Emperipolesis of Hematopoietic Cells within Megakaryocytes in Bone Marrow of the Rat

Abstract

Abstract. Emperipolesis of hematopoietic cells within megakaryocytes was found in rats. The incidence was less than 0.3% in young rats (2 to 12 months old) but increased to 2-5% among the aging rats (1 8 to 24 months old). The incidence increased markedly in hyperplastic bone marrow secondary to chronic suppurative or neoplastic lesions. Mature neutrophils appeared to be the most common marrow cell engulfed by megakaryocytes. By light microscopy, engulfed cells were separated from megakaryocyte cytoplasm by a narrow pencellular space. By electron microscopy, marrow cells engulfed by megakaryocytes were located in the open canalicular system. Cell membranes of both engulfed cells and megakaryocytes were intact, and there was no fusion of cell membranes or phagosome formation in the megakaryocytes.Emperipolesis, a word of Greek derivation, was defined as "the active penetration of one cell by another which remains intact" by Humble et al.4 It differs from phagocytosis in that an engulfed cell only temporarily exists within another cell and remains viable with intact normal structure. Emperipolesis has been recognized in association with human lymphocyte^,^ tumor cells, Sternberg-Reed cells, and r n e g a k a r y~c y t e s .~~~~~~~ Recently, Chiu2 described briefly the light microscopic observation of megakaryocytes containing marrow cells in rats that had been used for toxicity or chemical carcinogenicity testing. Under experimental conditions, megakaryoblasts or leukemic blast cells containing blood cells were observed incidentally in bone marrow of rats with experimentally induced-myelogenous leukemia.6 Megakaryocytic emperipolesis was also observed in bone marrow of rats under experimentally induced-blood loss. l o Since little information is available about the diagnostic significance or ultrastructure of spontaneously occurring megakaryocytic emperipolesis in animals, ultrastructural observations of this phenomenon in the bone marrow of rats are described. Materials and Methods AnimalsIn addition to 435 male and 148 female rats (Crl : CDBR) from 2 to 12 months old, 456 male and 467 female rats between 18 and 24 months old were selected at random to study megakaryocytic emperipolesis. These rats were used in experiments to evaluate the safety of chemicals between 1980 and 1987 at Haskell Laboratory, but hematopoietic organs of these rats were not affected by any of the compounds tested. The rats were obtained from a commercial breeder (Charles River Breeding Laboratories, Wilmington, MA and Kingston, NY), were housed in suspended stainless steel cages, and were fed a basic diet of ground Purina Laboratory Chow (Ralston Purina Co., St. Louis, MO). Some rats also received 1% corn oil that was added as a vehicle in selected studies. Food and water were provided ad libitum in climate controlled rooms (23 ? 2 C, 50% f 20 relative humidity). Animal rooms were maintained on a timer-controlled, 12 hour light/l2 hour dark cycle. Tissue preparationAfter rats were killed by chloroform euthanasia, two sternebrae from each...

Emperipolesis – A Review

“…Emperipolesis is a hallmark feature of Rosai -Dorfman disease (RDD) also called Sinus Histiocytosis with Massive Lymphadenopathy (SHML) but can also be part of other malignant conditions such as hematolymphoid disorders (Hodgkin's disease, leukaemia, acute and chronic myeloid leukaemia, Non -Hodgkin's lymphoma, myeloproliferative disorders, myelodysplastic syndrome) and Non haematological malignancies (multiple myeloma, nueroblastoma, Rhabdomyosarcoma) [4,5].…”

Emperipolesis of marrow cells within megakaryocytes in the bone marrow of sublethally irradiated mice

“…In particular, it has been linked to various states of malignancy, such as Hodgkin's disease, multiple myeloma, chronic or acute myelocytic leukemia, neuroblastoma, rhabdomyosarcoma, and myeloproliferative disorders [5, 7, 10, 13-16, 19, 21, 22, 25]. In animal models it has been observed with experimentally induced myelogenous leukemia [11], chronic and acute blood loss [18,22,23], granulocytic or erythropoietic cell hyperplasia [11,13,14], and soft tissue tumors [16,19,21]. Recently, there has been a report on megakaryocytic emperipolesis observed in dogs about 1 year after total-body X-irradiation, suggesting that this phenomenon is a late effect of irradiation [6].…”

“…It differs from phagocytosis because the engulfed cell only temporarily exists within another cell, remains viable with its normal structure intact, and can ultimately exit, apparently unaltered by the engulfing cells [4,11]. The first report concerning emperipolesis within human megakaryocytes was documented by Larsen [10].…”

Increased and pathologic emperipolesis of neutrophils within megakaryocytes associated with marrow fibrosis in GATA-1low mice

“…The MK abnormalities observed in patients with IM also include increased emperipolesis of neutrophils within MKs. 19,20 The significance, however, of this observation is not clear, because emperipolesis of neutrophils within MKs increases in other stress-related conditions not necessarily associated with marrow fibrosis, such as recovery after sublethal irradiation, 21 aging, 22 and altered MK maturation associated with the gunmetal mutation. 23 The aim of this study is to define at the ultrastructural level the stage of MK maturation blocked by the GATA-1 low mutation and to clarify whether this block is associated with increased emperipolesis of neutrophils within the MKs.…”