[Mechanism of immunosuppressive therapy for aplastic anemia]

The mechanism of therapeutic effect of anti-lymphocyte globulin (ALG) and cyclosporin A (CyA) on patients with aplastic anemia was studied. When peripheral CD8 positive cells obtained before therapy were cocultured with bone marrow CD34 positive cells obtained after hematological recovery, the number of colony forming unit granulocyte-macrophage (CFU-GM) and burst forming unit erythroid (BFU-E) were decreased. This result indicates that ALG and CyA inhibits CD8 positive cells which suppress the growth of progenitor cells, resulting in the recovery of hematopoiesis. Next we investigated the plasma concentrations of cytokines including G-CSF, GM-CSF, IL-6, IL-1 alpha and IL-1 beta after ALG treatment. Although the elevation of plasma concentrations of G-CSF and GM-CSF after ALG treatment were found in 11 of 13 patients and in 2 of 13 patients respectively, cytokine production by ALG appeared to be unrelated to the therapeutic effect of ALG for aplastic anemia.