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

Monocytic Myeloid-Derived Suppressor Cells Inhibit Myofibroblastic Differentiation in Mesenchymal Stem Cells Through IL-15 Secretion

Background: Accumulating evidence indicates that mesenchymal stem cells (MSCs) are precursors of myofibroblasts, which play a vital role in renal fibrosis. The close interaction between MSCs and other immune cells regulates the development of multiple fibrosis-related diseases. However, the effect of myeloid-derived suppressor cells (MDSCs) on MSCs remains unexplored. Here, we investigated the effect of MDSCs on the myofibroblastic differentiation of MSCs. Methods: MSCs were induced to undergo myofibroblastic differentiation with transforming growth factor beta 1 (TGF-β1). M-MDSCs and G-MDSCs were sorted by flow cytometry. Supernatants derived from MDSCs were administered to cultured bone marrow MSCs (BM-MSCs) undergoing TGF-β1-induced myofibroblastic differentiation. Myofibroblastic differentiation was evaluated by immunostaining. The expression of fibrosis-related genes was determined by quantitative PCR and western blot analysis. In vitro, M-MDSC supernatant or M-MDSC supernatant with interleukin (IL)-15 mAbs was administered following unilateral renal ischemia-reperfusion injury (IRI) to observe the myofibroblast differentiation of renal resident MSCs (RRMSCs) in a murine model. Results: Myofibroblastic differentiation of MSCs was hindered when the cells were treated with MDSC-derived supernatants, especially that from M-MDSCs. The inhibitory effect of M-MDSC supernatant on the myofibroblastic differentiation of MSCs was partially mediated by IL-15-Ras-Erk1/2-Smad2/3 signaling. Treatment with M-MDSC supernatant ameliorated renal fibrosis and myofibroblastic differentiation in RRMSCs through IL-15. Additionally, M-MDSC supernatant increased M-MDSC infiltration in the kidney in a mouse IRI model. M-MDSC supernatant downregulated the adhesion and migration marker CD44 on the cell membrane of MSCs via IL-15. Conclusion: M-MDSC-derived supernatant inhibited the TGF-β1-induced myofibroblastic differentiation of MSCs through IL-15. Our findings shed new light on the effect of MDSCs on myofibroblastic differentiation and adhesion of MSCs, which might provide a new perspective in the development of treatment strategies for renal fibrosis.

Recent advances and prospects of hyaluronan as a multifunctional therapeutic system

Hyaluronan (HA) is a naturally occurring non-sulfated glycosaminoglycan (GAG), cell-surface-associated biopolymer and is the key component of tissue extracellular matrix (ECM). Along with remarkable physicochemical properties, HA also has multifaceted biological effects that include but not limited to ECM organization, immunomodulation, and various cellular processes. Environmental cues such as tissue injury, infection or cancer change downstream signaling functionalities of HA. Unlike native HA, the fragments of HA have diversified effects on inflammation, cancer, fibrosis, angiogenesis and autoimmune response. In this review, we aim to discuss HA as a therapeutic delivery system development process, source, biophysical-chemical properties, and associated biological pathways (especially via cell surface receptors) of native and fragmented HA. We also tried to address an overview of the potential role of HA (native HA vs fragments) in the modulation of inflammation, immune response and various cancer targeting delivery applications. This review will also highlight the HA based therapeutic systems, medical devices and future perspectives of various biomedical applications were discussed in detail.

Astrocytes in multiple sclerosis and experimental autoimmune encephalomyelitis: Star-shaped cells illuminating the darkness of CNS autoimmunity

Neuropathology in the human autoimmune disease multiple sclerosis (MS) is considered to be mediated by autoreactive leukocytes, such as T cells, B cells, and macrophages. However, the inflammation and tissue damage in MS and its animal model experimental autoimmune encephalomyelitis (EAE) is also critically regulated by astrocytes, the most abundant cell population in the central nervous system (CNS). Under physiological conditions, astrocytes are integral to the development and function of the CNS, whereas in CNS autoimmunity, astrocytes influence the pathogenesis, progression, and recovery of the diseases. In this review, we summarize recent advances in astrocytic functions in the context of MS and EAE, which are categorized into two opposite aspects, one being detrimental and the other beneficial. Inhibition of the detrimental functions and/or enhancement of the beneficial functions of astrocytes might be favorable for the treatment of MS.

Glial influences on BBB functions and molecular players in immune cell trafficking

The blood-brain barrier (BBB) constitutes an elaborate structure formed by specialized capillary endothelial cells, which together with pericytes and perivascular glial cells regulates the exchanges between the central nervous system (CNS) and the periphery. Intricate interactions between the different cellular constituents of the BBB are crucial in establishing a functional BBB and maintaining the delicate homeostasis of the CNS microenvironment. In this review, we discuss the role of astrocytes and microglia in inducing and maintaining barrier properties under physiological conditions as well as their involvement during neuroinflammatory pathologies. This article is part of a Special Issue entitled: Neuro Inflammation edited by Helga E. de Vries and Markus Schwaninger.

Regulated Hyaluronan Synthesis by Vascular Cells

Cellular microenvironment plays a critical role in several pathologies including atherosclerosis. Hyaluronan (HA) content often reflects the progression of this disease in promoting vessel thickening and cell migration. HA synthesis is regulated by several factors, including the phosphorylation of HA synthase 2 (HAS2) and other covalent modifications including ubiquitination and O-GlcNAcylation. Substrate availability is important in HA synthesis control. Specific drugs reducing the UDP precursors are able to reduce HA synthesis whereas the hexosamine biosynthetic pathway (HBP) increases the concentration of HA precursor UDP-N-acetylglucosamine (UDP-GlcNAc) leading to an increase of HA synthesis. The flux through the HBP in the regulation of HA biosynthesis in human aortic vascular smooth muscle cells (VSMCs) was reported as a critical aspect. In fact, inhibiting O-GlcNAcylation reduced HA production whereas increased O-GlcNAcylation augmented HA secretion. Additionally, O-GlcNAcylation regulates HAS2 gene expression resulting in accumulation of its mRNA after induction of O-GlcNAcylation with glucosamine treatments. The oxidized LDLs, the most common molecules related to atherosclerosis outcome and progression, are also able to induce a strong HA synthesis when they are in contact with vascular cells. In this review, we present recent described mechanisms involved in HA synthesis regulation and their role in atherosclerosis outcome and development.

TLR-9 and IL-15 Synergy Promotes the In Vitro Clonal Expansion of Chronic Lymphocytic Leukemia B Cells

Clinical progression of B cell chronic lymphocytic leukemia (B-CLL) reflects the clone's Ag receptor (BCR) and involves stroma-dependent B-CLL growth within lymphoid tissue. Uniformly elevated expression of TLR-9, occasional MYD88 mutations, and BCR specificity for DNA or Ags physically linked to DNA together suggest that TLR-9 signaling is important in driving B-CLL growth in patients. Nevertheless, reports of apoptosis after B-CLL exposure to CpG oligodeoxynucleotide (ODN) raised questions about a central role for TLR-9. Because normal memory B cells proliferate vigorously to ODN+IL-15, a cytokine found in stromal cells of bone marrow, lymph nodes, and spleen, we examined whether this was true for B-CLL cells. Through a CFSE-based assay for quantitatively monitoring in vitro clonal proliferation/survival, we show that IL-15 precludes TLR-9-induced apoptosis and permits significant B-CLL clonal expansion regardless of the clone's BCR mutation status. A robust response to ODN+IL-15 was positively linked to presence of chromosomal anomalies (trisomy-12 or ataxia telangiectasia mutated anomaly + del13q14) and negatively linked to a very high proportion of CD38(+) cells within the blood-derived B-CLL population. Furthermore, a clone's intrinsic potential for in vitro growth correlated directly with doubling time in blood, in the case of B-CLL with Ig H chain V region-unmutated BCR and <30% CD38(+) cells in blood. Finally, in vitro high-proliferator status was statistically linked to diminished patient survival. These findings, together with immunohistochemical evidence of apoptotic cells and IL-15-producing cells proximal to B-CLL pseudofollicles in patient spleens, suggest that collaborative ODN and IL-15 signaling may promote in vivo B-CLL growth.

Hyaluronan - a functional and structural sweet spot in the tissue microenvironment

Transition from homeostatic to reactive matrix remodeling is a fundamental adaptive tissue response to injury, inflammatory disease, fibrosis, and cancer. Alterations in architecture, physical properties, and matrix composition result in changes in biomechanical and biochemical cellular signaling. The dynamics of pericellular and extracellular matrices, including matrix protein, proteoglycan, and glycosaminoglycan modification are continually emerging as essential regulatory mechanisms underlying cellular and tissue function. Nevertheless, the impact of matrix organization on inflammation and immunity in particular and the consequent effects on tissue healing and disease outcome are arguably under-studied aspects of adaptive stress responses. Herein, we review how the predominant glycosaminoglycan hyaluronan (HA) contributes to the structure and function of the tissue microenvironment. Specifically, we examine the evidence of HA degradation and the generation of biologically active smaller HA fragments in pathological settings in vivo. We discuss how HA fragments versus nascent HA via alternate receptor-mediated signaling influence inflammatory cell recruitment and differentiation, resident cell activation, as well as tumor growth, survival, and metastasis. Finally, we discuss how HA fragmentation impacts restoration of normal tissue function and pathological outcomes in disease.

Lymphocyte 'homing' and chronic inflammation

Chronic inflammation is a response to prolonged exposure to injurious stimuli that harm and destroy tissues and promote lymphocyte infiltration into inflamed sites. Following progressive accumulation of lymphocytes, the histology of inflamed tissue begins to resemble that of peripheral lymphoid organs, which can be referred to as lymphoid neogenesis or formation of tertiary lymphoid tissues. Lymphocyte recruitment to inflamed tissues is also reminiscent of lymphocyte homing to peripheral lymphoid organs. In the latter, under physiological conditions, homing receptors expressed on lymphocytes adhere to vascular addressin expressed on high endothelial venules (HEVs), initiating a lymphocyte migration process composed of sequential adhesive interactions. Intriguingly, in chronic inflammation, HEV-like vessels are induced de novo, despite the fact that the inflamed site is not originally lymphoid tissue, and these vessels contribute to lymphocyte recruitment in a manner similar to physiological lymphocyte homing. In this review, we first describe physiological lymphocyte homing mechanisms focusing on vascular addressins. We then describe HEV-like vessel-mediated pathogenesis seen in various chronic inflammatory disorders such as Helicobacter pylori gastritis, inflammatory bowel disease (IBD), autoimmune pancreatitis and sclerosing sialadenitis, as well as chronic inflammatory cell neoplasm MALT lymphoma, with reference to our work and that of others.

Enriched environment reduces glioma growth through immune and non-immune mechanisms in mice

Mice exposed to standard (SE) or enriched environment (EE) were transplanted with murine or human glioma cells and differences in tumour development were evaluated. We report that EE exposure affects: (i) tumour size, increasing mice survival; (ii) glioma establishment, proliferation and invasion; (iii) microglia/macrophage (M/Mφ) activation; (iv) natural killer (NK) cell infiltration and activation; and (v) cerebral levels of IL-15 and BDNF. Direct infusion of IL-15 or BDNF in the brain of mice transplanted with glioma significantly reduces tumour growth. We demonstrate that brain infusion of IL-15 increases the frequency of NK cell infiltrating the tumour and that NK cell depletion reduces the efficacy of EE and IL-15 on tumour size and of EE on mice survival. BDNF infusion reduces M/Mφ infiltration and CD68 immunoreactivity in tumour mass and reduces glioma migration inhibiting the small G protein RhoA through the truncated TrkB.T1 receptor. These results suggest alternative approaches for glioma treatment.

Characterization of the IL-15 niche in primary and secondary lymphoid organs in vivo

IL-15 is a cytokine critical for development, maintenance, and response of T cells, natural killer (NK) cells, NK T cells, and dendritic cells. However, the identity and distribution of IL-15-expressing cells in lymphoid organs are not well understood. To address these questions, we established and analyzed IL-15-CFP knock-in mice. We found that IL-15 was highly expressed in thymic medulla, and medullary thymic epithelial cells with high MHC class II expression were the major source of IL-15. In bone marrow, IL-15 was detected primarily in VCAM-1(+)PDGFRβ(+)CD31(-)Sca-1(-) stromal cells, which corresponded to previously described CXCL12-abundant reticular cells. In lymph nodes, IL-15-expressing cells were mainly distributed in the T-cell zone and medulla. IL-15 was expressed in some fibroblastic reticular cells and gp38(-)CD31(-) double-negative stromal cells in the T-cell zone. Blood endothelial cells, including all high endothelial venules, also expressed high IL-15 levels in lymph nodes, whereas lymphatic endothelial cells (LECs) lacked IL-15 expression. In spleen, IL-15 was expressed in VCAM-1(+) stromal cells, where its expression increased as mice aged. Finally, IL-15 expression in blood and LECs of peripheral lymphoid organs significantly increased in LPS-induced inflammation. Overall, we have identified and characterized several IL-15-expressing cells in primary and secondary lymphoid organs, providing a unique perspective of IL-15 niche in immune microenvironment. This study also suggests that some stromal cells express IL-7 and IL-15 differentially and suggests a way to functionally classify different stromal cell subsets.

Glycoconjugates and related molecules in human vascular endothelial cells

Vascular endothelial cells (ECs) form the inner lining of blood vessels. They are critically involved in many physiological functions, including control of vasomotor tone, blood cell trafficking, hemostatic balance, permeability, proliferation, survival, and immunity. It is considered that impairment of EC functions leads to the development of vascular diseases. The carbohydrate antigens carried by glycoconjugates (e.g., glycoproteins, glycosphingolipids, and proteoglycans) mainly present on the cell surface serve not only as marker molecules but also as functional molecules. Recent studies have revealed that the carbohydrate composition of the EC surface is critical for these cells to perform their physiological functions. In this paper, we consider the expression and functional roles of endogenous glycoconjugates and related molecules (galectins and glycan-degrading enzymes) in human ECs.

Hyaluronan as an immune regulator in human diseases

Accumulation and turnover of extracellular matrix components are the hallmarks of tissue injury. Fragmented hyaluronan stimulates the expression of inflammatory genes by a variety of immune cells at the injury site. Hyaluronan binds to a number of cell surface proteins on various cell types. Hyaluronan fragments signal through both Toll-like receptor (TLR) 4 and TLR2 as well as CD44 to stimulate inflammatory genes in inflammatory cells. Hyaluronan is also present on the cell surface of epithelial cells and provides protection against tissue damage from the environment by interacting with TLR2 and TLR4. Hyaluronan and hyaluronan-binding proteins regulate inflammation, tissue injury, and repair through regulating inflammatory cell recruitment, release of inflammatory cytokines, and cell migration. This review focuses on the role of hyaluronan as an immune regulator in human diseases.

IL-15 aggravates atherosclerotic lesion development in LDL receptor deficient mice

BACKGROUND

Interleukin 15 (IL-15) is a pro-inflammatory cytokine involved in inflammatory diseases and IL-15 is expressed in atherosclerotic plaques.

METHODS

To establish the role of IL-15 in atherosclerosis we studied the effect of IL-15 on atherosclerosis associated cells in vitro and in vivo by neutralizing IL-15 using a DNA vaccination strategy.

RESULTS

Upon feeding a Western type diet LDLr(-/-) mice do express higher levels of IL-15 within the spleen and the number of IL-15 expressing cells among blood leukocytes and spleen cells is increased. Addition of IL-15 to macrophages induces the expression TNF-α and CCL-2. After the mice were vaccinated against IL-15, we observe a reduction in plaque size of 75% plaque. Unexpectedly, the relative number of macrophages within the plaque was 2-fold higher in IL-15 vaccinated mice than in control mice. Vaccination against IL-15 leads to an increased cytotoxicity against IL-15 overexpressing target cells, resulting in a reduction in IL-15 expressing cells and macrophages in blood and spleen and a decreased CD4/CD8 ratio.

CONCLUSION

Hypercholesterolemia leads to upregulation of IL-15 within spleen and blood. DNA vaccination against IL-15 does markedly reduces atherosclerotic lesion size, but does not promote lesion stability.

Proinflammatory cytokines induce hyaluronan synthesis and monocyte adhesion in human endothelial cells through hyaluronan synthase 2 (HAS2) and the nuclear factor-kappaB (NF-kappaB) pathway

Chronic inflammation is now accepted to have a critical role in the onset of several diseases as well as in vascular pathology, where macrophage transformation into foam cells contributes in atherosclerotic plaque formation. Endothelial cells (EC) have a critical function in recruitment of immune cells, and proinflammatory cytokines drive the specific expression of several adhesion proteins. During inflammatory responses several cells produce hyaluronan matrices that promote monocyte/macrophage adhesion through interactions with the hyaluronan receptor CD44 present on inflammatory cell surfaces. In this study, we used human umbilical chord vein endothelial cells (HUVECs) as a model to study the mechanism that regulates hyaluronan synthesis after treatment with proinflammatory cytokines. We found that interleukin 1beta and tumor necrosis factors alpha and beta, but not transforming growth factors alpha and beta, strongly induced HA synthesis by NF-kappaB pathway. This signaling pathway mediated hyaluronan synthase 2 (HAS2) mRNA expression without altering other glycosaminoglycan metabolism. Moreover, we verified that U937 monocyte adhesion on stimulated HUVECs depends strongly on hyaluronan, and transfection with short interference RNA of HAS2 abrogates hyaluronan synthesis revealing the critical role of HAS2 in this process.

Matrix metalloproteinases, T cell homing and beta-cell mass in type 1 diabetes

The pathogenesis of type 1 diabetes begins with the activation of autoimmune T killer cells and is followed by their homing into the pancreatic islets. After penetrating the pancreatic islets, T cells directly contact and destroy insulin-producing beta cells. This review provides an overview of the dynamic interactions which link T cell membrane type-1 matrix metalloproteinase (MT1-MMP) and the signaling adhesion CD44 receptor with T cell transendothelial migration and the subsequent homing of the transmigrated cells to the pancreatic islets. MT1-MMP regulates the functionality of CD44 in diabetogenic T cells. By regulating the functionality of T cell CD44, MT1-MMP mediates the transition of T cell adhesion to endothelial cells to the transendothelial migration of T cells, thus, controlling the rate at which T cells home into the pancreatic islets. As a result, the T cell MT1-MMP-CD44 axis controls the severity of the disease. Inhibition of MT1-MMP proteolysis of CD44 using highly specific and potent synthetic inhibitors, which have been clinically tested in cancer patients, reduces the rate of transendothelial migration and the homing of T cells. Result is a decrease in the net diabetogenic efficiency of T cells and a restoration of beta cell mass and insulin production in NOD mice. The latter is a reliable and widely used model of type I diabetes in humans. Overall, existing experimental evidence suggests that there is a sound mechanistic rationale for clinical trials of the inhibitors of T cell MT1-MMP in human type 1 diabetes patients.

Molecular mechanism of systemic delivery of neural precursor cells to the brain: assembly of brain endothelial apical cups and control of transmigration by CD44

Systemically injected neural precursor cells (NPCs) were unexpectedly shown to reach the cerebral parenchyma and induce recovery in various diffuse brain pathologies, including animal models of multiple sclerosis. However, the molecular mechanisms supporting NPC migration across brain endothelium remain elusive. Brain endothelium constitutes the blood-brain barrier, which uniquely controls the access of drugs and trafficking of cells, including leukocytes, from the blood to the brain. Taking advantage of the availability of in vitro models of human and rat blood-brain barrier developed in our laboratory and validated by us and others, we show here that soluble hyaluronic acid, the major ligand of the adhesion molecule CD44, as well as anti-CD44 blocking antibodies, largely prevents NPC adhesion to and migration across brain endothelium in inflammatory conditions. We present further evidence that NPCs, surprisingly, induce the formation of apical cups at the surface of brain endothelial cells, enriched in CD44 and other adhesion molecules, thus hijacking the endothelial signaling recently shown to be involved in leukocyte extravasation. These results demonstrate the pivotal role of CD44 in the trans-endothelial migration of NPCs across brain endothelial cells: we propose that they may help design new strategies for the delivery of therapeutic NPCs to the brain by systemic administration.

Serum IL-15 in patients with early systemic sclerosis: a potential novel marker of lung disease

The pathogenesis of systemic sclerosis (SSc) is characterized by autoimmunity, vasculopathy and fibrosis. IL-15 is a pleiotropic cytokine that has impact on immune, vascular and connective tissue cells. We therefore investigated IL-15 in the circulation of patients with early SSc and explored possible associations of serum IL-15 with vasculopathy and fibrosis. Serum levels of IL-15 were analysed in 63 consecutive patients with SSc of disease duration less than 4 years and without disease-modifying treatment. Thirty-three age-matched healthy control individuals were enrolled. Serum IL-15 levels were increased in the sera of SSc patients compared with that of healthy control individuals (P < 0.01). Serum IL-15 levels correlated with impaired lung function, assessed both by the vital capacity (P < 0.05) and by the carbon monoxide diffusion capacity (P < 0.05). The association between IL-15 and the vital capacity remained after multiple linear regression analysis. Patients with intermediate serum IL-15 levels had a higher prevalence of increased systolic pulmonary pressure compared with patients with either low or high serum IL-15 levels (P < 0.05). Moreover, increased serum IL-15 levels were associated with a reduced nailfold capillary density in multivariable logistic regression analysis (P < 0.01). Serum IL-15 levels also correlated inversely with the systolic blood pressure (P < 0.01). We conclude that IL-15 is associated with fibrotic as well as vascular lung disease and vasculopathy in early SSc. IL-15 may contribute to the pathogenesis of SSc. IL-15 could also be a candidate biomarker for pulmonary involvement and a target for therapy in SSc.

Blockade of hyaluronan inhibits IL-2-induced vascular leak syndrome and maintains effectiveness of IL-2 treatment for metastatic melanoma

Vascular leak syndrome (VLS) is a life-threatening toxicity induced during IL-2 treatment of cancer patients. The mechanism of IL-2-induced VLS is still poorly understood. At present, there is no specific therapy for VLS. Previous studies from our laboratory demonstrated that hyaluronan (HA), a large glycosaminoglycan, abundant in the extracellular matrix and on the cell surface, caused a marked increase of IL-2-induced VLS in the lungs and liver of C57BL/6 mice. Conversely, blockade or knockout of its major receptor, CD44, resulted in a marked decrease of VLS, thereby suggesting a role for HA in VLS. In this study, we report a novel means to prevent IL-2-induced VLS by blocking endogenous HA with HA-specific binding peptide, Pep-1, a newly isolated peptide which specifically binds to soluble, cell-associated, and immobilized forms of HA. Our results demonstrated that blocking HA with Pep-1 dramatically inhibited IL-2-induced VLS in both normal mice as well as in mice bearing melanoma. Moreover, Pep-1 treatment maintained the effectiveness of IL-2 and prevented the metastasis of melanoma. IL-2-induced emigration of lymphocytes across the endothelium and cytotoxicity against tumor by lymphokine-activated killer cells were not affected by Pep-1. Instead, use of Pep-1 maintained endothelial integrity and reduced their apoptosis during IL-2-induced VLS. These data suggested that HA plays a critical role in regulating endothelial cell damage and induction of IL-2-mediated VLS. Also, blockade of HA using Pep-1 could constitute a novel therapeutic modality to prevent IL-2-mediated toxicity, thereby facilitating the effectiveness of high-dose IL-2 in the treatment of metastatic melanomas.

Interleukin-15 inhibits smooth muscle cell proliferation and hyaluronan production in rat ductus arteriosus

Neointimal cushion formation (NCF) is an important vascular remodeling for anatomical closure of the ductus arteriosus (DA). Inflammatory responses to vascular injury or atherosclerosis are known to be associated with the pathogenesis of NCF. We found that the expression of interleukin (IL)-15 mRNA was significantly higher in rat DA than in the aorta. IL-15 immunoreactivity was detected predominantly in the internal elastic laminae (IEL) and to a lesser extent in smooth muscle cells (SMCs) in rat DA. Prostaglandin E (PGE) increased the expression of IL-15 mRNA in cultured DA SMCs. IL-15 significantly attenuated the platelet-derived growth factor (PDGF)-BB-mediated SMC proliferation, but did not change SMC migration. IL-15 significantly attenuated PGE1-induced hyaluronic acid (HA) production in a dose-dependent manner, which is a potent stimulator of NCF. Accordingly, IL-15 might have an inhibitory effect on the physiologic vascular remodeling processes in closing the DA.

A role for CD44 in T cell development and function during direct competition between CD44+ and CD44- cells

The role of CD44 in T cell biology remains incompletely understood. Although studies using anti-CD44 antibodies have implicated this cell adhesion molecule in a variety of important T cell processes, few T cell defects have been reported in CD44-deficient mice. We have assessed the requirement for CD44 in T cell development and mature T cell function by analyzing mice in which CD44(-/-) and WT cells were produced simultaneously. In mixed (CD44(-/-) + CD44(+/+)) bone marrow chimeras, production of CD44(-/-) T cells was shown to be reduced compared to WT cells due to inefficient intrathymic development. In addition, mature CD44(-/-) CD8(+) T cells generated a substantially lower response than WT T cells after infection of mice with lymphocytic choriomeningitis virus, with the reduction in response apparent in both lymphoid and non-lymphoid tissues. Overall, these results demonstrate a poor capacity of CD44(-/-) T lineage cells to compete with WT cells at multiple levels, implicating CD44 in normal T cell function.

Immunologic roles of hyaluronan

Hyaluronan (HA), a large glycosaminoglycan composed of D-N-acetylglucosamine and D-glucuronic acid, is expressed in virtually all tissues and has long been considered to serve as a structural component or filling material in the tissue interstitium (Filler Theory). This idea was revised with the discovery of HA-binding proteins that introduced the concept that HA may also serve as an adhesive substrate for cellular trafficking (Adhesion Theory). Most recently, it has been shown that HA fragments can deliver maturational signals to dendritic cells (DCs) and high molecular weight HA polymers can deliver costimulatory signals to T-cells (Signaling Theory). Thus, HA may represent an important component of the immune system. Recently, we have evaluated the impact of HA on Langerhans cell (LC) maturation and migration using a novel peptide inhibitor of HA function, termed Pep-1 (GAHWQFNALTVR). As skin-specific members of the DC family, LCs are crucial for the initiation of cutaneous immune responses. Local injections of Pep-1 prevented hapten-induced LC migration from the epidermis, providing the first experimental evidence that HA facilitates their emigration. Moreover, Pep-1 also significantly inhibited the hapten-induced maturation of LCs in vivo as assessed by cell morphology, costimulatory molecule expression, and their ability to induce proliferation of allogeneic T-cells. HA therefore has dual functionality to facilitate LC migration and maturation, the two critical events for the initiation of adaptive immune responses. Finally, we have observed that DC-dependent, antigen-specific T-cell proliferation and cytokine secretion is blocked by Pep-1. These results have revealed a previously unrecognized role for HA in antigen presentation. Thus, far from an inert structural biopolymer, HA represents a multifunctional carbohydrate mediator of immune processes.

Suppressor activity and potency among regulatory T cells is discriminated by functionally active CD44

CD4CD25(+) regulatory T cells are fundamental to the maintenance of peripheral tolerance and have great therapeutic potential. However, efforts in this regard have been hampered by limiting cell numbers in vivo, an anergic phenotype in vitro, and a rudimentary understanding of the molecular basis for the functional state of CD4CD25(+) regulatory T cells (Treg cells). Here we show heterogeneity of suppressor activity among activated CD4CD25(+) Treg cells and that, within this population, the functionally active, hyaluronan-binding form of CD44 (CD44(act)) is strikingly correlated with superior suppressor activity. Within 16 hours after in vitro activation, CD44(act) can discriminate enhanced suppressive function in in vitro proliferation assays and in an in vivo bone marrow engraftment model. The expression of other surface markers and that of Foxp3 are similar irrespective of hyaluronan binding and associated degree of suppressor potency. Furthermore, CD44(act) is induced on resting CD4CD25(+) cells in vivo by allogeneic stimulation, with similar functional consequences. These results reveal a cell-surface marker that delineates functional activity within a population of activated CD4CD25(+) regulatory T cells, thereby providing a potential tool for identifying regulatory activity and enriching for maximal suppressor potency.

Thematic review series: The immune system and atherogenesis. Cytokines affecting endothelial and smooth muscle cells in vascular disease

The cellular and extracellular matrix accumulations that comprise the lesions of atherosclerosis are driven by local release of cytokines at sites of predilection for lesion formation, and by the specific attraction and activation of cells expressing receptors for these cytokines. Although cytokines were originally characterized for their potent effects on immune and inflammatory cells, they also promote endothelial cell dysfunction and alter smooth muscle cell (SMC) phenotype and function, which can contribute to or retard vascular pathologies. This review summarizes in vivo studies that have characterized endothelial- and smooth muscle-specific effects of altering cytokine signaling in vascular disease. Although multiple reports have identified cytokines as pivotal players in endothelial and SMC responses in vascular disease, they also have highlighted the need to delineate the critical genes and specific cellular functions regulated by individual cytokine signaling pathways.

Endothelial dysfunction and activation as an expression of disease: role of prostacyclin analogs

The endothelium is now considered a real endocrine-paracrine organ, important not only as a structural barrier between the circulation and surrounding tissue, but also because it plays an essential role for local hemodynamics, releasing substances that modulate the vascular calibre and blood cell activation. Here, after a brief but detailed analysis of the importance of the endothelium in vascular homeostasis, in the control of coagulation and in the relations with the different blood cells, we will explain the concept of endothelial dysfunction (altered NO release) and activation (amplified adhesion molecule expression) in inflammatory, connective tissue and post-trasplantation diseases. Furthermore, this review will focus on the activity of prostacyclin and synthetic analogs, especially their ability to interact with the vasodilatation system and their role in modulating cell interaction by surface adhesion molecule expression, cytokines and growth factors release as well as gene transcription factors. Finally, we will consider the therapeutic role of prostacyclin analogs in the prevention and treatment of connective tissue diseases.

CD44 in cancer progression: adhesion, migration and growth regulation

It is well established that the large array of functions that a tumour cell has to fulfil to settle as a metastasis in a distant organ requires cooperative activities between the tumour and the surrounding tissue and that several classes of molecules are involved, such as cell-cell and cell-matrix adhesion molecules and matrix degrading enzymes, to name only a few. Furthermore, metastasis formation requires concerted activities between tumour cells and surrounding cells as well as matrix elements and possibly concerted activities between individual molecules of the tumour cell itself. Adhesion molecules have originally been thought to be essential for the formation of multicellular organisms and to tether cells to the extracellular matrix or to neighbouring cells. CD44 transmembrane glycoproteins belong to the families of adhesion molecules and have originally been described to mediate lymphocyte homing to peripheral lymphoid tissues. It was soon recognized that the molecules, under selective conditions, may suffice to initiate metastatic spread of tumour cells. The question remained as to how a single adhesion molecule can fulfil that task. This review outlines that adhesion is by no means a passive task. Rather, ligand binding, as exemplified for CD44 and other similar adhesion molecules, initiates a cascade of events that can be started by adherence to the extracellular matrix. This leads to activation of the molecule itself, binding to additional ligands, such as growth factors and matrix degrading enzymes, complex formation with additional transmembrane molecules and association with cytoskeletal elements and signal transducing molecules. Thus, through the interplay of CD44 with its ligands and associating molecules CD44 modulates adhesiveness, motility, matrix degradation, proliferation and cell survival, features that together may well allow a tumour cell to proceed through all steps of the metastatic cascade.

CD44 potentiates the adherence of metastatic prostate and breast cancer cells to bone marrow endothelial cells

The aim of this current study was to examine the significance of CD44 expression in mediating cancer cell adhesion to human bone marrow endothelial cell(s) (hBMEC). Differential CD44 expression on two metastatic prostate cancer cell lines, PC3 (CD44 +ve) and DU145 (CD44 -ve) and four breast cancer cell lines was confirmed by immunoblotting and immunocytochemistry. In cell adhesion assays, PC3 but not DU145 cells demonstrated a rapid adhesion to hBMECs. Treatment of PC3 cells with a neutralizing antibody against CD44 standard (CD44s) and CD44 splice variants decreased PC3 cell adhesion to hBMECs. Similarly, depletion of CD44 expression using RNA interference decreased the ability of PC3 cells and two CD44 +ve breast cancer cell lines (MDA-MB-231 and MDA-MB-157) to bind FITC-conjugated hyaluronan (FITC-HA) and to adhere to hBMECs. In contrast, transfection of DU145 cells or the T47D and MCF-7 breast cancer cell lines to express CD44s increased cell surface binding of FITC-HA and cell adherence to hBMECs. Treatment of PC3 and MDA-MD-231 cells but not hBMECs with hyaluronidase attenuated cell adhesion, suggesting that cell surface expression of CD44 on prostate and breast cancer cells may promote the retention of a HA coat that facilitates their initial arrest on bone marrow endothelium.

Bimolecular complex between rolling and firm adhesion receptors required for cell arrest; CD44 association with VLA-4 in T cell extravasation

CD44 on activated T cells can initiate contact and mediate rolling on hyaluronan on endothelial cells. We have shown that the integrin VLA-4 is used preferentially over LFA-1 in conjunction with this rolling interaction for firm adhesion. Here, we show by coimmunoprecipitation and transfection studies that CD44 associates with VLA-4 but not LFA-1 on the plasma membrane of immune cells. Absence of the cytoplasmic portion of CD44 abrogates this coassociation and attendant firm adhesion. Moreover, in an in vivo model of lymphocyte homing, cells expressing only the truncated form of CD44 together with VLA-4 fail to traffic to an inflamed site, thereby defining a discrete biological role for the cytoplasmic domain. These studies demonstrate a molecular mechanism whereby coanchoring within a single bimolecular complex between a primary and secondary adhesion molecule regulates a cell's ability to firmly adhere, providing a fundamental alteration to the paradigm of leukocyte extravasation.

Chronic delayed-type hypersensitivity reaction as a means to treat alopecia areata

The acute phase of alopecia areata (AA) is characterized by an increase in CD44v3+ and CD44v10+ skin-infiltrating leucocytes (SkIL). Induction of a contact eczema, one of the therapeutic options in AA, can be mitigated strongly by a blockade of CD44v10. The observation that induction of a delayed type hypersensitivity (DTH) reaction abrogates an autoimmune reaction, where both responses apparently use similar effector mechanisms, is surprising and prompted us to search for the underlying mechanisms. AA-affected C3H/HeJ mice were treated with the contact sensitizer SADBE (squaric acid dibutylester) and leucocyte subpopulations and their activation state was evaluated in SkIL and draining lymph nodes. AA-affected mice exhibited an increased number of SkIL with a predominance of T lymphocytes. After treatment with the contact sensitizer SADBE recovery of SkIL was reduced and monocytes predominated. However, a significantly increased number of leucocytes was recovered from draining lymph nodes. Draining lymph node cells from untreated and treated AA mice exhibited all signs of recent activation with high-level expression of co-stimulatory and accessory molecules and an increased percentage of CD44v3+ and CD44v10+ leucocytes. In contrast, SkIL of SADBE-treated AA mice contained relatively few activated T cells and reduced numbers of CD44v3+ and CD44v10+ cells. Thus, the activation state and the distribution of leucocyte subsets in SADBE-treated AA mice are consistent with a blockade of leucocyte extravasation. Accordingly, the therapeutic effect of long-term SADBE treatment may rely on impaired leucocyte traffic.

Interleukin-6 and interleukin-15 are selectively regulated by lipopolysaccharide and interferon-gamma in primary pig adipocytes

3T3-L1 adipocytes express the lipopolysaccharide (LPS) receptor and respond to direct stimulation with the antigen by increasing the expression of inflammatory mediators. Activation of this receptor by its ligand in the macrophage causes the activation and translocation of nuclear factor-kappaB (NF-kappaB) to the nucleus where it regulates the expression of proinflammatory cytokines and other target genes. We investigated whether LPS could stimulate NF-kappaB translocation in primary pig adipocytes and regulate the expression and secretion of TNF-alpha and IL-6. LPS clearly induced the nuclear translocation of NF-kappaB and also upregulated (P < 0.05) the mRNA expression and secretion of IL-6 into the culture medium. An induction of TNF-alpha expression by LPS was not detected, but with extended incubation (8 h), there was a modest increase (P < 0.09) in the media concentration of this cytokine. Inhibition of either ERK1/2, PKC, or the inhibitory G protein (Gi) with U-0126, bisindolylmaleimide HCl, and pertussis toxin, respectively, blocked (P < 0.05) the increase in IL-6 expression caused by LPS. Because LPS administration in vivo increases circulating concentrations of IFN-gamma, and because this cytokine also regulates multiple immune modulators in the adipocyte, we also determined whether IFN-gamma regulates cytokine expression in primary adipocytes. Although the expression of IL-6 and TNF-alpha was unresponsive to IFN-gamma, the expression of IL-15 was markedly upregulated (P < 0.01). Furthermore, the induction of IL-15 expression by IFN-gamma was blocked by inhibition of PKC. These data indicate that NF-kappaB is responsive to LPS in the adipocyte and also identify key mediators of LPS-induced IL-6 expression. In addition, we provide novel evidence that IFN-gamma targets the adipocyte to induce IL-15 expression, thus indicating a possible role for the adipocyte in the regulation of T-cell function and muscle metabolism during the innate immune response.

Endoplasmic reticulum stress induces hyaluronan deposition and leukocyte adhesion

There is mounting evidence that perturbations in endoplasmic reticulum (ER) function play a key role in the pathogenesis of a broad range of diseases. We have examined the ability of ER stress to modulate leukocyte binding to colonic and aortic smooth muscle cells. In vitro, control smooth muscle cells bind few leukocytes, but treatment with compounds that induce ER stress, including tunicamycin, A23187, and thapsigargin, promotes leukocyte binding. Likewise, dextran sulfate, another agent capable of inducing ER stress and promoting inflammation in vivo, strongly induces leukocyte adhesion. The bound leukocytes are released by hyaluronidase treatment, indicating a critical role for hyaluronan-containing structures in mediating leukocyte binding. Affinity histochemistry demonstrated that hyaluronan accumulates and is present in cable-like structures in the treated, but not the untreated, cultures and that these structures serve as attachment sites for leukocytes. Hyaluronan-rich regions of both murine and human inflamed colon contain numerous cells that stain intensely for ER-resident chaperones containing the KDEL sequence, demonstrating a relationship between ER stress and hyaluronan deposition in vivo. These results indicate that ER stress may contribute to chronic inflammation by forming a hyaluronan-rich extracellular matrix that is conducive to leukocyte binding.

Mast cell-derived tumor necrosis factor induces hypertrophy of draining lymph nodes during infection

Palpable swelling of regional lymph nodes is a common sequela of microbial infections but the mechanism responsible for the sequestration and subsequent coordination of lymphocyte responses within these dynamic structures remains poorly understood. Here we show that draining lymph nodes of mast cell-deficient mice did not demonstrate swelling after intradermal bacterial challenge. Testing of individual mast cell-derived products in this model indicated that tumor necrosis factor was the main mediator of nodal hypertrophy, whereas tryptase and histamine had no effect. After peripheral mast cell activation, both tumor necrosis factor concentrations and the recruitment of circulating T cells were increased within draining nodes. These results show a critical function for peripheral mast cell-derived tumor necrosis factor in regulating the hypertrophy of draining lymph nodes during infection.

Targeted deletion of CD44v7 exon leads to decreased endothelial cell injury but not tumor cell killing mediated by interleukin-2-activated cytolytic lymphocytes

In the current study, we investigated the nature and role of CD44 variant isoforms involved in endothelial cell (EC) injury and tumor cell cytotoxicity mediated by IL-2-activated killer (LAK) cells. Treatment of CD44 wild-type lymphocytes with IL-2 led to increased gene expression of CD44 v6 and v7 variant isoforms and to significant induction of vascular leak syndrome (VLS). CD44v6-v7 knockout (KO) and CD44v7 KO mice showed markedly reduced levels of IL-2-induced VLS. The decreased VLS in CD44v6-v7 KO and CD44v7 KO mice did not result from differential activation and expansion of CD8+ T cells, NK, and NK-T cells or from altered degree of perivascular lymphocytic infiltration in the lungs. LAK cells from CD44v7 KO mice showed a significant decrease in their ability to adhere to and mediate lysis of EC but not lysis of P815 tumor cells in vitro. CD44v7-mediated lysis of EC by LAK cells was dependent on the activity of phosphatidylinositol 3-kinase and tyrosine kinases. Interestingly, IL-2-activated LAK cells expressing CD44hi but not CD44lo were responsible for EC lysis. Furthermore, lysis of EC targets could be blocked by addition of soluble or enzymatic cleavage of CD44v6-v7-binding glycosaminoglycans. Finally, anti-CD44v7 mAbs caused a significant reduction in the adherence to and killing of EC and led to suppression of IL-2-induced VLS. Together, this study suggests that the expression of CD44v7 on LAK cells plays a specific role in EC injury and that it may be possible to reduce EC injury but not tumor cell killing by specifically targeting CD44v7.

Hepatocyte growth factor enhances adhesion of breast cancer cells to endothelial cells in vitro through up-regulation of CD44

For cancer metastasis, tumor cells present in the circulation must first adhere to the endothelium. Integrins play a central role in leukocyte adhesion to the endothelium and subsequent migration into tissues. The majority of tumor cells derived from solid cancers, including breast cancer, do not express integrins. We investigated the mechanisms of adhesion and transendothelial migration of cancer cells using breast carcinoma cell lines. Our results showed the following features of breast cancer cells: (1) HGF stimulated breast cancer cells by up-regulating CD44 expression in a concentration-dependent manner. (2) the maximum level of HGF-induced CD44 up-regulation on breast cancer cell lines occurred within 3 h. (3) HGF-induced up-regulation of CD44 was mediated by the tyrosine kinase signaling pathway. (4) HGF induced CD44-mediated adhesion of tumor cell lines to bone marrow-derived endothelial cells. (5) HGF did not change rolling of breast cancer cell lines on bone marrow-derived endothelial cells, but enhanced firm adhesion of cancer cells on endothelial cells under shear stress conditions. (6) HGF increased transendothelial migration of cancer cells. Our results indicate that HGF stimulates CD44-mediated adhesion of breast cancer cells to bone marrow-derived endothelial cells, which subsequently results in transendothelial migration of tumor cells. These results suggest that CD44 may confer the metastatic properties of breast cancer cells and, therefore, could be used as a target in future molecular cancer therapy.

Associations of six candidate genes with antibody response kinetics in hens

The chicken B-cell marker (ChB6), caspase-1, inhibitor of apoptosis protein-1 (IAP-1), interleukin-15 receptor alpha-chain (IL-15Ralpha), interleukin-2 receptor gamma-chain (IL-2Rgamma), and immunoglobulin supfamily gene (ZOV3), as physiological candidate genes for chicken immune response, were selected to investigate associations with antibody kinetics to SRBC and killed B. abortus. An F2 population was derived from mating highly inbred (>99%) males of two MHC-congenic Fayoumi lines (named M5.1 and M15.2) with G-B1 Leghorn hens. Antibody response to SRBC and B. abortus after immunization at 19 and 22 wk were measured. Secondary phase parameters of maximum titers (Ymax) and time required to achieve Ymax (Tmax) were estimated from postsecondary titers by using a nonlinear regression model. The DNA polymorphisms of six genes were identified, and associations of single nucleotide polymorphisms (SNP) in the six genes with antibody response parameters were analyzed. Significant main effects of the gene polymorphisms were mostly found in the lineage of the M5.1 grandsire and primarily on antibody response to B. abortus. There was general agreement of allelic effect within antibody parameters among genes. These results suggest that the SNP characterized in the study may serve as markers for genetic enhancement of humoral immune capacity in the chicken.

CD44v7 interferes with activation-induced cell death by up-regulation of anti-apoptotic gene expression

Blockade of CD44v7 was described to cure trinitrobenzene sulfonic acid-induced colitis, a disease not developed by mice with targeted deletion of the CD44v7 exon. There was evidence for a reduction in activation-induced cell death on lamina propria lymphocytes of control as compared with CD44v7-deficient mice. To elucidate the mechanism underlying the relative apoptosis resistance of CD44v7-competent as compared with CD44v7-deficient lymphocytes, T cell activation and induction of apoptosis were analyzed on mesenteric lymph node cells and Peyer's patch lymphocytes of CD44v7-deficient and CD44v4-v7-transgenic mice, which overexpress rat CD44v4-v7 on T lymphocytes. CD44v7 deficiency was characterized by an increase in the percentage of apoptotic cells after stimulation, increased numbers of CD95L- and CD152-positive cells, low levels of the anti-apoptotic proteins Bcl-2 and Bcl-Xl, and decreased phosphorylation of the pro-apoptotic protein BAD. Also, lymphocytes from CD44v4-v7-transgenic mice displayed reduced levels of CD95L, low numbers of apoptotic cells, and constitutively elevated levels of Bcl-Xl. When stimulating lymphocytes by CD3 cross-linking, CD44v7 was not recruited toward the immunological synapse and preferentially associated with the cytoskeletal-linker protein ezrin. Thus, as opposed to the CD44 standard isoform, CD44v7 does not function as an accessory molecule; instead, it supports survival of activated T cells by interfering with activation-induced cell death.

Role of tumor necrosis factor-alpha in graft-versus-host disease and graft-versus-leukemia responses

Tumor necrosis factor-alpha (TNF-alpha) antagonist therapy has proven effective in inflammatory conditions such as rheumatoid arthritis and Crohn's disease. There is substantial evidence that TNF-alpha also plays a role in the development of graft-versus-host disease (GVHD) after allogeneic hematopoietic cell transplantation, which along with leukemia relapse remains one of the 2 major impediments to success of the approach. Using a recently developed potent rat/mouse chimeric monoclonal antibody directed against murine TNF-alpha (CNTO2213), the authors investigated the effect of TNF-alpha blockade on GVHD mediated by either CD4(+) or CD8(+) donor T cells. The results indicated that the treatment had only a moderate effect on both a CD8(+) T cell-mediated major histocompatibility complex-matched GVHD model involving multiple minor histocompatibility antigens and a p-->F(1) acute GVHD model directed against a haplo-mismatched major histocompatibility complex barrier involving both CD4(+) and CD8(+) T cells. In contrast, treatment with the anti-TNF-alpha antibody had a highly significant effect (100% survival rate) on the CD4(+) T cell-mediated component of this latter model. Importantly, anti-TNF-alpha antibody did not block the development of a graft-versus-leukemia effect against a murine myeloid leukemia challenge in either a syngeneic or allogeneic p-->F(1) setting. This suggests that the inhibition of TNF-alpha during allogeneic hematopoietic cell transplantation may be able to diminish the inflammatory GVHD reaction without hindering effective graft-versus-leukemia responses.

Interleukins in atherosclerosis: molecular pathways and therapeutic potential

Interleukins are considered to be key players in the chronic vascular inflammatory response that is typical of atherosclerosis. Thus, the expression of proinflammatory interleukins and their receptors has been demonstrated in atheromatous tissue, and the serum levels of several of these cytokines have been found to be positively correlated with (coronary) arterial disease and its sequelae. In vitro studies have confirmed the involvement of various interleukins in pro-atherogenic processes, such as the up-regulation of adhesion molecules on endothelial cells, the activation of macrophages, and smooth muscle cell proliferation. Furthermore, studies in mice deficient or transgenic for specific interleukins have demonstrated that, whereas some interleukins are indeed intrinsically pro-atherogenic, others may have anti-atherogenic qualities. As the roles of individual interleukins in atherosclerosis are being uncovered, novel anti-atherogenic therapies, aimed at the modulation of interleukin function, are being explored. Several approaches have produced promising results in this respect, including the transfer of anti-inflammatory interleukins and the administration of decoys and antibodies directed against proinflammatory interleukins. The chronic nature of the disease and the generally pleiotropic effects of interleukins, however, will demand high specificity of action and/or effective targeting to prevent the emergence of adverse side effects with such treatments. This may prove to be the real challenge for the development of interleukin-based anti-atherosclerotic therapies, once the mediators and their targets have been delineated.

CD44 in cancer

CD44 is a multistructural and multifunctional cell surface molecule involved in cell proliferation, cell differentiation, cell migration, angiogenesis, presentation of cytokines, chemokines, and growth factors to the corresponding receptors, and docking of proteases at the cell membrane, as well as in signaling for cell survival. All these biological properties are essential to the physiological activities of normal cells, but they are also associated with the pathologic activities of cancer cells. Experiments in animals have shown that targeting of CD44 by antibodies, antisense,and CD44-soluble proteins markedly reduces the malignant activities of various neoplasms, stressing the therapeutic potential of anti-CD44 agents. Furthermore, because alternative splicing and posttranslational modifications generate many different CD44 sequences, including, perhaps, tumor-specific sequences, the production of anti-CD44 tumor-specific agents may be a realistic therapeutic approach. However, in many cancers (renal cancer and non-Hodgkin's lymphomas are exceptions), a high level of CD44 expression is not always associated with an unfavorable outcome. On the contrary, in some neoplams CD44 upregulation is associated with a favorable outcome. Even worse, in many cases different research grows analyzing the same neoplastic disease reached contradictory conclusions regarding the correlation between CD44 expression and disease prognosis, possibly due to differences in methodology. These problems must be resolved before applying anti-CD44 therapy to human cancers.

Systemic administration of IL-15 augments the antigen-specific primary CD8+ T cell response following vaccination with peptide-pulsed dendritic cells

The systemic administration of IL-2 can act as a potent adjuvant for T cell-directed vaccine strategies. However, not only is the administration of IL-2 potentially toxic, but recent evidence suggests that it may also paradoxically limit the duration and magnitude of the cytotoxic T cell response. A recently identified cytokine, IL-15, shares many properties with IL-2 and may provide a preferential means of augmenting T cell-directed vaccine responses. Although well characterized in vitro, there are few data on the ability of IL-15 to augment T cell-mediated responses in vivo. We therefore evaluated the ability of systemic IL-15 to function as a T cell adjuvant in a murine vaccine model. To establish a population of easily identifiable Ag-responsive T cells, naive CD8(+) (OT-1) T cells were first adoptively transferred into mice. Vaccination with peptide-pulsed dendritic cells induced a modest expansion of OT-1 T cells. The addition of systemic IL-15 for 7 days following vaccination resulted in a significant increase in the expansion of responding T cells in the PBL, spleen, and lymph nodes. Importantly, the responding T cells were cytotoxic and maintained a Tc1-biased phenotype. We did not observe either enhanced resistance to activation-induced cell death or preferential generation of memory T cells as a result of treatment with IL-15 compared with IL-2. These studies show for the first time that IL-15 is capable of augmenting the primary CD8(+) T cell response to vaccination and contribute to the basis for future experiments exploring the clinical role of IL-15.

IL-15 up-regulates iNOS expression and NO production by gingival epithelial cells

To investigate the biological activity of epithelial cells in view of host defense, we analyzed the mRNA expression of inducible NOS (iNOS) as well as NO production by human gingival epithelial cells (HGEC) stimulated with IL-15. RT-PCR analysis revealed that HGEC expressed IL-15 receptor alpha-chain mRNA. In addition, stimulation with IL-15 enhanced iNOS expression by HGEC through an increase of both mRNA and protein levels. Moreover, IL-15 up-regulated the production of NO(2)(-)/NO(3)(-), a NO-derived stable end product, from HGEC. The enhanced NO production by IL-15 was inhibited by AMT, an iNOS-specific inhibitor. These results suggest that IL-15 is a potent regulator of iNOS expression by HGEC and involved in innate immunity in the mucosal epithelium.

Chondroitin sulfate A released from platelets blocks RANTES presentation on cell surfaces and RANTES-dependent firm adhesion of leukocytes

The sequestration of chemokines on the surface of microvascular endothelium is an early event in the selective recruitment of leukocytes. The sequestration and presentation of chemokines must be tightly controlled to confine the extravasation of leukocytes and to prevent uncontrolled inflammation. We investigated whether soluble molecules released under physiological conditions could control chemokine immobilization on cell surfaces and function as regulatory chemokine binding molecules. We determined that human serum contains a molecule that suppresses RANTES (CCL5) binding to endothelial cells, PBMC and CHO cells. Using platelet-rich and platelet-free plasma, serum from patients with thrombocytopenia, and purified platelets, we identified platelets as the source of the chemokine-binding molecule and further identified it as chondroitin sulfate A. In contrast to platelet-derived fully-sulfated chondroitin sulfate A, low-sulfated chondroitin sulfate A present in plasma was almost inactive. Under physiological flow conditions chondroitin sulfate A was found to block RANTES-mediated firm adhesion of monocytes to endothelial cells. It also prevented RANTES-mediated influx of calcium in CCR5-transfected CHO cells while internalization of CCR5 was only marginally reduced. Taken together, chondroitin sulfate A released from platelets appears to act as an important regulatory molecule for cellular responses to chemokines.

Expression of interleukin-15 in mouse and human atherosclerotic lesions

Atherosclerotic lesions are characterized by prominent macrophage and T-cell infiltration and atherosclerosis is widely recognized as an inflammatory disease. The cytokine interleukin-15 (IL-15) has T-cell chemotactic and pro-inflammatory properties and promotes the recruitment of T cells to sites of inflammation. We have therefore examined IL-15 expression in the atherosclerotic ApoE-deficient mouse model as well as in human atherosclerotic lesions. In gene expression arrays, a transcript corresponding to IL-15 mRNA was elevated in atherosclerotic aortas of ApoE-deficient mice fed a Western diet for 10 and 20 weeks, corresponding to lesions of the fatty streak and fibrofatty plaque stage, respectively. Immunostaining for IL-15 localized to aortic smooth muscle cells in nonatherosclerotic C57BL/6 mice, whereas both macrophages and smooth muscle cells stained positive for IL-15 in atherosclerotic lesions of ApoE-deficient mice. Finally, advanced atherosclerotic lesions of human carotid arteries were immunostained to determine whether IL-15 is involved in human disease. IL-15 protein was present also in the human lesions with a distribution primarily overlapping that of macrophages. In conclusion, IL-15 is up-regulated in both human and animal atherosclerotic lesions and may contribute to the recruitment of T cells and their activation during atherogenesis.

Hyaluronan synthases, hyaluronan, and its CD44 receptor in tissue around loosened total hip prostheses

Aseptic loosening of prosthetic components, the most common long-term complication after total hip replacement (THR), is characterized by the formation of a synovial membrane-like interface tissue (SMLIT). It was hypothesized that the hyaluronan synthase (HAS)/hyaluronan (HA)/HA receptor CD44 signalling system is responsible for the synovial-like differentiation of the interface membrane. SMLIT was therefore compared with osteoarthritis (OA) synovial membrane by using reverse transcriptase polymerase chain reaction (RT-PCR) of HAS 1, 2 and 3, histochemical HA assay, and immunohistochemistry of CD44 and its non-HA ligands. All three isoforms of HAS were found in these samples. HA and CD44 were most abundant in the lining, but the signal was actually stronger in aseptic loosening than in OA (p<0.01). The non-HA CD44 ligands, collagen type VI, fibronectin, osteopontin, and MCP-1, had a similar distribution pattern in both tissues. These results confirm the synovial-like structure of the interface tissue lining. The pressure waves and movement of the HA-rich pseudosynovial fluid seem to drive HA into the implant-to-host interface, which itself also produces HA. HA may be responsible for the induction of a synovial-like lining at the interface through HA-CD44 signalling.

CD44 ligation on peripheral blood polymorphonuclear cells induces interleukin-6 production

Polymorphonuclear cells (PMNs) contribute to the initiation and progression of the immune response by mediating cytotoxicity, phagocytosis, and cytokine secretion. Because CD44 serves as a cytotoxic-triggering molecule on PMNs, it was hypothesized that it could also trigger cytokine production. In this study, the effect of anti-CD44 antibodies on interleukin-6 (IL-6) production in human PMNs was assessed. By using a reverse transcriptase-polymerase chain reaction, it was shown that PMNs stimulated with a mouse monoclonal or a rabbit polyclonal F(ab)(2) anti-CD44 transcribe IL-6 messenger RNA. A similar effect was obtained when an anti-CD44 antibody was replaced with hyaluronic acid (HA). Kinetic studies showed that anti-CD44 and HA induced IL-6 gene transcription, initiated 3 hours after stimulation, peaked between 12 and 24 hours, and disappeared after 48 hours. Analogous results were achieved when secreted IL-6 protein was measured by enzyme-linked immunosorbent assay in the PMN culture supernatants. To characterize which metabolic pathways regulated CD44-dependent IL-6 production in PMNs, an RNA polymerase inhibitor, actinomycin D, and 2 protein kinase inhibitors, such as genistein and staurosporine, were tested. Actinomycin D and genistein blocked IL-6 production, whereas staurosporine did not, suggesting that CD44-dependent IL-6 production requires gene transcription and tyrosine kinase activity. Furthermore, the relationship between CD44 and cytokines that affect PMN function, including interferon gamma (IFNgamma) and IL-2, was investigated. Without CD44 cross-linking, IFNgamma did not trigger IL-6 production. However, on CD44 cross-linking, IFNgamma produced a strong synergistic effect on IL-6 syntheses in human PMNs. (Blood. 2001;97:3621-3627)