Construction and adhesive properties of a soluble MadCAM-1-Fc chimera expressed in a baculovirus system: phylogenetic conservation of receptor-ligand interaction

Conformation-sensitive targeting of lipid nanoparticles for RNA therapeutics

The successful in vivo implementation of gene expression modulation strategies relies on effective, non-immunogenic delivery vehicles. Lipid nanoparticles are one of the most advanced non-viral clinically approved nucleic-acid delivery systems. Yet lipid nanoparticles accumulate naturally in liver cells upon intravenous administration, and hence, there is an urgent need to enhance uptake by other cell types. Here we use a conformation-sensitive targeting strategy to achieve in vivo gene silencing in a selective subset of leukocytes and show potential therapeutic applications in a murine model of colitis. In particular, by targeting the high-affinity conformation of α₄β₇ integrin, which is a hallmark of inflammatory gut-homing leukocytes, we silenced interferon-γ in the gut, resulting in an improved therapeutic outcome in experimental colitis. The lipid nanoparticles did not induce adverse immune activation or liver toxicity. These results suggest that our lipid nanoparticle targeting strategy might be applied for selective delivery of payloads to other conformation-sensitive targets.

Leukocyte integrin α4β7 associates with heat shock protein 70

The leukocyte integrin cell adhesion molecules α4β7 and αEβ7 mediate the homing and retention of lymphocytes to the gut, and sites of inflammation. Here we have identified heat shock protein 70 (HSP70) as a major protein that associates with the cytoplasmic domain of the integrin β7 subunit. HSPs are molecular chaperones that protect cells from stress but more recently have been reported to also regulate cell adhesion and invasion via modulation of β1, β2, and β3 integrins and integrin-associated signalling molecules. Several HSP70 isoforms including HSP70-3, HSP70-1L, HSP70-8, and HSP70-9 were specifically precipitated from T cells by a bead-conjugated β7 subunit cytoplasmic domain peptide and subsequently identified by high-resolution liquid chromatography-tandem mass spectrometry. In confirmation, the β7 subunit was co-immunoprecipitated from a T cell lysate by an anti-HSP70 antibody. Further, recombinant human HSP70-1a was precipitated by β7 cytoplasmic domain-coupled beads. The HSP70 inhibitor KNK437 decreased the expression of HSP70 without affecting the expression of the β7 integrin. It significantly inhibited α4β7-mediated adhesion of T cells to mucosal addressin cell adhesion molecule 1 (MAdCAM-1), suggesting HSP70 is critical for maintaining β7 integrin signalling function. The functional implications of the association of β7 integrins with the different isoforms of HSP70 warrants further investigation.

Synthesis and SAR of a Library of Cell-Permeable Biotin-R8ERY* Peptidomimetics Inhibiting α4β7 Integrin Mediated Adhesion of TK-1 Cells to MAdCAM-1-Fc

The α4β7 integrin is a well‐known target for the development of drugs against various inflammatory disease states including inflammatory bowel disease, type 1 diabetes, and multiple sclerosis. The β7 subunit contains the cell adhesion regulatory domain (CARD) motif YDRREY within its cytoplasmic domain, which is an effective peptide agent for inhibiting T-cell adhesion. The synthesis of a library of cell-permeable β7 integrin inhibitors based on the shortened biotin-R8ERY (R8 = (l-arginine)8) motif is reported, wherein the tyrosine residue has been modified. The synthesised peptidomimetics were evaluated in a cell adhesion assay and shown to inhibit Mn2+-activated adhesion of mouse TK-1 T-cells to mouse MAdCAM-1. Several analogues exhibited improved activity to that of the tyrosine-containing lead compound 1 (biotin-R8ERY). Specifically, analogues 4, 10, and 22 bearing a 4-chloro, a 4-nitro, and a 3,3-diphenyl substituent showed an increase in activity of approximately two-fold compared with that of the initial lead compound. The six most active compounds of the tested series had IC50’s between 25 and 50 μM.

A pseudosymmetric cell adhesion regulatory domain in the beta7 tail of the integrin alpha4beta7 that interacts with focal adhesion kinase and src

The beta7 integrins alpha4beta7 and alphaEbeta7 play key roles in forming the gut-associated lymphoid tissue, and contribute to chronic inflammation. The alpha4beta7 integrin-mediated adhesion of activated lymphocytes is largely due to a transient increase in avidity from ligand-induced clustering of alpha4beta7 at the cell-surface. Here, we report that L and D enantiomers of a cell-permeable peptide YDRREY encompassing residues 735-740 of the cytoplasmic tail of the beta7 subunit inhibit the adhesion of T cells to beta7 integrin ligands. The YDRREY peptide abrogated mucosal addressin cell adhesion molecule-1-induced clustering of alpha4beta7 on the surface of activated T cells. A mutated form of the YDRREY peptide carrying either single or double conservative mutations at Tyr(735)Phe and Tyr(740)Phe was unable to inhibit T cell adhesion, suggesting that both tandem tyrosines are critical for activity. The YDRREY peptide was bound and phosphorylated by focal adhesion kinase and src, which may serve to sequester cytoskeletal proteins to the cytoplasmic domain of alpha4beta7. The quasi-palindromic sequence YDRREY within the beta7 cytoplasmic tail constitutes a cell adhesion regulatory domain that modulates the interaction of beta7-expressing leukocytes with their endothelial and epithelial ligands. Cell-permeable peptidomimetics based on this motif have utility as anti-inflammatory reagents for the treatment of chronic inflammatory disease.

Bioassay detects soluble MAdCAM-1 in body fluids

Mucosal addressin cell adhesion molecule (MAdCAM-1) is a key player in mediating the infiltration of leucocytes into chronically inflamed tissues. Five anti-MAdCAM-1 monoclonal antibodies (mAb), designated 17F5, 201F7, 314G8, 377D10 and 355G8, were generated by fusion of P3 x 63Ag8.653 myeloma cells with spleen cells from BALB/c mice immunized with recombinant human MAdCAM-1-Fc. The latter four mAb recognize the ligand-binding first Ig domain, and block T -cell adhesion to MAdCAM-1. The non-blocking mAb 17F5 recognizes the mucin domain. Extensive analysis of a large panel of paraffin-embedded human tissues revealed that the 314G8 mAb detected MAdCAM-1 on venules in the spleen and small intestine. MAdCAM-1 was strongly expressed in the synovium of osteoarthritis patients, predominantly on the endothelial lining of blood vessels, but also within the vessel lumen. An ELISA, based on mAb 377D10 and 355G8, was developed to determine whether soluble MAdCAM-1 was present in body fluids, and to measure the levels present. The assay detected soluble MAdCAM-1 in the serum and urine of healthy donors, at levels similar to those of soluble forms of the related CAM, ICAM-1 and VCAM-1. The anti-MAdCAM-1 antibodies and assay developed here may be useful therapeutically in the treatment of inflammation in humans. Similarly, they may be useful diagnostically to monitor the presence and levels of MAdCAM-1.

Mucosal vascular addressin cell adhesion molecule-1 is expressed outside the endothelial lineage on fibroblasts and melanoma cells

Mucosal vascular addressin cell adhesion molecule-1 (MAdCAM-1) is predominantly expressed on high endothelial venules in inflamed tissues where it assists with leucocyte extravasation. Here we report that MAdCAM-1 has the potential to be more widely expressed outside the endothelial cell lineage than previously appreciated. Thus, MAdCAM-1 RNA transcripts and cell-surface protein were expressed by NIH 3T3 fibroblasts following activation with tumour necrosis factor-alpha (TNF-alpha), and by freshly isolated and cultured primary mouse splenic and tail fibroblasts in the absence of TNF-alpha stimulation. They were constitutively expressed by B16F10 melanoma cells, and expression was enhanced by cell activation with TNF-alpha. Mucosal vascular addressin cell adhesion molecule-1 was expressed on the apical surface of isolated cells, but became predominantly localized to cell junctions in confluent cell monolayers, suggesting it may play a role in the homotypic aggregation of cells. Tumour necrosis factor-alpha enhanced the expression of a firefly luciferase reporter directed by the MAdCAM-1 promoter in NIH 3T3 and B16F10 cells. A DNA fragment extending from nt -1727 to -673 was sufficient to confer cell-type selective expression. Mucosal vascular addressin cell adhesion molecule-1 expressed by NIH 3T3 cells was biologically active, as it supported the adhesion of TK-1 T cells in an alpha4beta7-dependent fashion. The expression of MAdCAM-1 by fibroblasts, and melanomas suggests MAdCAM-1 may play a role in regulating host responses in the periphery, leucocyte transmigration across nonendothelial boundaries, or the homotypic interactions of some malignant melanomas.

Prevention of a chronic progressive form of experimental autoimmune encephalomyelitis by an antibody against mucosal addressin cell adhesion molecule-1, given early in the course of disease progression

A role for alpha4 and beta7 integrins in mediating leucocyte entry into the central nervous system in the multiple sclerosis (MS)-like disease experimental autoimmune encephalomyelitis (EAE) has been demonstrated. However, the individual contributions of their respective ligands mucosal addressin cell adhesion molecule-1 (MAdCAM-1), vascular cell adhesion molecule-1 (VCAM-1) and E-cadherin expressed on the blood-brain barrier has not been determined. In the present paper, it is shown that an antibody directed against MAdCAM-1, the preferential ligand for alpha4beta7, effectively prevented the development of a progressive, non-remitting, form of EAE, actively induced by injection of myelin oligodendrocyte glycoprotein peptide (MOG(35-55)) autoantigen. Combinational treatment with both anti-MAdCAM-1, VCAM-1, and intercellular adhesion molecule-1 (ICAM-1) (ligand for integrin lymphocyte function-associated antigen (LFA)-1) mAbs led to more rapid remission than that obtained with anti-MAdCAM-1 antibody alone. However, neither MAdCAM-1 monotherapy, nor combinational antibody blockade was preventative when administered late in the course of disease progression. In conclusion, MAdCAM-1 plays a major contributory role in the progression of chronic EAE and is a potential therapeutic target for the treatment of MS. Critically, antivascular addressin therapy must be given early in the course of disease prior to the establishment of irreversible damage if it is to be effective, as a single treatment modality.

Beta7 integrins contribute to demyelinating disease of the central nervous system

A role for alpha4 integrins in different forms of the multiple sclerosis-like disease experimental autoimmune encephalomyelitis (EAE) has been demonstrated, but the individual contributions of alpha4beta1, alpha4beta7, and the related alphaEbeta7 integrin have not been determined. The P7 integrins alpha4beta7 and alphaEbeta7 play a central role in chronic inflammation, mediating the trafficking, entry, and/or adhesion of lymphocytes in the inflamed pancreas and gut, and their ligands MAdCAM-1, VCAM-1 and E-cadherin are expressed on brain endothelial cells and/or on microvessels in the inflamed central nervous system. Here, we show that an antibody directed against the beta7 subunit greatly attenuates a non-remitting form of EAE, induced by adoptive transfer of myelin oligodendrocyte peptide (MOG35-55)-stimulated T cells. Combinational treatment with both anti-beta7 and alpha4 integrin subunit antibodies led to more rapid and complete remission than that obtained with anti-alpha4 antibody alone, potentially implicating a role for alphaEbeta7 in disease progression. Remission correlated with the down-regulation of the vascular addressins VCAM-1. MAdCAM-1, and ICAM-1 on cerebral blood vessels. Attenuated forms of disease were induced by adoptive transfer of either wild-type encephalitogenic T cells to beta7-deficient gene knockout mice, or of beta7-/-encephalitogenic T cells to wild-type recipients. The former finding indicates that beta7 + ve recruited cells contribute to disease progression. Thus alpha4beta1, alpha4beta7, and alphaEbeta7 integrins may all play a contributory role in the progression of chronic forms of demyelinating disease, and together with their ligands could represent potential targets for improved treatment of some forms of multiple sclerosis.

The small GTP-binding proteins Rho and Rac induce T cell adhesion to the mucosal addressin MAdCAM-1 in a hierarchical fashion

Here we report that an activator (AIF4-) of heterotrimeric GTP-binding proteins (G-proteins) and inhibitors (lovastatin and C3 exoenzyme) of small GTP-binding proteins regulate the induction of alpha4beta7-mediated adhesion of TK-1 T lymphoma cells (alpha4+beta7+beta1-) to the mucosal addressin cell adhesion molecule MAdCAM-1. Activation of cell adhesion by AIF4- was abrogated by lovastatin, thereby establishing a link between heterotrimeric G-proteins and small GTP-binding proteins in the regulation of alpha4beta7-mediated cell adhesion. Increased numbers of cells bound MAdCAM-1-coated microspheres following activation with AIF4-, discounting an obligatory role for cell spreading in alpha4beta7-mediated cell adhesion. MAdCAM-1-Fc dimers triggered ligand-induced clustering of alpha4beta7 in response to AIF4- and Mn2+-induced activation of integrins. Hence alpha4beta7 cluster formation may be responsible, at least in part, for inducing cell adhesion in response to both extracellular and intracellular signals that impact on integrin function. Electroporation of constitutively active V14RhoA and V12Rac1 recombinant proteins into TK-1 cells revealed that both RhoA and Rac1 induce alpha4beta7 adhesion to MAdCAM-1. Activation is hierarchical since Rac1 is unable to directly activate alpha4beta7, but induces cell adhesion via RhoA, whereas the transient induction of cell adhesion mediated by RhoA is dependent on the activities of protein tyrosine kinases and protein kinase(s) C.

Mouse M290 is the functional homologue of the human mucosal lymphocyte integrin HML-1: antagonism between the integrin ligands E-cadherin and RGD tripeptide

Human mucosal lymphocyte antigen-1 (HML-1, alphaEbeta7) and E-cadherin, two members of unrelated cell adhesion superfamilies, have evolved to play cooperative roles in gut mucosal immunity. Human E-cadherin is self-ligand mediating intercellular adhesion of epithelial cells, as well as adhesion of intra-epithelial lymphocytes to intestinal enterocytes via an interaction with HML-1. Herein we report that both dimeric and monomeric forms of recombinant mouse E-cadherin-human immunoglobulin Fc chimera self-associate and support attachment of E-cadherin+ mouse colon epithelial cells. Both forms also support the adhesion of mouse MTC-1 T cells via M290, thereby establishing M290 as the functional mouse homologue of HML-1 and revealing that E-cadherin homophilic and heterophilic binding sites are distinct. Adhesion of MTC-1 cells to E-cadherin-Fc was inhibited by arginine-glycine-aspartate (RGD) peptides and vice versa cells bound to immobilized RGD polymer in an M290-dependent fashion, where adhesion was inhibitable with soluble E-cadherin-Fc. Hence, E-cadherin and RGD integrin ligands antagonize cell binding by one another, either by inducing integrin cross-talk or by binding to shared or overlapping sites within M290. Binding of E-cadherin-Fc by HML-1 costimulated the CD3-induced proliferation of purified CD4+ T cells, suggesting that E-cadherin expressed on dendritic cells may play a T cell costimulatory role in addition to facilitating dendritic cell-keratinocyte adhesion.

MAdCAM-1 costimulates T cell proliferation exclusively through integrin alpha4beta7, whereas VCAM-1 and CS-1 peptide use alpha4beta1: evidence for "remote" costimulation and induction of hyperresponsiveness to B7 molecules

We have analyzed the effects of the alpha4 integrin ligands mucosal addressin cell adhesion molecule-1 (MAdCAM-1), vascular cell adhesion molecule-1 (VCAM-1), and the fibronectin CS-1 splice variant on T cell activation. Immobilized MAdCAM-1 and VCAM-1 IgG-Fc chimeras and a fibronectin CS-1 peptide efficiently costimulate T cell proliferation when antigen presentation is mimicked by anti-CD3 antibody. VCAM-1-Fc and fibronectin CS-1, which are adhesive ligands for both the alpha4beta1 and alpha4beta7 integrins, medicate T cell costimulation exclusively through integrin alpha4beta1, but not through alpha4beta7. The inability of VCAM-1-Fc to costimulate via alpha4beta7 suggests that cell adhesion per se is insufficient, and that exquisite recognition and activation events must be triggered. MAdCAM-1-Fc mediates costimulation exclusively via alpha4beta7, and can both synergize with and induce hyperresponsiveness to the classical costimulator B7-2. MAdCAM-1-Fc and VCAM-1-Fc, but not B7-2, effectively costimulate when immobilized on sites spatially distant from the anti-CD3 antibody ("remote" costimulation). In vitro, the relative potencies of the CAM were VCAM-1-Fc> ICAM-1-Fc> MAdCAM-1-Fc > B7-Fc, except at high concentrations where ICAM-1 was the most potent. Features of costimulatory CAM revealed by this study have important implications for the design of immunotherapeutic vaccine strategies to combat cancer and infection.

Concepts and principles of O-linked glycosylation

The biosynthesis, structures, and functions of O-glycosylation, as a complex posttranslational event, is reviewed and compared for the various types of O-glycans. Mucin-type O-glycosylation is initiated by tissue-specific addition of a GalNAc-residue to a serine or a threonine of the fully folded protein. This event is dependent on the primary, secondary, and tertiary structure of the glycoprotein. Further elongation and termination by specific transferases is highly regulated. We also describe some of the physical and biological properties that O-glycosylation confers on the protein to which the sugars are attached. These include providing the basis for rigid conformations and for protein stability. Clustering of O-glycans in Ser/Thr(/Pro)-rich domains allows glycan determinants such as sialyl Lewis X to be presented as multivalent ligands, essential for functional recognition. An additional level of regulation, imposed by exon shuffling and alternative splicing of mRNA, results in the expression of proteins that differ only by the presence or absence of Ser/Thr(/Pro)-rich domains. These domains may serve as protease-resistant spacers in cell surface glycoproteins. Further biological roles for O-glycosylation discussed include the role of isolated mucin-type O-glycans in recognition events (e.g., during fertilization and in the immune response) and in the modulation of the activity of enzymes and signaling molecules. In some cases, the O-linked oligosaccharides are necessary for glycoprotein expression and processing. In contrast to the more common mucin-type O-glycosylation, some specific types of O-glycosylation, such as the O-linked attachment of fucose and glucose, are sequon dependent. The reversible attachment of O-linked GlcNAc to cytoplasmic and nuclear proteins is thought to play a regulatory role in protein function. The recent development of novel technologies for glycan analysis promises to yield new insights in the factors that determine site occupancy, structure-function relationship, and the contribution of O-linked sugars to physiological and pathological processes. These include diseases where one or more of the O-glycan processing enzymes are aberrantly regulated or deficient, such as HEMPAS and cancer.

LPAM-1 (integrin alpha 4 beta 7)-ligand binding: overlapping binding sites recognizing VCAM-1, MAdCAM-1 and CS-1 are blocked by fibrinogen, a fibronectin-like polymer and RGD-like cyclic peptides

The alpha 4 integrin LPAM-1 (alpha 4 beta 7) mediates lymphocyte attachment within the extracellular matrix (ECM) by adhering to the connecting segment (CS)-1 site of fibronectin (FN). Here we reveal that very late antigen (VLA)-4 LPAM-1+ T cell lymphoma TK-1 cells bind via LPAM-1 to multiple copies of the RGD sequence engineered within an FN-like polymer. Further, the small conformationally restrained RGD-like cyclic peptides 1-adamantaneacetyl-Cys-Gly-Arg-Gly-Asp-Ser-Pro-Cys and Arg-Cys-Asp-thioproline-Cys inhibit the adhesion of TK-1 cells to immobilized CS-1 peptide, and to endothelial counterreceptors for LPAM-1, namely mucosal addressin cell adhesion molecule (MAdCAM)-1 and vascular cell adhesion molecule (VCAM)-1. Spontaneous adhesion of the VLA-4- LPAM-1+ B lymphoma cell line RPMI 8866 to CS-1 was likewise inhibited, confirming a previously undocumented ability of LPAM-1 to recognize the RGD tripeptide. The RGD-binding site in LPAM-1 either overlaps or is identical to sites required for interaction with MAdCAM-1, VCAM-1, and the CS-1. The binding of LPAM-1 and VLA-4 to RGD-containing ligands may have relevance in vivo given that fibrinogen at physiological concentrations is able to partially block the binding of TK-1 cells to MAdCAM-1. Hence fibrinogen and other vascular RGD-containing proteins may have mild anti-inflammatory activity required for maintaining effective homeostasis, analogous to the anti-thrombogenic activity of the vascular endothelium.

Pig lymphocytes utilise mouse MAdCAM-1 to enter fetal gut xenografts in SCID mice

Ileocecal junction (ICJ) and proximal intestine (PI) fragments from CD45(323-) allovariant fetal pigs were grafted subcutaneously into SCID mice. The xenografts were examined 8-12 weeks later using two-color immunohistology and the ICJ, but not PI, xenografts were found to contain three types of vessels. The first (the majority) was lined with mouse endothelium (mAb 9F1+), the second was lined with pig endothelium, and the third was chimeric. The ICJ vessels were specifically lined with mouse endothelium expressing MAdCAM-1, the mucosal addressin. Vessels lined with pig endothelium alone did not express the MAdCAM-1 epitopes. Radiolabeled allovariant pig peripheral blood lymphocytes (PBL) were introduced i.v. into the xenografted SCID mice, and entry into xenografts studied. Pig PBL were occasionally seen in MECA-367+ vessel walls after 4 h and within the ICJ but not PI xenografts after 24 h. This entry was specifically blocked by coinjection of the anti-MAdCAM-1 mAb MECA-367. The results demonstrate reendothelialization of xenografts by host endothelium that expresses its own addressin and is functional for xenogenic PBL.

Cloning of the mucosal addressin MAdCAM-1 from human brain: identification of novel alternatively spliced transcripts

The mucosal addressin cell adhesion molecule-1 (MAdCAM-1), expressed selectively on high endothelial venules (HEV) and lamina propria venules, directs lymphocyte traffic by binding the lymphocyte Peyer's patch adhesion molecule-1 (LPAM-1, alpha 4 beta 7). Full-length DNA encoding human MAdCAM-1 was obtained by combining sequences from an expressed sequence tag (EST) identified in an early stage human brain cDNA library, a polymerase chain reaction-derived clone, and a MAdCAM-1 genomic clone. The deduced amino acid sequence revealed an 18 amino acid signal peptide, two N-terminal immunoglobulin (Ig)-like domains conserved (59-65%) in sequence with those of the mouse homologue, an 86 amino acid mucin-like region rich in serine-threonine residues, a 20 amino acid transmembrane domain and a 43 amino acid charged cytoplasmic domain. No counterpart to the third IgA-like domain of mouse MAdCAM-1 was present; however, the serine-threonine-rich mucin domain was extended as two distinguishable major and minor mucin regions unrelated to the mouse domain. The major domain is formed from six tandem repeats of an eight amino acid sequence having the MUC-2-related consensus DTTSPEP/SP. Human MAdCAM-1 mRNA transcripts were restricted to small intestine, colon, spleen, pancreas and brain. Alternatively spliced MAdCAM-1 variants were identified that lack parts of the second Ig domain and all or part of the major mucin domain, indicating that the function of this vascular addressin is regulated by extensive modifications to its multi-domain structure.

Interaction of monocytoid cells with the mucosal addressin MAdCAM-1 via the integrins VLA-4 and LPAM-1

The differentiation of myeloid cells into macrophages and granulocytes is accompanied by marked changes in adhesive phenotype. Here we seek to understand the regulation of expression and functionality of the VLA-4 (alpha 4 beta 1), LPAM-1 (alpha 4 beta 7) and HML-1 (alpha E beta 7) integrins on monocytes/macrophages and granulocytes, given that these integrins including LFA-1 (alpha L beta 2) mediate the entry, retention and signalling events of pathogenic leucocytes within chronically inflamed tissues. Phorbol ester-induced monocytic differentiation of the promyelocyte cell line HL60 led to increases in the steady-state levels of beta 2 and beta 7 mRNA transcripts, requiring a period of 10 and 24 h, respectively, of de novo protein synthesis. There was a parallel de novo expression of LPAM-1 on the cell surface, despite the fact that alpha 4 mRNA transcripts were rapidly down-regulated. At 72 h, HML-1 was not coexpressed with LPAM-1 on HL60 cells, although it was weakly expressed on peripheral blood monocytes/macrophages after a prolonged period of in vitro culture. Retinoic acid-induced granulocytic differentiation of HL60 cells led to the appearance of low levels of LPAM-1 at the cell surface. LPAM-1 was not found expressed on peripheral blood neutrophils, raising the possibility that it is transiently expressed during granulocyte differentiation. In accord with the above findings, differentiated monocytes and HL60 cells bound to recombinant MAdCAM-1 in an alpha 4- and beta 7-integrin-dependent fashion, whereas a population of undifferentiated HL60 cells and Mn(+2)-activated monocytes bound in an alpha 4-integrin-dependent beta 7-integrin-independent manner via VLA-4 expressed abundantly at all stages of differentiation. Four h after attachment, some of these VLA-4+ LPAM-1- HL60 cells could be seen to start spreading. These finding suggest that MAdCAM-1 can bind to VLA-4 when LPAM-1 is absent, and thus has the potential to recruit both VLA-4-bearing monocytes and VLA-4+ LPAM-1+ macrophages into chronically inflamed tissues.