Hematopoiesis in the human spleen.

To assess the capacity of the human spleen to function as a hematopoietic organ, spleen mononuclear cells from patients undergoing splenectomy were cultured to assay CFU-E, BFU-E, and CFU-C. Although the peripheral blood from cases of hereditary spherocytosis, Gaucher disease, Thalassemia major, and idiopathic thrombocytopenic purpura yielded 3-20 BFU-E/5 X 10(5) cells plated and 1-7 CFU-C/5 X 10(5), suspensions of spleen cells failed to grow colonies. Histologically these spleens did not show extramedullary hematopoiesis. In contrast, peripheral blood from a patient with osteopetrosis (marble bone disease) yielded 130 BFU-E/5 X 10(5), 40 CFU-E/5 X 10(5), and 9 CFU-C/5 X 10(5). The spleen had extensive extramedullary hematopoiesis on microscopy and grew 180 BFU-E/10(5), 210 CFU-E/10(5), and 25 CFU-C/10(5). We conclude that spleens from patients without extramedullary hematopoiesis do not contain committed hematopoietic progenitors in spite of normal precursors in the blood. In osteopetrosis the spleen contained stem cells in a concentration comparable to bone marrow, and the embryonic role of the spleen in blood formation appeared to continue in postnatal life.