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Biomedical subjects

Stefan Bauer

Publications and source records attributed to Stefan Bauer.

At least 19 recordsLinked to original sources
PubMed2007

Concomitant aortic valve replacement and coronary bypass: the effect of valve type on the blood flow in bypass grafts.

OBJECTIVE: In cases of aortic valve replacement, the downstream flow profile and turbulence in the ascending aorta differ according to the prosthetic aortic valve implanted. The objective of this work is to study the influence of prosthetic valve type on the flow in the bypass grafts implanted to the ascending aorta in cases of concomitant aortic valve replacement and coronary artery bypass. METHODS: The study is conducted on 456 patients receiving concomitant aortic valve replacement and coronary bypass vein grafts anastomosed to the ascending aorta. The patients included in the study received a total number of 725 vein grafts, 249 biological aortic valves and 207 mechanical aortic valves. Intraoperative transit time flow measurement was done for all bypass grafts and a multiple regression model was calculated for the factors influencing the flow in the bypass grafts. RESULTS: The mean flow in vein grafts in patients receiving biological valves was 49.79+/-26.88 ml/min, while in patients receiving mechanical valves it was 46.54+/-26.68 ml/min. The multiple regression model revealed that receiving a mechanical valve is an independent risk factor for lower flow in the vein grafts. CONCLUSIONS: The type of the aortic valve implanted and consequently the downstream flow profile in the ascending aorta do affect the flow in the vein grafts in cases of concomitant aortic valve replacement and coronary bypass. Receiving a mechanical aortic valve is an independent risk factor for lower flow in the vein grafts.

Aged↗
PubMed2006

Structure-activity profiles of Ab-derived TNF fusion proteins.

TNF application in humans is limited by severe side effects, including life-threatening symptoms of shock. Therefore, TNF can be successfully applied as a tumor therapeutic reagent only under conditions that prevent its systemic action. To overcome this limitation, genetic fusion of TNF to tumor-selective Abs is a favored strategy to increase site-specific cytokine targeting. Because wild-type TNF displays its bioactivity as noncovalently linked homotrimer, the challenge is to define structural requirements for a TNF-based immunokine format with optimized structure-activity profile. We compared toxicity and efficacy of a dimerized CH2/CH3 truncated IgG1-TNF fusion protein and a single-chain variable fragment-coupled TNF monomer recognizing fibroblast-activating protein. The former construct preserves its dimeric structure stabilized by the natural disulfide bond IgG1 hinge region, while the latter trimerizes under native conditions. Analysis of complex formation of wild-type TNF and of both fusion proteins with TNFR type 1 (TNF-R1) using surface plasmon resonance correlated well with in vitro and in vivo toxicity data. There is strong evidence that TNF subunits in a trimeric state display similar toxicity profiles despite genetic fusion to single-chain variable fragment domains. However, LD(50) of either immunodeficient BALB/c nu/nu or immunocompetent BALB/c mice was significantly decreased following administration of TNF in the formation of IgG1-derived dimeric fusion protein. Reduction of unspecific peripheral complexation of TNF-R1 resulted in higher anticancer potency by immunotargeting of fibroblast-activating protein-expressing xenografts. The broader therapeutic window of the IgG1-derived TNF fusion protein favors the dimeric TNF-immunokine format for systemic TNF-based tumor immunotherapy.

Animals↗
PubMed2006

Development and application of a suite of polysaccharide-degrading enzymes for analyzing plant cell walls.

To facilitate analysis of plant cell wall polysaccharide structure and composition, we cloned 74 genes encoding polysaccharide-degrading enzymes from Aspergillus nidulans, Aspergillus fumigatus, and Neurospora crassa and expressed the genes as secreted proteins with C-terminal Myc and 6x His tags. Most of the recombinant enzymes were active in enzyme assays, and optima for pH and temperature were established. A subset of the enzymes was used to fragment polysaccharides from the irregular xylem 9 (irx9) mutant of Arabidopsis. The analysis revealed a decrease in the abundance of xylan in the mutant, indicating that the IRX9 gene, which encodes a putative family 43 glycosyltransferase, is required for xylan synthesis.

Arabidopsis↗
PubMed2006

Toll-like receptor 9 contributes to recognition of Mycobacterium bovis Bacillus Calmette-Guérin by Flt3-ligand generated dendritic cells.

Recognition of mycobacteria by the innate immune system is essential for the development of an adaptive immune response. Mycobacterial antigens stimulate antigen presenting cells (APCs) through distinct Toll-like receptors (TLRs) resulting in rapid activation of the innate immune system. The role of TLRs during infection with Mycobacterium bovis Bacillus Calmette-Guérin (BCG) has been evaluated for TLR2 and TLR4 only. Surprisingly, despite the fact that immune stimulatory CpG-motifs have been originally derived from BCG, for the vaccine strain the role of TLR9 has not been addressed before. To identify the set of TLRs involved in the recognition of BCG, we infected bone marrow-derived macrophages and bone marrow-derived dendritic cells (Flt3-ligand generated DCs) from TLR2, TLR3, TLR4, TLR7, TLR9, MyD88 knockout, TLR2/4 and TLR2/4/9 multiple knockout mice. The degree of activation and stimulation was determined by TNFalpha, IL-6 and IL-12p40 ELISA. Activation of DCs was measured by surface expression of the costimulatory molecule CD86. We observed the most dramatic reduction of the inflammatory response for TLR2-deficient antigen presenting cells. Both macrophages and DCs produce markedly decreased amounts of TNFalpha and IL-6 in the absence of TLR2 whereas no significant reduction could be observed for TLR3, 4, 7, 9 single TLR-knockouts. However, IL-12 production in DCs appears not exclusively dependent on TLR2 and only in TLR2/4/9-deficient DCs BCG-induced IL-12 is reduced to background levels. Similarly, up-regulation of CD86 is abolished only in TLR2/4/9-deficient DCs supporting a role of TLR9 in the recognition of M. bovis BCG by murine dendritic cells.

Animals↗
PubMed2006

Toll-like receptor 9-independent aggravation of glomerulonephritis in a novel model of SLE.

The generation of anti-DNA auto-antibodies is characteristic for the human autoimmune condition systemic lupus erythematosus (SLE) and its animal models. However, the contribution of the toll-like receptor (TLR) system of innate immunity receptors and, in particular, TLR9 to this B cell-mediated autoimmune process remains controversial. Here we report that in a novel murine model of SLE, based on hyper-reactive B cell activation mediated by mutant phospholipase Cg2, the genetic deficiency of TLR9 does not protect from spontaneous anti-DNA auto-antibody formation and glomerulonephritis. On the contrary, disease induction is aggravated and additional nucleolar antibody specificity develops in autoimmune TLR9-deficient mice. In vitro studies demonstrate that, in autoimmune-prone mice, dual signaling via the B cell receptor and non-CpG DNA results in synergistic B cell activation in a TLR9-independent manner. These results suggest that engagement of a TLR9-independent DNA activation pathway may promote autoimmunity, while TLR9 signaling can ameliorate SLE-like immune pathology in vivo.

Animals↗
PubMed2006

All is not Toll: new pathways in DNA recognition.

Immunological defense depends on the ability of the innate immune system to recognize invading microbes as foreign and thus eliminate them. The Toll-like receptors (TLRs) help detect foreign invaders by sensing various pathogen-associated molecules, including microbial RNA and DNA. At present, it is unclear whether and how the immune system distinguishes between microbial and self nucleic acids, as host-derived RNA and DNA also stimulate TLRs. In addition, recent studies have revealed the existence of TLR-independent pathways that are activated in response to microbial and host nucleic acids.

Animals↗
PubMed2006

CpG motif-independent activation of TLR9 upon endosomal translocation of "natural" phosphodiester DNA.

Endosomally translocated host (self) DNA activates Toll-like receptor 9 (TLR9), while extracellular self-DNA does not. This inconsistency reflects poor endosomal DNA translocation but also implies that host DNA contains DNA sequences that function as ligands for TLR9. Herein we report that contrary to phosphorothioate (PS)-stabilized oligonucleotides (ODN), "natural" phosphodiester (PD) ODN lacking CpG motifs activate TLR9. CpG motif-independent TLR9 activation of Flt3-L-induced dendritic cells (DC) was dependent on enforced endosomal translocation and triggered upregulation of CD40 and CD69 as well as production of IL-6 and IFN-alpha. Binding studies utilizing surface plasmon resonance technology (Biacore) revealed low TLR9 binding to single-stranded (ss) PD-ODN lacking CpG motifs. At higher concentrations their TLR9 binding activity compared well with TLR9 binding of canonical ss PD CpG-ODN. These results imply that both the chemical modification of the DNA backbone as well as the amount of endosomally translocated DNA represent determining factors that allow CpG motif-independent activation of TLR9 by ss PD-DNA.

Animals↗
PubMed2006

CD25+/Foxp3+ T cells regulate gastric inflammation and Helicobacter pylori colonization in vivo.

BACKGROUND & AIMS: Helicobacter pylori infects more than half of the world's population. In contrast to most other pathogens, the microbe persists for the virtual life of its host. It is unclear why the immune system is unable to eliminate the infection, but recent studies suggested that CD4+/CD25+/Foxp3+ regulatory T cells may be involved in this process. METHODS: By using a mouse model of infection and gastric biopsies from 108 patients, we performed a detailed descriptive and functional characterization of the Helicobacter-induced CD25+/Foxp3+ T-cell response. RESULTS: In C57BL/6 mice, H pylori induced a marked gastric Foxp3+ T-cell response, which increased over several months together with the severity of inflammation, until a stable homeostatic situation became established. Accordingly, in Helicobacter-infected patients, but not in uninfected individuals, large numbers of gastric Foxp3+ T cells were detected immunohistochemically. To define the functional in vivo relevance of this response, CD25+ cells were depleted systemically in mice by using an anti-CD25 monoclonal antibody (PC61). Already 4 weeks after infection, PC61-treated mice, but not untreated animals, developed a severe gastritis with heightened cytokine expression and increased numbers of mucosal T cells, B cells, and macrophages. This was accompanied by increased titers of H pylori-specific IgG1 and IgG2c antibodies in the sera of PC61-treated mice. This increased gastric inflammatory response in CD25-depleted mice was associated with reduced bacterial loads. CONCLUSIONS: CD25+/Foxp3+ T cells actively participate in the immune response to H pylori. In vivo depletion of these cells in infected mice leads to increased gastric inflammation and reduced bacterial colonization.

Animals↗
PubMed2006

Fibroblast activation protein is expressed by rheumatoid myofibroblast-like synoviocytes.

Fibroblast activation protein (FAP), as described so far, is a type II cell surface serine protease expressed by fibroblastic cells in areas of active tissue remodelling such as tumour stroma or healing wounds. We investigated the expression of FAP by fibroblast-like synoviocytes (FLSs) and compared the synovial expression pattern in rheumatoid arthritis (RA) and osteoarthritis (OA) patients. Synovial tissue from diseased joints of 20 patients, 10 patients with refractory RA and 10 patients with end-stage OA, was collected during routine surgery. As a result, FLSs from intensively inflamed synovial tissues of refractory RA expressed FAP at high density. Moreover, FAP expression was co-localised with matrix metalloproteinases (MMP-1 and MMP-13) and CD44 splice variants v3 and v7/8 known to play a major role in the concert of extracellular matrix degradation. The pattern of signals appeared to constitute a characteristic feature of FLSs involved in rheumatoid arthritic joint-destructive processes. These FAP-expressing FLSs with a phenotype of smooth muscle actin-positive myofibroblasts were located in the lining layer of the synovium and differ distinctly from Thy-1-expressing and non-proliferating fibroblasts of the articular matrix. The intensity of FAP-specific staining in synovial tissue from patients with RA was found to be different when compared with end-stage OA. Because expression of FAP by RA FLSs has not been described before, the findings of this study highlight a novel element in cartilage and bone destruction of arthritic joints. Moreover, the specific expression pattern qualifies FAP as a therapeutic target for inhibiting the destructive potential of fibroblast-like synovial cells.

Antigens, Neoplasm↗
PubMed2006

Body mass index: a risk factor for 30-day or six-month mortality in patients undergoing aortic valve replacement?

BACKGROUND AND AIM OF THE STUDY: In recent studies, the impact of a low or high body mass index (BMI) on outcome after cardiac surgery has been the subject of controversy. A retrospective study was conducted to determine the influence of BMI on 30-day and six-month mortality after aortic valve replacement (AVR). METHODS: A multivariable logistic regression was performed on data from 1,241 consecutive patients (mean age 69 +/- 11 years) who underwent AVR either with (n = 514; 41%) or without coronary artery bypass grafting CABG between 2000 and 2003. A wide spectrum of periprocedural variables was collected, including laboratory data as markers for nutritional status and comorbidity. Patients were followed up for six months after AVR (99% complete). RESULTS: Mortality rates after 30 days and after six months were 3.9% (n = 49) and 7.6% (n = 94), respectively. A low BMI was identified as an independent risk factor for 30-day (OR (odds ratio) 0.87; CI (confidence interval) 0.8-0.94) and six-month mortality (OR 0.91; CI 0.86-0.96). The relationship between the logit function and BMI was linear; however, a BMI value of 24 was considered an appropriate cut-off point. Both models containing the BMI linearly or dichotomic were equivalent. As patients with a lower BMI differ in their preoperative risk profile compared to those with a higher BMI, a saturated propensity score estimating the propensity towards having a BMI < 24 was calculated. The propensity score was not significant in the final models for 30-day and six-month mortality (0.24 and 0.73, respectively), and the OR for BMI remained largely unaltered (0.89 and 0.91, respectively). CONCLUSION: A BMI < 24 is predictive of an increased risk of mortality after AVR, independently of malnutrition, advanced heart disease, or valve size. Further studies are required to investigate the role of adipose tissue in extreme situations and chronic disease. It is mandatory to include BMI in outcome studies after AVR.

Aged↗
PubMed2005

U1 small nuclear ribonucleoprotein immune complexes induce type I interferon in plasmacytoid dendritic cells through TLR7.

Plasmacytoid dendritic cells (PDCs), which produce IFN-alpha in response to autoimmune complexes containing nuclear antigens, are thought to be critically involved in the pathogenesis of systemic lupus erythematosus (SLE). One of the immunostimulatory components of SLE immune complexes (SLE-ICs) is self DNA, which is recognized through Tlr9 in PDCs and B cells. Small nuclear ribonucleoproteins (snRNPs) are another major component of SLE-ICs in 30% to 40% of patients. In this study, we show that murine PDCs are activated by purified U1snRNP/anti-Sm ICs to produce IFN-alpha and proinflammatory cytokines and to up-regulate costimulatory molecules. The induction of IFN-alpha and IL-6 by U1snRNPs in murine bone marrow-derived PDCs required the presence of intact U1RNA and was largely dependent on Tlr7 but independent of Tlr3. Intracellularly delivered isolated U1snRNA and oligoribonucleotides derived from the stem loop regions and the Sm-binding site of U1snRNA efficiently induced IFN-alpha and IL-6 in Flt3L-cultured DCs in a Tlr7-dependent manner. The U1snRNA component of U1snRNP immune complexes, found in patients with SLE, acts as an endogenous "self" ligand for Tlr7 and triggers IFN-alpha and IL-6 production in PDCs.

Animals↗
PubMed2005

Immune stimulation mediated by autoantigen binding sites within small nuclear RNAs involves Toll-like receptors 7 and 8.

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the production of autoantibodies to certain cellular macromolecules, such as the small nuclear ribonucleoprotein particles (snRNPs), which had been considered to be passive targets of the autoimmune response. SLE is also characterized by the increased expression of type I interferon (IFN), which appears to be associated with the development and severity of disease. Here, we show that specific, highly conserved RNA sequences within snRNPs can stimulate Toll-like receptors (TLRs) 7 and 8 as well as activate innate immune cells, such as plasmacytoid dendritic cells (pDCs), which respond by secreting high levels of type I IFN. SLE patient sera containing autoantibodies to snRNPs form immune complexes that are taken up through the Fc receptor gammaRII and efficiently stimulate pDCs to secrete type I IFNs. These results demonstrate that a prototype autoantigen, the snRNP, can directly stimulate innate immunity and suggest that autoantibodies against snRNP may initiate SLE by stimulating TLR7/8.

Animals↗
PubMed2005

Cloning, expression, and characterization of an oligoxyloglucan reducing end-specific xyloglucanobiohydrolase from Aspergillus nidulans.

An oligoxyloglucan reducing end-specific xyloglucanobiohydrolase from the filamentous fungus Aspergillus nidulans was cloned and expressed in Pichia pastoris as a secreted histidine-tagged protein and purified by affinity chromatography. The enzyme acts on xyloglucan oligomers and releases the first two glycosyl residue segments from the reducing end, provided that neither the first glucose nor the xylose attached to the third glucose residue from the reducing end is not further substituted. The enzyme has a specific activity of 7 U/mg at the pH optimum of 3 and at the temperature optimum of 42 degrees C.

Amino Acid Sequence↗
PubMed2005

NKG2D-independent suppression of T cell proliferation by H60 and MICA.

The activating receptor NKG2D recognizes a wide range of different ligands, some of which are primarily expressed in "stressed" tissues or on tumor cells. Until now, similar stimulatory effects on natural killer and CD8+ T cells have been described for all NKG2D ligands, and the NKG2D receptor/ligand system has therefore been interpreted as a sensor system involved in tumor immune surveillance and activation of immune responses. We show here that the NKG2D ligands H60 and MIC class 1 chain-related protein A (MICA) can also mediate strong suppressive effects on T cell proliferation. Responsiveness to H60- and MICA-mediated suppression requires IL-10 and involves a receptor other than NKG2D. These findings might provide explanations for the observation that strong in vivo NKG2D ligand expression, such as that on tumor cells, sometimes fails to support effective immune responses and links this observation to a distinct subgroup of NKG2D ligands.

Animals↗
PubMed2005

Endosomal translocation of vertebrate DNA activates dendritic cells via TLR9-dependent and -independent pathways.

TLRs discriminate foreign from self via their specificity for pathogen-derived invariant ligands, an example being TLR9 recognizing bacterial unmethylated CpG motifs. In this study we report that endosomal translocation of CpG DNA via the natural endocytotic pathway is inefficient and highly saturable, whereas endosomal translocation of DNA complexed to the cationic lipid N-[1-(2,3-dioleoyloxy)propyl]-N,N,N-trimethylammonium methylsulfate (DOTAP) is not. Interestingly, DOTAP-mediated enhanced endosomal translocation of otherwise nonstimulatory vertebrate DNA or of certain noncanonical CpG motifs triggers robust dendritic cell activation in terms of both up-regulation of CD40/CD69 and cytokine production, such as type I IFN and IL-6. We report that the stimulatory activity of phosphorothioated noncanonical CpG oligodeoxynucleotides is TLR9 dependent, whereas phosphodiester DNA, such as vertebrate DNA, in addition trigger TLR9-independent pathways. We propose that the inefficiency of the natural route for DNA internalization hinders low affinity TLR9 ligands in endosomes to reach threshold concentrations required for TLR9 activation. Endosomal compartmentalization of TLR9 may thus reflect an evolutionary strategy to avoid TLR9 activation by self-DNA.

Adjuvants, Immunologic↗
PubMed2005

Toll-like receptor 9 signaling can sensitize fibroblasts for apoptosis.

Toll-like receptors (TLR) are activated by microbial components and transmit signals that induce cell activation and differentiation. A number of recent reports further indicate that TLR also have the potential to induce apoptosis upon ligand binding. Here we investigate the apoptosis-inducing capacity of TLR9, the receptor for microbial CpG-DNA. Unlike ligands for TLR2 and TLR4, CpG-DNA failed to induce apoptosis in RAW264.7 mouse macrophages. In human embryonic kidney fibroblasts transfected stably to express TLR9, CpG-DNA weakly induced apoptosis in one clone but not others without an obvious allocation to differences in TLR-signaling events. Analysis of the apoptotic signaling showed that the mitochondrial pathway of apoptosis was triggered by TLR9, as mitochondrial Bax was activated upstream of caspase-cleavage. CpG-DNA-induced apoptosis was reduced by cycloheximide suggesting that de novo protein synthesis was required. Strikingly, stimulation with CpG-DNA resulted in a strongly increased sensitivity of TLR9-expressing fibroblasts to apoptosis induced by staurosporine and UV-irradiation. These results identify a mitochondrial pathway to apoptosis that can be triggered by TLR9 and that may serve to sensitize cells from the innate immune system to apoptosis in the course of an immune response.

Animals↗
PubMed2005

Toll-like receptor engagement converts T-cell autoreactivity into overt autoimmune disease.

Autoimmune diabetes mellitus in humans is characterized by immunological destruction of pancreatic beta islet cells. We investigated the circumstances under which CD8(+) T cells specific for pancreatic beta-islet antigens induce disease in mice expressing lymphocytic choriomeningitis virus (LCMV) glycoprotein (GP) as a transgene under the control of the rat insulin promoter. In contrast to infection with LCMV, immunization with LCMV-GP derived peptide did not induce autoimmune diabetes despite large numbers of autoreactive cytotoxic T cells. Only subsequent treatment with Toll-like receptor ligands elicited overt autoimmune disease. This difference was critically regulated by the peripheral target organ itself, which upregulated class I major histocompatibility complex (MHC) in response to systemic Toll-like receptor-triggered interferon-alpha production. These data identify the 'inflammatory status' of the target organ as a separate and limiting factor determining the development of autoimmune disease.

Animals↗