Browsing by Subject "Phagocytosis"

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Dietary L-carnitine affects leukocyte count and function in dairy cows around parturition
(2022) Kononov, Susanne Ursula; Meyer, Jennifer; Frahm, Jana; Kersten, Susanne; Kluess, Jeannette; Bühler, Susanne; Wegerich, Anja; Rehage, Jürgen; Meyer, Ulrich; Huber, Korinna; Dänicke, Sven
In early lactation, an energy deficit leading to a negative energy balance (NEB) is associated with increased susceptibility to disease and has been shown to be an important factor during transition in dairy cows. L-carnitine as a key factor in the mitochondrial transport of fatty acids and subsequently for β-oxidation and energy release is known to modulate mitochondrial biogenesis and thus influence metabolism and immune system. In the current study, we characterized hematological changes around parturition and investigated the potential effects of dietary L-carnitine supplementation on immune cell functions. For this approach, dairy cows were assigned either to a control (CON, n = 30) or an L-carnitine group [CAR, n = 29, 25 g rumen-protected L-carnitine per cow and day (d)]. Blood samples were taken from d 42 ante partum (ap) until d 110 post-partum (pp), with special focus and frequent sampling from 0.5 to72 h post-calving to clarify the impact of L-carnitine supplementation on leukocyte count, formation of reactive oxygen species (ROS) in polymorphonuclear cells (PMN) and peripheral mononuclear cells (PBMC) and their phagocytosis activity. Blood cortisol concentration and the capacity of PBMC proliferation was also investigated. All populations of leukocytes were changed during the peripartal period, especially granulocytes showed a characteristic increase up to 4 h pp. L-carnitine supplementation resulted in increased levels of eosinophils which was particularly pronounced one day before to 4 h pp, indicating a possible enhanced support for tissue repair and recovery. Non-supplemented cows showed a higher phagocytic activity in PBMC as well as a higher phagocytic capacity of PMN during the most demanding period around parturition, which may relate to a decrease in plasma levels of non-esterified fatty acids reported previously. L-carnitine, on the other hand, led to an increased efficiency to form ROS in stimulated PMN. Finally, a short period around calving proved to be a sensitive period in which L-carnitine administration was effective.
Eliminierung apoptotischer Zellen durch professionelle Phagozyten: Generierung, Freisetzung und Erkennung des monozytären Attraktionssignals Lysophosphatidylcholin und Bedeutung von Annexin I als Brückenprotein in der phagozytotischen Synapse
(2007) Waibel, Michaela; Graeve, Lutz
The efficient elimination of apoptotic cells by neighbouring cells or professional phagocytes is essential for tissue homeostasis in multicellular organisms. Therefore, the apoptotic cell displays different so-called ?eat-me?-signals on its cell surface that are crucial for its recognition and engulfment. Especially in higher organisms, where the dying cell and the phagocyte are usually not located in immediate proximity, the release of soluble attraction signals is of special importance. Only recently, the phospholipid lysophosphatidylcholine (LPC) could be identified as a central ?find-me?-signal that is generated by the calcium-independent phospholipase A2 (iPLA2)-mediated hydrolysis of phosphatidylcholine. During apoptosis iPLA2 is processed in a caspase-3-dependent fashion. In the present thesis it could be demonstrated that iPLA2 is cleaved directly by caspase-3 and that this processing leads to its activation. The active iPLA2 is essential for the production of the phospholipid-?find-me?-signal LPC in apoptotic cells. However, the observation that overexpression of the active form of iPLA2 alone was not sufficient for the release of the attraction signal from vital cells implied that other apoptotic events might contribute to the generation and export of the ?find-me?-signal LPC. It turned out that the reactive oxygen species-driven oxidation of membrane lipids like phosphatidylcholine is an additional factor that leads to the enhanced production of LPC, probably because oxidized lipids are more susceptible for PLA2-mediated hydrolysis than non-oxidized lipids. Further studies about the detailed export mechanism of LPC revealed that the ATP-binding cassette transporter (ABC)-family member ABCA1 is essential for the release of the attraction signal during apoptosis. Thus, the oxidation of membrane lipids and the ABCA1-driven export of LPC could be identified as important elements of LPC-generation and its subsequent release during apoptosis. After the generation and the release of the attraction signal LPC could be demonstrated in more detail the consequent question arose which receptors might mediate the effects of LPC on the phagocytes. In the present thesis it could be demonstrated that the G-protein-coupled receptor G2A is responsible for the LPC-stimulated migration of monocytic cells. However, the molecular mechanisms that ultimately lead to the LPC-driven, G2A-mediated migration, are not known so far. Accordingly, a participation of other receptors or the existence of further chemotactic signals cannot be ruled out at this point. Moreover, there are some hints for chemotactically active proteins in literature. If these or other factors contribute to the LPC-mediated chemotaxis of monocytic cells is completely unknown and needs to be clarified in future studies. The recognition and internalization of dying cells is mediated by the interaction between different ?eat-me?-signals that are displayed on apoptotic cells, and specific surface receptors on phagocytes. In this scenario, the interaction can be of a direct nature ore rather indirect via bridging molecules. In this context, here it could be demonstrated that the calcium- and phospholipid-binding protein annexin I gets externalized by dying cells independently of the apoptotic stimulus applied, but dependent on the cell type. On the surface of the apoptotic cell, annexin I binds in a calcium-dependent fashion via its annexin-boxes to externalized phosphatidylserine, which represents a central ?eat-me?-signal. Thereby, annexin I is able to stimulate the elimination of these cells by professional phagocytes and thus fulfills the function of a bridging molecule in the phagocytic synapse. In contrast, the receptors that are responsible for the binding of annexin I to phagocytes are not known so far. As a conclusion it can be stated that the phenomena studied in this thesis represent important steps in the process of apoptotic cell elimination. The physiological relevance of apoptotic cell clearance is the fact that apoptosis, in contrast to necrotic cell death, is highly regulated at all stages and usually turns out without any harmful consequences to the organism. If this complex, multistep process is disturbed, non-cleared apoptotic cells can become a source for inflammatory reactions. In different animal models it could be demonstrated that defects in the attraction of phagocytes as well as deficiencies in the recognition and internalization via ?eat-me?-signals and the subsequent degradation of the apoptotic prey can be a reason for the onset of severe autoimmune disorders. In this context, the development of human systemic lupus erythematosus and of chronic arthritis is discussed to be initiated by the inefficient elimination of apoptotic cells.