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PubMed1992

Shedding of the CD44 adhesion molecule from leukocytes induced by anti-CD44 monoclonal antibody simulating the effect of a natural receptor ligand.

The CD44 adhesion molecule, playing an important role in leukocyte extravasation, was down-regulated by PMA and ionomycin on granulocytes and by an immobilized or soluble anti-CD44 mAb both on granulocytes and lymphocytes. Soluble labeled CD44 molecules of lower apparent molecular mass as compared to their membrane counterparts were isolated from culture supernatants of stimulated surface iodinated cells. Shedding rather than internalization is the mechanism found to be responsible for the loss of CD44 from the cell surface. The size of the soluble CD44 shed from the cells stimulated in vitro corresponds to soluble CD44 isolated from human serum. These data suggest that shedding, induced by anti-CD44 antibody simulating the effect of a natural CD44 ligand, is an important regulatory mechanism controlling surface CD44 expression on leukocytes in vivo.

Antibodies, Monoclonal↗
PubMed2002

Lack of a consistent relationship between demethylation of the CD44 promoter and CD44 expression.

Methylation of the CD44 promoter at one or more CpG dinucleotides has been proposed as being important in the control of CD44 expression. In vitro methylation of all CpGs occurring between bases -1 to -1374 upstream of the position of translation initiation repressed the promoter activity of mouse CD44 4.5- to 12-fold in transient transfection experiments. Assaying the methylation of these 29 CpGs by genomic sequencing using differential base modification by sodium bisulfite indicated that a cluster of three CpGs immediately upstream of the position of translation initiation was heavily methylated in the mouse CD44-negative T-cell lymphoma AKR1. All 19 CpGs between bases -4 and -447, including the cluster heavily methylated in AKR1, were demethylated in the CD44-positive T-cell lymphoma BW5147, while CpGs further upstream showed no change in methylation pattern. The cluster of heavily methylated CpGs remained methylated, however, when CD44 was activated by transient transfection of c-jun into an AKR1 subline expressing polyoma large-T or by treatment of this subline with sodium butyrate, and no significant demethylation of other CpGs was observed. It is concluded, therefore, that no consistent demethylation event in the promoter-containing region encompassing the 1374 base pairs upstream of the position of CD44 translation initiation is required for CD44 expression.

Animals↗
PubMed1993

Activated mouse astrocytes and T cells express similar CD44 variants. Role of CD44 in astrocyte/T cell binding.

The CD44 adhesion molecule is expressed by astrocytes, glial-type cells which exhibit features of accessory cells for immune responses in the central nervous system. In primary cultures of mouse astrocytes, we have observed that surface expression and mRNA levels of CD44 are induced following stimulation with either PMA, or tumor necrosis factor alpha plus gamma interferon. Comparison of CD44 splice variants expressed by astrocytes and a T cell hybridoma shows that upon activation, both cell types express a similar pattern of CD44 transcripts. Thus, in both cell types, CD44 transcripts are produced which contain additional exons, including the exon v6 (known to be expressed by in vivo activated lymphocytes and by metastatic variants of tumor cells) as well as variants of larger size. In the autoimmune disease multiple sclerosis, activated T cells cross the blood-brain barrier and lead to inflammation in the central nervous system. Analysis of mice with experimental allergic encephalomyelitis, frequently used as an animal model of multiple sclerosis, shows that CD44 is induced in vivo on glial cells surrounding inflammatory lesions. Using an in vitro model for adhesion between T cells and astrocytes, we have found a correlation between the activation state of these cells and their adhesion potential. Dose-dependent inhibition of adhesion by hyaluronate and by anti-CD44 monoclonal antibody KM81 shows that CD44 is involved in the adhesive interactions between T cells and astrocytes.

Animals↗
PubMed1996

Expression of CD44 and the pattern of CD44 alternative splicing in uveal melanoma.

In cutaneous melanoma, the standard CD44 molecule is abundantly expressed, whereas the expression of certain splice variants is related to tumour progression and to the metastatic potential of the cell line. In the present study we have investigated the expression of CD44 and the pattern of CD44 alternative splicing in uveal melanoma in relation to the cell type, diameter and invasiveness of the tumour. All uveal melanomas strongly stained with antibodies to the standard portion of CD44. No expression of the CD44 variant (v) exon CD44v7 was found, whereas v5, v6 and v10 were expressed (in 2/12, 5/12 and 8/12 cases, respectively). No correlation was observed between expression of particular splice variants and cell type, tumour diameter or invasion of the sclera or Bruch's membrane. All three uveal melanoma cell lines tested were strongly CD44 positive and expressed low levels of v6-containing isoforms at the cell surface, but v5, v7 and v10 were absent. Our results show that CD44 is strongly expressed in uveal melanoma and that the pattern of CD44 alternative splicing is similar to that observed in cutaneous melanoma. However, in uveal melanoma this alternative splicing does not appear to be related to prognostic parameters.

Alternative Splicing↗
PubMed1999

Requirements for signal delivery through CD44: analysis using CD44-Fas chimeric proteins.

CD44 is a transmembrane glycoprotein involved in various cell adhesion events, including lymphocyte migration, early hemopoiesis, and tumor metastasis. To examine the requirements of CD44 for signal delivery through the extracellular domain, we constructed a chimeric CD44 protein fused to the intracellular domain of Fas on its C-terminus. In cells expressing the CD44-Fas fusion protein, apoptosis could be induced by treatment with certain anti-CD44 mAbs alone, especially those recognizing the epitope group d, which has been previously shown to play a role in ligand binding, indicating that ligation of a specific region of the CD44 extracellular domain results in signal delivery. Of note was that appropriate ligation of the epitope h also resulted in the generation of apoptotic signal, although this region was not thought to be involved in ligand binding. In contrast, the so-called blocking anti-CD44 mAbs (epitope group f) that can abrogate the binding of hyaluronate (HA) failed to induce apoptosis even after further cross-linking with the secondary Ab, indicating that a mere mAb-induced oligomerization of the chimeric proteins is insufficient for signal generation. However, these blocking mAbs were instead capable of inhibiting apoptosis induced by nonblocking mAb (epitope group h). Furthermore, a chimeric protein bearing a mutation in the HA binding domain and hence lacking the ability to recognize HA was incapable of mediating the mAb-induced apoptosis, suggesting that the functional integrity of the HA binding domain is crucial to the signal generation in CD44.

Animals↗
PubMed2001

Liposome-encapsulated doxorubicin targeted to CD44: a strategy to kill CD44-overexpressing tumor cells.

Certain tumors, including many that are found in the lung, overexpress the CD44 cell-surface marker. CD44 is a receptor that binds to hyaluronan (HA), a carbohydrate consisting of beta1,3 N-acetyl glucosaminyl-beta1,4 glucuronide. We hypothesized that the incorporation of phosphatidylethanolamine lipid derivatives-containing HA oligosaccharides (HA-PE) into liposomes could target drug-containing liposomes to tumor cells that express CD44. HA-PE containing palmitoyl oleoyl phosphatidylethanolamine or dipalmitoyl phosphatidylethanolamine (HAn-PE) were incorporated into the lipid bilayer at various mole percentages of the total lipids; and the physicochemical properties (diameter, surface charge, and stability) of the resulting liposome preparations were characterized. HA-targeted liposomes (HALs) avidly bound to the CD44-high-expressing B16F10 murine melanoma cell line but not to the CV-1 African green monkey kidney cells, which express CD44 at low levels. Binding of the HALs to the B16F10 cells was rapid, concentration dependent, and saturated at a lipid concentration of about 250 microM. HAL binding to B16F10 was inhibited by HA with high Mr and by an anti-CD44 monoclonal antibody. Binding to the B16 melanoma cells occurred at a lipid composition that contained a > or =0.1 mol % of the HAn-PE lipid. The bound liposomes were internalized by a temperature-dependent process. The IC50s of doxorubicin (DOX) encapsulated in either HALs or nontargeted liposomes and of nonencapsulated DOX were compared in two protocols: continuous exposure of the cells to treatment for 24 h and transient exposure in which the treatment was applied for a 3-h period, and in which non-cell-associated drug was replaced with drug-free medium for the duration of the experiment. The IC50s of free DOX, DOX-loaded nontargeted liposomes, and DOX-loaded HAL (HAL-DOX) for the transient exposure were 6.4 microM, > 172 microM, and 0.78 microM, respectively. For the continuous exposure protocol, the IC50s were 0.60 microm, 25.0 microl, and 0.14 microm, respectively. Thus, in both protocols, delivered DOX was significantly more potent than the nonencapsulated DOX in cells expressing high levels of CD44, which suggests that HALs may be a useful targeted drug carrier to treat CD44-expressing tumors.

Animals↗
PubMed1997

In vivo inhibition of CD44 limits intra-abdominal spread of a human ovarian cancer xenograft in nude mice: a novel role for CD44 in the process of peritoneal implantation.

Ovarian cancer cells frequently metastasize by implanting onto the peritoneal mesothelial lining of the abdominal cavity. Data obtained from in vitro adhesion studies have suggested a possible role for the CD44 molecule in this process. The purpose of the present study was to determine the in vivo role of CD44 in ovarian cancer metastasis by using a nude mouse xenograft model of peritoneal implantation. Three groups of 10 athymic female nude mice each received an i.p. inoculum of 10 x 10(6) cells from a CD44-positive human ovarian cancer cell line (36M2) in the presence of either anti-D144 antibody (Ab; nonreactive IgG1), anti-DF3 Ab (reactive IgG1 Ab that does not inhibit in vitro binding), or neutralizing anti-CD44 Ab (IgG1). The number of peritoneal and diaphragmatic implants at 5 weeks for anti-D144 and anti-DF3-treated groups was 103 +/- 17 and 120 +/- 20, respectively (mean +/- SE; P > 0.2). In contrast, animals treated with anti-CD44 Ab experienced a significant reduction in the number of tumor implants (35 +/- 4; P < 0.002). Anti-CD44 Ab was not inhibitory to the growth of 36M2 cells in vitro and did not inhibit s.c. tumor growth in vivo, suggesting that the observed effect was related to inhibition of peritoneal implantation. These data suggest that the CD44 molecule plays an important in vivo role in ovarian cancer cell implantation and that strategies to inhibit CD44 function may represent a novel approach to limiting the intra-abdominal spread of this highly lethal tumor.

Animals↗
PubMed2000

Functional role of cyclin A on induction of fibroblast apoptosis due to ligation of CD44 matrix receptor by anti-CD44 antibody.

Ligation of cell surface matrix adhesion receptors such as integrins can increase expression of specific cell cycle regulatory proteins such as cyclin A, thereby regulating cell cycle progression. Disruption of cell surface matrix receptor interaction with the extracellular matrix can trigger apoptosis. Induction of apoptosis has been linked to unscheduled up-regulation of cyclin A and activation of cyclin-A-associated dependent kinase 2 activity due to cleavage of cyclin-dependent kinase inhibitors by caspases. We have found that ligation of the cell surface matrix adhesion receptor CD44 by anti-CD44 antibody induces cell detachment and triggers apoptosis. In this report we show that ligation of CD44 by anti-CD44 antibody increases the expression of cyclin A protein prior to activation of caspase-3-like activity and morphological changes of apoptosis. Down-regulation of cyclin A protein levels by cyclin A antisense oligonucleotides dramatically decreased fibroblast apoptosis in response to anti-CD44 antibody. These data identify an important functional role of cyclin A in the induction of fibroblast apoptosis due to the ligation of the cell surface adhesion receptor CD44 by anti-CD44 antibody.

3T3 Cells↗
PubMed2002

Changes in serum hyaluronic acid levels and expression of CD44 and CD44 mRNA in hepatic sinusoidal endothelial cells after major hepatectomy in cirrhotic rats.

Serum hyaluronic acid (HA) is widely distributed in connective tissues, and the majority of circulating HA is degraded by hepatic sinusoidal endothelial cells (SECs) via a receptor recycling pathway. Our previous clinical study revealed that monitoring serum HA levels after hepatectomy is useful in predicting the development of liver failure. In the present study, to determine the mechanism of the high HA levels after hepatectomy, especially in patients with liver cirrhosis, expression of the major HA receptor, CD44, and its mRNA was investigated in SECs isolated from rats with thioacetamide-induced liver cirrhosis subjected to 70% hepatectomy (group I) and from rats with a normal liver that were subjected to 70% hepatectomy (group II). The 48-hour postoperative survival rate in group I (13.3%) was significantly lower than in group II (100%). In group II, the expression of CD44 mRNA had increased significantly at 6 hours after hepatectomy, and this was followed by progressive increases in expression of CD44, indicating activation of SEC function. The increased serum HA levels after hepatectomy in group II became normal as CD44 expression increased. By contrast, the expression of CD44 and CD44 mRNA in group I was markedly attenuated after hepatectomy. The very low CD44 expression was followed by a significant and sustained increase in serum HA levels, indicating functional failure of the SECs. These results suggest that the significantly impaired functional reserve of SECs in liver cirrhosis is associated with increased mortality after 70% hepatectomy.

Alanine Transaminase↗
PubMedDate not supplied

Binding of human leukocytes to fibronectin is augmented by an anti-CD44 mAb (TL-1) and blocked by another anti-CD44 mAb (Hermes-3) but not by anti-VLA-4/VLA-5 mAbs.

Fibronectin (FN) forms meshworks in extracellular spaces, and it plays an important role in cellular trafficking. Lymphoid cells are activated by binding to FN of the VLA-4 and VLA-5 receptors. CD44 also acts as a receptor of FN, but the mechanism and physiologic regulation of their binding are poorly understood. We have developed an anti-CD44 monoclonal antibody (mAb) (TL-1) in which lymphoid cells are activated and form homotypic cell aggregation. In this study, we found that the adhesion of CEM, HSB2, and LAD lymphoid cells to FN was augmented by TL-1 treatment and was apparently blocked by another anti-CD44 mAb (Hermes-3), but TL-1 Fab' fragments treatment did not induce FN-binding. A similar phenomenon is reported in the binding of the CD44 molecule to HA. This augmentation was not inhibited by the CS1 and RGD peptides of FN or by anti-VLA-4 and -VLA-5 mAbs; it was energy-dependent and associated with cytoplasmic actin filaments. Tl-1 treatment did not alter the cell surface expression of CD44 molecules. These findings above suggested that activated and/or altered cell surface distribution of CD44 molecules via a conformational change augmented the avidity of its binding to FN, which may be similar to lymphocyte-hyaluronate and lymphocyte-endothelial cell binding. As the Hermes-3 binding site is also involved in the interaction between lymphocytes and endothelial cells, activation of lymphocytes via CD44 molecules may facilitate the binding of lymphocytes to endothelial cells, extravasation, and migration to inflammatory sites rich in FN.

Adjuvants, Immunologic↗
PubMed1999

Overexpression of CD44 on alveolar eosinophils with high concentrations of soluble CD44 in bronchoalveolar lavage fluid in patients with eosinophilic pneumonia.

BACKGROUND: High levels of interleukin-5 (IL-5) are found in the alveolar space of patients with eosinophilic pneumonia (EP). IL-5 promotes the growth and differentiation of eosinophils, as well as activating these cells. IL-5 also induces the expression of CD44 on eosinophils in vitro. To evaluate the contribution of CD44 to the pathogenesis of EP, we examined the expression of CD44 on eosinophils in bronchoalveolar lavage fluid (BALF) and measured the concentration of soluble CD44 (sCD44) in BALF from patients with EP. METHODS: The concentrations of IL-5, sCD44, and hyaluronic acid (HA) were measured in BALF. The expression levels of CD44 on eosinophils in BALF and peripheral blood in patients with EP were compared. RESULTS: The expression of CD44 on alveolar eosinophils and the concentration of sCD44 were increased in BALF of patients with EP. There was a significant correlation between IL-5 and sCD44 in BALF. A high concentration of HA was observed in BALF of EP patients. CONCLUSIONS: Our results suggest that the high expression of CD44 on eosinophils probably results from upregulation by IL-5 and could be important in the pathogenesis of EP.

Adult↗
PubMed1999

Identification and characterization of CD44RC, a novel alternatively spliced soluble CD44 isoform that can potentiate the hyaluronan binding activity of cell surface CD44.

Soluble CD44 proteins generated by proteolytic cleavage or aberrant intron retention have been shown to antagonize the ligand binding activity of the corresponding cell surface receptor, inducing apoptosis and inhibiting tumor growth. Interestingly, such findings appear to contradict recent studies demonstrating a correlation between the presence of high levels of soluble CD44 in the serum of cancer patients and poor prognosis. In the present study, we report the cloning of a novel, naturally occurring, differentially expressed, soluble CD44 isoform, designated CD44RC, which, in contrast to previously described soluble CD44 proteins, can dramatically enhance the hyaluronan binding activity of cell surface CD44. Sequence analysis suggests that CD44RC is generated by an alternative splicing event in which the 3' end of CD44 exon 2 is spliced into an internal splice acceptor site present within exon 18, altering reading frame and giving rise to a soluble protein with a unique COOH terminus. Functional studies suggest that CD44RC enhances hyaluronan binding by adhering to chondroitin sulfate side-chains attached to cell surface CD44, generating a multivalent complex with increased avidity for hyaluronan.

Adjuvants, Immunologic↗
PubMed2002

Proteinase-mediated release of epithelial cell-associated CD44. Extracellular CD44 complexes with components of cellular matrices.

CD44 is a receptor for the matrix glycosaminoglycan hyaluronan. Proteoglycan forms of CD44 also exhibit affinity for fibronectin and collagen as well as chemokines and growth factors. CD44 plays a role in autoimmunity, inflammation, and tumor progression. Soluble CD44 (sCD44) is found in plasma, and the levels of sCD44 correlate with immune function and some malignancies. The mechanisms by which sCD44 is generated and its function are unknown. We demonstrate here that normal bronchial epithelial cells spontaneously release sCD44. Exposure to phagocyte- and bacterium-derived proteinases markedly increased the release of sCD44 from epithelial cells. The spontaneously released sCD44 was incorporated into high molecular mass complexes derived from the matrix that also contained chondroitin sulfate, fibronectin, hyaluronan, and collagens I and IV. Enzymatic digestion with proteinases liberated sCD44 from the high molecular mass complex. Consistent with the homology of CD44 to proteoglycan core and link proteins, these data suggest that CD44 spontaneously released from normal bronchial epithelial cells can accumulate as an integral component of the matrix, where it may play a role in the organization of matrices and in anchoring growth factors and chemokines to the matrix. Increases in plasma CD44 during immune activation and tumor progression therefore may be a manifestation of the matrix remodeling that occurs in the face of the enhanced proteolytic activity associated with infection, inflammation, and tumor metastasis, leading to alterations in cell-matrix interactions.

Bronchi↗
PubMed2003

Inflammatory cytokines can enhance CD44-mediated airway epithelial cell adhesion independently of CD44 expression.

In airways, the cell surface molecule CD44 is upregulated on bronchial epithelial cells in areas of damage. We have shown that a blocking standard CD44 (CD44s) antibody caused a 77% (+/- 19%) inhibition of cell migration at 3 h after mechanical damage and decreased epithelial cell repair of cells grown on cell culture filter inserts. With the use of primary human bronchial epithelial cells and the bronchial epithelial cell line 16HBE 14o-, a CD44s antibody inhibited >95% (P < 0.01) of cell binding to hyaluronic acid (HA). The cytokines TNF-alpha, IFN-gamma, IL-1 beta, and IL-4 stimulated a 2- to 3.5-fold increase in CD44-dependent cell binding to HA. IFN-gamma treatment did not increase CD44 expression as assessed by flow cytometry, although phorbol myristate acetate treatment did. This indicates that IFN-gamma-induced cell binding to HA did not require increased CD44 expression. These data indicate that CD44 is important for bronchial epithelial cell binding to HA and that cytokines known to be expressed in inflammation can increase HA binding independently of the level of CD44 expression.

Adjuvants, Immunologic↗
PubMed1992

Schistosoma mansoni eggs induce antigen-responsive CD44-hi T helper 2 cells and IL-4-secreting CD44-lo cells. Potential for T helper 2 subset differentiation is evident at the precursor level.

Schistosoma mansoni eggs are potent inducers of biased Th2-like immune responses. Using a model system where mice are immunized with isolated schistosome eggs, we demonstrate that CD44 expression, up-regulation of which has been linked to Th cell development, is increased on Th2 cells. We also investigate the functional properties of CD44-lo Th cells recovered from the overtly Th2 environment constituted by lymph nodes draining sites of egg deposition. Production of high levels of IL-4, IL-5, and IL-10 by Th cells responding to egg Ag is shown to be the property of a subpopulation expressing CD44-hi. This population of Th cells cosegregates with a blasting subpopulation expressing more IL-4R (but similar amounts of IL-2R) than Th cells from normal mice. These results indicate that mature Th2 cells responding to schistosome eggs are CD44-hi and suggest that they use IL-4 as a growth factor. In contrast, CD44-lo cells sorted from lymph node populations responding to eggs are able to produce small amounts of IL-4 and IL-2, but no IL-5 or IL-10. This is surprising, because low expression of CD44 is considered a characteristic of Th cell naivite and concomitant ability to produce only IL-2. Thus, in lymph nodes responding to schistosome eggs, potential for Th2 subset differentiation is evident within the CD44-lo precursor Th subpopulation.

Animals↗
PubMed1993

A link between ras and metastatic behavior of tumor cells: ras induces CD44 promoter activity and leads to low-level expression of metastasis-specific variants of CD44 in CREF cells.

The activated oncogene c-Ha-ras induces expression of the surface glycoprotein CD44 in cloned rat embryonic fibroblasts (CREF). Induction is transcriptional as shown by transient cotransfections of c-Ha-ras expression constructs and CD44 promoter reporter gene constructs and depends on the presence of an AP-1 binding site at position -110. Increased transcript levels for the standard isoform of CD44 (CD44s) are accompanied by the appearance of alternatively spliced RNAs and the synthesis of variants of CD44 (CD44v). These CD44v molecules differ from the standard type by the addition of sequences in the extracellular portion of the molecules. The occurrence of CD44v molecules in CREF cells upon induction of the CD44 promoter is probably due to leakiness of the splice control in these cells since stable transfection with c-Ha-ras does not alter the CD44v/total CD44 ratio. Upon ras overexpression, however, using an inducible mouse mammary tumor virus-ras construct, a transient increase of CD44v/total CD44 ratio of 3-4 has been determined suggesting that a burst of ras expression, in the genetic background of CREF cells, influences both promoter activity and splice control or accuracy. The expression of CD44v proteins is responsible for the metastatic potential in a variety of tumors (U. Günthert et al., Cell, 65: 13-24, 1991). Also in CREF cells expression of CD44v correlates with metastatic behavior, ras-transfected CREF cells are not only fully transformed but also give rise to metastatic spread as measured in the spontaneous metastasis assay. The adenoviral oncogene E1A counteracts ras-induced promoter function and, consequently, inhibits metastatic behavior without extinguishing transformation.

Animals↗
PubMed1998

Identification of two regions in the cytoplasmic domain of CD44 through which PMA, calcium, and foskolin differentially regulate the binding of CD44 to hyaluronic acid.

CD44 contains two clustered basic residues of three arginines and three lysines in the membrane-proximal region of its cytoplasmic domain. These two clusters are conserved among different species and different splicing forms. The function of these two motifs is not known. We substituted either the three-arginine or the three-lysine motif with alanine (CD44.3R3A and CD44.3K3A) and established stable CD44 transfectants. The effects of these mutations on the binding of CD44 to one of its ligands, hyaluronic acid (HA), were studied. When stimulated with PMA, transfectants bearing CD44.3K3A and CD44.3R3A proteins have reduced HA-binding capacity. When stimulated with forskolin, an activator of cAMP-dependent PKC, CD44.3R3A transfectants were able to bind low but detectable level of fluorescent-conjugated HA (F-HA). In contrast, CD44.3K3A transfectants were unable to bind any F-HA. Elevation of intracellular calcium concentrations either by ionomycin or thapsigargin also induced binding of HA in CD44.3R3A but not in CD44. 3K3A transfectants. These results provide evidence that both the arginine and the lysine motifs are important in the binding of CD44 to high levels of HA when stimulated with PMA. In contrast, when transfectants were stimulated with either forskolin or a Ca2+ mobilizer to bind a low level of F-HA, the lysine cluster, but not the arginine cluster, is required. These two closely located basic clusters are, therefore, differentially involved in the binding of CD44 to HA, depending on the level of ligand binding and the nature of the stimulatory signals.

Arginine↗
PubMed1993

Characterization of monoclonal antibodies against rabbit CD44: evidence of a role for CD44 in modulating synoviocyte metabolism.

The CD44 adhesion receptor is a hyaluronan-binding cell surface glycoprotein whose major isoform is a 95 kDa molecule with a wide tissue distribution. We have characterized two MAbs, W4/86 and RPN3/24, by immunochemistry, flow cytometry and fluorescence staining and demonstrated that they recognize the rabbit CD44 molecule. The results show that CD44 in the rabbit has a similar molecular size and cell distribution to human CD44. These antibodies have demonstrated for the first time, the presence of CD44 on synoviocytes. Preincubation of the rabbit synovial cell line HIG-82 with W4/86 inhibited its synthesis of PGE2 in response to autocrine synovial cytokines. These results indicate that the CD44 molecule may help to modulate synoviocyte metabolism.

Animals↗