Summary. Aplastic anaemia is characterized by reduced haematopoiesis resulting in pancytopenia. It has been speculated that there is an injury in haematopoietic stem cells in the bone marrow; however, the precise nature of the injury has not been elucidated. In this study, the levels of expression of mRNAs for three transcription factors, GATA-2, SCL and AML1, which function in the early stages of haematopoiesis, were examined by quantitative polymerase chain reaction in patients with aplastic anaemia, idiopathic thrombocytopenic purpura (ITP) and normal subjects. Among these factors, expression of GATA-2 mRNA in purified CD34-positive cells was markedly decreased in aplastic anaemia compared with that in ITP and in normal subjects. The expression levels of SCL and AML1 mRNA in CD34-positive cells in aplastic anaemia were not different from those in normal subjects. When the expression of GATA-2 protein in CD34-positive cells was examined by immunocytochemical analysis, the percentage of GATA-2-positive cells in aplastic anaemia was lower than that in normal subjects. These findings strongly suggest that there is an aberrant expression of transcription factors in stem cells in aplastic anaemia, which may be responsible for the development of the disease.Keywords: transcription factors, stem cells, aplastic anaemia.Aplastic anaemia is characterized by a hypocellular bone marrow, reduced haematopoiesis and peripheral pancytopenia (Young, 1999). The clinical efficacy of immunosuppressive therapy (Young & Maciejewski, 1997; Marsh et al, 1999) and the result of in vitro studies (Maciejewski et al, 1996;Novitzky & Jacobs, 1999) suggested that there may be a certain immunological attack to haematopoietic stem cells that play a role in developing aplastic anaemia in most patients. On the other hand, the fact that some patients do not respond to immunosuppressive therapy clearly indicates that the immunological aberration is not the sole mechanism of the disease. However, limited information is available for the intrinsic characteristics of stem cells in aplastic anaemia, because most studies have focused on the extrinsic immunological abnormality.To date, several transcription factors have been described that function in the early stages of haematopoiesis (Shivdasani & Orkin, 1996). Among these factors, GATA-2, SCL and AML1 have been shown to be indispensable for early haematopoiesis at the stem cell level by both in vivo and in vitro study (Tsai et al, 1994;Okuda et al, 1996;Porcher et al, 1996). Furthermore, it has been shown that these factors are expressed in stem cells in the adult haematopoietic system (Mouthon et al, 1993;Erickson et al, 1996). Therefore, it is possible that changes in the expression level of these factors may lead to an aberrant proliferation and differentiation of stem cells, and may be partly responsible for developing stem cell diseases such as aplastic anaemia.In order to examine this question, the levels of expression of mRNA encoding GATA-2, SCL and AML1 were examined in haematopoietic s...
