Peter Ravn - Academia.edu (original) (raw)

Papers by Peter Ravn

FEMS Immunology & Medical Microbiology, 2011

In this study, we have used monocyte-derived dendritic cells (DCs) to design a screening model fo... more In this study, we have used monocyte-derived dendritic cells (DCs) to design a screening model for the selection of microorganisms with the ability to suppress DC-secreted IL-12p70, a critical cytokine for the induction of T-helper cell type 1 immune responses under inflammatory conditions. By the treatment of DCs with cocktails containing TLR agonists and proinflammatory cytokines, the cells increased the secretion of the Th1-promoting cytokine IL-12p70. Clinically used probiotics were tested for their IL-10-and IL-12p70-stimulating properties in immature DCs, and showed a dose-dependent change in the IL-10/IL-12p70 balance. Lactobacillus acidophilus NCFM TM and the probiotic mixture VSL#3 showed a strong induction of IL-12p70, whereas Lactobacillus salivarius Ls-33 and Bifidobacterium infantis 35624 preferentially induced IL-10. Escherichia coli Nissle 1917 induced both IL-10 and IL-12p70, whereas the probiotic yeast Saccharomyces boulardii induced low levels of cytokines. When combining these microorganisms with the Th1-promoting cocktails, E. coli Nissle 1917 and B. infantis 35624 were potent suppressors of IL-12p70 secretion in an IL-10-independent manner, indicating a suppressive effect on Th1-inducing antigen-presenting cells. The present model, using cocktail-stimulated DCs with potent IL-12p70-stimulating capacity, may be used as an efficient tool to assess the anti-inflammatory properties of microorganisms for potential clinical use.

Dairy Science and Technology, 2004

ABSTRACT: Bovine tissue-type plasminogen activator (tPA) was heterologously expressed in the meth... more ABSTRACT: Bovine tissue-type plasminogen activator (tPA) was heterologously expressed in the methylotrophic yeast Pichia pastoris and characterized structurally and kinetically. The bovine single-chain tPAmediated activation of bovine plasminogen was studied in the presence and absence of fibrinogen fragments. We have proposed a refined new method of kinetic analysis which allows examination of both stationary and prestationary phases of this process. The investigation revealed the presence of two interconvertible forms of the recombinant bovine tPA being in equilibrium at a 1 to 50 ratio. Only the minor form was able to bind and activate plasminogen. Saturation of the whole pool of tPA required high plasminogen concentration (K m g 5µM) in order to reverse the equilibrium between the two forms. Fibrinogen fragments activated the single-chain tPA due to preferential binding and stabilization of the minor "active" form of the enzyme until all the molecules of tPA were conve...

Applied and Environmental Microbiology, 2004

Lactococcus lactis , a food-grade nonpathogenic lactic acid bacterium, is a good candidate for th... more Lactococcus lactis , a food-grade nonpathogenic lactic acid bacterium, is a good candidate for the production of heterologous proteins of therapeutic interest. We examined host factors that affect secretion of heterologous proteins in L. lactis . Random insertional mutagenesis was performed with L. lactis strain MG1363 carrying a staphylococcal nuclease (Nuc) reporter cassette in its chromosome. This cassette encodes a fusion protein between the signal peptide of the Usp45 lactococcal protein and the mature moiety of a truncated form of Nuc (NucT). The Nuc secretion efficiency (secreted NucT versus total NucT) from this construct is low in L. lactis (∼40%). Twenty mutants affected in NucT production and/or in secretion capacity were selected and identified. In these mutants, several independent insertions mapped in the dltA gene (involved in d -alanine transfer in lipoteichoic acids) and resulted in a NucT secretion defect. Characterization of the dltA mutant phenotype with respect ...

Inflammatory Bowel Diseases, Mar 1, 2010

Background: The effect in vitro of six different probiotic strains including Lactobacillus acidop... more Background: The effect in vitro of six different probiotic strains including Lactobacillus acidophilus NCFM TM , Lactobacillus salivarius Ls-33, Lactobacillus paracasei subsp. paracasei YS8866441, Lactobacillus plantarum Lp-115, Bifidobacterium bifidum BI-504 and BI-98 was studied on splenic enteroantigenpresenting cells (APC) and CD4 þ CD25 þ T-regulatory cells (Tregs) in splenocyte-T cell proliferation assays. Methods: Splenocytes exposed to enteroantigen þ/À probiotics were used to stimulate cultured CD4 þ CD25 À T cells to which titrated numbers of Tregs were added. Cytokine assays were performed by use of neutralizing antibodies and ELISA. Results: Exposure of APCs to enteroantigens and the series of probiotic strains mentioned above did not influence the stimulatory capacity of APCs on proliferative enteroantigen-specific T cells. However, exposure to B. bifidum BI-98, BI-504 and L. acidophilus NCFM TM consistently reduced the suppressive activity of Tregs. The suppressive activity was analyzed using fractionated components of the probiotics, and showed that a component of the cell wall is responsible for the decreased Treg activity in the system. The probiotic-induced suppression of Treg function is not mediated by changes in APC-secretion of the inflammatory cytokines IL-6 or IL-1b. Conclusion: We conclude that certain probiotic strains can modify APCs to cause reduced Treg activity. This effect apparently depends on a direct APC-to-Treg cell contact. The APCmediated suppressive effect on Treg function of certain probiotic strains may constrain the anti-inflammatory activity, which is often desired from probiotic therapy. This unexpected function of certain probiotic strains should be taken into consideration when designing adjuvant therapies with these bacteria, or when probiotic strains are selected for improvement of gut-associated inflammation like IBD.

Molecular Microbiology, 1994

We have studied the formation of spontaneous mutations on plasmids present in the monomeric and d... more We have studied the formation of spontaneous mutations on plasmids present in the monomeric and dimeric states in a recF strain of Escherichia coli. Two test systems were employed: (i) the precise excision of Tn5 from the tetA gene of the plasmid pBR322 and (ii) operator constitutive (Oc) mutations on the pBR322-derived plasmid pPY97. The rate of Oc mutations was increased by a factor of three when this plasmid was present in the dimeric state compared to the monomeric state and the Oc phenotype was caused by small deletions in the operator sequence. No apparent mutational hot-spot was found. The rate of Tn5 excision was increased on dimeric compared to monomeric plasmids. Excision from a dimeric plasmid usually resulted in two types of mutant plasmids; a dimeric plasmid, where the Tn5 had excised from one of the plasmid units, and a monomeric parental pBR322. A mechanisms to account for this is suggested. Complementation tests revealed that the increased mutation rate on dimeric plasmids is the result of dimers being mutaphilic per se, rather than the result of a general, trans-acting increase in mutation rates of the host, induced by the presence of the dimeric plasmid. Furthermore, it was found that the rate of Tn5 excision from plasmids in the monomeric state was increased when the region carrying the inserted Tn5 was duplicated.

Microbiological Research, 2013

An important criterion for the selection of a probiotic bacterial strain is its ability to adhere... more An important criterion for the selection of a probiotic bacterial strain is its ability to adhere to the mucosal surface. Adhesion is usually mediated by proteins or other components located on the outer cell surface of the bacterium. In the present study we characterized the adhesive properties of two classical intracellular enzymes glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and enolase (ENO) isolated from the outer cell surface of the probiotic bacterium Lactobacillus plantarum 299v. None of the genes encoded signal peptides or cell surface anchoring motifs that could explain their extracellular location on the bacterial surface. The presence of the glycolytic enzymes on the outer surface was verified by western blotting using polyclonal antibodies raised against the specific enzymes. GAPDH and ENO showed a highly specific binding to plasminogen and fibronectin whereas GAPDH but not ENO showed weak binding to mucin. Furthermore, a pH dependent and specific binding of GAPDH and ENO to intestinal epithelial Caco-2 cells at pH 5 but not at pH 7 was demonstrated. The results showed that these glycolytic enzymes could play a role in the adhesion of the probiotic bacterium L. plantarum 299v to the gastrointestinal tract of the host. Finally, a number of probiotic as well non-probiotic Lactobacillus strains were analyzed for the presence of GAPDH and ENO on the outer surface, but no correlation between the extracellular location of these enzymes and the probiotic status of the applied strains was demonstrated.

Journal of Dairy Research, 2006

Bovine milk contains a number of indigenous proteolytic enzymes, of which plasmin is the most imp... more Bovine milk contains a number of indigenous proteolytic enzymes, of which plasmin is the most important (Grufferty & Fox, 1988; Bastian & Brown, 1996; Kelly & McSweeney, 2003). Plasmin (EC 3.4.21.7) is a serine proteinase with pH and temperature optima of 7·5 and 37 °C, respectively. In milk, most of the plasmin is present as its inactive precursor, plasminogen, which is converted to active plasmin by plasminogen activators (PA) present in milk, e.g., urokinase-type (u-PA) and tissue-type PA (t-PA) (Bastian & Brown, 1996). Since plasmin, plasminogen and PA are associated with casein micelles, they are incorporated into cheese curd, while plasmin inhibitors and inhibitors of PA are lost with the whey. Plasmin incorporated in cheese curd acts on its substrate, the caseins, contributing significantly to primary proteolysis during ripening (Upadhyay et al. 2004b).

Inflammatory Bowel Diseases, 2010

Inflammatory Bowel Diseases, 2012

Probiotics may alter immune regulation. Recently, we showed that the probiotic bacteria Lactobaci... more Probiotics may alter immune regulation. Recently, we showed that the probiotic bacteria Lactobacillus acidophilus NCFM™ influenced the activity of regulatory T cells (Tregs) in vitro. The aim of the present work was to demonstrate if L. acidophilus NCFM™ also affects the function of Tregs in vivo. Development of colitis after transfer of CD4+CD25- T cells and protection from colitis by Tregs was studied in immunodeficient SCID mice which were simultaneously tube-fed with L. acidophilus NCFM™ or L. salivarius Ls-33 for 5 weeks. Probiotic-fed SCID mice transplanted with low numbers of Tregs in addition to the disease-inducing T cells were completely protected from colitis. This was in contrast to the control group, which showed intermediate levels of inflammation. In addition, feeding with probiotics lowered serum levels of inflammatory cytokines in both colitic mice and in mice protected from colitis by Tregs. Gene expression patterns of rectum samples of protected mice that receive either one of the probiotics showed a closer resemblance to naïve SCID mice than did patterns of the control group. The mechanism of action of the probiotics appears to be an indirect effect by inducing a Treg-favorable environment rather than a direct effect on the Tregs. L. acidophilus NCFM™ and L. salivarius Ls-33 feeding of SCID mice increases the in vivo effect of Tregs, resulting in a gene expression pattern in the rectum resembling that of the naïve SCID mouse.