Wheeler K, Gordon J
Department of Immunology, The Medical School, Vincent Drive, Birmingham B15 2TT, UK.
Int Immunol. 1996 Jun;8(6):815-28. doi: 10.1093/intimm/8.6.815.
We have previously shown that dual occupancy of sigM and CD40 - essential receptors in T-dependent B cell responses - by antibodies held on CD32-L cells results in the rapid proliferation of resting human B lymphocytes in a cytokine-independent manner. Here we report the detailed phenotype of the blast population emerging in such cultures. By 3 days the levels of CD19 and CD20 have increased 4- and 2-fold respectively: such high level expression of these two pan-B markers is characteristic of cells of germinal centre (GC) origin. B cells co-stimulated via sIgM and CD40 express low level CD23 and almost half become CD5(+); they also acquire CD38 and - importantly - CD77, both of these being selective markers of GC B cells. Expression of sigM and IgD is down-regulated on these cells and a minor, but significant, population of IgG+ cells appears. In marked contrast to GC B cells, the population proliferating in response to dual occupancy of sigM and CD40 has up-regulated and strongly expresses CD44. Morphologically, the cells are heterogeneous but there is a dominant blastic cell type with relatively scanty cytoplasm and having multiple nucleoli, both of which are characteristic of centroblasts; nevertheless, these cells remain morphologically distinct from freshly isolated GC B cells and do not show hallmark features of centrocytes. Although there is substantial cell death occurring by days 6-7 in these cultures, there is no morphological evidence for apoptosis. Thus, the proliferating population that emerges from the dual engagement of antigen receptor and CD40 on resting B cells appears to be bestowed with some features of GC B cells but has others which are incompatible with that particular stage of differentiation. The possibility that it might represent (i) a blast stage that is transitional between activation in T zones and entry into the follicle or (ii) a precursor population that colonizes the primary follicle prior to GC formation is discussed.
我们之前已经表明，结合在CD32-L细胞上的抗体对T细胞依赖性B细胞应答中的关键受体sigM和CD40的双重占据，会导致静息的人B淋巴细胞以细胞因子非依赖性方式快速增殖。在此，我们报告在这类培养物中出现的母细胞群体的详细表型。到第3天时，CD19和CD20的水平分别增加了4倍和2倍：这两种泛B标志物的如此高水平表达是生发中心（GC）来源细胞的特征。通过sIgM和CD40共刺激的B细胞表达低水平的CD23，并且几乎一半变为CD5(+)；它们还获得CD38以及——重要的是——CD77，这两者都是GC B细胞的选择性标志物。这些细胞上sigM和IgD的表达下调，并且出现少量但显著的IgG+细胞群体。与GC B细胞形成鲜明对比的是，因sigM和CD40的双重占据而增殖的群体上调并强烈表达CD44。形态学上，细胞是异质性的，但有一种占主导的母细胞类型，其细胞质相对稀少且有多个核仁，这两者都是中心母细胞的特征；然而，这些细胞在形态上仍与新鲜分离的GC B细胞不同，并且不显示中心细胞的标志性特征。尽管在这些培养物中到第6 - 7天时发生大量细胞死亡，但没有凋亡的形态学证据。因此，静息B细胞上抗原受体和CD40的双重结合产生的增殖群体似乎具有一些GC B细胞的特征，但也有一些与该特定分化阶段不相符的其他特征。文中讨论了它可能代表（i）在T区激活和进入滤泡之间过渡的母细胞阶段，或（ii）在GC形成之前定殖于初级滤泡的前体细胞群体的可能性。
