Immunophenotypes of Bone Marrow Lymphocytes in Patients with Severe Aplastic Anemia

Background : Immune mediated suppression of hematopoiesis has been regarded as the most important pathogenetic mechanism of idiopathic severe aplastic anemia (AA). However, the immunophenotype of lymphocytes in the bone marrow (BM) of AA has not been comprehensively studied. We investigated the immunophenotype of lymphocytes in the BM to evaluate immune alteration and the possibility of involvement of lymphocytic lineage in AA. Methods : The flow cytometric analysis for 16 cell surface antigens using monoclonal antibodies in 20 patients with AA and 20 healthy persons was performed. The percentage of positive cell population was calculated in the gated region for lymphocytes and compared data between AA and normal controls. And the BM cellularity and lymphocyte population were evaluated by light microscopy. Results : The CD34＋ cells were significantly decreased in AA (0.790.76% vs 2.601.53%) compared to controls. The CD2＋, CD8＋ and CD4＋CD8＋ cells were significantly increased in number, but the other T cell antigens were similar to normal control. All the B cell antigens were decreased in AA. The CD56＋ cells and CD25＋CD56＋ cells were significantly increased in AA. The lymphocyte population was negatively correlated to B cell population and positively correlated to CD4＋CD8＋ cells. Conclusion : The BM lymphocytes populations are significantly altered in AA. The B cells are significantly decreased in AA than normal control whereas, the CD8＋ cells, CD4＋CD8＋ cells and CD56＋ cells seem to play an important role in destruction of hematopoietic progenitor cells in AA.