Immunology Department, Son Espases Hospital, Palma, Balearic Islands, Spain.
Human Immunopathology Research Laboratory, Institut d'Investigació Sanitària de les Illes Balears, Palma, Spain.
Cell Death Dis. 2018 Nov 21;9(12):1156. doi: 10.1038/s41419-018-1191-8.
Common variable immunodeficiency (CVID) is characterized by an abnormal B cell differentiation to memory and antibody-secreting B cells. The defective functionality of CVID patients' B cells could be the consequence of alterations in apoptosis regulation. We studied the balance of Bcl-2 family anti-/pro-apoptotic proteins to identify molecular mechanisms that could underlie B cell survival defects in CVID. We used flow cytometry to investigate Bcl-2, Bcl-XL, Bax, and Bim expression in B cells ex vivo and after anti-CD40 or anti-BCR activation with or without IL-21, besides to spontaneous and stimulation-induced Caspase-3 activation and viable/apoptotic B cell subpopulations. We found increased basal levels of Bax and Bim in CVID B cells that correlated with low viability and high Caspase-3 activation only in CD27 B cells, particularly in a subgroup of apoptosis-prone CVID (AP-CVID) patients with low peripheral B cell counts and high autoimmunity prevalence (mostly cytopenias). We detected a broad B cell defect in CVID regarding Bcl-2 and Bcl-XL induction, irrespective of the stimulus used. Therefore, peripheral CVID memory B cells are prompted to die from apoptosis due to a constitutive Bcl-2 family protein imbalance and defective protection from activation-induced apoptosis. Interestingly, anti-CD40 and IL-21 induced normal and even higher levels of Bcl-XL, respectively, in CD27 B cells from AP-CVID, which was accompanied by cell viability increase. Thus low-survival memory B cells from AP-CVID can overcome their cell death regulation defects through pro-survival signals provided by T cells. In conclusion, we identify apoptosis regulation defects as disease-contributing factors in CVID. B cell counts and case history of cytopenias might be useful to predict positive responses to therapeutic approaches targeting T-dependent signaling pathways.
普通变异型免疫缺陷症（CVID）的特征是 B 细胞向记忆 B 细胞和分泌抗体的 B 细胞分化异常。CVID 患者 B 细胞的功能缺陷可能是凋亡调控改变的结果。我们研究了 Bcl-2 家族抗/促凋亡蛋白的平衡，以确定可能导致 CVID 中 B 细胞存活缺陷的分子机制。我们使用流式细胞术研究了 CVID 患者 B 细胞体外和抗 CD40 或抗 BCR 激活后（有或没有 IL-21）Bcl-2、Bcl-XL、Bax 和 Bim 的表达，以及自发和刺激诱导的 Caspase-3 激活和存活/凋亡 B 细胞亚群。我们发现 CVID B 细胞中 Bax 和 Bim 的基础水平升高，这与仅在 CD27 B 细胞中低存活率和高 Caspase-3 激活相关，特别是在一组具有低外周 B 细胞计数和高自身免疫发生率（主要是血细胞减少症）的易发性 CVID（AP-CVID）患者中。我们检测到 CVID 中存在广泛的 B 细胞缺陷，无论使用何种刺激物，Bcl-2 和 Bcl-XL 的诱导均受到影响。因此，由于 Bcl-2 家族蛋白失衡和激活诱导的细胞凋亡保护缺陷，外周 CVID 记忆 B 细胞被促使凋亡。有趣的是，抗 CD40 和 IL-21 分别在 AP-CVID 的 CD27 B 细胞中诱导正常甚至更高水平的 Bcl-XL，同时细胞存活率增加。因此，来自 AP-CVID 的低存活率记忆 B 细胞可以通过 T 细胞提供的生存信号克服其细胞死亡调节缺陷。总之，我们将凋亡调节缺陷确定为 CVID 的致病因素。B 细胞计数和血细胞减少症的病史可能有助于预测针对 T 细胞依赖的信号通路的治疗方法的阳性反应。
