Molecular pathogenesis of bone marrow failure as a major cause of death in paroxysmal nocturnal hemoglobinuria

在日本，再生障碍性贫血和阵发性睡眠性血红蛋白尿症（PNH）的患病率相对较高，表现为致命的骨髓衰竭。骨髓衰竭对免疫抑制治疗反应良好，提示骨髓衰竭是免疫介导的。然而，包括淋巴细胞识别的造血细胞分子靶点在内的发病机制尚不清楚。PNH和再生障碍性贫血患者的粒细胞和骨髓CD 34+细胞上病理性表达ULBP和云母/B等NKG 2D配体，并且粒细胞在体外依赖于配体表达而被自体淋巴细胞损伤（Hanaoka，et.例如，Blood 2006）。然后，我们提出，配体是淋巴细胞在免疫介导的造血功能障碍的骨髓衰竭综合征，如PNH和再生障碍性贫血的分子靶点。为了支持这一假设，我们前瞻性地分析了3例再生障碍性贫血-PNH综合征和2例再生障碍性贫血患者1至5年的临床病程。然后，我们发现一种或多种应激诱导的NKG 2D配体在其粒细胞上表达。其表达不仅与反映骨髓衰竭的全血细胞计数密切相关，因此，我们得出结论，至少有一部分患有原发性骨髓衰竭综合征（包括PNH和再生障碍性贫血）的患者暴露于一定的应激，以诱导其血细胞上的NKG 2D配体，并且配体表达触发或促进NKG 2D的表达。通过自体淋巴细胞介导的血细胞损伤，导致骨髓衰竭（川口和Nakakuma，Int J Hematol 2007）。目前，我们正在使用NKG 2D及其配体抗体通过体外集落形成抑制试验证实NKG 2D介导的骨髓细胞损伤。

The prevalence of aplastic anemia and paroxysmal nocturnal hemoglobinuria (PNH) that manifest fatal marrow failure are relatively high in Japan. The marrow failure shows good response to immunosuppressive therapy, indicating that marrow failure is immune-mediated. However, the pathogenesis including molecular targets on hematopoietic cells recognized by lymphocytes is unknown yet.In the present study, we show both that stress-inducible membrane proteins (or NKG2D ligands) such as ULBP and MICA/B were pathologically expressed on granulocytes and bone marrow CD34+ cells of patients with PNH and aplastic anemia, and that the granulocytes were injured by autologous lymphocytes dependently on the ligand expression in vitro (Hanaoka, et. al., Blood 2006). We then propose that the ligands are the molecular targets for lymphocytes in immune-mediated impairment of hemotopoiesis in the marrow failure syndromes such as PNH and aplastic anemia. lb support the hypothesis, we prospectively analyzed the clinical courses for one up to five years of 3 patients with aplastic anemia-PNH syndromes and 2 patients with aplastic anemia. We then found that one or more of the sress-inducible NKG2D ligands were expressed on their granulocytes. The expression closely associated not only with pancytbpenia reflecting marrow failure, but also with a favorable response of marrow failure to immunosuppressive therapy.We thus conclude that at least a part of patients with idiopathic bone marrow failure syndromes including PNH and aplastic anemia are exposed to a certain stress to induce the NKG2D ligands on their blood cells and that the ligand expression triggers off or promotes the NKG2D-mediated blood cell injury by autologous lymphocytes, leading to marrow failure (Kawaguchi & Nakakuma, Int J Hematol 2007). Currently, we are confirming the NKG2D-mediated marrow cells injury by in vitro colony formation inhibition assays with antibodies to NKG2D and its ligands.