Department of Immunology, Landspítali-The National University Hospital of Iceland, Reykjavík, Iceland.
Faculty of Medicine, University of Iceland, Reykjavík, Iceland.
Front Immunol. 2019 Mar 18;10:403. doi: 10.3389/fimmu.2019.00403. eCollection 2019.
It has recently been shown that individuals with selective IgA deficiency (sIgAD) have defective B cell responses both to T cell dependent and independent mimicking stimulations. The complex intracellular signaling pathways from different stimuli leading to IgA isotype switching have not been fully elucidated. Thus, the main objective of this study was to delineate these pathways and their potential role in the immunopathology linked to sIgAD. PBMCs from 10 individuals with sIgAD and 10 healthy controls (HC) were activated via either a T cell dependent or independent mimicking stimulation. Intracellular phosphorylation of pSTAT3, pSTAT5, pSTAT6, and as pERK1/2 was evaluated in T and B cells using phosphoflow cytometry. By evaluating T cell dependent cytokine driven pathways linked to IgA isotype induction we identified a defect involving an IL-21 driven STAT3 activation isolated to B cells in sIgAD individuals. However, all other signaling pathways studied were found to be normal compared to HC. In T cell dependent cytokine driven stimulations linked to IgA isotype induction the following patterns emerged: (i) IL-10 led to significant STAT3 activation in both T- and B cells; (ii) IL-4 stimulation was predominantly confined to STAT6 activation in both T- and B cells, with some effects on STAT3 activation in T-cells; (iii) as expected, of tested stimuli, IL-2 alone activated STAT5 and some STAT3 activation though in both cases only in T-cells; (iv) IL-21 induced significant activation of STAT3 in both T- and B cells, with some effects on STAT5 activation in T-cells; and finally (v) synergistic effects were noted of IL-4+IL-10 on STAT5 activation in T-cells, and possibly STAT6 in both T- and B cells. On the other hand, CPG induced T cell independent activation was confined to ERK1/2 activation in B cells. Our results indicate a diminished STAT3 phosphorylation following IL-21 stimulation solely in B cells from sIgAD individuals. This can represent aberrant germinal center reactions or developmental halt. Thus, our work provides further insight into the unraveling of the previously hypothesized role of IL-21 to reconstitute immunoglobulin production in primary antibody deficiencies.
最近的研究表明，选择性 IgA 缺乏症（sIgAD）患者的 B 细胞对 T 细胞依赖性和非依赖性模拟刺激的反应均存在缺陷。不同刺激物诱导 IgA 同种型转换的复杂细胞内信号通路尚未完全阐明。因此，本研究的主要目的是描绘这些途径及其在与 sIgAD 相关的免疫病理学中的潜在作用。
从 10 名 sIgAD 患者和 10 名健康对照者（HC）的 PBMC 中，通过 T 细胞依赖性或非依赖性模拟刺激进行激活。使用磷酸化流式细胞术评估 T 和 B 细胞中 pSTAT3、pSTAT5、pSTAT6 和 pERK1/2 的细胞内磷酸化。
通过评估与 IgA 同种型诱导相关的 T 细胞依赖性细胞因子驱动途径，我们发现 sIgAD 个体中 B 细胞中涉及 IL-21 驱动的 STAT3 激活的缺陷。然而，与 HC 相比，所有其他研究的信号通路均正常。在与 IgA 同种型诱导相关的 T 细胞依赖性细胞因子驱动刺激中，出现以下模式：（i）IL-10 导致 T-和 B 细胞中 STAT3 的显著激活；（ii）IL-4 刺激主要局限于 T-和 B 细胞中 STAT6 的激活，而在 T 细胞中对 STAT3 的激活也有一些影响；（iii）如预期的那样，在测试的刺激物中，只有 T 细胞中 IL-2 单独激活 STAT5 和一些 STAT3 激活；（iv）IL-21 诱导 T-和 B 细胞中 STAT3 的显著激活，而在 T 细胞中对 STAT5 的激活也有一些影响；最后（v）在 T 细胞中观察到 IL-4+IL-10 对 STAT5 激活的协同作用，并且可能在 T-和 B 细胞中对 STAT6 也有协同作用。另一方面，CPG 诱导的 T 细胞非依赖性激活仅限于 B 细胞中 ERK1/2 的激活。
我们的结果表明，sIgAD 患者的 B 细胞中仅在 IL-21 刺激后 STAT3 的磷酸化减少。这可能代表异常的生发中心反应或发育停滞。因此，我们的工作为揭示先前假设的 IL-21 在重建原发性抗体缺陷中的免疫球蛋白产生中的作用提供了进一步的见解。
