Effect of biomaterial surface properties on fibronectin-alpha5beta1 integrin interaction and cellular attachment

The ability of fibronectin (Fn) to mediate cell adhesion through binding to alpha(5)beta(1) integrins is dependent on the conditions of its adsorption to the surface. Using a model system of alkylsilane SAMs with different functional groups (X=OH, COOH, NH(2) and CH(3)) and an erythroleukemia cell line expressing a single integrin (alpha(5)beta(1)), the effect of surface properties on the cellular adhesion with adsorbed Fn layers was investigated. (125)I-labeled Fn, a modified biochemical cross-linking/extraction technique and a spinning disc apparatus were combined to quantify the Fn adsorption, integrin binding and adhesion strength, respectively. This methodology allows for a binding equilibrium analysis that more closely reflects cellular adhesion found in stable tissue constructs in vivo. Differences in detachment strength and integrin binding were explained in terms of changes in the adhesion constant (psi, related to affinity) and binding efficiency of the adsorbed Fn for the alpha(5)beta(1) integrins (CH(3) approximately NH(2)相似文献   

Short-term effects of adhesion peptides on the responses of preosteoblasts to pBMP-9

Adhesion peptides are currently used to enhance the interactions of osteoblasts with biomaterials. However, little is known about the effects of adhesion peptides on cell responses to growth factors, especially the bone morphogenetic proteins (BMPs). We used adhesion peptides Ac-CGGNGERPRGDTYRAY-NH(2) (pRGD), derived from bone sialoprotein, and Ac-CGGDGEA-NH(2) (pDGEA), derived from collagen, which interact with alpha(v)beta(3) and alpha(2)beta(1) integrins, respectively. We analyzed the effects of pRGD- and pDGEA-coated polystyrene (PS) on the responses of murine MC3T3-E1 preosteoblasts to a peptide derived from human BMP-9 (pBMP-9) in serum-free medium. After 1h, pRGD favoured interactions with alpha(v) while pDGEA bound beta(1) integrin subunits. Adding pBMP-9 (400 ng/mL) increased the amount of alpha(v) integrin subunits in cell membranes on pRGD-coated PS, but had no effect on beta(1) integrin subunits. Only on this substratum, collagen type I mRNA was enhanced and the addition of pBMP-9 promoted the early cell differentiation, increasing their alkaline phosphatase (ALP) activity within 24 h. These cells also organized beta(1) integrin subunits at their focal adhesion points. Inhibiting alpha(2)beta(1) integrins by pDGEA pre-treatment decreased this ALP activity. It is therefore important to understand the impact of adhesion peptides on the early cell responses to growth factors in order to improve biomimetic materials.     

Transendothelial migration enhances integrin-dependent human neutrophil chemokinesis

Transendothelial migration of neutrophils induces phenotypic changes that influence the interactions of neutrophils with extravascular tissue components. To assess the influence of transmigration on neutrophil chemokinetic motility, we used polyethylene glycol hydrogels covalently modified with specific peptide sequences relevant to extracellular matrix proteins. We evaluated fMLP-stimulated human neutrophil motility on peptides Arg-Gly-Asp-Ser (RGDS) and TMKIIPFNRTLIGG (P2), alone and in combination. RGDS is a bioactive sequence found in a number of proteins, and P2 is a membrane-activated complex-1 (Mac-1) ligand located in the gamma-chain of the fibrinogen protein. We evaluated, via video microscopy, cell motility by measuring cell displacement from origin and total accumulated distance traveled and then calculated average velocity. Results indicate that although adhesion and shape change were supported by hydrogels containing RGD alone, motility was not. Mac-1-dependent motility was supported on hydrogels containing P2 alone. Motility was enhanced through combined presentation of RGD and P2, engaging Mac-1, alpha(V)beta(3), and beta(1) integrins. Na?ve neutrophil motility on combined peptide substrates was dependent on Mac-1, and alpha(4)beta(1) while alpha(6)beta(1) contributed to speed and linear movement. Transmigrated neutrophil motility was dependent on alpha(v)beta(3) and alpha(5)beta(1), and alpha(4)beta(1), alpha(6)beta(1), and Mac-1 contributed to speed and linear motion. Together, the data demonstrate that efficient neutrophil migration, dependent on multi-integrin interaction, is enhanced after transendothelial migration.     

Expression of integrin alphavbeta3 in gliomas correlates with tumor grade and is not restricted to tumor vasculature.

In malignant gliomas, the integrin adhesion receptors seem to play a key role for invasive growth and angiogenesis. However, there is still a controversy about the expression and the distribution of alpha(v)beta(3) integrin caused by malignancy. The aim of our study was to assess the extent and pattern of alpha(v)beta(3) integrin expression within primary glioblastomas (GBMs) compared with low-grade gliomas (LGGs). Tumor samples were immunostained for the detection of alpha(v)beta(3) integrin and quantified by an imaging software. The expression of alpha(v)beta(3) was found to be significantly higher in GBMs than in LGGs, whereby focal strong reactivity was restricted to GBMs only. Subsequent analysis revealed that not only endothelial cells but also, to a large extent, glial tumor cells contribute to the overall amount of alpha(v)beta(3) integrin in the tumors. To further analyze the integrin subunits, Western blots from histologic sections were performed, which demonstrated a significant difference in the expression of the beta(3) integrin subunit between GBMs and LGGs. The presented data lead to new insights in the pattern of alpha(v)beta(3) integrin in gliomas and are of relevance for the inhibition of alpha(v)beta(3) integrin with specific RGD peptides and interfering drugs to reduce angiogenesis and tumor growth.     

Activation of cell-survival transcription factor NFkappaB in L1Ig6-stimulated endothelial cells

Ligation of the integrin alpha(v)beta(3) in endothelial cells has been shown to be important for their survival. Such ligation induces signalling events merging into the Raf-Ras-ERK cascade that eventually induces activation of nuclear factor kappa B (NFkappaB), leading to its phosphorylation and nuclear translocation and thus inhibiting apoptosis. Here, the recombinant sixth immunoglobulin-like domain of cell adhesion molecules L1 (L1Ig6), a ligand for integrin alpha(v)beta(3), was explored as a component of vascular implant surfaces to initiate the NFkappaB-cell survival pathway. This supposition was supported. Specifically, NFkappaB-p65 was expressed in human umbilical vein endothelial cells (HUVECs) and when stimulated on L1Ig6, the phosphorylated form was found in the nucleus in over 60% of the cells. NFkappaB was not translocated into the nucleus on a number of other extracellular matrix substrates examined or when fibroblasts were cultured on L1Ig6. NFkappaB phosphorylation and nuclear translocation could be inhibited by blocking ligation of alpha(v)beta(3) by L1Ig6 with an antibody recognizing alpha(v)beta(3), with a cyclic RGD peptide, and with soluble L1Ig6. Moreover, blocking of alpha(v)beta(3) interaction with L1Ig6 was correlated with induction of apoptosis. Thus, these experiments demonstrate that L1Ig6 may be useful as alpha(v)beta(3) ligand for the induction of endothelial survival pathways mediated by NFkappaB-p65.     

Surface chemistry modulates fibronectin conformation and directs integrin binding and specificity to control cell adhesion

Integrin-mediated cell adhesion to proteins adsorbed onto synthetic surfaces anchors cells and triggers signals that direct cell function. In the case of fibronectin (Fn), adsorption onto substrates of varying properties alters its conformation/structure and its ability to support cell adhesion. In the present study, self-assembled monolayers (SAMs) of alkanethiols on gold were used as model surfaces to investigate the effects of surface chemistry on Fn adsorption, integrin binding, and cell adhesion. SAMs presenting terminal CH(3), OH, COOH, and NH(2) functionalities modulated adsorbed Fn conformation as determined through differences in the binding affinities of monoclonal antibodies raised against the central cell-binding domain (OH > COOH = NH(2) > CH(3)). Binding of alpha(5)beta(1) integrin to adsorbed Fn was controlled by SAM surface chemistry in a manner consistent with antibody binding (OH > COOH = NH(2) > CH(3)), whereas alpha(V) integrin binding followed the trend: COOH > OH = NH(2) = CH(3), demonstrating alpha(5)beta(1) integrin specificity for Fn adsorbed onto the NH(2) and OH SAMs. Cell adhesion strength to Fn-coated SAMs correlated with alpha(5)beta(1) integrin binding (OH > COOH = NH(2) > CH(3)), and experiments with function-perturbing antibodies demonstrated that this receptor provides the dominant adhesion mechanism in this cell model. This work establishes an experimental framework to analyze adhesive mechanisms controlling cell-surface interactions and provides a general strategy of surface-directed control of adsorbed protein activity to manipulate cell function in biomaterial and biotechnological applications.     

Expression and function of beta(1) and beta(3) integrins of human mesothelial cells in vitro.

Mesothelial cells (MC) and extracellular matrix (ECM) components are thought to play a pivotal regulatory role during the inflammatory-reparative response of serosal membranes. Integrins are known to serve as cellular ECM receptors, but mesothelial integrin expression and its function, particularly its role for attachment to different ECM components, remain to be elucidated. The aim of the present study was to characterize the integrin expression of human omentum majus derived MC (HOMC) in vitro by immunohistochemistry and to investigate their functional significance with regard to HOMC adhesion to fibronectin (fn), vitronectin (vn), collagen IV (coll IV), and laminin (ln). Mesothelial cells in vitro strongly expressed beta(1), beta(3), alpha(2), alpha(3), alpha(5), and alpha(v) chains. A weak reactivity was found for alpha(1) and alpha(6), but no alpha(4) reactivity was detectable. Compared to the control, fn, vn, coll IV, and ln caused a significant 2.6-, 2.2-, 2-, and 1.6-fold increase of HOMC adhesion, respectively. Inhibition studies revealed that HOMC attachment to fn is mediated by alpha(5)beta(1), alpha(v)beta(1), and alpha(v)beta(3), with a synergistic effect of alpha(5)beta(1) and alpha(v)beta(3). Adhesion to vn is mediated by alpha(v)beta(1) and alpha(v)beta(3). Integrins alpha(1)beta(1), alpha(2)beta(1), and alpha(3)beta(1) mediate adhesion to coll IV and ln. We suggest that the integrin expression and function of mesothelial cells described here play an important role in the interaction of MC with the ECM, particularly during the acute and chronic inflammatory-reparative response of serosal membranes.     

Effect of adsorbed fibronectin concentration on cell adhesion and deformation under shear on hydrophobic surfaces.

To facilitate tissue integration with biomaterials proteins and peptides frequently are immobilized on the biomaterial surface. In particular, extracellular matrix proteins--which interact specifically with integrin adhesion receptors on the cell surface--can stimulate initial cell attachment by serving both as a ligand for receptor-mediated attachment and as a stimulant of focal adhesion formation and cytoskeletal reorganization. Consequently, the strength of cell adhesion should depend both on the strength of cell/surface contacts and cytoskeleton-dependent properties of the cell (i.e., morphology, compliance). To examine this dual role of extracellular matrix proteins, murine fibroblasts were seeded onto self-assembled monolayers (SAMs) of dodecanethiolate coated with 0 to 0.45 microg/cm(2) of fibronectin (Fn) and then detached by hydrodynamic shear using a radial-flow chamber (RFC). Cell adhesion was characterized in terms of the critical wall shear stress for detachment (tau(wc)), and the compliance was evaluated from measurements of cell displacement and elongation as a function of the fibronectin concentration. Critical wall shear stress and cell displacement were found to be insensitive to Fn at concentrations below 0.23 microg/cm(2) while above this threshold tau(wc) increased and displacement decreased with increasing Fn concentration. Elongation of the cells in the direction of flow was independent of Fn concentration, but correlated linearly with tau(wc) for Fn densities below 0.23 microg/cm(2). These studies show that Fn concentration affects both tau(wc) and cell displacement under shear, and that tau(wc) is sensitive to cell compliance. In addition, they suggest that the dominant mechanism of cell detachment from hydrophobic substrates involves cell displacement.     

Cellular recognition of synthetic peptide amphiphiles in self-assembled monolayer films

The incorporation of lipidated cell adhesion peptides into self-assembled structures such as films provides the opportunity to develop unique biomimetic materials with well-organized interfaces. Synthetic dialkyl tails have been linked to the amino-terminus, carboxyl-terminus, and both termini of the cell recognition sequence Arg-Gly-Asp (RGD) to produce amino-coupled, carboxyl-coupled, and looped RGD peptide amphiphiles. All three amphiphilic RGD versions self-assembled into fairly stable mixed monolayers that deposited well as Langmuir-Blodgett films on surfaces, except for films containing amino-coupled RGD amphiphiles at high peptide concentrations. FT-IR studies showed that amino-coupled RGD head groups formed the strongest lateral hydrogen bonds. Melanoma cells spread on looped RGD amphiphiles in a concentration-dependent manner, spread indiscriminately on carboxyl-coupled RGD amphiphiles, and did not spread on amino-coupled RGD amphiphiles. Looped RGD amphiphiles promoted the adhesion, spreading, and cytoskeletal reorganization of melanoma and endothelial cells while control looped Arg-Gly-Glu (RGE) amphiphiles inhibited them. Antibody inhibition of the integrin receptor alpha3beta1 blocked melanoma cell adhesion to looped RGD amphiphiles. These results confirm that novel biomolecular materials containing synthetic peptide amphiphiles have the potential to control cellular behavior in a specific manner.     

Involvement of alpha(v)beta3 integrin-like receptor and glycosaminoglycans in Candida albicans germ tube adhesion to vitronectin and to a human endothelial cell line

The present study was undertaken to investigate the expression of alpha(v)beta3 and alpha(v)beta5 integrin-like vitronectin receptors (VNRs) on Candida albicans germ tube and their involvement in its adhesion to vitronectin (VN) and human endothelial cells. By immunofluorescence and FACS analysis, several monoclonal antibodies directed against human alpha(v) or beta3 integrin subunit or alpha(v)beta3 and alpha(v)beta5 heterodimers, positively stained C. albicans germ tubes. C. albicans germ tubes specifically adhered (45-50%) to VN and this adhesion was markedly inhibited by RGD-, but not RGE-containing peptides. Adhesion of C. albicans germ tubes to VN was strongly inhibited by anti-alphav, anti-beta3 or anti-alpha(v)beta3, but not by alpha(v)beta5 monoclonal antibody. C. albicans germ tube adhesion to VN was also inhibited by glycosaminoglycans (GAGs) such as heparin or chondroitin sulphate. Finally, we show that C. albicans germ tubes adhere to the human EA.hy 926 endothelial cell line. This adhesion is markedly blocked by anti-beta3 monoclonal antibody, GRGDSP peptide or heparin, and is completely abolished by their combination. Overall these results indicate that C. albicans germ tube adherence to VN and to a human endothelial cell line is mediated by alpha(v)beta3, but not by alpha(v)beta5-like integrin, and depends on GAGs which may act by regulating alpha(v)beta3 integrin-like/VN adhesive interaction.     

Expression of cell adhesion receptors in human osteoblasts cultured on biofunctionalized poly-(epsilon-caprolactone) surfaces

This study was aimed to investigate whether the activation of poly-(epsilon-caprolactone) (PCL) surface by low-energy irradiation and/or the biofunctionalization by absorption of arginine-glycine-aspartic sequences (RGD), can modify the expression of integrins closely related to the osteoblast activity. For this purpose, we analysed the physicochemical changes induced by irradiation and RGD immobilization, the consequences on cell adhesion and spreading, and the effects on integrin expression. PCL irradiated with 5 x 10(15)He(+)/cm(2) (10 keV energy) (irr-PCL) showed an altered surface layer with a partial loss of carboxyl species and the formation of carbonyl groups. Moreover, irr-PCL showed a small smoothening effect and a less polar character in comparison to the pristine ones. The RGD immobilization was observed only on irr-PCL (surface coverage: 7.0 pmol/cm(2)). Human osteoblasts (hOB) were cultured on untreated PCL (ut-PCL), ut-PCL+RGD, irr-PCL, and irr-PCL+RGD. After 24h, ut-PCL hindered the cell adhesion, while a discrete layer of hOB with a good cytoskeleton organization was detected on irr-PCL and irr-PCL+RGD. Before seeding, the single hOB suspension expressed alpha1, alpha2, alpha3, alpha5, beta1, and alphaVbeta3; after 24h, cells cultured on tissue-plastic expressed high levels of beta1 and alphaVbeta3, while alpha1 showed a low intensity and alpha2, alpha3, and alpha5 were negative. beta1 and alphaVbeta3 were selected to evaluate the interaction between cells and PCL samples. The beta1 expression was higher in hOB cultured on irr-PCL than on the other samples. A significant increase in alphaVbeta3 expression was observed only in irr-PCL+RGD, and confirmed by the gene expression analysis. In conclusion, ion irradiation and RGD adsorption on PCL surfaces modulate the expression of integrin involved in hOB growth and function, indicating the effectiveness of biomimetic surfaces in promoting cell adhesion. Ultimately, the study of integrin expression may suggest proper changes to the surface structure in order to improve the osteoconductivity of selected materials.     

NCO-sP(EO-stat-PO) surface coatings preserve biochemical properties of RGD peptides

We have previously reported that star shaped poly(ethylene oxide-stat-propylene oxide) macromers with 80% EO content and isocyanate functional groups at the distal ends [NCO-sP(EO-stat-PO)] can be used to generate coatings that are non-adhesive but easily functionalized for specific cell adhesion. In the present study, we investigated whether the NCO-sP(EO-stat-PO) surfaces maintain peptide configuration-specific cell-surface interactions or if differences between dissimilar binding molecules are concealed by the coating. To this end, we have covalently immobilized both linear-RGD peptides (gRGDsc) and cyclic-RGD (RGDfK) peptides in such coatings. Subsequently, SaOS-2 or human multipotent mesenchymal stromal cells (MSC) were seeded on these substrates. Cell adhesion, spreading and survival was observed for up to 30 days. The time span for cell adherence was not different on linear and cyclic RGD peptides, but was shorter in comparison to the unmodified glass surface. MSC proliferation on cyclic RGDfK modified coatings was 4 times higher than on films functionalized by linear gRGDsc sequences, underlining that the NCO-sP(EO-stat-PO) film preserves the configuration-specific biochemical peptide properties. Under basal conditions, MSC expressed osteogenic marker genes after 14 days on cyclic RGD peptides, but not on linear RGD peptides or the unmodified glass surfaces. Our results indicate specific effects of these adhesion peptides on MSC biology and show that this coating system is useful for selective testing of cellular interactions with adhesive ligands.     

Inhibition of in vitro chondrogenesis in RGD-modified three-dimensional alginate gels

The goal of this study was to investigate the effects of adhesion to the arginine-glycine-aspartic acid (RGD) sequence on the chondrogenesis of bone marrow stromal cells (BMSCs). Synthetic RGE- and RGD-containing peptides were conjugated to sodium alginate, and bovine BMSCs were seeded onto 2D alginate surfaces or encapsulated in 3D gels. BMSCs spread specifically on RGD-modified surfaces, and spreading was inhibited by a soluble RGD peptide and by anti-beta1 and anti-alpha(v)beta3 integrin blocking antibodies. After 7 days in 3D gel culture, the chondrogenic supplements (TGF-beta1 and dexamethasone) significantly stimulated chondrocytic gene expression (collagen II, aggrecan, and Sox-9) and matrix accumulation (collagen II and sGAG) in RGE-modified gels, but this response was inhibited in the RGD-modified gels. Inhibition of sGAG synthesis increased with increasing RGD density, and synthesis was partially rescued by adding a soluble RGD peptide. Addition of an anti-alpha(v)beta3 integrin blocking antibody had no effect on chondrogenesis, while an anti-alpha5 antibody reduced sGAG accumulation. Overall, this study demonstrates that interaction with the RGD motif significantly inhibits the initial chondrogenesis of BMSCs within 3D alginate gels. These results provide new insights into the role of cell-matrix interactions in regulating chondrogenesis and highlight the importance of choosing appropriate biomaterials for tissue engineering therapies.     

Interactions between human monocytes and fibronectin are suppressed by interferons beta and gamma,but not alpha: correlation with Rho-paxillin signaling

Modulation of the adhesive responses of monocytic cells may reflect their motility at sites of diseased tissues (inflammation, tumors). Integrins alpha5beta1 mediate fibronectin (Fn)-dependent adhesion of human monocytes and their precursors. The effect of type I IFNs (alpha, beta) and type II IFN (gamma) was assessed on the adhesive capacities of promonocytic U937 cells and monocytes. IFN-beta and IFN-gamma abrogated monocytic cell adhesion to Fn, but such impaired cell attachment was not due to altered levels of alpha5beta1 integrins. In contrast, IFN-alpha did not affect cell adhesion to Fn. Participation of cytoskeleton assembly in IFN-mediated cell detachment was evaluated. Activation of RhoA activity with lysophosphatidic acid (LPA) increased 2-fold the adhesion of monocytic cells to Fn in a alpha5beta1-mediated fashion, and IFN-gamma treatment reversed the enhancing effect of LPA. Moreover, U937 cells and monocytes dominantly expressed the 44-46 kDa paxillin forms and IFN-beta and IFN-gamma led to the accumulation of 66-70 kDa paxillin forms. These results indicate that IFN-mediated loss of monocyte adhesion to Fn is associated with changes in the cytoskeleton associated proteins paxillin and Rho.     

RGD peptides and monoclonal antibodies, antagonists of alpha(v)-integrin, enter the cells by independent endocytic pathways.

Cyclic synthetic peptides containing the arginine-glycine-aspartate motif (cRGD) and monoclonal antibodies (mAbs) targeted for individual integrins have been developed as potential therapeutic drugs for the treatment of several diseases. We showed that a cRGD peptide targeted for alpha(v)beta(3) was internalized in alpha(v)-integrin expressing and nonexpressing melanoma cells by an integrin independent fluid-phase endocytosis pathway that does not alter the number of functional integrin receptors at the cell surface. In contrast, a blocking mAb directed to alpha(v) was internalized by an integrin-dependent endocytosis pathway that reduced the number of functional integrin receptors at the cell surface. We prove that melanoma cells pretreated with the mAb do not readhere to the substrate, whereas cells pretreated with cRGD peptide retain their readhesion capacity. Given the growing importance of RGD peptides, knowledge of these cellular mechanisms is required to improve the development of antiangiogenic and anti-inflammatory drugs.     

Streptococcal pyrogenic exotoxin B-induced apoptosis in A549 cells is mediated through alpha(v)beta(3) integrin and Fas

Our previous work suggested that streptococcal pyrogenic exotoxin (SPE) B-induced apoptosis is mediated through a receptor-like mechanism. In this study, we have identified alpha(v)beta(3) and Fas as the SPE B receptors for this function. The SPE B fragment without the RGD motif and G308S, a SPE B mutant with the RSD motif, induced less apoptosis than did native SPE B, suggesting that the RGD motif is critical for SPE B-induced apoptosis. Fluorescein isothiocyanate-SPE B binding assays and immunoprecipitation analysis showed that SPE B specifically interacted with alpha(v)beta(3). Anti-alpha(v)beta(3) antibody partially inhibited SPE B-induced apoptosis but had no effect on G308S-induced apoptosis. In addition, Fas binding to SPE B was verified in an affinity column and an immunoprecipitation analysis. Anti-Fas antibody inhibited SPE B- and G308S-induced apoptosis in a dose-dependent manner, suggesting that Fas-mediated SPE B-induced apoptosis also occurs RGD independently. Both anti-alpha(v)beta(3) and anti-Fas antibodies synergistically inhibited SPE B-induced apoptosis. The apoptotic cascades were activated by SPE B and G308S, with a little delay by the latter. After SPE B binding, the cell surface level of alpha(v)beta(3), but not of Fas, was decreased. The decreased alpha(v)beta(3) level was restored by treatment with the proteasome inhibitor MG132, suggesting a SPE B-mediated endocytosis of integrin alpha(v)beta(3) via the ubiquitin-proteasome system. Taken together, our results demonstrate that SPE B-induced apoptosis is mediated through alpha(v)beta(3) integrin and Fas in a synergistic manner.     

Adhesion to fibronectin primes eosinophils via alpha 4 beta 1 (VLA-4).

Human peripheral blood eosinophils adhered specifically to microtitre plates coated with plasma fibronectin (Fn) in a dose- and time-dependent fashion. Adhesion was optimal at 60 min at a concentration of 100 micrograms/ml. Adherence to Fn was up-regulated by platelet-activating factor (PAF; optimum concentration of 10(-6) M) and was significantly inhibited by a polyclonal anti-Fn antibody (P < 0.05). The following evidence suggested that eosinophil adhesion to Fn was mediated by alpha 4 beta 1: (1) eosinophil adherence to Fn was not inhibited by an Arg-Gly-Asp-Ser (RGDS) synthetic peptide; (2) there was a dose-dependent adherence of eosinophils to microtitre plates coated with the 40,000 MW proteolytic fragment of Fn that contains the CS-1 alpha 4 beta 1 binding region, whereas adherence to the 120,000 MW chymotryptic fragment of Fn, which contains the RGD-dependent binding site, was weak and only observed at high concentrations (> 250 micrograms/ml); (3) significant inhibition of eosinophil adherence to Fn was achieved by monoclonal antibodies (mAb) against the alpha chain of VLA-4 but not by a mAb against CD45 or a mouse myeloma antibody as negative controls. After adhesion to Fn, eosinophils were investigated for their capacity to release leukotriene C4 in response to stimulation with a suboptimal concentration of calcium ionophore (2 x 10(-6) M). Significant enhancement of release was detected with Fn-coated plates but not with the control bovine serum albumin (BSA) (P < 0.01). Furthermore, this enhancement was significantly inhibited by the alpha 4 beta 1 mAb HP2/1 (P < 0.05) but not by an anti-CD45 mAb. From these studies we conclude that (1) alpha 4 beta 1 (VLA-4) integrin is a major receptor for Fn on human eosinophils and (2) adhesion to Fn may prime eosinophils for mediator release during allergic inflammation.     

Development of RGD peptides grafted onto silica surfaces: XPS characterization and human endothelial cell interactions.

The attachment of human umbilical vein endothelial cells (HUVECs) on substrates that had been covalently grafted with the cell adhesion peptides Arg-Gly-Asp (RGD) was investigated. This approach was used to provide substrates that are adhesive to cells even in the absence of serum proteins and to cells that have had no prior treatment of the surface with proteins that promote cell adhesion. We wanted to improve control of cellular interactions with cell-adhesive materials by providing fixedly bound adhesion ligands. Silica was examined as a model surface. The peptides were grafted using three different steps: grafting of aminosilane molecules; reaction with a maleimide molecule; and immobilization of cell-binding peptides containing the RGD sequence. The RGD-grafted surface was characterized by X-ray photoelectron spectroscopy (XPS) and contact-angle measurements.