ASH Meeting 2016: developments in hemostaseology.

During the annual meeting of the American Society of Hematology (ASH) in San Diego/California, novel developments in the field of hemostaseology were presented. Alternative treatment strategies besides factor replacement were discussed for patients with hemophilia. One of the highlights of the meeting in this year's plenary session was the presentation of successful adeno-associated virus mediated gene transfer in patients with hemophilia B leading to sustained elevation of factor IX:C (FIX:c). Other alternative treatment approaches in patients with hemophilia A may include bispecific antibodies mimicking factor VIIIa (FVIIIa) activity or disrupting anticoagulant proteins. Focusing on anticoagulation, data on the use of direct oral anticoagulants (DOACs) in cancer patients with atrial fibrillation as well as treatment of superficial vein thrombosis with rivaroxaban were presented. In this short review, we try to highlight the most important presentations during the ASH meeting 2016.

Bone Involvement in Rosai-Dorfman Disease (RDD): a Case Report and Systematic Literature Review.

PURPOSE OF REVIEW: Rosai-Dorfman disease (RDD) is a rare histiocytic disorder typically presenting as painless cervical lymphadenopathy. Extranodal involvement is common and may also affect bones. Here, we present a patient with typical nodal disease and multifocal bone manifestations. Further, a systematic literature review was performed to better understand the phenotype, clinical course and treatment options of such patients. RECENT FINDINGS: RDD is a nonmalignant, classically sporadic histiocytosis. Nevertheless, increasing evidence also suggests familial forms of the disease. According to our literature review, bone involvement is exceedingly rare and heterogeneous. Clinical outcome in terms of mortality seems to be favorable in most cases. Currently, therapy strategies include surgical and immunosuppressive treatments, but the optimal treatment of osseous RDD remains to be defined. Patients with osseous RDD may present to rheumatologists with arthralgia or arthritis. Due to the rarity of the disease, diagnosis and treatment remain challenging.

Enhancement of fibrinogen-triggered pro-coagulant activation of monocytes in vitro by matrix metalloproteinase-9.

BACKGROUND: Interaction of fibrinogen with specific leukocyte integrins of monocytes may link coagulation and inflammation, however, the precise mechanism of fibrinogen leading to the pro-inflammatory and pro-coagulatory response on monocytes is yet unknown. RESULTS: Fibrinogen and its digestion fragment D induced pro-coagulant activation of monocytes as assessed in a cellular coagulation assay by reductions in clotting times. Pro-coagulant activation was reversed by blocking antibodies against Mac-1 or LFA-1. Pre-exposure of monocytes to the p38 MAPK inhibitor SB 202190 and the MEK1.2 inhibitor U0126 led to significant increasees in coagulation times whereas blocking JNKII with its inhibitor had no such effect. Blocking NFkappaB with MG-132 also inhibited pro-coagulant activation of monocytes by fibrinogen. A selective inhibitor of matrix metalloproteinase-9 increased times to clot formation whereas other matrix metalloproteinase inhibitors did not significantly interfere with fibrinogen-augmented clot formation in this assay. Treatment of monocytes with fibrinogen increased concentrations of matrix metalloproteinase-9 immunoreactivity in their supernatants. CONCLUSIONS: Fibrinogen induces monocyte pro-coagulant activation in an integrin-, nuclear factor kappaB-, p38 MAPK-, and MEK1.2-dependent manner. Activation of monocytes by fibrinogen increases metalloproteinase-9 secretion, metalloproteinase-9 itself enhances monocyte coagulation by an autocrine mechanism. Results provide further evidence that mediators of hemostasis have a profound impact on cells of the immune system and are closely related to inflammatory pathways.

Immunomodulation by alpha(1)-proteinase inhibitor: lack of chemotactic effects of recombinant human alpha(1)-proteinase inhibitor from yeast on human peripheral blood granulocytes.

INTRODUCTION: Recombinant alpha(1)-proteinase inhibitor, clinically developed for inhalative augmentation therapy in patients with alpha(1)-proteinase inhibitor deficiency or cystic fibrosis, may directly contribute to leukocyte accumulation as it may function as a chemoattractant. The migratory effects of yeast-derived human recombinant alpha(1)-proteinase inhibitor on human peripheral blood neutrophils and eosinophils were therefore tested in vitro. MATERIALS AND METHODS: Human peripheral blood leukocytes were prepared from forearm venous blood and tested for migration toward various preparations of yeast-derived recombinant alpha(1)-proteinase inhibitor in modified Boyden-chamber micropore filter assays. RESULTS: No direct effects of yeast-derived recombinant human alpha(1)-proteinase inhibitor on in vitro migration of isolated neutrophils or eosinophils were seen. CONCLUSIONS: The lack of direct chemotactic effects of recombinant human alpha(1)-proteinase inhibitor despite anti-inflammatory effects in other biological activities of leukocytes may contribute to the preserved antibacterial defense mechanisms observed in patients under experimental augmentation therapy with inhaled alpha(1)-proteinase inhibitor.

Visfatin, an adipocytokine with proinflammatory and immunomodulating properties.

Adipocytokines are mainly adipocyte-derived cytokines regulating metabolism and as such are key regulators of insulin resistance. Some adipocytokines such as adiponectin and leptin affect immune and inflammatory functions. Visfatin (pre-B cell colony-enhancing factor) has recently been identified as a new adipocytokine affecting insulin resistance by binding to the insulin receptor. In this study, we show that recombinant visfatin activates human leukocytes and induces cytokine production. In CD14(+) monocytes, visfatin induces the production of IL-1beta, TNF-alpha, and especially IL-6. Moreover, it increases the surface expression of costimulatory molecules CD54, CD40, and CD80. Visfatin-stimulated monocytes show augmented FITC-dextran uptake and an enhanced capacity to induce alloproliferative responses in human lymphocytes. Visfatin-induced effects involve p38 as well as MEK1 pathways as determined by inhibition with MAPK inhibitors and we observed activation of NF-kappaB. In vivo, visfatin induces circulating IL-6 in BALB/c mice. In patients with inflammatory bowel disease, plasma levels of visfatin are elevated and its mRNA expression is significantly increased in colonic tissue of Crohn's and ulcerative colitis patients compared with healthy controls. Macrophages, dendritic cells, and colonic epithelial cells might be additional sources of visfatin as determined by confocal microscopy. Visfatin can be considered a new proinflammatory adipocytokine.

Heparan sulfate proteoglycan-dependent neutrophil chemotaxis toward PR-39 cathelicidin.

Cathelicidins are mammalian proteins containing a C-terminal cationic antimicrobial domain. Porcine PR-39 cathelicidin affects leukocyte biology. Mechanisms of action may involve alteration of heparan sulfate proteoglycan-dependent functions in inflammatory cells. It was tested whether PR-39 affects human neutrophil migration and if such effects involve heparan sulphate proteoglycans. Neutrophils were from forearm venous blood of healthy donors. Migration was tested in modified Boyden chamber assays. Involvement of heparan sulfate proteoglycans was tested by their chemical modification and by the use of specific antibodies. PR-39 induced migration in neutrophils in a concentration dependent manner. Modification of heparan sulfate proteoglycans with sodium chlorate inhibited migration whereas chemotaxis toward the chemoattractant formyl-Met-Leu-Phe was not affected. Removal of heparan sulfates or chondroitin sulfates from the surface of neutrophils by heparinase or chondroitinase inhibited migration toward PR-39. In conclusion, antimicrobial PR-39 stimulates human neutrophil chemotaxis in a heparan sulfate proteoglycan-dependent manner. Involvement of syndecans is likely as both heparinase and chondroitinase were abrogating. Data suggest active participation of heparan sulfate proteoglycans of neutrophils in cathelicidin peptide-mediated regulation of the antimicrobial host defense.

Inhibition of cyclooxygenase (COX)-2 affects endothelial progenitor cell proliferation.

Growing evidence indicates that inducible cyclooxygenase-2 (COX-2) is involved in the pathogenesis of inflammatory disorders and various types of cancer. Endothelial progenitor cells recruited from the bone marrow have been shown to be involved in the formation of new vessels in malignancies and discussed for being a key point in tumour progression and metastasis. However, until now, nothing is known about an interaction between COX and endothelial progenitor cells (EPC). Expression of COX-1 and COX-2 was detected by semiquantitative RT-PCR and Western blot. Proliferation kinetics, cell cycle distribution and rate of apoptosis were analysed by MTT test and FACS analysis. Further analyses revealed an implication of Akt phosphorylation and caspase-3 activation. Both COX-1 and COX-2 expression can be found in bone-marrow-derived endothelial progenitor cells in vitro. COX-2 inhibition leads to a significant reduction in proliferation of endothelial progenitor cells by an increase in apoptosis and cell cycle arrest. COX-2 inhibition leads further to an increased cleavage of caspase-3 protein and inversely to inhibition of Akt activation. Highly proliferating endothelial progenitor cells can be targeted by selective COX-2 inhibition in vitro. These results indicate that upcoming therapy strategies in cancer patients targeting COX-2 may be effective in inhibiting tumour vasculogenesis as well as angiogenic processes.

Endothelial protein C receptor-dependent inhibition of migration of human lymphocytes by protein C involves epidermal growth factor receptor.

The protein C pathway is an important regulator of the blood coagulation system. Protein C may also play a role in inflammatory and immunomodulatory processes. Whether protein C or activated protein C affects lymphocyte migration and possible mechanisms involved was tested. Lymphocyte migration was studied by micropore filter assays. Lymphocytes that were pretreated with protein C (Ceprotin) or activated protein C (Xigris) significantly reduced their migration toward IL-8, RANTES, MCP-1, and substance P, but not toward sphingosine-1-phosphate. The inhibitory effects of protein C or activated protein C were reversed by Abs against endothelial protein C receptor and epidermal growth factor receptor. Evidence for the synthesis of endothelial protein C receptor by lymphocytes is shown by demonstration of receptor mRNA expression and detection of endothelial protein C receptor immunoreactivity on the cells' surface. Data suggest that an endothelial protein C receptor is expressed by lymphocytes whose activation with protein C or activated protein C arrests directed migration. Exposure of lymphocytes to protein C or activated protein C stimulates phosphorylation of Tyr845 of epidermal growth factor receptor, which may be relevant for cytoprotective effects of the protein C pathway.

Angiopoietin affects neutrophil migration.

OBJECTIVE: After an ischemic event vascular growth factors are involved in regulating leukocyte infiltration in inflammatory processes. This study focused on effects of 2 other angiogenic growth factors, angiopoietin-1 and angiopoietin-2, on human neutrophils and on the involvement of the angiopoietin receptor Tie-2. METHODS: Neutrophils were from venous blood of healthy donors and cell migration was studied by micropore filter assays. Receptor expression was investigated by reverse transcriptase-polymerase chain reaction (PCR) for mRNA and fluorescence-activated cell-sorter scanner (FACS) analysis. Signaling mechanisms required for angiopoietin-dependent effects were tested functionally by using signaling enzyme blockers. RESULTS: The angiopoietins were chemotactic for neutrophils. They showed antagonistic effects on each other and both inhibited VEGF-directed migration of neutrophils. The effects of both angiopoietins were Tie-2 dependent. Tie-2 receptor immunoreactivity was confirmed on neutrophils by FACS. De novo synthesis is suggested by Tie-2 receptor mRNA expression as demonstrated by reverse transcriptase PCR. CONCLUSIONS: Data suggest that a Tie-2 receptor is expressed by human neutrophils whose active site ligation with either angiopoietin-1 or angiopoietin-2 exerts migratory effects on the one hand and arrests VEGF-mediated chemotaxis on the other. These effects suggest a role of angiopoietins in modulating neutrophilic inflammation.

Expression and function of syndecan-4 in human platelets.

Platelet recruitment crucially depends on amplification systems provided by autocrine and paracrine factors such as adenosine diphosphate. In inflammatory states, consumption of coagulation proteins, such as antithrombin aggravates the procoagulant state. In this study, we report that platelets express syndecan-4, an antithrombin-binding cell surface heparan sulphate proteoglycan, whose ligation with antithrombin inhibits activated platelet-dependent superoxide anion release from neutrophils by the limitation of adenosine diphosphate and adenosine triphosphate secretion in activated platelets. Adenosine triphosphate-induced platelet aggregation is reduced after treatment of platelets with antithrombin, which is reversed by blockade of syndecan-4. We further observed that antithrombin limits CD40 ligand expression in adenosine diphosphate-activated platelets and inhibits the shedding of syndecan-4 from activated platelets. Syndecan-4 appears to be directly involved in regulating platelet aggregation as anti-syndecan-4 antibody augments platelet aggregation. We suggest that antithrombin might exert beneficial effects in disseminated intravascular coagulation by reducing platelet activation, observed as inhibited CD40 ligand expression, syndecan-4 shedding, and adenosine diphosphate- and adenosine triphosphate-release from activated platelets with subsequent inhibition of neutrophil respiratory burst. From these data it is concluded that syndecan-4 may play important roles in the regulation of inflammatory effects of platelets.

CD40-ligand-dependent induction of COX-2 gene expression in endothelial cells by activated platelets: inhibitory effects of atorvastatin.

Increasing evidence shows the importance of platelet-endothelial cell interactions in the progression of atherosclerosis. Platelets contribute to coronary events both as major components of thrombi and as a triggering factor in inflammation that leads to plaque vulnerability. Recent data suggest that statins, besides their lipid-lowering properties, exert pleiotropic effects that may be beneficial in atherosclerosis. Whether activated platelets influence cyclooxygenase-2 (COX-2) expression in human umbilical vein endothelial cells (HUVEC), the effect of atorvastatin, and possible mechanisms were investigated. COX-2 gene expression in HUVEC was studied using real-time polymerase chain reaction. CD40 ligand surface expression of platelets was tested by fluorescence-activated cell sorting analyses. Activated platelets significantly up-regulated COX-2 gene expression in HUVEC. Co-incubation of platelets with atorvastatin was shown to reverse this up-regulation via reduction of CD40 ligand surface expression on platelets. Data suggest that atorvastatin influences CD40-CD40-ligand-dependent platelet-endothelial interaction and that this influence affects platelet-induced COX-2 expression in HUVEC.

Src tyrosine kinase-dependent migratory effects of antithrombin in leukocytes.

Tyrosine kinases are known to play a critical role in the regulation of leukocyte function. Antithrombin mediates its effects via syndecan-4 which is known to be linked to the Src tyrosine kinases. In this study, we investigated the role of Src tyrosine kinases in antithrombin-regulated leukocyte migration and Src tyrosine kinase phosphorylation in response to stimulation with antithrombin. Neutrophils and monocytes obtained from forearm venous blood were pre-treated by various Src-family selective tyrosine kinase inhibitors with or without antithrombin followed by washing and assessment of their migratory response toward antithrombin, interleukin-8, or RANTES using Boyden microchemotaxis chambers. Activation status of the two major Src tyrosine kinase phosphorylation sides Tyr416 and Tyr527 was tested using Western blot analysis. Dose-dependent reversal of the antithrombin-mediated effects on neutrophil and monocyte migration was induced by the selective Src kinase inhibitors PP1 and PP2. In Western blot analyses, antithrombin increased Tyr416 and decreased Tyr527 phosphorylation of Src tyrosine kinases in a time- and dose-dependent manner. Moreover, co-incubation with antithrombin lowered the level of RANTES-induced Tyr416 phosphorylation. Therefore, Src tyrosine kinases linked to signaling of antithrombin-binding sites on leukocytes may play an important role in modulating effects on cells function.

Syndecan-1 is involved in osteoprotegerin-induced chemotaxis in human peripheral blood monocytes.

Chronic inflammation is characterized by tissue infiltration with monocytes/macrophages, which possess broad proinflammatory, destructive, and remodeling capacities. Elevated levels of osteoprotegerin, an important regulator of differentiation and activation of osteoclasts that also affects different cells of the immune system, were found in the serum of patients with chronic inflammatory diseases. The study of whether osteoprotegerin affects monocyte locomotion in vitro and the possible mechanisms and pathways involved was investigated using Boyden microchemotaxis chambers and Western blot analyses. Osteoprotegerin significantly stimulated monocyte chemotaxis, whereas preincubation of monocytes with osteoprotegerin inhibited monocyte migration toward optimal concentrations of regulated upon activation normal T cell expressed and secreted, monocyte chemotactic protein -1, and procalcitonin. The effects of osteoprotegerin were abolished by pretreating cells with heparinase I and chondroitinase or antibodies against the ectodomain of syndecan-1. Osteoprotegerin signaling was shown to involve protein kinase C, phosphatidylinositol 3-kinase/Akt, and tyrosine kinase. Data suggest that osteoprotegerin affects monocyte mi-gration and protein kinase C and phosphatidylinositol 3-kinase/Akt activation via syndecan-1. Osteoprotegerin-induced deactivation of monocyte chemotaxis toward different chemokines is due to interaction of osteoprotegerin with heparan sulfate and chondroitin sulfate.

Effects of the neuropeptide secretoneurin on natural killer cell migration and cytokine release.

Secretoneurin has a widespread occurrence in airway mucosal innervation of patients with allergic diseases and may play an important role in the local traffic of immune cells in human airway mucosa. Whether secretoneurin affects natural killer cell migration and cytokine release in vitro was tested. Natural killer cells were obtained from venous blood of healthy donors. Cell migration was studied by micropore filter assays. Signalling mechanisms required for secretoneurin-dependent migration were tested using signalling enzyme blockers. Cytokine release was measured in natural killer cell supernatants by ELISA. Secretoneurin significantly stimulated natural killer cell chemotaxis via activation of phosphatidylinositol 3'-kinase and protein kinase C. IL-2 stimulated natural killer cells showed a stronger response toward secretoneurin than unstimulated cells. Moreover, secretoneurin increased the release of interleukin-5 in a dose-dependent manner but did not affect Th1 cytokine release by natural killer cells. Data suggest that secretoneurin stimulates directed migration of natural killer cells and may modulate Th1/Th2-response via affecting chemokine release. Thus, secretoneurin may play an important role in the early stages of allergic inflammation.

The immunomodulator FTY720 interferes with effector functions of human monocyte-derived dendritic cells.

The potent immunomodulator FTY720 elicits immunosuppression via acting on sphingosine 1-phosphate receptors (S1PR), thereby leading to an entrapment of lymphocytes in the secondary lymphoid tissue. To elucidate the potential in vitro effects of this drug on human monocyte-derived DC, we used low nanomolar therapeutic concentrations of FTY720 and phosphorylated FTY720 (FTY720-P) and investigated their influence on DC surface marker expression, protein levels of S1PR and DC effector functions: antigen uptake, chemotaxis, cytokine production, allostimulatory and Th-priming capacity. We report that both FTY720 and FTY720-P reduce chemotaxis of immature and mature DC. Mature DC generated in the presence of FTY720 or FTY720-P showed an impaired immunostimmulatory capacity and reduced IL-12 but increased IL-10 production. T cells cultured in the presence of FTY720- or FTY720-P-treated DC showed an altered cytokine production profile indicating a shift from Th1 toward Th2 differentiation. In treated immature and mature DC, expression levels for two S1PR proteins, S1P1 and S1P4, were reduced. We conclude that in vitro treatment with FTY720 affects DC features that are essential for serving their role as antigen-presenting cells. This might represent a new aspect of the overall immunosuppressive action of FTY720 and makes DC potential targets of further sphingolipid-derived drugs.

Expression and function of the angiopoietin receptor Tie-2 in human eosinophils.

BACKGROUND: Increased vascularity of bronchial mucosa is closely related to the expression of angiogenic factors, which contribute to the pathogenesis of diseases such as asthma bronchiale. OBJECTIVE: Here we examine the effects of the angiogenic growth factors angiopoietin 1 and angiopoietin 2 on eosinophil function in vitro and possible involvement of the angiopoietin receptor Tie-2. METHODS: Eosinophil migration was studied by micropore filter assays. Signaling mechanisms required for angiopoietin-dependent migration were tested by using signaling enzyme blockers. Tie-2 mRNA and receptor expression on the cell surface of eosinophils was demonstrated in RT-PCR and by fluorescence-activated cell sorting analysis. RESULTS: Angiopoietin 1 significantly stimulated eosinophil chemotaxis via activation of phosphodiesterase, phosphatidylinositol 3'-kinase, and tyrosine kinases. The effect on eosinophil migration of angiopoietin 1 was reversed by an antibody against the Tie-2 receptor and by angiopoietin 2. Incubation of eosinophils with angiopoietin 1 abolished the chemotactic effects of vascular endothelial growth factor on human eosinophils via the Tie-2 receptor. Finally, Tie-2 expression by human eosinophils was demonstrated on the transcriptional and protein level. CONCLUSIONS: Data suggest that angiopoietin 1 stimulates directed migration and possibly inhibits vascular endothelial growth factor-induced eosinophil chemotaxis via its Tie-2 receptor, which is expressed by eosinophils. Thus, angiopoietin 1 may play an important role in the modulation of eosinophilic inflammation.

Inhibition of thrombin-induced signaling by resveratrol and quercetin: effects on adenosine nucleotide metabolism in endothelial cells and platelet-neutrophil interactions.

BACKGROUND: Thrombin downregulates endothelial ectonucleotidase activity resulting in high levels of adenosine diphosphate (ADP) and adenosine triphosphate (ATP) which lead to platelet, leukocyte and endothelial activation. Depending on adenosine nucleotide levels, resting platelets inhibit and thrombin-activated platelets increase respiratory burst of neutrophils. Whether the red wine polyphenols quercetin and resveratrol affect thrombin-dependent adenosine nucleotide, metabolism and thrombin-induced signaling is unknown. MATERIALS AND METHODS: ATP and ADP secretion by platelets, the impact on subsequent oxidative burst activity in neutrophils and CD39/ATPdase function in endothelial cells (ECs)was studied. Cell migration was measured in modified Boyden chambers; adenosine metabolites were quantified by high-performance liquid chromatography (HPLC). Signal transduction was studied by Western blotting. RESULTS: Quercetin and resveratrol inhibited thrombin-induced ADP and ATP secretion from platelets in a concentration-dependent manner. Augmented respiratory burst of neutrophils in response to thrombin-activated platelets was also inhibited by the two polyphenols as was neutrophil migration toward thrombin-induced supernatants of platelets. Quercetin and resveratrol restored the decreased CD39/ATPdase activity in human umbilical vein endothelial cells, in response to thrombin as demonstrated by adenosine monophosphate (AMP) and adenosine increases in endothelial culture supernatants. Both polyphenols inhibited thrombin-induced MAPK, JNK and focal adhesion kinase activities in endothelial cells. CONCLUSION: Quercetin and resveratrol interfere with the proinflammatory signaling of thrombin resulting in the inhibition of adenosine nucleotide secretion from activated platelets and decreased neutrophil function. Moreover, the polyphenols protect endothelial adenosine nucleotide metabolism when downregulated by thrombin. These observations may explain cardioprotective effects of grape products.

Thrombin affects eosinophil migration via protease-activated receptor-1.

BACKGROUND: Protease-activated receptors (PARs) are a unique class of G-protein-coupled receptors, which are activated by proteolytic cleavage of the amino terminus of the receptor itself. Although expression of the PAR1, which is typically activated by thrombin, on human eosinophils has been demonstrated, no effect of thrombin on eosinophil function has been shown yet. Thus we investigated whether thrombin affects eosinophil migration in vitro. METHODS: Eosinophils were obtained from venous blood of healthy donors. Cell migration was studied by micropore filter assays. Involvement of PARs in thrombin-dependent migration was tested functionally using selective agonist peptides for PARs and a cleavage blocking PAR1 antibody. RESULTS: Thrombin significantly stimulated eosinophil chemotaxis in a dose-dependent manner. This effect was mimicked by the PAR1 but not the PAR2 agonist and was reversed by the cleavage blocking PAR1 antibody. Checkerboard experiments indicated that eosinophil migration depends on the presence of thrombin in a concentration gradient. CONCLUSIONS: Data suggest that activation of PAR1 by thrombin stimulates directed migration of human eosinophils and thereby may affect eosinophils in tissue and allergic inflammation.

Expression and function of RANK in human monocyte chemotaxis.

OBJECTIVE: RANKL, a member of the tumor necrosis factor superfamily, is a central regulator of osteoclast recruitment and activation. Whether RANKL affects monocyte locomotion in vitro via RANK and a possible signaling pathway were investigated. METHODS: Monocytes were obtained from venous blood of healthy donors. Cell migration was studied by micropore filter assays. The signaling mechanisms required for RANKL-dependent migration were tested using signaling enzyme blockers and Western blot analyses. Expression of RANK messenger RNA (mRNA) in monocytes was demonstrated by reverse transcriptase-polymerase chain reaction, and receptor expression on cell surface was investigated by fluorescence-activated cell sorting analyses. RESULTS: RANKL significantly stimulated monocyte chemotaxis via activation of phosphatidylinositol 3-kinase, phosphodiesterase, and Src kinase. The effect on migration was inhibited by osteoprotegerin, which is the decoy receptor for RANKL. Expression of RANK receptor mRNA was shown, and synthesis of RANK in monocytes was suggested by the detection of RANK immunoreactivity on the cell surface. CONCLUSION: These data suggest that RANK is expressed by monocytes whose activation by RANKL stimulates directed migration involving phosphatidylinositol 3-kinase, phosphodiesterase, and Src kinases.

The immune modulator FTY720 targets sphingosine-kinase-dependent migration of human monocytes in response to amyloid beta-protein and its precursor.

Accumulation of inflammatory mononuclear phagocytes in Alzheimer's senile plaques, a hallmark of the innate immune response to beta-amyloid fibrils, can initiate and propagate neurodegeneration characteristic of Alzheimer's disease. Phagocytes migrate toward amyloid beta-protein involving formyl peptide receptor like-1-dependent signaling. Using human peripheral blood monocytes in Boyden chamber micropore filter assays, we show that the amyloid beta-protein- and amyloid beta-precursor protein-induced migration was abrogated by dimethylsphingosine, a sphingosine kinase inhibitor. Amyloid beta-protein stimulated in monocytes the gene expression for sphingosine-1-phosphate receptors 2 and 5, but not 1, 3, and 4. FTY720 that acts as a sphingosine-1-phosphate receptor agonist after endogenous phosphorylation by sphingosine kinase, as well as various neuropeptides that are known to be monocyte chemoattractants, dose-dependently inhibited amyloid beta-protein-induced migration. These data demonstrate that the migratory effects of beta-amyloid in human monocytes involve spingosine-1-phosphate signaling. Whereas endogenous neuropeptides may arrest and activate monocytes at sites of high beta-amyloid concentrations, interference with the amyloid beta-protein-dependent sphingosine-1-phosphate pathway in monocytes by FTY720, a novel immunomodulatory drug, suggests that FTY720 may be efficacious in beta-amyloid-related inflammatory diseases.