The chemotactic properties of Bradyrhizobium japonicum in the presence of natural fine-grained minerals

The natural argillaceous minerals montmorillonite and palygorskite were found to enhance the motility of Bradyrhizobium japonicum cells and to slow down their chemotactic motion to glucose. The latter effect of the minerals is probably due to the adsorption of mineral particles on the cell surface and the blockade of the receptors that are responsible for the chemotactic behavior of the bacterium.     

The macrophage chemotactic activity of Streptococcus agalactiae and Streptococcus iniae extracellular products (ECP)

The ability of Streptococcus agalactiae and Streptococcus iniae to attract macrophages of Nile tilapia (Oreochromis niloticus) was investigated. The extracellular products (ECP) from S. agalactiae and S. iniae were tested in vitro for macrophage chemotaxis using blind-well chambers. The macrophages were obtained from the peritoneal cavity 4-5 days after intraperitoneal injection of squalene. Both macrophage chemotactic and chemokinetic activities were demonstrated using the S. agalactiae ECP. However, only chemotactic activity was shown for S. iniae ECP. High-pressure liquid chromatography fractionation revealed that semi-purified S. agalactiae and S. iniae ECPs had estimated molecular weights of 7.54 and 19.2kDa, respectively. The prominent chemotactic activities of ECP from S. agalactiae and S. iniae are likely to be involved in the proinflammatory responses of macrophages to S. agalactiae and S. iniae infections.     

Stimulus-specificity of the chemotactic deactivation of human neutrophilis by lipoxygenase products of arachidonic acid

Preincubation of human neutrophils with chemotactic concentrations of 5(S)-hydroxy-eicosatetraenoic acid (5-HETE) or 5(S), 12(R)-dihydroxy-6, 14 cis-8, 10 trans-eicosatetraenoic acid (leukotriene B₄) induces a state of preferential chemotactic unresponsiveness to the homologous factor, termed deactivation, and less suppression of the responses to other chemotactic stimuli. The ratio of the concentration required for maximal chemotactic deactivation of neutrophils to that which stimulates chemotaxis optimally is greater for 5-HETE and leukotriene B₄ than for peptide and protein factors. In contrast to other chemotactic factors, 5-hydroperoxy-eicosatetraenoic acid (5-OOHETE) induces neutrophil chemotactic deactivation that is independent of the nature of the subsequent stimulus and is more slowly reversible after elimination of the fluid-phase deactivating factor. The unique characteristics of the chemotactic deactivation of human neutrophils by 5-OOHETE may be attributable in part to its endogenous metabolism to potent deactivating factors or to covalent derivatization of subcellular structures of the neutrophils by the highly reactive 5-OOHETE.     

Stimulus-specificity of the chemotactic deactivation of human neutrophils by lipoxygenase products of arachidonic acid

Preincubation of human neutrophils with chemotactic concentrations of 5(S)-hydroxy-eicosatetraenoic acid (5-HETE) or 5(S), 12(R)-dihydroxy-6,14 cis-8,10 trans-eicosatetraenoic acid (leukotriene B4) induces a state of preferential chemotactic unresponsiveness to the homologous factor, termed deactivation, and less suppression of the responses to other chemotactic stimuli. The ratio of the concentrations required for maximal chemotactic deactivation of neutrophils to that which stimulates chemotaxis optimally is greater for 5-HETE and leukotriene B4 than for peptide and protein factors. In contrast to other chemotactic factors, 5-hydroperoxy-eicosatetraenoic acid (5-OOHETE) induces neutrophil chemotactic deactivation that is independent of the nature of the subsequent stimulus and is more slowly reversible after elimination of the fluid-phase deactivating factor. The unique characteristics of the chemotactic deactivation of human neutrophils by 5-OOHETE may be attributable in part to its endogenous metabolism to potent deactivating factors or to covalent derivatization of subcellular structures of the neutrophils by the highly reactive 5-OOHETE.     

A structural model that explains the effects of hyperglycemia on collagenolysis

Prior investigations into the effects hyperglycemia on collagen degradation have yielded conflicting results. We present a new formalism for understanding the biochemistry of collagenolysis and the effects of hyperglycemia on collagen degradation. The analysis is based on an understanding of environments that affect the conformational stability of collagen. We suggest that collagen can exist in two distinct conformational states-a native state and a vulnerable state. Vulnerable collagen corresponds to a non-native conformation where partially unfolded regions near collagenase cleavage sites enable collagenases to efficiently degrade collagen. Theoretical calculations on collagen-like model peptides suggest that relatively short periods of hyperglycemia can alter the equilibrium distribution of states to favor vulnerable states of collagen. These data provide new insights into the mechanism of collagenolysis and resolve apparently discrepant experimental data on the effects of hyperglycemia on collagen degradation.     

Production of cyclooxygenase products and superoxide anion by macrophages in response to chemotactic factors

Mononuclear phagocytes are known to play a key role in various phlogistic reactions by synthesizing and releasing products that may potentiate or inhibit inflammatory processes. The expression of these products appears to be dependent on the source of the macrophage population as well as the stimulus employed. We have studied superoxide anion (O-2) production as well as the generation of PGE2, PGF2 alpha, and TXB2 from resident, oil-elicited and thioglycollate-induced peritoneal macrophages in mice in the presence and absence of chemotactic peptides. Production of O-2, occurred only in elicited macrophages stimulated with high concentrations of FMLP or C5a; resident cells stimulated with either of the chemotactic peptides were completely unresponsive. Although resident peritoneal macrophages incubated with chemotactic peptides did not generate O-2, these cells did secrete significant levels of PGE2, PGF2 alpha, and TXB2 in response to C5a. FMLP had no stimulatory effect. Elicited macrophages generated increased levels of PGE2 and PGF2 alpha when incubated with C5a. However, production of TXB2 was not stimulated. FMLP was inactive in stimulating PGE2, PGF2 alpha, and TXB2 in all types of macrophages studied. These studies indicate a heterogeneity in the production of inflammatory mediators from various macrophage populations in response to chemotactic factors.     

Production of cyclooxygenase products and superoxide anion by macrophages in response to chemotactic factors

Mononuclear phagocytes are knwon to play a key role in various phlogistic reactions by synthesizing and releasing products that may potentiate or inhibit inflammatory processes. The expression of these products appears to be dependent on the source of the macrophage population as well as the stimulus employed. We have studied superoxide anion (O₂⁻) production as well as the generation of PGE₂, PGF_2α, and TXB₂ from resident, oil-elicited and thiogylcollate-induced peritoneal macrophages in mice in the presence and absence of chemotactic peptides. Production of O₂⁻, occurred only in elicited macrophages stimulated with high concentrations of FMLP or C5a; resident cells stimulated with either of the chemotactic peptides were completely unresponsive. Although resident peritoneal macrophages incubated with chemotactic peptides did not generate O₂⁻, these cells did secrete significant levels of PGE₂, PGF_2α, and TXB₂ in response to C5a. FMLP had no stimulatory effect. Elicited macrophages generated increased levels of PGE₂ and PGF_2α when incubated with C5a. However, production of TXB₂ was not stimulated. FMLP was inactive in stimulating PGE₂, PGF_2α, and TXB₂ in all types of macrophages studied. These studies indicate a heterogeneity in the production of inflammatory mediators from various macrophage populations in response to chemotactic factors.     

Difference in requirement of macrophage products for concanavalin A-induced production of eosinophil chemotactic factor and macrophage chemotactic factor from guinea pig lymphocytes in vitro

Differences between the conditions for an eosinophil chemotactic factor (ECF) and macrophage chemotactic factor (MCF) production by lymphoid cells of mesenteric lymph nodes and spleen were studied in guinea pigs. If lymphoid cells were washed less than 4 hr after concanavalin A (Con A) stimulation and were cultured for an additional 24 hr, they failed to produce ECF, whereas Con A stimulation for 1 hr before washing was sufficient to stimulate them to produce MCF. Subsequently, it was shown that heat-labile soluble factors (termed ECF-PF) with potentiating activity for ECF production are produced from macrophages by 5 micrograms/ml Con A activation. When ECF-PF were added to the cell culture with 5 micrograms/ml Con A, the lymphoid cells could produce ECF even when they were washed 2 hr after Con A stimulation and were cultured for an additional 24 hr, suggesting that ECF-PF plays a critical role in the early stage of ECF production. The lymphoid cells were also able to produce ECF even when they were cultured with ECF-PF and a suboptimal dose of Con A (1 microgram/ml) for ECF production. Protein synthesis seemed to be essential for ECF-PF production. The ECF-PF activity was associated with two separated molecular fractions with m.w. of about 50,000 to 70,000 and of 10,000 to 20,000. It is thus suggested that ECF is produced from T cells by Con A stimulation under conditions which differ, at least, from those for MCF in the requirement of ECF-PF.     

Insulin, at physiological concentrations, enhances the polymorphonuclear leukocyte chemotactic properties.

We investigated the influence of insulin on human polymorphonuclear leukocyte (PMN) chemotaxis induced by mediators in a microchamber assay. Insulin increased, with a dose-response relationship, chemotaxis induced by formyl-methionyl-leucyl-phenylalanine, calcium ionophore and phorbol-miristyl acetate (p = 0.0057, p = 0.0001 and p = 0.0215, respectively). The hormone effect was present also at the physiological concentration of 40 microU/ml. Our data show that insulin affects PMN activity in normal subjects and therefore support the hypothesis that insulin deficiency may be responsible for the impaired PMN function observed in diabetic patients in poor metabolic control.     

The chemotactic behavior of computer-based surrogate bacteria

BACKGROUND: Chemotaxis is the process by which organisms migrate toward nutrients and favorable environments and away from toxins and unfavorable environments. In many species of bacteria, this occurs when extracellular signals are detected by transmembrane receptors and relayed to flagellar motors, which control the cell's swimming behavior. RESULTS: We used a molecularly detailed reaction-kinetics model of the chemotaxis pathway in Escherichia coli coupled to a graphical display based on known swimming parameters to simulate the responses of bacteria to 2D gradients of attractants. The program gives the correct phenotype of over 60 mutants in which chemotaxis-pathway components are deleted or overexpressed and accurately reproduces the responses to pulses and step increases of attractant. In order to match the known sensitivity of bacteria to low concentrations of attractant, we had to introduce a set of "infectivity" reactions based on cooperative interactions between neighboring chemotaxis receptors in the membrane. In order to match the impulse response to a brief stimulus and to achieve an effective accumulation in a gradient, we also had to increase the activities of the adaptational enzymes CheR and CheB at least an order of magnitude greater than published values. Our simulations reveal that cells develop characteristic levels of receptor methylation and swimming behavior at different positions along a gradient. They also predict a distinctive "volcano" profile in some gradients, with peaks of cell density at intermediate concentrations of attractant. CONCLUSIONS: Our results display the potential use of computer-based bacteria as experimental objects for exploring subtleties of chemotactic behavior.     

Cell surface collagenolysis requires homodimerization of the membrane-bound collagenase MT1-MMP

Pericellular degradation of interstitial collagens is a crucial event for cells to migrate through the dense connective tissue matrices, where collagens exist as insoluble fibers. A key proteinase that participates in this process is considered to be membrane-type 1 matrix metalloproteinase (MT1-MMP or MMP-14), but little is known about the mechanism by which it cleaves the insoluble collagen. Here we report that homodimerization of MT1-MMP through its hemopexin (Hpx) domain is essential for cleaving type I collagen fibers at the cell surface. When dimerization was blocked by coexpressing either a membrane-bound or a soluble form of the Hpx domain, cell surface collagenolytic activity was inhibited in a dose-dependent manner. When MMP-13, a soluble collagenase active as a monomer in solution, was expressed as a membrane-anchored form on the cell surface, homodimerization was also required to cleave collagen. Our results introduce a new concept in that pericellular collagenolysis is regulated by correct molecular assembly of the membrane-anchored collagenase, thereby governing the directionality of the cell to migrate in tissue.     

Antibacterial properties of antimicrobial-finished textile products

The antibacterial properties of five kinds of antimicrobial-finished textile products (AFTPs) were examined against Staphylococcus aureus, including methicillin-resistant (MRSA) strains and Pseudomonas aeruginosa, under wet and dry conditions. Textile products containing Ag. Zn. ammonium Zeolite and chitosan were found to be effective against methicillin-sensitive S. aureus (MSSA) for up to 6 hr of incubation under wet and dry conditions, and effective against MRSA for up to 24 hr of incubation only under wet conditions. Under dry conditions, however, all AFTPs were ineffective against one MRSA strain. When organic matter was added to the incubation mixture, textile products containing Ag. Zn. ammonium Zeolite and chitosan still showed antibacterial activities, but not as strongly. The results of this study suggested the following: (1) There are differences in antibacterial properties among commercially available AFTPs; (2) Determining effectiveness requires several hours of incubation; (3) Water content as an environmental factor can affect effectiveness; and (4) Some bacterial species and strains are not affected by AFTPs. The antibacterial properties of AFTPs in the clinical setting may be of limited value.     

Effect of an induced conformational change on the physical properties of two chemotactic receptor molecules.

The physical properties and conformational dynamics of the Salmonella typhimurium ribose and galactose receptors have been examined. Studies involving circular dichroism, fluorescence, absorption spectroscopy, and sedimentation analysis show that the two receptor proteins have different morphologies and exhibit diverse responses to sugar binding. The ribose receptor lacks both tryptophan and disulfide residues, and the galactose receptor lacks disulfides and has only a single tryptophan residue. By virtue of these fortuitous properties, the conformational changes induced in these proteins by sugar binding can be dissected by utilizing a variety of physical probes. A ligand-induced conformational change in the ribose receptor is shown by circular dichroism and fluorescence spectroscopy, which reveal spectral changes assignable to tyrosine, phenylalanine, and methionine residues. A conformational change in the galactose receptor has been demonstrated by fluorescence spectroscopy involving the distant reporter group method, which shows changes assignable to tryptophan and methionine sites and which is corroborated by sedimentation analysis. It is clear that there are extensive conformational changes in the two receptor proteins and that the different physical methods provide complementary information on the nature of these changes.     

The effect of thaumatins on the chemotactic behaviour of Escherichia coli

Thaumatin, an intensely sweet-tasting protein, completely blocksthe motility of Escherichia coli at concentrations 0.01%. Thismotility is restored if the phosphate concentration in the suspensionis increased to 0.025 mol/l. Unlike native thaumatin, chemicallymodified thaumatin with one acetyl group attached to the -aminogroup of the lysine residue is a good attractant for E. colilike, e.g., L-serine. Hypotheses have been constructed to explainthe action observed for thaumatins and phosphate. It is suggestedthere might be a similarity between the chemotactic activitiesof bacteria and the sensory responses in humans.     

The effect of the cyclopropyl group on the conformation of chemotactic formyl tripeptides

Certain formyl peptides are powerful chemoattractants towards neutrophils. In this study, several formyl tripeptides were synthesized and used to investigate the effects of different amino acid residues in position 1 on their ability to stimulate neutrophil chemotaxis. Pig neutrophil chemotaxis towards the formyl tripeptide, HCO-Ac(3)C-Leu-Phe-OMe 1, where Ac(3)C represents 1-amino-1-cyclopropane carboxylic acid, was observed. Pig neutrophil chemotaxis towards a very similar formyl tripeptide, HCO-Aib-Leu-Phe-OMe 2, where Aib represents alpha-amino isobutyric acid, was not observed. Compared to the isopropyl group, it was shown that the cyclopropyl group induces a greater percentage of the E conformation about the formamide functionality in these peptides. For 1 and 2, the E isomer distributions in CDCl3 are 36 and 9%, respectively. Since a major difference between these two peptides is the Z/E isomeric distribution, one implication is that the peptide-receptor site interactions involving the E conformer are more effective than those of the Z conformer. No pig neutrophil chemotaxis towards the formyl tripeptides, HCO-Ala-Leu-Phe-OMe 3 and HCO-Gly-Leu-Phe-OMe 4 was observed. These formyl tripeptides exhibit a low percentage of the E isomer, similar to that of peptide 2.     

The chemotactic characteristics of the S and R dissociants of Bacillus thuringiensis

The chemotactic responses of Bacillus thuringiensis subsp. dendrolimus (strain 49) and thuringiensis (strain 2002) and their morphological dissociants were studied by using some natural and artificial substances as effectors. The 12-h-old wild-type cells (S variants) of both strains were found to be motile and similar in their chemotactic responses, whereas the chemotactic responses of R variants were different.