Studies in the Pathogenesis of Systemic Capillary Leak Syndrome

在典型急性SCLS患者中，由于血浆外渗（高达总血浆量的70%）导致的休克和水肿的快速发展伴随着全身无力、疲劳、肌痛和偶尔发热、呕吐、腹痛和腹泻的典型前驱症状。 这被称为SCLS的渗漏期，在没有继发性休克原因的情况下，可进展为低血压、血液浓缩和低白蛋白血症的特征性三联征。低血压通常持续数天，并伴有广泛的第三间隔液体。症状几乎和出现时一样快地逆转，大量液体从组织动员到循环和利尿中。这是泄漏后阶段。正是在毛细血管渗漏后阶段，大多数患者死亡，通常是由于过度液体复苏后的心血管超负荷。发作的严重程度和频率通常在个体患者中是可预测的，但在患者之间差异很大。SCLS的总体10年死亡率约为25- 34%。 继发性并发症包括筋膜室综合征（由于液体和蛋白质渗漏到肌肉中引起的压力增加）、低灌注引起的急性肾小管坏死引起的肾衰竭或继发于肌肉坏死的肌红蛋白尿，以及静脉和动脉血栓形成，包括血液浓缩引起的肺栓塞。 一些证据表明，免疫失调可能有助于在SCLS中观察到的病理生理学结果。首先，意义不明的单克隆丙种球蛋白病（MGUS）存在于大多数SCLS病例中。 MGUS是多发性骨髓瘤（MM）的癌前前病变，其中克隆浆细胞群分泌大量可在患者血清中检测到的单克隆免疫球蛋白（IG，也称为副蛋白）。 同样，在急性SCLS发作期间，已经注意到皮肤中循环CD 25 + T细胞的数量增加和CD 8+淋巴细胞的毛细血管周围浸润。最后，有几名SCLS患者在MGUS演变为坦率的骨髓瘤或浆细胞白血病后经历了较少的毛细血管渗漏发作化疗的造血系统疾病。 综合考虑，这些结果表明，来自调节异常的浆细胞群的单克隆副蛋白可能是观察到的病理生理学结果的直接或间接来源，可能通过激活T淋巴细胞。 我们正在通过检测单克隆IG在体外血管病理学发展中的作用来探索SCLS的分子机制。使用SCLS患者的单克隆IG，我们将确定其是否与特定细胞类型、靶抗原（如果有）结合，以及对内皮细胞的影响（直接或间接）。我们还对SCLS血清蛋白质组进行了表征，包括发作前和发作后，以确定是否可以识别急性症状的特定生物标志物。 在2009-2010年期间，我们根据该方案在NIH临床中心收治了14例患者。 一篇综述描述了SCLS的临床症状和治疗，我们在国际血管生物学会议和马约血管生成研讨会上介绍了我们的研究结果。我们现在是SCLS研究的主要全球转诊中心。 我们发现，在一些SCLS患者的血浆中，与血管通透性（VEGF和Ang 2）相关的因子升高，这与疾病症状相关。相反，血浆IL-2和TNF-α正常。从4名急性严重渗漏发作的SCLS患者中采集的外周血单核细胞（PBMC）的RNA微阵列分析发现，与基线时从患者中获得的细胞相比，IL-8表达发生了几个对数倍的变化。尽管部分纯化的SCLS患者单克隆IgG的F（ab）2片段不与健康供体的PBMC结合，但与自体PBMC孵育可诱导一部分T细胞活化（CD 154表达）。 这些结果表明，T淋巴细胞活化，可能导致分泌致病细胞因子，可能是与SCLS相关的短暂内皮屏障功能障碍的基础。

In patients with the classical acute form of SCLS, the rapid development of shock and edema due to plasma extravasation (up to 70% of total plasma volume) follows a typical prodrome of generalized weakness, fatigue, myalgias, and occasionally fevers, vomiting, abdominal pain, and diarrhea. This is called the leak phase of SCLS, and can progress to the characteristic triad of hypotension, hemoconcentration, and hypoalbuminemia in the absence of secondary causes of shock. The hypotension usually lasts for several days accompanied by extensive third-spacing of fluids. The symptoms reverse almost as quickly as they arise, with massive fluid mobilization from tissues into circulation and diuresis. This is the post-leak phase. It is during the post-capillary leak phase that most patients die, often from cardiovascular overload secondary to the after-effects of overzealous fluid resuscitation. The severity and frequency of episodes is often predictable in an individual patient but varies widely from patient to patient. The overall 10-year mortality of SCLS is approximately 25-34%. Secondary complications include compartment syndromes (due to increased pressure induced by leakage of fluid and proteins into muscles), renal failure from hypoperfusion-induced acute tubular necrosis or myoglobinuria secondary to muscle necrosis, and venous and arterial thrombosis including pulmonary embolism from hemoconcentration. Several lines of evidence suggest that immune dysregulation may contribute to the pathophysiologic findings seen in SCLS. First, a monoclonal gammopathy of unknown significance (MGUS) is present in a majority of SCLS cases. MGUS is a premalignant precursor to multiple myeloma (MM), in which a clonal plasma cell population secretes large amounts of monoclonal immunoglobulin (Ig, also referred to as a paraprotein) detectable in patient sera. Likewise, increased numbers of circulating CD25+ T cells and peri-capillary infiltration of CD8+ lymphocytes in skin have been noted during acute SCLS attacks. Finally, several patients with SCLS in whom MGUS evolved into frank myeloma or plasma cell leukemia experienced fewer capillary leak episodes after chemotherapy for the hematopoietic disorder. Considered together, these findings suggest that the monoclonal paraprotein from the dysregulated plasma cell population may be the direct or indirect source of the pathophysiologic findings observed, possibly through activation of T lymphocytes. We are exploring the molecular mechanisms of SCLS by examining the function of the monoclonal Ig in the development of vascular pathology in vitro. Using monoclonal Ig from SCLS patients, we will determine whether it binds to a specific cell type, target antigen (if any), and resulting effect (direct or indirect) on endothelial cells. We are also characterizing the proteome of SCLS serum, both pre- and post-attack, to determine whether specific biomarkers of acute symptoms can be identified. During 2009-2010, we admitted 14 patients to the NIH clinical center under this protocol. A review describing the clinical symptoms and treatment of SCLS was published, and we presented our findings at the International Meeting of Vascular Biology and the Mayo Angiogenesis Symposium. We are now the primary worldwide referral center for research on SCLS. We found elevations in factors associated with vascular permeability (VEGF and Ang2) in the plasma of several SCLS patients, which correlated with disease symptoms. In contrast, plasma IL-2 and TNF-alpha were normal. RNA microarray analysis of peripheral blood mononuclear cells (PBMC) taken from 4 SCLS patients during an acute, severe leak episodes identified several log-fold changes in IL-8 expression compared to cells obtained from the patients at baseline. Although partially purified F(ab)2 fragments of monoclonal IgG from SCLS patients did not bind PBMC from healthy donors, incubation with autologous PBMC induced activation (CD154 expression) in a fraction of T cells. These results suggest that T lymphocyte activation, perhaps leading to secretion of pathogenic cytokines, might underlie the transient endothelial barrier dysfunction associated with SCLS.