In chemotaxing fibroblasts, both high-fidelity and weakly biased cell movements track the localization of PI3K signaling

Cell movement biased by a chemical gradient, or chemotaxis, coordinates the recruitment of cells and collective migration of cell populations. During wound healing, chemotaxis of fibroblasts is stimulated by platelet-derived growth factor (PDGF) and certain other chemoattractants. Whereas the immediate PDGF gradient sensing response has been characterized previously at the level of phosphoinositide 3-kinase (PI3K) signaling, the sensitivity of the response at the level of cell migration bias has not yet been studied quantitatively. In this work, we used live-cell total internal reflection fluorescence microscopy to monitor PI3K signaling dynamics and cell movements for extended periods. We show that persistent and properly aligned (i.e., high-fidelity) fibroblast migration does indeed correlate with polarized PI3K signaling; accordingly, this behavior is seen only under conditions of high gradient steepness (>10% across a typical cell length of 50 μm) and a certain range of PDGF concentrations. Under suboptimal conditions, cells execute a random or biased random walk, but nonetheless move in a predictable fashion according to the changing pattern of PI3K signaling. Inhibition of PI3K during chemotaxis is accompanied by loss of both cell-substratum contact and morphological polarity, but after a recovery period, PI3K-inhibited fibroblasts often regain the ability to orient toward the PDGF gradient.     

Inhibition of human neutrophil chemotaxis by the protein kinase inhibitor, 1-(5-isoquinolinesulfonyl) piperazine

The protein kinase inhibitor, 1-(5-isoquinolinesulfonyl) piperazine (C-I), inhibits superoxide release from human neutrophils (PMN) stimulated with phorbol myristate acetate or synthetic diacylglycerol, without inhibiting superoxide release from PMN stimulated with the chemoattractants C5a or N-formyl-methionyl-leucyl-phenylalanine (f-Met-Leu-Phe). In this study, we investigated the effect of C-I on human PMN chemotaxis to C5a, f-Met-Leu-Phe, leukotriene B4 (LTB4), and fluoresceinated N-formyl-methionyl-leucyl-phenylalanine-lysine (f-Met-Leu-Phe-Lys-FITC). PMN, preincubated for 5 min at 37 degrees C with 0 to 200 microM C-I, were tested for their migratory responses to the chemoattractants. C-I (greater than or equal to 1 microM) significantly inhibited PMN chemotaxis to f-Met-Leu-Phe, f-Met-Leu-Phe-Lys-FITC, and C5a without affecting random migration. Maximal inhibition of chemotaxis to these attractants occurred with greater than or equal to 50 microM C-I, at which chemotaxis was inhibited by 80 to 95%. The C-I inhibition was reversible. In contrast, 200 microM C-I did not inhibit the number of PMN migrating to LTB4, although, the leading front of PMN migration to LTB4 was inhibited by C-I. C-I inhibited PMN orientation to C5a and f-Met-Leu-Phe without affecting orientation to LTB4. C-I did not inhibit the binding of radiolabeled f-Met-Leu-Phe or f-Met-Leu-Phe-Lys-FITC to PMN. These findings suggest that the chemotactic responses of PMN to f-Met-Leu-Phe and C5a involve a protein kinase-dependent reaction which is inhibited by C-I.     

Anthrax toxin components stimulate chemotaxis of human polymorphonuclear neutrophils

Effects of the three-component toxin of Bacillus anthracis on chemotaxis of human polymorphonuclear leukocytes (PMN) were investigated in an effort to determine the basis of the reported antiphagocytic effect of the toxin. The three toxin components, edema factor (EF), protective antigen (PA), and lethal factor (LF), were tested alone and in various combinations for their effect on PMN chemotaxis under agarose to formyl peptides and zymosan-activated serum. No component was active alone; combinations of EF + PA, LF + PA, and EF + LF + PA markedly stimulated chemotaxis (directed migration), but had little or no effect on unstimulated random migration. The toxin components were not themselves chemoattractants. EF in combination with PA had previously been identified as an adenylate cyclase in Chinese hamster ovary (CHO) cells. We found that EF + PA produced detectable cyclic adenosine 3'-5'monophosphate (cAMP) in PMN, but the level of cAMP was less than 1% of that produced in CHO cells by EF + PA, and in PMN by other bacterial adenylate cyclases. LF + PA (which stimulated chemotaxis to an equivalent extent) had no effect on cAMP levels. Thus, the enhancement of chemotaxis by anthrax toxin (at least by LF + PA) does not seem to be related to adenylate cyclase activity.     

Neutrophil thrombospondin receptors are linked to GTP-binding proteins

The extracellular matrix (ECM) protein thrombospondin (TSP) binds to specific receptors on polymorphonuclear leukocytes (PMNs) and stimulates motility. TSP can also enhance the response of PMNs to the formylated peptide, N-formyl-methionyl-leucyl-phenylalanine (FMLP). Our initial evidence suggesting that PMN TSP receptors were linked to GTP-binding proteins (G-proteins) came from studies using pertussis toxin (PT) and cholera toxin (CT) to inhibit TSP-mediated motility. Both PT and CT inhibited TSP-mediated chemotaxis and substrate-associated random migration. Inhibition was not indirectly caused by a rise in cAMP since neither dibutyryl cAMP (300 μM) nor 8-bromo-cAMP (300 μM) significantly affected TSP-mediated motility. In fact, TSP itself caused a significant rise in intracellular cAMP levels (from 7.2 ± 0.3 to 14.2 ± 0.1 pmol/10⁶ cells). Although we could not test the PT sensitivity of TSP priming for FMLP-mediated chemotaxis (as PT inhibits FMLP-mediated chemotaxis itself), we evaluated the effect of CT on this response. CT completely abolished TSP-dependent priming of FMLP-mediated chemotaxis. Direct evidence for an interaction between TSP receptors and G-proteins was obtained by examining the effect of TSP on α-subunit ADP-ribosylation, GTPase activity, and GTPγS binding. We observed a decrease in the ability of FMLP to stimulate GTPase activity on membranes isolated from PMNs incubated with TSP. Furthermore, the PT-dependent ribosylation of G_iα2,3 stimulated by FMLP was eliminated by TSP treatment. These data indicated that the two receptors share a pool of G-proteins. However, TSP did not block the CT-dependent ribosylation stimulated by FMLP, suggesting that TSP receptors may also interact with a different pool of G_iα2,3. TSP itself significantly (P < 0.005) increased GTP hydrolysis in PMN membranes (to 110.6 ± 2.7% of control values). In addition, GTPγS binding to membranes increased significantly (P < 0.005) following exposure to 10 nM TSP (to 108 ± 1.4% of control values). Conversely, GTP treatment reduced the affinity of TSP for its receptor without altering total binding. These data demonstrate that TSP receptors are linked to G-proteins, a subpopulation of which also associates with FMLP receptors. © 1996 Wiley-Liss, Inc.     

Thrombospondin stimulates motility of human neutrophils

Polymorphonuclear leukocytes (PMNs) migrate to sites of inflammation or injury in response to chemoattractants released at those sites. The presence of extracellular matrix (ECM) proteins at these sites may influence PMN accumulation at blood vessel walls and enhance their ability to move through tissue. Thrombospondin (TSP), a 450-kD ECM protein whose major proteolytic fragments are a COOH-terminal 140-kD fragment and an NH2-terminal heparin-binding domain (HBD), is secreted by platelets, endothelial cells, and smooth muscle cells. TSP binds specifically to PMN surface receptors and has been shown, in other cell types, to promote directed movement. TSP in solution at low concentrations (30-50 nM) "primed" PMNs for f-Met-Leu-Phe (fMLP)- mediated chemotaxis, increasing the response two- to fourfold. A monoclonal antibody against the HBD of TSP totally abolished this priming effect suggesting that the priming activity resides in the HBD of TSP. Purified HBD retains the priming activity of TSP thereby corroborating the antibody data. TSP alone, in solution at high concentrations (0.5-3.0 microM), stimulated chemotaxis of PMNs and required both the HBD and the 140-kD fragment of TSP. In contrast to TSP in solution, TSP bound to nitrocellulose filters in the range of 20- 70 pmol stimulated random locomotion of PMNs. The number of PMNs migrating in response to bound TSP was approximately two orders of magnitude greater than the number of cells that exhibited chemotaxis in response to soluble TSP or fMLP. Monoclonal antibody C6.7, which recognizes an epitope near the carboxyl terminus of TSP, blocked migration stimulated by bound TSP, suggesting that the activity resides in this domain. Using proteolytic fragments, we demonstrated that bound 140-kD fragment, but not HBD, promoted migration of PMNs. Therefore, TSP released at injury sites, alone or in synergy with chemotactic peptides like fMLP, could play a role in directing PMN movement.     

Chemotactic activity of pertussis toxin on murine lymphocytes. Its potential role on lymphocyte accumulation in the lung

The effects of pertussis toxin on lymphocyte migration were studied in vitro. In this study pertussis toxin significantly stimulated lymphocyte migration at concentrations of 0.1 and 1 microgram ml-1 using a microchamber and the leading-front method. Checkerboard analysis demonstrated that pertussis toxin causes directed migration of lymphocytes (chemotaxis). Heat-treatment pertussis toxin abolished its capacity to cause this migration. When murine lymphocytes were preincubated with different concentrations of pertussis toxin, an inhibition of chemotaxis at the dosages of 0.1 and 1 microgram ml-1 was observed. On the other hand, lymphocytes derived from mice treated with pertussis toxin were not inhibited after subsequent exposure to pertussis toxin in vitro. Since lymphocyte accumulation in the lungs of mice treated with pertussis toxin has been well demonstrated, the results of our study could suggest a chemotactic activity of pertussis toxin in determining accumulation of lymphocytes in this organ.     

The difference between random movement and chemotaxis. Effects of antitubulins on neutrophil granulocyte locomotion

The antitubulins demecolcine and podophyllic acid ethylhydrazide (SPI) were used in experiments designed to elucidate the role of centriole-associated cytoplasmic microtubules in the locomotion of human neutrophil granulocytes (PMNs). The PMN locomotion was studied as chemotaxis and as the velocity of random movement. The PMN chemotaxis was inhibited by demecolcine (0.01 μg/ml) and SPI (0.1 μg/ml), i.e. concentrations below the reported threshold ones for mitotic arrest in metaphase. The velocity of single PMNs during random movement was only slightly reduced by treatment with 0.5 μg/ml of SPI. PMN locomotion was not appreciably inhibited by SPI, 0.5 μg/ml. The discrepancies mentioned suggest that centriole-associated microtubules are essential structures in the PMN direction-finding or PMN directional movement of chemotaxis but not in the mechanism of PMN locomotion. The present observations might, at least in part, explain the beneficial effects of antitubulins on acute gout.     

In vitro stimulation of neutrophil motility by levamisole: maintenance of cgmp levels in chemotactically stimulated levamisole-treated neutrophils.

Levamisole at concentrations of 10(-3) M or 10(-4) M consistently increased neutrophil random motility and chemokinesis (stimulated random migration). Similar concentrations also increased directional movement of polymorphonuclear leukocytes to both endotoxin-activated serum and hydrolyzed casein. This effect on chemotaxis was due to a true stimulation and was not due solely to increased random movement. The effect of levamisole on the neutrophils could be removed by washing, but persisted if the cells were initially treated with levamisole and serum or endotoxin-activated serum. After neutrophil stimulation with chemotactic factor an initial rise in intracellular cyclic AMP levels was detected which was not influenced by prior levamisole treatment. Intracellular cyclic GMP levels after an initial slight depression, returned to resting levels and gradually diminished over a 60-minute period. Levamisole-treated cells consistently showed higher cyclic GMP levels and it is postulated that by maintaining intracellular cyclic GMP levels, microtubular assembly and cell motility might be enhanced.     

The combined action of hyaluronic acid and fibronectin stimulates neutrophil migration

Previous investigations have demonstrated that the chemotactic response of polymorphonuclear leukocytes (PMN) was stimulated by hyaluronic acid (HA) when serum was present. The aim of the present investigation was to identify the serum factor necessary for the stimulation of PMN chemotaxis by HA. By means of gel filtration, the m.w. of the serum component was shown to be greater than 350,000. Immunoprecipitation of serum with anti-fibronectin, but not with anti-IgM and anti-alpha 2-macroglobulin, inhibited the stimulation of PMN chemotaxis by HA. Preincubation of PMN with HA (10 to 500 micrograms/L) and isolated fibronectin (0.1 to 100 mg/L) significantly stimulated the chemotactic response of PMN. Also, random migration of PMN was significantly increased by preincubation of the cells with HA (10 to 500 micrograms/L) and isolated fibronectin (50 to 200 mg/L). Additionally, PMN preincubated with HA (10 to 50 micrograms/L) and with fibronectin (10 to 50 mg/L) added afterwards, and PMN preincubated with fibronectin (10 mg/L) and with HA (5 to 10 micrograms/L) added after the preincubation, showed a significant stimulation of the chemotactic response. PMN preincubated with serum and chondroitin sulfate, or with fibrinogen and HA, demonstrated no stimulation of the chemotactic response. The present investigation suggests that the combined action of HA and fibronectin, which probably takes place at the cellular membrane, is a major mechanism in the HA-mediated stimulation of PMN migration.     

Chemotactic activity of pertussis toxin on murine lymphocytes. Its potential role on lymphocyte accumulation in the lung

Abstract The effects of pertussis toxin on lymphocyte migration were studied in vitro. In this study pertussis toxin significantly stimulated lymphocyte migration at concentrations of 0.1 and 1 μg ml⁻¹ using a microchamber and the leading-front method. Checkerboard analysis demonstrated that pertussis toxin causes directed migration of lymphocytes (chemotaxis). Heat-treatment of pertussis toxin abolished its capacity to cause this migration. When murine lymphocytes were preincubated with different concentrations of pertussis toxin, an inhibition of chemotaxis at the dosages of 0.1 and 1 μg ml⁻¹ was observed. On the other hand, lymphocytes derived from mice treated with pertussis toxin were not inhibited after subsequent exposure to pertussis toxin in vitro. Since lymphocyte accumulation in the lungs of mice treated with pertussis toxin has been well domenstrated, the results of our study could suggest a chemotactic activity of pertussis toxin in determining accumulation of lymphocytes in this organ.     

In vitro modulation of canine polymorphonuclear leukocyte function by granulocyte-macrophage colony stimulating factor

Granulocyte-macrophage colony stimulating factor (GMCSF) promotes the growth of granulocytes and macrophages from undifferentiated bone marrow cells and modulates the oxidative responses of polymorphonuclear leukocytes (PMN) to endogenous chemoattractants. We found that,in vitro, naturally occurring glycolsylated human GMCSF does not disturb the resting canine PMN membrane potential, may attentuate PMN oxidative responses to PMA, and is, to a small degree, chemotaxigenic. GMCSF, however, inhibits PMN chemotaxis to zymosanactivated plasma (ZAP). Compared to temperature controls, GMCSF (1-100 U/ml) produced up to 1.5-fold increases in H₂O₂ production after 15 minutes, while phorbol myristate acetate (PMA) treated cells increased H₂O₂ production 8–12-fold after 15 minutes. Preincubation of cells with GMCSF (1–100 U/ml) prior to PMA stimulation significantly reduced the H₂O₂ levels induced by PMA. H202 production was inhibited up to 15% after 15 minutes of GMCSF preincubation and up to 40% after 60 minutes of preincubation. As a chemotaxigenic agent, GMCSF (10–1000 U/ml) was able to elicit 49%–102% increases in quantitative cellular migration, compared to random migration. Total cellular chemotaxis to GMCSF was < 30% of the response to ZAP. Preincubation of PMNs with GMCSF for 15 minutes significantly inhibited ZAP-induced cellular migration. Human GMCSF does not appear to activate canine PMNin vitro and may actually down-regulate PMN inflammatory responses.Supported by the Armed Forces Radiobiology Research Institute, Defense Nuclear Agency, under work unit No. 00082. Views presented in this paper are those of the authors; no endorsement by the Defense Nuclear Agency has been given or should be inferred. Research was conducted according to the principles enunciated in the Guide for the Care and Use of Laboratory Animals prepared by the Institute of Laboratory Animal Resources, National Research Council.     

Effect ofPseudomonas aeruginosa rhamnolipid on human neutrophil migration

The effect ofPseudomonas aeruginosa heat-stable hemolysin (rhamnolipid) on human neutrophil migration has been investigated. Rhamnolipid was prepared from culture filtrate and characterized by thin-layer chromatography. The lytic activity of rhamnolipid was quantitated by titration against neutrophils. Leukocyte migration response was measured using⁵¹Cr-labeled neutrophils with a double-filter technique in modified Boyden chambers. The results suggest rhamnolipid stimulated chemotaxis as well as chemokinesis. Moreover, rhamnolipid impaired a chemotactic response toN-formyl-methionyl-leucyl-phenylalanine. These effects may be important in host-parasite interactions.     

Effects of taxol on human neutrophils

Taxol, a plant alkaloid, promotes and stabilizes microtubule assembly in cells and cellfree systems. In the present study, the effects of taxol on various functional, morphologic, and biochemical phenomena in human peripheral blood PMN (Hypaque-Ficoll) were examined. Taxol (10(-7) M) inhibited PMN chemotaxis stimulated by N-formyl-methionyl-leucyl-phenylalanine (f-met-leu-phe) or endotoxin-activated serum by more than 60%. The inhibition was not readily reversed by washing, and taxol itself was not a chemoattractant, nor is it a secretagogue. Spontaneous nondirected migration, cell spreading on a glass surface, and orientation of cell organelles in response to a chemoattractant gradient were also inhibited by taxol. Taxol (10(-5) M) decreased killing of Staphylococcus aureus, but did not alter phagocytosis of heat-killed Candida or hexose monophosphate shunt activity in resting or stimulated PMN. Ultrastructural studies showed that PMN incubated in f-met-leu-phe, taxol, or both had increased (p less than 0.001) numbers of centrosome-associated microtubules, and the microtubules of cells incubated in taxol with or without f-met-leu-phe were organized into bundles. Taxol (10(-5) M) markedly inhibited post-translational tyrosinolation of alpha-chains of tubulin in both resting and f-met-leu-phe-stimulated PMN. The data indicate that taxol inhibits PMN locomotion and bacterial killing, supporting a role for microtubules in these processes. The ultrastructural and biochemical data also support the view that taxol mediates its effects on PMN by its effect on microtubules.     

Development of a new method of analysing chemotactic deactivation of human neutrophil granulocytes

Measurement of chemotactic migration of human neutrophil granulocytes (PMN) induced by chemotaxins serves as a simple and reliable method for assessing the expression of chemotaxin receptors. Incubation of PMN with a certain chemotaxin leads to a diminished chemotactic migration towards this chemotaxin. This is called chemotactic deactivation. We developed a new deactivation chamber to determine chemotaxis and chemotactic deactivation of human PMN. This novel chamber is a modification of the commercially available acrylic 48-well microchemotaxis chamber consisting of an upper block with wells drilled all the way through the block and a blind-well lower block. Both blocks are separated by a polycarbonate membrane. PMN from the wells in the upper block migrate through the pores of the membrane into the wells of the lower block containing the chemoattractants. Migrated PMN on the lower side of the PC membrane were quantified after staining by measuring specific light absorbance. The chemotactic activity is quantified as a ratio of stimulated migration and random migration (chemotactic index=CI). For our novel chamber, only the upper blocks of this commercial chamber were connected like a sandwich, including a polyvinylpyrrolidone-free polycarbonate membrane with a pore size of 3 microm. The wells in the upper compartment were filled with 5 x 10(4) PMN and deactivating chemotaxin. The lower block was then filled with the chemotactic stimulus and the chamber was then incubated in humidified air with 5% CO2 atmosphere at 37 degrees C. The influence of cell concentration, incubation time, chemotactic factor concentration, pore size and alkaline treatment of polycarbonate membranes on migrational activity of PMN have been investigated. The technique was rigorously standardized in order to optimize the assay conditions. The method is relatively simple, sensitive and fast. The determination of chemotaxis and deactivation are performed in the same chamber, thus avoiding cell loss due to nonspecific adherence in other incubation tubes. The chamber can be used to characterize the chemotactic activity of chemoattractants of unknown structure via known and unknown receptors. This new chamber can be very helpful in detecting unknown chemotactic stimuli, which are not detectable by, for example, antibodies.     

Adenosine and related compounds counteract tumor necrosis factor-alpha inhibition of neutrophil migration: implication of a novel cyclic AMP-independent action on the cell surface

Human rTNF-alpha (greater than or equal to U/ml) decreased PMN nondirected and directed migration to FMLP to approximately 50% of control. Adenosine (100 microM) almost completely restored hrTNF-inhibited migration (nondirected from 54 to 92% and directed migration to from 54 to 93% of control). The lowest concentration of adenosine that restored hrTNF-inhibited migration was 3 microM, and the adenosine analogue, 5'-(N-cyclopropyl)-carboxamido-adenosine (CPCA) was more potent than adenosine. Although CPCA binds to A2-receptors and stimulates adenylate cyclase, the reversal of hrTNF-inhibited chemotaxis was found to be independent of both PMN cAMP content and binding to A2-receptors, because neither 8-Br-cAMP nor pertussis adenylate cyclase restored hrTNF-inhibited PMN chemotaxis and the A2-receptor antagonist, 1,3-dipropyl-7-methylxanthine decreased CPCA stimulated cAMP but enhanced CPCA-restoration of hrTNF-inhibited chemotaxis. The effect of adenosine could be augmented by inhibition of adenosine uptake and decreased by adenosine deamination. Pentoxifylline, (3,7 dimethyl-1-[5 oxo-hexyl] xanthine), like adenosine also restored PMN chemotaxis inhibited by hrTNF. The adenosine receptor antagonist, 1,3-dipropyl-8(phenyl-p-acrylate)-xanthine (BW A1433U), decreased restoration of hrTNF-inhibited chemotaxis by CPCA or pentoxifylline. Thus, the inhibitory effect of hrTNF on PMN migration can be counteracted by adenosine, CPCA, pentoxifylline, and compounds that increase adenosine availability to the surface of the PMN. Inasmuch as an A1-selective agonist N6-cyclopentyladenosine was less active, and the action of the A2-selective agonist CPCA was enhanced by an A2-receptor antagonist, we hypothesize that neither A1 or A2 receptors are involved in adenosine restoration of hrTNF-inhibited chemotaxis. Further, increased cAMP, an A2-regulated event, does not cause the effect, and adenosine restoration of hrTNF-inhibited migration does not appear to be mediated by changes in PMN [F-actin], FMLP receptor expression, or cytosolic calcium. Hence, the restoration of hrTNF-inhibited chemotaxis is controlled by a novel cyclic AMP-independent action on the PMN surface.     

Icm/Dot‐dependent inhibition of phagocyte migration by Legionella is antagonized by a translocated Ran GTPase activator

The environmental bacterium Legionella pneumophila causes a severe pneumonia termed Legionnaires' disease. L. pneumophila employs a conserved mechanism to replicate within a specific vacuole in macrophages or protozoa such as the social soil amoeba Dictyostelium discoideum. Pathogen–host interactions depend on the Icm/Dot type IV secretion system (T4SS), which translocates approximately 300 different effector proteins into host cells. Here we analyse the effects of L. pneumophila on migration and chemotaxis of amoebae, macrophages or polymorphonuclear neutrophils (PMN). Using under‐agarose assays, L. pneumophila inhibited in a dose‐ and T4SS‐dependent manner the migration of D. discoideum towards folate as well as starvation‐induced aggregation of the social amoebae. Similarly, L. pneumophila impaired migration of murine RAW 264.7 macrophages towards the cytokines CCL5 and TNFα, or of primary human PMN towards the peptide fMLP respectively. L. pneumophila lacking the T4SS‐translocated activator of the small eukaryotic GTPase Ran, Lpg1976/LegG1, hyper‐inhibited the migration of D. discoideum, macrophages or PMN. The phenotype was reverted by plasmid‐encoded LegG1 to an extent observed for mutant bacteria lacking a functional Icm/Dot T4SS.Similarly, LegG1 promoted random migration of L. pneumophila‐infected macrophages and A549 epithelial cells in a Ran‐dependent manner, or upon ‘microbial microinjection’ into HeLa cells by a Yersinia strain lacking endogenous effectors. Single‐cell tracking and real‐time analysis of L. pneumophila‐infected phagocytes revealed that the velocity and directionality of the cells were decreased, and cell motility as well as microtubule dynamics was impaired. Taken together, these findings indicate that the L. pneumophila Ran activator LegG1 and consequent microtubule polymerization are implicated in Icm/Dot‐dependent inhibition of phagocyte migration.     

μ-Slide Chemotaxis: A new chamber for long-term chemotaxis studies

Background

Effective tools for measurement of chemotaxis are desirable since cell migration towards given stimuli plays a crucial role in tumour metastasis, angiogenesis, inflammation, and wound healing. As for now, the Boyden chamber assay is the longstanding "gold-standard" for in vitro chemotaxis measurements. However, support for live cell microscopy is weak, concentration gradients are rather steep and poorly defined, and chemotaxis cannot be distinguished from migration in a single experiment.

Results

Here, we describe a novel all-in-one chamber system for long-term analysis of chemotaxis in vitro that improves upon many of the shortcomings of the Boyden chamber assay. This chemotaxis chamber was developed to provide high quality microscopy, linear concentration gradients, support for long-term assays, and observation of slowly migrating cells via video microscopy. AlexaFluor 488 dye was used to demonstrate the establishment, shape and time development of linear chemical gradients. Human fibrosarcoma cell line HT1080 and freshly isolated human umbilical vein endothelial cells (HUVEC) were used to assess chemotaxis towards 10% fetal calf serum (FCS) and FaDu cells' supernatant. Time-lapse video microscopy was conducted for 48 hours, and cell tracking and analysis was performed using ImageJ plugins. The results disclosed a linear steady-state gradient that was reached after approximately 8 hours and remained stable for at least 48 hours. Both cell types were chemotactically active and cell movement as well as cell-to-cell interaction was assessable.

Conclusions

Compared to the Boyden chamber assay, this innovative system allows for the generation of a stable gradient for a much longer time period as well as for the tracking of cell locomotion along this gradient and over long distances. Finally, random migration can be distinguished from primed and directed migration along chemotactic gradients in the same experiment, a feature, which can be qualified via cell morphology imaging.     

A generalized transport model for biased cell migration in an anisotropic environment

 A generalized transport model is derived for cell migration in an anisotropic environment and is applied to the specific cases of biased cell migration in a gradient of a stimulus (taxis; e.g., chemotaxis or haptotaxis) or along an axis of anisotropy (e.g., contact guidance). The model accounts for spatial or directional dependence of cell speed and cell turning behavior to predict a constitutive cell flux equation with drift velocity and diffusivity tensor (termed random motility tensor) that are explicit functions of the parameters of the underlying random walk model. This model provides the connection between cell locomotion and the resulting persistent random walk behavior to the observed cell migration on longer time scales, thus it provides a framework for interpreting cell migration data in terms of underlying motility mechanisms. Received: 8 April 1999     

Intravital two‐photon microscopy of host–pathogen interactions in a mouse model of Staphylococcus aureus skin abscess formation

Staphylococcus (S.) aureus is a frequent cause of severe skin infections. The ability to control the infection is largely dependent on the rapid recruitment of neutrophils (PMN). To gain more insight into the dynamics of PMN migration and host–pathogen interactions in vivo, we used intravital two‐photon (2‐P) microscopy to visualize S. aureus skin infections in the mouse. Reporter S. aureus strains expressing fluorescent proteins were developed, which allowed for detection of the bacteria in vivo. By employing LysM‐EGFP mice to visualize PMN, we observed the rapid appearance of PMN in the extravascular space of the dermis and their directed movement towards the focus of infection, which led to the delineation of an abscess within 1 day. Moreover, tracking of transferred labelled bone‐marrow neutrophils showed that PMN localization to the site of infection is dependent on the presence of G‐protein‐coupled receptors on the PMN, whereas Interleukin‐1 receptor was required on host cells other than PMN. Furthermore, the S. aureus complement inhibitor Ecb could block PMN accumulation at thesite of infection. Our results establish that 2‐P microscopy is a powerful tool to investigate the orchestration of the immune cells, S. aureus location and gene expression in vivo on a single cell level.     

Mycobacterial cord factor enhances migration of neutrophil‐like HL‐60 cells by prolonging AKT phosphorylation

Trehalose 6,6′‐dimycolate (TDM), or cord factor, is a crucial stimulus of immune responses during Mycobacterium tuberculosis infection. Although TDM has immuno‐stimulatory properties, including adjuvant activity and the ability to induce granuloma formation, the mechanisms underlying these remain unknown. We hypothesized that TDM stimulates transendothelial migration of neutrophils, which are the first immune cells to infiltrate the tissue upon infection. In this study, it was shown that TDM enhances N‐formylmethionyl‐leucyl‐phenylalanine (fMLP)‐induced chemotaxis and transendothelial movement by prolonging AKT phosphorylation in human neutrophils. TDM induced expression of macrophage‐inducible C‐type lectin, a receptor for TDM, and induced secretion of pro‐inflammatory cytokines and chemokines in differentiated HL‐60 cells. In 2‐ and 3‐D neutrophil migration assays, TDM‐stimulated neutrophils showed increased fMLP‐induced chemotaxis and transendothelial migration. Interestingly, following fMLP stimulation of TDM‐activated neutrophils, AKT, a crucial kinase for neutrophil polarization and chemotaxis, showed prolonged phosphorylation at serine 473. Taken together, these data suggest that TDM modulates transendothelial migration of neutrophils upon mycobacterial infection through prolonged AKT phosphorylation. AKT may therefore be a promising therapeutic target for enhancing immune responses to mycobacterial infection.