Untersuchung der immunstimulatorischen Eigenschaften des Phospholipids Cardiolipin

The aim of this research was the investigation of the immunostimulatory properties of the phospholipid cardiolipin. Cardiolipin meets the criteria of a PAMP and is a component of LDL particles, which are recognized by receptors of the innate immune system as a result of oxidative modification. Previous publications suggest that cardiolipin acts immunogenic. In stimulation experiments, it could initially be detected that cardiolipin is able to induce IL-6 response in human monocytes; however, this induction depends on the co-incubation with platelet and DOTAP. As previous experiments by our Research Group have shown that platelets cause co-stimulation of monocytes through the ERK pathway, this study investigated the mechanism by which DOTAP influences the stimulation of monocytes via cardiolipin. By replacing DOTAP with complex-forming substances, it could not be proven that DOTAP is needed for cardiolipin uptake. Results of kinetic analyses also indicated that DOTAP does not mediate the uptake of cardiolipin into monocytes, as fluorescencent dye helped to detect that cardiolipin independently enters the cells. The fluorescent staining also allowed the observation that cardiolipin forms particulate structures within the monocytes. Further studies are needed to show in which cellular compartment cardiolipin localizes after entering the cells. Microscopical examination further demonstrated that platelets also take up cardiolipin. Thus, it was shown that cardiolipin passively enters the cell. The fluorescent staining revealed that the platelets attach to the monocytes during the stimulation, therefore it could be seen that platelets contribute to the activation of monocytes by directly interacting with them. Furthermore, Western blot was used to examine whether DOTAP exerts its effect by inducing a co-stimulatory signalling cascade. Indeed it could be shown that DOTAP induces the ERK pathway, without giving evidence to activate monocytes through this mechanism. Further investigation into how the MAP kinase pathways influence each other must seek to clarify the intracellular processes which lie behind the cytokine production after stimulation with cardiolipin. Parallel to these examinations, it was investigated whether exogenous cardiolipin is recognized by the inflammasome. This could be demonstrated in the case of co-stimulation with DOTAP and platelets. However, the role of DOTAP could not be fully understood in the context of this work. It is possible that it stabilizes cardiolipin within the cytosol, allowing it to be detected there by Nlrp3-inflammasome.