Immune mechanism is considered to exert in the pathogenesis of marrow failure in paroxysmal nocturnal hemoglobinuria (PNH), idiopathic aplastic anemia (AA) and myelodysplastic syndromes (MDS); however, the molecular events are unknown. We have currently reported the appearance of NKG2D ligands such as cytomegalovirus glycoprotein UL16 binding proteins (ULBPs) and MHC class I-related chains A and B (MICA/B) on granulocytes and CD34+ marrow cells of some patients with PNH and its related diseases (

Hanaoka N, et al. Blood. 2006;107:1184–1191
). ULBP and MICA/B are stress-inducible membrane proteins that appear in infection and transformation. The ligands share NKG2D receptor on lymphocytes such as NK, CD8+ T, and γδ T-cells and promote activation of the lymphocytes. Cells expressing the ligands are then deadly injured by NKG2D+ lymphocytes (Groh, PNAS 1996; Cosman, Immunity 2001). Indeed, cells expressing NKG2D ligands were killed in vitro by autologous NKG2D+ lymphocytes of our patients (
Hanaoka N, et al. Blood. 2005;106:304a
;
Blood. 2006;108:295a
). In further analysis, ligands were detected on granulocytes in 47 (53%) of 88 patients: 11 (58%) of 19 PNH, 28 (60%) of 47 AA, and 8 (36%) of 22 refractory anemia. Ligands were also detected on immature bone marrow cells in all 11 patients (3 PNH, 5 AA, and 3 refractory anemia) who permitted analysis of their marrow cells. In the patients, it is conceivable that blood cells were exposed to a certain stress to induce NKG2D ligands, leading to NKG2D-mediated marrow injury. We also observed a close association of the ligand expression with pancytopenia and favorable response to immunosuppressive therapy by prospective analysis of 5 patients (3 AA-PNH syndrome and 2 AA) for more than one year up to 5 years. Thus, we here propose that NKG2D-mediated immunity, which drives both NK and T-cells, is critically implicated in the pathogenesis of bone marrow failure of PNH and its related disorders.

Topics:
paroxysmal nocturnal hemoglobinuria, ligands, pancytopenia, refractory anemias, stress, aplastic anemia, idiopathic, carrier proteins, cd34 antigens, glycoprotein, infections

Author notes

Disclosure: No relevant conflicts of interest to declare.

2007, The American Society of Hematology
2007
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