Abstract
A 32-yr-old black female with pure red cell aplasia and thymoma showed complete hematologic remission after thymectomy. Bioassay of preoperative serum and urine in exhypoxic polycythemic mice revealed the presence of significant levels of erythropoiesis-stimulating factor (ESF or erythropoietin). Antierythropoietin completely neutralized the erythropoietic effect of these samples. Utilizing both normal and exhypoxic polycythemic mice, the preoperative serum and urine were also found to contain a potent inhibitor of erythropoiesis. However, no such activity was demonstrated in saline extracts of the tumor tissue. The inhibitor was present in the serum IgG fraction. Serum to which excess ESF had been added, after prior neutralization of endogenous ESF with anti-ESF, failed to stimulate erythropoiesis in the polycythemic mouse.
