィイD1-ィエD1) showed no changes. Bcl-2 expression in mantle zone and memory B cells was reduced by approximately one-half ; however, GCFC and GC b cells continued to express little Bcl-2 and this did not change. Our findings strongly suggested that FDC play a part in the modulation of the susceptibility to apoptosis on B cells within GC.