Acquired pure red-cell aplasia: a consequence of increased natural killer cell activity?

A 19-year-old man with severe pure red-cell aplasia is described. An unusually high proportion of this patient's lymphocytes were large granular lymphocytes (LGL), both in the blood (40%) and in the bone marrow (50%). His blood leukocytes displayed a strongly elevated natural killer (NK) cell activity in vitro against the erythroblastic leukemia line K562. The patient's non-T blood lymphocytes inhibited in vitro erythroid colony formation (BFU-E and CFU-E) but not the granulocyte-monocyte colony growth (CFU-GM) from autologous and allogeneic bone marrow. Neither T-cell-mediated cytotoxicity nor circulating antibodies against erythroid precursors could be demonstrated. The patient's haemoglobin values returned to normal levels after three weeks of glucocorticoid treatment and have since then remained stable with continued prednisone administration. Attempts to reduce the prednisone dose to less than 10 mg/day have led to relapses. It is tempting to suggest that the patient's disease might be caused by hyperactivity of cytotoxic non-T (NK) cells specific for K562 cells and early erythroid precursors.