Expression of interferon-γ and tumor necrosis factor-α in bone marrow T cells and their levels in bone marrow plasma in patients with aplastic anemia

Immune-mediated stem cell damage has been postulated to be responsible for disease initiation and progression in aplastic anemia (AA). It is hypothesized that T lymphocytes play a major role in destroying the bone marrow (BM) stem cells of AA patients by infiltrating the BM and secreting excessive levels of anti-hematopoietic cytokines, interferon-gamma (IFN-γ), and tumor necrosis factor-alpha (TNF-α). We undertook this study to assess the pathogenic significance of anti-hematopoietic cytokines such as IFN-γ and TNF-α in BM T cells and plasma of AA patients. Significantly elevated levels of IFN-γ and TNF-α were found in the BM plasma of AA patients compared to controls (p=0.05 and 0.006, respectively). Intracellular IFN-γ and not TNF-α in BM CD3⁺ T cells of AA patients was significantly higher compared to controls (p=0.04 and p=0.2, respectively). A follow-up analysis of expression of these cytokines in BM T cells and their levels in BM plasma in five AA patients before and 180 days (6 months) after antithymocyte globulin (ATG) and cyclosporin A (CsA) therapy showed a decline 180 days after therapy compared to pre-therapy. We thus conclude that increased production of both IFN-γ and TNF-α in the BM may contribute to disease pathogenesis in AA and ATG therapy may induce hematological remission by suppressing the elevated levels of IFN-γ and TNF-α in AA BM.