THE RELATIONSHIP BETWEEN INCREASED EMPERIPOLESIS INDEX AND SEVERE HEMATOPOIETIC CELL HYPERPLASIA IN THE BONE MARROW OF LPS-TREATED RATS

To investigate the relationship between the frequency of megakaryocytic emperipolesis and the number of hematopoietic cells, the animals were administered lipopolysaccharide (LPS) intravenously at a daily dose of 0.5mg/kg body weight for up to 7 days, and histopathology of bone marrow and hematology of peripheral bloods were examined on Hour 2, 8, and 24 and Day 3, 5, and 7 of LPS-treatment. Mature neutrophils appeared to be the most common hematocytes engulfed by megakar-yocytes. Engulfed blood cells were observed in the demarcation membrane system of mature megakar-yocytes. Cell membranes of both megakaryocytes and entering cells were intact. Although megakar-yocytic emperipolesis was also found in control rats, its incidence increased markedly in LPS-treated rats which showed hyperplasia of granulocytes and megakaryocytes in their bone marrows. The index of emperipolesis showed a minimal change from 2.25 to 3.04 during the experimental period in control rats, whereas it rose from Hour 8 (9.78) and peaked on Day 3 (46.04) in LPS-treated rats. Hyperplasia of hematopoietic cells such as megakaryocytes and segmented neutrophils also peaked on Day 3 of LPS-treatment. These changes suggest that emperipolesis is a phenomenon closely related to severe hematopoietic hyperplasia in the bone marrow.