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Results for “Integrin alpha4”

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PubMed1997

The role of the integrin family of adhesion molecules in the development of tumors metastatic to the orbit.

Tumors metastatic to the orbit frequently originate from certain primary tumors such as breast, lung, prostate, and melanoma. The site-specific nature of orbital metastases, as well as that of other metastatic lesions, cannot be the result of random seeding. We present evidence from a review of the literature demonstrating that tumor cells express adhesion molecules of the integrin family, and that these receptors play a pivotal role in the development of a metastatic colony. We investigated orbital metastatic lesions from prostate carcinoma, malignant melanoma, and lobular breast carcinoma to determine the level of integrin expression by immunohistochemistry. Several integrin subunits (alpha2, alpha4, beta3) were found to have increased expression in the metastasis when compared to normal prostate tissue and normal melanocytes. The increased expression of these integrins may be responsible for the tendency of these tumors to metastasize to the orbit, as well as for the tendency of prostate tumors to metastasize to bone. The results from the staining of the breast metastasis were inconclusive.

Aged↗

PubMed1996

Identification of receptors binding fibronectin and laminin on fetal rat lung cells.

Fibronectin and laminin have been implicated in regulating lung morphogenesis. In the present study, the cell surface receptors involved in fetal lung cell binding to laminin and fibronectin were identified. Messages for alpha5- and beta1-integrin subunits were detected in both fetal lung epithelial cells and fibroblasts. The presence of alpha5 beta1 -integrin on both cell types was demonstrated by immunocytochemistry and confirmed by cell adhesion experiments with fibronectin and RGD-containing peptides. Epithelial cells adhered more readily to laminin than fibroblasts. The alpha4 beta1-integrin, and RGD-independent fibronectin receptor, was weakly expressed on either cell type. Both cell types expressed alpha6-integrin subunit mRNA and stained immunopositive for the alpha6-subunit. Although either cell type expressed nonintegrin 67-kDa laminin-elastin receptor mRNA, no positive immunoreactivity for this laminin-elastin binding protein was detected. None of these findings explain the enhanced attachment of distal fetal lung epithelial cells to laminin compared with fibroblasts. Previously, we have reported that epithelial cells were enriched in alpha3-integrin subunit mRNA and protein expression. Herein, we found that epithelial cell attachment to laminin was nearly completely inhibited by alpha3- but only partially by alpha6 -monoclonal antibodies. A peptide near the globular region at the long arm of the laminin A-chain, which contained the IKVAV sequence, and the laminin A-chain amino acid sequence representing the alpha3 beta1 -integrin binding site, inhibited the adherence of epithelial cells to laminin. Fetal lung epithelial cells attached to substrata coated with the alpha3 beta1-integrin binding site peptide and the peptide containing the IKVAV sequence. These data suggest that both fetal lung cell types bind to fibronectin via the fibronectin receptor, alpha5 beta1, and fetal lung epithelial cells interact with laminin via alpha3 beta1 and proteins that recognize the IKVAV-containing sequence on the laminin A-chain.

Amino Acid Sequence↗

PubMed1998

The expression of alpha(v) and beta3 integrin subunits in the normal human Fallopian tube epithelium suggests the occurrence of a tubal implantation window.

The co-expression of alpha1beta1, alpha4beta1 and alphavbeta3 integrins in the human endometrium coincides with the implantation window. The alphavbeta3 integrin is expressed in the apical surface of the luminal epithelium and may serve to anchor trophoblast cells in the adhesion phase of implantation. Using immunohistochemistry, we compared the expression of alphav, alpha1, alpha4 and beta3 integrin subunits in samples of normal human Fallopian tube and endometrium obtained from five women in the non-receptive period (luteal phase days 2-4) and from another five women in the receptive period (luteal phase days 6-8). The staining was quantified visually on a scale of 0 to ++, according to the intensity and density of stained cells. The alphav subunit is expressed in the Fallopian tube epithelium during both periods in a pericellular distribution. The beta3 subunit is also expressed in the same location, but it is up-regulated during the period of endometrial receptivity. The other subunits are expressed in localizations which are not relevant to trophoblast adhesion and exhibit little or no difference in the level of expression between the non-receptive and receptive periods. Based on these results we postulate that the expression of the beta3 subunit in the human tubal epithelium is under the same systemic controlling signals as in the endometrium and that the normal tubal epithelium may have an implantation window, at about the same time as the endometrium, that affords the opportunity for trophoblast attachment should a 5-7 day embryo be unduly retained in the tube.

Antigens, CD↗

PubMedDate not supplied

Progressive renal disease: fibroblasts, extracellular matrix, and integrins.

Progressive renal disease is characterized by expansion of the tubulo-interstitium and accumulation of extracellular matrix within this tissue compartment. Interstitial fibroblasts are the primary producers of the interstitial matrix, and in the evolution of tubulo-interstitial fibrosis these cells undergo changes, namely increased proliferation, differentiation to myofibroblasts, and altered extracellular matrix metabolism, all of which, in other cell types, have been shown to be regulated by the major family of extracellular matrix receptors, the integrins. In the normal kidney, interstitial fibroblasts express alpha1, alpha4, alpha5, and beta1 integrins, and fibrosis is associated with increased expression of alpha1, alpha2, alpha5, alphav, and beta1 integrins. In particular, alpha5, beta1, and alphav are suggested to be linked with the fibrotic process. In vitro, renal fibroblasts express a similar range of integrins, and ligation of selected receptors is associated with specific functions. Ligation of alpha6 stimulates proliferation, while alpha5 promotes expression of myofibroblastic phenotype, and beta1 integrin has been implicated in cell contraction. Recent studies suggest that renal fibroblasts also express the non-integrin matrix receptors, discoidin domain receptors, and that changes in activation of these receptors may be associated with fibrogenic events. Thus the current, albeit limited, data suggest an important role for receptors for extracellular matrix molecules in the pathogenesis of progressive renal fibrosis.

Animals↗

PubMed1997

Human peripheral blood eosinophils express a functional c-kit receptor for stem cell factor that stimulates very late antigen 4 (VLA-4)-mediated cell adhesion to fibronectin and vascular cell adhesion molecule 1 (VCAM-1).

We evaluated mature peripheral blood eosinophils for their expression of the surface tyrosine kinase, c-kit, the receptor for the stromal cell-derived cytokine, stem cell factor (SCF). Cytofluorographic analysis revealed that c-kit was expressed on the purified peripheral blood eosinophils from 8 of 8 donors (4 nonatopic and 4 atopic) (mean channel fluorescence intensity 2.0- 3. 6-fold, average 2.8 +/- 0.6-fold, greater than the negative control). The uniform and selective expression of c-kit by eosinophils was confirmed by immunohistochemical analysis of peripheral blood buffy coats. The functional integrity of c-kit was demonstrated by the capacity of 100 ng/ml (5 nM) of recombinant human (rh) SCF to increase eosinophil adhesion to 3, 10, and 30 microg/ml of immobilized FN40, a 40-kD chymotryptic fragment of plasma fibronectin, in 15 min by 7.7 +/- 1.4-, 5.3 +/- 3.3-, and 5.4 +/- 0. 2-fold, respectively, and their adhesion to 0.1, 0.5, and 1.0 microg/ml vascular cell adhesion molecule-1 (VCAM-1), by 12.7 +/- 9. 2-, 3.8 +/- 2.5-, and 1.7 +/- 0.6-fold, respectively. The SCF-stimulated adhesion occurred without concomitant changes in surface integrin expression, thereby indicating an avidity-based mechanism. rhSCF (100 ng/ml, 5 nM) was comparable to rh eotaxin (200 ng/ml, 24 nM) in stimulating adhesion. Cell adhesion to FN40 was completely inhibited with antibodies against the alpha4 and beta1 integrin subunits, revealing that the SCF/c-kit adhesion effect was mediated by a single integrin heterodimer, very late antigen 4 (VLA-4). Thus, SCF represents a newly recognized stromal ligand for the activation of eosinophils for VLA-4-mediated adhesion, which could contribute to the exit of these cells from the blood, their tissue localization, and their prominence in inflammatory lesions.

Cell Adhesion↗

PubMed1997

Adhesion molecule expression in normal skin and melanocytic lesions. Role of UV-irradiation and architectural characteristics in nevi.

Cell adhesion between surfaces of cells and to extracellular matrices represents a fundamental mechanism in tissue organization and influences the biological behaviour and the architecture of tumors. We investigated the expression of various adhesion molecules in normal skin (n=5), nevi (n=29), and malignant melanoma (n=10) by immunohistochemistry. Special attention was paid to the correlation between adhesion molecule expression and the respective architectural features, e.g. UV-induced morphological changes, and the arrangement of melanocytes in congenital nevi. In nevi, a single erythemagenic dose of UV-light did not influence the integrin expression of melanocytes, but results in an upregulation of alpha3 beta1- and alpha6 beta1-integrin within the suprabasal layers of the epidermis. This suprabasal labelling was associated with an increased number of suprabasal melanocytes in UV-irradiated nevi which were detected with HMB-45 antibody. Nine of 10 congenital nevi demonstrated a labelling of alpha4 beta1-integrin only in melanocytes of the deeper dermis. This integrin previously has been associated with high tumor thickness and the clinical outcome in melanomas. The integrin profile observed in melanomas differed in part from that seen in nevi with expression of beta2- and beta3-integrins in some cases. The results may indicate a correlation between adhesion molecule expression and histopathological findings in melanocytic lesions.

Cell Adhesion Molecules↗

PubMed1997

Activation of beta1 integrins on CML progenitors reveals cooperation between beta1 integrins and CD44 in the regulation of adhesion and proliferation.

Adhesion of normal colony-forming cells (CFC) to bone marrow (BM) stroma and the extracellular matrix (ECM) component fibronectin (FN) depends at least in part on the alpha4beta1 and alpha5beta1 integrins and the CD44 receptor. Aside from anchoring progenitors in the marrow microenvironment, beta1 integrin-dependent adhesion of normal CFC is associated with inhibition of their proliferation. In contrast to normal CFC, chronic myelogenous leukemia (CML) Ph+ CFC adhere significantly less to either stroma or FN. CML Ph+ CFC proliferation is also not inhibited by coculture with stroma or FN. However, equal numbers of alpha4, alpha5, and beta1 integrins and CD44 are present on CML and normal CD34+ cells. We have previously demonstrated that beta1-dependent adhesion to and subsequent proliferation inhibition by FN can be restored when CML Ph+ CFC are incubated with the beta1 integrin activating antibody, 8A2, and demonstrated a role for the alpha5beta1 integrin in this phenomenon. Since the integrin alpha4beta1 and the proteoglycan form of CD44 may cooperate in establishing normal CFC adhesion to FN, we examined if treatment of CML Ph+ CFC with 8A2 also restores the cooperativity between beta1 integrins and CD44. We demonstrate that 8A2 induces adhesion of CML Ph+ CFC not only to intact FN but also to alpha4beta1, alpha5beta1, and proteoglycan binding fragments of FN. 8A2-induced adhesion to these fragments and peptides also results in a significant inhibition of the proliferation of CML Ph+ CFC. Addition of antibodies to either the alpha5, alpha4, or beta1 integrins, antibodies against the CD44 receptor, or removal of chondroitin sulfate glycosaminoglycans from the surface of CML CD34+ HLA-DR+ cells significantly reduced the 8A2-induced adhesion to and adhesion-mediated inhibition of proliferation by FN. These studies demonstrate that activation of beta1 integrins on CML Ph+ CFC not only results in upregulation of beta1 integrin-dependent adhesion and adhesion-mediated inhibition of proliferation, but also in the restoration of cooperation between beta1 integrins and CD44. These studies suggest that decreased beta1 integrin avidity may also affect the function of the proteoglycan adhesion receptor CD44, both of which may contribute to the abnormal circulation and expansion of malignant progenitors in CML.

Antigens, CD↗

PubMed1996

Immunological abnormality in C3H/HeJ mice with heritable inflammatory bowel disease.

To explore the immunological abnormality of a heritable inflammatory bowel disease developed in a new substrain of C3H/HeJ mice, we examined the expression of integrins beta7 and other cell adhesion molecules on normal and disease mice lymphocytes by flow cytometry. We also examined the cytotoxicity of small intestinal intraepithelial lymphocytes to epithelial cells and the proliferation and aggregation of intestinal lymphocytes. There are several significant changes in the expression levels of alpha4 and alphaM290beta7 integrins, CD11a, ICAM-1, CD45RB, CD4, CD44, and CD45 in different lymphocyte populations. The cytotoxicity of small intestinal intraepithelial lymphocytes from disease mice was higher than that from normal mice and could be stimulated by PHA and inhibited by mAb to alphaM290beta7. The proliferation of both normal and disease small intestinal intraepithelial lymphocytes was enhanced by costimulation by mAb to CD2 or CD3 and ProNectin. In comparison to disease mice, normal small intestinal intraepithelial lymphocytes proliferated at a significantly higher rate in response to sheep RBC and mAb to CD2 or CD3 and ProNectin costimulation. Homotypic aggregation of small intestinal intraepithelial lymphocytes isolated from disease mice was greater than in those from normal mice. The abnormality of expression of integrin beta7 and other cell adhesion molecules and cytotoxic, proliferative, and aggregative responses of lymphocytes from disease mice may play important roles in the pathogenesis of this heritable inflammatory bowel disease.

Animals↗

PubMed1999

Expression of integrin receptors in the human trabecular meshwork.

PURPOSE: To examine the expression of integrin receptors in the human trabecular meshwork. METHODS: The expression of integrins in human tissues was visualized by immunohistochemical staining using integrin-specific antibodies. Immunoprecipitation was performed after biotin labeling of cell surface proteins. Reverse transcriptase-polymerase chain reaction was used to detect the presence of mRNA species for integrin subunits. RESULTS: Human trabecular meshwork tissues obtained from donors 2 to 65 years old stained positively for integrins alpha1, alpha3, alpha4, alpha5, alpha6, alphav, beta1, beta3, beta4 and beta5. The staining was observed mostly around the edges of trabecular beams in association with trabecular meshwork cells. The staining intensity did not appear to vary with donor age. In addition, immunoprecipitation of tissue extracts revealed the presence of integrin alpha2 and confirmed the absence of beta2. Results from polymerase chain reactions were consistent with these findings. CONCLUSIONS: A spectrum of integrin receptors that may have important roles in the cell-matrix interactions are demonstrated in the human trabecular meshwork. The repertoire identified in tissues is similar to that found in cultured cells except that the beta4 expression in tissues is lost in cultures.

Adult↗

PubMed1997

Presentation of integrins on leukocyte microvilli: a role for the extracellular domain in determining membrane localization.

Adhesion of blood leukocytes to the endothelium involves multiple steps including initial attachment (tethering), rolling, and firm arrest. Presentation of adhesion molecules on leukocyte microvilli can substantially enhance tethering. Localization of L-selectin to microvilli and of CD44 to the planar cell body have been shown to depend upon their transmembrane and cytoplasmic domains. We investigated the role of leukocyte integrin transmembrane and cytoplasmic domains in initiating adhesion under flow and in microvillous localization. Integrins alpha4beta7, alphaLbeta2, and alphaMbeta2 were heterologously expressed in K562 cells. alpha4beta7 initiated adhesion under flow and localized to microvilli, whereas beta2 integrins did not initiate adhesion and localized to the cell body. Chimeric integrins were produced by replacing the alpha4beta7 cytoplasmic and/or transmembrane domains with the homologous domains of alphaLbeta2 or alphaMbeta2. Unexpectedly, these chimeras efficiently mediated adhesion to the alpha4beta7 ligand mucosal addressin cell adhesion molecule-1 under flow and localized to microvilli. Therefore, differences between the transmembrane and cytoplasmic domains of alpha4 and beta2 integrins do not account for differences in ability to support attachment under flow or in membrane localization. Integrins alpha4beta1, alpha5beta1, alpha6Abeta1, alphavbeta3, and alphaEbeta7 also localized to microvilli. Transmembrane proteins known or suspected to associate with extracellular domains of microvillous integrins, including tetraspans and CD47, were concentrated on microvilli as well. These findings suggest that interactions between the extracellular domains of integrins and associated proteins could direct the assembly of multimolecular complexes on leukocyte microvilli.

Cell Adhesion↗

PubMed2002

3D QSAR (COMFA) of a series of potent and highly selective VLA-4 antagonists.

The integrin VLA-4 (alpha4,beta1) is involved in the migration of white blood cells to sites of inflammation, and is implicated in the pathology of a variety of diseases including asthma and multiple sclerosis. We report the structure-activity relationships of a series of VLA-4 antagonists that were based upon the integrin-binding sequence of the connecting segment peptide of fibronectin (Leu-Asp-Val), and of VCAM-1 (Ile-Asp-Ser), both natural ligands of VLA-4. We explore variation in the ligand derived peptide portion of these antagonists and also in the novel N-terminal cap, which have discovered through chemical optimization, and which confers high affinity and selectivity. Using the X-ray derived conformation of the Ile-Asp-Ser region of VCAM-1, we rationalize the structure-activity relationships of these antagonists using 3D QSAR (COMFA). The COMFA model was found to be highly predictive with a cross-validated R2CV of 0.7 and a PRESS of 0.49. The robustness of the model was confirmed by testing the influence of various parameters, including grid size, column filtering, as well as the role of orientation of the aligned molecules. Our results suggest that the VCAM-1 structure is useful in generating highly predictive models of our VLA-4 antagonists. The COMFA model coupled with the knowledge that the peptide amides are tolerant to methylation should prove useful in future peptidomimetic design studies.

Binding Sites↗

PubMed2002

CCR7-mediated physiological lymphocyte homing involves activation of a tyrosine kinase pathway.

Homing of blood-borne lymphocytes to peripheral lymph nodes (PLNs) is a multistep process dependent on the sequential engagement of L-selectin, which mediates lymphocyte rolling along the luminal surface of high endothelial venules (HEVs), followed by activation of lymphocyte integrins and transmigration through HEVs. Within lymphoid tissue, B and T lymphocytes then migrate toward specific microenvironments such as B-cell follicles and the paracortex, respectively. The lymphocyte-expressed chemokine receptor CCR7 is playing an important role during this process, as its HEV-presented ligands CCL19 and CCL21 can trigger rapid integrin activation under flow in addition to inducing a chemotactic response, which may participate in transmigration and/or interstitial migration. Here, we report that Tyrphostin (Tyr) AG490, a pharmacological inhibitor of Janus family tyrosine kinases (Jaks), blocked the chemotactic response of primary mouse lymphocytes to CCL19 and CCL21 in a dose-dependent manner. Furthermore, Tyr AG490 inhibited rapid CCL21-mediated up-regulation of alpha4 and beta2 integrin adhesiveness in static adhesion assays and under physiological flow, whereas adhesion induced by phorbol myristate acetate remained unaltered. Using intravital microscopy of subiliac PLNs in mice, we found that adoptively transferred Tyr AG490-treated lymphocytes adhered significantly less in HEVs compared with control cells, although L-selectin-mediated rolling was similar in both samples. Finally, we observed rapid Jak2 phosphorylation in CCL21-stimulated primary mouse lymphocytes. Thus, our study suggests a role for Jak tyrosine kinases during CCR7-mediated lymphocyte recirculation.

Animals↗

PubMed2005

Molecules mediating cell-ECM and cell-cell communication in human heart valves.

The specific phenotype of different tissues depends on the interactions of cells with neighboring cells and the surrounding extracellular matrix, which is mediated by cell adhesion receptors including integrins, immunoglobulin family members, syndecans, and selectins. The aim of this study was to investigate the adhesion profile of native human valve interstitial cells (ICs) in situ and in vitro by analyzing these adhesion receptors. Flow cytometry and immunocytochemistry was used to quantify the expression of the specific receptors on ICs cultured from all human cardiac valves, and immunohistochemistry were used to profile their distribution pattern in valve tissue sections. The valve leaflets and cultured ICs from all valves expressed alpha1, alpha2, alpha3, alpha4, and alpha5 integrins to varying degrees and percentages with very little expression of alpha6 and alphaV. Valve leaflet ICs from all valves, expressed predominantly beta1 integrin but no beta3 or beta4 integrin. Syndecan-1 and Syndecan-4 were not detected. Intercellular adhesion molecule-1 was weakly detected, whereas vascular adhesion molecule-1 was barely detectable and E-selectin was not detected. This study has delineated the identity of some of the integrins synthesized and expressed by human valve ICs and the specificity of adhesion molecules with which the valve ICs interact with the extracellular matrix and mediate intercellular interactions. This pattern of expression of cell surface adhesion molecules may be considered as a basis for a fingerprint on which to base future cell alternatives and would provide useful information for valve tissue engineering.

Cell Adhesion↗

PubMed1997

Spatial and temporal analyses of integrin and Muc-1 expression in porcine uterine epithelium and trophectoderm in vitro.

The expression of the glycoproteins Muc-1 and integrin subunits (alpha1, alpha3, alpha4, alpha5, alpha(v), beta1, and beta3), all of which may be involved in the control of uterine receptivity, was examined in cultured porcine uterine epithelial (pUE) cells. Integrin subunit expression was also determined in trophoblastic vesicles generated from Day 12 and Day 15 pig conceptuses. Immunocytochemistry was performed on pUE cells cultured on several substrates (glass, serum, fibronectin, or Matrigel) in DME/F12 medium with 5% charcoal/dextran-stripped fetal bovine serum either containing no steroids or supplemented with estrogen, progesterone, or estrogen plus progesterone, or in medium with 5% complete fetal bovine serum. In addition, pUE cells were grown on Matrigel-coated Millicell filter inserts to facilitate development of structurally and functionally distinct apical and basal domains (i.e., polarized pUE cells) and were maintained in the same medium with supplements. The major findings in this investigation are that 1) Muc-1 and alpha1, alpha3, alpha4, alpha5, alpha(v), beta1, and beta3 integrin subunits are expressed on pUE cells in vitro; 2) Muc-1 and several integrin subunits are modulated by steroid hormones if culture conditions are provided that permit development of cell polarity; 3) the expression and steroid-induced modulation of Muc-1 and several integrin subunits in polarized pUE cells are similar to those detected in vivo; and 4) the expression of alpha1, alpha3, alpha4, alpha5, alpha(v), beta1, and beta3 integrin subunits by trophoblastic vesicles is identical to their expression on trophectoderm of intact conceptuses in vivo. These results suggest that the properties of polarized pUE cells and trophoblastic vesicles are comparable to those of their counterparts in vivo and are, therefore, useful as in vitro model systems to study conceptus-endometrial interactions during the periimplantation period and the control of uterine receptivity to implantation.

Animals↗

PubMed2005

Integrin alpha4beta1 promotes focal adhesion kinase-independent cell motility via alpha4 cytoplasmic domain-specific activation of c-Src.

The fibronectin binding integrins alpha5beta1 and alpha4beta1 generate signals pivotal for cell migration through distinct yet undefined mechanisms. For alpha5beta1, beta1-mediated activation of focal adhesion kinase (FAK) promotes c-Src recruitment to FAK and the formation of a FAK-Src signaling complex. Herein, we show that FAK expression is essential for alpha5beta1-stimulated cell motility and that exogenous expression of human alpha4 in FAK-null fibroblasts forms a functional alpha4beta1 receptor that promotes robust cell motility equal to the alpha5beta1 stimulation of wild-type and FAK-reconstituted fibroblasts. alpha4beta1-stimulated FAK-null cell spreading and motility were dependent on the integrity of the alpha4 cytoplasmic domain, independent of direct paxillin binding to alpha4, and were not affected by PRNK expression, a dominant-negative inhibitor of Pyk2. alpha4 cytoplasmic domain-initiated signaling led to a approximately 4-fold activation of c-Src which did not require paxillin binding to alpha4. Notably, alpha4-stimulated cell motility was inhibited by catalytically inactive receptor protein-tyrosine phosphatase alpha overexpression and blocked by the p50Csk phosphorylation of c-Src at Tyr-529. alpha4beta1-stimulated cell motility of triple-null Src(-/-), c-Yes(-/-), and Fyn(-/-) fibroblasts was dependent on c-Src reexpression that resulted in p130Cas tyrosine phosphorylation and Rac GTPase loading. As p130Cas phosphorylation and Rac activation are common downstream targets for alpha5beta1-stimulated FAK activation, our results support the existence of a novel alpha4 cytoplasmic domain connection leading to c-Src activation which functions as a FAK-independent linkage to a common motility-promoting signaling pathway.

Amino Acid Sequence↗

PubMed2002

Effect of extracellular matrix proteins on platelet-activating factor-induced eosinophil chemotaxis.

BACKGROUND: Eosinophils accumulate in tissues during various allergic inflammatory processes. Selective eosinophil recruitment is the result of orchestrated events involving cell adhesion molecules and chemoattractants. However, the exact mechanism of the regulation of integrin avidity during interstitial migration is poorly understood. OBJECTIVE: The purpose of this study was to investigate whether extracellular matrix proteins might activate human eosinophil chemotaxis and, if so, to clarify the mechanism in terms of integrin avidity. METHOD: Eosinophils were purified from the peripheral blood of healthy donors. Eosinophil migration was measured using Boyden chambers with filter membranes coated with fibronectin (Fn), vitronectin (Vn), laminin (Ln), hyaluronic acid, collagen type IV, or bovine serum albumin (BSA) overnight. Platelet-activating factor (PAF) was introduced into the lower chamber of each well. Eosinophils were placed in the upper chamber after incubation with IL-5 for 15 min. The number of eosinophils that transmigrated into the lower chamber was calculated by measuring the eosinophil peroxidase activity. RESULTS: Fn, Ln and BSA enhanced PAF-induced chemotaxis of eosinophils. Inhibition experiments using blocking monoclonal antibodies showed that in the early phase of chemotaxis, Fn and Ln facilitated eosinophil chemotaxis that was mediated by alpha4 and alpha6 integrins, respectively. In the late phase of chemotaxis, BSA, but not other matrix proteins, facilitated both chemokinesis and chemotaxis that was mediated by beta2 integrin. CONCLUSION: Our data strongly suggest that during chemotaxis, matrix proteins might activate eosinophils via binding with integrins to facilitate PAF-induced chemotaxis, and that such a mechanism might participate in allergic inflammatory processes.

Animals↗

PubMed1998

beta1 integrins are critically involved in neutrophil locomotion in extravascular tissue In vivo.

Recruitment of leukocytes from blood to tissue in inflammation requires the function of specific cell surface adhesion molecules. The objective of this study was to identify adhesion molecules that are involved in polymorphonuclear leukocyte (PMN) locomotion in extravascular tissue in vivo. Extravasation and interstitial tissue migration of PMNs was induced in the rat mesentery by chemotactic stimulation with platelet-activating factor (PAF; 10(-7) M). Intravital time-lapse videomicroscopy was used to analyze migration velocity of the activated PMNs, and the modulatory influence on locomotion of locally administered antibodies or peptides recognizing various integrin molecules was examined. Immunofluorescence flow cytometry revealed increased expression of alpha4, beta1, and beta2 integrins on extravasated PMNs compared with blood PMNs. Median migration velocity in response to PAF stimulation was 15.5 +/- 4.5 micron/min (mean +/- SD). Marked reduction (67 +/- 7%) in motility was observed after treatment with mAb blocking beta1 integrin function (VLA integrins), whereas there was little, although significant, reduction (22 +/- 13%) with beta2 integrin mAb. Antibodies or integrin-binding peptides recognizing alpha4beta1, alpha5beta1, or alphavbeta3 were ineffective in modulating migration velocity. Our data demonstrate that cell surface expression of beta1 integrins, although limited on blood PMNs, is induced in extravasated PMNs, and that members of the beta1 integrin family other than alpha4beta1 and alpha5beta1 are critically involved in the chemokinetic movement of PMNs in rat extravascular tissue in vivo.

Animals↗

PubMed1998

Immunolocalization of extracellular matrix proteins and integrins in sarcoid lymph nodes.

To improve our understanding of the role of extracellular matrix (ECM) proteins and integrins during the processes of granuloma formation in sarcoidosis, we examined the distribution of ECM proteins and the expression of integrins in sarcoid lymph nodes by immunohistochemical methods. We also examined the expression of transforming growth factor-beta1 (TGF-beta1), which is one of major regulators for synthesis of ECM proteins. Most ECM proteins were detected in the periphery of the granulomas in a concentric pattern, and fibronectin was diffusely detected from an early to a regressive stage. Compared with normal lymph nodes, most beta1-integrin subfamilies (alpha1, alpha4, alpha5 and alpha6) were more strongly expressed on lymphocytes around the granulomas. Epithelioid cells exhibited strong expression of the alpha5 molecule. Fibroblasts exhibited the expression of the alpha2 and alpha5 molecules surrounding ECM proteins. The alpha5beta1 molecule had a distribution similar to that of fibronectin. TGF-beta1 was detected in epithelioid cells throughout the various evolutional stages and its expression was especially marked in mature granulomas. Interaction of fibronectin and the alpha5beta1 molecule may have an important role in the process of formation of sarcoid granuloma. The expression of TGF-beta1 may be involved in the regression of sarcoid granuloma by initiating fibrosis and atrophy of epithelioid cells.

Extracellular Matrix Proteins↗