Studies in the Pathogenesis of Systemic Capillary Leak Syndrome

在经典的急性SCLS患者中，由于血浆外渗(高达总血浆容量的70%)而迅速发展的休克和水肿伴随着典型的前驱症状，即全身无力、乏力、肌痛，偶尔还会发烧、呕吐、腹痛和腹泻。这被称为SCLS的渗漏期，在没有继发性休克原因的情况下，可以进展为低血压、血液浓缩和低蛋白血症的特征三联症。低血压通常持续数天，并伴有广泛的第三间隙液体。症状逆转的速度几乎和出现症状的速度一样快，大量的液体从组织中动员进入循环和利尿。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，通常是由于过度热心液体复苏的后遗症继发于心血管负荷过重。发作的严重程度和频率在个别患者中通常是可以预测的，但在不同患者之间差别很大。SCLS的总10年死亡率约为25%-34%。继发性并发症包括间隔室综合征(由于液体和蛋白质渗入肌肉而导致压力增加)，低灌注量导致的急性肾小管坏死引起的肾功能衰竭或肌肉坏死继发的肌红蛋白尿，以及静脉和动脉血栓形成，包括血液浓缩引起的肺血栓。 一些证据表明，免疫失调可能是导致SCLS病理生理学改变的原因之一。首先，在大多数SCLS病例中存在一种意义不明的单克隆性伽马病(MGUS)。MGUS是多发性骨髓瘤(MM)的癌前病变，在MM中，克隆性浆细胞群分泌大量可在患者血清中检测到的单克隆性免疫球蛋白(Ig，也称为副蛋白)。同样，在急性SCLS发作期间，循环中CD25+T细胞的数量和皮肤中CD8+淋巴细胞的毛细血管周围浸润也被注意到。最后，几名小细胞淋巴瘤患者在化疗后出现较少的毛细血管渗漏事件。综上所述，这些发现表明，来自失调浆细胞群体的单克隆性副蛋白可能是观察到的病理生理结果的直接或间接来源，可能是通过激活T淋巴细胞。 我们正在通过检测单抗Ig在体外血管病理发展中的作用来探索SCLS的分子机制。使用来自SCLS患者的单抗Ig，我们将确定它是否与特定的细胞类型、靶抗原(如果有)结合，以及由此产生的对内皮细胞的影响(直接或间接)。我们还对发病前和发病后SCLS血清的蛋白质组进行了鉴定，以确定是否可以识别急性症状的特定生物标记物。 在2009-2010年间，我们根据这一方案在NIH临床中心接纳了14名患者。我们发表了一篇描述SCLS临床症状和治疗的综述，并在国际血管生物学会议和Mayo血管生成研讨会上介绍了我们的发现。我们现在是SCLS研究的主要全球转诊中心。 我们发现与血管通透性相关的因子(血管内皮生长因子和血管紧张素2)在几个SCLS患者的血浆中升高，这与疾病症状有关。而血浆IL-2和肿瘤坏死因子-α水平正常。对4名SCLS患者在急性严重渗漏期间采集的外周血单个核细胞(PBMC)进行RNA微阵列分析，发现IL-8的表达与基线时患者的细胞相比发生了对数倍的变化。尽管部分纯化的SCLS患者单抗Ig G的F(Ab)2片段不能与健康供者的PBMC结合，但与自体PBMC孵育可诱导部分T细胞的活化(CD154表达)。这些结果表明，T淋巴细胞的激活可能导致致病细胞因子的分泌，这可能是与SCLS相关的暂时性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.