Enhanced cross-presentation and improved CD8+ T cell responses after mannosylation of synthetic long peptides in mice

The use of synthetic long peptides (SLP) has been proven to be a promising approach to induce adaptive immune responses in vaccination strategies. Here, we analyzed whether the efficiency to activate cytotoxic T cells by SLP-based vaccinations can be increased by conjugating SLPs to mannose residues. We could demonstrate that mannosylation of SLPs results in increased internalization by the mannose receptor (MR) on murine antigen-presenting cells. MR-mediated internalization targeted the mannosylated SLPs into early endosomes, from where they were cross-presented very efficiently compared to non-mannosylated SLPs. The influence of SLP mannosylation was specific for cross-presentation, as no influence on MHC II-restricted presentation was observed. Additionally, we showed that vaccination of mice with mannosylated SLPs containing epitopes from either ovalbumin or HPV E7 resulted in enhanced proliferation and activation of antigen-specific CD8⁺ T cells. These findings demonstrate that mannosylation of SLPs augments the induction of a cytotoxic T cell response in vitro and in vivo and might be a promising approach to induce cytotoxic T cell responses in e.g. cancer therapy and anti-viral immunity.

Cross-presentation: how to get there - or how to get the ER

Antigen cross-presentation enables dendritic cells (DCs) to present extracellular antigens on major histocompatibility complex (MHC) I molecules, a process that plays an important role in the induction of immune responses against viruses and tumors and in the induction of peripheral tolerance. In order to allow intracellular processing for cross-presentation, internalized antigens are targeted by distinct endocytic receptors toward specific endosomal compartments, where they are protected from rapid lysosomal degradation. From these compartments, antigens are processed for loading onto MHC I molecules. Such processing generally includes antigen transport into the cytoplasm, a process that is regulated by members of the ER-associated degradation (ERAD) machinery. After proteasomal degradation in the cytoplasm, antigen-derived peptides have been shown to be re-imported into the same endosomal compartment by endosomal transporter associated with antigen processing, another ER protein, which is recruited toward the endosomes after DC maturation. In our review, we highlight the recent advances on the molecular mechanisms of cross-presentation. We focus on the necessity of such antigen storage compartments and point out important parallels to MHC I-restricted presentation of endogenous antigens. We discuss the composition of such endosomes and the targeting of extracellular antigens into this compartment by specific endocytic receptors. Finally, we highlight recent advances on the recruitment of the cross-presentation machinery, like the members of the MHC I loading complex and the ERAD machinery, from the ER toward these storage compartments, a process that can be induced by antigen encounter or by activation of the dendritic cell after contact with endotoxins.

Alcoholic liver disease associated with increased gamma-glutamyltransferase activities in serum and liver

Chronic alcohol consumption leads to increased activities of gamma-glutamyltransferase (GGT) in the serum which are associated with an enhancement of GGT activities in the liver. These findings suggest that increased GGT activities commonly found in alcoholic liver disease can be ascribed primarily to hepatic enzyme induction rather than to liver cell injury, since hepatic GGT activities were increased but not reduced. Moreover, at the fatty liver stage the fetal form of GGT in the serum is much higher in activity that the adult form, whereas the reverse constellation can be found in patients with alcoholic liver cirrhosis. Thus, these preliminary data suggest that the determination of various forms of GGT in the serum of alcoholics may be useful in establishing the particular stage of alcoholic liver disease by a simple enzyme test in the serum.

[Clinical aspects of alcohol induced liver injury (author's transl)]

Chronic alcohol consumption results in early biochemical and ultrastructural alterations of the hepatocyte which in turn may lead to alcoholic fatty liver as well as alcoholic hepatitis and via the central hyaline sclerosis to fibrosis and cirrhosis of the liver. Already at the stage of the alcoholic fatty liver an isolated increase of serum gamma-glutamyltransferase activity can often be observed; it results from hepatic microsomal enzyme induction and may facilitate early recognition of alcoholic liver injury. To establish the diagnosis, however, a histological examination of the liver is necessary. The therapy of alcohol-induced liver injury is based upon an absolute alcohol abstinence since alcohol itself or one of its metabolites are hepatotoxic.