Human platelets target dendritic cell differentiation and production of proinflammatory cytokines

Platelets and inter-cellular communication in immune responses: Dialogue with both professional and non-professional immune cells

Platelets, derived from bone marrow megakaryocytes, are essential for vascular integrity and play multifaceted roles in both physiological and pathological processes within the vasculature. Despite their small size and absence of a nucleus, platelets are increasingly recognized for their diverse immune functions. Recent research highlights their pivotal role in interactions with various immune cells, including professional cells like macrophages, dendritic cells, natural killer cells, T cells, and B cells, influencing host immune responses. Platelets also engage with non-professional immune cells, contributing to immune responses and structural maintenance, particularly in conditions like inflammation and atherosclerosis. This review underscores the emerging significance of platelets as potent immune cells, elucidating their interactions with the immune system. We explore the mechanisms of platelet activation, leading to diverse functions, such as aggregation, immunity, activation of other immune cells, and pathogen clearance. Platelets have become the predominant immune cells in circulation, involved in chronic inflammation, responses to infections, and autoimmune disorders. Their immunological attributes, including bioactive granule molecules and immune receptors, contribute to their role in immune responses. Unlike professional antigen-presenting cells, platelets process and present antigens through an MHC-I-dependent pathway, initiating T-cell immune responses. This review illuminates the unique features of platelets and their central role in modulating host immune responses in health and disease.

Evaluation of the neutrophil-to-lymphocyte and platelet-to-lymphocyte ratios in critically ill dogs

OBJECTIVE

To evaluate whether the neutrophil-to-lymphocyte ratio (NLR) and platelet-to-lymphocyte ratio (PLR) are accurate prognostic indicators and correlate with illness severity scores in critically ill dogs.

DESIGN

Prospective observational study from December 2016 to May 2017.

SETTING

ICU at a veterinary teaching hospital.

ANIMALS

Seventy-two client-owned dogs admitted to the ICU with CBCs and abbreviated and complete acute patient physiologic and laboratory evaluation (APPLE_fast and APPLE_full ) scores were enrolled.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The NLR, PLR, APPLE_fast , and APPLE_full scores were calculated for each patient on the day of admission. Patients were followed from admission to discharge, and diagnosis, survival, and length of hospitalization were recorded. The patient population was assessed as a whole and as subcategories of patients with neoplastic disease, infectious disease, sepsis, and severe hemorrhage. Dogs with nonseptic disease processes (n = 52) that died had a significantly higher median PLR (P = 0.04) of 441 (range: 106-986) compared to those that survived with a median PLR of 217 (range: 28.4-3225). The PLR was strongly predictive of ICU length of stay in dogs with severe hemorrhage (P = 0.03, Spearman's rho = 0.84). The NLR had a poor positive correlation with APPLE_full score (P = 0.04, Spearman's rho = 0.24), and PLR had a poor negative correlation with APPLE_fast score (P = 0.02, Spearman's rho = -0.27).

CONCLUSIONS

The PLR correlated with ICU length of stay for patients with severe hemorrhage and with survival for patients with nonseptic disease processes. The PLR and NLR correlated with illness severity as measured by APPLE scores. Future studies with larger sample sizes are warranted to further determine the merit of NLR and PLR as indicators of morbidity, mortality, and illness severity.

Identifying platelet-derived factors as amplifiers of B. burgdorferi-induced cytokine production

Previous studies have shown that monocytes can be 'trained' or tolerized by certain stimuli to respond stronger or weaker to a secondary stimulation. Rewiring of glucose metabolism was found to be important in inducing this phenotype. As we previously found that Borrelia burgdorferi (B. burgdorferi), the causative agent of Lyme borreliosis (LB), alters glucose metabolism in monocytes, we hypothesized that this may also induce long-term changes in innate immune responses. We found that exposure to B. burgdorferi decreased cytokine production in response to the TLR4-ligand lipopolysaccharide (LPS). In addition, B. burgdorferi exposure decreased baseline levels of glycolysis, as assessed by lactate production. Using GWAS analysis, we identified a gene, microfibril-associated protein 3-like (MFAP3L) as a factor influencing lactate production after B. burgdorferi exposure. Validation experiments proved that MFAP3L affects lactate- and cytokine production following B. burgdorferi stimulation. This is mediated by functions of MFAP3L, which includes activating ERK2 and through activation of platelet degranulation. Moreover, we showed that platelets and platelet-derived factors play important roles in B. burgdorferi-induced cytokine production. Certain platelet-derived factors, such chemokine C-X-C motif ligand 7 (CXCL7) and (C-C motif) ligand 5 (CCL5), were elevated in the circulation of LB patients in comparison to healthy individuals.

Platelet Derivatives and the Immunomodulation of Wound Healing

Besides their primary role in hemostasis, platelets contain a plethora of immunomodulatory molecules that profoundly affect the entire process of wound repair. Therefore, platelet derivatives, such as platelet-rich plasma or platelet lysate, have been widely employed with promising results in the treatment of chronic wounds. Platelet derivatives provide growth factors, cytokines, and chemokines targeting resident and immigrated cells belonging to the innate and adaptive immune system. The recruitment and activation of neutrophils and macrophages is critical for pathogen clearance in the early phase of wound repair. The inflammatory response begins with the release of cytokines, such as TGF-β, aimed at damping excessive inflammation and promoting the regenerative phase of wound healing. Dysregulation of the immune system during the wound healing process leads to persistent inflammation and delayed healing, which ultimately result in chronic wound. In this review, we summarize the role of the different immune cells involved in wound healing, particularly emphasizing the function of platelet and platelet derivatives in orchestrating the immunological response.

Recent advances in the mechanisms and treatment of immune thrombocytopenia

Primary immune thrombocytopenia is an autoimmune disease associated with a reduced peripheral blood platelet count. The phenotype is variable with some patients suffering no bleeding whilst others have severe bleeding which may be fatal. Variability in clinical behaviour and treatment responses reflects its complex underlying pathophysiology. Historically the management has relied heavily on immune suppression. Recent studies have shown that the older empirical immune suppressants fail to alter the natural history of the disease and are associated with a poor quality of life for patients. Newer treatments, such as the thrombopoietin receptor agonists, have transformed ITP care. They have high efficacy, are well tolerated and improve patients’ quality of life. A greater understanding of the underlying pathophysiology of this disorder has helped develop a number of new targeted therapies. These include inhibitors of the neonatal Fc receptor inhibitors, Bruton tyrosine kinase and complement pathway. Here we discuss the mechanisms underlying ITP and the new approach to ITP care.

Monocytes complexed to platelets differentiate into functionally deficient dendritic cells

In addition to their role in hemostasis, platelets store numerous immunoregulatory molecules such as CD40L, TGFβ, β2-microglobulin, and IL-1β and release them upon activation. Previous studies indicate that activated platelets form transient complexes with monocytes, especially in HIV infected individuals and induce a proinflammatory monocyte phenotype. Because monocytes can act as precursors of dendritic cells (DCs) during infection/inflammation as well as for generation of DC-based vaccine therapies, we evaluated the impact of activated platelets on monocyte differentiation into DCs. We observed that in vitro cultured DCs derived from platelet-monocyte complexes (PMCs) exhibit reduced levels of molecules critical to DC function (CD206, dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin, CD80, CD86, CCR7) and reduced antigen uptake capacity. DCs derived from PMCs also showed reduced ability to activate naïve CD4+ and CD8+ T cells, and secrete IL-12p70 in response to CD40L stimulation, resulting in decreased ability to promote type-1 immune responses to HIV antigens. Our results indicate that formation of complexes with activated platelets can suppress the development of functional DCs from such monocytes. Disruption of PMCs in vivo via antiplatelet drugs such as Clopidogrel/Prasugrel or the application of platelet-free monocytes for DCs generation in vitro, may be used to enhance immunization and augment the immune control of HIV.

Inhibition of Dendritic Cell Activation and Modulation of T Cell Polarization by the Platelet Secretome

Platelet transfusions are a frequently administered therapy for especially hemato-oncological patients with thrombocytopenia. Next to their primary function in hemostasis, currently there is increased attention for the capacity of platelets to affect the function of various cells of the immune system. Here, we investigate the capacity of platelets to immuno-modulate monocyte-derived dendritic cells (moDC) as well as primary dendritic cells and effects on subsequent T cell responses. Platelets significantly inhibited pro-inflammatory (IL-12, IL-6, TNFα) and increased anti-inflammatory (IL-10) cytokine production of moDCs primed with toll-like receptor (TLR)-dependent and TLR-independent stimuli. Transwell assays and ultracentrifugation revealed that a soluble factor secreted by platelets, but not microvesicles, inhibited DC activation. Interestingly, platelet-derived soluble mediators also inhibited cytokine production by human ex vivo stimulated myeloid CD1c+ conventional DC2. Moreover, platelets and platelet-derived soluble mediators inhibited T cell priming and T helper differentiation toward an IFNγ+ Th1 phenotype by moDCs. Overall, these results show that platelets are able to inhibit the pro-inflammatory properties of DCs, and may even induce an anti-inflammatory DC phenotype, with decreased T cell priming capacity by the DC. The results of this study provide more insight in the potential role of platelets in immune modulation, especially in the context of platelet transfusions.

Pathogen-reduced PRP blocks T-cell activation, induces Treg cells, and promotes TGF-β expression by cDCs and monocytes in mice

Alloimmunization against platelet-rich plasma (PRP) transfusions can lead to complications such as platelet refractoriness or rejection of subsequent transfusions and transplants. In mice, pathogen reduction treatment of PRP with UVB light and riboflavin (UV+R) prevents alloimmunization and appears to induce partial antigen-specific tolerance to subsequent transfusions. Herein, the in vivo responses of antigen-presenting cells and T cells to transfusion with UV+R-treated allogeneic PRP were evaluated to understand the cellular immune responses leading to antigen-specific tolerance. Mice that received UV+R-treated PRP had significantly increased transforming growth factor β (TGF-β) expression by CD11b+ CD4+ CD11cHi conventional dendritic cells (cDCs) and CD11bHi monocytes (P < .05). While robust T-cell responses to transfusions with untreated allogeneic PRP were observed (P < .05), these were blocked by UV+R treatment. Mice given UV+R-treated PRP followed by untreated PRP showed an early significant (P < .01) enrichment in regulatory T (Treg) cells and associated TGF-β production as well as diminished effector T-cell responses. Adoptive transfer of T-cell-enriched splenocytes from mice given UV+R-treated PRP into naive recipients led to a small but significant reduction of CD8+ T-cell responses to subsequent allogeneic transfusion. These data demonstrate that pathogen reduction with UV+R induces a tolerogenic profile by way of CD11b+ CD4+ cDCs, monocytes, and induction of Treg cells, blocking T-cell activation and reducing secondary T-cell responses to untreated platelets in vivo.

Role of platelet biomarkers in inflammatory response

Beyond hemostasis, thrombosis and wound healing, it is becoming increasingly clear that platelets play an integral role in inflammatory response and immune regulation. Platelets recognize pathogenic microorganisms and secrete various immunoregulatory cytokines and chemokines, thus facilitating a variety of immune effects and regulatory functions. In this review, we discuss recent advances in signaling of platelet activation-related biomarkers in inflammatory settings and application prospects to apply for disease diagnosis and treatment.

Extracellular Vesicles of Alzheimer's Disease Patients as a Biomarker for Disease Progression

Alzheimer's disease (AD) is a progressive neurodegenerative brain pathology and the most common form of dementia. Evidence suggests that extracellular vesicles (EVs) containing cytokines and microRNA are involved in inflammation regulation. The current study aimed to explore a potential impact of AD patients' EVs on disease progression. Blood samples were collected after obtaining signed informed consent (No. 0462-14-RMB) from 42 AD patients at three stages of disease severity and from 19 healthy controls (HC). EV size and concentration were studied by nanotracking analysis. EV membrane antigens were defined by flow cytometry and Western blot; EV protein contents were screened by protein array; the miRNA content was screened by nanostring technology and validated by RT-PCR. HC and AD patients' EVs consisted of a mixture of small (< 100 nm) and larger vesicles. The myelin oligodendrocyte glycoprotein (MOG) expression on EVs correlated with disease severity. EVs of patients with moderate and severe AD had significantly higher levels of MOG, compared with mild AD patients. Levels of EVs expressing the axonal glycoprotein CD171 were significantly higher in severe AD patients than in HC. Increase in endothelial EVs was observed in AD patients. An above twofold increase was found in the content of inflammatory cytokines and > 50% decrease in growth factors in AD patients' EVs compared with HC-EVs. Levels of let-7g-5p, miR126-3p, miR142-3p, miR-146a-5p, and mir223-3p correlated with disease severity. Neural damage, specific miRNA downregulation, and inflammatory cytokine upregulation, found in patients' EVs, might be used as a biomarker reflecting AD severity.

Innate and Adaptive Immune Responses in HELLP Syndrome

Innate and adaptive immune involvement in hemolysis, elevated liver enzymes and low platelet (HELLP) syndrome is an understudied field, although it is of high clinical importance. This syndrome implies a risk of serious morbidity and mortality to both the mother and the fetus during pregnancy. It was proposed that HELLP syndrome occurs in a circulatory inflammatory milieu, that might in turn participate in a complex interplay between the secreted inflammatory immunomodulators and immune cell surface receptors. Meanwhile, reported immune cell attenuation during HELLP may consequently lead to a prolonged immunoactivation and tissue damage. In this regard, learning more about the immune components of this syndrome should widen the understanding of the HELLP pathophysiology and eventually enable development of novel immune-based therapeutics. This review aims to summarize and discuss the recent and previous findings of the innate and adaptive immune responses during HELLP in order to update the current knowledge of the immune involvement in HELLP pathogenesis.

A Champion of Host Defense: A Generic Large-Scale Cause for Platelet Dysfunction and Depletion in Infection

Thrombocytopenia is commonly associated with sepsis and infections, which in turn are characterized by a profound immune reaction to the invading pathogen. Platelets are one of the cellular entities that exert considerable immune, antibacterial, and antiviral actions, and are therefore active participants in the host response. Platelets are sensitive to surrounding inflammatory stimuli and contribute to the immune response by multiple mechanisms, including endowing the endothelium with a proinflammatory phenotype, enhancing and amplifying leukocyte recruitment and inflammation, promoting the effector functions of immune cells, and ensuring an optimal adaptive immune response. During infection, pathogens and their products influence the platelet response and can even be toxic. However, platelets are able to sense and engage bacteria and viruses to assist in their removal and destruction. Platelets greatly contribute to host defense by multiple mechanisms, including forming immune complexes and aggregates, shedding their granular content, and internalizing pathogens and subsequently being marked for removal. These processes, and the nature of platelet function in general, cause the platelet to be irreversibly consumed in the execution of its duty. An exaggerated systemic inflammatory response to infection can drive platelet dysfunction, where platelets are inappropriately activated and face immunological destruction. While thrombocytopenia may arise by condition-specific mechanisms that cause an imbalance between platelet production and removal, this review evaluates a generic large-scale mechanism for platelet depletion as a repercussion of its involvement at the nexus of responses to infection.

Automated mononuclear cell collection: a feasibility study employing a new software for extracorporeal photopheresis

BACKGROUND AND OBJECTIVES

Very recently, Fresenius Kabi, improved the software (autoMNC lymphocytes, SW 04.03.08) for mononuclear cells (MNCs) collection with the aim to ameliorate the quality of harvest, employing the automated autoMNC lymphocytes software SW 04.03.09. Herein, we report the results of an observational study evaluating the feasibility of MNCs collection in patients undergoing extracorporeal photopheresis (ECP) at our centre, using the new COM.TEC software 04.03.08c for MNC collection, afterwards integrated in the software 04.03.09, available on the market since November 2018.

MATERIALS AND METHODS

Thirty adult patients (21 males and 9 females) with GvHD, Chronic Lung Allograft Dysfunction or renal rejection, were consecutively enrolled to undergo 1 ECP procedure by the offline technique, according to our internal protocol, processing 1·5 blood volumes. Feasibility of collection was defined as: Hct in collection bag ≤5%, MNCs purity (percentage of MNCs/bag) ≥80%, MNCs collection efficiency (CE2) ≥60%, patient's platelet depletion ≤50%.

RESULTS

Thirty ECP procedures were evaluated. Feasibility (defined by the four parameters previously described) of MNCs collection was observed in 1 out of the 30 harvests analysed. Median Hct in the product was 3·45% (IQR: 2·6-5·0), and median MNCs purity was 97·2% (IQR 89·1-98·6). Median CE2 for MNCs was 21·4% (IQR: 11·9-41·2), and median patient's platelet depletion was 36·2% (IQR 21·9-51·4).

CONCLUSION

The autoMNC lymphocytes software SW 04.03.08c for MNCs collection in ECP setting demonstrated to collect a good quality product in terms of purity and RBC contamination even if the collection efficiency and platelet contamination must be improved.

Using Dendritic Cell-Based Immunotherapy to Treat HIV: How Can This Strategy be Improved?

Harnessing dendritic cells (DC) to treat HIV infection is considered a key strategy to improve anti-HIV treatment and promote the discovery of functional or sterilizing cures. Although this strategy represents a promising approach, the results of currently published trials suggest that opportunities to optimize its performance still exist. In addition to the genetic and clinical characteristics of patients, the efficacy of DC-based immunotherapy depends on the quality of the vaccine product, which is composed of precursor-derived DC and an antigen for pulsing. Here, we focus on some factors that can interfere with vaccine production and should thus be considered to improve DC-based immunotherapy for HIV infection.

Platelets Enhance Dendritic Cell Responses against Staphylococcus aureus through CD40-CD40L

Staphylococcus aureus is a major human pathogen that can cause mild to severe life-threatening infections in many tissues and organs. Platelets are known to participate in protection against S. aureus by direct killing and by enhancing the activities of neutrophils and macrophages in clearing S. aureus infection. Platelets have also been shown to induce monocyte differentiation into dendritic cells and to enhance activation of dendritic cells. Therefore, in the present study, we explored the role of platelets in enhancing bone marrow-derived dendritic cell (BMDC) function against S. aureus We observed a significant increase in dendritic cell phagocytosis and intracellular killing of a methicillin-resistant Staphylococcus aureus (MRSA) strain (USA300) by thrombin-activated platelets or their releasates. Enhancement of bacterial uptake and killing by DCs is mediated by platelet-derived CD40L. Coculture of USA300 and BMDCs in the presence of thrombin-activated platelet releasates invokes upregulation of the maturation marker CD80 on DCs and enhanced production of the proinflammatory cytokines tumor necrosis factor alpha (TNF-α), interleukin 12 (IL-12), and IL-6. Overall, these observations support our hypothesis that platelets play a critical role in the host defense against S. aureus infection. Platelets stimulate DCs, leading to direct killing of S. aureus and enhanced DC maturation, potentially leading to adaptive immune responses against S. aureus.

Additive-manufactured microporous polymer membranes for biomedical in vitro applications

Microscale porous membranes are used in a wide range of technical and medical applications such as water treatment, dialysis and in vitro test systems. A promising approach to control membrane properties and overcome limitations of conventional fabrication techniques is given by additive manufacturing (AM). In this study, we designed and printed a microporous membrane via digital light processing and validated its use for biomedical in vitro applications based on the example of a cell culture insert. A multi-layer technique was developed, resulting in an eight-layer membrane with an average pore diameter of 25 µm. Image analyses proved the printing accuracy to be high with small deviations for an increasing number of layers. Permeability tests with brilliant blue FCF (E133, triarylmethane dye) and growth factors comparing the printed to track-etched membranes showed similar transfer dynamics and confirmed sufficient separation properties. Overall, the results showed that printing microporous polymer membranes is possible and highlight the potential of AM for biomedical in vitro applications such as cell culture inserts, scaffolds for tissue engineering or bioreactors.

Role of platelets in immune system and inflammation

Platelets have significant role in modulating clot formation. Additionally, emerging data indicates that platelets have considerable roles in inflammation and immune response. Platelets gather at the damaged cite and adhere to white blood cells. Subsequently, they release cytokines and chemokines which are chemotactic for neutrophils and monocytes. Therefore, platelets are necessary for targeting lymphocytes, neutrophils and monocytes to inflammation site. Those interactions enhance inflammation. Moreover, platelets serve as an immune cell by engulfing microbes. Presence of platelets affect prognosis in some bacterial or viral infection and several other diseases.

First comparative analysis concerning the plasma platelet contamination during MNC collection

BACKGROUND AND OBJECTIVES

Monocytes can be cultured into dendritic cells with addition of autologous plasma, which is highly prone to platelet contamination due to the apheresis process. Since platelets affect the maturation process of monocytes into dendritic cells and might even lead to a diminished harvest of dendritic cells, it is very important to reduce the platelet contamination. A new collection device (Spectra Optia) was analyzed, compared to two established devices (COM.TEC, Cobe Spectra) and evaluated regarding the potential generation of source plasma.

MATERIALS AND METHODS

Concurrent plasma collected during leukapheresis was analyzed for residual cell contamination in a prospective study with the new Spectra Optia apheresis device (n=24) and was compared with COM.TEC and Cobe Spectra data (retrospective analysis, n=72). Donor pre-donation counts of platelets were analyzed for their predictive value of contaminating PLTs in plasma harvests.

RESULTS

The newest apheresis device showed the lowest residual platelet count of the collected concurrent plasma (median 3.50×10⁹/l) independent of pre-donation counts. The other two devices and sets had a higher platelet contamination. The contamination of the plasma with leukocytes was very low (only 2.0% were higher than 0.5×10⁹/l).

CONCLUSIONS

This study showed a significant reduction of platelet contamination of the concurrent plasma collected with the new Spectra Optia device. This plasma product with low residual platelets and leukocytes might also be used as plasma for fractionation.

Platelets as immune-sensing cells

Publisher's Note: This article has a companion Point by Brass et al. Publisher's Note: Join in the discussion of these articles at Blood Advances Community Conversations.

Platelets in Pulmonary Immune Responses and Inflammatory Lung Diseases

Platelets are essential for physiological hemostasis and are central in pathological thrombosis. These are their traditional and best known activities in health and disease. In addition, however, platelets have specializations that broaden their functional repertoire considerably. These functional capabilities, some of which are recently discovered, include the ability to sense and respond to infectious and immune signals and to act as inflammatory effector cells. Human platelets and platelets from mice and other experimental animals can link the innate and adaptive limbs of the immune system and act across the immune continuum, often also linking immune and hemostatic functions. Traditional and newly recognized facets of the biology of platelets are relevant to defensive, physiological immune responses of the lungs and to inflammatory lung diseases. The emerging view of platelets as blood cells that are much more diverse and versatile than previously thought further predicts that additional features of the biology of platelets and of megakaryocytes, the precursors of platelets, will be discovered and that some of these will also influence pulmonary immune defenses and inflammatory injury.

The nonhemostatic immune functions of platelets

Platelets are megakaryocyte-derived cellular fragments, which lack a nucleus and are the smallest circulating cells and are classically known to have a major role in supporting hemostasis. Apart from this well-established role, it is now becoming evident that platelets are also capable of conveying other important functions, such as during infection and inflammation. This paper will outline these nonhemostatic functions in two major sections termed "Platelets versus pathogens" and "Platelet-target cell communication". Platelets actively contribute to protection against invading pathogens and are capable of regulating immune functions in various target cells, all through sophisticated and efficient mechanisms. These relatively novel features will be highlighted, illustrating the multifunctional role of platelets in inflammation.

Thrombopoietin is associated with δ's intercept, and only in Non-Hispanic Whites

INTRODUCTION

Serum thrombopoietin (THPO) is a biomarker of Alzheimer's disease (AD) and the latent dementia phenotype, "δ". Both associations may be specific to non-Hispanic whites (NHW), not Mexican-Americans (MA). In this analysis, we examine ethnicity's effect on THPO's association with change in δ scores, in the Texas Alzheimer's Research and Care Consortium (TARCC).

METHODS

We constructed an ethnicity equivalent δ homolog ("dEQ") among n = 1113 MA and n = 1958 NHW. dEQ was output as a composite "dEQ-score" for each of five annual TARCC waves. Those composites were used as indicators of a latent growth curve (LGC). The mean dEQ intercept (idEQ) and slope (ΔdEQ) were estimated in a random subset of N = 1528 participants and replicated in the remainder (n = 1544). THPO was regressed onto idEQ and ΔdEQ. Those associations were tested separately in MA and NHW.

RESULTS

dEQ correlated strongly with CDR-SB (r = 0.99, P < .001) and achieved high AUCs for AD diagnosis at each wave (range = 0.95-0.99). THPO was significantly associated with idEQ but not ΔdEQ. That effect was observed in NHW only. In MA, THPO had no associations with either idEQ or ΔdEQ.

DISCUSSION

We confirm THPO's ethnicity-specific association with δ in NHW. It is further clarified that this association is specific to δ's intercept and not its slope. This analysis provides a model for how dementia's specific serum biomarkers can be characterized.

Nouvelle cuisine: platelets served with inflammation

Platelets are small cellular fragments with the primary physiological role of maintaining hemostasis. In addition to this well-described classical function, it is becoming increasingly clear that platelets have an intimate connection with infection and inflammation. This stems from several platelet characteristics, including their ability to bind infectious agents and secrete many immunomodulatory cytokines and chemokines, as well as their expression of receptors for various immune effector and regulatory functions, such as TLRs, which allow them to sense pathogen-associated molecular patterns. Furthermore, platelets contain RNA that can be nascently translated under different environmental stresses, and they are able to release membrane microparticles that can transport inflammatory cargo to inflammatory cells. Interestingly, acute infections can also result in platelet breakdown and thrombocytopenia. This report highlights these relatively new aspects of platelets and, thus, their nonhemostatic nature in an inflammatory setting.

Soluble Mediators in Platelet Concentrates Modulate Dendritic Cell Inflammatory Responses in an Experimental Model of Transfusion

The transfusion of platelet concentrates (PCs) is widely used to treat thrombocytopenia and severe trauma. Ex vivo storage of PCs is associated with a storage lesion characterized by partial platelet activation and the release of soluble mediators, such as soluble CD40 ligand (sCD40L), RANTES, and interleukin (IL)-8. An in vitro whole blood culture transfusion model was employed to assess whether mediators present in PC supernatants (PC-SNs) modulated dendritic cell (DC)-specific inflammatory responses (intracellular staining) and the overall inflammatory response (cytometric bead array). Lipopolysaccharide (LPS) was included in parallel cultures to model the impact of PC-SNs on cell responses following toll-like receptor-mediated pathogen recognition. The impact of both the PC dose (10%, 25%) and ex vivo storage period was investigated [day 2 (D2), day 5 (D5), day 7 (D7)]. PC-SNs alone had minimal impact on DC-specific inflammatory responses and the overall inflammatory response. However, in the presence of LPS, exposure to PC-SNs resulted in a significant dose-associated suppression of the production of DC IL-12, IL-6, IL-1α, tumor necrosis factor-α (TNF-α), and macrophage inflammatory protein (MIP)-1β and storage-associated suppression of the production of DC IL-10, TNF-α, and IL-8. For the overall inflammatory response, IL-6, TNF-α, MIP-1α, MIP-1β, and inflammatory protein (IP)-10 were significantly suppressed and IL-8, IL-10, and IL-1β significantly increased following exposure to PC-SNs in the presence of LPS. These data suggest that soluble mediators present in PCs significantly suppress DC function and modulate the overall inflammatory response, particularly in the presence of an infectious stimulus. Given the central role of DCs in the initiation and regulation of the immune response, these results suggest that modulation of the DC inflammatory profile is a probable mechanism contributing to transfusion-related complications.

Immune-relevant thrombocytes of common carp undergo parasite-induced nitric oxide-mediated apoptosis

Common carp thrombocytes account for 30-40% of peripheral blood leukocytes and are abundant in the healthy animals' spleen, the thrombopoietic organ. We show that, ex vivo, thrombocytes from healthy carp express a large number of immune-relevant genes, among which several cytokines and Toll-like receptors, clearly pointing at immune functions of carp thrombocytes. Few studies have described the role of fish thrombocytes during infection. Carp are natural host to two different but related protozoan parasites, Trypanoplasma borreli and Trypanosoma carassii, which reside in the blood and tissue fluids. We used the two parasites to undertake controlled studies on the role of fish thrombocytes during these infections. In vivo, but only during infection with T. borreli, thrombocytes were massively depleted from the blood and spleen leading to severe thrombocytopenia. Ex vivo, addition of nitric oxide induced a clear and rapid apoptosis of thrombocytes from healthy carp, supporting a role for nitric oxide-mediated control of immune-relevant thrombocytes during infection with T. borreli. The potential advantage for parasites to selectively deplete the host of thrombocytes via nitric oxide-induced apoptosis is discussed.

Platelets in inflammation and atherogenesis

Platelets contribute to processes beyond thrombus formation and may play a so far underestimated role as an immune cell in various circumstances. This review outlines immune functions of platelets in host defense, but also how they may contribute to mechanisms of infectious diseases. A particular emphasis is placed on the interaction of platelets with other immune cells. Furthermore, this article outlines the features of atherosclerosis as an inflammatory vascular disease highlighting the role of platelet crosstalk with cellular and soluble factors involved in atheroprogression. Understanding, how platelets influence these processes of vascular remodeling will shed light on their role for tissue homeostasis beyond intravascular thrombosis. Finally, translational implications of platelet-mediated inflammation in atherosclerosis are discussed.

The role of P2Y₁₂ receptor and activated platelets during inflammation

Platelets play an important role not only during thrombosis, but also in modulating immune responses through their interaction with immune cells and by releasing inflammatory mediators upon activation. The P2Y12 receptor is a Gi-coupled receptor that not only regulates ADP-induced aggregation but can also dramatically potentiate secretion, when platelets are activated by other stimuli. Considering the importance of P2Y12 receptor in platelet function, a class of antiplatelet drugs, thienopyridines, have been designed and successfully used to prevent thrombosis. This review will focus on the role of activated platelets in inflammation and the effects that P2Y12 antagonism exerts on the inflammatory process. A change in platelet functions was noted in patients treated with thienopyridines during inflammatory conditions, suggesting that platelets may modulate the inflammatory response. Further experiments in a variety of animal models of diseases, such as sepsis, rheumatoid arthritis, myocardial infarction, pancreatitis and pulmonary inflammation have also demonstrated that activated platelets influence the inflammatory state. Platelets can secrete inflammatory modulators in a P2Y12-dependent manner, and, as a result, directly alter the inflammatory response. P2Y12 receptor may also be expressed in other cells of the immune system, indicating that thienopyridines could directly influence the immune system rather than only through platelets. Overall the results obtained to date strongly support the notion that activated platelets significantly contribute to the inflammatory process and that antagonizing P2Y12 receptor can influence the immune response.

Platelet-derived RANK ligand enhances CCL17 secretion from dendritic cells mediated by thymic stromal lymphopoietin

Dendritic cells (DCs) play an integral role in cellular cascade that initiate and maintain Th2 responses in allergy. In this study, we examined the interaction between platelets and DCs to determine the role of platelets in the intervention of immune responses through modulation of DC functions. Blood-purified myeloid DCs, which had been stimulated with thymic stromal lymphopoietin (TSLP-DCs), formed aggregates with activated platelets. TSLP-DC maturation was induced after the interaction with TRAP6-activated platelets as indicated by an increase in the expression of CD86, CD40, and CD83. In addition, production of a Th2 cell-attracting chemokine, CCL17, was clearly upregulated by coculture of TSLP-DCs with TRAP6-activated platelets. We further found that an expression of RANK ligand (RANKL) on platelets was upregulated by the TRAP6 activation, and that, using the neutralizing antibody against RANKL, the platelet-derived RANKL induces the activation of TSLP-DCs. Thus, activated platelets can intervene in adaptive immune responses through induction of functional modulation of TSLP-DCs. Platelets have the ability to enhance the DC-mediated Th2 response and may contribute to the allergic inflammation. In conclusion, our study provides new insights in platelet functions and the possible mechanism of allergic responses that stem from DCs.

Platelets and autoimmunity

Vascular injury is the initial manifestation of inflammation resulting in the recruitment and activation of various cell types. The integrity of the vascular wall is monitored by platelets that become activated in the presence of exposed subendothelium. Besides their well-established role in haemostasis, ample data are now emerging on the many immunoregulatory functions of platelets. Platelets store and release a large plethora of cytokines, chemokines and growth factors. They also represent the largest circulating pool of many inflammatory mediators like P-selectin, CD40L and non-neuronal serotonin. Furthermore, complement activation occurs on the platelet surface and deposition of complement results in platelet activation. Overall, platelets have multiple functions in both innate and adaptive immunity. Further insight into the multifaceted role of platelets could therefore provide important clues into how we could implement current platelet therapy to reduce both platelet-induced thrombosis and inflammation. In this review, we discuss the current perceptions of platelet involvement in various autoimmune diseases like rheumatoid arthritis, systemic lupus erythematosus, systemic sclerosis and multiple sclerosis.

Platelets in atherosclerosis and thrombosis

Rupture of an atherosclerotic plaque exposes a thrombogenic matrix, which instantly triggers platelet tethering and activation. We here delineate the sequence of events during arterial thrombus formation and dissect the specific role of the various platelet receptors in this process. We also discuss the interplay of platelets with circulating immune cells, which support arterial thrombosis by fibrin formation in a process that involves extracellular nucleosomes. In the second part of this chapter we describe the role of platelets in atherosclerotic lesion formation. Platelets adhere to the dysfunctional endothelium early during atherogenesis. They contain a large machinery of proinflammatory molecules, which can be released upon their activation. This prepares the ground for subsequent leukocyte recruitment and infiltration, and boosts the inflammatory process of the arterial wall. Together, platelets play a critical role in both acute and chronic processes of the vascular wall, which makes them an attractive target for pharmacological strategies to treat arterial thrombosis and, potentially, also atheroprogression.

Leukapheresis in non-cytokine-stimulated donors with a new apheresis system: first-time collection results and evaluation of subsequent cryopreservation

BACKGROUND

Adoptive cell therapy based on mononuclear cells (MNCs) became an important modality of cancer immunotherapy. Data about collection results and donor response of leukapheresis with the Spectra Optia v.5.0 (Terumo BCT) in nonmobilized donors are required.

STUDY DESIGN AND METHODS

Twelve MNC collections were performed using the Spectra Optia v.5.0 in non-cytokine-stimulated donors. Leukapheresis products and peripheral blood samples from donors were assayed for CD45+, CD34+, CD3+, and CD14+ cells by flow cytometry. Prefreeze and postthaw cell counts, cell viability, and numbers of colony-forming units were assessed in cryobags and compared to data from cryovials.

RESULTS

Leukapheresis yielded a mean of 5.26×10(9) ±2.2×10(9) CD45+ cells, 1.5×10(9) ±0.77×10(9) CD14+ monocytes, and 2.28×10(9) ±1.2×10(9) CD3+ Tcells by processing 6690±930mL of whole blood. A significant positive correlation between yield of CD3+ Tcells and residual platelets (PLTs) and red blood cells (RBCs) was observed. This did not apply for CD34+ and CD14+ white blood cell subsets. Mean collection efficiencies for CD14+ monocytes and CD3+ Tcells were 61.8±17 and 37.2±18%, respectively. Recovery of CD14+ cells after cryopreservation was 75.2±8.2%, which was significantly lower than recovery of CD45+ cells (81.4±5.5%; p=0.01).

CONCLUSION

This study of a small cohort demonstrates that the Spectra Optia v.5.0 is capable of collecting low product volumes with satisfactory MNC yields and low residual RBCs and PLTs in non-cytokine-mobilized apheresis. Our data suggest that cryovials can serve as a representative surrogate for the primary product cryobag.

Thrombin and vascular inflammation

Vascular endothelium is a key regulator of homeostasis. In physiological conditions it mediates vascular dilatation, prevents platelet adhesion, and inhibits thrombin generation. However, endothelial dysfunction caused by physical injury of the vascular wall, for example during balloon angioplasty, acute or chronic inflammation, such as in atherothrombosis, creates a proinflammatory environment which supports leukocyte transmigration toward inflammatory sites. At the same time, the dysfunction promotes thrombin generation, fibrin deposition, and coagulation. The serine protease thrombin plays a pivotal role in the coagulation cascade. However, thrombin is not only the key effector of coagulation cascade; it also plays a significant role in inflammatory diseases. It shows an array of effects on endothelial cells, vascular smooth muscle cells, monocytes, and platelets, all of which participate in the vascular pathophysiology such as atherothrombosis. Therefore, thrombin can be considered as an important modulatory molecule of vascular homeostasis. This review summarizes the existing evidence on the role of thrombin in vascular inflammation.

Platelets: versatile effector cells in hemostasis, inflammation, and the immune continuum

Platelets are chief effector cells in hemostasis. In addition, however, their specializations include activities and intercellular interactions that make them key effectors in inflammation and in the continuum of innate and adaptive immunity. This review focuses on the immune features of human platelets and platelets from experimental animals and on interactions between inflammatory, immune, and hemostatic activities of these anucleate but complex and versatile cells. The experimental findings and evidence for physiologic immune functions include previously unrecognized biologic characteristics of platelets and are paralleled by new evidence for unique roles of platelets in inflammatory, immune, and thrombotic diseases.

Dendritic cell generation and CD4+ CD25high FOXP3+ regulatory t cells in human head and neck carcinoma during radio-chemotherapy

Background

Regulatory T cells (Treg) and dendritic cells (DC) play an important role in tumor immunity and immune escape. However, their interplay and the effects of anti-cancer therapy on the human immune system are largely unknown.

Methods

For DC generation, CD14⁺ monocytes were enriched by immunomagnetic selection from peripheral blood of advanced head and neck squamous cell carcinoma (HNSCC) patients and differentiated into immature DC using GM-SCF and IL-4. DC maturation was induced by addition of TNFα. The frequency of CD4⁺CD25^highF0XP3⁺ Treg in HNSCC patients was analyzed before and after radio-chemotherapy (RCT) by four-color flow cytometry.

Results

In HNSCC patients, the frequency of Treg (0.33 ± 0.06%) was significantly (p = 0.001) increased compared to healthy controls (0.11 ± 0.02%), whereas RCT had variable effects on the Treg frequency inducing its increase in some patients and decrease in others. After six days in culture, monocytes of all patients had differentiated into immature DC. However, DC maturation indicated by CD83 up-regulation (70.7 ± 5.5%) was successful only in a subgroup of patients and correlated well with lower frequencies of peripheral blood Treg in those patients.

Conclusion

The frequency of regulatory T cells is elevated in HNSCC patients and may be modulated by RCT. Monocyte-derived DC in HNSCC patients show a maturation deficiency ex vivo. Those preliminary data may have an impact on multimodality clinical trials integrating cellular immune modulation in patients with advanced HNSCC.

Optimization of leukocyte collection and monocyte isolation for dendritic cell culture

Leukapheresis is the method of choice to collect monocytes for dendritic cell (DC) culture. Improvement of cell separators and cell collection software have enabled the collection of 10(9) monocytes for the generation of monocyte-derived DCs, which is sufficient to prepare a DC vaccine series. However, leukapheresis works with the technique of differential centrifugation which is not applicable to selectively collect mononuclear cells of similar density. After leukapheresis, thus, additional preparation steps are required to isolate and enrich the desired monocyte population. The cell isolation and cultivation techniques depend on the quality of the original leukocyte harvest due to the monocyte yield and the content of residual erythrocytes and platelets. Monocyte elutriation from the leukapheresis product shows a high monocyte recovery of 80%. However, only 30% of the isolated monocytes can be developed into mature DCs. The factors responsible for DC maturation and the development of different DC subsets are the subject of current research.

Infections, antigen-presenting cells, T cells, and immune tolerance: their role in the pathogenesis of immune thrombocytopenia

In the last 20 years, many publications have shed new light on the complex immunopathogenesis of immune thrombocytopenic purpura. They are associated with 3 interrelated areas of environmental autoimmunity, for example, infectious influences, antigen-presenting cell (APC) function, and T-cell abnormalities, particularly tolerance induction. This article highlights the recent literature and argues that infectious agents and platelets can significantly modulate APCs, which create an environment that dysregulates autoreactive T cells, leading to the production of autoantibodies.

Differentiation of monocyte-derived dendritic cells under the influence of platelets

BACKGROUND

Monocytapheresis has been established to collect a sufficient number of monocytes (MO) for differentiation to dendritic cells (DC) as a cancer vaccine. Platelets (Plt) are invariably found as a contaminant in the final monocytapheresis product. The aim of this study was to investigate DC differentiation under the influence of Plt with regard to their function and phenotype.

METHODS

MO were isolated and co-cultured with autologous Plt at different MO:Plt ratios (1:1.7, 1:5, 1:15, 1:45 and 1:135) in the presence of interleukin-4 (IL-4) and granulocyte-macrophage colony-stimulating factor (GM-CSF). IL-12p70 release after ligation of CD40L was determined in the supernatant by enzyme-linked immunosorbent assay (ELISA). For T-cell stimulation, tetanus toxoid was added to immature DC and maturation was induced by adding cytokines (IL-1beta, IL-6, tumor necrosis factor-alpha and prostaglandin E(2)). Stimulated T cells were analyzed for activation and proliferation as well as for intracellular cytokines by flow cytometry.

RESULTS

All DC cultures were strongly positive for CD83. At a contaminating concentration of 5 Plt/MO, matured DC showed the highest expression of HLA-DR, CD80 and CD86, inducing a strong T-cell proliferation with high production of IL-4 and interferon-gamma. The highest level of IL-12p70 production was observed by the same DC group.

DISCUSSION

Plt did not negatively influence DC maturation but enhanced the expression of co-stimulatory molecules and the release of IL-12. Functionally this was reflected by a strong T-cell response that involved T-helper 1 (Th1)- as well as Th2-biased T cells. Our findings show that controlling the Plt concentration may provide important advantages for the generation of DC for use in immunotherapy.