Identification of activated T cells and the suppressor/inducer subset in patients suffering from severe aplastic anemia

Summary In patients with severe aplastic anemia (SAA), lymphocyte subpopulations were examined for the presence of HLA-DR and 2H4 (suppressor/inducer subset) antigen-expressing cells by flow cytometric analysis. Investigations were performed on peripheral blood lymphocytes before and after therapy with antithymocyte globulin (ATG) and methylprednisolone (MP), as well as on bonemarrow lymphocytes before therapy. Before treatment, only the absolute numbers of CD4⁺ T cells and the CD4⁺HLA^–DR⁺/CD8⁺HLA-DR⁺ activated T cell ratio were significantly decreased (p<0.01 and p<0.001, respectively). Following successful ATG/MP treatment, a decrease in the CD4⁺/CD8⁺T cell ratio was found. Regarding the suppressor/inducer subset, only absolute numbers of CD4⁺/2H4⁺ cells were somewhat higher in treated patients; the percentages were the same in all groups of patients. Studies performed on bonemarrow lymphocytes showed significantly decreased percentages of CD4⁺ and CD8⁺ T lymphocytes, which also express HLA-DR antigen. No significant changes in the distribution of activated T cells following ATG/MP therapy were found, suggesting that these cells play no major role in the pathogenesis of the disease.