Entzündungshemmende Effekte von ionisierender Strahlung, untersucht in Co-Kultur Systemen humaner Endothelzellen und Leukozyten

The treatment of chronic inflammatory diseases such as ankylosing spondylitis with low doses of ionizing radiation (α-rays, photons) is used successfully for several decades. However, the molecular and cellular mechanisms that underlie this effect are not understood. The aim of this study was to investigate inflammation-related inhibitory effects of ionizing radiation on the cellular and molecular level. Since the local dose deposition of densely-ionizing radiation is not homogeneous, sparsely and densely ionizing radiation were compared especially in the low-dose range (0,1-1Gy). For this purpose X-ray or accelerated ions were used for the experiments presented in the frame of this thesis. For the performed experiments various cell types were used, which are involved in inflammatory processes and could therefore potentially be involved in the anti-inflammatory effects. Therefore vascular endothelial cells and cells of the immune system (lymphocytes, monocytes and macrophages) were investigated regarding the following biological endpoints: induction of apoptosis, phagocytic activity of macrophages in co-culture with apoptotic lymphocytes, adhesion of lymphocytes to endothelial cells and the release of cytokines in vascular and immune cells. The induction of apoptosis was investigated in connection with a possible anti-inflammatory effect of apoptotic cells on phagocytes. Inflammatory processes are partially regulated by the adhesion of immune cells to the endothelial cell layer of blood vessels followed by the transmigration into the tissue. This process is a potential indicator of anti-inflammatory effects of low-dose irradiation. The studies presented here were mainly carried out in human primary cells. Their differentiation into functional cells in vitro was partially established during this thesis. In order to adapt as close as possible to the situation in vivo, two different co-culture systems were established and an experimental system to mimic the blood flow were developed. Preliminary experiments for the examination of effects related to the radon exposure were performed with blood samples of patients which received a radon therapy. The results of the present work confirmed that peripheral blood lymphocytes proved to be particularly radiosensitive, both for sparsely-and densely-ionizing radiation. Therefore a clear dose dependent increase of apoptosis could be detected in lymphocytes even after low dose irradiation. Neither endothelial cells nor macrophages showed a significant induction of apoptosis after irradiation. In blood cells of patients which received a radon therapy a trend to increased levels of apoptotic lymphocytes after multiple radon treatments was observed. However, this increase was not statistical significant. In co-culture experiments with primary cells, it could be demonstrated that the induction of apoptosis in lymphocytes by ionizing radiation affects the phagocytic activity of macrophages, in particular of the M-CSF subtype which plays a role in anti-inflammatory processes. An increase in phagocytic activity was clearly detectable after irradiation of lymphocytes with X-rays or carbon ions. Thereby the increase was dependent on the dose and thus on the number of apoptotic cells. It could not be clarified whether the increase in phagocytic activity in the co-culture causes an altered release of inflammatory cytokines, as it is discussed regarding the regulation of inflammatory processes. The release of the cytokines TNF-α and TGF-β was only poorly affected by irradiation, whereas for the release of IL-10 in the primary cells significant variations between individual donors were observed. In the monocultures of different cell types (lymphocytes, monocytes, macrophages and endothelial cells) no radiation-induced changes concerning the release of TNF-α, TGF-β and IL-10 were observed. Furthermore the radiation induced changes in cytokine release were investigated in vivo. Therefore additional factors were examined in blood plasma of radon therapy patients, but as well no significant changes were observed even after multiple radon treatments. Radiation-induced changes in adhesion of lymphocytes to endothelial cells, which were stimulated by a pro-inflammatory cytokine (TNF-α), were investigated in this study under static conditions. No response to irradiation was seen in pulmonary endothelial cells from the aorta. However, in microvascular endothelial cells from skin, a significant reduction of adhesion was observed after irradiation. This reduction occurred, however, both at low and at high doses. The experiments to alter the adhesion under dynamic conditions confirmed the results of the static adhesion assay, the inhibition was even stronger compared to the static assay. Furthermore the performed experiments have shown that TGF-β plays an essential role in the process of radiation-induced reduction of lymphocyte adhesion to endothelial cells. Taken together the obtained results indicate a specific contribution of the microvasculature to a radiation induced inhibition of an existing inflammation, which was observed both for sparsely-and densely-ionizing radiation. However, in the in vitro systems this could not be proved as a specific low-dose effect