Parasecretion of the hematopoietic cytokines is considered as one of the mechanisms account for bone marrow hematopoiesis disorder. In this study, the level of IL-6 secreted by bone marrow stromal cells from a mouse model of aplastic anemia was analyzed. The aplastic anemia mouse model was established with cyclophosphamide in combination with chloramphenicol and 60Coγ radiation. The impairment of bone marrow hematopoiesis induced by irradiation and chemotherapeutic drugs was subsequently characterized by peripheral blood cell count, pathomorphological changes, and apoptosis rate. Furthermore, the in vitro proliferation of bone marrow stromal cells (BMSC) and the IL-6 secretion levels of BMSC were analyzed. In our model of aplastic anemia, the number of peripheral blood cells and bone marrow cells (BMC) were notably decreased, and the apoptosis rate of BMC increased. Furthermore, the proliferation of BMSC was obviously impeded while the IL-6 secretion levels of BMSC significantly increased. The findings of our study suggested that the IL-6 secretion level may be enhanced to some extent by the induction of aplastic anemia caused by irradiation and chemotherapeutic drugs and that the abnormal level of IL-6 might probably interfere with the stability of the bone marrow hematopoietic microenvironment. 1. Introduction Bone marrow is the major hematopoietic organ. Bone marrow hematopoietic tissues are highly sensitive to toxins, including radiation and chemotherapeutics, which may induce myelosuppression. The cytoactivities of primitive hematopoietic cells may, therefore, be depressed, and the number of peripheral blood cells may decrease substantially. In addition, severe myelosuppression may cause infections, inflammation, and bleeding [1, 2]. It is generally accepted that maintenance of normal hematopoiesis relies on the stabilization of the hematopoietic microenvironment. As the major component of this microenvironment, hematopoietic cytokines play a key role in the regulation of hematopoiesis, controlling the proliferation, differentiation, and maturation of primitive hematopoietic cells [3, 4]. IL-6 is a kind of cytokine with a wide range of biological activities, produced mainly by T and B lymphocytes, monocytes, fibroblasts, and so forth [5, 6]. Recent studies showed that IL-6 involved not only in the progress of the stress reaction, autoimmune, and neoplastic diseases of the body but also in regulation of the proliferation and differentiation of primitive hematopoietic cells, and it is considered as a permissive factor of primitive hematopoiesis [7].
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