The Results Of The T Regulatory Cells In The Mechanisms In The Pathogenesis Of Aplastic Anemia

Aplastic Anemia (AA) is a heterogeneous disease characterized by failure of bone marrow hematopoiesis resulting in varying degrees of pancytopenia with a markedly hypocellular bone marrow. Clinically, patients with AA may present with anemia, bleeding and serious infection. Despeite the exacts causes of AA are unknown, the disease may result from the accumulated effects of multiple noxious exposures of plurpotential stem cells. Potential mechanisms responsible for acquired AA include induced defects in heatopoietic stem cells, failure of the bone marrow microenvironment which impaired production or release of hematopoietic growth factors, and cellular or humoral immune suppression of the marrow. The introduction of immunosuppression therapies such as antithymocyte globulin, and cyclosporine A in the treatment of AA has improved the prognosis. Almost 70ï¼…patients recovered following immunosuppression therapy suggest that immunosuppression may be the most important mechanism. T lymphocyte mediated suppression has been considered the most important in the development of AA. Further study T cells, especially abnormal activated T cells, were not only a useful marker to understand the pathegenesis of AA, but may have great implication on clinical application.Over the past few years, a variety of T-cell subsets that can inhibit T-cell responses in vitro and in vivo and can prevent and ameliorate disease in several animal models of autoimmunity have been described. These cells have been named T regulatory (T-regs)cells. There are two main categories of T-regs cells-one emerging from the thymus as a population already planned to suppress the response against self antigens (natural T-regs cells), and another population which also emerges from the thymus, but acquires its suppressive activity in the periphery and is devoted to regulationg the response not only against self but also against nonself antigens(adaptive T-regs cells), and both natural and adaptive Treg cells are antigen-specific, but they exert their regulatory activity in a non-specific way, which may be based on cell-to-cell contact or on the release of suppressive cytokines.Some surface molecules have been reported to be responsible for the contact-mediated Suppressive activity(CTLA-4,membrane YGF-β), but so far there is no general consensus on one mechanism being consistently involved. One of the most important populations of either natural or adaptive Treg cells is characterized by the surface expression of the IL-2 receptorαchain, CD25.It is possible, however, that the reduced production of IL-12 and IFN-Tmay favor the synthesis of IL-4,which at least in humans, has been found o be more active than IL-10 as a suppressive cytokine.Finally, although it has been postulated that under some conditions dendritic cell stimulation may directly result in activation of Treg instead of effector T-cell responses.If exclude T-regs cells or the deficit of T-regs cells effector, it may result autoimmune disease. So we try to establish the model of aplastic anemia in vitro, we want to research the results of the T regulatory cells in the mechanisms in the pathogenesis of Aplastic Anemia. Then we can find the new way of immunesuppressive therapy to cure the aplitic anemia.Objective To establish a mouse model of immune-mediated marrow failure for the study the effects of T regulatory cells in pathogenesis Of Aplastic Anemia and the role of mesenchymal stem cells infusion in reconstitution of hemopoiesis of AA mouse was also investigated.Methods Male B6 (C57BL/6) mouse and female BALB/cBy mouse were used at the ages of 6-16weeks, then hybrid the cBy/B₆F₁ mouse. We use the lymphocyte from the (B6) to establish the model of AA.Use the cytometry analysis to determine the expression of the T-regs. The femurs and humeri of human fetuses were removed and washed twice, culture human mesenchymal stem cells, then mesenchymal stem cells were injected into the cBy/B₆F₁ that have already proved aplatstic anemia through lateral tail veins. We want to study the support of the hemapoiesis and the change of the T-regs.Results Infusion of B6 LN cells into the cBy/B₆F₁ receipients induced BM failure. Development of pancytopenia and marrow failure was cell dose-dependent, the lymphocytes is at 10-40×10⁶ cells/mouse, mostly of them may become pancytopenia. Through the BM cytomorphology scopy and the pathologic biopsy, it may prove the cBy/B₆F₁ mice becoming Aplastic Anemia, then we take the periphery blood to Flow cytometry analysis, we find the notable change in the CD4⁺CD25⁺, CD8⁺CD28^- regulatory T cells, and the progress in the expression of the CD103,CD62L,CD152,GITR.Remove the fermus and humeri from the 12-16 weeks old human fetuses, and rinse the BM cells repeatly, then a few MSC like cells were detected in fetal BM cells of initial culture. When the culture time is increased, it may appear fibroblast-like. The second-passage cells present homogeneous population of spindle fibroblast-like cells. Flow cytometry analysis showed these cells express CD29,CD44,CD49E,low express CD106,CD54,CD11b,and didn't express hematopoietic lineage markers such as CD34.Passage the mesenchymal cells for 4-6, singe to the aplastic anemia cBy/B₆F₁ mice, we find the partly recover of the hemapoiesis, and the progress in the Regulatory T cells. Then we see the spleen,liver,gastrine,we didn't find the acute GVHD.Conclusion In the mode of Aplastic Anemia, we find the reduction of CD4⁺CD25⁺,CD8⁺CD28^-,and the progress of the CD8⁺CD28⁺,the different degree reduction of CD8⁺CD25⁺,CD4⁺CD28⁺,CD4⁺CD152⁺,CD8⁺CD152⁺,CD4⁺CD103⁺,CD8⁺CD103⁺,CD4⁺GITR.But we also find the progress of the CD4⁺CD62L⁺,CD8⁺CD62L⁺.It may relate the decrease of the regulatory T cells, the decrease of the T-regs may impair the suppression of the autoimmune reactivity. In the patients of Aplastic Anemia, the activation of T cells play the key role. T cells selectively home to the BM tissues and proliferate before the pathogens, when the active T cells home to the BM,they will harm to the stem cells or the progenitor cells, then BM failure. The abnormally progress of th CD62L let the active T cells homing to the BM, then induct the immune response to the BM. And the breakdown of the regulatory T cells, may let the reduction of the immunesuppressing to the auto antigen. And the MSC from the human fetal can improve the hematopoiesis.Then it prove that MSCs can enhance hematopoietic engraftment.The regulatory T cells may have notable improvement after the signement of the MSCs.We can conclude MSCs may influent the regulatory T cells, enhance the T-regs,then induce the immune tolerance.