Chemokine and chemokine receptor mRNA expression in human platelets

MCP-3 as a prognostic biomarker for severe fever with thrombocytopenia syndrome: a longitudinal cytokine profile study

Introduction

Severe fever with thrombocytopenia syndrome (SFTS) is characterized by a high mortality rate and is associated with immune dysregulation. Cytokine storms may play an important role in adverse disease regression, this study aimed to assess the validity of MCP-3 in predicting adverse outcomes in SFTS patients and to investigate the longitudinal cytokine profile in SFTS patients.

Methods

The prospective study was conducted at Yantai Qishan Hospital from May to November 2022. We collected clinical data and serial blood samples during hospitalization, patients with SFTS were divided into survival and non-survival groups based on the clinical prognosis.

Results

The levels of serum 48 cytokines were measured using Luminex assays. Compared to healthy controls, SFTS patients exhibited higher levels of most cytokines. The non-survival group had significantly higher levels of 32 cytokines compared to the survival group. Among these cytokines, MCP-3 was ranked as the most significant variable by the random forest (RF) model in predicting the poor prognosis of SFTS patients. Additionally, we validated the predictive effects of MCP-3 through receiver operating characteristic (ROC) curve analysis with an AUC of 0.882 (95% CI, 0.787-0.978, P <0.001), and the clinical applicability of MCP-3 was assessed favorably based on decision curve analysis (DCA). The Spearman correlation analysis indicated that the level of MCP-3 was positively correlated with ALT, AST, LDH, α-HBDH, APTT, D-dimer, and viral load (P<0.01).

Discussion

For the first time, our study identified and validated that MCP-3 could serve as a meaningful biomarker for predicting the fatal outcome of SFTS patients. The longitudinal cytokine profile analyzed that abnormally increased cytokines were associated with the poor prognosis of SFTS patients. Our study provides new insights into exploring the pathogenesis of cytokines with organ damage and leading to adverse effects.

Platelet-derived chemokines promote skeletal muscle regeneration by guiding neutrophil recruitment to injured muscles

Skeletal muscle regeneration involves coordinated interactions between different cell types. Injection of platelet-rich plasma is circumstantially considered an aid to muscle repair but whether platelets promote regeneration beyond their role in hemostasis remains unexplored. Here, we find that signaling via platelet-released chemokines is an early event necessary for muscle repair in mice. Platelet depletion reduces the levels of the platelet-secreted neutrophil chemoattractants CXCL5 and CXCL7/PPBP. Consequently, early-phase neutrophil infiltration to injured muscles is impaired whereas later inflammation is exacerbated. Consistent with this model, neutrophil infiltration to injured muscles is compromised in male mice with Cxcl7-knockout platelets. Moreover, neo-angiogenesis and the re-establishment of myofiber size and muscle strength occurs optimally in control mice post-injury but not in Cxcl7ko mice and in neutrophil-depleted mice. Altogether, these findings indicate that platelet-secreted CXCL7 promotes regeneration by recruiting neutrophils to injured muscles, and that this signaling axis could be utilized therapeutically to boost muscle regeneration.

Matrix stiffness-induced platelet activation determines immunomodulation of macrophages

Although various bone defect repair materials have been used clinically, the influence of the material properties on bone repair and regeneration as well as the underlying mechanisms are not fully understood. We hypothesize that the material stiffness affects initial platelet activation during hemostasis phase, which in turn mediates subsequent osteoimmunomodulation of macrophages, finally determining clinical outcomes. To verify the hypothesis, the present work used polyacrylamide hydrogels with different stiffness (10, 70, and 260 kPa) as model materials to investigate matrix stiffness induced platelet activation behavior and its mediation on osteoimmunomodulation of macrophages. The results showed that the matrix stiffness was positively related with activation degree of platelets. However, the extracts of platelets incubated on middle-stiff matrix polarized macrophages to pro-healing M2 phenotype when compared with that on soft and stiff matrixes. ELISA results showed when compared with that on soft and stiff matrixes, the platelets incubated on middle-stiff matrix released more TGF-β and PGE₂, both of which could polarize macrophages to M2 phenotype. The M2 macrophages could promote angiogenesis of endothelial cells and osteogenesis of bone marrow mesenchymal stem cells, two important and coupled processes involved in bone repair and regeneration. These findings suggest bone repair materials with 70 kPa stiffness can mediate proper platelet activation, which can polarize macrophages to pro-healing M2 phenotype, potentially contributing to bone repair and regeneration.

Thromboembolic Events in Patients with Inflammatory Bowel Disease: A Comprehensive Overview

Inflammatory bowel disease (IBD), Crohn’s disease and ulcerative colitis are chronic inflammatory disorders of the intestines. The underlying inflammation activates the coagulation cascade leading to an increased risk of developing arterial and venous thromboembolic events such as deep vein thrombosis and pulmonary embolism. Patients with IBD are at a 2–3-fold increased risk of developing thromboembolism. This risk increases in patients with active IBD disease, flare-ups, surgery, steroid treatment, and hospitalization. These complications are associated with significant morbidity and mortality making them important in clinical practice. Clinicians should consider the increased risk of thromboembolic events in patients with IBD and manage them with appropriate prophylaxis based on the risk. In this review, we discuss the literature associated with the pathophysiology of thromboembolism in patients with IBD, summarize the studies describing the various thromboembolic events, and the management of thromboembolism in patients with IBD.

CCR4 and CCR5 Involvement in Monocyte-Derived Macrophage Migration in Neuroinflammation

Microglia, resident macrophages in the brain, play major roles in neuroinflammation after an acute many neurological diseases, including stroke. Our recent animal stroke model showed that interleukin (IL)-4 and IL-13 released by microglia are converted into monocyte-derived macrophages. However, the correlation with the migration mechanism of these cells is still unclear. This study aimed to clarify the effect of these cells on their migration and to identify potential targets that influence neuroinflammatory conditions. Inflammatory conditions were induced by lipopolysaccharide (LPS) treatment in in vitro and in vivo models. Cell migration was observed using transwell assay, and target chemokines were screened using the proteome profiler array in the in vitro model. Intravital, IVIS, and CLARITY imaging were used in the in vivo model. After LPS (1 ng/ml) treatment in BV2 (microglia cell line) and J774 (monocyte/macrophage cell line) cells, BV2 migration was approximately two-fold more enhanced compared to J774 migration. Overall, six types of chemokine C-C motif ligands (CCLs) were detected from the BV2 conditioned medium with LPS. These CCLs were related to C-C motif receptor (CCR)4 and CCR5. In the in vivo model, CCR4 and CCR5 antagonist significantly inhibited the migration of monocyte-derived macrophages to brain tissue following LPS (5 µg) treatment. In conclusion, the chemokines released by microglia may influence migration of monocyte-derived macrophages in necroinflammation conditions inducted by microglial activation. CCR4 and CCR5 expressed on monocyte-derived macrophages interacted with these chemokines and induced migration. Therefore, CCR4 and CCR5 may be explored as new therapeutic targets for neuroinflammation.

Recent Advances in the Discovery and Function of Antimicrobial Molecules in Platelets

The conventional function described for platelets is maintaining vascular integrity. Nevertheless, increasing evidence reveals that platelets can additionally play a crucial role in responding against microorganisms. Activated platelets release molecules with antimicrobial activity. This ability was first demonstrated in rabbit serum after coagulation and later in rabbit platelets stimulated with thrombin. Currently, multiple discoveries have allowed the identification and characterization of PMPs (platelet microbicidal proteins) and opened the way to identify kinocidins and CHDPs (cationic host defense peptides) in human platelets. These molecules are endowed with microbicidal activity through different mechanisms that broaden the platelet participation in normal and pathologic conditions. Therefore, this review aims to integrate the currently described platelet molecules with antimicrobial properties by summarizing the pathways towards their identification, characterization, and functional evaluation that have promoted new avenues for studying platelets based on kinocidins and CHDPs secretion.

Platelets and tumor-associated RNA transfer

Until recently, the nucleic acid content of platelets was considered to be fully determined by their progenitor megakaryocyte. However, it is now well understood that additional mediators (eg, cancer cells) can intervene, thereby influencing the RNA repertoire of platelets. Platelets are highly dynamic cells that are able to communicate and influence their environment. For instance, platelets have been involved in various steps of cancer development and progression by supporting tumor growth, survival, and dissemination. Cancer cells can directly and/or indirectly influence platelet RNA content, resulting in tumor-mediated "education" of platelets. Alterations in the tumor-educated platelet RNA profile have been described as a novel source of potential biomarkers. Individual platelet RNA biomarkers as well as complex RNA signatures may be used for early detection of cancer and treatment monitoring. Here, we review the RNA transfer occurring between cancer cells and platelets. We explore the potential use of platelet RNA biomarkers as a liquid biopsy biosource and discuss methods to evaluate the transcriptomic content of platelets.

Considerations for Soluble Protein Biomarker Blood Sample Matrix Selection

Blood-based soluble protein biomarkers provide invaluable clinical information about patients and are used as diagnostic, prognostic, and pharmacodynamic markers. The most commonly used blood sample matrices are serum and different types of plasma. In drug development research, the impact of sample matrix selection on successful protein biomarker quantification is sometimes overlooked. The sample matrix for a specific analyte is often chosen based on prior experience or literature searches, without good understanding of the possible effects on analyte quantification. Using a data set of 32 different soluble protein markers measured in matched serum and plasma samples, we examined the differences between serum and plasma and discussed how platelet or immune cell activation can change the quantified concentration of the analyte. We have also reviewed the effect of anticoagulant on analyte quantification. Finally, we provide specific recommendations for biomarker sample matrix selection and propose a systematic and data-driven approach for sample matrix selection. This review is intended to raise awareness of the impact and considerations of sample matrix selection on biomarker quantification.

Isolation of B-cells using Miltenyi MACS bead isolation kits

This article describes the procedures used to isolate pure B-cell populations from whole blood using various Miltenyi magnetic-activated cell sorting (MACS) bead Isolation kits. Such populations are vital for studies investigating the functional capacity of B-cells, as the presence of other cell types may have indirect effects on B-cell function through cell-cell interactions or by secretion of several soluble molecules. B-cells can be isolated by two main approaches: 1) Negative selection—in which B-cells remain “untouched” in their native state; this is advantageous as it is likely that B-cells remain functionally unaltered by this process. 2) Positive selection–in which B-cells are labelled and actively removed from the sample. We used three Negative B-cell isolation kits as well as the Positive B-cell isolation kit from Miltenyi and compared the purity of each of the resulting B-cells fractions. Contamination of isolated B-cell fractions with platelets was the conclusive finding for all of the isolation techniques tested. These results illustrate the inefficiency of current available MACS B-cell isolation kits to produce pure B-cell populations, from which concrete findings can be made. As such we suggest cell sorting as the preferred method for isolating pure B-cells to be used for downstream functional assays.

Tumor-educated platelets

Liquid biopsies have been considered the holy grail in achieving effective cancer management, with blood tests offering a minimally invasive, safe, and sensitive alternative or complementary approach for tissue biopsies. Currently, blood-based liquid biopsy measurements focus on the evaluation of biomarker types, including circulating tumor DNA, circulating tumor cells, extracellular vesicles (exosomes and oncosomes), and tumor-educated platelets (TEPs). Despite the potential of individual techniques, each has its own advantages and disadvantages. Here, we provide further insight into TEPs.

Effect of Chemokine (C-C Motif) Ligand 7 (CCL7) and Its Receptor (CCR2) Expression on Colorectal Cancer Behaviors

Colorectal cancer is the source of one of the most common cancer-related deaths worldwide, where the main cause of patient mortality remains metastasis. The aim of this study was to determine the role of CCL7 (chemokine (C-C motif) ligand 7) in tumor progression and finding whether it could predict survival of colorectal cancer patients. Initially, our study focused on the crosstalk between mesenchymal stem cells (MSCs) and CT26 colon carcinoma cells and resulted in identifying CCL7 as a chemokine upregulated in CT26 colon cancer cells cocultured with MSCs, compared with CT26 in monoculture in vitro. Moreover, we showed that MSCs enhance CT26 tumor cell proliferation and migration. We analyzed the effect of CCL7 overexpression on tumor progression in a murine CT26 model, where cells overexpressing CCL7 accelerated the early phase of tumor growth and caused higher lung metastasis rates compared with control mice. Microarray analysis revealed that tumors overexpressing CCL7 had lower expression of immunoglobulins produced by B lymphocytes. Additionally, using Jh mutant mice, we confirmed that in the CT26 model, CCL7 has an immunoglobulin-, and thereby, B-cell-dependent effect on metastasis formation. Finally, higher expression of CCL7 receptor CCR2 (C-C chemokine receptor type 2) was associated with shorter overall survival of colorectal cancer patients. Altogether, we showed that CCL7 is essentially involved in the progression of colorectal cancer in a CT26 mouse model and that the expression of its receptor CCR2 could be related to a different outcome pattern of patients with colorectal carcinoma.

Platelet-Activation Mechanisms and Vascular Remodeling

This overview article for the Comprehensive Physiology collection is focused on detailing platelets, how platelets respond to various stimuli, how platelets interact with their external biochemical environment, and the role of platelets in physiological and pathological processes. Specifically, we will discuss the four major functions of platelets: activation, adhesion, aggregation, and inflammation. We will extend this discussion to include various mechanisms that can induce these functional changes and a discussion of some of the salient receptors that are responsible for platelets interacting with their external environment. We will finish with a discussion of how platelets interact with their vascular environment, with a special focus on interactions with the extracellular matrix and endothelial cells, and finally how platelets can aid and possibly initiate the progression of various vascular diseases. Throughout this overview, we will highlight both the historical investigations into the role of platelets in health and disease as well as some of the more current work. Overall, the authors aim for the readers to gain an appreciation for the complexity of platelet functions and the multifaceted role of platelets in the vascular system. © 2017 American Physiological Society. Compr Physiol 8:1117-1156, 2018.

Crosstalk between CCL7 and CCR3 promotes metastasis of colon cancer cells via ERK-JNK signaling pathways

Chemokine ligand 7 (CCL7) enhances cancer progression and metastasis via epithelial-mesenchymal transition (EMT). However, little is known about the molecular mechanism of CCL7-induced EMT signaling cascade in colon cancer. Thus, the objective of this study was to investigate CCL7-induced EMT signaling pathway and its role in the progression and metastasis of colon cancer. To demonstrate the effect of CCL7 on EMT induction, HCT116 and HT29 cells overexpressing CCL7 were generated. CCL7-induced EMT and its downstream signaling pathway were evaluated by both in vitro and in vivo experiments. In in vitro studies, CCL7 was found to interplay with CC chemokine receptor 3 (CCR3), resulting in enhanced cellular proliferation, invasion, and migration via ERK and JNK signaling pathway. To validate these findings, we established ectopic and orthotopic mouse models injected with CCL7-overexpressed cells. In ectopic mouse models, we observed that CCL7-overexpressed cells grew significantly faster than control cells. In orthotopic mouse models, we found that liver and lung metastasis developed only in mice injected with CCL7-overexpressed cells. This study is the first one focusing on the EMT cascade via CCL7-CCR3-ERK-JNK signaling axis in colon cancer. Our novel findings will improve our understanding on the mechanism of metastatic process and provide potential therapeutic strategies for preventing metastasis in colon cancer.

Elevation of Activated Platelet-Dependent Chemokines in Patients With Anti-CD20 Monoclonal Antibody (Rituximab)−Treated Non-Hodgkin's Lymphoma

.ocn.ne.jp. This study measured and compared levels of some chemokines in patients with rituximab-treated non-Hodgkin lymphoma because they may participate in the mechanism of efficacy of rituximab in non-Hodgkin lymphoma patients. Monocytic chemotactant protein-1, RANTES (regulated on activation, normally T-cell expressed and secreted), eotaxin, interleukin-8, neutrophil-activating protein-78, stromal cell-derived factor-1, and growth-regulating oncogene-α in patients with rituximab-treated non-Hodgkin lymphoma were measured by enzyme-linked immunosorbent assay. Levels of RANTES were higher in non-Hodgkin lymphoma patients than in controls. Levels of monocytic chemotactant protein-1, RANTES, and neutrophil-activating protein-78 were significantly elevated before and after chemotherapy with rituximab treatment. However, the level of stromal cell-derived factor-1 did not exhibit a significant change. Before to after chemotherapy without rituximab treatment, all chemokine levels did not exhibit significant changes. These findings suggest that activated platelet-dependent chemokines such as RANTES and neutrophil-activating protein-78 may modulate the efficacy of rituximab in antibody-dependent cellular cytotoxity.

Platelet-derived CXCL12 (SDF-1α): basic mechanisms and clinical implications

Platelets are a major source of CXCL12 (stromal cell-derived factor -1α, SDF-1α) and store CXCL12 as part of their α-granule secretome. Platelet activation enhances surface expression and release of CXCL12. Platelets and megakaryocytes express CXCR4, the major receptor for CXCL12, and interaction of CXCL12 with CXCR4 regulates megakaryopoiesis and the function of circulating platelets. Platelet-derived CXCL12 also modulates paracrine mechanisms such as chemotaxis, adhesion, proliferation and differentiation of nucleated cells, including progenitor cells. Platelet-derived CXCL12 enhances peripheral recruitment of progenitor cells to the sites of vascular and tissue injury both in vitro and in vivo and thereby promotes repair mechanisms. CXCL12 expression on platelets is elevated in patients with acute myocardial infarction, correlates with the number of circulating progenitor cells, is associated with preservation of myocardial function and is an independent predictor of clinical outcome. Administration of recombinant CXCL12 reduces infarct size following transient ischemia in mice. The present review summarizes the role of platelet-derived CXCL12 in cardiovascular biology and its diagnostic and therapeutic implications.

Decreased plasma cytokines are associated with low platelet counts in aplastic anemia and immune thrombocytopenic purpura

BACKGROUND

We previously found plasma levels of CD40 ligand (CD40L), chemokine (C-X-C motif) ligand 5 (CXCL5), chemokine (C-C motif) ligand 5 (CCL5) and epidermal growth factor (EGF) to be low in aplastic anemia (AA) patients and to be correlated with platelet count.

OBJECTIVES

To study the association of CD40L, CXCL5, CCL5 and EGF with platelets.

METHODS

We measured cytokines in the plasma of immune thrombocytopenic purpura (ITP) and AA patients using the Luminex assay and confirmed the results in a mouse model and in vitro experiments.

RESULTS

Both ITP and AA showed similarly low levels of CD40L, CXCL5, CCL5 and EGF, compared with healthy controls. In ITP, levels of these proteins were significantly greater in patients with higher platelet counts than in those with lower platelet counts. In a murine thrombocytopenia model, levels of CD40L, CXCL5, CCL5 and EGF decreased with platelet count after immune-mediated destruction, while the cytokine levels increased when the platelet count recovered. In vitro, concentrations of these cytokines in the supernatants of platelet suspensions were proportional to platelet numbers, and levels in sera prepared by simple blood coagulation were equivalent to those in platelet-rich plasma-converted sera. mRNA expression for CXCL5, CCL5 and EGF was higher in platelets than in megakaryocytes, peripheral blood mononuclear cells, granulocytes and non-megakaryocytic bone marrow cells.

CONCLUSIONS

Plasma CD40L, CXCL5, CCL5 and EGF are mainly platelet-derived, suggesting a role of platelets in immune responses and inflammation. Measurement of CD40L, CXCL5, CCL5 and EGF in human blood allowed testable inferences concerning physiology and pathophysiology in quantitative platelet disorders.

CC chemokine ligand 7 expression in liver metastasis of colorectal cancer

The main cause of death for colorectal cancer (CRC) patients is the development of metastatic lesions at sites distant from the primary tumor. Therefore, it is important to find biomarkers that are related to the metastasis and to study the possible mechanisms. Recent data have shown that soluble attractant molecules called chemokines support the metastasis of certain cancers to certain organs. To identify molecular regulators that are differentially expressed in liver metastasis of CRC, PCR array analysis was performed and CC chemokine ligand 7 (CCL7) showed remarkable overexpression in liver metastatic tumor tissues. To validate the results of the PCR array, 30 patients with primary CRC and liver metastases were selected. Immunohistochemistry and real-time PCR analysis showed that CCL7 was expressed in normal colonic epithelium and the expression was higher in liver metastases compared to primary CRC (p<0.001). Real-time PCR showed that the expression of CCR1, CCR2 and CCR3 was also higher in liver metastases compared to primary CRC (p=0.001, p=0.033 and p<0.001, respectively). In conclusion, correlation of CCL7 overexpression and its receptor expression with colon cancer liver metastasis suggests that CCL7 as a novel target in liver metastasis of CRC may be of potential clinical value for the prevention of hepatic recurrences.

Internalization of IgG-coated targets results in activation and secretion of soluble CD40 ligand and RANTES by human platelets

Platelets are crucial elements for maintenance of hemostasis. Other functions attributable to platelets are now being appreciated, such as their role in inflammatory reactions and host defense. Platelets have been reported to bind immunological stimuli like IgG complexes, and for nearly 50 years it has been speculated that platelets may participate in immunological reactions. Platelets have been reported to bind and internalize various substances, similar to other leukocytes, such as macrophages and dendritic cells. In the present study, we tested the hypothesis that human platelets can bind and internalize IgG-coated particles, similar to leukocytes. To this end, we observed that interaction with IgG-coated beads resulted in platelet activation (as measured by CD62P expression), internalization of targets, and significant soluble CD40 ligand (sCD40L) and RANTES (regulated upon activation, normal T cell expresses and secreted) secretion. Blocking FcγRIIA with monoclonal antibody (MAb) IV.3 or inhibiting actin remodeling with cytochalasin D inhibited platelet activation, internalization, and cytokine production. These data suggest that platelets are capable of mediating internalization of IgG-coated particles, resulting in platelet activation and release of both sCD40L and RANTES.

Ccl22/MDC, is a prostaglandin dependent pyrogen, acting in the anterior hypothalamus to induce hyperthermia via activation of brown adipose tissue

CC Chemokine ligand 22 (Ccl22) is a selective, high affinity ligand at the CC chemokine receptor 4 (Ccr4). We have identified cDNAs encoding both ligand and receptor of the Ccl22-Ccr4 pair in cDNA libraries of the anterior hypothalamus/pre-optic area (AH/POA) by PCR. The AH/POA is the key brain region where endogenous pyrogens have been shown to act on warm sensitive neurons to affect thermogenesis in brown adipose tissue (BAT) and other thermogenically responsive tissues. We show that functional Ccr4 receptors are present in the AH/POA neurons as injection of Ccl22 into the POA but not to other hypothalamic nuclei induces an increase in core body temperature as measured by radiotelemetry. Indomethacin (5 mg/kg s.c) pre-treatment markedly reduced the hyperthermia evoked by POA injection of Ccl22 (10 ng/0.5 ul) and thus suggests that this hyperthermia is mediated through cyclooxygenase activation and thus likely through the formation and action of the pyrogen prostaglandin E2. The temperature elevation involves a decrease in the respiratory exchange ratio and increased activation of the brown adipose tissue as demonstrated by ¹⁸F-FDG-PET imaging. We describe a novel role to the ligand Ccl22 and its receptor Ccr4 in the anterior hypothalamus in temperature regulation that depends on the synthesis of the endogenous pyrogen, prostaglandin E2.

Platelet-derived chemokines: pathophysiology and therapeutic aspects

The identification of chemokines in blood platelets has strengthened our view of these cells as participants in immune host defense. Platelet chemokines representing prestored and rapidly releasable proteins may play a major role as first-line inflammatory mediators. This is evident from their capability to recruit early inflammatory cells such as neutrophil granulocytes and monocytes and even to exhibit direct antimicrobial activity. However, insight is growing that platelet chemokines may be also long-term regulators, e.g., by activating T lymphocytes, by modulating the formation of endothelium and even thrombocytopoiesis itself. This review deals with the individual and cooperative functionality of platelet chemokines, as well as their potential as a basis for therapeutic intervention in the pathology of inflammation, infection, allergy and tumors. Within this context, therapeutic strategies based on the use of antibodies, modified chemokines, chemokine-binding proteins and chemokine receptor antagonists as well as first clinical studies will be addressed.

Role of platelets in neuroinflammation: a wide-angle perspective

OBJECTIVES

This review summarizes recent developments in platelet biology relevant to neuroinflammatory disorders. Multiple sclerosis (MS) is taken as the "Poster Child" of these disorders but the implications are wide. The role of platelets in inflammation is well appreciated in the cardiovascular and cancer research communities but appears to be relatively neglected in neurological research.

ORGANIZATION

After a brief introduction to platelets, topics covered include the matrix metalloproteinases, platelet chemokines, cytokines and growth factors, the recent finding of platelet PPAR receptors and Toll-like receptors, complement, bioactive lipids, and other agents/functions likely to be relevant in neuroinflammatory diseases. Each section cites literature linking the topic to areas of active research in MS or other disorders, including especially Alzheimer's disease.

CONCLUSION

The final section summarizes evidence of platelet involvement in MS. The general conclusion is that platelets may be key players in MS and related disorders, and warrant more attention in neurological research.

Transfusion-related acute lung injury (TRALI): current concepts and misconceptions

Transfusion-related acute lung injury (TRALI) is the most common cause of serious morbidity and mortality due to hemotherapy. Although the pathogenesis has been related to the infusion of donor antibodies into the recipient, antibody negative TRALI has been reported. Changes in transfusion practices, especially the use of male-only plasma, have decreased the number of antibody-mediated cases and deaths; however, TRALI still occurs. The neutrophil appears to be the effector cell in TRALI and the pathophysiology is centered on neutrophil-mediated endothelial cell cytotoxicity resulting in capillary leak and ALI. This review will detail the pathophysiology of TRALI including recent pre-clinical data, provide insight into newer areas of research, and critically assess current practices to decrease it prevalence and to make transfusion safer.

Molecular requirements for sorting of the chemokine interleukin-8/CXCL8 to endothelial Weibel-Palade bodies

Sorting of proteins to Weibel-Palade bodies (WPB) of endothelial cells allows rapid regulated secretion of leukocyte-recruiting P-selectin and chemokines as well as procoagulant von Willebrand factor (VWF). Here we show by domain swap studies that the exposed aspartic acid in loop 2 (Ser(44)-Asp(45)-Gly(46)) of the CXC chemokine interleukin (IL)-8 is crucial for targeting to WPB. Loop 2 also governs sorting of chemokines to alpha-granules of platelets, but the fingerprint of the loop 2 of these chemokines differs from that of IL-8. On the other hand, loop 2 of IL-8 closely resembles a surface-exposed sequence of the VWF propeptide, the region of VWF that directs sorting of the protein to WPB. We conclude that loop 2 of IL-8 constitutes a critical signal for sorting to WPB and propose a general role for this loop in the sorting of chemokines to compartments of regulated secretion.

Increased urinary levels of CXCL5, CXCL8 and CXCL9 in patients with Type 2 diabetic nephropathy

CXC chemokines are particularly significant for leukocyte infiltration in inflammatory diseases. Recent reports have shown that inflammation is one of potential pathogenic mechanisms for diabetic nephropathy. However, information on inflammation related with CXC chemokines in human Type 2 diabetic nephropathy still remains scarce. We measured urinary and serum levels of three CXC chemokines, CXCL5, CXCL8 and CXCL9, in 45 Type 2 diabetic patients (DM), 42 primary renal disease (PRD) patients and 22 healthy controls by enzyme-linked immunosorbent assay. Urinary levels of CXCL5, CXCL8 and CXCL9 in DM were significantly elevated compared to those in controls (P<.0001, P<.01, P<.001; respectively). They increased consistent with urinary albumin excretion rate (UAER) and correlated with UAER in partial correlation analyses (r=0.41, P<.01; r=0.40, P<.01; r=0.45, P<.01; respectively). Urinary levels of CXCL5 in DM were significantly interrelated to HbA(1c) (r=0.42, P<.01). On the other hand, PRD showed significant increased levels of urinary CXCL8 and CXCL9 compared to controls (P<.001, P<.01; respectively), and so did PRD as UAER increased. However, there were no significant elevations of urinary levels of CXCL5 in PRD in spite of the increased UAER. We found significant associations of UAER in DM with diabetes duration, 1/serum creatinine, urinary CXCL5 (adjusted R(2)=0.67, P<.0001) or CXCL9 (adjusted R(2)=0.69, P<.0001) in a stepwise multiple regression analysis. These results suggest that these three CXC chemokines may be involved in the progression of human Type 2 diabetic nephropathy and that CXCL5 may be of use for telling diabetic nephropathy from primary renal diseases.

Regulation of chemerin bioactivity by plasma carboxypeptidase N, carboxypeptidase B (activated thrombin-activable fibrinolysis inhibitor), and platelets

Chemerin is a potent chemoattractant for cells expressing the serpentine receptor CMKLR1 (chemokine-like receptor 1), such as plasmacytoid dendritic cells and tissue macrophages. The bioactivity of chemerin is post-translationally regulated; the attractant circulates in blood in a relatively inactive form (prochemerin) and is activated by carboxyl-terminal proteolytic cleavage. We discovered that plasma carboxypeptidase N (CPN) and B (CPB or activated thrombin-activable fibrinolysis inhibitor, TAFIa) enhanced the bioactivity of 10-mer chemerin peptide NH(2)-YFPGQFAFSK-COOH by removing the carboxyl-terminal lysine (K). Sequential cleavages of either a prochemerin peptide (NH(2)-YFPGQFAFSKALPRS-COOH) or recombinant full-length prochemerin by plasmin and CPN/CPB substantially increased their chemotactic activities. Endogenous CPN present in circulating plasma enhanced the activity of plasmin-cleaved prochemerin. In addition, we discovered that platelets store chemerin protein and release it upon stimulation. Thus circulating CPN/CPB and platelets may potentially contribute to regulating the bioactivity of leukocyte chemoattractant chemerin, and further extend the molecular link between blood coagulation/fibrinolysis and CMKLR1-mediated immune responses.

Multiple pathogenic roles of microvasculature in inflammatory bowel disease: a Jack of all trades

The etiology of Crohn's disease and ulcerative colitis, the two major forms of inflammatory bowel disease (IBD), is still largely unknown. However, it is now clear that the abnormalities underlying pathogenesis of intestinal inflammation are not restricted to those mediated by classic immune cells but also involve nonimmune cells. In particular, advances in vascular biology have outlined a central and multifaceted pathogenic role for the microcirculation in the initiation and perpetuation of IBD. The microcirculation and its endothelial lining play a crucial role in mucosal immune homeostasis through tight regulation of the nature and magnitude of leukocyte migration from the intravascular to the interstitial space. Chronically inflamed IBD microvessels display significant alterations in microvascular physiology and function compared with vessels from healthy and uninvolved IBD intestine. The investigation into human IBD has demonstrated how endothelial activation present in chronically inflamed IBD microvessels results in a functional phenotype that also includes leakiness, chemokine and cytokine expression, procoagulant activity, and angiogenesis. This review contemplates the newly uncovered contribution of intestinal microcirculation to pathogenesis and maintenance of chronic intestinal inflammation. In particular, we assess the multiple roles of the microvascular endothelium in innate immunity, leukocyte recruitment, coagulation and perfusion, and immune-driven angiogenesis in IBD.

Multiple pathogenic roles of microvasculature in inflammatory bowel disease: a Jack of all trades

The etiology of Crohn's disease and ulcerative colitis, the two major forms of inflammatory bowel disease (IBD), is still largely unknown. However, it is now clear that the abnormalities underlying pathogenesis of intestinal inflammation are not restricted to those mediated by classic immune cells but also involve nonimmune cells. In particular, advances in vascular biology have outlined a central and multifaceted pathogenic role for the microcirculation in the initiation and perpetuation of IBD. The microcirculation and its endothelial lining play a crucial role in mucosal immune homeostasis through tight regulation of the nature and magnitude of leukocyte migration from the intravascular to the interstitial space. Chronically inflamed IBD microvessels display significant alterations in microvascular physiology and function compared with vessels from healthy and uninvolved IBD intestine. The investigation into human IBD has demonstrated how endothelial activation present in chronically inflamed IBD microvessels results in a functional phenotype that also includes leakiness, chemokine and cytokine expression, procoagulant activity, and angiogenesis. This review contemplates the newly uncovered contribution of intestinal microcirculation to pathogenesis and maintenance of chronic intestinal inflammation. In particular, we assess the multiple roles of the microvascular endothelium in innate immunity, leukocyte recruitment, coagulation and perfusion, and immune-driven angiogenesis in IBD.

Inflammation and the mucosal microcirculation in inflammatory bowel disease: the ebb and flow

PURPOSE OF REVIEW

Inflammatory bowel disease pathogenesis involves the interplay of multiple biological factors, among which nonimmune cells, including the endothelium, represent a crucial component of disease pathogenesis.

RECENT FINDINGS

Endothelial cells play a key role in chronic inflammation through multiple and disparate activities. The mucosal microvasculature in inflammatory bowel disease is dysfunctional, overexpresses inflammatory molecules and undergoes intense angiogenesis, failing to exert its physiological antiinflammatory and anticoagulant activities.

SUMMARY

The mucosal microcirculation is abnormal in inflammatory bowel disease and represents a novel component of disease pathogenesis; targeting the various abnormalities of the inflammatory bowel disease microcirculation may lead to new forms of therapeutic intervention.

Platelets as immune cells: bridging inflammation and cardiovascular disease

Beyond an eminent role in hemostasis and thrombosis, platelets are characterized by expert functions in assisting and modulating inflammatory reactions and immune responses. This is achieved by the regulated expression of adhesive and immune receptors on the platelet surface and by the release of a multitude of secretory products including inflammatory mediators and cytokines, which can mediate the interaction with leukocytes and enhance their recruitment. In addition, platelets are characterized by an enormous surface area and open canalicular system, which in concert with specialized recognition receptors may contribute to the engulfment of serum components, antigens, and pathogens. Platelet-dependent increases in leukocyte adhesion may not only account for an exacerbation of atherosclerosis, for arterial repair processes, but also for lymphocyte trafficking during adaptive immunity and host defense. This review compiles a selection of platelet-derived tools for bridging inflammation and vascular disease and highlights the molecular key components governing platelet-mediated mechanisms operative in immune surveillance, vascular remodeling, and atherosclerosis.

Inflammation and coagulation in inflammatory bowel disease: The clot thickens

Inflammation and coagulation play crucial roles in the pathogenesis of multiple chronic inflammatory disorders. Growing evidence highlights a tight mutual network in which inflammation, coagulation, and fibrinolysis play closely related roles. Crohn's disease (CD) and ulcerative colitis (UC), the two major forms of inflammatory bowel disease (IBD), are chronic inflammatory conditions, characterized by a hypercoagulable state and prothrombotic conditions, and accompanied by abnormalities in coagulation. From a pathophysiological point of view, cells and molecules classically implicated in the physiological process of coagulation have now been shown to behave abnormally in IBD and possibly to also play an active role in disease pathogenesis and/or disease progression. This paper reviews studies performed on the coagulation profile and risk factors for thrombosis in IBD. In particular, an overview is provided of the epidemiology, clinical features, and etiology of thromboembolic complications in IBD. Furthermore, we review hemostatic abnormalities in IBD, as well as the cell types involved in such processes. Finally, we highlight the coagulation system as a dynamic participant in the multifaceted process of chronic intestinal inflammation. Overall, an overview is provided that the coagulation system represents an important, though previously underestimated, component of IBD pathogenesis, and may be a possible target for therapeutic intervention.

Cytokine accumulation in photochemically treated and gamma-irradiated platelet concentrates during storage

BACKGROUND

Photochemical treatment (PCT) for pathogen reduction of platelet concentrates (PCs) affects all cells containing DNA and/or RNA. Soluble mediators, which may cause transfusion reactions, are determined by the balance between secretion and/or cell destruction and binding and/or degradation.

STUDY DESIGN AND METHODS

Ten double-dose single-donor leukoreduced PCs were split in two identical units. Two study arms were created: Study Arm A consisting of five PCT PCs with corresponding untreated control PCs and Study Arm B consisting of five PCT PCs with corresponding gamma-irradiated control PCs. PCs that had added PAS-III (Intersol) were treated with amotosalen and ultraviolet A light. Corresponding controls PCs, to which PAS-II (T-sol) were added, received no treatment or were gamma-irradiated before storage. Platelet (PLT)-derived (CCL5/RANTES, CXCL4/PF4, CCL3/MIP-1alpha, transforming growth factor [TGF]-beta, CXCL8/interleukin [IL]-8, IL-1beta) as well as white blood cell (WBC)-associated (IL-6, IL-10, IL-11, IL-12, tumor necrosis factor, interferon-gamma) cytokines were investigated by enzyme-linked immunosorbent assay and cytometric bead array during storage for up to 12 days.

RESULTS

Independent of previous treatment we observed that all concentrates showed low levels of WBC-associated cytokines. PLT-derived cytokines were detected at higher levels and showed significant increase during storage. Statistical analysis showed lower PLT content per unit in PCT PCs, higher levels of activation variables in PCT PCs, and higher levels and accumulation rate of CCL5, CXCL4, TGF-beta, and CXCL8 in PCT PCs.

CONCLUSION

PLTs are the main source of released cytokines during storage of untreated, gamma-irradiated, and PCT PCs. PCT may affect the level of PLT-derived cytokines in PCs. No additional reduction of WBC-associated cytokines were observed after PCT in prestorage leukoreduced PCs.

Role of platelet-derived chemokines (RANTES and ENA-78) after stem cell transplantation

Stem cell transplantation (SCT) is being used for hematopoietic reconstitution following high-dose chemotherapy for malignancy. Some patients seem to have an imbalance of the immune response after SCT and cytokines are known to regulate this response. Recently, platelets have been shown to contain members of the chemokine family, suggesting a role of platelets as inflammatory cells. We measured and compared levels of platelet activation markers, chemokines, and soluble factors in patients undergoing SCT. IL-8 and GROalpha exhibited a significant elevation in the early phase (1 or 2 weeks) after SCT; this trend was marked after autologous SCT. Furthermore, these levels significantly and positively correlated with the change in G-CSF. In contrast, ENA-78 exhibited a significant elevation in the later phase (3 or 4 weeks) after SCT. In addition, its level negatively correlated with the change in G-CSF. Soluble CD40 ligand and platelet-derived microparticles significantly increased after both auto- and allo-SCT. In addition, ENA-78 positively correlated with the level of platelet-derived microparticles. The increase of RANTES seems to be related to platelet activation, since RANTES was in the dynamic phase similar to soluble CD40 ligand and platelet-derived microparticles. RANTES exhibited changes similar to IL-6, TNFalpha, and soluble IL-2 receptors, which are GVHD markers. Thus, the platelet-derived chemokines ENA-78 and RANTES exhibited particular changes after SCT. Our results suggest that ENA-78 play a role in hematopoietic conditions in which G-CSF is not involved, and RANTES generation after allo-SCT relates to GVHD.

Increased platelet purinergic sensitivity in peripheral arterial disease--a pilot study

Peripheral arterial disease (PAD) is associated with platelet hyperaggregability as well as an increase in morbidity and mortality from myocardial infarction (MI) and stroke. Purinergic signaling has been shown, both experimentally and clinically, to play an important role in the activation of platelets. Platelets express three different purinergic receptors: P2Y1, P2Y12 and P2X1. We assessed the hypothesis that the hyperaggregability associated with PAD is partly due to an increased P2 receptor expression at the transcriptional and/or translational level. Patients with PAD (n=8) and controls (n=8) were studied. Using a high-resolution channelyzer, platelet shape change (PSC) was assessed by measuring the median platelet volume (MPV). The fall in free platelet count following the addition of ADP was also assessed. Real-time PCR was used to quantify the mRNA expression and Western blots to quantify the protein expression of P2 receptors in platelets. The median (and range) fall in free platelet count after adding ADP was significantly (P=0.02) greater for patients [11% (5-24); n=8] than for controls [0.5% (0-10); n=8] despite using a lower concentration of ADP for the patient samples. The MPV did not differ significantly. The mRNA levels for the three P2 receptors were similar in PAD patients and controls. Western blot detected no significant differences in protein expression between these groups. Thus, platelets from PAD patients show an increased activation after stimulation with ADP (even though all patients were on aspirin). This hyperactivity was neither due to an obvious up-regulation of the mRNA levels nor to altered protein levels of P2 receptors in the platelets. It is suggested that the increased sensitivity to ADP in PAD is caused by post-receptor mechanisms.

Blood platelet and monocyte activations and relation to stages of liver cirrhosis

AIM: Blood platelets (plt) and monocytes are the cells that play a crucial role in the pathogenesis of liver damage and liver cirrhosis (LC). In this paper, the analysis of mutual relationship between platelets and monocytes activation in LC was conducted.

METHODS: Immunofluorescent flow cytometry was used to measure the percentage of activated platelet populations (CD62P, CD63), the percentage of plt-monocyte aggregates (pma) (CD41/CD45), and activated monocytes (CD11b, CD14, CD16) in the blood of 20 volunteers and 40 patients with LC. Platelet activation markers: sP-selectin, platelet factor 4 (PF4), beta-thromboglobulin (βTG) and monocyte chemotactic peptide-1 (MCP-1) were measured and compared in different stages of LC.

RESULTS: Platelet activation with the increase in both βTG serum concentration and elevation of plt population (CD62P and CD63 as well as MIF CD62P and CD63) is elevated as LC develops and thrombocytopenia rises. There is a positive correlation between medial intensity of fluorescence (MIF) CD62P and MIF CD63 in LC. We did not show any relationship between monocyte activation and pma level. SP-selectin concentration correlates positively with plt count and pma, and negatively with stage of plt activation and MIF CD62P and MIF CD63. There was no correlation between MCP-1 concentration and plt, monocyte activation as well as pma level in LC. CD16 monocytes and MIF CD16 populations are significantly higher in the end stage of LC. A positive correlation occurs between the value of CD11b monocyte population and MIF CD14 and MIF CD16 on monocytes in LC.

CONCLUSION: Platelet and monocyte activation plays an important role in LC. Platelet activation stage does not influence monocyte activation and production of plt aggregates with monocytes in LC. With LC development, thrombocytopenia may be the result of plt consumption in platelet-monocyte aggregates.

Human platelets exhibit chemotaxis using functional N-formyl peptide receptors

OBJECTIVE

Activated platelets participate in inflammatory and microbicidal processes by upregulation of surface selectins, shedding of CD40 ligand, and release of platelet microbicidal proteins and microparticles. Given their myeloid lineage, we hypothesized that platelets express functional N-formyl peptide receptors and respond to the bacterially derived chemotactic peptide N-formyl peptide with gradient-driven chemotaxis.

METHODS AND RESULTS

Here we show specific binding of N-formyl peptides to the surface of activated platelets. Platelet expression and function of the formyl peptide receptor, FPR, was verified by RT-PCR of the differentiated megakaryocyte MEG-01 cell line, immunoblotting of platelet proteins, and calcium mobilization in platelets with formyl peptide binding. Furthermore, we demonstrate gradient-driven chemotaxis of platelets by video microscopy and transwell migration toward formyl peptides. We also show that endogenous formyl peptides, released by eukaryotic mitochondria from necrotic cells, induce chemotaxis using formyl peptide receptors expressed by thrombin-activated platelets. Conversely, supernatants from cells undergoing apoptotic cell death do not induce platelet chemotaxis. Platelet chemotaxis to formyl peptides was blocked with FPR-specific antibody as well as by pertussis toxin inhibition of the formyl peptide G-coupled receptor.

CONCLUSION

These data establish a new role for platelets in host defense and suggest reexamination of their active function in microbicidal and other host defense activities.

CCR4-deficient mice show prolonged graft survival in a chronic cardiac transplant rejection model

Chronic graft rejection mediated by cellular immune responses still poses a serious clinical problem in transplant surgery. Chemokines coordinate the recruitment of leukocytes in inflammatory and immune responses. Their precise functions in the rejection of allografts are still ill defined. This study investigates the role of chemokine receptor 4 (CCR4) in acute and chronic cardiac allograft rejection in mice. Allogeneic hearts were transplanted into CCR4 deficient (CCR4(-/-)) and control recipients. Reverse transcription-PCR showed transcription of macrophage-derived chemokine and thymus and activation-regulated chemokine, the cognate chemokine ligands of CCR4, within the graft. Compared to wild-type controls, acute allograft rejection in CCR4(-/-) recipients was only slightly prolonged. In contrast, in a gallium nitrate chronic cardiac allograft rejection model, cardiac graft survival was significantly prolonged in CCR4(-/-) recipients. A relative increase in the percentage of graft infiltrating CD8(+) T cells in CCR4(-/-) recipients was observed 30 days after transplantation and was accompanied by a decrease in CD4(+) T cells. Moreover, the percentage of NK1.1(+)CD3(+) graft-infiltrating cells was significantly reduced on day 5 and day 30 post transplantation. These findings indicate that CCR4 is involved in the recruitment of NK1.1(+)CD3(+) cells into cardiac allografts and clearly establish an important and novel role for CCR4 in chronic graft rejection.

Platelets and Inflammation

Platelets play a major physiological role in control of vascular integrity at the site of vascular lesions. However, the pathophysiological role of platelets is much broader than regulation of hemostasis and thrombosis. Platelets are critical elements in linking and modulating thrombosis, inflammation, and tissue repair. Platelets are stimulated by a variety of agonists including thrombin or ADP and also by inflammatory agents such as antibodies, complement, bacteria, and others. Platelets contribute to inflammation by interacting with inflammatory cells via adhesion and secretion of prestored proinflammatory mediators. Thus, platelets are critical elements in the pathophysiology of inflammation and modulate significantly a variety of inflammatory diseases. A profound understanding of the molecular mechanisms underlying the role of platelet in inflammation may result in new therapeutic strategies in acute and chronic inflammatory diseases.

Gene expression profile of primary human CD34+CD38lo cells differentiating along the megakaryocyte lineage

OBJECTIVE

To identify genes involved in megakaryopoiesis, high-density oligonucleotide microarrays were used to compare transcript profiles from undifferentiated CD34+CD38lo cells and culture-derived megakaryocytes (MKs).

MATERIALS AND METHODS

Megakaryocyte differentiation was achieved in vitro by inducing primary human CD34+CD38lo cells in serum-deprived media supplemented with the cytokine combination of interleukin-3, interleukin-6, stem cell factor, and thrombopoietin for 10 days. Three replicate microarray experiments were performed using hematopoietic cells isolated from three different organ donors and high-density oligonucleotide microarrays.

RESULTS

Analysis of gene array data resulted in 304 differentially expressed genes (p < or = 0.001, fold change > or = 3). A third of the 25 most highly up-regulated genes were known to participate in hemostasis (z = 6.75), and no genes known to be associated with MKs were among the down-regulated genes. We also found a large proportion of up-regulated transcripts in gene ontology categories of adhesion and receptor activity (85%) and signal transduction activity (68%). At the same time, 70% of genes within transcription factor functions were down-regulated. Confirmatory studies indicated that the array results correlated with mRNA and protein expression levels in primary MKs.

CONCLUSION

This study provides a global expression profile of human MKs and a list of novel and previously uncharacterized candidate genes that are important components of megakaryopoiesis.

Platelets in inflammatory bowel disease: clinical, pathogenic, and therapeutic implications

Both Crohn's disease (CD) and ulcerative colitis (UC) are associated with abnormalities of platelet number and function. In the peripheral circulation the state of platelet activation is typically increased, and inflammatory bowel disease (IBD)-involved mucosa frequently contains platelet aggregates within mucosal microthrombi. The relevance of platelet dysfunction to IBD pathogenesis is still unclear, but there is solid evidence demonstrating that platelets, in addition to their traditional role in hemostasis, can also function as potent proinflammatory cells. Upon activation, platelets secrete a large number of biologically active molecules able to induce or amplify an inflammatory process through many of the same cellular and molecular pathways conventionally utilized by immune cells mediating IBD. The aim of this article is to review data on the existence of platelet dysfunction in IBD, substantiate platelets' inflammatory potential, discuss the implications of abnormal platelet activity for chronic intestinal inflammation, and consider the potential benefits of platelet modulation for treatment of IBD.

Platelet activation in heart transplant recipients

An inappropriate and persistent immune activation has been suggested to contribute to long-term mortality and morbidity after heart transplantation. Several lines of evidence suggest that platelets do not only promote thrombus formation, but also act as inflammatory cells. In the present study, we investigated if long-time survivors of heart transplantation (mean time since transplantation 6.5 yr) were characterized by enhanced platelet activation as assessed by different experimental approaches. Our main findings when comparing heart transplant recipients (n = 52) and age- and sex-matched healthy controls (n = 38) were: (i) platelets from heart transplant recipients showed enhanced expression of both P-selectin and CD63 as assessed by flow cytometry; (ii) platelets from these patients also contained significantly increased levels of soluble CD40 ligand and tended to release higher levels of this cytokine upon SFLLRN stimulation as assessed by enzyme immunoassay; (iii) heart transplant recipients had increased levels of soluble P-selectin in platelet-free plasma; and (iv) the enhanced platelet activation after heart transplantation was most pronounced in those with concomitant hypertension. These findings suggest that long-term survivors of heart transplantation are characterized by enhanced activation of platelets, possibly contributing to the persistent immune activation and clinical complications in these patients.

Integration of proteomics and genomics in platelets: a profile of platelet proteins and platelet-specific genes

Platelets, while anucleate, contain RNA, some of which is translated into protein upon activation. Hypothesising that the platelet proteome is reflected in the transcriptome, we identified 82 proteins secreted from activated platelets and compared these, as well as published proteomic data, to the transcriptional profile. We also compared the transcriptome of platelets to other tissues to identify platelet-specific genes and used ontology to determine gene categories over-represented in platelets. RNA was isolated from highly pure platelet preparations for hybridization to Affymetrix oligonucleotide arrays. We identified 2,928 distinct messages as being present in platelets. The platelet transcriptome was compared with the proteome by relating both to UniGene clusters. Platelet proteomic data correlated well with the transcriptome, with 69% of secreted proteins detectable at the mRNA level, and similar concordance was obtained using two published datasets. While many of the most abundant mRNAs are for known platelet proteins, messages were detected for proteins not previously reported in platelets. Some of these may represent residual megakaryocyte messages; however, proteomic analysis confirmed the expression of many previously unreported genes in platelets. Transcripts for well-described platelet proteins are among the most platelet-specific messages. Ontological categories related to signal transduction, receptors, ion channels, and membranes are over-represented in platelets, while categories involved in protein synthesis are depleted. Despite the absence of gene transcription, the platelet proteome is mirrored in the transcriptome. Conversely, transcriptional analysis predicts the presence of novel proteins in the platelet. Transcriptional analysis is relevant to platelet biology, providing insights into platelet function and the mechanisms of platelet disorders.

Platelet chemokines and chemokine receptors: linking hemostasis, inflammation, and host defense

Blood platelets play critical roles in hemostasis, providing rapid essential protection against bleeding and catalyzing the important slower formation of stable blood clots via the coagulation cascade. They are also involved in protection from infection by phagocytosis of pathogens and by secreting chemokines that attract leukocytes. Platelet function usually is activated by primary agonists such as adenosine diphosphate (ADP), thrombin, and collagen, whereas secondary agonists like adrenalin do not induce aggregation on their own but become highly effective in the presence of low levels of primary agonists. Current research has revealed that chemokines represent an important additional class of agonists capable of causing significant activation of platelet function. Early work on platelet alpha-granule proteins suggested that platelet factor 4, now known as CXCL4, modulated aggregation and secretion induced by low agonist levels. Subsequent reports revealed the presence in platelets of messenger RNA for several additional chemokines and chemokine receptors. Three chemokines in particular, CXCL12 (SDF-1), CCL17 (TARC), and CCL22 (MDC), recently have been shown to be strong and rapid activators of platelet aggregation and adhesion after their binding to platelet CXCR4 or CCR4, when acting in combination with low levels of primary agonists. CXCL12 can be secreted by endothelial cells and is present in atherosclerotic plaques, whereas CCL17 and CCL22 are secreted by monocytes and macrophages. Platelet activation leads to the release of alpha-granule chemokines, including CCL3 (MIP-1alpha), CCL5 (RANTES), CCL7 (MCP-3), CCL17, CXCL1 (growth-regulated oncogene-alpha), CXCL5 (ENA-78), and CXCL8 (IL-8), which attract leukocytes and further activate other platelets. These findings help to provide a direct linkage between hemostasis, infection, and inflammation and the development of atherosclerosis.

Platelet activation induced by human antibodies to interleukin-8

Some cases of heparin-induced thrombocytopenia (HIT) have been reported to be associated with antibodies against interleukin-8 (IL-8), a chemokine related to platelet factor 4. We found that sera from 5 HIT patients containing immunoglobulin G (IgG) or IgM antibodies to IL-8, as evidenced using surface plasmon resonance spectroscopy, were able to trigger IL-8-dependent activation of washed platelets, leading to procoagulant activity. This activation occurred at IL-8 concentrations achievable in vivo and was facilitated by heparin (0.1 U/mL). Activation was also induced by affinity-purified anti-IL-8 IgG and involved FcgammaRIIa. In the 2 patients who could be followed up, antibodies were no longer detectable 4 months after heparin withdrawal. One additional patient with paraneoplastic recurrent thrombosis without thrombocytopenia was found to have platelet-activating anti-IL-8 IgM, but in this case heparin was inhibitory. This is another example of potentially pathogenic platelet activation by antibodies.

Quantification of ADP and ATP receptor expression in human platelets

The mechanism of ADP-mediated platelet activation has been difficult to unravel due to the large number of receptors for extracellular nucleotides (P2 receptors). mRNA levels in circulating platelets are very low, but have been shown to be translationally active. By optimizing mRNA extraction and using real time (RT)-PCR we were able to establish a protocol for highly sensitive platelet mRNA quantification in human regular blood samples. In platelets from healthy volunteers, only P2X1, P2Y1 and P2Y12 were found in significant levels, with the following order of expression: P2Y12 >> P2X1 > P2Y1. Other P2 receptors (P2Y2, P2Y4, P2Y6, P2Y11, P2Y13, P2X4, P2X7) had very low expression. As a control measurement to exclude contamination, P2 receptors in buffy coat were quantified but had a completely different profile. Incubation in vitro revealed a more rapid degradation rate for P2X1 receptor mRNA than for P2Y1 and P2Y12, indicating that the level of P2X1 may be relatively higher in newly released platelets and in megacaryocytes. In conclusion, we have developed the first protocol for quantifying mRNA expression in human platelets limiting the P2 receptor drug development targets to P2Y12, P2Y1 and P2X1. Furthermore, the method could be used to study platelet expression for any gene in human materials.

Host defense role of platelets: engulfment of HIV and Staphylococcus aureus occurs in a specific subcellular compartment and is enhanced by platelet activation

Platelets can bind and phagocytose infectious microorganisms and so enable their transport for a prolonged time. To investigate the subcellular events of these interactions, platelets were incubated either with Staphylococcus aureus or with HIV and analyzed by electron microscopy (EM) and immuno-EM. HIV and bacteria internalization occurred exclusively within platelets showing morphological evidence of activation. Platelet activation enhanced the degree of bacterial internalization. Immunolabeling revealed that the engulfing vacuoles and the open canalicular system (OCS) were composed of distinct antigens. The engulfing vacuoles eventually became the site of prominent alpha-granule release. In platelets incubated with HIV, characteristic endocytic vacuoles were identified close to the plasma membrane, tightly surrounding 1 or 2 HIV particles. Virus particles were also located within the OCS. Immunogold labeling for the viral core protein p24 confirmed the presence of HIV within platelets. Finally, examination of platelets from a patient with acquired immunodeficiency syndrome and high viremia suggested that HIV endocytosis may also occur in vivo.