T-CELL-MEDIATED INHIBITION OF ERYTHROPOIESIS IN APLASTIC-ANEMIA - THE POSSIBLE ROLE OF IFN-GAMMA AND TNF-ALPHA

The inhibitory activity of T cells on autologous erythroid colony-forming units (CFU-E) (T cell inhibitory activity) in patients with aplastic anaemia (AA) was investigated. In 11 (32.4%) out of 34 AA cases, T cell inhibition on autologous CFU-E growth was greater than that in normal individuals. In order to evaluate the mechanism of this inhibitory activity, T cell surface markers, interferon (IFN) production in peripheral blood mononuclear cell (PBMNC) liquid culture, and cytokine levels such as IFN and tumour necrosis factor-alpha (TNF-alpha) in CFU-E clot cocultured with T cells, were measured in a portion of the patients. In five patients investigated for IFN production in PBMNC liquid culture, all produced statistically more IFN activity than normal individuals under phytohaemagglutinin (PHA-P) stimulation (P < 0.01) with no relation to T cell inhibitory activity. In only one patient whose T cells displayed increased CD8 and HLA-DR antigen (CD8+HLA-DR+) and inhibitory activity, a significant amount of IFN-gamma was observed in CFU-E clot cocultured with T cells, and the addition of anti-IFN-gamma antibody to the coculture resulted in recovered CFU-E colony growth. These results suggest that IFN-gamma production by T cells may explain, at least in part, the pathogenesis of haematopoietic defects in AA. In other patients however, T cell inhibitory activity neither correlated to the T cell subpopulations (CD4+/CD8+, CD8+HLA-DR+), IFN production in PBMNC liquid culture, nor to IFN and TNF-alpha-levels in CFU-E clot culture. The roles played by cytokines other than IFN and TNF-alpha on haematopoietic precursor cells require further evaluation in a larger sample of patients with AA.