Specific Carbohydrate Ligands Research Articles

Modulating Myeloid Immune Cell Migration Using Multivalently Presented Monosaccharide Ligands for Advanced Immunotherapy

Due to their importance for the outcome of the inflammatory response, the motile myeloid cells are a focus of novel treatment options. The interplay of selectins and their ligands with leukocytes and endothelial cells, which mediate endothelial attachment and transmigration of immune cells, can be modulated by selectin-binding structures. Here, a library of selectin-targeting ligands coupled to either gold, silver, iron oxide nanospheres, or quantum dots of 5–10 nm in size is used to systematically study their impact on immune cell motility. The multivalent presentation of the carbohydrate mimetics results in very low sub-nanomolar binding to L-selectin. Using human primary monocytes, granulocytes, lymphocytes, and macrophages, it is shown that the ligands exhibit only minor effects on uptake, whereas the motility of leukocytes is critically affected as observed in migration assays evaluated by flow cytometry. The carbohydrate mimetic ring structure, sulfation, in particular, and the degree of ligand presentation, are constituents which cohere in this process. Specific carbohydrate ligands can thus selectively regulate leukocyte subsets. These data form the basis for advanced immunotherapy which inhibits the amplification of inflammation by restricting leukocyte influx to injured tissue sites. Furthermore, the targeting ligands may complement existing treatment options for inflammatory diseases.

Взаимодействие MxyR Mycobacterium tuberculosis c ксиланами: необычные лиганды транскрипционных регуляторов семейства MarR

Among the repertoire of MarR family transcriptional regulators in Mycobacterium tuberculosis, gene rv3095 (mxyR) encodes Mycobacterial Xylan Regulator, MxyR. Gene mxyR is divergently oriented from a hydrolase (rv3094c), oxidoreductase (rv3093c) and an ABC transporter (rv3092c) and convergently oriented with xylanase (rv3096). Xylanase is commonly used by plant pathogenic microbes where they degrade xylan, the major component of hemicellulose. We have purified the transcriptional regulatory protein encoded by rv3095 and its molecular interactions were studied in detail using electrophoretic mobility shift assay. MxyR interacts with its upstream intergenic region mxyO with high specificity and at a dissociation constant of 5.01 ± 0.017 nM. Notably, this binding is attenuated by specific carbohydrate ligands such as xylan, L-Arabinose and D-Galactose with an IC50 values of 22.7 ± 1.02 ng/μL, 360.8 ± 24.25 ng/μL and 2320.0 ± 96.97 μg/μL, respectively. Consequently, it is evident that this association changes the conformation of the DNA binding helix α4 making the transcriptional regulator incompatible with binding to its cognate DNA, allowing xylanase and other genes to be transcribed. This study establishes the natural ligands of MxyR of M. tuberculosis providing insight on metabolic regulation of the carbohydrate, xylan.

Surface plasmon resonance imaging coupled to on-chip mass spectrometry: a new tool to probe protein-GAG interactions.

A biosensor device for the detection and characterization of protein-glycosaminoglycan interactions is being actively sought and constitutes the key to identifying specific carbohydrate ligands, an important issue in glycoscience. Mass spectrometry (MS) hyphenated methods are promising approaches for carbohydrate enrichment and subsequent structural characterization. In the study herein, we report the analysis of interactions between the glycosaminoglycans (GAGs) heparin (HP) and heparan sulfate (HS) and various cytokines by coupling surface plasmon resonance imaging (SPRi) for thermodynamic analysis method and MALDI-TOF MS for structural determination. To do so, we developed an SPR biochip in a microarray format and functionalized it with a self-assembled monolayer of short poly(ethylene oxide) chains for grafting the human cytokines stromal cell-derived factor-1 (SDF-1α), monocyte chemotactic protein-1 (MCP-1), and interferon-γ. The thermodynamic parameters of the interactions between these cytokines and unfractionated HP/HS and derived oligosaccharides were successively determined using SPRi monitoring, and the identification of the captured carbohydrates was carried out directly on the biochip surface using MALDI-TOF MS, revealing cytokine preferential affinity for GAGs. The MS identification was enhanced by on-chip digestion of the cytokine-bound GAGs with heparinase, leading to the detection of oligosaccharides likely involved in the binding sequence of GAG ligands. Although several carbohydrate array-based assays have been reported, this study is the first report of the successful analysis of protein-GAG interactions using SPRi-MS coupling.

Identification of putative adhesins and carbohydrate ligands of Lactobacillus paracasei using a combinatorial in silico and glycomics microarray profiling approach.

Commensal bacteria must colonize host mucosal surfaces to exert health-promoting properties, and bind to gastrointestinal tract (GIT) mucins via their cell surface adhesins. Considerable effort has been directed towards discovery of pathogen adhesins and their ligands to develop anti-infective strategies; however, little is known about the lectin-like adhesins and associated carbohydrate ligands in commensals. In this study, an in silico approach was used to detect surface exposed adhesins in the human commensal Lactobacillus paracasei subsp. paracasei, a promising probiotic commonly used in dairy product fermentation that presents anti-microbial activity. Of the 13 adhesin candidates, 3 sortase-dependent pili clusters were identified in this strain and expression of the adhesin candidate genes was confirmed in vitro. Mass spectrometry analysis confirmed the presence of surface adhesin elongation factor Tu and the chaperonin GroEL, but not pili expression. Whole cells were subsequently incubated on microarrays featuring a panel of GIT mucins from nine different mammalian species and two human-derived cell lines and a library of carbohydrate structures. Binding profiles were compared to those of two known pili-producing lactobacilli, L. johnsonii and L. rhamnosus and all Lactobacillus species displayed overlapping but distinct signatures, which may indicate different abilities for regiospecific GIT colonization. In addition, L. paracasei whole cells favoured binding to α-(2→3)-linked sialic acid and α-(1→2)-linked fucose-containing carbohydrate structures including blood groups A, B and O and Lewis antigens x, y and b. This study furthers our understanding of host-commensal cross-talk by identifying potential adhesins and specific GIT mucin and carbohydrate ligands and provides insight into the selection of colonization sites by commensals in the GIT.

Modulating Myeloid Immune Cell Migration Using Multivalently Presented Monosaccharide Ligands for Advanced Immunotherapy

AbstractDue to their importance for the outcome of the inflammatory response, the motile myeloid cells are a focus of novel treatment options. The interplay of selectins and their ligands with leukocytes and endothelial cells, which mediate endothelial attachment and transmigration of immune cells, can be modulated by selectin‐binding structures. Here, a library of selectin‐targeting ligands coupled to either gold, silver, iron oxide nanospheres, or quantum dots of 5–10 nm in size is used to systematically study their impact on immune cell motility. The multivalent presentation of the carbohydrate mimetics results in very low sub‐nanomolar binding to L‐selectin. Using human primary monocytes, granulocytes, lymphocytes, and macrophages, it is shown that the ligands exhibit only minor effects on uptake, whereas the motility of leukocytes is critically affected as observed in migration assays evaluated by flow cytometry. The carbohydrate mimetic ring structure, sulfation, in particular, and the degree of ligand presentation, are constituents which cohere in this process. Specific carbohydrate ligands can thus selectively regulate leukocyte subsets. These data form the basis for advanced immunotherapy which inhibits the amplification of inflammation by restricting leukocyte influx to injured tissue sites. Furthermore, the targeting ligands may complement existing treatment options for inflammatory diseases.

Interactions of ficolin-3 with ovarian cancer cells

BackgroundFicolin-3 is a pattern-recognition molecule with the ability to activate the lectin pathway of complement. It is found in lung, liver and blood, but its physiological role is unclear. We have investigated interaction of recombinant ficolin-3 with malignant cells and tissues. Material and MethodsCells of various lines of human origin as well as ovarian tissue sections have been studied with the use of flow cytometry and immunohistochemistry. ResultsRecombinant (but not serum-derived) ficolin-3 was found to bind strongly to the ovarian cancer cell lines, SKOV-3, OVCAR-3 and ES-2, at concentrations of 2.5 μg/ml and above. Moreover, His-tagged recombinant ficolin-3 (10 μg/ml) preferentially stained ovarian tissue sections from patients with malignant tumours compared with those from patients without. Binding to cell lines was inhibited by EDTA and specific carbohydrate ligands, indicating involvement of the fibrinogen-like domain. Binding was enhanced under mildly acidic conditions and at physiological pH after pre-incubation of cells with mildly acidic buffer. ConclusionBasing on data concerning recombinant protein, it may be suggested that ficolin-3 is involved in immune response in ovarian cancer. However, unidentified serum factor(s) seem(s) to protect cancer cells from recognition by natural or rficolin-3.

Glycomics for Microbes and Microbiologists.

ABSTRACTThe recent article “Lectin-Glycan Interaction Network-Based Identification of Host Receptors of Microbial Pathogenic Adhesins” by Ielasi et al. describes a new development in microbial carbohydrate analysis [Ielasi FS, Alioscha-Perez M, Donohue D, Claes S, Sahli H, Schols D, Willaert RG, mBio 7(4):e00584-16, 2016, http://dx.doi.org/10.1128/mbio.00584-16]. Specific carbohydrate ligands have been identified from the patterns of lectin binding to oligosaccharides printed on a chip. The new technique links the output to a comprehensive glycan database and offers a number of data visualization options. The graphs highlight the occurrence of potential ligands, organized by organism, tissue, and patterns of association with disease states. The analysis has successfully predicted novel glycoprotein ligands for microbial lectins, including an interaction of E. coli FimH with HIV gp120.

Mechanistic insights into the distribution of carbohydrate clusters on cell membranes revealed by dSTORM imaging.

Cell surface carbohydrates play significant roles in many physiological processes and act as primary markers to indicate various cellular physiological states. The functions of carbohydrates are always associated with their expression and distribution on cell membranes. Based on our previous work, we found that carbohydrates tend to form clusters; however, the underlying mechanism of these clusters remains unknown. Through the direct stochastic optical reconstruction microscopy (dSTORM) strategy, we found that with the contributions of lipid raft as a stable factor and actin cytoskeleton as a restrictive factor, carbohydrate clusters can stably exist with restricted size. Additionally, we revealed that the formation of most carbohydrate clusters (Gal and GlcANc clusters) depended on the carbohydrate-binding proteins (i.e., galectins) cross-linking their specific carbohydrate ligands. Our results clarify the organizational mechanism of carbohydrates on cell surfaces from their formation, stable existence and size-restriction, which promotes a better understanding of the relationship between the function and distribution of carbohydrates, as well as the structure of cell membranes.

Pilzliche Adhäsine: Klebstoffe für soziales Verhalten und Pathogenität

Adhesion of cells to biotic and abiotic surfaces is a key for the exchange of genetic material, multicellular development, and colonization of the environment. In fungi, these functions are mediated by fungal adhesins, a family of secreted cell wall glycoproteins that recognize specific carbohydrate or peptide ligands. High-resolution 3D structures of adhesins from apathogenic and pathogenic yeasts now reveal how these proteins confer social interactions and fungal pathogenesis.

Mannose receptor and macrophage galactose-type lectin are involved inBordetella pertussismast cell interaction

Mast cells are crucial in the development of immunity against Bordetella pertussis, and the function of TLRs in this process has been investigated. Here, the interaction between mast cells and B. pertussis with an emphasis on the role of CLRs is examined. In this study, two CLRs, MGL and MR, were detected for the first time on the surface of mast cells. The involvement of MR and MGL in the stimulation of mast cells by heat-inactivated BP was investigated by the use of blocking antibodies and specific carbohydrate ligands. The cell wall LOS of BP was also isolated to explore its role in this interaction. Mast cells stimulated with heat-inactivated BP or BP LOS induced TNF-α, IL-6, and IFN-γ secretion, which was suppressed by blocking MR or MGL. Inhibition of CLRs signaling during BP stimulation affected the ability of mast cells to promote cytokine secretion in T cells but had no effect on the cell-surface expression of ICAM1. Blocking MR or MGL suppressed BP-induced NF-κB expression but not ERK phosphorylation. Syk was involved in the CLR-mediated activation of mast cells by BP. Bacterial recognition by immune cells has been predominantly attributed to TLRs; in this study, the novel role of CLRs in the BP-mast cell interaction is highlighted.

Are multivalent cluster glycosides a means of controlling ligand density of glycoarrays?

Bacterial adhesion to the glycocalyx of human host cells is of biological and medicinal importance. This process is often initiated by the interaction of bacterial lectins and specific carbohydrate ligands. Thus, adhesion of bacterial cells to glycosylated surfaces is a suitable model system to study various parameters of lectin-mediated carbohydrate recognition. Glycoarrays have become important tools to study such lectin-mediated carbohydrate recognition. However, it is difficult to adjust the characteristics of a specific glycoarray regarding its carbohydrate density or the clustering of sugar ligands, respectively. Thus, we have made an attempt to use synthetic cluster glycosides of different valencies to vary carbohydrate density on a polystyrene surface. A series of mono-, di- and trivalent mannosides were synthesised for immobilisation on pre-functionalised polystyrene microtiter plates and the resulting glycoarrays were tested as adhesive surfaces in mannose-specific adhesion of Escherichia coli. Our measurements give first promising hints about the potential of this approach to alter ligand density of glycoarrays in a systematic way.

Abstract 5712: Identification and characterization of high affinity thioaptamer ligands against E-selectin

Abstract E-selectin (CD62E, ELAM-1 or LECAM-2) is a calcium dependent cell surface glycoprotein that mediates an adhesion of leukocytes on inflamed endothelium through recognition of specific carbohydrate ligands, sialyl Lewis X (sLeX) and sialyl Lewis A (sLeA). E-selectin expression is transcriptionally induced by NF-κB and AP-1 in response to inflammatory cytokines such as IL-1 and TNF-alpha. Accordingly, elevated E-selectin expression was reported in many types of acute and chronic inflammatory diseases including cancer. Aberrant homing of leukocytes to tumor results in tumor progression and local invasion. In addition, E-selectin and its counter ligands have also been reported to trigger the initial adhesive step of circulating cancer cells to endothelial cells. Therefore, blockade of E-selectin is a promising therapeutic strategy to control pathological infiltration of leukocytes and/or metastatic cancer cells. Thioaptamers (TA) are single stranded DNA molecules with thio substitution in the phosphate backbone, which provide stability against nucleases. Thioaptamer can fold into tertiary structures and bind with high affinity and specificity to a target molecule, and thus suitable for in vivo applications. In this study, we aimed to identify thioaptamer ligands that bind to E-selectin with high affinity and specificity. To achieve this goal, we used two-step selection strategies, recombinant protein based thioaptamer selection from a combinatorial thioaptamer library that contains 10E14 random sequences, followed by a cell based binding to tetracycline inducible E-selectin endothelial cells. We selected 14 different groups of thioaptamer candidates following 10 iterative cycles of binding to recombinant E-selectin protein. Using Tet-on inducible E-selectin endothelial cells, we identified the lead three TA candidates that bind to E-selectin on the surface of endothelial cells at high affinity (nM range) and specificity. In addition, the TA bound to tumor associated vasculature that express E-selectin. Moreover, the TA selected demonstrated significant inhibition of leukocyte adhesion to E-selectin positive endothelial cells at low nanomolar concentrations. In summary, we identified antagonistic TA against E-selectin that binds to endothelial cells and interferes with leukocyte bindings at nM range. Potential applications of this TA could be for 1) inflamed tumor vasculature selective targeted delivery of therapeutic molecules or drug delivery carriers 2) the prevention of pathological diapedesis of leukocytes and/or metastatic cancer cells. We are currently investigating potential clinical applications of the TA. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5712.

Specific Interaction of the Legume Lectins, Concanavalin A and Peanut Agglutinin, with Phycocyanin

In a recent study, we found that jacalin, a T-antigen specific lectin could interact with phycocyanin (PC) in a carbohydrate-independent manner. We show here that concanavalin A and peanut agglutinin too can interact with PC, although the nature of the interaction is distinctly different from that for jacalin. The legume lectins bind PC weaker in the presence of their specific carbohydrate ligands. Like jacalin, the legume lectins too interact with PC via two distinct sites. Higher ionic strengths resulted in a weakening of the interaction at site 1 and did not affect the interaction at site 2, clearly indicating that the interactions involve charged residues at the former and hydrophobic interactions at the latter site. The implications for the use of these lectin-PC complexes in photodynamic therapy and other clinical applications are discussed.

Critical Role of the Solvent Environment in Galectin-1 Binding to the Disaccharide Lactose

Galectin-1 (Gal-1), a member of a family of evolutionarily conserved glycan-binding proteins, binds specifically to poly-N-acetyllactosamine-enriched glycoconjugates. Through interactions with these glycoconjugates, this protein modulates inflammatory responses and contributes to tumor progression and immune cell homeostasis. The carbohydrate recognition domain includes the single protein tryptophan (Trp68). UV resonance Raman spectroscopy and molecular dynamic simulation were used to examine the change in the environment of the Trp on ligand binding. The UV Raman spectra and the calculated water radial distribution functions show that, while no large structural changes in the protein follow lactose binding, substantial solvent reorganization occurs. These new insights into the microscopic role of water molecules in Gal-1 binding to its specific carbohydrate ligands provides a better understanding of the physicochemical properties of Gal-1-saccharide interactions, which will be useful for the design of synthetic inhibitors for therapeutic purposes.

Pseudomonas aeruginosa lectin LecB is located in the outer membrane and is involved in biofilm formation

Pseudomonas aeruginosa is an opportunistic pathogen which causes a variety of diseases, including respiratory tract infections in patients suffering from cystic fibrosis. Therapeutic treatment of P. aeruginosa infections is still very difficult because the bacteria exhibit high intrinsic resistance against a variety of different antibiotics and, in addition, form stable biofilms, e.g. in the human lung. Several virulence factors are produced by P. aeruginosa, among them the two lectins LecA and LecB, which exert different cytotoxic effects on respiratory epithelial cells and presumably facilitate bacterial adhesion to the airway mucosa. Here, the physiology has been studied of the lectin LecB, which binds specifically to L-fucose. A LecB-deficient P. aeruginosa mutant was shown to be impaired in biofilm formation when compared with the wild-type strain, suggesting an important role for LecB in this process. This result prompted an investigation of the subcellular localization of LecB by cell fractionation and subsequent immunoblotting. The results show that LecB is abundantly present in the bacterial outer-membrane fraction. It is further demonstrated that LecB could be released specifically by treatment of the outer-membrane fraction with p-nitrophenyl alpha-L-fucose, whereas treatment with D-galactose had no effect. In contrast, a LecB protein carrying the mutation D104A, which results in a defective sugar-binding site, was no longer detectable in the membrane fraction, suggesting that LecB binds to specific carbohydrate ligands located at the bacterial cell surface. Staining of biofilm cells using fluorescently labelled LecB confirmed the presence of these ligands.

Antitumour activity of cytotoxic liposomes equipped with selectin ligand SiaLe X, in a mouse mammary adenocarcinoma model

The overexpression of lectins by malignant cells compared with normal ones can be used for the targeting of drug-loaded liposomes to tumours with the help of specific carbohydrate ligands (vectors). Recently we have shown that liposomes bearing specific lipid-anchored glycoconjugates on a polymeric matrix bind in vitro to human malignant cells more effectively and, being loaded with a lipophilic prodrug of merphalan, reveal higher cytotoxic activity compared with unvectored liposomes. In this study, carbohydrate-equipped cytotoxic liposomes were tested in vivo in a mouse breast cancer model, BLRB-Rb (8.17)1Iem strain with a high incidence of spontaneous mammary adenocarcinoma (SMA). Firstly, a cell line of the SMA was established which was then used to determine the specificity of the tumour cell lectins. After screening of the lectin specificity of a number of fluorescent carbohydrate probes, SiaLe X was shown to be the ligand with the most affinity, and a lipophilic vector bearing this saccharide was synthesised. Then different liposomal formulations of the synthetic merphalan lipid derivative and SiaLe X vector were prepared and applied in the treatment of mice with grafted adenocarcinomas. The results of the tumorigenesis data show that the therapeutic efficacy of merphalan increases sharply after its insertion as a lipophilic prodrug into the membrane of SiaLe X-vectored liposomes.

A Combined Molecular Modelling and CIDNP Study of Similarities in the Pattern of Ligand Binding in Mammalian and Avian Galectins

Galectins (Galactose binding lectins) from bacteria, plants and animals have been shown to possess tyrosine or tryptophan residues that form hydrophobic contacts with their ligands in the binding sites. At the present time, the X-ray structures of only two galectins from human and bovine tissues are known. In the present study we applied X-ray data of bovine heart galectin-1 as a template for homology modelling of a number of galectins from mammalian and avian tissues. The conservation of one tryptophan and at least one histidine in binding pocket can be observed from the comparison of the model structures. We also show that it is possible to obtain information of the architecture of the binding pocket of several galectins in solution using CIDNP (Chemically Induced Dynamic Nuclear Polarisation) techniques. The CIDNP approach offers a possibility to analyse these lectins in solution thereby providing supplementary information to the available X-ray data. All studied galectins show comparable alterations when they are r ecorded by CIDNPtechnique in the absence and in the presence of their specific carbohydrate ligands.

Oligomerization of the Hemolytic Lectin CEL-III from the Marine Invertebrate Cucumaria echinata Induced by the Binding of Carbohydrate Ligands

The hemolytic lectin CEL-III is a Ca2+-dependent, galactose/GalNAc-specific lectin purified from the marine invertebrate Cucumaria echinata (Holothuroidea). We found that this lectin forms ion-permeable pores in erythrocyte and artificial lipid membranes that have specific carbohydrate ligands on the surface. The hemolytic activity of CEL-III exhibited characteristic pH dependence; activity increased remarkably with pH in the alkaline region, especially above pH 9. When rabbit erythrocyte membrane was examined by immunoblotting using anti-CEL-III antiserum after treatment with CEL-III, the irreversible binding of the CEL-III oligomer increased with pH, indicating that the increase in hemolytic activity at higher pH is associated closely with the amount of oligomer irreversibly bound to the membrane. Surface hydrophobicity of CEL-III, as measured by the fluorescent probe 8-anilino-1-naphthalenesulfonate, increased markedly with the binding of specific ligands such as lactose, lactulose, and N-acetyllactosamine at pH 9-10 in the presence of 1 M NaCl. The enhancement of surface hydrophobicity induced by the binding of carbohydrates was also accompanied by the formation of a CEL-III oligomer, which was found to be the same size on sodium dodecyl sulfate-polyacrylamide gel electrophoresis as the oligomer that formed in CEL-III-treated erythrocyte membranes. Far-UV circular dichroism spectra of CEL-III and the oligomer revealed a definite difference in secondary structure. These data suggest that the binding of CEL-III to specific carbohydrate ligands on the erythrocyte surface induces a conformational change in the protein, leading to the exposure of a hydrophobic region which triggers oligomerization and the irreversible binding of the protein to the membrane.

Neutrophils and deep venous thrombosis.

A case can be made for the participation of polymorphonuclears (PMN) in the initiation and propagation of venous thrombosis. In animal models leukocytes adhered to areas of veins that serve as sites for initiation of thrombi in patients. In addition, PMN are found in white layers of thrombin where they may interact with platelets to attract more of each. This would add bulk and promote coagulation so that red layers are formed. Lidocaine and one of its derivatives inhibited leukocyte adhesion to veins in dogs and lidocaine reduced the incidence of deep venous thrombosis (DVT) in patients after hip replacement, suggesting but not proving that inhibition of PMN adhesion might have contributed. A new approach for preventing PMN contribution to DVT is suggested by recent studies which identified three families of adhesive receptors (integrins, intercellular adhesion molecules and selectins) on endothelium, leukocytes and platelets. Monoclonal antibodies against beta 2-integrins on leukocytes reduced leukocyte adhesion, emigration and PMN-dependent tissue injury in infection, inflammation and ischemia-reperfusion injury in animals. Selectins bind to specific carbohydrate ligands containing sialylated Lewis X, suggesting that relatively small analogues might inhibit PMN adhesion. Both platelets and PMN adhere to polymerizing fibrin through undefined mechanisms. Inhibition of this process might inhibit the buildup of white layers of thrombi.

Homing Receptors and the Control of Lymphocyte Migration

The traffic of lymphocytes is controlled in part by the selective interaction of circulating lymphocytes with specialized high endothelial venule (HEV) cells at sites of lymphocyte exit from the blood. At least three independent receptor systems are responsible for controlling lymphocyte traffic to different lymphoid organs or to sites of inflammation: one mediates lymphocyte interaction with HEV in peripheral lymph nodes, another in mucosa-associated lymphoid tissues, and a third in inflamed synovium. The receptors mediating lymphocyte recognition of HEV in different organs appear to be structurally related yet antigenically and functionally distinct 90 kD glycoproteins. Receptors for lymph node HEV can function as mammalian lectins, and probably interact with specific carbohydrate ligands on high endothelial cells. Mouse and human homing receptors share both antigenic and structural features, indicating a high conservation of lymphocyte-endothelial recognition systems during evolution. They play an essential part in the immune process by controlling lymphocyte traffic during B- and T-cell differentiation, and by segregating effector cells derived from stimulation in different tissues, thus simultaneously increasing the efficiency of organ-specific immune responses and decreasing possibilities for autoimmune crossreactions. Homing receptors are also expressed by many mouse and human lymphoid neoplasms, and appear to play a role in lymphoma metastasis. Related if not identical receptors are expressed by other leukocyte types, including polymorphonuclear leukocytes, monocytes, and large granular lymphocytes (natural killer cells). Thus lymphocyte homing receptors are members of a family of glycoprotein receptors for endothelium that control the extravasation of lymphocytes as well as other leukocytes, and help regulate both non-specific and specific immune responses in vivo.