Localization of megakaryocytes in normal mice and following administration of platelet antiserum, 5-fluorouracil, or radiostrontium: evidence for the site of platelet production.

The relative contributions of various organs to platelet production is controversial. In this study, serial histologic sections of bone marrow, spleen, liver, and lung from normal C57BL/6J mice and mice that had received three different agents which perturb normal murine thrombopoiesis (platelet antiserum, 5-fluorouracil, and radioactive strontium) were examined for the presence of megakaryocytes, utilizing morphologic and immunohistochemical techniques for their identification. In liver and lung tissue, megakaryocytes (including their naked nuclei or large cytoplasmic fragments) were rare in whole cross-sections (which included blood vessels) from normal and perturbed mice, even during periods of strong stimulation of thrombopoiesis. In contrast, megakaryocyte numbers were greatly increased in bone marrow and/or spleen tissue in these circumstances. We conclude that: 1) the bone marrow and spleen are the major thrombopoietic organs in the mouse, and 2) an insignificant fraction of thrombocytopoiesis occurs in the murine liver or lung, even during periods of greatly increased platelet production or following loss of the spleen and/or bone marrow.