Emperipolesis: Sternal and Femoral Microenvironment Induces Megakaryiocyte Emperipolesis in the Wistar Strain

Emperipolesis is considered a physiological phenomena often present in various pathophysiological conditions, but its etiology is still unknown. In this study, we analyzed the number of megakaryocytes and the percentage of emperipoletic cells in the sternal and femoral bone marrow of Wistar rats. Five types in the thrombopoiesis lineage (megakaryoblasts, promegakaryocytes and megakaryocytes - acidophilic, basophilic and thrombocytogenic) were determined. Except for basophilic megakaryocytes, significant differences were found for number of thrombopoietic cells in the sternal and femoral bone marrow. A larger number of thrombocytogenic megakaryocytes were present in the sternal bone marrow. Emperipoletic cells were significantly present in the femoral compared to the sternal bone marrow. Emperipolesis was typical for lymphocytes and neutrophils individually, while emperipolesis with two or more cells within thrombopoietic cell was also present (1-7 %) and significant differences between the sternal and femoral bone marrow were detected. Emperipolesis was found in all analysed rats and it most commonly occured within mature megakaryocytes and rarely megakaryoblasts, while it was not recorded in the promegakaryocytes. The high incidence of megakaryocytes with emperopolesis in rats could be a consequence of “normal” cell retention in the cytoplasm of megakaryocytes while passing blood cells to circulation or related to haematopoietic response due to high incidence of inbreeding.