Li Y S, Dearden-Badet M T, Revillard J P
INSERM U80, CNRS URA1177, UCBL, Hôpital E. Herriot, Lyon, France.
J Immunol. 1991 Sep 15;147(6):1752-8.
To understand mechanisms of signal transduction involved in the regulation of isotype differentiation of B lymphocytes, we investigated effects of activation of protein kinase C (PKC) by phorbol esters and elevation of intracellular free calcium (Ca2+) by the calcium ionophore ionomycin (Ion) on Ig secretion by mouse Peyer's patch (PP) and spleen B cells. Results show that Ion suppressed production of IgM, IgG, and IgA by LPS-stimulated B cells whereas PKC-activating phorbol esters also inhibited LPS-induced IgM and IgG secretion, but induced a substantial IgA synthesis, as well as alpha-chain mRNA transcription, in B cells whether stimulated or not by LPS. Phorbol esters enhanced IgA response by directly activating PKC, inasmuch as the other phorbol ester, 4 alpha-phorbol 12,13-didecanoate, which is inactive with respect to PKC, had no effect on B cell differentiation. The increase in IgA secretion occurred in whole PP B cells, but not in the membrane IgA- B cell subset, suggesting that PKC activation does not promote the switching rate of IgM+ cells to IgA+ cells. Results from double staining studies of mIgA using FITC-labeled anti-IgA antibodies and DNA content using the DNA-binding propidium iodide showed that enhanced IgA response was not caused by IgA B cell clonal expansion. PMA induced low level of IL-6 production by highly purified PP B cells. However, addition of anti-mouse IL-6 antibody did not prevent PMA-enhanced IgA secretion, suggesting that IL-6 was not responsible for IgA induction by PMA. Collectively, the present data demonstrate that PKC activation and Ca2+ mobilization, which synergistically trigger cell proliferation, have differential effects on B cell isotype differentiation. Elevation of intracellular Ca2+ suppresses Ig production, but activation of PKC selectively enhances IgA secretion by directly promoting terminal differentiation of IgA-committed PP B cells into IgA-secreting plasma cells.
为了解参与B淋巴细胞同种型分化调控的信号转导机制，我们研究了佛波酯激活蛋白激酶C（PKC）以及钙离子载体离子霉素（Ion）提高细胞内游离钙（Ca2+）水平对小鼠派伊尔结（PP）和脾脏B细胞分泌免疫球蛋白（Ig）的影响。结果显示，Ion抑制脂多糖（LPS）刺激的B细胞产生IgM、IgG和IgA，而激活PKC的佛波酯也抑制LPS诱导的IgM和IgG分泌，但无论是否受到LPS刺激，均可诱导B细胞大量合成IgA以及α链mRNA转录。佛波酯通过直接激活PKC增强IgA反应，因为另一种对PKC无活性的佛波酯4α-佛波醇12,13-十二烷酸酯对B细胞分化没有影响。IgA分泌增加发生在整个PP B细胞中，而非膜IgA-B细胞亚群中，这表明PKC激活不会促进IgM+细胞向IgA+细胞的转换率。使用异硫氰酸荧光素（FITC）标记的抗IgA抗体对mIgA进行双重染色研究以及使用碘化丙啶结合DNA对DNA含量进行研究的结果表明，增强的IgA反应并非由IgA B细胞克隆扩增引起。佛波醇酯（PMA）诱导高度纯化的PP B细胞产生低水平的白细胞介素-6（IL-6）。然而，添加抗小鼠IL-6抗体并不能阻止PMA增强的IgA分泌，这表明IL-6并非PMA诱导IgA产生的原因。总体而言，目前的数据表明，协同触发细胞增殖的PKC激活和Ca2+动员对B细胞同种型分化具有不同的影响。细胞内Ca2+水平升高会抑制Ig产生，但PKC激活通过直接促进已定向分化为分泌IgA的浆细胞的PP B细胞的终末分化，选择性地增强IgA分泌。
