Biomedical subjects

Annette Kolb-Mäurer

Publications and source records attributed to Annette Kolb-Mäurer.

14 recordsLinked to original sources

PubMed2005

Polymorphism of Candida albicans is a major factor in the interaction with human dendritic cells.

Morphological plasticity of Candida albicans is a major virulence factor. Using pH-dependent dimorphism we show, that human dendritic cells (DC) recognize filamentous forms and blastoconidia of a virulent C. albicans isolate (strain SC5314). Heat inactivated and viable blastoconidia are rapidly phagocytosed by human DC. However, viable yeast cells start to filament inside the DC at later stages of infection, leading to penetration and loss of cellular integrity. The cytokine burst of human DC induced upon contact with Candida is dominated by the granulocyte-activating, chemotactic factor IL-8 and the proinflammatory mediator TNF-alpha. Blastoconidia induce markedly lower cytokine levels than filamentous forms. Whereas IL-8 secretion is mainly cell mass dependent, release of TNF-alpha, a major proinflammatory cytokine, is clearly dependent on the morphology of Candida.

Candida albicans↗

PubMed2005

Bacterial delivery of functional messenger RNA to mammalian cells.

The limited access to the nuclear compartment may constitute one of the major barriers after bacteria-mediated expression plasmid DNA delivery to eukaryotic cells. Alternatively, a self-destructing Listeria monocytogenes strain was used to release translation-competent mRNA directly into the cytosol of epithelial cells, macrophages and human dendritic cells. Enhanced green fluorescent protein (EGFP)-encoding mRNA, adapted for translation in mammalian cells by linking an IRES element to the 5'-end of the egfp coding sequence, was produced by T7 RNA polymerase in the carrier bacteria upon entry into the cytosol where the mRNA is efficiently released from the lysed bacteria and immediately translated in eukaryotic host cells. Besides the much earlier expression of EGFP being detectable already 4 h after infection, the number of EGFP expressing mammalian cells obtained with this novel RNA delivery technique is comparable to or - especially in phagocytic cells - even higher than that obtained with the expression plasmid DNA delivery strategy. Accordingly, bacteria-mediated delivery of ovalbumin-encoding mRNA to macrophages resulted in efficient antigen processing and presentation in vitro indicating that this approach may also be adapted for the in vivo delivery of antigen-encoding mRNA leading to a more efficient immune response when applied to vaccine development.

Animals↗

PubMed2005

Carbohydrate composition of meningococcal lipopolysaccharide modulates the interaction of Neisseria meningitidis with human dendritic cells.

Meningococcal lipopolysaccharide (LPS) is of crucial importance for the pathogenesis of invasive infection. We show that sialylation and elongation of the alpha-chain effectively shields viable unencapsulated Neisseria meningitidis from recognition by human dendritic cells (DC). In contrast, beta- and gamma- chain of the LPS carbohydrate moiety play only a minor role in the interaction with DC. The protective function of the LPS for the bacteria can be counteracted in vivo by phase variation of the lgtA gene encoding LPS glycosyltransferase A. Capsule expression protects N. meningitidis efficiently from recognition and phagocytosis by DC independent of the LPS structure. Despite the significant impact of LPS composition on the adhesion and phagocytosis of N. meningitidis no differences were found in terms of cytokine levels secreted by DC for IL1-beta, IL-6, IL-8, TNF-alpha, IFN-gamma and GM-CSF. However, significantly lower levels of the regulatory mediator IL-10 were induced by encapsulated strains in comparison to isogenic unencapsulated derivatives. IL-10 secretion was shown to depend on phagocytosis because poly alpha-2,8 sialic acid did not influence IL-10 secretion. The use of truncated LPS isoforms in vaccine preparations can therefore not only result in attenuation but also in more efficient targeting of DC.

Bacterial Capsules↗

PubMed2004

[Systemic mastocytosis. Classification, symptoms, therapy].

BACKGROUND: Systemic mastocytoses are a group of diseases, which are characterized by accumulation and unusual growth of mast cells infiltrating two different organs or types of tissue. Two case reports are introduced. CLASSIFICATION: According to the new WHO classification of 2000, mastocytoses are separated into cutaneous and systemic mastocytoses. Systemic mastocytosis is subdivided into an indolent course with good prognosis and four subgroups with poor prognosis (systemic mastocytosis with associated clonal hematologic non-mast-cell disease, aggressive systemic mastocytosis, mast cell leukemia, and mast cell sarcoma). GENETICS: Systemic mastocytoses are clonal disorders of mast cells and their progenitor cells, which may show point mutations of the protooncogene c-kit. This gene codes for the stem cell receptor (CD117). THERAPY: Therapy of systemic mastocytosis depends on patient's symptoms. There is no known cure of the disease. Besides diet and avoidance of skin irritations, symptoms are treated with H(1)- or H(2)-blockers, steroids, leukotriene receptor antagonists, and PUVA therapy. If patients suffer from systemic reactions such as hypotension or syncope, epinephrine solution should be prescribed for emergency use.

Adult↗

PubMed2004

Bacterial infection of human hematopoietic stem cells induces monocytic differentiation.

Differentiation of hematopoietic stem cells (HSCs) can be influenced by different stimuli, including cytotoxic agents, certain cytokines, and contact with pathogens. Infection may result in dysregulation of these important progenitor cells and therefore interfere with the availability of blood cells. In this study we analyzed the effect of bacterial infection on HSCs concerning surface marker expression and cytokine release. Listeria monocytogenes and Yersinia enterocolitica accelerated maturation of hematopoietic progenitor cells along the myeloid lineage, as demonstrated by the upregulation of CD13, CD14, and costimulatory signals. By screening cytokine secretion, granulocyte-macrophage colony-stimulating factor, interleukin (IL)-6, IL-8, IL-10, IL-12, and tumor necrosis factor-alpha were found to be induced by bacterial infection. These data indicate that infection of HSCs with L. monocytogenes and Y. enterocolitica affects the differentiation of CD34(+) hematopoietic progenitors in vitro and may lead to secretion of cytokines that can influence the HSC differentiation capacity and immune response.

Antigens, CD↗

PubMed2003

Susceptibility of hematopoietic stem cells to pathogens: role in virus/bacteria tropism and pathogenesis.

Human hematopoietic stem cells (HSCs) are generated in the bone marrow and differentiate into erythrocytes, granulocytes, monocytes, megacaryocytes, and lymphocytes. HSCs may be manipulated under different conditions. Advances in cell biology result in a better understanding of the relationship between viruses/bacteria and hematopoietic cells. Microbial infections can lead to profound disturbance of hematopoiesis. Infection may augment the production of cytokines, with proliferation and differentiation of the stem cells. Alternatively, infection may lead to destruction of progenitor cells. This results in defective hematopoiesis in certain infections. Since circulating CD34+ cells represent a distinct progenitor pool responsible for seeding extramedullary sites of hematopoiesis, infected peripheral blood-derived CD34+ progenitor cells may serve to disseminate pathogens into diverse anatomic sites. Therefore, progenitor cell infection may additionally effect long-term functional consequences within extramedullary sites of lymphopoiesis. A variety of viruses have been reported to target HSCs, whereas quiescent human HSCs are fully resistant to infection by different bacteria. For susceptibility of HSCs to infectious agents pathogen-receptor interaction plays an important role in virus/bacteria tropism and pathogenesis.

Bacteria↗

PubMed2003

Production of IL-12 and IL-18 in human dendritic cells upon infection by Listeria monocytogenes.

Dendritic cells (DCs) are major antigen-presenting cells of the immune system, which need to be activated in order to initiate an immune response. Here, we describe the immunostimulatory effects on human monocyte-derived DCs observed upon infection with Listeria monocytogenes or after treatment with listerial lipoteichoic acid (LTA) and lipopolysaccharide (LPS), respectively. All stimuli caused upregulation of costimulatory molecules, induced T-cell proliferative responses and secretion of cytokines in vitro. Infection of DCs with L. monocytogenes induced release of interleukin (IL)-12 and IL-18. In contrast treatment with purified listerial LTA yielded high levels of IL-18 release, but only minimal IL-12 production. Treatment of DCs with LPS conversely induced significant amounts of IL-12 production, but no IL-18. The release of both stimulating cytokines IL-12 and IL-18 upon infection with entire bacteria suggests that attenuated strains of L. monocytogenes may be a valuable tool for subunit vaccine delivery.

Adult↗

PubMed2003

The role of dendritic cells during infection.

The skin and the mucosa of the respiratory and gastrointestinal tracts are continuously exposed to microorganisms, but only a limited number of these enter the body and cause disease. To resist microbial infection, the host has developed a multitude of defense mechanisms involving the innate and adaptive immune systems. Dendritic cells (DCs) provide the link between these arms of the immune system. The initiation of an immune response is critically dependent on the activation of DCs, which can discriminate between different classes of microorganisms and elicit tailored antimicrobial immune responses. They have an extraordinary capacity to stimulate naive T cells and initiate primary immune responses. In turn, some pathogens interfere with DC function to block or delay their elimination by the host. Progress in understanding the role of DCs in the host response to microbes is reviewed.

Adaptive Immunity↗

PubMed2003

The role of human dendritic cells in meningococcal and listerial meningitis.

Few bacteria are capable of causing infections of the central nervous system (CNS), one of the most subtly shielded anatomical structures within the human body. Neisseria meningitidis is an important cause of bacterial meningitis and commonly affects otherwise healthy infants and adolescents. In contrast, Listeria monocytogenes is a cause of septicaemia and meningitis in neonates and immunocompromised adults. Dendritic cells (DCs) provide the physical link between the innate and adaptive immune system and play a crucial role in host defence against invading bacterial pathogens. The mechanisms of interaction of L. monocytogenes and N. meningitidis with DCs are entirely distinct. Whereas L. monocytogenes is readily phagocytosed by DCs by a serum-dependent mechanism, N. meningitidis is largely protected against phagocytotic uptake by its polysaccharide capsule. In addition, the pattern of secreted cytokines induced by L. monocytogenes is dominated by interleukin (IL)-12 and IL-18, capable of initiating a Th-1 response, whereas N. meningitidis induces high levels of proinflammatory cytokines. Therefore, we propose distinct functions of DCs in both types of bacterial meningitis.

Cytokines↗

PubMed2003

Deletion of the gene encoding p60 in Listeria monocytogenes leads to abnormal cell division and loss of actin-based motility.

Protein p60 encoded by the iap gene is regarded as an essential gene product of Listeria monocytogenes. Here we report, however, the successful construction of a viable iap deletion mutant of L. monocytogenes EGD. The mutant, which produces no p60, shows abnormal septum formation and tends to form short filaments and hooked forms during logarithmic growth. These abnormal bacterial cells break into almost normal sized single bacteria in the late-stationary-growth phase. The iap mutant is strongly attenuated in a mouse model after intravenous injection, demonstrating the importance of p60 during infection, and the invasiveness of the Deltaiap mutant for 3T6 fibroblasts and Caco-2 epithelial cells is slightly reduced. Upon uptake by epithelial cells and macrophages, the iap mutant escapes from the phagosome into the cytosol with the same efficiency as the wild-type strain, and the mutant bacteria also grow intracellularly at a rate similar to that of the wild-type strain. Intracellular movement and cell-to-cell spread are drastically reduced in various cell lines, since the iap-negative bacteria fail to induce the formation of actin tails. However, the bacteria are covered with actin filaments. Most intracellular bacteria show a nonpolar and uneven distribution of ActA around the cell, in contrast to that for the wild-type strain, where ActA is concentrated at the old pole. In an iap(+) revertant strain that produces wild-type levels of p60, intracellular movement, cell-to-cell spread, and polar distribution of ActA are fully restored. In vitro analysis of ActA distribution on the filaments of the Deltaiap strain shows that the loss of bacterial septum formation leads to ActA accumulation at the presumed division sites. In the light of data presented here and elswhere, we propose to rename iap (invasion-associated protein) cwhA (cell wall hydrolase A).

Actins↗

PubMed2002

Interaction of human hematopoietic stem cells with bacterial pathogens.

Primitive hematopoietic stem cells (HSCs) in the bone marrow are rare pluripotent cells with the capacity to give rise to all lineages of blood cells. During commitment, progenitor cells are composed mainly of cells with the potential for differentiation into 1 or 2 lineages. This commitment involves the acquisition of specific growth factor receptors and the loss of others. Viral and bacterial infections may lead to profound disturbance of hematopoiesis, which is possibly due to different susceptibility of HSCs to infectious agents. Here, we show that quiescent human HSCs are fully resistant to infection by the intracellular bacteria, Listeria monocytogenes and Salmonella enterica serovariation typhimurium, and the extracellular pathogen Yersinia enterocolitica. During myeloid/monocytic differentiation induced by incubation with stem cell factor, thrombopoietin, and flt-3 ligand, partially differentiated HSCs emerge, which readily take up these pathogens and also latex beads by macropinocytosis. After further monocytic differentiation, bacterial uptake by macropinocytosis still occurs but internalization of the pathogens is now mainly achieved by receptor-mediated phagocytosis. These results suggest that in the case of HSCs uptake mechanisms for bacteria develop sequentially.

Antigens, CD34↗

PubMed2002

A polymorphism in the human cytotoxic T-lymphocyte antigen 4 ( CTLA4) gene (exon 1 +49) alters T-cell activation.

The cytotoxic T-lymphocyte antigen 4 (CTLA4) is an important modifier of T-cell activation with down-regulatory properties upon B7 engagement. An allelic polymorphism in exon 1 of the CTLA4 gene coding for the peptide leader sequence of CTLA4 was recently described. This polymorphism was detected in association with several autoimmune diseases. In this study, we investigated the functional impact of the CTLA4 exon 1 +49 A/G dimorphism on T-cell activation and cellular localization. We examined the T-cell response from healthy donors either homozygous for A or G at position +49 of the exon 1. Under suboptimal stimulation conditions we found a greater proliferative response of cells from donors homozygous for G at position +49. FACS analysis of CTLA4 expression revealed a reduced up-regulation of CTLA4 from G/G donors upon T-cell activation, if compared with wild-type cells. Intracellular CTLA4 distribution demonstrated qualitatively different staining patterns between the two genotypes as determined using confocal fluorescence microscopy. Our results suggest that the G allele at position +49 of exon 1 affects the CTLA4-driven down-regulation of T-cell activation and may be an important factor in the pathogenesis of autoimmune diseases.

Abatacept↗

PubMed2002

Delivery of protein antigens and DNA by attenuated intracellular bacteria.

On the basis of attenuated intracellular bacteria, we have developed two delivery systems for either heterologous proteins or DNA vaccine vectors. The first system utilizes attenuated strains of Gram-negative bacteria which are engineered to secrete heterologous antigens via the alpha-hemolysin secretion system (type I) of Escherichia coli. The second system is based on attenuated suicide strains of Listeria monocytogenes, which are used for the direct delivery of eukaryotic antigen expression vectors into professional antigen-presenting cells (APC) like macrophages and dendritic cells in vitro and can be also used in animal models.

Animals↗

PubMed2002

Lipooligosaccharide and polysaccharide capsule: virulence factors of Neisseria meningitidis that determine meningococcal interaction with human dendritic cells.

In this work we analyzed the roles of meningococcal lipooligosaccharide (LOS) and capsule expression in the interaction of Neisseria meningitidis with human dendritic cells (DC). Infection of DC with serogroup B wild-type meningococci induced a strong burst of the proinflammatory cytokines and chemokines tumor necrosis factor alpha, interleukin-6 (IL-6), and IL-8. In contrast, a serogroup B mutant strain lacking LOS expression barely led to cytokine induction, demonstrating that meningococcal LOS is the main mediator of the proinflammatory response in human DC. Sialylation of meningococcal LOS did not influence cytokine secretion by DC. However, we found the phagocytosis of N. meningitidis by human DC to be inhibited by LOS sialylation. In addition, the expression of the meningococcal serogroup A, B, and C capsules dramatically reduced DC adherence of N. meningitidis and phagocytosis to some extent. Hence, LOS sialylation and capsule expression are independent mechanisms protecting N. meningitidis from the phagocytic activity of human DC.

Bacterial Capsules↗