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Biomedical subjects

P Falk

Publications and source records attributed to P Falk.

At least 37 records · Page 2Linked to original sources
PubMed2000

Vancomycin-resistant enterococci.

After they were first identified in the mid-1980s, vancomycin-resistant enterococci (VRE) spread rapidly and became a major problem in many institutions both in Europe and the United States. Since VRE have intrinsic resistance to most of the commonly used antibiotics and the ability to acquire resistance to most of the current available antibiotics, either by mutation or by receipt of foreign genetic material, they have a selective advantage over other microorganisms in the intestinal flora and pose a major therapeutic challenge. The possibility of transfer of vancomycin resistance genes to other gram-positive organisms raises significant concerns about the emergence of vancomycin-resistant Staphylococcus aureus. We review VRE, including their history, mechanisms of resistance, epidemiology, control measures, and treatment.

Anti-Bacterial Agents↗
PubMed1999

The morphological transition of Helicobacter pylori cells from spiral to coccoid is preceded by a substantial modification of the cell wall.

The peptidoglycan (murein) of Helicobacter pylori has been investigated by high-performance liquid chromatography and mass spectrometric techniques. Murein from H. pylori corresponded to the A1gamma chemotype, but the muropeptide elution patterns were substantially different from the one for Escherichia coli in that the former produced high proportions of muropeptides with a pentapeptide side chain (about 60 mol%), with Gly residues as the C-terminal amino acid (5 to 10 mol%), and with (1-->6)anhydro-N-acetylmuramic acid (13 to 18 mol%). H. pylori murein also lacks murein-bound lipoprotein, trimeric muropeptides, and (L-D) cross-linked muropeptides. Cessation of growth and transition to coccoid shape triggered an increase in N-acetylglucosaminyl-N-acetylmuramyl-L-Ala-D-Glu (approximately 20 mol%), apparently at the expense of monomeric muropeptides with tri- and tetrapeptide side chains. Muropeptides with (1-->6)anhydro-muramic acid and with Gly were also more abundant in resting cells.

Cell Wall↗
PubMed1998

Thrombin signal transduction of the fibrinolytic system in human adult venous endothelium in vitro.

Thrombin can regulate the-fibrinolytic system by increasing the endothelial production of both tissue plasminogen activator (t-PA) and plasminogen activator inhibitor type-1 (PAI-1). The thrombin receptor transducts signals through the GTP-binding protein system, the classical pathway being the Galpha q-protein. The purpose of the present study was to examine the roles of Galpha i-protein and tyrosine kinases in the thrombin signal transduction of t-PA and PAI-1 production from human adult vein endothelial cells (HAVEC). t-PA and PAI-1 antigen were analysed in conditioned medium from cultured HAVEC after 16 h incubation. Data are expressed as percentages of basal release (100%), means +/- 95% confidence intervals. Thrombin increased t-PA and PAI-1 production (234 +/- 42% and 211 +/- 42%, respectively). Pertussis toxin (PTX) (inhibiting Galpha i-pathway) reduced basal PAI-1 (66 +/- 8%), but had only a weak influence on basal t-PA production. Pertussis toxin and genistein (inhibiting tyrosine kinase) significantly reduced the thrombin induction of both t-PA and PAI-1 (PTX: 142 +/- 23% and 146 +/- 19%, respectively, genistein: 156 +/- 42% and 76 +/- 24%, respectively). The present study demonstrated that thrombin can increase the production of t-PA and PAI-1 by transducting signals through the Galpha i and tyrosine kinase pathway, in addition to the Galpha q/protein kinase C pathway as has been found previously.

Adult↗
PubMed1998

Characterization and fibrinolytic properties of mesothelial cells isolated from peritoneal lavage.

Human peritoneal mesothelial cells were harvested from patients undergoing open or laparoscopic surgery for non-septic conditions using three different approaches: (1) from a peritoneal biopsy, (2) from peritoneal fluid, and (3) from lavage fluid collected from peritoneal cavity. When these different methods were compared, cells derived from peritoneal fluid or lavage were more likely to result in established cultures than those obtained from biopsies. The cells displayed morphological, immunohistochemical and ultrastructural characteristics of mesothelial cells. The cultured mesothelial cells produced tissue type plasminogen activator (t-PA), urokinase plasminogen activator (uPA), and plasminogen activator inhibitor type-1 and type-2 (PAI-1 and PAI-2) during unstimulated conditions. Treatment with the proinflammatory mediators LPS and TNF-alpha resulted in an overall decreased fibrinolytic capacity with a decrease in the release of t-PA and an increase in plasminogen activator inhibitors PAI-1 and PAI-2. TNF-alpha had a more profound effect than LPS, especially on the release of t-PA. This may be an important mechanism by which inflammatory mediators disrupt the fibrin degradation. In conclusion, peritoneal lavage is a convenient and reproducible source of mesothelial cells for culture.

Cell Division↗
PubMed1997

The effect of linomide, an immunoregulator in experimental autoimmune diseases, on humoral antibody responses in mice.

Linomide (quinoline-3-carboxamide), a well tolerated, orally administered compound was recently shown to be effective in the prevention and treatment of several autoimmune diseases in experimental animal models. We have investigated its effect on specific humoral immune responses directed to T-cell-dependent soluble or particulate antigens and to a T cell-independent antigen in several mouse strains. Linomide administered after antigen priming did not affect primary and secondary antibody responses directed to T-cell particulate antigens (SRBC) or soluble antigens given with or without complete Freund's Adjuvant (CFA). Linomide treatment given prior to antigen priming did not affect the antibody response to a soluble antigen (TNP-KLH) given with an adjuvant. In contrast, dose-dependent down regulation of primary antibody responses was observed when T cell-dependent (BSA-dextran) or T-cell-independent (TNP-Ficoll) antigens were administered in an immunogenic form without adjuvant after starting Linomide treatment. The primary anti-SRBC antibody response was also suppressed by high dose Linomide given prior to immunization although normal secondary responses were retained. It is worth noting that no immunosuppressive effects on antibody responses were found at low dose ranges which effectively reversed T cell dependent autoimmune manifestation.

Animals↗
PubMed1996

Outcome of unrelated donor bone marrow transplantation in 40 children with Hurler syndrome.

Long-term survival and improved neuropsychological function have occurred in selected children with Hurler syndrome (MPS I H) after successful engraftment with genotypically matched sibling bone marrow transplantation (BMT). However, because few children have HLA-identical siblings, the feasibility of unrelated donor (URD) BMT as a vehicle for adoptive enzyme therapy was evaluated in this retrospective study. Forty consecutive children (median, 1.7 years; range, 0.9 to 3.2 years) with MPS I H received high-dose chemotherapy with or without radiation followed by BMT between January 27, 1989 and May 13, 1994. Twenty-five of the 40 patients initially engrafted. An estimated 49% of patients are alive at 2 years, 63% alloengrafted and 37% autoengrafted. The probability of grade II to IV acute graft-versus-host disease (GVHD) was 30%, and the probability of extensive chronic GVHD was 18%. Eleven patients received a second URD BMT because of graft rejection or failure. Of the 20 survivors, 13 children have complete donor engraftment, two children have mixed chimeric grafts, and five children have autologous marrow recovery. The BM cell dose was correlated with both donor engraftment and survival. Thirteen of 27 evaluable patients were engrafted at 1 year following URD BMT. Neither T-lymphocyte depletion (TLD) of the bone marrow nor irradiation appeared to influence the likelihood of engraftment. Ten of 16 patients alive at 1 year who received a BM cell dose greater than or equal to 3.5 x 10(8) cells/kg engrafted, and 62% are estimated to be alive at 3 years. In contrast, only 3 of 11 patients receiving less than 3.5 x 10(8) cells/kg engrafted, and 24% are estimated to be alive at 3 years (P = .05). The mental developmental index (MDI) was assessed before BMT. Both baseline and post-BMT neuropsychological data were available for 11 engrafted survivors. Eight children with a baseline MDI greater than 70 have undergone URD BMT (median age, 1.5 years; range, 1.0 to 2.4 years). Of these, two children have had BMT too recently for developmental follow-up. Of the remaining six, none has shown any decline in age equivalent scores. Four children are acquiring skills at a pace equal to or slightly below their same age peers; two children have shown a plateau in learning or extreme slowing in their learning process. For children with a baseline MDI less than 70 (median age, 2.5 years; range, 0.9 to 2.9 years), post-BMT follow-up indicated that two children have shown deterioration in their developmental skills. The remaining three children are maintaining their skills and are adding to them at a highly variable rate. We conclude that MPS I H patients with a baseline MDI greater than 70 who are engrafted survivors following URD BMT can achieve a favorable long-term outcome and improved cognitive function. Future protocols must address the high risk of graft rejection or failure and the impact of GVHD in this patient population.

Bone Marrow Transplantation↗
PubMed1996

Helicobacter pylori--can the mechanisms of pathogenesis guide us towards novel strategies for treatment and prevention?

Helicobacter pylori establishes a chronic infection in the stomach of humans. The infection is associated with a low grade inflammatory response in the epithelium that can develop into chronic active gastritis, peptic ulcer disease or neoplasia. Antibiotics have dramatically decreased the rate of recurrence of peptic ulcers. However, antibiotic resistance is already evident, casting doubts on the future efficacy of these strategies. The link between childhood infection and severe health problems, including increased risk for gastric tumours motivate efforts to develop vaccines. Characterization of the molecular mechanisms of pathogenesis will pave the way for novel strategies for treatment and prevention of H. pylori infection.

Acute Disease↗
PubMed1995

Human milk kappa-casein and inhibition of Helicobacter pylori adhesion to human gastric mucosa.

Readily digested caseins, which account for almost half of the protein content in human milk, are important as nutritional protein for breast-fed infants. It has also been advocated that part of the antimicrobial activity of human milk resides in the caseins, most likely the glycosyated K-casein. Top explore this possibility, we purified K-casein from human milk to homogeneity by a two-step size-exclusion chromatography procedure. Purified human K-casein, in contrast to K-casein purified from bovine milk, effectively inhibited the cell lineage-specific adhesion of fluoroisothiocyanate-labeled Helicobacter pylori to human gastric surface mucous cells. The inhibitory activity was abolished by metaperiodate oxidation and considerably reduced by preincubation with alpha-L-fucosidase but not with alpha-N-acetylneuraminidase or endo-beta-galactosidase. These results strongly support the view that fucose containing carbohydrate moieties of human K-casein are important for inhibition of H. pylori adhesion and, thus, infection. They also suggest that breastfeeding may protect from infection by H. pylori during early life and that species-specific glycosylation patterns, as illustrated by human bovine K-casein, partly determine both the narrow host spectrum of this human gastric pathogen and the capacity to resist infection.

Animals↗
PubMed1995

Moluccella laevis lectin, a marker for cellular differentiation programs in mouse gut epithelium.

We have assembled a system for testing the hypothesis that changes in glycoconjugate production represent markers for defining developmental, spatial, and environmental influences on the proliferation and differentiation programs of various mouse gut epithelial cell lineages. Multilabel immunohistochemical methods were used to survey the interactions of purified lectins with 1) normal fetal, neonatal, and adult FVB/N mouse gut, 2) gastric and intestinal isografts harvested at various developmental stages, and 3) transgenic mouse models of intestinal epithelial cell hyperplasia, dysplasia, and/or neoplasia. As a demonstration of the system's utility, we used the recently purified, alpha-N-acetyl-D-galactosamine-specific, Moluccella laevis lectin (MLL). In the adult FVB/N mouse stomach, MLL only recognizes glycoconjugates produced by a population of nonproliferating neck and prezymogenic cells that occupy a pivotal point in the complex, migration-associated differentiation program of the zymogenic cell lineage. In the developing FVB/N stomach, MLL binds to members of the zymogenic and pit lineages even before morphogenesis of gastric units is completed. Expression of MLL epitopes in pit cells is restricted to the period before the gastric epithelium has completed its morphoregulatory program. Analysis of gastric isografts indicates that these lineage- and developmental stage-specific patterns of glycoconjugate accumulation are not influenced by normal luminal contents. In the adult FVB/N intestine, MLL binding can be used to operationally define variations in the differentiation programs of 1) members of the enteroendocrine and goblet cell lineages during their migration along the crypt-to-villus axis and 2) cells comprising the follicle-associated epithelium overlying Peyer's patches. Accumulation of MLL epitopes in villus-associated enterocytes does not appear to be affected when these cells are induced to reenter the cell cycle by simian virus 40 large T antigen (SV40 TAg). MLL reactivity is not diminished when enterocytes begin to dedifferentiate as a result of production of SV40 TAg, human K-rasVal12, and a dominant negative human p53 mutant. The lack of change in MLL binding properties may reflect the brief residence time of enterocytes on the villus. These results indicate that glycoconjugate production represents a very useful tool for studying gut epithelial cell biology. Preliminary studies suggest that this is also true in the human gut.

Animals↗
PubMed1994

Paneth cell differentiation in the developing intestine of normal and transgenic mice.

Paneth cells represent one of the four major epithelial lineages in the mouse small intestine. It is the only lineage that migrates downward from the stem-cell zone located in the lower portion of the crypt of Lieberkühn to the crypt base. Mature Paneth cells release growth factors, digestive enzymes, and antimicrobial peptides from their apical secretory granules. Some of these factors may affect the crypt stem cell, its transit-cell descendants, differentiating villus-associated epithelial lineages, and/or the gut microflora. We used single and multilabel immunocytochemical methods to study Paneth cell differentiation during and after completion of gut morphogenesis in normal, gnotobiotic, and transgenic mice as well as in intestinal isografts. This lineage emerges coincident with cytodifferentiation of the fetal small intestinal endoderm, formation of crypts from an intervillus epithelium, and establishment of a stem-cell hierarchy. The initial differentiation program involves sequential expression of cryptdins, a phospholipase A2 (enhancing factor), and lysozyme. A dramatic increase in Paneth cell number per crypt occurs during postnatal days 14-28, when crypts proliferate by fission. Accumulation of fucosylated and sialylated glycoconjugates during this period represents the final evolution of the lineage's differentiation program. Establishment of this lineage is not dependent upon instructive interactions from the microflora. Transgenic mice containing nucleotides -6500 to +34 of the Paneth cell-specific mouse cryptdin 2 gene linked to the human growth hormone gene beginning at its nucleotide +3 inappropriately express human growth hormone in a large population of proliferating and nonproliferating cells in the intervillus epithelium up to postnatal day 5. Transgene expression subsequently becomes restricted to the Paneth cell lineage in the developing crypt. Cryptdin 2 nucleotides -6500 to +34 should be a useful marker of crypt morphogenesis and a valuable tool for conducting gain-of-function or loss-of-function experiments in Paneth cells.

Animals↗
PubMed1994

Helicobacter pylori: molecular basis for host recognition and bacterial adherence.

The bacterium Helicobacter pylori is tropic for epithelial cells and the mucus layer in the stomach lining, and is associated with the development of gastritis, ulcers and possibly also gastric malignancies. Adherence to the gastric epithelial cells is mediated by fucosylated blood-group antigens associated with blood-group O phenotype, which could explain the higher prevalence of ulcerative disease in individuals with this blood group.

ABO Blood-Group System↗
PubMed1994

Sequence changes in the pilus subunit lead to tropism variation of Neisseria gonorrhoeae to human tissue.

Pili of Neisseria gonorrhoeae are correlated with increased bacterial attachment to epithelial cells and undergo both phase and antigenic variation. Phase variation of gonococcal pili can be brought about by recombination events in the pilin structural gene, pilE, or by the on/off switch in expression of PilC, a pilus biogenesis protein for which two loci exist. We have studied the binding to epithelial cell lines and to fixed tissue sections of N. gonorrhoeae MS11 derivatives and mutants carrying structurally defined PilE and PilC proteins. In situ binding studies of N. gonorrhoeae to formalin-fixed tissue sections resulted in a binding pattern similar to that obtained using viable epithelial cell lines of different origin. Piliated gonococcal clones, containing different pilE sequences, varied dramatically from one another in their efficiencies at binding to corneal and conjunctival tissue, but bound equally well to cervical and endometrial tissues. Further, the binding data suggested that PilC expression by itself, i.e. without pili, cannot confer bacterial binding and that expression of either PilC1 or PilC2 does not confer different binding properties to the bacterial cells. Possible receptors for piliated gonococci were expressed in human tissues, such as cervix, endometrium, cornea, intestine, stomach, mid-brain and meninges, but not in human kidney. Pretreatment of the target tissues with Proteinase K decreased the gonococcal binding dramatically, whereas pretreatment with neuraminidase and meta-periodate, which cleave carbon-carbon linkages between vicinal hydroxyl groups in carbohydrates, did not affect attachment of gonococci. These data argue that pilus-dependent attachment of N. gonorrhoeae to human tissue may be mediated by a eukaryotic receptor having protein characteristics, and that the pilus subunit sequence may play an important role in the interaction with human cornea.

Amino Acid Sequence↗
PubMed1994

The amino-terminal domain of the P-pilus adhesin determines receptor specificity.

Pyelonephritic isolates of Escherichia coli commonly express P-pili, which mediate bacterial attachment to glycolipids on epithelial cell surfaces. Three classes of P-pili have been defined, based on varying specificity for galabiose-containing glycolipids. Variation in adhesive capacity is correlated with a shift in preferred host, suggesting that host tropism depends largely on detailed specificity for the globoseries glycolipids. In this study we examined the importance of the PapG adhesin in determining receptor specificity. Translational fusions were constructed between the amino-terminus of the PapG adhesin from each of the three pilus classes and a reporter protein. The binding specificity of the purified fusion proteins in vitro was identical to that seen with whole bacteria. Adherence of intact bacteria to cultured kidney cells was markedly reduced by a monoclonal antibody specific for the Class III adhesin (previously denoted PrsG), confirming the importance of the amino-terminus of PapG in mediating attachment to a receptor when presented on the eukaryotic cell surface. These results suggest that the detailed receptor specificity resides solely within the amino-terminus of the PapG adhesin and is independent of the complex pilus architecture.

Adhesins, Escherichia coli↗
PubMed1994

Lectins are sensitive tools for defining the differentiation programs of mouse gut epithelial cell lineages.

We have used histochemical methods to survey the cellular patterns of binding of a panel of 45 lectins with well-defined carbohydrate specificities to sections prepared from various regions of the gastric-to-colonic axis of fetal, neonatal, and adult FVB/N mouse gut. The results suggest that lectins can be used as remarkably sensitive tools to describe the differentiation programs of gastric and intestinal epithelial cell lineages as a function of their position along the cephalocaudal axis of the gut and as a function of developmental stage. Studies of intestinal isografts and transgenic mice that express Simian virus-40 T antigen in enterocytes suggest that many of these cell lineage-specific and spatial patterns of glycoconjugate production can be established and maintained in the absence of exposure to luminal contents and in the presence of specific proliferative abnormalities. This lectin panel should be useful for operationally defining subpopulations of the principal gut epithelial cell lineages in normal strains of mice, for describing variations in gut epithelial cell differentiation programs in mutant and transgenic mice, and for recovering specific epithelial cell lineages or subpopulations.

Aging↗
PubMed1994

Regional differences in glycoconjugates of intestinal M cells in mice: potential targets for mucosal vaccines.

We have used a panel of lectins and antibodies to describe the composition of complex carbohydrates associated with M cells in various regions of the intestinal tract of adult BALB/c mice. The fucose-specific lectin Ulex europaeus agglutinin type I (UEA I) is a marker of M cells in the small intestine and recognized M cells at an early stage of differentiation. Subpopulations of M cells in a single follicle-associated epithelium (FAE) could be distinguished by different fucose-specific probes. Certain lectins revealed that M cells have basal processes that extend into the underlying lymphoid tissue. Colonic and rectal M cells display glycosylation patterns distinct from M cells of Peyer's patches and are characterized by terminal galactose. UEA I selectively adhered to Peyer's patch M cells in mucosal explants and in ligated intestinal loops in vivo. The lectin was taken up into endocytic vesicles and transported to the intra-epithelial pocket and other domains of the basolateral membrane. Thus M cell-specific glycoconjugates could serve as "receptors" for targeting of lectin-antigen conjugates to the mucosal immune system.

Animals↗
PubMed1994

M protein and protein F act as important determinants of cell-specific tropism of Streptococcus pyogenes in skin tissue.

The pathogenic gram-positive bacterium Streptococcus pyogenes (group A streptococcus) causes numerous diseases of cutaneous tissue, each of which is initiated after the interaction of the bacterium with the cells of the epidermis. In this study, we show that different surface proteins of S. pyogenes play important roles in determining the cell-specific tropism of the bacterium in skin. Using streptococcal strains with defined mutations in the genes which encode surface proteins in combination with primary cultures of human skin and an in situ adherence assay which uses histological sections of human skin, we show that the M protein of S. pyogenes mediates the binding of the bacterium to keratinocytes, while a second streptococcal surface protein, protein F, directs the adherence of the organism to Langerhans' cells. Characterization of binding revealed that adherence was inhibited by purified streptococcal proteins and pretreatment of both host cells with the protease trypsin. Adherence was only slightly affected by the state of keratinocyte differentiation in vitro, but was considerably modulated in response to environmental conditions known to regulate expression of M protein and protein F, suggesting that the interaction between these bacterial cell-surface structures/adhesins and keratinocytes and Langerhans' cells may play an important role in streptococcal skin disease.

Antigens, Bacterial↗