Requirement for CD44 in activated T cell extravasation into an inflammatory site

Inflammation and clearance of Chlamydia trachomatis in enteric and nonenteric mucosae

Immunization(s) fostering the induction of genital mucosa-targeted immune effectors is the goal of vaccines against sexually transmitted diseases. However, it is uncertain whether vaccine administration should be based on the current assumptions about the common mucosal immune system. We investigated the relationship between mucosal sites of infection, infection-induced inflammation, and immune-mediated bacterial clearance in mice using the epitheliotropic pathogen Chlamydia trachomatis. Chlamydial infection of the conjunctival, pulmonary, or genital mucosae stimulated significant changes in tissue architecture with dramatic up-regulation of the vascular addressin, VCAM, a vigorous mixed-cell inflammatory response with an influx of alpha4beta1+ T cells, and clearance of bacteria within 30 days. Conversely, intestinal mucosa infection was physiologically inapparent, with no change in expression of the local MAdCAM addressin, no VCAM induction, no histologically detectable inflammation, and no tissue pathology. Microbial clearance was complete within 60 days in the small intestine but bacterial titers remained at high levels for at least 8 months in the large intestine. These findings are compatible with the notion that VCAM plays a functional role in recruiting cells to inflammatory foci, and its absence from the intestinal mucosa contributes to immunologic homeostasis at that site. Also, expression of type 1 T cell-mediated immunity to intracellular Chlamydia may exhibit tissue-specific variation, with the rate and possibly the mechanism(s) of clearance differing between enteric and nonenteric mucosae. The implications of these data for the common mucosal immune system and the delivery of vaccines against mucosal pathogens are discussed.

CD44 binds a chondroitin sulfate proteoglycan, aggrecan

Here we report that CD44 binds a chondroitin sulfate (CS) proteoglycan, aggrecan, a major component of cartilage. Soluble CD44-IgG and CD44(+) cells bound to aggrecan from rat chondrosarcoma and bovine cartilage, immobilized on microtiter plates. In both cases, binding was blocked by a neutralizing anti-CD44 mAb or by the pretreatment of aggrecan with chondroitinase, but not hyaluronidase or keratanase, indicating that CD44 binds aggrecan in a manner dependent on CS side chains of aggrecan and that hyaluronic acid is not involved in the binding. Structural analysis showed that glycosaminoglycans of aggrecan from rat chondrosarcoma and bovine articular cartilage consist of mainly CS A and a mixture of CS A and C respectively. When immobilized on microtiter plates, both CS A and C bound CD44-IgG, and the reaction was specifically inhibited by an anti-CD44 mAb. In addition, aggrecan augmented apoptosis in cells expressing CD44-Fas chimeric molecules in synergy with a non-blocking anti-CD44 mAb IRAWB14.4, suggesting that CD44-aggrecan interaction can induce oligomerization of the chimeric molecules. These results suggest that aggrecan interacts with CD44 to mediate cell adhesion and to trigger oligomerization of CD44 molecules, which may lead to intracellular signaling.

Cell surface-expressed moesin-like receptor regulates T cell interactions with tissue components and binds an adhesion-modulating IL-2 peptide generated by elastase

The adhesion of leukocytes to the extracellular matrix (ECM) depends on their responses to variations in the chemotactic signals in their milieu, as well as on the functioning of cytoskeletal and context-specific receptors. Ezrin, radixin, and moesin constitute a family of proteins that link the plasma membrane to the actin cytoskeleton. The surface expression of moesin on T cells and its role in cell adhesion has not been fully elucidated. Recently, we found that IL-2 peptides generated by elastase modified the adhesion of activated T cells to ECM ligands. Here, we further examined the adhesion regulatory effects of EFLNRWIT, one of the IL-2 peptides, as well as the existence and putative function of its receptor on T cells. We found that when presented to T cells in the absence of another activator, the EFLNRWIT peptide induced cell adhesion to vessel wall and ECM components. Binding of a radiolabeled peptide to T cells, precipitation with the immobilized peptide, and amino acid sequencing of the precipitated protein revealed that EFLNRWIT exerts its function via a cell surface-expressed moesin-like moiety, whose constitutive expression on T cells was increased after activation. This notion was further supported by our findings that: 1) anti-moesin mAb inhibited the binding of T cells to the immobilized EFLNRWIT peptide, 2) immobilized recombinant moesin bound the IL-2 peptide, and 3) soluble moesin inhibited the EFLNRWIT-induced T cell adhesion to fibronectin. Interestingly, moesin appears to be generally involved in T cell responses to adhesion-regulating signals. Thus, the IL-2 peptide EFLNRWIT appears to exert its modulating capacities via an adhesion-regulating moesin-like receptor.

Negative regulation of epithelium-neutrophil interactions via activation of CD44

Polymorphonuclear neutrophil (PMN) migration across epithelia is a common feature of active inflammation. Given the suggested role of carbohydrates in this process, we examined the receptor CD44. The standard CD44 isoform was expressed at the cell surface of PMN. PMN migration across model polarized intestinal epithelia was reduced (by 60%) if the CD44 receptor was activated by either a specific antibody (clone IM7) or the natural soluble ligand, hyaluronic acid. This inhibitory effect following receptor activation occurred with both basolateral-to-apical- and apical-to-basolateral-directed migration. The anti-CD44 antibody similarly reduced PMN migration through filters in the absence of epithelia, while preincubation of the antibody with the epithelium did not alter subsequent PMN transepithelial migration. These data suggest that PMN, rather than epithelial, CD44 is responsible for these effects. A similar inhibitory effect of anti-CD44 antibody was also observed on migration of intraepithelial lymphocytes. The molecular mechanism involved in such negative signaling following CD44 activation may include modulation of outside-in cell signaling. While neither the anti-CD44 antibody nor CD44 ligand affected PMN mobilization of intracellular Ca(2+), both led to increased adenylate cyclase activity, an inhibitory signal for PMN migration. Together, these results suggest that CD44 of PMN may potentially serve as a negative regulator of leukocyte migration across biological surfaces such as columnar epithelia.

Lymphotoxin alpha-/- mice develop functionally impaired CD8+ T cell responses and fail to contain virus infection of the central nervous system

Recent observations have indicated that viral persistence and tumor spreading could occur because of effector function-defective CD8(+) T cells. Although chronic exposure to Ag, lack of CD4 help, and epitope dominance are suggested to interfere with CTL differentiation, mechanisms underlying the defective effector function remain obscure. We demonstrate in this report that lymphotoxin alpha-deficient mice develop CD8(+) T cells at normal frequencies when infected with HSV or immunized with OVA Ag but show impaired cytotoxic and cytokine-mediated effector functions resulting in enhanced susceptibility to HSV-induced encephalitis. Although these cells display near normal levels of perforin and Fas ligand, they remain largely at a naive state as judged by high expression of CD62 ligand and failure to up-regulate activation or memory markers. In particular, these CD8(+) T cells revealed inadequate expression of the IL-12 receptor, thus establishing a link between CTL differentiation and LTalpha possibly through regulation of IL-12 receptor. Viruses and tumors could evade immunity by targeting the same pathway.

Activated T lymphocytes regulate hyaluronan binding to monocyte CD44 via production of IL-2 and IFN-gamma

Interactions of the cell surface proteoglycan CD44 with the extracellular matrix glycosaminoglycan hyaluronan (HA) are important during inflammatory immune responses. Our previous studies indicated that monocyte HA binding could be induced by TNF-alpha. Moreover, monocyte HA binding could be markedly up-regulated by culturing PBMC with anti-CD3 (TCR complex) mAbs. The present study was undertaken to identify soluble factors and/or cell surface molecules of activated T lymphocytes that might regulate HA binding to monocytes. Abs to IL-1 alpha, IL-1 beta, IL-2, IL-3, IL-10, IL-15, GM-CSF, IFN-gamma, and TNF-alpha were tested for their effects on anti-CD3 mAb-, Con A-, and PMA/ionomycin-mediated monocyte HA binding in PBMC cultures. Anti-TNF-alpha, anti-IL-2, and anti-IFN-gamma Abs, when added together to PBMC cultures, completely blocked Con A- and partially blocked anti-CD3- and PMA/ionomycin-induced monocyte HA binding. Furthermore, when added together to PBMC cultures, IL-2 and TNF-alpha induced high levels of monocyte HA binding. Likewise, IFN-gamma augmented TNF-alpha-induced monocyte HA binding. To investigate the role of T cell-monocyte direct contact in induction of monocyte HA binding, we studied PMA/ionomycin-activated, paraformaldehyde-fixed CD4(+) T cells in these assays. Fixed, PMA/ionomycin-activated CD4(+) T lymphocytes induced monocyte HA binding, but direct T cell-monocyte contact was not required. Moreover, anti-IFN-gamma and anti-TNF-alpha Abs blocked fixed PMA/ionomycin-activated CD4(+) T cell-induced monocyte HA binding. Taken together, these studies indicate roles for soluble T lymphocyte-derived factor(s), such as IL-2 and IFN-gamma, and a role for monocyte-derived TNF-alpha in Con A-, TCR complex-, and PMA/ionomycin-induced HA binding to monocyte CD44.

Expression of c-Met and heparan-sulfate proteoglycan forms of CD44 in colorectal cancer

In colorectal cancer patients, prognosis is not determined by the primary tumor but by the formation of distant metastases. Molecules that have been implicated in the metastatic process are the proto-oncogene product c-Met and CD44 glycoproteins. Recently, we obtained evidence for functional collaboration between these two molecules: CD44 isoforms decorated with heparan sulfate chains (CD44-HS) can bind the c-Met ligand, the growth and motility factor hepatocyte growth factor/scatter factor (HGF/SF). This interaction strongly promotes signaling through the receptor tyrosine kinase c-Met. In the present study, we explored the expression of CD44-HS, c-Met, and HGF/SF in the normal human colon mucosa, and in colorectal adenomas and carcinomas, as well as their interaction in colorectal cancer cell lines. Compared to the normal colon, CD44v3 isoforms, which contain a site for HS attachment, and c-Met, were both overexpressed on the neoplastic epithelium of colorectal adenomas and on most carcinomas. Likewise, HGF/SF was expressed at increased levels in tumor tissue. On all tested colorectal cancer cell lines CD44v3 and c-Met were co-expressed. As was shown by immunoprecipitation and Western blotting, CD44 on these cells lines was decorated with HS. Interaction with HS moieties on colorectal carcinoma (HT29) cells promoted HGF/SF-induced activation of c-Met and of the Ras-MAP kinase pathway. Interestingly, survival analysis showed that CD44-HS expression predicts unfavorable prognosis in patients with invasive colorectal carcinomas. Taken together, our findings indicate that CD44-HS, c-Met, and HGF/SF are simultaneously overexpressed in colorectal cancer and that HS moieties promote c-Met signaling in colon carcinoma cells. These observations suggest that collaboration between CD44-HS and the c-Met signaling pathway may play an important role in colorectal tumorigenesis.

CD44 supports T cell proliferation and apoptosis by apposition of protein kinases

T cell activation is supposed to require two signals via the TCR and a co-stimulatory molecule. However, the signaling cascade of co-stimulatory molecules has remained elusive. Here we provide evidence that CD44, which is constitutively associated with Ick and fyn, supports proliferation as well as apoptosis mainly, if not exclusively, by enhancing signal transduction via the TCR/CD3 complex. Antigenic stimulation of a T helper line in the presence of a CD44 receptor globulin was accompanied by a significant decrease in IL-2 production. To evaluate the underlying mechanism, CD44 was cross-linked via an immobilized antibody (IM-7). Cross-linking of CD44 induces proliferation of peripheral T cells and apoptosis of thymocytes and a T helper line in the presence of subthreshold levels of anti-CD3. Several proteins are rapidly tyrosine phosphorylated; erk and c-jun are strongly activated; expression of CD69 and CD25 is up-regulated on mature T cells; and expression of CD95 and CD95L is up-regulated on the T helper line. All these phenomena become less dependent of CD44 in the presence of high amounts of anti-CD3. Furthermore, cross-linking of CD44 is only effective when supporting co-localization of CD44 with the TCR/CD3 complex, since mixtures of beads coated with either anti-CD3 (low dose) or anti-CD44 do not induce T cell activation. These findings imply the rearrangement of adhesion molecules with apposition of protein kinases as a critical event for the initiation of signaling via the TCR/CD3 complex.

Expression of mucosal homing receptor alpha4beta7 is associated with enhanced migration to the Chlamydia-infected murine genital mucosa in vivo

The CD4 T helper cell type 1 (Th1) response is essential for the resolution of chlamydial genital infection in mice. However, not all Th1 clones are equally protective in eradicating the infection. Since oral immunization regimens produce protective immunity, we evaluated the role of the mucosa-associated homing receptor, alpha4beta7, in trafficking to the genital mucosa. Using a panel of CD4, Th1 cell lines and clones, we compared the lymphocyte homing patterns of a Chlamydia-specific, protective clone (P-MoPn), a nonprotective clone (N-MoPn), and a keyhole limpet hemocyanin (KLH)-specific cell line (KLH-1). T cells were labeled with the fluorescent dye PKH-26, adoptively transferred into Chlamydia-infected mice, and monitored at different time points throughout the course of a genital infection. We found that clones P-MoPn and N-MoPn migrated to similar extents to the genital tract and in significantly greater numbers than the KLH-specific T-cell line. Both clones and the KLH-1 line expressed similar levels of the adhesion molecules alpha4, beta1, CD44, and CD11a. However, clones P-MoPn and N-MoPn expressed higher levels of the mucosal homing receptor, alpha4beta7. Also, clones P-MoPn and N-MoPn but not the KLH-1 line migrated to the mesenteric lymph node, suggesting a mucosal recirculation pattern. Moreover, blocking alpha4beta7 adhesion interaction in vivo significantly reduced the recruitment of P-MoPn but not KLH-1 to the genital tract. These findings show that the mucosal homing receptor alpha4beta7 is utilized by a subset of CD4 cells during migration to the Chlamydia-infected genital tract.

Kinetics of in vivo homing and recruitment into cycle of hematopoietic cells are organ-specific but CD44-independent

In this study, we investigated the homing and initiation of division of fluorescently labelled adult mouse bone marrow cells after their intravenous injection into lethally irradiated congenic mice. After 2 h, only 3% of the transplanted cells remained in the blood, and approximately 35% could be retrieved from the marrow, liver and spleen in approximately equal numbers. Subsequently, the proportion of injected cells found in blood, liver and spleen decreased further, but increased slightly (to approximately 17%) in the marrow. Homing of progenitors followed a similar pattern. At 22 h post transplant, almost half of the injected cells in the blood, liver and spleen had completed a first mitosis; although these did not include progenitors with in vitro clonogenic ability. At the same time, >90% of the injected cells recovered from the marrow had not yet divided. Parallel studies with CD44-/- mice showed these to contain a numerically and functionally normal stem cell population whose homing and activation in either CD44+/+ or CD44-/- hosts appeared unaltered. These results indicate homing mechanisms that favor more stable retention of transplanted marrow cells in the marrow of the recipient, more rapid activation of some of those cells that home to other sites, and a lack of change in either of these responses when either the transplanted or the recipient cells do not express CD44.

Murine model of interstitial cytomegalovirus pneumonia in syngeneic bone marrow transplantation: persistence of protective pulmonary CD8-T-cell infiltrates after clearance of acute infection

Interstitial pneumonia (IP) is a severe organ manifestation of cytomegalovirus (CMV) disease in the immunocompromised host, in particular in recipients of bone marrow transplantation (BMT). Diagnostic criteria for the definition of CMV-IP include clinical evidence of pneumonia together with CMV detected in bronchoalveolar lavage or lung biopsy. We have used the model of syngeneic BMT and simultaneous infection of BALB/c mice with murine CMV for studying the pathogenesis of CMV-IP by controlled longitudinal analysis. A disseminated cytopathic infection of the lungs with fatal outcome was observed only when reconstituting CD8 T cells were depleted. Neither CD8 nor CD4 T cells mediated an immunopathogenesis of acute CMV-IP. By contrast, after efficient hematolymphopoietic reconstitution, viral replication in the lungs was moderate and focal. The histopathological picture was dominated by preferential infiltration of CD8 T cells confining viral replication to inflammatory foci. Notably, after clearance of acute infection, CD62L(lo) and CD62L(hi) subsets of CD44(+) memory CD8 T cells were found to persist in lung tissue. One can thus operationally distinguish an early CMV-positive IP (phase 1) and a late CMV-negative IP (phase 2). According to the definition, phase 2 histopathology would not be diagnosed as a CMV-IP and could instead be misinterpreted as a CMV-induced immunopathology. We document here that phase 1 as well as phase 2 pulmonary CD8 T cells are capable of exerting effector functions and are effectual in protecting against productive infection. We propose that antiviral "stand-by" memory-effector T cells persist in the lungs to prevent virus recurrence from latency.

Significance of VLA-4-VCAM-1 interaction and CD44 for transendothelial invasion in a bone marrow metastatic myeloma model

In previous work, we established the B9/BM1 syngeneic murine bone marrow metastasis model. Interleukin (IL)-6-dependent. IL-1-producing B9/BM1 cells, which colonize the vertebral and femoral marrow after i.v. injection, show great similarity in cell surface phenotype to human myeloma cells, especially the expression of 3 adhesion molecules, CD44, VLA-4 and ICAM-1. Here we investigated the function of these adhesion molecules by binding and transendothelial invasion assays using a newly established bone marrow-derived endothelial cell line (BMEC). A combination of monoclonal antibodies against CD44 and VLA-4 significantly inhibited the adherence of B9/BM1 cells to BMEC and anti-CD44 mAb especially blocked B9/BM1 transendothelial invasion of unstimulated BMEC cells. Results of additional experiments, in which the cells were treated with anti-CD44 and hyaluronidase, demonstrated that the interaction of CD44 molecules on B9/BM1 cells with hyaluronan on BMEC cells was a critical factor in both adhesion and transendothelial invasion in this model. However, stimulation of BMEC with TNFalpha resulted in increased invasion by B9/BM1 cells, which was completely suppressed by anti-VCAM-1 mAb, implicating a significant role of this adhesion molecule in this process during inflammation.

Induction of interactions between CD44 and hyaluronic acid by a short exposure of human T cells to diverse pro-inflammatory mediators

Migration of T cells into extravascular sites of inflammation is mediated by cell-cell and cell-matrix adhesion receptors, including the hyaluronan-binding glycoprotein, CD44. The biochemical nature of CD44 variants and the ligand specificity, function and the regulation of activation of CD44 expressed on various cell types have been extensively studied. However, little is still known about the short-term influence of cytokines and chemokines on the activation of CD44 on human T cells. Therefore, we studied the role of inflammatory mediators in regulating the adhesion of T cells from human peripheral blood to immobilized hyaluronan under static or shear stress conditions. We found that the CD44-dependent adhesion, under static and shear stress (i.e. relative gradual resistance to flow of 150 and 1500 s-1) conditions, of T cells to hyaluronan requires a T-cell activation of 2-3 hr and is regulated by the cross-linking of CD3, cytokines (e.g. interleukin-2 and tumour necrosis factor-alpha), and chemokines (e.g. MIP-1beta, interleukin-8, and RANTES). This T-cell adhesion was manifested by polarization, spreading and co-localization of cell surface CD44 with a rearranged actin cytoskeleton in hyaluronan-bound T cells. Thus, cytokines and chemokines present in the vicinities of blood vessel walls or present intravascularly in tissues where immune reactions take place, can rapidly activate the CD44 molecules expressed on T cells.

Abrogation of experimental colitis correlates with increased apoptosis in mice deficient for CD44 variant exon 7 (CD44v7)

Experimental colitis in mice is characterized by infiltration of activated T helper (Th) cells and macrophages into the lamina propria. Particularly, these cells expressed CD44 variant exon 7 (CD44v7)-containing isoforms. Upregulation of CD44v7 isoforms was induced by CD40 ligation, an inflammation-driving interaction between activated Th cells and macrophages. To define the role of CD44v7 in colitis, mice bearing a targeted deletion for exon v7 were generated. In trinitrobenzene sulfonic acid-induced colitis, wild-type mice developed severe signs of persistent inflammation. Mice lacking CD44v7 initially showed unspecific inflammation, then recovered completely. The pathogenic origin was shown to reside in bone marrow-derived CD44v7(+) cells, because adoptive transfer experiments demonstrated an absolute requirement for CD44v7 on hematopoietic cells for maintenance of colitis. Interleukin (IL)-10-deficient mice, which develop a chronic Th1-driven enterocolitis, were crossbred with CD44v6/v7 null mice. In IL-10 x CD44v6/v7 double deficient mice, intestinal inflammation developed only weakly and at an older age. Analysis of cell death in the inflamed lesions revealed that mononuclear cells in the CD44v7 null infiltrates had higher rates of apoptosis than those from wild-type mice. Thus, the region encoded by CD44v7 appears to be essential for survival of effector lymphocytes, resulting in persistence of inflammation.

Lymphocyte migration through monolayers of endothelial cell lines involves VCAM-1 signaling via endothelial cell NADPH oxidase

Lymphocytes migrate from the blood across endothelial cells to reach foreign substances sequestered in peripheral lymphoid organs and inflammatory sites. To study intracellular signaling in endothelial cells during lymphocyte migration, we used murine endothelial cell lines that promote lymphocyte migration and constitutively express VCAM-1. The maximum rate of resting splenic lymphocyte migration across monolayers of the endothelial cells occurred at 0-24 h. This migration was inhibited by anti-VCAM-1 or anti-alpha4 integrin, suggesting that VCAM-1 adhesion was required for migration. To determine whether signals within the endothelial cells were required for migration, irreversible inhibitors of signal transduction molecules were used to pretreat the endothelial cell lines. Inhibitors of NADPH oxidase activity (diphenyleneiodonium and apocynin) blocked migration >65% without affecting adhesion. Because NADPH oxidase catalyzes the production of reactive oxygen species (ROS), we examined whether ROS were required for migration. Scavengers of ROS inhibited migration without affecting adhesion. Furthermore, VCAM-1 ligand binding stimulated NADPH oxidase-dependent production of ROS by the endothelial cells lines and primary endothelial cell cultures. Finally, VCAM-1 ligand binding induced an apocynin-inhibitable actin restructuring in the endothelial cell lines at the location of the lymphocyte or anti-VCAM-1-coated bead, suggesting that an NADPH oxidase-dependent endothelial cell shape change was required for lymphocyte migration. In summary, VCAM-1 signaled the activation of endothelial cell NADPH oxidase, which was required for lymphocyte migration. This suggests that endothelial cells are not only a scaffold for lymphocyte adhesion, but play an active role in promoting lymphocyte migration.

Hyaluronan anchoring and regulation on the surface of vascular endothelial cells is mediated through the functionally active form of CD44

CD44 on lymphocytes binding to its carbohydrate ligand hyaluronan can mediate primary adhesion (rolling interactions) of lymphocytes on vascular endothelial cells. This adhesion pathway is utilized in the extravasation of activated T cells from the blood into sites of inflammation and therefore influences patterns of lymphocyte homing and inflammation. Hyaluronan is a glycosaminoglycan found in the extracellular matrix and is involved in a number of biological processes. We have shown that the expression of hyaluronan on the surface of endothelial cells is inducible by proinflammatory cytokines. However, the manner through which hyaluronan is anchored to the endothelial cell surface so that it can resist shear forces and the mechanism of the regulation of the level of hyaluronan on the cell surface has not been investigated. In order to characterize potential hyaluronan receptors on endothelial cells, we performed analyses of cell surface staining by flow cytometry on intact endothelial cells and ligand blotting assays using membrane fractions. Hyaluronan binding activity was detected as a major species corresponding to the size of CD44, and this was confirmed to be the same by Western blotting and immunoprecipitation. Moreover, alterations in the surface level of hyaluronan after tumor necrosis factor-alpha stimulation is regulated primarily by changes in the cell surface levels of the hyaluronan-binding form of CD44. In laminar flow assays, lymphoid cells specifically roll on hyaluronan anchored by purified CD44 coated on glass tubes, indicating that the avidity of the endothelial CD44/hyaluronan interaction is sufficient to support rolling adhesions under conditions mimicking physiologic shear forces. Together these studies show that CD44 serves to anchor hyaluronan on endothelial cell surfaces, that activation of CD44 is a major regulator of endothelial surface hyaluronan expression, and that the non-covalent interaction between CD44 and hyaluronan is sufficient to provide resistance to shear under physiologic conditions and thereby support the initial steps of lymphocyte extravasation.

Red blood cell surface adhesion molecules: their possible roles in normal human physiology and disease

Human erythrocytes express a relatively large number of known adhesion receptors, despite the fact that red blood cells (RBCs) are generally considered to be nonadhesive for endothelial cell surfaces. Some of these adhesion receptors are expressed by many other tissues, while others have more limited tissue distribution. Some adhesion receptors, including CD36 and VLA-4, are only expressed by immature erythroid cells, while others are present on mature erythrocytes. The structure and function of these proteins is reviewed here. LW, CD36, CD58, and CD147 have been shown in other tissues to mediate cell-cell interaction. Other receptors, such as CD44, VLA-4, and B-CAM/LU, can mediate adhesion to components of extracellular matrix. In addition, their roles in normal erythropolesis, as well as in the pathophysiology of human disease, are summarized. The most convincing evidence for a pathophysiologic role for any of these receptors on erythrocytes comes from studies of cells from patients homozygous for hemoglobin S, as RBC adhesion is thought to contribute to vaso-occlusion. Thus, receptors such as B-CAM/LU may become targets for future therapy aimed at preventing or ameliorating this thrombotic process.

Cell adhesion receptors in lymphoma dissemination

Regulated lymphocyte trafficking is essential for the control and integration of systemic immune responses. This homing process disperses the immunologic repertoire, guides lymphocyte subsets to the specialized microenvironments that control their differentiation and survival, and targets immune effector cells to sites of antigenic insult. This review discusses data indicating that the adhesion receptors regulating the trafficking of normal lymphocytes are also expressed and functionally active in their malignant counterparts, the non-Hodgkin lymphomas. These “homing receptors” appear to mediate the highly tissue-specific dissemination of specific lymphoma subtypes, such as lymphomas of the mucosa-associated lymphoid tissues and lymphomas of the skin. Furthermore, as a result of their capability to enhance lymphoma dissemination and to transduce signals into the cell, promoting cell growth and survival, adhesion receptors may contribute to lymphoma aggressiveness. Taken together, the data offer a framework for understanding the dissemination routes of non-Hodgkin lymphomas and suggest that adhesion receptors, specifically those of the CD44 family, may present useful tools to predict prognosis in patients with lymphomas.

Mediation of the immunomodulatory effect of beta-estradiol on inflammatory responses by inhibition of recruitment and activation of inflammatory cells and their gene expression of TNF-alpha and IFN-gamma

BACKGROUND

Estrogen has long been reported to show immunomodulatory effects on immune responses, yet, its specific anti-inflammatory mechanism is not clear.

METHODS

In this study, we analyzed the effects of beta-estradiol (E2), at its contraceptive dose, on both T cell-independent and T cell-dependent inflammations, and the associated immune mechanism, in female mice. The T cell-independent inflammation was locally induced either with an intradermal injection of olive oil in the footpad, or by an intraperitoneal injection of proteose peptone (PP). The T cell-dependent inflammation was induced by an intraperitoneal injection of the purified protein derivatives (PPD).

RESULTS

While E2 inhibited olive oil-induced inflammation as monitored by the decrease in footpad swelling, it did not affect the gene expression of monocyte chemoattractant protein-1 and IL-6 by cells at the inflammatory locus. E2 also inhibited PP-induced inflammation as monitored by the decrease in the number of inflammatory peritoneal exudate cells (PEC) coinciding with a marked decrease in the number of macrophages and granulocytes (Gr. 1+). While E2 did not affect the gene expression of monocyte chemoattractant protein-1 and IL-6 by PP-elicited PEC, it decreased both gene expression and production of TNF-alpha. E2 also decreased the number of cells expressing the lymphocyte function-activated protein-1 in PP-elicited PEC, but not for CD62L. In purified protein derivative-induced T cell-dependent inflammation, E2 decreased the total cellularity of PEC and the relative numbers of CD3+ and CD4+ T cells, and the number of cells expressing the lymphocyte activation markers CD40, CD44, CD69 and IL-2Ralpha in PEC. Furthermore, while E2 did not affect the gene expression of the early T lymphocyte activation protein-1 by PEC, it decreased the gene expression of INF-gamma.

CONCLUSION

Collectively, the results suggest that E2-mediated inhibition of inflammatory responses may be due to a combination of suppression of homing and activation of inflammatory cells and their production of TNF-alpha and IFN-gamma.

The CD44-initiated pathway of T-cell extravasation uses VLA-4 but not LFA-1 for firm adhesion

Leukocytes extravasate from the blood in response to physiologic or pathologic demands by means of complementary ligand interactions between leukocytes and endothelial cells. The multistep model of leukocyte extravasation involves an initial transient interaction ("rolling" adhesion), followed by secondary (firm) adhesion. We recently showed that binding of CD44 on activated T lymphocytes to endothelial hyaluronan (HA) mediates a primary adhesive interaction under shear stress, permitting extravasation at sites of inflammation. The mechanism for subsequent firm adhesion has not been elucidated. Here we demonstrate that the integrin VLA-4 is used in secondary adhesion after CD44-mediated primary adhesion of human and mouse T cells in vitro, and by mouse T cells in an in vivo model. We show that clonal cell lines and polyclonally activated normal T cells roll under physiologic shear forces on hyaluronate and require VCAM-1, but not ICAM-1, as ligand for subsequent firm adhesion. This firm adhesion is also VLA-4 dependent, as shown by antibody inhibition. Moreover, in vivo short-term homing experiments in a model dependent on CD44 and HA demonstrate that superantigen-activated T cells require VLA-4, but not LFA-1, for entry into an inflamed peritoneal site. Thus, extravasation of activated T cells initiated by CD44 binding to HA depends upon VLA-4-mediated firm adhesion, which may explain the frequent association of these adhesion receptors with diverse chronic inflammatory processes.

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.

CD4(+) T-cell subsets that mediate immunological memory to Mycobacterium tuberculosis infection in mice

We have studied CD4(+) T cells that mediate immunological memory to an intravenous infection with Mycobacterium tuberculosis. The studies were conducted with a mouse model of memory immunity in which mice are rendered immune by a primary infection followed by antibiotic treatment and rest. Shortly after reinfection, tuberculosis-specific memory cells were recruited from the recirculating pool, leading to rapidly increasing precursor frequencies in the liver and a simultaneous decrease in the blood. A small subset of the infiltrating T cells was rapidly activated (<20 h) and expressed high levels of intracellular gamma interferon and the T-cell activation markers CD69 and CD25. These memory effector T cells expressed intermediate levels of CD45RB and were heterogeneous with regard to the L-selectin and CD44 markers. By adoptive transfer into nude mice, the highest level of resistance to a challenge with M. tuberculosis was mediated by CD45RB(high), L-selectin(high), CD44(low) cells. Taken together, these two lines of evidence support an important role for memory cells which have reverted to a naive phenotype in the long-term protection against M. tuberculosis.

Induction of resistance to diabetes in non-obese diabetic mice by targeting CD44 with a specific monoclonal antibody

Inflammatory destruction of insulin-producing beta cells in the pancreatic islets is the hallmark of insulin-dependent diabetes mellitus, a spontaneous autoimmune disease of non-obese diabetic mice resembling human juvenile (type I) diabetes. Histochemical analysis of diabetic pancreata revealed that mononuclear cells infiltrating the islets and causing autoimmune insulitis, as well as local islet cells, express the CD44 receptor; hyaluronic acid, the principal ligand of CD44, is detected in the islet periphery and islet endothelium. Injection of anti-CD44 mAb 1 hr before cell transfer of diabetogenic splenocytes and subsequently on alternate days for 4 weeks induced considerable resistance to diabetes in recipient mice, reflected by reduced insulitis. Contact sensitivity to oxazolone was not influenced by this treatment. A similar antidiabetic effect was observed even when the anti-CD44 mAb administration was initiated at the time of disease onset: i.e., 4-7 weeks after cell transfer. Administration of the enzyme hyaluronidase also induced appreciable resistance to insulin-dependent diabetes mellitus, suggesting that the CD44-hyaluronic acid interaction is involved in the development of the disease. These findings demonstrate that CD44-positive inflammatory cells may be a potential therapeutic target in insulin-dependent diabetes.

The CD44 variant isoforms CD44v6 and CD44v7 are expressed by distinct leukocyte subpopulations and exert non-overlapping functional activities

We have described recently that anti-CD44s, anti-CD44v6 and anti-CD44v7 interfere with delayed-type hypersensitivity (DTH) reactions. Yet, TNBS-induced colitis can be cured only by anti-CD44v7. To clarify the mechanisms underlying the divergent functional activities of CD44v6 and CD44v7 we explored their contribution to lymphocyte activation in vivo and in vitro. CD44v6 and CD44v7 are distinctly expressed on subpopulations of activated lymphocytes. Expression of CD44v6 is mainly restricted to T cell blasts. CD44v7 has been detected on CD4(+) cells, B cells and monocytes. Mitogenic and antigenic stimulation of lymphocytes in vitro was impaired in the presence of anti-CD44v6 and anti-CD44v7. Accordingly, anti-CD44v6 and anti-CD44v7 mitigated the DTH reaction in 2,4-dinitro-1-fluorobenzene-sensitized and challenged mice. However, the seemingly similar effects of CD44v6- and CD44v7-specific antibodies resulted from different activities. Anti-CD44v6 treatment led to a down-regulation of IL-2 and IFN-gamma production predominantly by CD8(+) cells. In anti-CD44v7-treated mice expression of IL-12 was decreased. Elevated levels of IL-10 accompanied this reduction. The latter resulted from an anti-CD44v7-mediated blockade of interactions between CD4(+) cells and monocytes as well as an active triggering of B cells. Thus, anti-CD44v6 and anti-CD44v7 interfere with lymphocyte activation at very specific points. CD44v6 functions predominantly at the T cell level. CD44v7 influences production of proinflammatory cytokines by B cells as well as an interaction between CD4(+) cells and antigen-presenting cells. As CD44 isoforms do not differ in their intracytoplasmatic tail, the distinct activities must result from expression on different leukocyte subsets and interactions with distinct ligands.

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.

A transgenic mouse model to analyze CD8(+) effector T cell differentiation in vivo

Antigen-specific effector T cells are prerequisite to immune protection, but because of the lack of effector cell-specific markers, their generation and differentiation has been difficult to study. We report that effector cells are highly enriched in a T cell subset that can be specifically identified in transgenic (T-GFP) mice expressing green fluorescent protein (GFP) under control of the murine CD4 promoter and proximal enhancer. Consistent with previous studies of these transcriptional control elements, GFP was strongly and specifically expressed in nearly all resting and short-term activated CD4(+) and CD8(+) T cells. However, when T-GFP mice were challenged with vaccinia virus, allogeneic tumor cells, or staphylococcal enterotoxin A, the cytotoxic and IFN-gamma-producing T cells lost GFP expression. Upon T cell receptor (TCR) ligation by alphaCD3, sorted GFP(+) cells fluxed calcium and proliferated vigorously. In contrast, GFP(-) effector cells showed a diminished calcium flux and did not proliferate. Instead, they underwent apoptosis unless supplied with exogenous IL-2. By reverse transcription-PCR analysis, the GFP(-) cells up-regulated the pro-apoptotic molecule, Fas-L, and down-regulated gene expression of the proximal TCR signaling molecule, CD3zeta, and c-jun, a component of the AP-1 transcription factor. Thus, differential regulation of TCR signaling may explain the divergent responses of naïve and effector T cells to antigen stimulation.

Naive, Effector, and Memory CD8 T Cells in Protection Against Pulmonary Influenza Virus Infection: Homing Properties Rather Than Initial Frequencies Are Crucial

The goal of adoptive immunotherapy is to target a high number of persisting effector cells to the site of a virus infection or tumor. In this study, we compared the protective value of hemagglutinin peptide-specific CD8 T cells generated from the clone-4 TCR-transgenic mice, defined by different stages of their differentiation, against lethal pulmonary influenza infection. We show that the adoptive transfer of high numbers of Ag-specific unprimed, naive CD8 T cells failed to clear the pulmonary virus titer and to promote host survival. The same numbers of in vitro generated primary Ag-specific Tc1 effector cells, producing high amounts of IFN-γ, or resting Tc1 memory cells, generated from these effectors, were protective. Highly activated CD62Llow Tc1 effectors accumulated in the lung with rapid kinetics and most efficiently reduced the pulmonary viral titer early during infection. The resting CD62Lhigh naive and memory populations first increased in cell numbers in the draining lymph nodes. Subsequently, memory cells accumulated more rapidly and to a greater extent in the lung lavage as compared with naive cells. Thus, effector cells are most effective against a localized virus infection, which correlates with their ability to rapidly distribute at the infected tissue site. The finding that similar numbers of naive Ag-specific CD8 T cells are not protective supports the view that qualitative differences between the two resting populations, the naive and the memory population, may play a major role in their protective value against disease.

Signal transduction via CD44: role of plasma membrane microdomains

CD44 is the principal cell surface receptor for extracellular matrix glycosaminoglycan hyaluronan. CD44-hyaluronan mediated cell adhesion is important in several pathophysiological processes such as inflammation and metastatic spread of cancer cells. It has been recently recognized that CD44 also functions as a signaling receptor in a variety of cell types. Cell stimulation by monoclonal anti-CD44 antibody or natural CD44 ligands activate several signaling pathways that culminate in cell proliferation, cytokine secretion, chemokine gene expression and cytolytic effector functions. One of the earliest signaling events following stimulation via CD44 is tyrosine phosphorylation of intracellular proteins substrates, and CD44 mediated cellular activation could be abolished by protein tyrosine kinase (PTK) inhibitors. The Src-family non-receptor PTKs such as Lck, Fyn, Lyn and Hck were shown to be coupled to CD44 via sphingolipid-rich microdomains (lipid rafts) of the plasma membrane. Studies on T cell receptor and IgE receptor mediated signaling in lymphocytes and mast cells have consolidated the notion that microdomains consist of signaling platforms where components of multiple signaling pathways are assembled. Co-isolation of CD44 with microdomains strongly suggests that CD44 generates cellular activation signals utilizing the signaling machinery of the plasma membrane microdomains.

Mononuclear leukocytes preferentially bind via CD44 to hyaluronan on human intestinal mucosal smooth muscle cells after virus infection or treatment with poly(I.C)

Pathological changes in inflammatory bowel disease include an increase in intestinal mucosal mononuclear leukocytes and hyperplasia of the muscularis mucosae smooth muscle cells (M-SMCs). Because virus infections have correlated with disease flare, we tested the response of cultured M-SMCs to respiratory syncytial virus, measles virus, and the viral analogue, poly(I.C). Adhesion of U937 cells and peripheral blood mononuclear cells was used to measure the leukocyte-interactive potential of M-SMCs. Untreated M-SMCs, only minimally adhesive for leukocytes, bound U937 cells after treatment with respiratory syncytial virus or measles virus. Mononuclear leukocytes also bound to poly(I.C)-treated M-SMCs. Although both vascular cell adhesion molecule-1 mRNA and protein increased 3-4-fold in poly(I.C)-treated M-SMC cultures, U937 cell adhesion was not blocked by an anti-vascular cell adhesion molecule-1 monoclonal antibody. However, hyaluronidase digestion of poly(I.C)- or virus-treated M-SMCs dramatically reduced leukocyte adhesion ( approximately 75%). Fluorophore-assisted carbohydrate electrophoresis demonstrated a approximately 3-fold increase in surface-bound hyaluronan on poly(I.C)-treated M-SMCs compared with untreated controls. In addition, pretreatment of mononuclear cells with a blocking anti-CD44 antibody, greatly decreased adhesion to poly(I.C)-treated M-SMCs. Recognition of this virus-induced hyaluronan/CD44 mechanism of mesenchymal cell/leukocyte interaction introduces a new avenue in the research of gut inflammation.

Roles of Integrins and CD44 on the Adhesion and Migration of Fetal Liver Cells to the Fetal Thymus

Adhesion and migration of mouse fetal liver (FL) cells to the thymus were investigated using cells from green fluorescent protein transgenic (GFP+) mice. FL cells from GFP+ embryos at 12 gestational days (E12) of mice were incubated with 2′-deoxyguanosine-treated fetal thymus lobe (from E14) by thymic repopulation (hanging drop) culture methods. GFP+ cells were observed in the thymus lobe at the end of the repopulation culture period. A large part of the infiltrated cells expressed CD44 until day 2 of culture on a permeable membrane, then lost the expression. CD25 expression was observed from day 1 to day 4. Around day 8, GFP+ cells became both CD4+ and CD8+. The results support the early observation of the sequential expression of CD44, CD25, and CD4/8 during the early stages of thymocyte development. When anti-CD44 mAb was added at the beginning of the repopulation culture period, GFP+ FL cells adhered to the surface of the thymus lobe but did not migrate into the thymus. Pretreatment of the thymus with hyaluronidase or hyaluronate produced results similar to the results of anti-CD44 treatment. On the other hand, the addition of anti-integrin α4 mAb inhibited adhesion to the thymus, and almost no GFP+ cells were seen on the surface of the thymus lobe. The data suggest that integrin α4 and CD44 play different roles, i.e., integrin α4 is required for the adhesion of FL cells to the thymus lobe and CD44 is required for the migration of the cells into the thymus.

CD44 involvement in experimental collagen-induced arthritis (CIA)

CD44 is a pro-inflammatory cell surface molecule that supports cell migration and cell lodgment in target organs. Therefore, CD44 targeting with specific monoclonal antibodies (mAbs) should be useful for the inhibition of collagen-induced arthritis (CIA) as well as other autoimmune diseases that are dependent on inflammatory cells. In the present paper, we confirm and expand previous reports showing the anti-arthritogenic effect of anti-CD44 mAbs directed against constant epitopes of the CD44 receptor. We demonstrate that such anti-CD44 mAbs can induce resistance to CIA after disease onset. Even accelerated disease developed after two injections of type II collagen was markedly inhibited by IM7.8.1 anti-CD44 mAb. Although KM81 anti-CD44 mAb is a less efficient anti-arthritogenic reagent than IM7.8.1, its Fab' fragments partially inhibit CIA. This finding implies that the antibody blocks CD44 function rather than modulating CD44 cell surface expression or mediating Fc-dependent activities. Histopathological analysis revealed that the anti-CD44 mAb markedly reduces the synovial inflammatory cellular response and the consequent damage to the joint. As CD44 is an alternatively spliced multistructural molecule, similar anti-arthritogenic effects may be achieved by mAbs directed against CD44 isoforms expressed on the pathological cells in question, but not on normal cells, thus leaving the physiological functions intact.

CD44 cell adhesion molecules

The CD44 proteins form a ubiquitously expressed family of cell surface adhesion molecules involved in cell-cell and cell-matrix interactions. The multiple protein isoforms are encoded by a single gene by alternative splicing and are further modified by a range of post-translational modifications. CD44 proteins are single chain molecules comprising an N-terminal extracellular domain, a membrane proximal region, a transmembrane domain, and a cytoplasmic tail. The CD44 gene has only been detected in higher organisms and the amino acid sequence of most of the molecule is highly conserved between mammalian species. The principal ligand of CD44 is hyaluronic acid, an integral component of the extracellular matrix. Other CD44 ligands include osteopontin, serglycin, collagens, fibronectin, and laminin. The major physiological role of CD44 is to maintain organ and tissue structure via cell-cell and cell-matrix adhesion, but certain variant isoforms can also mediate lymphocyte activation and homing, and the presentation of chemical factors and hormones. Increased interest has been directed at the characterisation of this molecule since it was observed that expression of multiple CD44 isoforms is greatly upregulated in neoplasia. CD44, particularly its variants, may be useful as a diagnostic or prognostic marker of malignancy and, in at least some human cancers, it may be a potential target for cancer therapy. This review describes the structure of the CD44 gene and discusses some of its roles in physiological and pathological processes.

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.

Interferon-gamma inhibits CD44-hyaluronan interactions in normal human B lymphocytes

The interaction of CD44 with its ligand hyaluronan (HA) plays a vital role in lymphopoiesis, lymphocyte homing, T cell activation, and metastasis. This study addresses the effect of cytokines involved in B cell growth on CD44-HA interactions in normal human B cells. Activation of B lymphocytes with LPS, pokeweed mitogen, or anti-IgM antibodies with or without IL-2 or IL-4 failed to induce HA adhesion. Stimulation of B cells with the phorbol ester PMA, however, induced strong HA recognition, which was inhibited by IFN-gamma and to some extent by IL-4. Investigation of the potential molecular mechanism involved revealed that PMA-induced HA adhesion correlated with enhanced expression of CD44-H- and V6-containing isoforms, as determined by flow cytometry, and the differential induction of V4- and V5-containing isoforms, as determined by reverse transcriptase-based polymerase chain reaction analysis. The inhibition of PMA-induced adhesion by IFN-gamma and IL-4 correlated with the downregulation of CD44 H expression and altered usage of exons V4 and V5. However, changes in the electrophoretic mobility of CD44 proteins, as a measure of posttranslational modifications, were not detected in response to PMA and IFN-gamma or PMA and IL-4. These results suggest that the inhibition of PMA-induced HA adhesion by IFN-gamma and IL-4 may influence B cell migration through their ability to downregulate CD44-HA interactions.

Interleukin 15 induces endothelial hyaluronan expression in vitro and promotes activated T cell extravasation through a CD44-dependent pathway in vivo

T cell recruitment to extralymphoid tissues is fundamental to the initiation and perpetuation of the inflammatory state during immune and autoimmune responses. Interleukin (IL)-15 is a proinflammatory cytokine whose described functions largely overlap with those of IL-2. The latter is attributable in large part to its binding of the heterotrimeric receptor that contains the beta and gamma chains of the IL-2R in combination with an unique IL-15R alpha chain. However, unlike IL-2, IL-15 and its receptor have a wide tissue and cell type distribution, including endothelial cells. Here, we examine the effect of IL-15 on hyaluronan expression by endothelial cells, and investigate its role in vivo in promoting the extravasation of antigen-activated T cells through a CD44-dependent pathway. The expression of hyaluronan on primary endothelial cells and microvascular endothelial cell lines is induced by IL-15, whereas IL-2 has no such activity. Moreover, intraperitoneal administration of IL-15 or TNF-alpha in the absence of other exogenous proinflammatory stimuli allows the extravasation of superantigen-stimulated T cells into this site in vivo in a CD44-dependent manner. T cell recruitment induced by IL-15 requires expression of an intact IL-2R beta chain, indicating that IL-15 operates in this context through the traditional IL-15R. The results suggest that IL-15 can regulate endothelial cell function and thereby enables a CD44-initiated adhesion pathway that facilitates entry of activated T lymphocytes into inflammatory sites. They further demonstrate a novel role for IL-15 (distinct from any of IL-2) in regulating microvascular endothelial cell adhesive function help to understand the role of IL-15R expression on endothelium, and further support a central position for this cytokine in orchestrating multiple sequential aspects of T cell effector function and therefore chronic inflammatory processes.

Mitigation of delayed-type hypersensitivity reactions by a CD44 variant isoform v3-specific antibody: blockade of leukocyte egress

In allergic alterations of human skin the majority of infiltrated leukocytes express CD44v3, but no other CD44 variant isoform. Vessel endothelium, too, is brightly stained with a CD44v3-specific antibody. Being concerned about therapeutic intervention, it became of importance to define whether expression of CD44v3 on the endothelial cells or on the leukocytes or on both is of functional importance. As expression of CD44v3 in the mouse on activated endothelium and on subpopulations of activated CD4+ cells, B cells and monocytes was similar to the expression in the human, we answered the question in a mouse delayed-type hypersensitivity model. The effect of anti-CD44v3 was compared with the effect of anti-CD44s and anti-CD44v10, both known to suppress delayed-type hypersensitivity reactions. Anti-CD44v3 mitigated the delayed-type hypersensitivity reaction in dinitrofluorobenzene sensitized and challenged mice comparable with anti-CD44s and anti-CD44v10. The seemingly similar effects of CD44 isoform-specific antibodies, however, resulted from a distinct modulation of response. Anti-CD44s mainly suppressed T cell activation and interleukin-2 as well as interferon-gamma expression. Anti-CD44v10 inhibited the activation of monocytes in the draining lymph nodes and in the infiltrate, which led to a strong reduction in the proinflammatory cytokines tumor necrosis factor-alpha and interleukin-12 and in edema formation. Anti-CD44v3 had only a weak effect on cytokine expression by isolated subpopulations of leukocytes, but suppressed cytokine production by helper T cells when cocultured with antigen-presenting cells, i.e., blocked an interaction between antigen-presenting cells and helper T cells. The dominating effect of anti-CD44v3, however, relied on a blockade of leukocyte extravasation. As leukocytes transferred into dinitrofluorobenzene sensitized, anti-CD44v3-treated and lethally irradiated mice did not infiltrate the sensitized skin, anti-CD44v3 most likely prevented leukocyte extravasation by blocking CD44v3 on endothelial cells.

Antibodies to CD44 and integrin alpha4, but not L-selectin, prevent central nervous system inflammation and experimental encephalomyelitis by blocking secondary leukocyte recruitment

The role of various adhesion molecules in lymphocyte homing to the brain and in inflammatory autoimmune disease of the central nervous system (CNS) was examined in mice. Activated T cell lines and clones expressed CD44 and integrin alpha4, but not L-selectin, and entered the CNS independent of their antigen specificity. mAbs directed against CD44 and integrin alpha4 prevented the transfer of experimental autoimmune encephalomyelitis (EAE) by myelin basic protein-specific T cells. T cells preincubated with anti-CD44 or antiintegrin alpha4 were blocked only partially from entering the brain parenchyma. However, both antibodies efficiently prevented CNS inflammation and clinical expression of EAE when injected in vivo. This effect lasted as long as antibodies were administered. Antibodies specific for L-selectin had no effect on homing of encephalitogenic T cells to the brain or development of EAE. Antiintegrin alpha4 and anti-CD44 did not impair the activation and function of encephalitogenic T cells in vitro and did not deplete integrin alpha4- or CD44-positive cells in vivo. These data suggest that, in the absence of leukocyte recruitment, the entry of a reduced number of activated myelin basic protein-reactive T cells in the CNS is not sufficient for the development and expression of EAE. We propose that antibodies to integrin alpha4 and CD44 prevent clinical disease by partially targeting the primary influx of encephalitogenic T cells and by preventing the secondary influx of leukocytes to lesions initiated by the transferred T cells.

Acquisition of selectin binding and peripheral homing properties by CD4(+) and CD8(+) T cells

Different T cell subsets exhibit distinct capacities to migrate into peripheral sites of inflammation, and this may in part reflect differential expression of homing receptors and chemokine receptors. Using an adoptive transfer approach, we examined the ability of functionally distinct subsets of T cells to home to a peripheral inflammatory site. The data directly demonstrate the inability of naive T cells and the ability of effector cells to home to inflamed peritoneum. Furthermore, interleukin (IL)-12 directs the differentiation of either CD4(+) or CD8(+) T cells into effector populations that expresses functional E- and P-selectin ligand and that are preferentially recruited into the inflamed peritoneum compared with T cells differentiated in the presence of IL-4. Recruitment can be blocked by anti-E- and -P-selectin antibodies. The presence of antigen in the peritoneum promotes local proliferation of recruited T cells, and significantly amplifies the Th1 polarization of the lymphocytic infiltrate. Preferential recruitment of Th1 cells into the peritoneum is also seen when cytokine response gene 2 (CRG-2)/interferon gamma-inducible protein 10 (IP-10) is used as the sole inflammatory stimulus. We have also found that P-selectin binds only to antigen-specific T cells in draining lymph nodes after immunization, implying that both antigen- and cytokine-mediated signals are required for expression of functional selectin-ligand.

Characterization of circulating T cells specific for tumor-associated antigens in melanoma patients

We identified circulating CD8+ T-cell populations specific for the tumor-associated antigens (TAAs) MART-1 (27-35) or tyrosinase (368-376) in six of eleven patients with metastatic melanoma using peptide/HLA-A*0201 tetramers. These TAA-specific populations were of two phenotypically distinct types: one, typical for memory/effector T cells; the other, a previously undescribed phenotype expressing both naive and effector cell markers. This latter type represented more than 2% of the total CD8+ T cells in one patient, permitting detailed phenotypic and functional analysis. Although these cells have many of the hallmarks of effector T cells, they were functionally unresponsive, unable to directly lyse melanoma target cells or produce cytokines in response to mitogens. In contrast, CD8+ T cells from the same patient were able to lyse EBV-pulsed target cells and showed robust allogeneic responses. Thus, the clonally expanded TAA-specific population seems to have been selectively rendered anergic in vivo. Peptide stimulation of the TAA-specific T-cell populations in other patients failed to induce substantial upregulation of CD69 expression, indicating that these cells may also have functional defects, leading to blunted activation responses. These data demonstrate that systemic TAA-specific T-cell responses can develop de novo in cancer patients, but that antigen-specific unresponsiveness may explain why such cells are unable to control tumor growth.

The molecular characterization of the fetal stem cell marker AA4

We have identified and characterized the stem cell antigen AA4. This molecule is a type I transmembrane protein whose overall structure suggests a role in cell adhesion. During fetal ontogeny (days 9-14 of development), AA4 is expressed in three major cell types: vascular endothelial cells, aorta-associated hematopoietic clusters, and primitive fetal liver hematopoietic progenitors. In the adult, AA4 is abundant in lung, heart, and whole bone marrow. In the adult hematopoietic compartment, aa4 transcripts are present in bone marrow CD34(-/lo) Lin- Sca-1+ c-Kit+ and CD34hi Lin- Sca-1+ c-Kit+ stem and progenitor cell subsets. Our observations suggest that AA4 plays a role in cell-cell interactions during hematopoietic and vascular development.

Regulation of CD44-hyaluronan interactions in Burkitt's lymphoma and Epstein-Barr virus-transformed lymphoblastoid B cells by PMA and interleukin-4

In this study, we investigated the regulation of CD44-hyaluronan (HA) interactions in a panel of EBV+ Burkitt's lymphoma (BL) and lymphoblastoid B cell lines (B-LCL) generated by in vitro EBV transformation of normal human B cells. The results show that among B cell mitogens, phorbol 12-myristate 13-acetate (PMA) alone induced strong HA recognition in EBV+ BL-30/B95-8 cells. Among the cytokines that affect B cell growth and differentiation, IL-4 alone induced HA recognition in BL-30/B95-8 cells. Attempts to delineate the molecular mechanism for this increased HA adhesion in BL-30/B95-8 cells revealed an enhanced expression of CD44 H, isoforms containing V3, V6, and V9 exons, alterations in the splicing pattern of the V4 exon, and the increased electrophoretic mobility of the CD44 H protein. In contrast, the ability to recognize HA was not observed in B-LCL cells stimulated with either PMA or IL-4, even though these cells respond to IL-4, as observed by upregulation of CD23 expression. The molecular pathways that regulate CD44 expression and CD44-mediated HA binding may be selectively inactivated in B-LCL cells. These results may have implications with respect to the generation and spread of B cell tumors.

Immunomodulatory functions of low-molecular weight hyaluronate in an acute rat renal allograft rejection model

Low molecular weight hyaluronate (LMW-HA) blocks interactions between T lymphocyte CD44 and hyaluronate (HA), a heteropolysaccharide that is expressed on the surface of endothelial cells and ubiquitously in the extracellular matrix. This study was undertaken to assess the ability of LMW-HA to modify the course of experimental acute renal allograft rejection. Lewis (LEW) rats were bilaterally nephrectomized and received an orthotopic, fully MHC-mismatched, Wistar-Furth (WF) kidney transplant. Animals received either no treatment, low doses of cyclosporin A (CsA) on days 0 to 5, LMW-HA on days 0 to 5, or CsA plus LMW-HA on days 0 to 5 after transplantation. With no treatment, CsA monotherapy, or HA monotherapy, animals rejected their allografts at a median of 15, 13, and 7.5 d, respectively (P = NS). In contrast, combined CsA plus LMW-HA therapy prevented acute rejection and significantly prolonged graft survival (P = 0.008) to a median of 49.0 d. CsA/LMW-HA-treated grafts also demonstrated better preservation of renal function at day 30 (serum creatinine level, 1.38+/-0.8 mg/dl), compared with surviving animals treated with CsA alone (2.9+/-0.55 mg/dl, P<0.05). Histologic graft analysis of CsA/LMW-HA-treated animals at day 7 after transplantation showed minimal rejection and leukocyte infiltration, compared with all other groups. Intragraft gene expression analysis, using semiquantitative reverse transcription-PCR, at the same time point showed reductions of CD4, CD8, and interferon-gamma transcript levels in the combined-treatment group. This is the first study demonstrating the immunomodulatory functions of LMW-HA in vivo in the setting of organ transplantation. Defining the exact mechanisms that underlie this immunomodulation may provide the rationale to develop novel strategies for use in clinical transplantation.

Cutting Edge: An Inducible Sialidase Regulates the Hyaluronic Acid Binding Ability of CD44-Bearing Human Monocytes

Previous studies established that variable degrees and types of glycosylation can account for differences in the ability of CD44 to function as a receptor for hyaluronic acid. We have now used neuraminidase treatment to conclude that sialylation negatively regulates CD44 on the human monocytic cell line THP-1 and peripheral blood monocytes. Both of these cell types displayed increased receptor activity after overnight culture with LPS. Of particular interest, the sialidase inhibitor 2-deoxy-2,3-dehydro-N-acetylneuraminic acid completely blocked the LPS induced recognition of hyaluronic acid by THP-1 cells. Furthermore, acquisition of this characteristic paralleled induction of one type of sialidase activity. Monocytes may be capable of enzymaticly remodeling cell surface CD44, altering their ability to interact with the extracellular matrix.

TNFalpha and IL-4 regulation of hyaluronan binding to monocyte CD44 involves posttranslational modification of CD44

Our previous studies have identified TNFalpha as a positive regulator and IL-4 as a negative regulator of human monocyte CD44-HA binding. In order to determine the mechanisms of IL-4- and TNFalpha-mediated regulation of monocyte HA binding, we measured HA binding and CD44 expression on peripheral blood monocytes following monocyte treatment with TNFalpha or IL-4, as well as following monocyte treatment with inhibitors of protein synthesis, N- and O-linked glycosylation, and chondroitin sulfation. IL-4 decreased CD44-HA binding on monocytes initially treated with TNFalpha. Similarly, pretreatment of monocytes with IL-4 prevented subsequent TNFalpha-mediated HA binding. Cycloheximide (protein synthesis inhibitor), tunicamycin (N-linked glycosylation inhibitor), and beta-d-xyloside (chondroitin sulfation inhibitor) all inhibited IL-4-mediated downregulation of TNFalpha-induced monocyte HA binding. Western blot analysis of CD44 from TNFalpha-treated monocytes revealed a 5-10 Mr decrease in the standard isoform of CD44. In contrast, IL-4 treatment of monocytes inhibited CD44-HA binding and reversed the 5- to 10-kDa decrease in monocyte CD44 Mr. Finally, studies with F10.44.2, a CD44 mab that enhances CD44-HA binding, indicated that IL-4 treatment of monocytes not only diminished constitutive HA binding, but also diminished CD44 mab-induced HA binding. Taken together, these data suggested that IL-4-mediated inhibition of TNFalpha-induced monocyte HA binding was dependent not only on protein synthesis, but also on N-linked glycosylation and chondroitin-sulfate modification of either CD44 or, alternatively, another monocyte protein(s) that may regulate the ability of CD44 to bind HA.