Identification of Two Laminin-Binding Fimbriae, the Type 1 Fimbria of Salmonella enterica Serovar Typhimurium and the G Fimbria of Escherichia coli, as Plasminogen Receptors

Escherichia coli strains carrying recombinant plasmids encoding either the type 1 fimbria of Salmonella enterica serovar Typhimurium or the G fimbria of E. coli exhibited binding of human ¹²⁵I-Glu-plasminogen and enhanced the tissue-type plasminogen activator-catalyzed conversion of plasminogen to plasmin. Purified type 1 or G fimbriae similarly bound plasminogen and enhanced its activation. The binding of plasminogen did not involve the characteristic carbohydrate-binding property of the fimbriae but was inhibited at low concentrations by the lysine analog -aminocaproic acid. Because these fimbrial types bind to laminin of basement membranes (M. Kukkonen et al., Mol. Microbiol. 7:229–237, 1993; S. Saarela et al., Infect. Immun. 64:2857–2860, 1996), the results demonstrate a structural unity in the creation and targeting of bacterium-bound proteolytic plasmin activity to basement membranes.     

Morphology of cells and hemagglutinogens of Bordetella species: resolution of substructural units in fimbriae of Bordetella pertussis.

The morphology of cells and the hemagglutinogens isolated from cultures of Bordetella pertussis, Bordetella bronchiseptica, and Bordetella parapertussis were studied by electron microscopy with the negative-staining technique. Cells of all three species had long, thin (3 nm thick), peritrichously arranged fimbriae on the cell surface. Similar structures were found in purified hemagglutinogen preparations together with shorter fimbrial structures 3 nm thick and from 40 to 100 nm long. In one experiment, long, thin fimbriae isolated from B. pertussis were found to be arranged in a crystalline structure on the specimen grid after negative staining. Optical diffraction analysis with a filtering technique performed on micrographs of these structures revealed 12.5-nm-long substructures within individual fimbriae. Further analysis resolved each of these structures into three globules, a central globule 3.5 nm in diameter and two diametrically opposed globules 2.5 nm in diameter. Based on this substructural composition, it is suggested that subunits of the individual fimbriae are connected by fragile regions. The presence of such regions would explain the size heterogeneity of the filamentous structures observed in preparations of hemagglutinogens isolated from cultures of B. pertussis and B. bronchiseptica. The concept that the short filamentous structures present in purified preparations of hemagglutinogens originate from the surface fimbriae present on the cells is supported.     

Biomimetic porous scaffolds with high elasticity made from mineralized collagen--an animal study

Histological investigations of a new hydroxyapatite-collagen composite material were carried out to evaluate its possible suitability as a bone substitute. The three-dimensional scaffolds made from biomimetically mineralized collagen exhibit an interconnecting pore structure and elastic mechanical properties. They were implanted into the subcutaneous tissue and bone defects made in the femur of rats and harvested with the surrounding tissue at 1, 2, 4, 8, and 12 weeks after surgery. The materials implanted in the subcutaneous tissue were covered by fibrous connective tissue with a slight inflammatory response, and many foreign-body giant cells were observed on the surface of the scaffolds. Most of the material implanted in the subcutaneous tissue was resorbed at 8 weeks by phagocytosis. In the bone defects, new bone formation was observed on the surface of the material at 1 week. New bone increased with time, and osteoclasts were seen on the surface of the scaffolds at 2 weeks. Resorption and replacement by new bone of many parts of the materials implanted in the femur were observed by 12 weeks. These responses occurred faster than those of other hydroxyapatite-collagen composites. The results suggested that the new biomimetically mineralized collagen scaffolds were suitable as an implant material for bone-tissue reconstruction.     

Specific effects on human neutrophils of antibodies to a membrane protein constituent of neutrophil receptors for chemotactic formyl-methionyl peptides

IgG and Fab were prepared from goat antisera to MP-2, the quantitatively predominant membrane protein constituent of human neutrophil receptors for chemotactic formyl-methionyl peptides. Only 10%–25% of the f-Met-Leu-Phe combining sites of MP-2 purified from neutrophil membranes that had been solubilized in Nonidet P40 exhibited binding constants similar in magnitude to those of the receptors in intact neutrophils, while the remainder of the sites retained a mean of 2% of the affinity of native receptors. Purified MP-2 elicited IgG antibodies predominantly to framework determinants, rather than the combining site, of the f-Met-Leu-Phe receptors. IgG antibodies, but not Fab, evoked the release of significant quantities of β-glucuronidase and lysozyme from neutrophils. Saturating concentrations of Fab bound to a mean of 65,000 determinants per neutrophil, as assessed with ¹²⁵I-Fab, but failed to stimulate neutrophil chemotaxis or chemokinesis, and inhibited by 15% or less the binding of [³H]f-Met-Leu-Phe to intact neutrophils. Fab of anti-MP-2 inhibited neutrophil chemotactic responses to f-Met-Leu-Phe by up to 80%, without influencing the responses to equally chemotactic concentrations of fragments of C5 and of leukotriene B₄. Preincubation of neutrophils for 2–30 min at 37° with concentrations of f-Met-Leu-Phe which suppressed significantly the number of receptors available to [³H]f-Met-Leu-Phe, increased the number of receptors detected by ¹²⁵I-Fab of anti-MP-2, while neither fragments of C5 nor leukotriene B₄ altered the number of receptors determined by either assay. Antibodies to non-combining site determinants of chemotactic peptide receptors provide a novel immunospecific probe for studies of the regulation of neutrophil chemotaxis.     

Extensive cytological damage caused by measles in African children

The occurrence of mitotic and chromosomal aberrations was examined in cultured lymphocytes from 25 African children suffering from acute measles at an early stage (0-5 days after onset of rash).

In eight cases the mitotic response to phytohaemagglutinin was impaired. In two cases extensive changes were observed, involving the formation of giant polykaryotic syncytia with chromosome pulverization. It is suggested that the development of giant cells in vivo and the damage to epithelial membranes characteristic of severe measles in the tropics are to be correlated with these changes.

A varying incidence of minor chromosome aberrations, mostly small gaps, was found in 15 cases of measles as well as in controls. The specific relationship of this type of aberration to the virus is questionable.

Mitotic activity was induced in two replicate lymphocyte cultures in the absence of phytohaemagglutinin.

The possible oncogenic potential of the measles virus is discussed in connection with the fusion-pulverization phenomenon.

     

Nondetection of the S antigen due to the presence of sodium hypochlorite

Low concentrations of sodium hypochlorite (chlorine bleach) are known to destroy S antigen on intact fresh red blood cells (RBCs). Sodium hypochlorite is commonly used as a disinfectant. We report nondetection of the S antigen in tube and microplate saline indirect antiglobulin testing (SIAT) with a lot of commercial saline utilized in our donor screening and reference laboratories. Known S+s+ RBCs were found to be nonreactive with anti-S by SIAT in our reference laboratory. Our investigation demonstrated the presence of chlorine in the commercial saline. The saline lot was used for several days of donor screening and recall of FFP and platelet concentrates was initiated. Two lots of saline were recalled from blood banks across North America.     

A computer protocol to predict myocardial infarction in emergency department patients with chest pain

To achieve more appropriate triage to the coronary care unit of patients presenting with acute chest pain, we used clinical data on 1379 patients at two hospitals to construct a simple computer protocol to predict the presence of myocardial infarction. When we tested this protocol prospectively in 4770 patients at two university hospitals and four community hospitals, the computer-derived protocol had a significantly higher specificity (74 vs. 71 percent) in predicting the absence of infarction than physicians deciding whether to admit patients to the coronary care unit, and it had a similar sensitivity in detecting the presence of infarction (88.0 vs. 87.8 percent). Decisions based solely on the computer protocol would have reduced the admission of patients without infarction to the coronary care unit by 11.5 percent without adversely affecting the admission of patients in whom emergent complications developed that required intensive care. Although this protocol should not be used to override careful clinical judgment in individual cases, the computer protocol for the most part yields accurate estimates of the probability of myocardial infarction. Decisions about admission to the coronary care unit based on the protocol would have been as effective as those actually made by the unaided physicians who cared for the patients, and less costly. Whether physicians who are aided by the protocol perform better than unaided physicians cannot be determined without further study.     

The Dominant Epitope of Borrelia garinii Outer Surface Protein C Recognized by Sera from Patients with Neuroborreliosis Has a Surface-Exposed Conserved Structural Motif

Epitope mapping of outer surface protein C (OspC) by using sera from patients with neuroborreliosis led to the identification of one single major immunodominant epitope within the C-terminal 10 amino acid residues. Peptide binding studies and alanine replacement scanning of the C-terminal decapeptide, PVVAESPKKP, revealed a critical role for the PKKP sequence and its terminal carboxyl group for the binding of immunoglobulin M (IgM) antibodies from patients with Lyme borreliosis. Electron microscopy of antibody-labeled spirochetes indicated that the C-terminal region is exposed on the surface of the spirochete. Based on homology to proteins of known function, this region most probably adopts a polyproline II-like helix, which is found in surface-exposed structures involved in protein-protein interactions. This structural motif is highly conserved in Borrelia species causing Lyme borreliosis and subjected to purifying selection. We suggest that the abundance of the C-terminal region of OspC on the surface of B. burgdorferi allows a multimeric high-avidity interaction between the spirochete and surface Igs on B cells. The resulting cross-linking of surface Igs on B cells may induce a T-cell-independent B-cell activation without IgM-to-IgG switching, thus explaining the lack of IgG antibodies to OspC in neuroborreliosis.     

Differential effects of pentoxifylline on the production of tumour necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) by monocytes and T cells.

Pentoxifylline (PTX) is a methylxanthine compound known to inhibit the production of tumour necrosis factor-alpha (TNF-alpha) by monocytic cells. In this study, we found that PTX differentially regulates the production of TNF-alpha and interleukin-6 (IL-6). Indeed, PTX at high concentrations triggers the production of IL-6 but not of TNF-alpha by peripheral blood mononuclear cells (PBMC). Further experiments indicated that monocytes are responsible for this PTX-induced IL-6 production. When PBMC were stimulated with LPS, PTX was found to inhibit the secretion of TNF-alpha as well as the accumulation of TNF-alpha messenger RNA (mRNA). In contrast, no inhibitory effect was observed on the induction of IL-6. Similar results were obtained when PBMC were stimulated with OKT3 monoclonal antibody (mAb). In addition, the in vivo administration of PTX in transplant patients receiving the first dose of OKT3 allowed to decrease the systemic release of TNF-alpha but not of IL-6. Since monocytes represent a major source of TNF-alpha and IL-6 in these settings, additional experiments were performed in vitro on purified T cells stimulated with the CLB-T3/3, an anti-CD3 mAb which does not require the presence of accessory cells to activate T cells. In this system, PTX was found to inhibit the secretion of both TNF-alpha and IL-6 by T cells. We suggest that cAMP could be involved in these differential effects of PTX on production of TNF-alpha and of IL-6.