Increased hyaluronic acid is associated with dermal delayed-type hypersensitivity

The interaction of hyaluronate with the cell surface: the hyaluronate receptor and the core protein

Two distinct mechanisms are discussed by which hyaluronate interacts with the surfaces of cells: first, through a receptor which binds to hyaluronate with high affinity; and second, through a hydrophobic protein which is covalently linked to hyaluronate. The hyaluronate receptor is a transmembrane glycoprotein of Mr 85,000 which appears to interact with actin filaments of the cytoskeleton. It recognizes a sequence of six sugar residues of hyaluronate and also binds to chondroitin sulphate with a lower affinity. On the cell surface the receptors bind hyaluronate in cooperative fashion whereby two or more receptors can bind to the same molecule of hyaluronate, resulting in a high affinity. Immunohistochemical staining with a monoclonal antibody to the receptor indicates that it is present on epithelia, macrophages and other mononuclear phagocytes as well as some type of neurons. In epithelia the receptors presumably help to mediate cell attachment to the basement membrane which is often rich in hyaluronate. The receptor also appears to be preferentially expressed on proliferating epithelial cells and may serve as a marker for some types of carcinomas. Macrophages and related cells also have large amounts of the receptor, where it may serve in cell migration and/or in the homing of the cells to certain types of tissues. Recent studies have suggested that cell surface hyaluronate is covalently attached to a membrane-associated core protein. First, if cultured rat fibrosarcoma cells are fixed with glutaraldehyde the cell surface hyaluronate remains associated with the cells even under conditions expected to break non-covalent bonds. Second, when cell surface hyaluronate is partitioned with Triton X-114 a significant fraction is recovered in the hydrophobic phase, suggesting attachment to a hydrophobic protein. And finally, the binding of cell surface hyaluronate to nitrocellulose appears to be mediated through a covalent linkage to a protein.

Biosynthesis of glycosaminoglycans and proteoglycans by the lymph node

Previous studies of hyaluronan uptake and catabolism by lymph nodes indicated that the nodes might also add some HA of low molecular weight to the unabsorbed fraction that passes through from afferent to efferent lymph vessels. The ability of lymph nodes to synthesise HA and proteoglycans was therefore examined (i) by perfusion of [(3)H] acetate through an afferent lymph vessel in vivo, and recovery of labeled products from the efferent lymph vessel and from the node after perfusion; and (ii) by tissue culture of lymph nodes with [(3)H] acetate. Perfusion of lymph nodes with [(3)H] acetate in situ yielded: (a), in outflowing lymph, small amounts of chondroitin/dermatan sulfate within the first hour which continued to be produced for up to 24 h; heparin in the second hour and HA in the third. In the nodes removed 17 to 19 h later, equal amounts of hyaluronan and chondroitin/dermatan sulfate and heparan sulfate proteoglycans were detected. In the tissue culture of lymph nodes: (1) HA, heparin and proteoglycans of heparan sulfate and chondroitin/dermatan sulfate were released into the medium but in the cell extract only heparan sulfate proteoglycan was detected; and (ii) molecular weight of the released hyaluronan ranged widely but was mostly less than 4-5x10(5)D; heparan sulfate proteoglycan was 2.8x10(4) to 9.4x10(5)D; heparin 7.9x10(4)D and chondroitin sulfate 1.3x10(4)D, suggesting that the chondrotin sulfate were released from their proteoglycans core by enzymic degradation. It is concluded that lymph nodes can release HA, heparin, heparan sulfate and chondroitin/dermatan sulfate proteoglycans into efferent lymph but the amount of hyaluronan is likely to be small without immune or other stimulation and its molecular weight is lower than in other tissues.

A role for the cell adhesion molecule CD44 and sulfation in leukocyte-endothelial cell adhesion during an inflammatory response?

CD44 is a widely expressed cell adhesion molecule that has been implicated in a variety of biological processes including lymphopoiesis, angiogenesis, wound healing, leukocyte extravasation at inflammatory sites, and tumor metastasis. The adhesive function of CD44, like other molecules involved in inducible adhesion, is tightly regulated. Post-translational modifications, isoform expression, aggregation state, and protein associations all can affect the ligand binding properties of CD44, and these can vary depending on the cell type and the activation state of the cell. The most extensively characterized ligand for CD44 is hyaluronan, a component of the extracellular matrix. Interactions between CD44 and hyaluronan can mediate both cell-cell and cell-extracellular matrix adhesion. In the immune system, both the selectin molecules and CD44 have been implicated in the initial binding of leukocytes to endothelial cells at an inflammatory site. Sulfation is required for selectin-mediated leukocyte-endothelial cell interactions, and, recently, inducible sulfation also was shown to regulate CD44-mediated leukocyte adhesion to endothelial cells. Sulfation, therefore, may be important in the regulation of cell adhesion at inflammatory sites. In this commentary we have reviewed the molecular aspects of CD44 and the mechanisms that regulate its binding to hyaluronan. In addition, we have summarized the role of CD44 and hyaluronan in mediating leukocyte-endothelial cell interactions and have discussed how this interaction may be regulated. Finally, we examined the potential role of sulfation as an inducible means to regulate CD44-mediated leukocyte adhesion and as a more general mechanism to regulate leukocyte-endothelial cell interactions.

Modulation of hyaluronan receptor (CD44) function in vivo in a murine model of rheumatoid arthritis

OBJECTIVE

To determine how in vivo modulation of CD44 function by antibodies influences disease severity in a murine model of rheumatoid arthritis.

METHODS

Mice with proteoglycan (PG)-induced arthritis were subjected to systemic treatment with 3 different monoclonal antibodies against CD44. Joint swelling and serum levels of hyaluronan (HA) and soluble CD44 (sCD44) were monitored. Inflammatory leukocyte infiltration in the joints, cell surface CD44 expression, and leukocyte adhesion to HA were compared. The effects of anti-CD44 treatment on the immune status of arthritic animals were also determined.

RESULTS

Antibody IRAWB14, which enhances HA binding, aggravated the inflammatory symptoms, while KM201, which blocks ligand binding, reduced the severity of arthritis. The most effective suppression of inflammation was noted upon treatment with antibody IM7, whose epitope lies outside the HA binding domain of CD44. Serum levels of sCD44 increased, and HA levels decreased, in response to IM7. KM201 and IM7 treatment reduced, but IRAWB14 treatment enhanced, the adhesion of leukocytes to HA. However, these antibodies had little effect on PG-specific immune responses.

CONCLUSION

Each antibody acted in vivo by virtue of its combined effects on CD44-HA binding and CD44 shedding. The dramatic reduction in arthritis severity effected by IM7 treatment was associated with extensive shedding of cell surface CD44 molecules. Loss of CD44 appears to be a major factor in preventing CD44- and HA-dependent cell-matrix interactions at the inflammatory site. Our study indicates a critical role for CD44 in the pathology of joint inflammation and reveals a unique mechanism of receptor down-regulation, which can be used therapeutically.

Activation-dependent modulation of hyaluronate-receptor expression and of hyaluronate-avidity by human monocytes

During inflammation, activated monocytes (Mo) migrate into tissues where they interact with extracellular matrix components such as hyaluronate (HA), produced in high amounts at inflammatory sites. We determined whether Mo that had invaded sites of cutaneous inflammation bind HA and express the putative HA receptors CD44 isoforms, ICAM-1, or receptor for hyaluronate-mediated motility (RHAMM). In cutaneous inflammation, activated infiltrating Mo displayed high HA avidity and expressed epitopes encoded by CD44s, CD44 variant exons v3, v4, v5, v6, v7, and v9, and ICAM-1, but not RHAMM. We further investigated how activation affects the avidity of Mo for HA and which receptors were responsible for such binding. Mo freshly purified from human peripheral blood bound little HA and expressed CD44s but no epitopes encoded by CD44v exons, ICAM-1, or RHAMM. During short-term tissue culture, Mo upregulated their HA avidity and expression of ICAM-1, CD44s, and epitopes encoded by CD44v, all of which were further augmented by IFN-gamma or lipopolysaccharide, whereas RHAMM was not detectable. Thus in vitro activated Mo resembled Mo that had migrated to inflammatory sites in vivo. Lipolysaccharide or IFN-gamma-induced HA binding was inhibited by more than 90% with monoclonal antibodies directed against N-terminal HA binding domains of CD44s, but not by monoclonal antibodies against CD44v epitopes or ICAM-1. In conclusion, we show that upon in vitro or in vivo activation, Mo enhance their capacity to bind HA. This is critically dependent upon the expression ofCD44s epitopes. Regulated CD44-HA interactions may be important for the ability of Mo to migrate into and within sites of inflammation and for Mo effector functions.

Proinflammatory stimuli regulate endothelial hyaluronan expression and CD44/HA-dependent primary adhesion

The localization of circulating leukocytes within inflamed tissues occurs as the result of interactions with and migration across vascular endothelium, and is governed, in part, by the expression of adhesion molecules on both cell types. Recently, we have described a novel primary adhesion interaction between the structurally activated form of the adhesion molecule CD44 on lymphocytes and its major ligand hyaluronan on endothelial cells under physiologic laminar flow conditions, and have proposed that this interaction functions in an extravasation pathway for lymphocytes in vascular beds at sites of inflammation. While the regulation of activated CD44 on leukocytes has been characterized in depth, regulation of hyaluronate (HA) on endothelial cells has not been extensively studied. Here we demonstrate that the expression of HA on cultured endothelial cell lines and primary endothelial cultures is inducible by the proinflammatory cytokines TNFalpha and IL-1beta, as well as bacterial lipopolysaccharide. In addition, this inducibility appears strikingly restricted to endothelial cells derived from microvascular, but not large vessel, sources. The elevated HA levels thus induced result in increased CD44-dependent adhesive interactions in both nonstatic shear and laminar flow adhesion assays. Changes in mRNA levels for the described HA synthetic and degradative enzymes were not found, suggesting other more complex mechanisms of regulation. Together, these data add to the selectin and immunoglobulin gene families a new inducible endothelial adhesive molecule, hyaluronan, and help to further our understanding of the potential physiologic roles of the CD44/HA interaction; i.e., local cytokine production within inflamed vascular beds may enhance surface hyaluronan expression on endothelial cells, thereby creating local sites receptive to the CD44/HA interaction and thus extravasation of inflammatory cells.

CD44 and its ligand hyaluronate mediate rolling under physiologic flow: a novel lymphocyte-endothelial cell primary adhesion pathway

The extravasation of leukocytes from the blood into tissues occurs as a multistep process: an initial transient interaction ("rolling"), generally thought to be mediated by the selectin family of adhesion molecules, followed by firm adhesion, usually mediated by integrins. Using a parallel plate flow chamber designed to approximate physiologic flow in postcapillary venules, we have characterized a rolling interaction between lymphoid cells and adherent primary and cultured endothelial cells that is not selectin mediated. Studies using blocking monoclonal antibodies indicate that this novel interaction is mediated by CD44. Abrogation of the rolling interaction could be specifically achieved using both soluble hyaluronate (HA) and treatment of the adherent cells with HA-reactive substances, indicating that HA is the ligand supporting this rolling interaction. Some B and T cell lines, as well as normal lymphocytes, either constitutively exhibit rolling or can be induced to do so by phorbol ester or in vivo antigen activation. These studies indicate that CD44 and its principal ligand hyaluronate represent another receptor/carbohydrate ligand pair mediating a novel activation-dependent pathway of lymphocyte/endothelial cell adhesion.

Anti-CD44 treatment abrogates tissue oedema and leukocyte infiltration in murine arthritis

A ubiquitous cell adhesion receptor, CD44, preferentially binds hyaluronan, a polysaccharide macromolecule that is present in most extracellular matrices. Hyaluronan molecules have large hydrodynamic volumes that entrap substantial amounts of water and can therefore control tissue hydration (swelling). CD44 is overexpressed by synovial cells and leukocytes, and hyaluronan is overproduced in the rheumatoid synovium and in other inflammatory sites. Nevertheless, the role of the CD44-hyaluronan interaction during inflammation is unclear. Our evidence shows that the CD44 receptor plays a critical role in governing the migration of inflammatory leukocytes into the extravascular compartment of the synovium in murine arthritis. An anti-CD44 antibody induces a rapid loss of CD44 from both leukocytes and synovial cells and displays an inhibitory effect on cell-extracellular matrix interactions in the synovium. As a result, the administration of such an antibody abrogates tissue swelling and leukocyte infiltration, two major components of inflammation.

Defective phosphorylation and hyaluronate binding of CD44 with point mutations in the cytoplasmic domain

CD44 is a cell surface adhesion molecule that plays a role in leukocyte extravasation, leukopoiesis, T lymphocyte activation, and tumor metastasis. The principal known ligand for CD44 is the glycosaminoglycan hyaluronate, (HA), a major constituent of extracellular matrices. CD44 expression is required but is not sufficient to confer cellular adhesion to HA, suggesting that the adhesion function of the receptor is regulated. We recently demonstrated that CD44 in primary leukocytes is phosphorylated in a cell type- and activation state-dependent fashion. In this study we demonstrate that serines 325 and 327 within the cytoplasmic domain of CD44 are required for the constitutive phosphorylation of CD44 in T cells. Furthermore, we demonstrate that cells expressing mutated CD44 containing a serine to glycine substitution at position 325 or a serine to alanine substitution at amino acid 327 are defective in HA binding, CD44-mediated adhesion of T cells to smooth muscle cells, as well as ligand-induced receptor modulation. The effect of these mutations can be partially reversed by a monoclonal anti-CD44 antibody that enhances CD44-mediated HA binding.

CD44 is necessary for optimal contact allergic responses but is not required for normal leukocyte extravasation

The in vivo administration of certain monoclonal antibodies (mAbs) against the adhesion receptor, CD44, into normal mice induces both a modulation of CD44 from the surface of peripheral lymphocytes, and a concomitant increase in the amount of soluble CD44 in the serum. CD44-negative lymphocytes isolated from anti-CD44-treated mice exhibit normal homing patterns upon adoptive transfer, and are capable of reexpressing CD44 upon activation. The treatment of haptensensitized mice with anti-CD44 mAb inhibits their ability to mount a cutaneous delayed-type hypersensitivity (DTH) response within the first 24 h after hapten challenge. This inhibition reflects a block in both the edema and leukocyte infiltration of the cutaneous site of DTH, whereas the extravasation and accumulation of leukocytes in the draining lymph nodes progress normally. After 72 h, the leukocytes that extravasate into the site of antigen challenge express CD44. These results indicate that CD44 is not necessary for normal leukocyte circulation but is required for leukocyte extravasation into an inflammatory site involving nonlymphoid tissue.

The glycosaminoglycans in cultures of stimulated rat peritoneal macrophages. 2. Gel chromatographic studies and the behaviour of heparan sulfate

The molecular weight distribution of pMP-derived glycosaminoglycans (GAG), i.e. non-sulfated GAG, chondroitin sulfate (CS), and heparin sulfate (HS)-like material was determined. The peritoneal macrophages (pMP) were harvested from rats normal or stimulated by i.p. injection of thioglycolate, carrageenan or BCG, and maintained in culture. The GAG of cell layer and medium were isolated separately after labeling with 35S-sulfate and 3H-acetate. Treatment with nitrous acid served to remove HS-like material. Labeling with 3H-acetate served to detect synthesis of the high m. w. hyaluronic acid (HA). Gel chromatic separation was done using Sephadex G-200 columns. The maximal size of 35S-labeled GAG, especially HS (36 kDa), was reduced in cultural medium and cell layer after stimulation in vivo. Reduction was most pronounced after application of carrageenan followed by thioglycolate and BCG/LPS stimulation. The extracellular GAG of BCG-stimulated pMP were smallest, probably due to degradation. Heparan sulfate-like material made up a larger proportion in monolayer and medium, comprising the total m.w. range up to 36 kDa. The GAG sensitive to nitrous acid were maximal in cultures of carrageenan-stimulated pMP and minimal in those of thioglycolate-stimulated pMP. This type of HS was sensitive to hyaluronidase, too. Any synthesis of high molecular hyaluronic acid was not found in normal or stimulated rat pMP. Therefore MP-associated HA must be adsorbed from other sources or synthesized by early forms of macrophages.

A novel secretory tumor necrosis factor-inducible protein (TSG-6) is a member of the family of hyaluronate binding proteins, closely related to the adhesion receptor CD44

TSG-6 cDNA was isolated by differential screening of a lambda cDNA library prepared from tumor necrosis factor (TNF)-treated human diploid FS-4 fibroblasts. We show that TSG-6 mRNA was not detectable in untreated cells, but became readily induced by TNF in normal human fibroblast lines and in peripheral blood mononuclear cells. In contrast, TSG-6 mRNA was undetectable in either control or TNF-treated human vascular endothelial cells and a variety of tumor-derived or virus-transformed cell lines. The sequence of full-length TSG-6 cDNA revealed one major open reading frame predicting a polypeptide of 277 amino acids, including a typical cleavable signal peptide. The NH2-terminal half of the predicted TSG-6 protein sequence shows a significant homology with a region implicated in hyaluronate binding, present in cartilage link protein, proteoglycan core proteins, and the adhesion receptor CD44. The most extensive sequence homology exists between the predicted TSG-6 protein and CD44. Western blot analysis with an antiserum raised against a TSG-6 fusion protein detected a 39-kD glycoprotein in the supernatants of TNF-treated FS-4 cells and of cells transfected with TSG-6 cDNA. Binding of the TSG-6 protein to hyaluronate was demonstrated by coprecipitation. Our data indicate that the inflammatory cytokine (TNF or IL-1)-inducible, secretory TSG-6 protein is a novel member of the family of hyaluronate binding proteins, possibly involved in cell-cell and cell-matrix interactions during inflammation and tumorigenesis.

The glycosaminoglycans of the macrophage-like cell line PeMa in suspension and monolayer culture

The macrophage-like cell line PeMa was cultured both in suspension and in monolayer for biochemical studies. It is concluded that adherent PeMa when compared with suspended cells --contain three times more GAG in medium, cell coat, and cells: --contain higher amounts of HS and CS in the cell coat; --release a minor proportion of sulfated GAG (HS) into the medium; --contain in their medium longer chains of HS and CS/DS; --contain in cell coat and cells higher amounts of a family of HS chains with high to low molecular weights. In suspension and monolayer cultures, the cell coat GAG were scarcely labelled; they are likely to be produced at another time and to turn over slowly. It is suggested that this study will be helpful to understand the behaviour of macrophages and other cells.

Circulating hyaluronate in psoriasis

A radioassay method allowing measurements of low concentrations of circulating hyaluronate was used in a study of serum hyaluronate concentrations in 44 patients with psoriasis. Twenty-three of them had only skin lesions and 21 had both skin lesions and arthropathy. In both of these groups significantly elevated serum levels of hyaluronate were found. The highest values were observed in those with widespread and active skin disease and/or active arthritis. Serum hyaluronate positively correlated with the plasma concentrations of alpha 1-antitrypsin and haptoglobin and also with ESR, which may indicate a relationship between acute inflammation and increased production of hyaluronate. Seven patients with widespread atopic dermatitis included for comparison had normal hyaluronate values. In blister fluid from lesional skin in two patients with acute psoriasis, very high concentrations of hyaluronate were found, in comparison with the concentrations in blister fluid from non-involved skin. The increased concentration of serum hyaluronate in psoriasis indicates involvement of dermal and synovial tissue in psoriasis, in addition to the epidermal changes.