WO2000052211A9 - Vascular and mucosal shear analysis system for host-pathogen interactions - Google Patents

Abstract

An apparatus and related devices and methods are described that provide physiologically relevant conditions for the in vitro evaluation of the adhesion of cells and various molecules, particularly microbes and pathogens and their adhesion-related molecules, to the tissues and molecular components of a host.

Description

VASCULAR AND MUCOSAL SHEAR ANALYSIS SYSTEM FOR HOST-PATHOGEN INTERACTIONS

INVENTORS: Robert Bargatze, Patricia Glee, James Cutler and Barry Pyle

FIELD OF THE INVENTION The present invention relates to apparatus and related devices to provide physiologically relevant conditions for the in vitro evaluation of the adhesion of cells, particularly microbes and pathogens, to the tissues and molecular components of a host.

ACKNOWLEDGMENT OF FEDERAL SUPPORT

The disclosed invention was supported by the National Institute of Allergy and Infectious Diseases Grants RO1 AI24912 and PO1 AI37194. The United States government has certain rights in the invention.

BACKGROUND OF THE INVENTION

Many true and opportunistic microbial pathogens interact with different host tissues and components during pathogenic processes. The capacity of bacterial, fungal, viral, and protozoan pathogens to bind to host tissues is broadly considered a virulence trait because it anchors subsequent invasive activity of the microorganism. For example, Candida albicans is an opportunistic fungal pathogen that interacts with many different host components and tissues as it moves between normal flora locations and internal organs during pathogenesis. The Candida dissemination process likely begins by fungal cells gaining access to the bloodstream through persorption from gastrointestinal colonization, by seeding from a biofilm-fouled intramedic device, or through a trauma-related inoculation. Once in the bloodstream, the fungal cells are systemically distributed with the potential to cause disease at many host sites, especially certain organs like the kidney and liver. Because hematogenous spread is an important step in pathogenesis, Candida interaction with epithelial and endothelial cells is crucial for tissue invasion and development of organ pathologies. Of the various adhesion interactions during dissemination, Candida attachment to vascular endothelium would occur under the highest shear forces encountered. And yet, intravenously administered C. albicans cells drop rapidly out of the circulating blood either by trapping in certain organs or by vascular attachment events.

Prior in vitro assays for microbial adhesion events are not optimal for various significant reasons. For example, the microbial attachment steps occur under static conditions in currently utilized adhesion assays. See, e.g., C. L. Mayer, S. G. Filler, and J. E. Edwards, Jr. (1992) Candida albicans adherence to endothelial cells. Microvascular Research 43:218-226; and E. Rozdzinski and E. Tuomanen (1995), Adhesion of microbial pathogens to leukocyte integrins: Methods to study ligand mimicry, Methods in Enzymology 253: 3-26. This static assay format cannot account for a crucial variable which is the shear force across the fluid-tissue interface at epithelial and endothelial cell surfaces. Prior in vitro assays for microbial attachment generally are limited by a single time assessment of the number of adhesion events for the sample field. The length of the incubation time in static assays is generally determined empirically without the advantage of continuous sampling and real-time monitoring of the assay fields for relevant events or specific changes. This severely limits the amount and type of information available for evaluation. The previous assays cannot monitor physiologic changes over time that may occur to the host cells or to the microbial cells. Such time- and adhesion-dependent changes may critically impact progression of disease. They also cannot monitor time- course assays for the effects of test compounds on adhesion or cellular events in a physiologically relevant system. In other conventional assays, mammalian cells are disrupted from a physiologically relevant orientation in order to mix with the microorganisms. See, for example, a typical buccal epithelial cell assay as reported in L. Yu, et al. (1994), Partial characterization of a Candida albicans fimbrial adhesin. Infect Immun 62:2834-2842. However, cellular orientation may be crucial in determining which adhesion interactions actually occur in vivo because different host components are present on the basal and lumenal surface of epithelial and endothelial cell types.

Other assay formats reported in the medical literature simply do not utilize mammalian cells or purified host ligands for microbial cells to interact within the assay. (See, e.g., H.J. Busscher and H.C. van der Mei. (1995), Use of flow chamber devices and image analysis methods to study microbial adhesion. Methods in Enzymology

253:455-476).

Moreover, some known systems do not avoid coadhesion or homotypic binding behavior of the microorganism to itself in static assay formats, which must be reduced in order to obtain accurate data. For example, see C. L. Mayer, S. G. Filler, and J. E.

Edwards, Jr. (1992), Candida albicans adherence to endothelial cells. Microvascular

Research 43:218-226. This limitation prohibits study of microbial adhesion events that may have substantial impact on pathogenic progression of disease.

The characterization of physiologically relevant shear-dependent adhesion events of leukocytes, and fine distinction for receptor ligand interactions that account for neutrophil rolling and tight adhesion events also have been reported. See, e.g., R. F.

Bargatze, S. Kurk, G. Watts, T. K. Kishimoto, C. A. Speer, and M. A. Jutila. 1994. In vivo and in vitro functional examination of a conserved epitope of L- and E- selectin crucial for leukocyte-endothelial cell interactions. J Immunol 152:5814-5825. Various other systems for evaluating interactions are disclosed by Springer et al, U.S. Patent No.

5,460,945 (1995); Cutler et al, U.S. Patent No. 5,578,309 (1996) and Pascual et al, PCT

Published Application No. WO/97/18790.

To overcome the foregoing limitations of other systems, a new adhesion analysis model system has been needed to present appropriate physiological conditions of fluid movement across tissue-fluid interfaces, to present relevant host cells in physiologically correct orientation, to facilitate real-time microscopic monitoring of microbial adhesion behaviors with potential relevance in vivo, and to provide a physiologically relevant shear system for testing compounds that block or modulate adhesion interactions between host cells pathogens. SUMMARY OF THE INVENTION

Microbial virulence factors include surface adhesins that direct and define interactions with host cells during the onset and course of pathogenesis. Microbial trafficking in the mammalian host is based upon adhesion-mediated movement into and through various host tissues and organs. Because most pathogenic attacks begin at mucosal sites and involve vascular dissemination or hematogenous stages during disease, evaluation of these adhesion events under relevant physiological conditions is crucial. It is an object of the present invention to provide a novel approach to the physiologically relevant analysis of host-pathogen interactions with application to the medical and pharmaceutical fields of knowledge.

Accordingly, it is an object of the present invention to provide an apparatus that comprises a chamber or conduit, such as a tube or an elongated tube having an inner surface adapted to support a substrate and a means for producing in the tube a flow of fluid comprising test molecules, test cellular components or test cells. Also included are means for monitoring the interaction of said test molecules, test cellular components or test cells with said substrate.

In a preferred embodiment, the conduit is substantially cylindrical. Further, the conduit can comprise a vessel which can be modified to support various cell types and provide specific environments for examination of selected physiological events. For example, modification of the vessel surface to allow study of isolated receptors, synthetic ligands, molecular expressing transfectants, endothelial cells (of all types), epithelial cells (of all types) and the use of matrix proteins and porous membranes is included. For example, such vessels may comprise inductive factors including cytokines, chemokines, growth factors, and hormones to allow for the study of diapedesis and chemotaxis of leukocytes after adhesion under shear flow. Further, vascular growth and regeneration can be monitored by modification of vessel surfaces via coating said surfaces with matrix proteins, synthetic ligands, porous membranes and inductive factors , including cytokines, chemokines, growth factors, and hormones. In a preferred embodiment, such a vessel environment would be used to study angiogenesis. In another embidiment, modification of the vessel surface can provide environments to allow the study of tumor metastasis and neoplastic transformation of cells.

Also, in a preferred embodiment, the apparatus can produce either a time invariant or a time variant fluid flow. In general, the fluid flow may be pulsatory, continuous, invariant or recirculating flow. Preferably, the time variant flow generates a shear force that is substantially the physiological equivalent of the shear force across the fluid-tissue interface at the epithelial or endothelial cell surfaces in a host. Further, a recirculating pump can be used as opposed to a single pass. The system should be adaptable in that flow can be adjusted to be single pass for certain application (e.g., for pathogen and tumor cells). Further, a convertable system comprising a syringe or a peristaltic pumping mechanism is also envisaged.

Preferred substrates are cells, extracellular matrix proteins, various molecules, such as pathogen or host attachment molecules, receptors and signaling molecules like integrins or selectins, cellular components such as cell membranes or combinations thereof. Substrate cells may be endothelial cells, epithelial cells activated endothelial cells, and activated epithelial cells. In a preferred embodiment, the cells are oriented in a substantially physiologically correct orientation such that said cells present to the fluid flow their characteristic cell surface membranes and membrane associated moieties such as receptors, integrins and other receptor or signaling molecules. In another embodiment, incorporation of a laser scanning cytometer is envisaged for studying molecular expression, adhesion and signaling (e.g., via calcium flux) under shear flow. Such studies would include examination of shear force effects on leukocytes and endothelial cells; tumor cells; pathogenic microbes, including viruses, bacteria, fungi and parasites; assay of synthetic beads or nanoparticles coated with cells or substrates, including antibodies, mimotopes and adhsion molecules.

Preferred test molecules, cellular components or cells are mammalian pathogens or pathogen-associated molecules. Preferred test cells are selected from the group consisting of viruses, bacteria, fungi, protozoa and parasites. A preferred test cell is yeast from the Candida genus, particularly Candida albicans.

It is a further object of the system according to the present invention, to monitor physiological parameters of the cells of the substrate. Means for such monitoring may include conventional optical, chemical or electrical sensors or probes to measure optical, electrical or chemical parameters. Preferably such monitoring activities monitor parameters such adhesion events, binding events, cell viability, pH, oxygen tension, CO₂ levels or temperature. Preferred binding events include attachment of a pathogen to a host's cell, as well as heterotypic and homotypic binding between the substrate cells and said test cells.

It is another object of the present invention to provide an apparatus that monitors and/or records a real-time analysis of such parameters. Preferably, the apparatus and system according to the present invention also include a computer for correlating, processing and storing information produced by said monitoring means. Optionally, a microscope and video-capture system also are utilized. Preferably, the video-capture system comprises a video camera, a video monitor and a VCR, such as time-lapse VCR, and/or a CD recorder.

It is another object of the present invention that the monitoring include digital as well as analog capture of video images. Further, it is preferable that the video images be subjected to image analysis for quantification of cell numbers and cell velocities. Moreover, low-light camera systems or image intensification for the detection of fluorescently labeled molecules or cells is envisaged, including the use of fluorescent tags to label molecules or cells to distinguish/quantify molecules or cell populations. For example, digital monitoring can be used to acquire images for qualification of cell numbers and cell velocities where said cells are labeled fluorescently. Moreover, signaling events, including but not limited to uptake of molecules, molecular expression and activation of transduction pathways, can be monitored with fluorescent tags.

The shear assay system of the present invention also provides a method of determining the adhesion of pathogens (and pathogen associated molecules such as adhesins) under physiological shear stress conditions. Utilizing the foregoing apparatus, this method involves the steps of introducing test molecules, test cellular components or test cells into the fluid flow through the conduit or tube, permitting test molecules, test cellular components or test cells in the fluid flow to interact with said substrate cells, substrate extracellular matrix proteins, substrate molecules, substrate cellular components or combinations thereof present on the interior surface of the conduit and then monitoring their interactions.

Preferably, this monitoring is effected by use of a probe means to generate information about these interactions. Various types of probes are contemplated, including electrical or electro-chemical probes.

In other aspects of the present invention, the apparatus utilizes a plurality of conduits which may be arranged in a serial flow or parallel flow configuration, including multi-channel capacity and automated analysis. In yet another aspect of the invention, the cells of the substrate in the conduit are endothelial cells that are characteristic of intestinal, respiratory and vascular tissues. The substrate cells also may be characteristic of vaginal, bladder, parenchymal and interstitial tissues.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The accompanying drawing, which is incorporated in and constitutes a part of this specification, illustrate one embodiment of the invention and together with the description, serve to explain the principles on of the invention.

Fig. 1 shows diagram of the basic components of an in vitro shear system according to the present invention.

Fig. 2 graphically demonstrates the influence of IL-lβ activation of HUVECs on C. albicans adhesion. Comparative binding of hydrophobic C. albicans A9wt yeast cells to cytokine activated and unactivated endothelium. Cytokine activation significantly increased the average number oi Candida foci per field of view. This assay suggests that vascular perturbations and inflammation events may help direct hydrophobic cell attachment during fungemia incidents. Fig. 3 graphically demonstrates the influence of surface hydrophobicity on Candida adhesion to activated HUVECs during shear. Fig. 3A shows a comparison of hydrophobic and hydrophilic C. albicans A9wt yeast cell binding to activated HUVECs. Fig. 3B shows a comparison of hydrophobic and hydrophilic C. albicans ATCC 90029 yeast cell binding to activated HUVECs. For both cell strains, hydrophobic cells bound to a significantly greater extent than did hydrophilic cells in heterotypic and homotypic adhesion interactions.

Fig. 4 graphically demonstrates the effect of hydrophobic C. albicans on IL-lβ activated HUVECs and neutrophil adhesion. When hydrophobic C. albicans yeast cells are allowed to bind to endothelial cells prior to injection of neutrophils, dramatic decreases approximately 10- fold) in the number of bound neutrophils are observed.

Fig. 5 is a photomicrograph showing E. coli O157:H7 bound to magnetic beads binding to activated intestinal epithelial cells during pulsatory wave flow.

Fig. 6 graphically demostrates the real-time sampling capabilities of the in vitro shear apparatus. A single field of activated bovine epithelial cells was monitored for about four minutes with periodic counting of the number of attached E. coli O157:H7 - coated magnetic beads. The graph demonstrates rapid accumulation, especially during the first 2 minutes of sampling time. Comparison of the two lower lines on the graph shows the dynamic relationship between heterotypic and homotypic binding events in contributing to the overall numbers of organisms attached to the epithelial layer.

DETAILED DESCRIPTION OF THE INVENTION

The system according to the present invention provides physiologically relevant conditions for the in vitro evaluation of microbial adhesion to host tissues and components. This system establishes relevant shear forces across fluid-tissue interfaces to simulate conditions in the host. This system thus provides significant advantages over existing assays for microbial adhesion that are performed under static conditions or that do not utilize correctly oriented host tissues and components. Additional advantage is demonstrated by this system in the real-time monitoring and visualization of adhesion interactions between microbial cells and host tissues and components.

This system of the present invention includes the novel use of an in vitro analysis apparatus and the evaluation of host-pathogen analysis under conditions of physiologically relevant shear. The present invention is useful in the adhesion analysis of various classes of microorganisms and pathogens, including viruses, fungi, bacteria and parasites such as protozoa and other microbial parasites. An analysis of these different types of pathogens and their unique types of adhesion is facilitated by the present invention. For example, many of the adhesion ligands (including toxin ligands) for these microorganism and pathogens are known (see Table I). These ligands can be exploited to facilitate analysis of microbe-ligand interactions using the shear system of the present invention. The system of the present invention also provides unique capacities for identifying and exploiting microbial and mammalian adhesion molecules in the development of diagnostics, therapeutics and vaccine technologies.

Table I. Microorganisms and Reported ligands

Salmonella typhimurium Sialic acid

Vibrio cholera Sialic acid

Trypanosoma cruzi Sialic acid

Chlamydia Sialic acid Escherichia coli (p-fibriated) Gala l-4Gal

Bandeiraea simplicifolia Gala l-4Gal

Streptococcus suis Gala l-4Gal, NeuAcα2-3Galβl-4GlcNAcβl-3Gal

Plasmodium falciparum (Malaria) Gala l-4Gal, NeuAcα2-3Galβl-4GlcNAcβl-3Gal

Entamoeba histolytica Galβl-4GlcNac Pseudomonus aeruginosa GalNAcβl-4Gal, GalNAcβl-3Gal

Haemophilus influenza GalNAcβ 1 -4Gal, GalNAcβ 1 -3Gal Streptococcus aureus GalNAcβl-3Gal Leishmania species Galβl-3Galαl-4 Galβl-4Glcβl-lCer Helicobacter pylori NeuAcα2-3Galβ 1 -4GlcNAcβ 1 -3Gal Neisseria gonorrhoeae GalNAcβ 1 -4Galβ 1 -4Glcβ 1 - 1 Cer and

Galβl-3GalNAcβl-4Galβl-4Glcβl-lCer

Yersinia α-3 integrins

Legionella mannosylated proteins

Candida albicans phosphomannanoprotein complex

Histoplasma CR3/LFA-1/P150,95

Trichomonas lipophosphoglycan

Pneumoccus PAF receptor

Mycobacterium tuberculosis (TB) surfactant protein A

Borrelia burgdorferi (Lyme) integrins: αvβ3, α2bβ3, α5βl

Myxovirus Sialic acid

Encephalomyocarditis virus Sialic acid Bluetongue virus Sialic acid

Chronavirus Sialic acid and 9-OAc Sialic acid

Reovirus Sialic acid and Galβl-lCer

Sendi virus NeuAcα2-3Gal

Paramyxovirus (Newcastle, Mumps) Sialic acid and Galβl-lCer Rubella virus Sialic acid and other anionic sugars

Herpes virus Sialic acid, Galβl-lCer and other anionic sugars

Rotavirus Sialic acid, 9-OAc Sialic acid and

Galβl-3GalNAcβl-4Galβl-4Glcβl-lCer

Encephalomyelitis virus 9-OAc Sialic acid Paramyxovirus (Measles) Sialic acid containing oligosaccharides

Adenovirus Galβl-lCer

Polyoma virus NeuAcα2-3Galβ 1 -3GlcNAc

Hantavirus β-3 integrins

Orthomyxovirus Galβl-lCer

Human Immunodeficiency Virus Galβl-lCer and CD₄

Epsein-Barr virus CD21/HLA-DR

Rhinovirus (cold) ICAM-1

Ebola virus CD16

Cytomegalovirus herpran sulfate proteoglycans (gB)

Sulfate polysaccharides

TOXINS: reported ligand

Pertussis toxin sialyl Lewis x or a Shiga-like toxins I and II Gb₃

Clostridia toxin A GalNAcβl-3Galβl-4GlcNAcβl-3Galβl-4GlcβlCer, Galαl-3Galβl-4GlcNAc, Le^x, Le^y

Cholera toxin Gb₃, GM„ Galβl-3GalNAc Tetanus Galβ 1 -3GalNAcβ 1 -4Galβ 1 -4(NeuAcα8-2)(NeuAcα3-2)Galβ 1 - 4GlcβlCer Bacterial delta toxin GalNAcβ 1 -4(NeuAcα3-2)Galβ 1 -4Glcβ 1 Cer

The in vitro analysis system of the present invention is useful, for example, in the study of leukocyte interactions with vascular endothelium or purified host ligands under simulated physiological shear. As an example of such interactions, see, R. F. Bargatze, S. Kurk, G. Watts, T. K. Kishimoto, C. A. Speer, and M. A. Jutila (1994), In vivo and in vitro functional examination of a conserved epitope of L- and E- selectin crucial for leukocyte-endothelial cell interactions, J Immunol 152:5814-5825.

Cell surface moieties characteristic for either endothelial or epithelial cells are markers which can be used to distinguish between cell types. For example, vascular endothelial cadherin (VE-cadherin) is a cell surface moiety characteristic of endothelial cells, other markers include von Willibrand factor , EL AM, VCAM-1 and ICAM-1. For epithelial cell types, surface moieties would include P-cadherin, CD44 and LFA-1. Shear stress applied in the present apparatus generate useful flow rates from between 0.9-6 dynes/cm², preferably, the flow rate is between 4-5 dynes/cm², more preferably the flow rate is between 1-2 dynes/cm².

Definitions

"Conduit" means a channel for conveying or transporting fluids with, optionally, various cellular or molecular components. Preferred conduits may be made of glass or plastic, used in serological tubes, preferably those which have a relatively low tolerance for non-specific binding of serum protein, but which support the adhesion of cells such as endothelial or epithelial cells or other cells lines. Glass thin-wall capillary tubes are also preferred.

"Elongated tube" means any hollow cylinder which can allow the adherence of cells to the inner surface thereof while also allowing the flow of fluids comprising various components through the elongated tube. Glass thin-wall capillary tubes are also preferred.

"Inner surface" means the interior surface of a tube or other conduit.

"Interstitial" means or refers to the small spaces between cells, tissues or parts of an organ (e.g., interstitial cells). "Parenchymal" means a tissue characteristic of an organ, as distinguished from associated connective or supporting tissues.

"Pathogen associated molecule" means a composition which is derived from a microbial organism (e.g., virus, bacteria, fungi or parasite), for example, such as its fimbriae, membranes, envelopes or cell walls. Particularly contemplated are pathogen associated molecules such as adhesin molecules that may be involved with the attachment of a pathogen to a hosts' cells or tissues or extracellular matrices or which otherwise utilize the host's molecular addresses or signaling molecules, such as integrins and selectins, that allow the pathogen access to the host such that infection is facilitated.

"Physiologically correct orientation" means the polarity or orientation of cells in an elongated tube or other conduit of the present invention that is similar to the natural polarity or orientation of such cells with respect to the flow of fluids across the cells. For example, with respect to endothelial cells, the basal surface of the cells face the inner surface of the elongated tube or conduit and the lumenal surface of the cells face the interior or cavity of the elongated tube or other conduit. "Real time" means the analysis of an event as it occurs.

"Shear force" means the capacity to deform an elastic body by producing an opposite but parallel sliding motion of the body in the body's plane. For example, a pathogen that has adhered to a substrate in an elongated tube experiences a shear force from the fluid flowing past the pathogen that tends to move the pathogen in the direction of the fluid flow. In a related aspect, the phrase "substantially the physiological equivalent" when referring to shear force, means a shear force that is similar to the shear force naturally produced in various tissues or organs which experience time variant flow, such as the vasculature and cardiac muscle. "Substrate" means a molecular or cellular (or combined molecular and cellular) coating or layer which is attached, adsorbed or otherwise coated onto the inner surface of a tube or other conduit.

"Time variant flow" means the variable rate of movement of a fluid past a fixed point in an elongated tube or other conduit, wherein said rate is varied as a function of time. Peristaltic pumps, syringe pumps, vacuum pump or displacement pumps may be used to produce a fluid flow and particularly time variant flow.

General Description

Reference will now be made in detail to the presently preferred embodiments of the invention, an example of which is illustrated in the accompanying drawings. In accordance with the invention, Fig. 1 shows a preferred configuration for the in vitro shear analysis apparatus which provides a reproducible, real-time monitoring and quantification of leukocyte adhesive interactions during simulated physiological shear. The system uses mammalian target cells that express the ligand or purified ligands coated on the lumenal surface of a capillary tube reaction chamber. (The techniques for establishing the adhesive substrates and for analysis under high and low physiological shear forces are known. (See, e.g., R. F. Bargatze, S. Kurk, G. Watts, T. K. Kishimoto, C. A. Speer, and M. A. Jutila (1994), In vivo and in vitro functional examination of a conserved epitope of L- and E- selectin crucial for leukocyte-endothelial cell interactions. J Immunol 152:5814-5825.) A fluid medium of choice is circulated via a peristaltic pump through the loop system and host leukocytes, antibodies, or other reagents can be injected and circulated across the surface of the mammalian target cells. The inverted microscope with mechanical stage and video-capture system permits the operator or user of the system to survey the entire target cell monolayer and to make a high resolution phase contrast recording of the interactive field for subsequent analysis. (A Macintosh computer system (Apple Computers, Cupertino, CA), LG-3 video frame grabber board, (Scion Corporation, Frederick, MD), and Image software (NTH, Bethesda, MD) are preferred for real-time and off-line video analysis of adhesion events.) In a preferred use of the present system, microbial cells may be injected in order to observe their interaction(s) with mammalian cells or purified host ligands on the "attachment" substrate present in the system. For example, Fig. 2 demonstrates the influence of cytokine activation of the HUVECs on shear-dependent adhesion interactions with C. albicans. It has not previously been possible to combine injections of microbial pathogens with leukocytes to determine the effect(s) of leukocyte-microbial interactions under simulated physiologic shear. Similarly, Fig. 4 demonstrates dramatic suppression of neutrophil binding to activated HUVECs when C. albicans has already bound to the endothelial cells. Analysis of such physiologically relevant and complex interactions between phagocytic, endothelial, and microbial cell types is a significant use of the present invention.

Other contemplated uses of the present invention include the collection and analysis of data from numerous fields of view across the capillary tube as described in Example 1, in order to provide sufficient sampling to facilitate statistical analysis of, e.g., microbial adhesion events. It is contemplated that the culture of host cells on the lumenal surface establishes their basal and lumenal molecular characteristics. This provides a clear advantage over microbial adhesion assays utilizing harvested and disrupted cellular orientations. The system according to the present invention also provides a clear advantage over flow systems that do not include host cells cultured within or on the experimental solid material. Without the presence of host cells in the flow system, key host-produced extracellular components that could condition the surface of the bio-implant materials, like catheter plastic tubing, would be missing from the assays. The present system thus includes the conditioning of intramedic devices material either by culture with host cells or coating with purified host cell components. The conditioning molecules may influence microbial adhesion events important for bio-film development, and can be selected or determined by skilled artisans in order to evaluate various cell-types and/or host cell components.

It is also contemplated that the microscopic monitoring of adhesion events will provide a substantial advantage over techniques that must control coadhesion or homotypic binding behavior. The system of the present invention permits an analysis of complex adhesion behaviors that can occur in simulated physiologic shear. For example, Fig. 3 demonstrates the difference in homotypic binding events correlated with CSH differences in C. albicans. In another example, Fig. 6 shows the changing ratio of homotypic binding to total binding for E. coli O157:H7 attachment to epithelial cells and demonstrates the capabilities of the present invention to record complex attachment behaviour.

Other static adhesion assays known in the art that involve host cell monolayers could not distinguish between the fine details of adhesion events that were gravity driven as compared to those that would not occur given shear forces relevant to the fluid-tissue interface like gastrointestinal peristaltic motion across epithelial cell surfaces or blood flow shear forces at vascular sites. Additional advantages afforded by the present shear assay system include the elimination of potential perturbations to microbial binding interactions that occur during the washing steps of prior art assays. The perturbations of temporarily and repeatedly causing the monolayer to interface with air instead of assay medium is a detrimental contrast to the fluid interface conditions that occur in vivo. The system according to the present invention maintains a physiologically relevant host tissue interface for microbial adhesion interactions and unbound microorganisms stay in the bulk flow of the loop system and are easily distinguished from adherent organisms. In light of the foregoing general discussion, the specific examples presented below are illustrative only and are not intended to limit the scope of the invention. Other generic configurations will be apparent to one skilled in the art.

EXAMPLES

Example 1 : Protocol for Shear Assays of Candida Attachment.

Shear assays according to the present invention are performed in HEPES- buffered, Hank's balanced salts solution (plus Ca²+/Mg²+) containing 5% human serum. Final Candida concentrations of either 1 x 10⁷ spheres/ml or 5 x 10⁶ spheres/ml are utilized for adhesion assays involving yeast and HUVECs. The final Candida concentration is 1 x 10⁸ spheres/ml in combination assays of yeast, neutrophils and HUVECs. Aliquots of Candida cells are suspended in 12 ml assay medium and injected into the loop under high flow rates of 4-5 dynes/cm². Video recording is initiated and after 1 minute, the flow rate is adjusted down to 1-2 dynes/cm². At 8 - 12 minutes post- injection, the HUVEC monolayer is scanned by stopping a non-overlapping fields of view along the length of the capillary tube. For each field of view, the microscope is adjusted through multiple focal planes to insure distinction of yeast bound to the HUVEC surface. Combination assays with yeast, neutrophils, and HUVECs are done as follows.

Control neufrophil binding to IL-lβ activated HUVECS is done as described herein. In brief, 1 x 10⁷ neutrophils are injected with high flow rates for one minute and then adjusted to a slower rate as above. A single field of view is selected for recording the number of interacting neutrophils over a 15 minute period. To determine the influence of pre-attached Candida upon neufrophil binding, yeast cells are injected as described above and allowed to bind under simulated flow for 15 minutes. Unbound yeast cells are removed by replacement of the circulating medium and injecting neutrophils in to the loop. Neufrophil interactions are monitored from a single field of view over an additional 15 minute period.

Example 2: Evaluation of Fungal Adhesion.

Candida albicans isolates A9wt, ATCC 90029 and LGH1095 were cultured aerobically in 2% glucose-0.3% yeast extract- 1% peptone broth (GYEP), in 0.55 M sodium phosphate (pH 7.2) buffered yeast nitrogen base plus amino acids containing 2% glucose as previously described (P. M. Glee, P. Sundstrom, and KC Hazen. 1995. Expression of surface hydrophobic proteins by Candida albicans in vivo. Infect Immun 63: 1373-1379) or in antibiotic medium 3 (Difco) containing 2% glucose (Am3-2G). Briefly, yeast cells were harvested, washed three times in cold sterile d-H₂O, counted, and hydrophobicity values assessed by the hydrophobic microsphere assay (K. C. Hazen and B. W. Hazen. 1987. A polystyrene microsphere assay for detecting cell surface hydrophobicity within Candida albicans populations. J Microbiol Methods 6:289-299). Yeast cells grown to stationary phase at 23 °C were hydrophobic (CSH 95%), while those grown to stationary phase at 37°C were hydrophilic (CSH 5%). Yeast aliquots were held on ice as pellets and used within 4 hours. The yeast populations were assessed for their sphere to cell unit ratios (S:CU), which is a measurement reflecting the abundance of singlet blastoconidia in the population. For example, a mother-daughter combination would be 2 spheres, but 1 contiguous cell unit. All harvested yeast populations had acceptable S :CU values of = 2 : 1 , reflecting stationary phase yeast cultures. The S:CU values were important for establishing the amount of Candida-Candida adhesion observed in these assays.

Mammalian cells and growth conditions: Human neutrophils, serum, and human umbilical vein endothelial cells (HUVECS) were harvested and prepared as previously described (R. F. Bargatze, S. Kurk, G. Watts, T. K. Kishimoto, C. A. Speer, and M. A. Jutila. 1994. In vivo and in vitro functional examination of a conserved epitope of L- and E- selectin crucial for leukocyte-endothelial cell interactions. J Immunol 152:5814-5825). HUVECs were grown 48 h to confluency on the lumenal surface of sterile glass capillary tubes (1.36 mm dia x 2 cm) in endothelial-cell growth medium (EGM, Clonetics, San Diego, CA). Prior to the assay, some HUVEC monolayers were activated by incubating with interleukin-1 (10 ng/ml, 1 h), gently rinsed and EGM replaced for 2 h before the monolayer was utilized for adhesion assays. Only capillary tubes having at least 75% monolayer development along the tube length were utilized for the assays. Assays were performed in HEPES-buffered, Hank's balanced salts solution (plus Ca2+/Mg²+) containing 5% human serum.

The HUNEC capillary tube was attached to silicone tubing (1.5 mm internal dia.) which had two extension sets (Abbot Laboratories) and a three-way stopcock in line to form a closed system (approx. 105 cm long with 3 ml total volume). The tubing is attached to an adjustable peristaltic pump to establish re-circulating flow. The capillary tube is placed on the mechanical, heated stage of an inverted microscope that is equipped with phase contrast optics and high-resolution video monitoring and recording apparatus.

Candida adhesion studies: Aliquots of Candida cells were suspended in 1 ml loop medium and injected immediately into the loop under high flow rates (4-5 dynes/cm2). Assays were run at a final Candida concentration of either 1 x 10⁷ spheres/ml or 5 x 10⁷ spheres/ml. Video recording was initiated and after 1 minute, the flow rate was adjusted to 1-2 dynes/cm². Adhesion was evaluated 8 - 12 minutes post-injection by microscopic sampling of 8 or more non-overlapping fields of view along the HUVEC monolayer. At each field of view, multiple focal planes were recorded to insure capture of the refractive distinction of bound yeast on the HUNEC monolayer.

Data analysis: Video records were utilized to assess the number of adhesion events in each assay. At least 10 fields of view were analyzed for each assay except for combination yeast-neutrophil experiments where yeast adhesion events were assess from 8 fields. Different fields of view were chosen in the 8 - 12 minute window by using the internal time stamp per frame.

Two types of binding events were observed in the Candida adhesion studies. They were classified as heterotypic (Candida to HUVEC) and homotypic (Candida to Candida) binding. The number of focal adhesion events for each field of view was counted to represent the heterotypic binding. In addition, the number of Candida cells per focal adhesion, i.e., the homotypic binding, was recorded as ranked data with the following values: 1, 2, 3, 4, 5-9, 10-15, and >16 spheres (i.e., blastoconidia) attached. The average number of focal adhesion events for each assay was calculated from sampling at 8 or more views. To generate averages for homotypic binding events, the relative percent contribution of ranked groups of three or more spheres to the average focal adhesion events was calculated. Sigmaplot v4.0 and SigmaStat v2.0 were utilized for graphing and statistical analysis of the data.

Example 3: Activation of HUVEC Monolayer by IL-lβ

Activation of the HUVEC monolayer by IL-lβ significantly increases binding by hydrophobic C. albicans A9wt yeast cells (growth in GYEP). The graph (Fig. 2) shows heterotypic binding events expressed as the average number of Candida foci per field (n=14 for each condition). Cytokine activation increased homotypic binding events in the 56.3 % of foci were in groups of 3 or more blastoconidia compared to 36.3 % for unactivated conditions.

IL-1 activation of the HUVEC layer increases expression surface proteins like cell adhesion molecules (CAMs) and selectins (E- and P-selectin) whereas intercellular CAM-2 is expressed constitutively on the cells. The difference in yeast binding observed here may be based on Cam upregulation in that hydrophobic cells surfaces would display the integrin analogue molecules as well as hydrophobic proteins that bind to numerous host molecules.

These in vitro shear assay results showing a significant difference for Candida adhesion related to activation state of the endothelial cells appears to contrast with results obtained by Filler and colleagues (10). They found that attachment of yeast to HUVECs in a microtiter-based adhesion assay was not influenced by cytokine activation. Whether the difference in binding can be classified as a shear-dependent interaction has not been determined. The foregoing data was obtained in assays involving pooled donor HUVECs. In other experiments with HUVECs from single donors, we noted differences in the average heterotypic binding supported by HUVECs (data not shown). The donor differences were not unexpected, as that variable has been identified in other Candida adhesion studies (11). Example 4: Comparison of Hydrophobic and Hydrophilic Yeast

Hydrophobic and hydrophilic yeast were compared in the shear assay system as described above for differences in binding to activated HUVECs. Fig 3 A shows the results of C. albicans ATCC 90029 grown in AM3-2G while Fig. 3B shows C. albicans grown in GYEP. Each graph shows the significant difference between hydrophobic and hydrophilic cell binding to endothelium.

The stacked bars show the comparative differences in homotypic binding events for hydrophilic and hydrophobic yeast cells. The tendency of hydrophobic cells to produce more Candida-Candida binding events than hydrophilic cells was consistent in more than 8 in vitro shear experiments comparing hydrophobic and hydrophilic cell binding. By way of general observations, Candida to endothelial cell binding interactions occur very rapidly without any apparent intermediate stage involving rolling or slow velocities. Candida cells appear to be moving with the bulk flow one moment, and in the next video frame they are not moving. In some cases, the Candida cells appear to be tethered to the endothelial surface and "wave" with liquid movement. This might be due to fibronectin streamers that are possible on the lumenal surface of the endothelial cells.

Example S: Suppression of Neutrophil Attachment to Activated HUVECs with Pre-attached Candida Cells. Neutrophils utilize selectin interactions to roll upon endothelial cells and integrin interactions to provide tight binding events. The shear assay as described above was used to evaluate neutrophil interactions. Compared to the control, the total number of neutrophil interactions (rolling + tight adhesion) was decreased approximately 10-fold for endothelial surfaces that had pre-attached yeast. In this assay, the average number of C. albicans A9wt foci per field (n+8) was 56.4 (SD±16.7). These data are presented in Fig. 4. Example 6: Evaluation of Bacterial Adhesion -- Evaluation of cultural conditions predisposing to development of adhesion molecules

The ability of VTEC (i.e., VERO cytotoxic-hemmoraghic E. coli) organisms to attach to host cells in an in vitro shear assay served as an indicator of adhesin activity. Investigators found (see, e.g., Junkins, A.D. and M.P. Doyle. 1989 Comparison of adherence properties of Escherichia coli O157:H7 and a 60-megadalton plasmid-cured derivative. Curr. Microbiol. 19:21-27) that cell adhesion by E. coli 0157 was influenced by growth conditions provided for the bacteria. The effects of (i) oxygen tension, (ii) growth stage, (iii) culture medium, and (iv) temperature on the adhesion of VTEC to target cells were evaluated. Results showed that adhesion molecules appeared to be optimally expressed only when cells were grown on blood agar. VTEC grown in broth culture or on other culture media failed to develop attachment (epithelial cells) properties when tested in the shear assay system according to the present invention.

Example 7: Evaluation of Bacterial Adhesion — Detection of adhesion events in VTEC-target cell interactions

Epithelial cells were isolated from bovine fetuses by isolation and dissection of the small intestine followed by treatment with trypsin-EDTA in Hanks balanced salt solution. Cells were plated and grown to confluence in T-25 flask and then collected and frozen in liquid nitrogen. Cells were tested for their phenotype using anti-bovine monoclonal antibodies previously shown the be specific for bovine epithelium and were shown to be greater than 95% epithelial cells. Epithelial cells were thawed and plated into borasilicate capillary tubes (1.3 mm internal diameter) in epithelial cell growth medium and allowed to grow to confluence. Epithelial cells bound to the internal surface of capillary tubes were either activated with 100 mM phorbol myristate acetate (PMA) for four hours or not activated before incorporation into the closed recirculating shear loop system.

Upon incorporation of the epithelial lined capillary tube in the loop system a flow induced shear force was established as a pulsatory wave flow peaking at 2 dynes using Hanks balanced salt solution, HEPES (pH 7.0) as the medium. To prepare VTEC (0157 serotype) organisms for adherence assays, they were grown on sheep blood agar plates for 24 hours to enhance adhesin levels, scraped free of the agar surface and suspended and washed twice in PBS. The washed VTEC were reacted with magnetic beads coated with anti-0157 antiserum, washed with phosphate buffered saline, and suspended in PBS for infusion into the shear flow via an injection port. Interactions of E. coli coated beads with epithelial cells were observed by video microscopy and recorded to video tape as a permanent record and for offline computer image analysis.

Adhesion of E. co/ϊ-coated magnetic beads was analyzed for interaction type (rolling or sticking) and the characteristics of binding (e.g., heterotypic/homotypic binding events). Assays were performed either to monitor adhesion events over time for a single field of view or by sampling multiple fields of view during a particular window of time during the assay.

Figure 6 shows the number of of E. coli O157:H7- coated bead attachments over time for a single field of activated bovine epithelial cells. These results demonstrate the unique capability of real-time analysis of complex heterotypic and homotypic binding behaviours of pathogenic cells.

Results in other experiments indicate that unactivated epithelial cells support less binding of E. coli O157:H7 cells. For example, the average number of attached E. coli- coated beads was 2.75±1.62 for 20 fields sampled between five and seven minutes time in the assay. That contrasts dramatically with the four minute values for activated epithelium shown in Figure 6.

Example 8\ Evaluation of Pathogen-Host Cell Adhesion or Signaling Events

Using the shear analysis system described above, the flow through the system includes one or more of selected pathogen-related molecules such as proteins, glycoproteins, glycolipids and carbohydrates or microbial analogs and mimics of host molecules. The adhesion interactions and/or signaling events associated with adhesion of such molecules to the host cells are observed. Example 9: A method of identifying molecular targets for inhibiting biofilm formation

The formation of biofilms requires the interaction of planktonic cells with a surface in response to environmental signals (O'Toole et al., Mol Microbiol (1998) 30(2): 295-304, Davies et al, Science (1998) 280(5361): 295-298; Rozalska et al, MedDosw Mikrobiol (1998) 50(1-2): 115-122). For example, P. aeruginosa requires type IV pili formation in order for monolayers of cells to develop microcolonies that lead to biofilm formation (characterized by multilayered colonies). Mutants lacking type IN pili can form monolayers, however, they are unable to form biofilms. From studying the interactions of such normal biofilms and mutant monolayers, for example, with the shear assay system of the present invention, it is possible to use type IV pili-producing organisms or mutants as a target for potential anti-biofilm agents. Therefore, the identification of mutant strains which can form monolayers on abiotic surfaces but are unable to form biofilms on those surfaces are useful in determining potential targets for agents which can inhibit biofilm formation for wild type strains.

Various abiotic surfaces (e.g., polytetrafluorethylene, polyvinyl chloride, siliconized latex and heparinized polyethylene) presented, for example, in capillary tube form; and appropriate biotic surfaces involved in biofilm formation presented as a substrate in a conduit or tube according to the present invention, are seeded in multiple conduits or tubes in parallel flow with organisms that are most often isolated in medical device-associated infections (e.g., S. aureus, S. epidermidis, E. faecalis, E. coli, P. vulgaris, P. aeruginosa and C. albicans; see Rozalska et al, Med Dosw Mikrobiol (1998) 50(1-2): 115-122). Through this approach, attachment mutants are identified and agents that reduce biofilm formation are assayed. Preferably, the capillary tubes will be attached to biofilm resistant tubing comprising a stop-cock to form a closed system. After injection of the appropriately selected strains of pathogens, the tubing is attached to an adjustable pump to establish a circulating flow. The capillary tubes are placed on a mechanical stage comprising a heater and an inverted phase-contrast microscope and high resolution video monitoring and recording apparatus. The development from monolayers to microcolonies to biofilms is followed at appropriate intervals post injection to observe, for example, wild type and mutant cells at non-overlapping fields using multiple focal planes. The inability of a pathogen to form microcolonies is be scored as a surface attachment defective mutant and said mutant may be further analyzed to identify the molecular defect (i.e., the "target" in a wild type pathogen) which inhibits the formation of microcolonies and biofilms. Once the molecular target has been identified, then conduit or tube surfaces are coated with the molecular target and agents can be assayed to determine whether they interfere with molecular target-cell interactions.

Example 10: Evaluation of Virus-Host Cell Adhesion or Signaling Events

Using the shear analysis system described above, the flow through the system includes one or more of selected virus-related molecules such as viral proteins, envelope proteins, glycoproteins, glycolipids and carbohydrates or viral analogs and mimics of host molecules. The adhesion interactions and/or signaling events associated with adhesion of the virus or such viral-related molecules to the host cells are observed.

It should be understood that the foregoing discussion and examples present merely present a detailed description of certain preferred embodiments. For instance, the foregoing examples illustrate the adhesion analysis of an opportunistic fungal pathogen and a toxin-producing bacterial isolate. However, the skilled artisan readily will understand that the systems of the present invention have a broader application to many different genera of microorganisms including other bacteria, fungi, viruses, and protozoans. Various modifications to the systems described in the foregoing examples available to the skilled artisan include the direct injection of microorganisms of appropriate size, such as protozoans, and also would include bead-bound preparations of smaller microbes like viral particles. The systems of the present invention thus offer novel capacities for identifying and exploiting microbial and mammalian adhesion molecules in the development of diagnostics, therapeutics and vaccine technologies. It therefore should be apparent to those of ordinary skill in the art that various modifications and equivalents can be made without departing from the spirit and scope of the invention. All articles, patents and patent applications and other documents that are identified in this application are incorporated by reference in their entirety.

References

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3. Hostetter, M.K., 1998. Linkage of adhesion, morphogenesis, and virulence in Candida albicans. J. Lab. Clin.Med. 132:258.

4. Cole, G.T., A.A. Halawa and E.J. Anaissie. 1996. The role of the gastrointestinal tract in hematogenous candidiasis: from the laboratory to the bedside. Clin.Infect.Dis. 22:S73.

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9. Chafffin, W.L., J.-L. Lopez-Ribot, M. Casanova, D. Gozalbo and J.P. Martinez, 1998. Cell wall and secreted proteins of Candida albicans: identification, function, and expression. Microbiology and Molecular Biology Reviews 62:130.

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Microbio Methods 6:289.

Claims

We Claim:

1. An apparatus comprising: an elongated tube having an inner surface adapted to support a substrate; means for producing in said tube a flow of fluid comprising test molecules, test cellular components or test cells; means for monitoring the interaction of said test molecules, test cellular components or test cells with said substrate.

2. The apparatus of claim 1, wherein said tube is substantially cylindrical.

3. The apparatus of claim 1, wherein said producing means provides a time variant flow.

4. The apparatus of claim 2, wherein said time variant flow generates a shear force that is substantially the physiological equivalent of the shear force across the fluid- tissue interface at epithelial or endothelial cell surfaces in a host.

5. The apparatus of claim 3, wherein said fluid flow is selected from the group consisting of pulsatory, continuous, invariant and recirculating flow.

6. The apparatus of claim 3, wherein said substrate comprises substrate cells, substrate extracellular matrix proteins, substrate molecules, substrate cellular components or combinations thereof.

7. The apparatus of claim 6, wherein said substrate cells are selected from the group consisting of endothelial cells, epithelial cells activated endothelial cells, and activated epithelial cells.

8. The apparatus of claim 7, wherein the cells are oriented in a substantially physiologically correct orientation such that said cells present to the fluid flow their characteristic cell surface moieties.

9. The apparatus of claim 3, wherein said test molecules, test cellular components or test cells test cells are mammalian pathogens or pathogen-associated molecules.

10. The apparatus of claim 9, wherein said test cells are selected from the group consisting of viruses, bacteria, fungi, protozoa and parasites.

11. The apparatus of claim 1 , wherein said monitoring means monitors physiological parameters.

12. The apparatus of claim 11, wherein said monitoring means monitors a parameter selected from the group consisting of optical, electrical or chemical parameters.

13. The apparatus of claim 11 , wherein said monitoring means monitors a parameter selected from the group consisting of adhesion events, binding events, cell viability, pH, oxygen tension, CO₂ levels or temperature.

14. The apparatus of claim 13, wherein said binding events are selected from the group consisting of heterotypic and homotypic binding between said substrate cells and said test cells.

15. The apparatus of claim 11 , wherein the monitoring and/or recording means is capable of real-time analysis.

16. The apparatus of claim 1, further comprising computer means for correlating, processing and storing information produced by said monitoring means.

17. The apparatus of claim 11 , wherein said monitoring means comprises a microscope and video-capture system.

18. The apparatus of claim 17, wherein the video-capture system comprises a video camera, a video monitor and a NCR and/or CD recorder.

19. The apparatus of claim 18, wherein the VCR is a time-lapse VCR.

20. An apparatus comprising: a conduit having an inner surface adapted to support a substrate comprising substrate cells, substrate exfracellular matrix proteins, substrate molecules, substrate cellular components or combinations thereof; means for producing in said conduit a flow of fluid comprising test molecules, test cellular components or test cells; means for monitoring the interaction of said test molecules, test cellular components or test cells with said substrate cells, substrate extracellular matrix proteins, substrate molecules, substrate cellular components or combinations thereof.

21. The apparatus of claim 20, wherein said test molecules, test cellular components or test cells are mammalian pathogens or pathogen-associated molecules.

22. The apparatus of claim 21, wherein said substrate cells are selected from the group consisting of endothelial cells, epithelial cells activated endothelial cells, and activated epithelial cells.

23. The apparatus of claim 20, wherein said conduit is substantially cylindrical.

24. A method of determining the adhesion of pathogens under physiological shear stress conditions using the apparatus of any of claims 1 to 23, comprising the steps of: introducing test molecules, test cellular components or test cells into said fluid flow; permitting said test molecules, test cellular components or test cells to interact with said substrate cells, substrate extracellular matrix proteins, substrate molecules, substrate cellular components or combinations thereof; and monitoring the interactions.

25. The method of claim 24, wherein said monitoring is effected by use of a probe means to generate information about the interactions.

26. The method of claim 24, wherein the probe means are electrical probes.

27. The method of claim 24, wherein the apparatus comprises at least two conduits or tubes are arranged in a series flow configuration.

28. The method of claim 24, wherein the apparatus comprises at least two conduits or tubes are arranged in a parallel flow configuration.

29. The method of claim 24, wherein said substrate cells are endothelial cells that are characteristic of the tissues selected from the group consisting of intestinal, respiratory and vascular tissues.

30. The method of claim 24, wherein said substrate cells are characteristic of the tissues selected from the group consisting of vaginal, bladder, parenchymal and interstitial tissues.