Background:
Several mechanisms have been proposed to account for bone marrow failure in aplastic anemia (AA), including deficiency in hematopoietic stem cells, a secondary stem cell defect involving immune regulation and defective marrow
stroma, or microenvironment. We investigated the pathophysiology of AA through long-term bone marrow cultures (LTBMCs) using bone marrow of AA patients before treatment and of patients responded to immunosuppressive therapy with anti-thymocyte globulin (ATG) and/or cyclosporine.
Methods:
We investigated the hematopoietic defect in severe aplastic anemia (SAA) patients by using long-term bone marrow cultures (LTBMCs). Twenty patients with SAA have been studied. In these patients, 10 had been treated with ATG plus cyclosporine and the remainders were studied before therapy was begun. Subsequent assays of the production of negative-acting hematopoietic cytokines (TNF-α, IFN-γ, MIP-1α and TGF-β) by AA stroma in LTBMCs were peformed.
Results:Initial assessment of CD34+ cells, CFU-GM and CFU-MK from LTBMCs in AA demonstrated severely reduced or absent in patients with SAA, even following hematologic recovery with immunosuppressive therapy, when compared with normal
controls. Significant difference in concentrations of TNF-α,IFN-γ, and MIP-1α between the AA and control groups were apparent. Interestingly, the levels of those negative-acting hematopoietic cytokines were decreased in SAA patients receiving immunosuppressive therapy, but not the levels of controls. However, the mean TGF-β concentrations in the AA patients and normal controls were not signficantly different. The percent of CD34+ cells and CFU-MK in bone marrow was lower in SAA patients before
immunosuppressive therapy was begun than that in SAA patients receiving immunosuppressive therapy and that in normal controls (mean 0.54±0.32% vs 0.96±0.32% vs 1.94±0.61%).
Conclusions:
These results indicate the presence of a in vitro
functional deficiency in the hematopoietic system of patients with AA, including those that achieved partial or complete remission after immunosuppressive treatment, and add to the available evidence for defect of microenvironment with hematopoeitic stem cell in some cases of AA.

Keywords: Aplastic anemia, Long-term bone marrow cultures, Pathophysiology