Macrocytic megakaryocytes in cultures of S1/S1d bone marrow.

The thrombocytopoietic system of S1/S1d mice is characterized by macromegakaryocytosis and megakaryocytopenia, but the mechanisms responsible for reciprocal abnormalities of megakaryocyte number and size are unknown. These mice have a genetically determined abnormality of their hemopoietic microenvironment that can, in part, be reproduced as abnormal adherent stromal cells in bone marrow cultures. Cultures of bone marrow were therefore done to determine if the megakaryocytic abnormalities of S1/S1d marrow would also be reproduced in them. Cultures composed entirely of S1/S1d cells showed persistent macrocytosis of megakaryocytes when compared with cultures of normal +/+ marrow. At various times of culture, there were also reduced numbers of megakaryocytes, total cells, and granulocytes in the supernatants of S1/S1d cultures. Mixed cultures of S1/S1d and +/+ cells yielded inconclusive findings. The fact that macromegakaryocytosis occurred in cultures of S1/S1d marrow strongly suggests that its in vivo determinants were, in part, reproduced in culture.