Charakterisierung zellulärer Mechanismen zur Etablierung einer effektiven antiviralen Immunität gegen eine Hepatitis B Infektion

Neuesten Schätzungen zufolge gibt es weltweit über 240 Millionen Menschen, welche unter einer chronischen Infektion mit dem Hepatitis B Virus leiden. Es kommt zu einer nicht ausreichenden antiviralen Immunantwort und induziert somit eine Immuntoleranz gegen HBV-spezifische Antigene mit dem klinischen Bild einer chronischen Hepatitis. Diese Patienten bergen ein erhöhtes Risiko für die Entwicklung einer Leberzirrhose und des hepatozellulären Karzinoms. Obwohl eine gut verträgliche prophylaktische HBV-Impfung zur Verfügung steht, gibt es jedoch kaum eine vollständige klinische Ausheilung chronisch HBV-infizierter Patienten. In dieser Arbeit wurde die Rolle von regulatorischen T Zellen (TREG Zellen) während einer persistenten AdHBV-Infektion in der Maus untersucht, welches als Modellsystem der chronischen HBV-Infektion des Menschen dient. Es konnte gezeigt werden, dass TREG Zellen HBV-spezifische B Zellen unterdrücken und die Etablierung einer humoralen Immunantwort verhindern. Werden TREG Zellen depletiert, so können B Zellen eine partielle Immunität gegen HBsAg induzieren. B Zellen sind dann in der Lage anti-HBs Antikörper zu produzieren und führen somit zu einer HBs-spezifischen Serokonversion. Weiterhin ermöglichen B Zellen die Expansion von HBs-spezifischen CD8+ T Zellen, welche nach Differenzierung in CTL und folgender Aktivierung der Effektorfunktionen die Anzahl HBV-infizierter Hepatozyten reduzieren. Dies konnte sowohl im zeitkinetischen Verlauf HBV-spezifischer Serumparameter als auch mittels immunhistochemischer Analyse des Leberparenchyms gezeigt werden. Diese B Zell-vermittelte partielle HBs-spezifische Immunität konnte jedoch weder eine Expansion klärender HBc-spezifischer CTL noch eine vollständige Eliminierung HBV-infizierter Hepatozyten induzieren. Insgesamt zeigen die Ergebnisse erstmals, dass TREG Zellen die Etablierung einer HBs-spezifischen adaptiven T Zell-Antwort in einer B Zell-anhängigen Art supprimieren. Darüber hinaus deuten die Ergebnisse auf die Existenz mindestens einer weiteren Zellpopulation, welche eine klärende und robuste HBc-spezifische T Zell-Antwort inhibiert und zudem unabhängig vom Mechanismus der TREG Zell-vermittelten Inhibition zu agieren scheint. Im Hinblick auf moderne therapeutische Strategien ermöglichen diese Erkenntnisse einen neuen Ansatz zur Optimierung der antiviralen Behandlung chronisch HBV-infizierter Patienten.Characterisation of cellular mechanisms for the establishment of an effective antiviral immunity against Hepatitis B infection According to the latest estimations, worldwide there are over 240 million people that suffer from a chronic infection with the Hepatitis B Virus. An insufficient antiviral immune response is mounted and induces thereby an immune tolerance against HBV-specific antigens with the clinical picture of chronic hepatitis. These patients display an increased risk for the development of liver-cirrhosis and hepatocellular carcinoma. Although a well-tolerated prophylactic vaccination against HBV is readily available, there is only rarely a complete clinical recovery of chronically HBV-infected patients. In this study, the role of regulatory T cells (TREG cells) during a persistent AdHBV-infection in mice was analysed, which serves as a model system of chronic HBV-Infection in humans. It could be shown that TREG cells suppress HBV-specific B cells and inhibit the establishment of a humoral immune response. When TREG cells are depleted, B cells are able to induce a partial immunity against HBsAg. B cells are capable of producing neutralising anti-HBs antibodies and thereby induce an HBs-specific seroconversion. Further, B cells enable the expansion of HBs-specific CD8+ T cells, which reduce the number of HBV-infected hepatocytes upon their differentiation into CTL and consequent activation of their effector functions. This could be clearly seen in the time-kinetic analysis of HBV-specific serum parameters as well as in immunohistochemical analysis of liver tissue. This B cell-mediated partial immunity could, however, neither induce the expansion of HBc-specific CTL nor lead to a complete elimination of HBV-infected hepatocytes. Taken together, the presented results show for the first time that TREG cells suppress the establishment of an HBs-specific adaptive T cell response in a B cell-dependent manner. Furthermore, the results indicate the existence of at least another cell population, which inhibits an effective and robust HBc-specific T cell response and additionally seems to act independently of the mechanism of a TREG cell-mediated inhibition. In the context of modern therapeutic strategies, these findings facilitate a new approach for optimising current antiviral treatments for chronically HBV-infected patients

Vascular CXCR4 Limits Atherosclerosis by Maintaining Arterial Integrity Evidence From Mouse and Human Studies

BACKGROUND: The CXCL12/CXCR4 chemokine ligand/receptor axis controls (progenitor) cell homeostasis and trafficking. So far, an atheroprotective role of CXCL12/CXCR4 has only been implied through pharmacological intervention, in particular, because the somatic deletion of the CXCR4 gene in mice is embryonically lethal. Moreover, cell-specific effects of CXCR4 in the arterial wall and underlying mechanisms remain elusive, prompting us to investigate the relevance of CXCR4 in vascular cell types for atheroprotection. METHODS: We examined the role of vascular CXCR4 in atherosclerosis and plaque composition by inducing an endothelial cell (BmxCreERT2-driven)-specific or smooth muscle cell (SMC, SmmhcCreERT2-or TaglnCre-driven)-specific deficiency of CXCR4 in an apolipoprotein E-deficient mouse model. To identify underlying mechanisms for effects of CXCR4, we studied endothelial permeability, intravital leukocyte adhesion, involvement of the Akt/WNT/beta-catenin signaling pathway and relevant phosphatases in VE-cadherin expression and function, vascular tone in aortic rings, cholesterol efflux from macrophages, and expression of SMC phenotypic markers. Finally, we analyzed associations of common genetic variants at the CXCR4 locus with the risk for coronary heart disease, along with CXCR4 transcript expression in human atherosclerotic plaques. RESULTS: The cell-specific deletion of CXCR4 in arterial endothelial cells (n=1215) or SMCs (n=13-24) markedly increased atherosclerotic lesion formation in hyperlipidemic mice. Endothelial barrier function was promoted by CXCL12/\CXCR4, which triggered Akt/WNT/beta-catenin signaling to drive VE-cadherin expression and stabilized junctional VE-cadherin complexes through associated phosphatases. Conversely, endothelial CXCR4 deficiency caused arterial leakage and inflammatory leukocyte recruitment during atherogenesis. In arterial SMCs, CXCR4 sustained normal vascular reactivity and contractile responses, whereas CXCR4 deficiency favored a synthetic phenotype, the occurrence of macrophage-like SMCs in the lesions, and impaired cholesterol efflux. Regression analyses in humans (n=259 796) identified the C-allele at rs2322864 within the CXCR4 locus to be associated with increased risk for coronary heart disease. In line, C/C risk genotype carriers showed reduced CXCR4 expression in carotid artery plaques (n=188), which was furthermore associated with symptomatic disease. CONCLUSIONS: Our data clearly establish that vascular CXCR4 limits atherosclerosis by maintaining arterial integrity, preserving endothelial barrier function, and a normal contractile SMC phenotype. Enhancing these beneficial functions of arterial CXCR4 by selective modulators might open novel therapeutic options in atherosclerosis