Molecular mechanisms of proliferation and differentiation of germinal center B cells

生发中心（GC）在二级淋巴组织中对胸腺依赖（TD）抗原（Ag）作出反应。为了研究小鼠GC - B细胞分化的分子机制，阐明x -联免疫缺陷（Xid）小鼠GC - B细胞的功能，我们在体外实验中，从TD ag免疫小鼠脾脏富集GC - B细胞，监测功能分子的表达，并测定其在抗cd40单抗和细胞因子作用下向ag特异性IgGI抗体形成细胞（AFCs）的分化。GC B细胞表达IL-4受体(R)，约5%的GC B细胞表达IL-5R。IL-4在抗cd40单抗存在下诱导野生型小鼠GC B细胞向ag特异性IgGI AFCs分化，并增强野生型小鼠GC B细胞IL-5R的表达。IL-5进一步增强IgGI AFC应答。来自Xid小鼠的GC B细胞对抗cd40单抗和IL-4有应答，导致IgGI应答，而IL-5没有增强应答。这些发现表明，抗cd40单抗、IL-4和IL-5在小鼠GC B细胞的分化中起关键作用。Xid小鼠GCB细胞在il -5介导的分化方面存在功能缺陷。然后，我们检测了CD40和CD38对GC和滤泡套（FM）B细胞分化的影响。结果表明，IL-5Ralpha阳性细胞主要分布在GC细胞中，同时表达CD40，而CD38在GC B细胞中表达下调。用IL-5加抗cd38单抗刺激GC B细胞不诱导IgGI反应。IL-5Ralpha、CD38和CD40在xid小鼠中的表达与野生型小鼠相似。此外，il - 5rα缺陷小鼠对TD Ag的反应正常，涉及GC的发展和Ag特异性IgGI的产生。这些结果表明，IL-5在小鼠GC - B细胞的分化过程中作为共刺激因子而非必需因子发挥关键作用。

Germinal center (GC) develops in secondary lymphoid tissues in response to thymus-dependent (TD) antigens (Ag). To investigate the molecular mechanism of mouse GC B cell differentiation and elucidate the function of GC B cells from X-linked immunodeficient(Xid)mice, we enriched GC B cells from spleen of TD Ag-immunized mice, monitored the expression of functional molecules, and determined the differentiation into Ag-specific IgGI antibody forming cells (AFCs) in response to anti-CD40 mAb and cytokines in vitro. GC B cells expressed IL-4 receptor (R), and approximately 5% of GC B cells expressed IL-5R.IL-4 in the presence of anti-CD40 mAb induced the differentiation of GC B cells from wild-type mice into Ag-specific IgGI AFCs, and enhanced the IL-5R expression on GC B cells from wild-type mice. IL-5 enhanced further the IgGI AFC response. The GC B cells from Xid mice responded to anti-CD40 mAb and IL-4 resulting in the IgGI response, whereas IL-5 did not enhance the response. These findings suggest that anti-CD40 mAb, IL-4, and IL-5 play a critical role in differentiation of mouse GC B cells. The GCB cells from Xid mice show functional defect with respect to IL-5-mediated differentiation.We then examined effect of CD40 and CD38 on differentiation of GC and follicular mantle(FM)B cells. The results showed that IL-5Ralpha positive cells were mainly distributed in GC which also expressed CD40, whereas CD38 expression was down-regulated on GC B cells. Stimulation of GC B cells with IL-5 plus anti-CD38 mAb did not induce the IgGI response. The expression of IL-5Ralpha, CD38, and CD40 in Xidmice was similar to that in wild-type mice. Furthermore, IL-5Ralpha deficient mice showed normal response to TD Ag, regarding GC development and Ag-specific IgGI production. These results suggest that IL-5 plays a critical role in differentiation of mouse GC B cells as a costimulatory factor rather than an essential factor.