The Role Of Immunological Factors In The Pathogenesis Of Aplastic Anemia

Aplastic Anemia(AA) is characterized by bone marrow failure and its exact cause is still unknow. Early studies demonstrate that lack of stem/progenitor cells was the main pathogenesis machanism and the culture of patients' bone marrow cells also indicated that hematopoietic stem cells(HSC) in patients' bone marrow decreased significantly. Recently, immunosuppression treatment of AA has improved the prognosis greatly and about 2/3 patients recovered following ATG/ALG and CyA treatment, which suggested that the disorder of immune system may play an important role in the development of AA.The activation of naive T cells is the key link of immune response, and this process requires two signals. The first signal is the binding of TCR and MHC-Ag compound and the co-stimulatory signal acts as the second signal. After being activated, excessive activated T cells are cleared by the way of AICD, which plays an important part in maintaining the organic balance. AICD of activated T cells can also avoid auto-damage that excessive activated T cells made to self target organs. As an important apoptosis inhibitor protein, FLIP also engages in the control of AICD. Recent researches suggested that abnormal expression of co-stimulatory molecules and FLIP participated in the development of many autoimmune diseases. Whether there is abnormal expression of co-stimulatory molecules and FLIP in the patients with AA and what the relationship is between them are unknown. Also there is few study aimed at this aspect.1. The levels of soluble CD40L in peripheral blood and bonemarrow of patients with aplastic anemia decreased significantlyPeripheral blood(PB) and bone marrow level of soluble CD40L in 40 AA patients and 20 normal controls was detected by enzyme linked immunosorbent assay(ELISA); Lymphocyte phenotype was analyzed by immunofluorescence and flow cytometry. The results show that the levels of sCD40L in peripheral blood and bone marrow are both decreased significantly(p<0.001); the sCD40L level of AA is related to the count of peripheral WBC and platelet; the percentage of CD4+Tcells decreased and the ratio of CD4/CD8 decreased. These results indicate that the decreased level of sCD40L may be the potential reason of AA, detection of peripheral blood and bone marrow may be helpful for the diagnosis of AA and the application of CD40L will probably be an new method for the therapy of AA.2. sCD40L can facilitate ex vivo colony forming of umbilical cord blood CD34+ cells The influence of sCD40L and sCD40L with other hematopoietic growth factors(HGFs) to the colony forming was detected by ex vivo colony forming test of umbilical cord blood CD34+ cells. The result demonstrated that: sCD40L alone has no effect to facilitate colony forming of CD34+ stem cells; . when SCF+IL-3+EPO+GM-CSF were used, the quantity and morphology of colony were both small; but when sCD40L combined with these HGFs, sCD40L can reinforced the colony forming effect of these HGFs. The result suggested that sCD40L has synergistic effect with these HGFs. Combined sCD40L with other HGFs may have better clinical application for hematopoiesis recovery in AA.3. CD28 expressed abnormally in different T cell subset in patients with aplastic anemia We use two colors immuno flourescence and flow cytometry to analyze the proportion of CD4+CD28- andCD8+CD28-T cells in patients with AA before and after treatment with CyA, the change of CD28 expression after culture with CyA was also analyzed. The results demonstrated that the expression of CD28 on CD8+T cells decreased significantly(p<0.01). After effective treatment with CyA the CD28 expression increased greatly (p<0.01 ) ; The proportion of CD8+CD28-T cells is parallel inversely to the ANC. In addition, 48 hours after culture with CyA in vitro the proprtion of CD8+CD28-T cells also decreased significantly(p<0.01). What we can induce from the results is that there is an oligoclonal CTLs which proliferate at the stimulation of specific antigen and this subset T cells...