Identification of autoantigens in autoimmune aplastic anemia

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Idiopathic aplastic anemia (AA) is considered to be a kind of autoimmune disease caused by a T-cell attack against hematopoi*stem cells although little is know about target antigens of the immune attack. We isolated a CD4+ T-cell clone termed ZN1 from the bone marrow of a patient with immume-mediated aplastic anemia. Using the combinatorial random peptide library, we attempted to identify a candidate epitope of ZN1. Several 11-mer peptides were found to stimulate proliferation to the T-cell clone, however, none of them proved to be related to hematopoietic cells. Since a CLIP-replacement peptide library has been shown to be useful in identify an epitope of CD4+ T-cell clone, we are planning to test this library. On the other hand, there has been no evidence that cytotoxic T cells (CTIs) indeed participate in the attack of hematopoietic stem cells in AA.We previously demonstrated that hematopoietic cells need to express glycosylphosphatidylinositol (GPI)-anchored membrane proteins such … More as CD59 and CD58, to be efficiently killed by a CTL, NT4.2, that was isolated from the bone marrow of an immune-mediated AA patient. To estimate how frequent CTLs are involved in the development of bone marrow failure, we examined peripheral blood of newly diagnosed AA patients for the presence of granulocytes deficient of GPI-anchored proteins using a sensitive flow cytometry. A significant increase in the percentage of CD55-CD59- (PNH) in CD11b+ granulocytes (_0.003%) was observed in 31 of 35 patients (88.6%). When peripheral blood of 19 patients showing increased PNH granulocytes was studied again at 6 months after antithymocyte globalin therapy, the percentage of PNH granulocytes had decreased to 0.01-90% of the pretreatment values in 15 of 18 recovering patients. These findings suggest that the increased percentage of PNH granulocytes reflects the presence of CTL attack against normal hematopoietic stem cells and that such immune mechanisms may be operative in approximately 90% of AA patients. Less