Search

Previous studies that used peptide-MHC (pMHC) tetramers to identify self-specific T cells have questioned the effectiveness of thymic-negative selection. Here, we used pMHCI tetramers (tet) to enumerate CD8 T cells specific for the immunodominant gp33 epitope of lymphocytic choriomeningitis virus (LCMV) glycoprotein (GP) in mice transgenically engineered to express high levels of GP as a self-antigen in the thymus. In GP-transgenic mice (GP+), monoclonal P14 TCR+ CD8 T cells that express a GP-specific TCR could not be detected by gp33/Db -tet staining, indicative of their complete intrathymic deletion. By contrast, in the same GP+ mice, substantial numbers of polyclonal CD8 T cells identifiable by gp33/Db -tet were present. The gp33-tet staining profiles of polyclonal T cells from GP+ and GP-negative (GP-) mice were overlapping but mean fluorescence intensities were ∼15% lower in cells from GP+ mice. Remarkably, the gp33-tet+ T cells in GP+ mice failed to clonally expand after LCMV infection, whereas those of GP- mice did so. In Nur77GFP -reporter mice, dose-dependent responses to gp33 peptide-induced TCR stimulation revealed that gp33-tet+ T cells with high ligand sensitivity are lacking in GP+ mice. Hence, pMHCI tetramer staining identifies self-specific CD8 T cells but tends to overestimate the number of truly self-reactive cells.

Across the animal kingdom, multivalency discriminates antibodies from all other immunoglobulin superfamily members. The evolutionary forces conserving multivalency above other structural hallmarks of antibodies remain, however, incompletely defined.Here, we engineer monovalent either Fc-competent or -deficient antibody formats to investigate mechanisms of protection of neutralizing antibodies (nAbs) and non-neutralizing antibodies (nnAbs) in virus-infected mice. Antibody bivalency enables the tethering of virions to the infected cell surface, inhibits the release of virions in cell culture, and suppresses viral loads in vivo independently of Fc gamma receptor (Fc gamma R) interactions. In return, monovalent antibody formats either do not inhibit virion release and fail to protect in vivo or their protective efficacy is largely Fc gamma R dependent. Protection in mice correlates with virus-release-inhibiting activity of nAb and nnAb rather than with their neutralizing capacity.These observations provide mechanistic insights into the evolutionary conservation of antibody bivalency and help refining correlates of nnAb protection for vaccine development.

The free radical theory of aging proposes that ROS (reactive oxygen species) are major driving forces of aging, and are also critically involved in cellular senescence. Besides the mitochondrial respiratory chain, alternative sources of ROS have been described that might contribute to cellular senescence. Noxs (NADPH oxidases) are well-known sources of superoxide, which contribute to the antimicrobial capabilities of macrophages, a process involving the prototypical member of the family referred to as Nox2. However, in recent years non-phagocytic homologues of Nox2 have been identified that are involved in processes other than the host defence. Superoxide anions produced by these enzymes are believed to play a major role in signalling by MAPKs (mitogen-activated protein kinases) and stress-activated kinases, but could also contribute to cellular senescence, which is known to involve oxygen radicals. In HUVECs (human umbilical vein endothelial cells), Nox4 is predominantly expressed, but its role in replicative senescence of HUVECs remains to be elucidated. Using shRNA (small-hairpin RNA)-mediated knockdown of Nox4, implicating lentiviral vectors, we addressed the question of whether lifelong depletion of Nox4 in HUVECs would influence the senescent phenotype. We found a significant extension of the replicative lifespan of HUVECs upon knockdown of Nox4. Surprisingly, mean telomere length was significantly reduced in Nox4-depleted cells. Nox4 depletion had no discernable influence on the activity of MAPKs and stress-activated kinases, but reduced the degree of oxidative DNA damage. These results suggest that Nox4 activity increases oxidative damage in HUVECs, leading to loss of replicative potential, which is at least partly independent of telomere attrition.

Insulin-like growth factor (IGF) binding protein-3 (IGFBP-3) is an important regulator of cell proliferation and survival, which plays an important role in a variety of epithelial cancers, including prostate cancer, cervical cancer and breast cancer. IGFBP-3 was described as a tumor suppressor in the prostate and identified as a functional cellular target for the E7 oncoprotein of human papillomaviruses. IGFBP-3 interacts with IGF-I outside the cell; however, IGF-independent actions of IGFBP-3 were also described which are mediated by intracellular IGFBP-3, including nuclear IGFBP-3. The mechanisms by which extracellular proteins can reach the nucleus are still largely unknown. We show here that the addition of IGFBP-3 to living cells results in the rapid appearance of nuclear IGFBP-3 by confocal microscopy of IGFBP-3 uptake in live cells, supported by electron microscopy and cell fractionation studies. IGFBP-3 is internalized through a dynamin-dependent pathway, traffics through endocytic compartments and is finally delivered into the nucleus. We observed docking of IGFBP-3 containing structures to the nuclear envelope and found IGFBP-3 containing dot-like structures to permeate the nuclear envelope. In summary, our findings establish the pathway by which this tumor suppressor protein is delivered from extracellular space to the nucleus.

CD4+ Th cells deliver the cognate and cytokine signals that promote the production of protective virus-neutralizing IgG by specific B cells and are also able to mediate direct antiviral effector functions. To quantitatively and qualitatively analyze the antiviral functions of CD4+ Th cells, we generated transgenic mice (tg7) expressing an MHC class II (I-Ab)-restricted TCR specific for a peptide derived from the glycoprotein (G) of vesicular stomatitis virus (VSV). The elevated precursor frequency of naive VSV-specific Th cells in tg7 mice led to a markedly accelerated and enhanced class switching to virus-neutralizing IgG after immunization with inactivated VSV. Furthermore, in contrast to nontransgenic controls, tg7 mice rapidly cleared a recombinant vaccinia virus expressing the VSV-G (Vacc-IND-G) from peripheral organs. By adoptive transfer of naive tg7 CD4+ T cells into T cell-deficient recipients, we found that 105 transferred CD4+ T cells were sufficient to induce isotype switching after challenge with a suboptimal dose of inactivated VSV. In contrast, naive transgenic CD4+ T cells were unable to adoptively confer protection against peripheral infection with Vacc-IND-G. However, tg7 CD4+ T cells that had been primed in vitro with VSV-G peptide were able to adoptively transfer protection against Vacc-IND-G. These results demonstrate that the antiviral properties of CD4+ T cells are governed by the differentiation status of the CD4+ T cell and by the type of effector response required for virus elimination.

In einer Gemeinschaftsarbeit zwischen vier deutschen Stahlunternehmen und dem Fraunhofer-Institut für Betriebsfestigkeit (LBF) in Darmstadt wurde an bis zu 20 Jahren an zwei Industriestandorten ausgelagerten Proben aus dem allgemeinen Baustahl S355J2G3 (St 52-3) und dem wetterfesten Baustahl S355J2G1W (WTSt 52-3) ihr Dauerschwingverhalten in Abhängigkeit von der Probenform (ungeschweißt, geschweißt) und der Auslagerungsdauer ermittelt. Bei den ungeschweißten Proben fällt die Schwingfestigkeit innerhalb einer zweijährigen Bewitterung um bis zu 30 Prozent ab (bis zu 35 Prozent bei bis zu 20 Jahren Bewitterung); dabei wies der wetterfeste Baustahl stets eine geringere Abrostung auf als der allgemeine Baustahl. Für die Bauteilbemessung ist das Schwingfestigkeitsverhalten geschweißter Proben wichtiger. Bei den Formelementen Stumpfstoß und Quersteife bleibt die Beanspruchbarkeit von der Dauer der Bewitterung unabhängig. Der Grund dafür ist, daß der Einfluß der Korrosion von der schwingfestig keitsmindernden Wirkung der Einbrandkerben beim Schweißen überdeckt wird. Die Untersuchungsergebnisse tragen dazu bei, die Berechnung von Bauwerken aus wetterfestem Baustahl auch für Fälle mit Wechselbeanspruchung zu sichern. In den gängigen Zulassungs- und Bemessungsregeln ist das Schwingfestigkeitsverhalten in Abhängigkeit von der Bewitterungsdauer nicht einheitlich und ausreichend erfaßt.

Participation of transmembrane (TM) and glycosyl-phosphatidylinositol (GPI) anchored H-2Db molecules in antigen presentation and thymic selection events was investigated using transgenic mice. Both GPI-Db and TM-Db can efficiently present H-Y antigen, influenza and lymphocytic choriomeningitis virus (LCMV) peptides to primed cytotoxic, H-2Db-restricted T cells. Transgenic mice expressing GPI-Db, although unable to reject TM-Db skin grafts, nevertheless generate secondary CTL responses which can lyse TM-Db-bearing targets, indicating that GPI-Db mice fail to delete all TM-Db-reactive T cells. Furthermore, double-transgenic mice bearing GPI-Db and a T-cell receptor (TcR) for H-2Db+LCMV do not positively select receptor positive, CD8+CD4- T cells. This paradoxical behaviour of GPI-Db molecules suggests that the structural requirements for antigen presentation and thymic selection by class I molecules are different and may explain why GPI-linked class I molecules, such as Qa-2, do not appear to function as restriction elements in vivo.

To study self reactivity, a transgenic mouse model has been established in which the lymphocytic choriomeningitis virus (LCMV) glycoprotein (gp) is expressed in the beta-islet cells of the pancreas (rat insulin promoter (RIP)-gp). These mice (H-2b) do not spontaneously develop diabetes; however, infection with the LCMV strain WE rapidly induces hyperglycemia. In this study, comparative analysis of H-2k RIP-gp-transgenic animals demonstrated that the haplotype influences the incidence and kinetics of diabetes and alters the requirement for the CD4+ T cell subset. This study also showed that the properties of the virus expressing the self target Ag determined whether hyperglycemia occurred in RIP-gp-transgenic mice. Various LCMV strains were able to induce diabetes in RIP-gp-transgenic animals, whereas infection with a recombinant vaccinia virus expressing LCMV-gp (vacc-gp) did not induce diabetes. However, vacc-gp could induce diabetes in double (RIP-gp/TCR)-transgenic mice, where the majority of CD8+ T cells expressed a receptor specific for LCMV-gp, suggesting that a critical number of self-reactive T cells must be activated to induce disease. Notably, histologic analysis of pancreata taken various days after LCMV or vacc-gp infections indicated that induction of diabetes coincided with an increase in MHC class I expression on the islets of Langerhans. Additional studies with vacc-gp were done to determine other factors that possibly enhance autoimmune attack. Transgenic mice expressing both LCMV-gp and TNF-alpha under the control of the RIP were infected with vacc-gp, and 50% of RIP-gp/TNF-alpha-transgenic animals became hyperglycemic. These data suggest that the increased local lymphocyte traffic as a result of TNF-alpha expression attracts activated gp-specific T cells, enhancing the possibility of hyperglycemia. Collectively, these results demonstrate that the induction of diabetes in this model is influenced by the MHC haplotype, the infectious agent, TNF-alpha expression, the level of MHC class I expression, and the induction of a threshold number of self-reactive CTL.