| Dendritic cells (DCs) are the most potent antigen presenting cells (APCs). These cells can stimulate naive T lymphocytes very effectively due to their robust expression of co-stimulatory molecules and potent immunostimulatory cytokines. DCs exist in two different stages: immature and mature. Depending on their different states, DCs possess different functional properties. In the steady state, immature DCs (iDCs) take up proteins from dying cells undergoing normal cell turnover. In the absence of inflammatory signals these iDCs expressing low amounts of co-stimulatory molecules migrate to the draining lymph nodes and induce anergic, apoptotic, or regulatory T cells. During an infection, iDCs take up antigens in the context of inflammatory signals, which cause activation and functional transformation into mature DC. Therefore, mature DCs enter the lymphoid tissues, prime naive or resting T cells and induce the development of effector T cell responses. In conclusion, the functional properties of DC are mainly dependent on their status of maturation and activation; accordingly subsets of iDC induce and maintain peripheral tolerance whereas terminal differentiated mature DCs efficiently induce the development of effector T cells.However, the mature process is often disturbed by other factors, like gene defects and transplantation, which could induce autoimmune diseases and graft versus host disease (GVHD). In systemic lupus erythematosus (SLE) it has been reported that DCs are chronically activated via IFN-α; in a murine model, inactivation of host DCs was associated with a significant reduction in acute GVHD. So controlling the states of DC may be an effective therapy for these diseases.Mesenchymal stem cells (MSCs) are highly attractive candidates for clinic therapy because they exhibit potent regulatory function. Current studies have found that MSCs can suppress the activation of CD8+ cytotoxic T lymphocytes (CTLs) and nature killer (NK) cells; they also inhibit T lymphocyte proliferation induced by cellular or nonspecific mitogenic stimuli. Although MSCs can perform a direct immunosuppressive effect on many other immune cells in vitro, it is unclear whether they also modulate the immune system by acting on the very first step of immune response ----- the maturation of DC.This study was divided into two parts which investigated how the in vitro maturation process of DCs was affected by murine and human MSCs respectively. In the first part, murine iDCs were first generated by culturing bone marrow (BM) cells in the presence of mGM-CSF and mIL-4 for 5 days, followed by adding LPS for another 4 days with (Coculture) or without (Control) mouse mesenchymal stem cell line, C3H10T1/2, coculture. Our data showed that Control became nonadherent and clustered, and displayed different protruding veils, a typical morphology of mature DCs, while Coculture were round, scattered, lacking in veiled appearance. Also C3H10T1/2 cells coculture inhibited the expression of CD11c, MHC-Ⅱ, CD86 and CD40 on the surface of DCs. Moreover, the cell number of Coculture was less than that of Control, which implies the proliferation viability of DCs was also inhibited by C3H10T1/2 cells. Functionally, C3H10T1/2 cell treatment resulted in impairment of immunostimulation ability of spleenocyte proliferation by DCs, correlating well with reduction of IFN-γand IL-10 secretion.In the second part, human placenta derived MSCs (PMSCs) were isolated and identified firstly, followed by the investigation of the effects of human PMSCs on the maturation of monocyte derived DCs (mono-DCs) from both peripheral blood (PB) and umbilical cord blood (UCB). The placenta tissues were digested by collagenaseⅣand cultured. The adherent cells were collected and passaged. The morphology and phenotypes of the cultured cells were detected by inverted microscope and flow cytometry, which identified the cells we generated are MSCs. We also induced and generated mono-DCs by culturing the adherent cells from PB or UCB derived mononuclear cells in the presence of hGM-CSF and hIL-4 for 6 days. Then mono-DCs were cocultured with or without PMSCs. Our results showed that: in the presence of LPS, the expression of CD80, CD86, CD83 and CD40 on mono-DCs was effectively suppressed by the treatment of PMSCs while the CD14 expression was increased. Furthermore, in contrast to mature DCs, the stimulatory activity of PMSC-treated DCs was also impaired, which was similar to the result of first part.In summary, this study suggested that both murine and human MSCs could suppress DCs into mature state, which correlates with changes in morphology, phenotype, allostimulatory ability and cytokine secretion. These data may provide useful information to clarify the molecular mechanisms of the immunoregulatory activity of MSCs on the maturation of DCs both in vitro and in vivo, which will be clinical beneficial too.
|
PDF Full Text Request