Studies on the mechanisms of the maturation of germinal center B cells.

在T细胞依赖的免疫反应中，抗原激活的B细胞改变其IgH链的表达，并高度突变其VH和VL区域，以提高其抗体的亲和力。这种成熟过程被认为发生在生发中心。为了了解生发中心在B细胞成熟和生发中心细胞相互作用中的作用，我们对生发中心B细胞进行了免疫组织化学和功能分析。(1)我们发现生发中心B细胞在光区、边缘区和套区的部分生发中心B细胞表达CD38。IL-5Rα阳性B细胞定位于光区，部分B细胞共表达CD38。(2)IL-4和IL-5在抗CD40单抗作用下诱导半纯化的B细胞分化为抗原特异性的IgG1抗体分泌细胞。流式细胞仪分析显示，IL-4和抗CD40单抗刺激半纯化的B细胞可促进IL-5Rα的表达。(3)CD38连接于B细胞可诱导野生型小鼠B细胞的增殖、IgM分泌和Bruton‘s酪氨酸激酶(BTK)的酪氨酸磷酸化，而XID小鼠的B细胞则无此作用。CD38可以与IL-5协同作用，促进B细胞增殖、Blimp-1基因表达和IgM产生。(4)利用IL-5Rα的突变突变体进行突变分析，发现IL-5Rα胞浆结构域(Pro352-Pro353-X-Pro355)中的一个Pro352或Pro355是细胞增殖和JAKs/STAT5途径激活所必需的。

In a T-cell dependent immune response, antigen-activated B cells switch their IgH chain expression and hypermutate their VH and VL regions to improve the affinity of its antibodies. This maturation processes are believed to occur in the germinal center. To understand the role of the germinal center for B cell maturation and cellular interactions in germinal centers, we carried out immunohistochemical and functional analysis of germinal center B cell.(1) We found that some of germinal center B cells in light zone, marginal zone and mantle zone express CD38. IL-5Ralpha positive B cells were localized in light zone and some of them appear to co-express CD38.(2) IL-4 and IL-5 in the presence of anti-CD40 mAb induced semi-purified GB B cells to differentiate into antigen specific IgG1 antibody-secreting cells. FACS analysis revealed that stimulation of semi-purified GB B cells with IL-4 and anti-CD40 mAb enhanced expression of IL-5Ralpha.(3) CD38 ligation on B cells induced proliferation, IgM secretion, and tyrosine phosphorylation of Bruton's tyrosine kinase (Btk) in B cells from wild-type mice but not in B cells from XID mice. CD38 ligation can cynergistically acts with IL-5 to enhance B-cell proliferation, Blimp-1 gene expression, and IgM production. Flow cytometry analysis revealed that CD38 ligation enhanced the expression of the IL-5Ralpha on B cells.(4) Mutational analysis using substitution mutants of IL-5Ralpha revealed that one of the proline residues, particularly Pro352 or Pro355, in the membrane proximal proline-rich sequence (Pro352-Pro353-X-Pro355) of the cytoplasmic domain of IL-5Ralpha is required for cell proliferation and for activation of JAKs/STAT5 pathway.