Abnormal splenic megakaryopoiesis in MPSV-induced myeloproliferative disease.

The myeloproliferative sarcoma virus (MPSV) induces a murine myeloproliferative syndrome characterized by an erythromyelemia, an anemia, a thrombocytopenia associated with a myeloproliferation in the spleen and a splenic and medullar fibrosis. We have used the in-vitro plasma clot technique to measure megakaryocytic precursors in the spleen and bone-marrow of MPSV-infected mice. We report that megakaryocytic colonies are increased, in number (X75), in concentration (X9) and in size, in the spleen but not in the bone-marrow of neoplastic mice. Furthermore, these splenic precursors are hypersensitive to growth factors present in the anemic mouse serum used in the culture system. These data show that the thrombocytopenia observed in the MPSV-induced neoplasia does not result from a lack of megakaryocyte precursors, but rather from an excess of megakaryocyte destruction. This ineffective splenic megakaryopoiesis associated with the presence of a massive splenic fibrosis make the MPS-induced neoplasia a suitable model for studying the perturbation of megakaryopoiesis in myeloproliferative syndrome associated with fibrosis.