Human germinal center B cells express the apoptosis-inducing genes Fas, c-myc, P53, and Bax but not the survival gene bcl-2.
During T cell-dependent antibody responses, B cells within germinal centers (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 control of germinal center B cell, the expression of four apoptosis-inducing genes, Fas, c-myc, Bax, and P53, together with the survival gene bcl-2, has been analyzed herein among purified tonsillar naive, GC, and memory B cells. IgD+CD38- naive B cells were separated into CD23- (mature B cell [Bm]1) subset and CD23+ (Bm2), IgD-CD38+ GC B cells were separated into subsets of CD77+ centroblasts (Bm3) and CD77- centrocytes (Bm4), whereas IgD-CD38- cells represented the Bm5 memory B cell subset. Sequence analysis of IgV region genes indicated that somatic hypermutation was triggered in the Bm3 centroblast subset. Here we show that bcl-2 is only detectable with naive (Bm1 and 2) and memory B cell (Bm5) subsets, whereas all four apoptosis-inducing genes were most significantly expressed within GC B cells. Fas was equally expressed in Bm3 centroblasts and Bm4 centrocytes, whereas Bax was most significantly expressed in Bm4 centrocytes. c-myc, a positive regulator of cell cycle, was most significantly expressed in proliferating Bm3 centroblasts, whereas P53, a negative regulator of cell cycle, was most signficantly expressed in nonproliferating Bm4 centrocytes. The present results indicate that the survival/death of GC B cells are regulated by the up- and downregulation of multiple genes, among which the expression of c-myc and P53 in the absence of bcl-2 may prime the proliferating Bm3 centroblasts and nonproliferating Bm4 centrocytes to apoptosis.
Martinez-Valdez
H
H
Schering-Plough, Laboratory for Immunological Research, Dardilly, France.
Guret
C
C
de Bouteiller
O
O
Fugier
I
I
Banchereau
J
J
Liu
Y J
YJ
D017209:Apoptosis / Q000235:genetics*; D016175:B-Lymphocyte Subsets / Q000276:immunology*; D001402:B-Lymphocytes / Q000276:immunology*; D001483:Base Sequence; D015139:Blotting, Southern; D017931:DNA Primers; D015870:Gene Expression; D016259:Genes, myc; D016158:Genes, p53; D018858:Germinal Center / Q000276:immunology; D006801:Humans; D007150:Immunohistochemistry; D008969:Molecular Sequence Data; D014066:Palatine Tonsil / Q000276:immunology; D016133:Polymerase Chain Reaction; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis*; D019253:Proto-Oncogene Proteins c-bcl-2; D016271:Proto-Oncogene Proteins c-myc / Q000096:biosynthesis*; D016159:Tumor Suppressor Protein p53 / Q000096:biosynthesis; D051028:bcl-2-Associated X Protein; D019014:fas Receptor / Q000096:biosynthesis*
C494826:BAX protein, human; D017931:DNA Primers; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D016271:Proto-Oncogene Proteins c-myc; D016159:Tumor Suppressor Protein p53; D051028:bcl-2-Associated X Protein; D019014:fas Receptor