Bcl-x rather than Bcl-2 mediates CD40-dependent centrocyte survival in the germinal center

Both rapid B-cell proliferation and programmed cell death (PCD) occur during the differentiation and selection of B cells within the germinal center. To help elucidate the role of Bcl-x in B-cell antigen selection and PCD within the germinal center, we examined its expression in defined B-cell populations and by immunochemistry of tonsil tissue. Purified B-cell fractions enriched for centrocytes express high amounts of Bcl-x and relatively low amounts of Bcl-2, whereas fractions enriched for centroblasts lack significant levels of both proteins. Consistent with this observation, immunocytochemistry localized Bcl-x within cells scattered throughout the germinal center. Stimulation of tonsil B cells with either CD40 or Staphylococcus aureus Cowan increase bcl-x mRNA and protein levels. Treatment of a cell line with a germinal center phenotype (RAMOS) or the tonsillar B-cell centroblast fraction with CD40 rapidly increased Bcl-x levels and partially rescued B cells from PCD. These data suggest that Bcl-x rather than Bcl-2 may rescue centrocytes during selection in the germinal center.     

人参叶中微量新皂甙-La的分离与鉴定

前已报道从人参(Panax ginseng C.A.Meyer)叶中分到三种微量新皂甙。在继续研究的基础上,又得到一个微量新皂甙,命名为人参皂甙-La(ginsenoside-La)。人参皂甙-La,无色针晶(MeOH),[α]D~(20)—18.4(Pyridine-d_5)。负离子FAB-MS