Hematopoiesis in the human spleen

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Abstract
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 × 105 cells plated and 1–7 CFU‐C/5 × 105, 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 × 105, 40 CFU‐E/5 × 105, and 9 CFU‐C/5 × 105. The spleen had extensive extramedullary hematopoiesis on microscopy and grew 180 BFU‐E/105, 210 CFU‐E/105, and 25 CFU‐C/105. 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.