Circulating Activated Suppressor T Lymphocytes in Aplastic Anemia

Abstract We studied the mechanism of hematopoietic suppression in aplastic anemia by means of two-color flow microfluorometric analysis of lymphocyte subpopulations and correlated the results with the occurrence in vitro of hematopoietic suppression and interferon production. In 12 patients with aplastic anemia a striking increase was observed in a population of "activated" suppressor T lymphocytes, which were defined by binding of both anti-Leu-2 and anti-HLA-DR monoclonal antibodies (patients with aplastic anemia, 6.8±3.2 per cent [mean ±S.D.]; normal subjects, 1.7±1.3; patients given multiple transfusions, 2.5±1.7). Tac antigen expression, another surface marker of lymphocyte activation, was increased on suppressor lymphocytes in all five patients examined (patients with aplastic anemia, 31±17 per cent; normal subjects, 0.7±0.24; patients given multiple transfusions, 2.3±1.2). When Tac+ and Tac cells were separated in a cell sorter, only Tac+ cells produced interferon. When lymphocytes of patients with...