Penner S J, George J, Claflin L
Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor 48109, USA.
J Immunol. 1995 Sep 1;155(5):2387-95.
We wished to resolve a paradox of how the response to the phosphocholine (PC) determinant of Proteus morganii could be initiated from a precursor B cell whose receptor, in unmutated form as Ab, appears to be unable to bind Ag. Unmutated VH and unmutated VL constructs were co-transfected into the B cell lymphoma M12.4 to study stimulation via membrane lg (mlg). The same VH construct was expressed in an L+, H- hybridoma line to characterize Ab binding. The unmutated Ab showed no detectable binding in ELISA to the PC-containing Ag from P. morganii PC(PM). By contrast, the unmutated mlg mediated mobilization of calcium in response to the PC(PM) Ag. Single-positive B cell lines of mlgM, mlgD double-positive lines were all capable of responding. The degree of signaling depended greatly on high receptor number, and only a fraction of cells in the population responded. Inhibition of the PC(PM)-induced calcium response by free PC indicated that the response was Ag-specific. A transfectant B cell line expressing moderate levels of a high affinity, mutated mlgM readily responded to PC(PM). These observations indicate that the unmutated lg as a receptor is capable of interacting with PC(PM) and suggest that the immune response to PC(PM) could originate from the precursor B cell expressing the unmutated mlg. The role of mlgD vs mlgM is discussed in terms of the requirement for high receptor number in the signaling process.
我们希望解决一个矛盾，即针对摩根氏变形杆菌磷胆碱（PC）决定簇的反应如何能从一个前体B细胞启动，而该前体B细胞的受体以未突变形式作为抗体时似乎无法结合抗原。将未突变的重链可变区（VH）和未突变的轻链可变区（VL）构建体共转染到B细胞淋巴瘤M12.4中，以研究通过膜免疫球蛋白（mlg）的刺激。相同的VH构建体在L⁺、H⁻杂交瘤细胞系中表达以表征抗体结合情况。未突变的抗体在酶联免疫吸附测定（ELISA）中对来自摩根氏变形杆菌PC（PM）的含PC抗原未显示出可检测到的结合。相比之下，未突变的mlg介导了对PC（PM）抗原的钙动员反应。mlgM单阳性B细胞系、mlgM和mlgD双阳性细胞系均能够产生反应。信号传导程度很大程度上取决于高受体数量，并且群体中只有一部分细胞产生反应。游离PC对PC（PM）诱导的钙反应的抑制表明该反应具有抗原特异性。表达中等水平高亲和力、突变型mlgM的转染B细胞系很容易对PC（PM）产生反应。这些观察结果表明，未突变的免疫球蛋白作为受体能够与PC（PM）相互作用，并表明对PC（PM）的免疫反应可能起源于表达未突变mlg的前体B细胞。根据信号传导过程中对高受体数量的需求，讨论了mlgD与mlgM的作用。
