HUMAN GERMINAL CENTER B-CELLS EXPRESS THE APOPTOSIS-INDUCING GENES FAS, C-MYC, P-53, AND BAX BUT NOT THE SURVIVAL GENE BCL-2

During T cell-dependent antibody responses, B cells within germinal ce nters (GC) alter the affinity of their antigen receptor by introducing somatic mutations into variable region of immunoglobulin (IgV) genes. During this process, GC B cells are destined to die unless positively selected by antigens and CD40-ligand. To understand survival/death co ntrol of germinal center B cell, the expression of four apoptosis-indu cing genes, Fas, c-myc, Bax, and p(53), together with the survival gen e bcl-2, has been analyzed herein among purified tonsillar naive, GC, and memory B cells. IgD(+)CD38(-) naive B cells were separated into CD 23(-) (mature B cell [Bm) 1) subset and CD23(+) (Bm2), IgD(-)CD38(+) G C B cells were separated into subsets of CD77(+) centroblasts (Bm3) an d CD77(-) centrocytes (Bm4), whereas IgD(-)CD38(-) cells represented t he Bm5 memory B cell subset. Sequence analysis of IgV region genes ind icated that somatic hypermutation was triggered in the Bm3 centroblast subset. Here we show that bcl-2 is only detectable with naive (Bm1 an d 2) and memory B cell (Bm5) subsets, whereas all four apoptosis-induc ing genes were most significantly expressed within GC B cells. Fas was equally expressed in Bm3 centroblasts and Bm4 centrocytes, whereas Ba x was most significantly expressed in Bm4 centrocytes. c-myc, a positi ve regulator of cell cycle, was most significantly expressed in prolif erating Bm3 centroblasts, whereas P-53, a negative regulator of cell c ycle, was most significantly expressed in nonproliferating Bm4 centroc ytes. The present results indicate that the survival/death of GC B cel ls are regulated by the up- and downregulation of multiple genes, amon g which the expression of c-myc and P-53 in the absence of bcl-2 may p rime the proliferating Bm3 centroblasts and nonproliferating Bm4 centr ocytes to apoptosis.