The immune system in 40 aplastic anemia patients receiving conventional therapy

Forty patients with aplastic anemia who were being considered for bone marrow transplantation were studied by in vivo and in vitro techniques to determine if the immune system in aplastic anemia is generally affected. It was found that patients with aplastic anemia had mild lymphopenia, with levels of circulating thymus-derived and bone-marrow-derived cells that were apparently secondarily depressed. Marked monocytopenia was observed, but this finding was migrated by recovery of essentially normal numbers of mononuclear phagocytic cells (using a discontinuous Hypaque-Ficoll density gradient) and by the ability of patient mononuclear cells to participate at least as well as control cells in proliferative responses in vitro. More patients had abnormally low levels of the immunoglobulin classes than would be predicted from the laboratory normal range; however, no consistent pattern of immunoglobulin deficiency was found. Levels of complement component, antiviral antibody, and isohemagglutinins were essentially normal. However, cutaneous delayed hypersensitivity responses were impaired. Proliferative responses in vitro to mitogens and antigens (except staphylococcal filtrate) were at least as vigorous as the responses of controls. Patients mononuclear cells stimulated allogeneic cells as well as did MHC-identical sibling cells, and they responded at least as well to allogeneic unrelated cells. Clinically the patients did not suffer from fungal or protozoal infections, which are common in immune deficiency syndromes. Thus these aplastic anemia patients were little different from normal subjects. The mild lymphopenia, impaired delayed hypersensitivity, and modestly depressed IgG and IgM levels were correlated with corticosteroid therapy.