The role of platelets in the pathophysiology of asthma

Dysregulated haemostasis in thrombo-inflammatory disease

Inflammatory disease is often associated with an increased incidence of venous thromboembolism in affected patients, although in most instances, the mechanistic basis for this increased thrombogenicity remains poorly understood. Acute infection, as exemplified by sepsis, malaria and most recently, COVID-19, drives 'immunothrombosis', where the immune defence response to capture and neutralise invading pathogens causes concurrent activation of deleterious prothrombotic cellular and biological responses. Moreover, dysregulated innate and adaptive immune responses in patients with chronic inflammatory conditions, such as inflammatory bowel disease, allergies, and neurodegenerative disorders, are now recognised to occur in parallel with activation of coagulation. In this review, we describe the detailed cellular and biochemical mechanisms that cause inflammation-driven haemostatic dysregulation, including aberrant contact pathway activation, increased tissue factor activity and release, innate immune cell activation and programmed cell death, and T cell-mediated changes in thrombus resolution. In addition, we consider how lifestyle changes increasingly associated with modern life, such as circadian rhythm disruption, chronic stress and old age, are increasingly implicated in unbalancing haemostasis. Finally, we describe the emergence of potential therapies with broad-ranging immunothrombotic functions, and how drug development in this area is challenged by our nascent understanding of the key molecular and cellular parameters that control the shared nodes of proinflammatory and procoagulant pathways. Despite the increasing recognition and understanding of the prothrombotic nature of inflammatory disease, significant challenges remain in effectively managing affected patients, and new therapeutic approaches to curtail the key pathogenic steps in immune response-driven thrombosis are urgently required.

Association of Red Cell Index and Adverse Hospitalization Outcomes in Chronic Obstructive Pulmonary Disease Patients with Acute Exacerbation: A Retrospective Cohort Study

Purpose

Previous studies have shown that the red cell index (RCI) can be considered as a simple and useful method to evaluate respiratory function. However, at present its association with adverse hospitalization outcomes in patients with acute exacerbation of chronic obstructive pulmonary disease (AECOPD) is not fully understood. Our study aimed to examine the relationship between adverse hospitalization outcomes and RCI among AECOPD patients.

Patients and Methods

We performed a retrospective analysis of consecutive patients from January 2015 to October 2021. In this study, RCI was the independent variable, measured at baseline, and adverse hospitalization outcome was the dependent variable. According to the RCI median (RCI=2.221), we divided 377 patients into two roughly equal groups (188 and 189, respectively). Next, the association between RCI and adverse hospitalization outcomes was explored using multivariable logistic regression models. To identify any non-linear relationship, a generalized additive model (GAM) was employed.

Results

With a total of 377 patients with AECOPD, we divided them into two roughly equal groups to compare the clinical factors and RCI levels. The patients in the higher RCI group showed poorer outcome incidence (18 [9.57%] vs 31 [16.40%]; p = 0.049). After accounting for potential confounders, the results showed that RCI was positively associated with adverse hospitalization outcomes (odds ratio [OR] = 1.15, 95% CI: 1.01-1.32). In addition, a non-linear relationship was detected between RCI and adverse hospitalization outcomes, which had an inflection point of 3.2. There were odds ratios and confidence intervals of 0.8 (0.7-1.0) and 1.3 (1.2-1.4) on the left and right sides of the inflection point, respectively.

Conclusion

The RCI and adverse hospitalization outcomes exhibited a non-linear relationship in the AECOPD patients. RCI is strongly positively correlated with adverse hospitalization outcomes when it was greater than 3.2.

Atypical Roles of the Chemokine Receptor ACKR3/CXCR7 in Platelet Pathophysiology

The manifold actions of the pro-inflammatory and regenerative chemokine CXCL12/SDF-1α are executed through the canonical GProteinCoupledReceptor CXCR4, and the non-canonical ACKR3/CXCR7. Platelets express CXCR4, ACKR3/CXCR7, and are a vital source of CXCL12/SDF-1α themselves. In recent years, a regulatory impact of the CXCL12-CXCR4-CXCR7 axis on platelet biogenesis, i.e., megakaryopoiesis, thrombotic and thrombo-inflammatory actions have been revealed through experimental and clinical studies. Platelet surface expression of ACKR3/CXCR7 is significantly enhanced following myocardial infarction (MI) in acute coronary syndrome (ACS) patients, and is also associated with improved functional recovery and prognosis. The therapeutic implications of ACKR3/CXCR7 in myocardial regeneration and improved recovery following an ischemic episode, are well documented. Cardiomyocytes, cardiac-fibroblasts, endothelial lining of the blood vessels perfusing the heart, besides infiltrating platelets and monocytes, all express ACKR3/CXCR7. This review recapitulates ligand induced differential trafficking of platelet CXCR4-ACKR3/CXCR7 affecting their surface availability, and in regulating thrombo-inflammatory platelet functions and survival through CXCR4 or ACKR3/CXCR7. It emphasizes the pro-thrombotic influence of CXCL12/SDF-1α exerted through CXCR4, as opposed to the anti-thrombotic impact of ACKR3/CXCR7. Offering an innovative translational perspective, this review also discusses the advantages and challenges of utilizing ACKR3/CXCR7 as a potential anti-thrombotic strategy in platelet-associated cardiovascular disorders, particularly in coronary artery disease (CAD) patients post-MI.

Platelets: a potential role in chronic respiratory diseases?

Platelets are small anucleate cells known for their role in haemostasis and thrombosis. In recent years, an increasing number of observations have suggested that platelets are also immune cells and key modulators of immunity. They express different receptors and molecules that allow them to respond to pathogens, and to interact with other immune cells. Platelets were linked to the pathogenesis of some inflammatory disorders including respiratory diseases such as asthma and idiopathic pulmonary fibrosis. Here, we discuss the involvement of platelets in different immune responses, and we focus on their potential role in various chronic lung diseases.

In addition to their essential role in haemostasis and thrombosis, platelets are strong modulators of different immune responses, and could be involved in the physiopathology of several chronic airway diseaseshttps://bit.ly/3cB6Xnj

Imbalanced Coagulation in the Airway of Type-2 High Asthma with Comorbid Obesity

Asthma is a common, chronic airway inflammatory disease marked by airway hyperresponsiveness, inflammation, and remodeling. Asthma incidence has increased rapidly in the past few decades and recent multicenter analyses have revealed several unique asthma endotypes. Of these, type-2 high asthma with comorbid obesity presents a unique clinical challenge marked by increased resistance to standard therapies and exacerbated disease development. The extrinsic coagulation pathway plays a significant role in both type-2 high asthma and obesity. The type-2 high asthma airway is marked by increased procoagulant potential, which is readily activated following damage to airway tissue. In this review, we summarize the current understanding of the role the extrinsic coagulation pathway plays in the airway of type-2 high asthma with comorbid obesity. We propose that asthma control is worsened in obesity as a result of a systemic and local airway shift towards a procoagulant and anti-fibrinolytic environment. Lastly, we hypothesize bariatric surgery as a treatment for improved asthma management in type-2 high asthma with comorbid obesity, facilitated by normalization of systemic procoagulant and pro-inflammatory mediators. A better understanding of attenuated coagulation parameters in the airway following bariatric surgery will advance our knowledge of biomolecular pathways driving asthma pathobiology in patients with obesity.

Exosomes: A Key Piece in Asthmatic Inflammation

Asthma is a chronic disease of the airways that has an important inflammatory component. Multiple cells are implicated in asthma pathogenesis (lymphocytes, eosinophils, mast cells, basophils, neutrophils), releasing a wide variety of cytokines. These cells can exert their inflammatory functions throughout extracellular vesicles (EVs), which are small vesicles released by donor cells into the extracellular microenvironment that can be taken up by recipient cells. Depending on their size, EVs can be classified as microvesicles, exosomes, or apoptotic bodies. EVs are heterogeneous spherical structures secreted by almost all cell types. One of their main functions is to act as transporters of a wide range of molecules, such as proteins, lipids, and microRNAs (miRNAs), which are single-stranded RNAs of approximately 22 nucleotides in length. Therefore, exosomes could influence several physiological and pathological processes, including those involved in asthma. They can be detected in multiple cell types and biofluids, providing a wealth of information about the processes that take account in a pathological scenario. This review thus summarizes the most recent insights concerning the role of exosomes from different sources (several cell populations and biofluids) in one of the most prevalent respiratory diseases, asthma.

Analysis of serum polyunsaturated fatty acid metabolites in allergic bronchopulmonary aspergillosis

BACKGROUND

The importance of lipid mediators in allergic diseases has been long recognized, whereas little is known about their role in allergic bronchopulmonary aspergillosis (ABPA). We investigated whether lipid mediators are associated with ABPA.

METHODS

We recruited 12 ABPA patients, 23 asthma patients and 12 healthy control in our study. Serum of 11 ABPA patients were collected before and following treatment. 36 polyunsaturated fatty acid metabolites were measured in serum samples by using liquid chromatography-mass spectrometry. This study was approved by the Ethics Committee of the First Affiliated Hospital of Guangzhou Medical University, with ethics number GYFYY-2016-73.

RESULTS

Levels of arachidonic acid (AA), 15(S)-hydroxyeicosatetraenoic acid (HETE), 12(S)-HETE, 8(S)-HETE, 5(S)-HETE, LTB₄, PGB₂, 12(S)-hydroxyeicosapentaenoic acid (HEPE), 12-hydro-xyheptadecatrienoic acid (HHTrE) were significantly higher in ABPA patients than that in HC groups. Compared with asthma group, ABPA group expressed lower levels of 15(S)-hy-droperoxyeicosatetraenoic acid (HPETE), 5(S)-HPETE, 13(S)-hydroperoxyoctadecadienoic acid (HPODE) and 9(S)-HPODE. In APBA patients, AA level was positively correlated with serumtotal IgE (tIgE). The levels of 12(S)-HPETE, 15(S)-HEPE and 12(S)-HEPE correlated with Asp-ergillus fumigatus specific IgE(A. fumigatus sIgE) positively. Peripheral blood eosinophilia correlated with high levels of 12(S)-HETE and 15(S)-HETE. In addition, the serum levels of15(S)-HETE and 12(S)-HETE in ABPA subjects both declined with the decrease of tIgE, A. fumigatus sIgE and sIgG concentrations after treatment.

CONCLUSIONS

We present data regarding the role of polyunsaturated fatty acid metabolites in APBA for the first time. Most of the tested metabolites increased in ABPA when co-mpared with healthy controls and 15(S)-HETE and 12(S)-HETE may play a role in the pat-hogenesis of ABPA. These findings can provide new ideas for diagnosis, therapy and mon-itor of ABPA.

Extracellular vesicles and asthma: A review of the literature

Asthma is a chronic, recurrent and incurable allergy-related respiratory disease characterized by inflammation, bronchial hyperresponsiveness and narrowing of the airways. Extracellular vesicles (EVs) are a universal feature of cellular function and can be detected in different bodily fluids. Recent evidence has shown the possibility of using EVs in understanding the pathogenesis of asthma, including their potential as diagnostic and therapeutic tools. Studies have reported that EVs released from key cells involved in asthma can induce priming and activation of other asthma-associated cells. A literature review was conducted on all current research regarding the role and function of EVs in the pathogenesis of asthma via the PRISMA statement method. An electronic search was performed using EMBASE and PubMed through to November 2018. The EMBASE search returned 76 papers, while the PubMed search returned 211 papers. Following duplicate removal, titles and abstracts were screened for eligibility with a total of 34 studies included in the final qualitative analysis. The review found evidence of association between the presence of EVs and physiological changes characteristic of asthma, suggesting that EVs are involved in the pathogenesis, with the weight of evidence presently favouring deleterious effects of EVs in asthma. Numerous studies highlighted differences in exosomal contents between EVs of healthy and asthmatic individuals, which could be employed as potential diagnostic markers. In some circumstances, EVs were also found to be suppressive to disease, but more often promote inflammation and airway remodelling. In conclusion, EVs hold immense potential in understanding the pathophysiology of asthma, and as diagnostic and therapeutic markers. While more research is needed for definitive conclusions and their application in medical practice, the literature presented in this review should encourage further research and discovery within the field of EVs and asthma.

Increased thrombin-activatable fibrinolysis inhibitor levels in patients with chronic rhinosinusitis with nasal polyps

BACKGROUND

Chronic rhinosinusitis (CRS) is a heterogeneous chronic inflammatory disease subdivided based on the presence or absence of nasal polyps (NPs). Histologic features of chronic rhinosinusitis with nasal polyps (CRSwNP) include inflammatory cell infiltration and excessive fibrin deposition in NPs. Thrombin-activatable fibrinolysis inhibitor (TAFI) is an enzyme that plays an antifibrinolytic role in the body. The significance of TAFI has been documented in patients with chronic inflammatory diseases, including chronic lung disease; however, it has not been evaluated in the pathogenesis of NPs.

OBJECTIVE

The objective of this study was to evaluate the potential role of TAFI in the pathogenesis of NPs.

METHODS

Nasal lavage fluid was collected from control subjects and patients with CRS. We measured levels of thrombin/anti-thrombin complex (TATc) and TAFI protein using an ELISA.

RESULTS

TATc levels in nasal lavage fluid were significantly increased in patients with CRSwNP and patients with chronic rhinosinusitis without nasal polyps (CRSsNP) compared with control subjects, and TAFI levels in nasal lavage fluid were also significantly increased in patients with CRSwNP compared with those in control subjects and patients with CRSsNP. There was a significant correlation between TATc and TAFI levels in nasal lavage fluid. Interestingly, patients with CRS and asthma showed increased TATc and TAFI levels in nasal lavage fluid compared with those in patients with CRS without asthma, especially patients with CRSwNP.

CONCLUSIONS

Increased TATc and TAFI levels in nasal passages of patients with CRSwNP might participate in fibrin deposition in NPs and might play a role in the pathogenesis of CRSwNP and asthma.

Comorbidity of asthma and hypertension may be mediated by shared genetic dysregulation and drug side effects

Asthma and hypertension are complex diseases coinciding more frequently than expected by chance. Unraveling the mechanisms of comorbidity of asthma and hypertension is necessary for choosing the most appropriate treatment plan for patients with this comorbidity. Since both diseases have a strong genetic component in this article we aimed to find and study genes simultaneously associated with asthma and hypertension. We identified 330 shared genes and found that they form six modules on the interaction network. A strong overlap between genes associated with asthma and hypertension was found on the level of eQTL regulated genes and between targets of drugs relevant for asthma and hypertension. This suggests that the phenomenon of comorbidity of asthma and hypertension may be explained by altered genetic regulation or result from drug side effects. In this work we also demonstrate that not only drug indications but also contraindications provide an important source of molecular evidence helpful to uncover disease mechanisms. These findings give a clue to the possible mechanisms of comorbidity and highlight the direction for future research.

Platelet Biogenesis in the Lung Circulation

Megakaryocytes are normal cellular components of the blood returning to the heart and entering the lungs, and historical data has pointed to a role of the lungs in platelet production. Recent studies using intravital microscopy have demonstrated that platelet release occurs in the lung from bone marrow megakaryocytes that embolize into the lung circulation.

Effect of acetylsalicylic acid intake on platelet derived microvesicles in healthy subjects

Platelet-derived microvesicles (pMVs) are released from platelets in physiological and pathological conditions and exhibit a wide range of prothrombotic, antithrombotic, proatherogenic, and pro-inflammatory properties. Antiplatelet agents, such as acetylsalicylic acid (ASA), are widely used for the prevention and treatment of vascular diseases, but their impact on pMV release remains poorly understood and contradictory mainly because of discrepancies in the methodology and lack of well-standardized MV assessment protocols. The present study investigated the effects of ASA not only on total pMV release but also on their phenotypes defined using the surface expression of pro-inflammatory (CD40L, CD62P, CD31) and procoagulant (PS, PAC-1) markers in healthy subjects. Fifty healthy volunteers were enrolled in the study and received a daily dose of 150 mg ASA for 3 consecutive days. Circulating pMVs were characterized and quantified before and after the intervention period using flow cytometry. Serum levels of thromboxane B2 (TXB2) and whole blood impedance platelet aggregation under arachidonic acid (AA) stimulation were also investigated to assess ASA compliance. In general, ASA did not effect pMV numbers in healthy subjects despite its effective inhibition of platelet aggregation Moreover, in premenopausal women, we noticed an increase in the number of pMVs. Further studies are needed to assess whether dose modification of ASA or combinations or changes in antiplatelet therapy would reduce pMV formation, especially in patients with cardiovascular risk factors.

Platelet reactivity in patients with chronic kidney disease undergoing percutaneous coronary intervention

This study aimed to evaluate the platelet reactivity in real-world patients with different chronic kidney disease (CKD) stages after percutaneous coronary intervention (PCI), and to examine whether high residual platelet reactivity (HRPR) is associated with higher incidence of adverse cardiovascular events in a 2-year follow up. A total of 10 724 consecutive patients receiving DAPT with aspirin and clopidogrel after PCI throughout 2013 were enrolled. We applied modified thromboelastography (mTEG) in 6745 patients. Kaplan-Meier analysis and Cox proportional regression analysis were applied to illustrate end points for patients. The prevalence of HRPR for adenosine diphosphate (ADP) was higher in patients with CKD3-5 than patients with CKD1-2 (47.0% vs. 37.3%, p = 0.002), but not for arachidonic acid (AA). No significant difference was observed for MACCE between patients with or without HRPR for ADP (HR 1.004, 95%CI: 0.864-1.167, p = 0.954). Patients with HRPR for ADP was associated with less bleeding events than patients without HRPR for ADP (HR 0.795, 95%CI: 0.643-0.982, p = 0.034). In this large cohort of real-world patients after PCI, the deterioration of renal function was linked to HRPR for ADP. HRPR was not associated with MACCE in patients with CKD in a 2-year follow up. Bleeding risks were significantly lower in PCI patients with versus without HRPR for ADP.

Effect of antigen challenge on dynamics of CD62P and CD41/61 expression on platelets in horses with recurrent airway obstruction (RAO)

Recurrent airway obstruction (RAO), also known as heaves, is an allergic respiratory condition that develops in horses following an exposure to aeroallergens in hay and straw. This is manifested by airway hyperreactivity, inflammation, bronchoconstriction, as well as a leukocyte and platelet infiltration into the airways. Platelet activation and an increase in circulating platelet-leukocyte aggregates may lead to airway remodeling. The aim of this study was to explore the effect of seven-day antigen challenge on dynamics of platelet indices and CD41/61 and CD62 P expression on platelets in horses with RAO. Ten RAO-affected horses and ten healthy horses were included in this study. All horses were exposed to 7 days hay and straw challenge. Blood samples were collected prior to the challenge (Pre-challenge) and 1, 2, 3, 7 and 14 days after the initiating the antigen challenge. Blood samples were obtained to determine the platelet count (PLT), mean platelet volume (MPV) and platelet large cell ratio (P-LCR). Expression of CD62 P and CD41/61 was detected by flow cytometry on activated platelets. Antigen challenge resulted in a significant gradual decrease of PLT in RAO horses, but not in controls. MPV and P-LCR in control and RAO-affected horses remained unchanged after antigen challenge. The expression of CD62 P and CD41/61 in RAO horses was significantly higher compared to control horses. The antigen challenge resulted in an increase expression of CD62 P and CD41/61 on the platelets of RAO-affected horses, while did not lead to significant changes in the control group. An increased expression of CD62 P and CD41/61 indicates platelet activation what may contribute to the formation of platelet aggregates in their respiratory system.

Recent advances in understanding the roles of blood platelets in the pathogenesis of allergic inflammation and bronchial asthma

Platelets play an essential role in hemostasis to minimize blood loss due to traumatic injury. In addition, they contain various immune-associated molecules and contribute to immunological barrier formation at sites of vascular injury, thereby protecting against invading pathogens. Platelets are also crucially involved in development of allergic diseases, including bronchial asthma. Platelets in asthmatics are more activated than those in healthy individuals. By using a murine asthma model, platelets were shown to be actively involved in progression of the disease, including in airway eosinophilia and airway remodeling. In the asthmatic airway, pathological microvascular angiogenesis, a component of airway remodeling, is commonly observed, and the degree of abnormality is significantly associated with disease severity. Therefore, in order to repair the newly formed and structurally fragile blood vessels under inflammatory conditions, platelets may be continuously activated in asthmatics. Importantly, platelets constitutively express IL-33 protein, an alarmin cytokine that is essential for development of bronchial asthma. Meanwhile, the concept of development of allergic diseases has recently changed dramatically, and allergy researchers now share a belief in the centrality of epithelial barrier functions. In particular, IL-33 released from epithelial barrier tissue at sites of eczema can activate the antigen-non-specific innate immune system as an alarmin that is believed to be necessary for subsequent antigen-specific acquired immunological responses. From this perspective, we propose in this review a possible mechanism for how activated platelets act as an alarmin in development of bronchial asthma.

Association of thrombocytosis with COPD morbidity: the SPIROMICS and COPDGene cohorts

BACKGROUND

Thrombocytosis has been associated with COPD prevalence and increased all-cause mortality in patients with acute exacerbation of COPD (AECOPD); but whether it is associated with morbidity in stable COPD is unknown. This study aims to determine the association of thrombocytosis with COPD morbidity including reported AECOPD, respiratory symptoms and exercise capacity.

METHODS

Participants with COPD were included from two multi-center observational studies (SPIROMICS and COPDGene). Cross-sectional associations of thrombocytosis (platelet count ≥350 × 10⁹/L) with AECOPD during prior year (none vs. any), exertional dyspnea (modified Medical Research Council (mMRC) score ≥ 2), COPD Assessment Test (CAT) score ≥ 10, six-minute-walk distance (6MWD), and St. George Respiratory questionnaire (SGRQ) were modeled using multivariable logistic or linear regression. A pooled effect estimate for thrombocytosis was produced using meta-analysis of data from both studies.

RESULTS

Thrombocytosis was present in 124/1820 (6.8%) SPIROMICS participants and 111/2185 (5.1%) COPDGene participants. In meta-analysis thrombocytosis was associated with any AECOPD (adjusted odds ratio [aOR] 1.5; 95% confidence interval [95% CI]: 1.1-2.0), severe AECOPD (aOR 1.5; 95% CI: 1.1-2.2), dyspnea (mMRC ≥ 2 aOR 1.4; 95% CI: 1.0-1.9), respiratory symptoms (CAT ≥ 10 aOR 1.6; 95% CI: 1.1-2.4), and higher SGRQ score (β 2.7; 95% CI: 0.5, 5). Thrombocytosis was also associated with classification into Global Initiative for Chronic Obstructive Lung Disease (GOLD) group D (aOR 1.7 95% CI: 1.2-2.4).

CONCLUSIONS

Thrombocytosis was associated with higher likelihood of prior exacerbation and worse symptoms. Platelet count, a commonly measured clinical assay, may be a biomarker for moderate-severe COPD symptoms, guide disease classification and intensity of treatment. Future longitudinal studies investigating the role of platelets in COPD progression may be warranted.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT01969344 (SPIROMICS) and NCT00608764 (COPDGene).

Lung as a Niche for Hematopoietic Progenitors

Platelets are released from megakaryocytes. The bone marrow has been proposed to be the major site where this process occurs. Lefrançais et al. (2017) using state-of-the-art techniques including two-photon microscopy, in vivo lineage-tracing technologies, and sophisticated lung transplants reveal that the lung is also a primary site for platelet biogenesis. Strikingly, lung megakaryocytes can completely reconstitute platelet counts in the blood in mice with thrombocytopenia. This study also shows that hematopoietic progenitors, with capacity to repopulate the bone marrow after irradiation, are present in the lungs. This work brings a novel unexpected role for the lung as a niche for hematopoiesis. The emerging knowledge from this research may be important for the treatment of several disorders.

Bacterial proteases and haemostasis dysregulation in the CF lung

BACKGROUND

Pathogenic bacteria which chronically colonise the cystic fibrosis (CF) lung produce a number of virulence determinants, including distinct proteolytic activities. The potential role bacterial proteases play on haemostatic dysregulation within the CF lung is, however, poorly defined, despite haemoptysis being a common complication in CF.

METHODS

The potential impact of known CF pathogens (Pseudomonas aeruginosa and Burkholderia cepacia complex spp.) on haemostasis was examined for their ability to degrade fibrinogen and dysregulate fibrin clot formation and platelet aggregation.

RESULTS

Results demonstrate that key CF pathogens growing as a biofilm on mucin exhibit considerable fibrinogenolytic activity, resulting in fibrinogen breakdown, impaired clot formation, and modulation of platelet aggregation. Human neutrophil elastase may also contribute to fibrinogen breakdown and dysregulated clot formation at high concentration.

CONCLUSION

Bacterial-derived proteases may play an important role in the dysregulation of airway haemostasis, and potentially contribute to episodes of haemoptysis within the CF lung.

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.

Impaired P2X1 Receptor-Mediated Adhesion in Eosinophils from Asthmatic Patients

Eosinophils play an important role in the pathogenesis of asthma and can be activated by extracellular nucleotides released following cell damage or inflammation. For example, increased ATP concentrations were reported in bronchoalveolar lavage fluids of asthmatic patients. Although eosinophils are known to express several subtypes of P2 receptors for extracellular nucleotides, their function and contribution to asthma remain unclear. In this article, we show that transcripts for P2X1, P2X4, and P2X5 receptors were expressed in healthy and asthmatic eosinophils. The P2X receptor agonist α,β-methylene ATP (α,β-meATP; 10 μM) evoked rapidly activating and desensitizing inward currents (peak 18 ± 3 pA/pF at -60 mV) in healthy eosinophils, typical of P2X1 homomeric receptors, which were abolished by the selective P2X1 antagonist NF449 (1 μM) (3 ± 2 pA/pF). α,β-meATP-evoked currents were smaller in eosinophils from asthmatic patients (8 ± 2 versus 27 ± 5 pA/pF for healthy) but were enhanced following treatment with a high concentration of the nucleotidase apyrase (17 ± 5 pA/pF for 10 IU/ml and 11 ± 3 pA/pF for 0.32 IU/ml), indicating that the channels are partially desensitized by extracellular nucleotides. α,β-meATP (10 μM) increased the expression of CD11b activated form in eosinophils from healthy, but not asthmatic, donors (143 ± 21% and 108 ± 11% of control response, respectively). Furthermore, α,β-meATP increased healthy (18 ± 2% compared with control 10 ± 1%) but not asthmatic (13 ± 1% versus 10 ± 0% for control) eosinophil adhesion. Healthy human eosinophils express functional P2X1 receptors whose activation leads to eosinophil αMβ2 integrin-dependent adhesion. P2X1 responses are constitutively reduced in asthmatic compared with healthy eosinophils, probably as the result of an increase in extracellular nucleotide concentration.

Platelets constitutively express IL-33 protein and modulate eosinophilic airway inflammation

BACKGROUND

Although platelets play a key role in allergic inflammation in addition to their well-established role in hemostasis, the precise mechanisms of how platelets modulate allergic inflammation are not fully understood. IL-33 is an essential regulator of innate immune responses and allergic inflammation.

OBJECTIVE

We sought to determine the expression of IL-33 protein by platelets and its functional significance in airway inflammation.

METHODS

IL-33 protein in human platelets, the human megakaryocyte cell line MEG-01, and bone marrow-derived mouse megakaryocytes was detected by using Western blot analysis and fluorescent immunostaining. We examined the functional relevance of IL-33 protein in platelets by comparing platelet-intact and platelet-depleted groups in a murine model of IL-33-dependent airway eosinophilia elicited by intranasal administration of papain. We further compared the additive effect of administration of platelets derived from wild-type versus IL-33-deficient mice on the papain-induced eosinophilia.

RESULTS

Platelets and their progenitor cells, megakaryocytes, constitutively expressed IL-33 protein (31 kDa). Papain-induced IL-33-dependent airway eosinophilia in mice was significantly attenuated by platelet depletion. Conversely, concomitant administration of platelets derived from wild-type mice but not IL-33-deficient mice enhanced the papain-induced airway eosinophilia.

CONCLUSIONS

Our novel findings suggest that platelets might be important cellular sources of IL-33 protein in vivo and that platelet-derived IL-33 might play a role in airway inflammation. Therefore platelets might become an attractive novel therapeutic target for asthma and probably allergic inflammation.

Role of platelets in allergic airway inflammation

Increasing evidence suggests an important role for platelets and their products (e.g., platelet factor 4, β-thromboglobulin, RANTES, thromboxane, or serotonin) in the pathogenesis of allergic diseases. A variety of changes in platelet function have been observed in patients with asthma, such as alterations in platelet secretion, expression of surface molecules, aggregation, and adhesion. Moreover, platelets have been found to actively contribute to most of the characteristic features of asthma, including bronchial hyperresponsiveness, bronchoconstriction, airway inflammation, and airway remodeling. This review brings together the current available data from both experimental and clinical studies that have investigated the role of platelets in allergic airway inflammation and asthma. It is anticipated that a better understanding of the role of platelets in the pathogenesis of asthma might lead to novel promising therapeutic approaches in the treatment of allergic airway diseases.

Platelet aggregation, secretion, and coagulation changes in children with asthma

The chronic inflammation in asthma evolves by cells including eosinophils, mast cells and lymphocytes. Despite their principal function in hemostasis, platelets contribute to pathogenesis of asthma that activation of platelets occurs following antigen provocation and during asthma attack. Our aim was to evaluate the platelet functions and other hemostatic features of children with asthma, both during symptom-free period and asthma attack. We enrolled patients with asthma attack (n = 33), mild intermittent asthma (n = 18), mild persistent asthma (n = 15) and healthy children (n = 20). Demographic characteristics and disease-related features were noted. Platelet aggregation and secretion tests (expressed as ATP release) were performed by lumiaggregometer method by stimulation with collagen, epinephrine, ADP, thrombin, ristocetin and arachidonic acid. Plasma levels of D-dimer, factor VIII (FVIII) and von Willebrand factor (vWF) were assessed. There were no differences in platelet aggregation induced by agonists between study groups. ATP release from platelets of patients with asthma exacerbation induced by ADP was lower compared with mild intermittent asthma (P < 0.001). Epinephrine-stimulated ATP secretion was also lower in patients with asthma attack than mild intermittent (P = 0.039) and mild persistent asthma (P = 0.011) and controls (P = 0.018). vWF measurements were higher in children with asthma attack than other study groups (P = 0.001). However, FVIII was increased in patients with severe asthma attack. Asthma is a disease in which many immune cells play a role, one of which is the platelet. Distinctions in platelet secretion profiles and plasma levels of vWF and FVIII provide evidence that coagulation mechanisms might be critical for asthma pathogenesis.

Chronic Rhinosinusitis and the Coagulation System

Chronic rhinosinusitis (CRS) is one of the most common chronic diseases in adults and severely affects quality of life in patients. Although various etiologic and pathogenic mechanisms of CRS have been proposed, the causes of CRS remain uncertain. Abnormalities in the coagulation cascade may play an etiologic role in many diseases, such as asthma and other inflammatory conditions. While studies on the relationship between asthma and dysregulated coagulation have been reported, the role of the coagulation system in the pathogenesis of CRS has only been considered following recent reports. Excessive fibrin deposition is seen in nasal polyp (NP) tissue from patients with chronic rhinosinusitis with nasal polyp (CRSwNP) and is associated with activation of thrombin, reduction of tissue plasminogen activator (t-PA) and upregulation of coagulation factor XIII-A (FXIII-A), all events that can contribute to fibrin deposition and crosslinking. These findings were reproduced in a murine model of NP that was recently established. Elucidation of the mechanisms of fibrin deposition may enhance our understanding of tissue remodeling in the pathophysiology of NP and provide new targets for the treatment of CRSwNP.

New frontiers for platelet CD154

The role of platelets extends beyond hemostasis. The pivotal role of platelets in inflammation has shed new light on the natural history of conditions associated with acute or chronic inflammation. Beyond the preservation of vascular integrity, platelets are essential to tissue homeostasis and platelet-derived products are already used in the clinics. Unanticipated was the role of platelets in the adaptative immune response, allowing a renewed conceptual approach of auto-immune diseases. Platelets are also important players in cancer growth and dissemination. Platelets fulfill most of their functions through the expression of still incompletely characterized membrane-bound or soluble mediators. Among them, CD154 holds a peculiar position, as platelets represent a major source of CD154 and as CD154 contributes to most of these new platelet attributes. Here, we provide an overview of some of the new frontiers that the study of platelet CD154 is opening, in inflammation, tissue homeostasis, immune response, hematopoiesis and cancer.

Expression of surface platelet receptors (CD62P and CD41/61) in horses with recurrent airway obstruction (RAO)

Recurrent airway obstruction (RAO) is an allergic disease of horses similar to human asthma, which is characterized by airway inflammation and activation of neutrophils, lymphocytes and platelets. Platelet activation and an increase in circulating platelet-leukocyte aggregates may lead to airway remodeling. The aim of this study was to investigate platelet status in RAO-affected horses based on the platelet morphology and platelet surface expression of CD41/61 and CD62P. Ten RAO-affected horses and ten healthy horses were included in this study. Blood samples were obtained to determine the platelet count (PLT), mean platelet volume (MPV) and platelet large cell ratio (P-LCR). Expression of CD62P and CD41/61 was detected by flow cytometry on activated platelets. The median PLT was significantly reduced in horses with RAO compared to the controls. The MPV and the P-LCR values were significantly higher in RAO horses than controls. Expression of CD41/61 on platelets was increased in RAO horses, while CD62P expression was reduced. This study demonstrated the morphological changes in platelets and expression of platelet surface receptors. Despite the decrease of CD62P expression, the observed increased surface expression of CD41/61 on platelets in horses with RAO may contribute to the formation of platelet aggregates in their respiratory system.

Platelets in inflammation: regulation of leukocyte activities and vascular repair

There is now a large body of evidence that platelets are central actors of inflammatory reactions. Indeed, platelets play a significant role in a variety of inflammatory diseases. These diseases include conditions as varied as atherosclerosis, arthritis, dermatitis, glomerulonephritis, or acute lung injury. In this context, one can note that inflammation is a convenient but imprecise catch-all term that is used to cover a wide range of situations. Therefore, when discussing the role of platelets in inflammation, it is important to clearly define the pathophysiological context and the exact stage of the reaction. Inflammatory reactions are indeed multistep processes that can be either acute or chronic, and their sequence can vary greatly depending on the situation and organ concerned. Here, we focus on how platelets contribute to inflammatory reactions involving recruitment of neutrophils and/or macrophages. Specifically, we review past and recent data showing that platelets intervene at various stages of these reactions to regulate parameters such as endothelial permeability, the recruitment of neutrophils and macrophages and their effector functions, as well as inflammatory bleeding. The mechanisms underlying these various modulating effect of platelets are also discussed.

Lipoxin generation is related to soluble epoxide hydrolase activity in severe asthma

RATIONALE

Severe asthma is characterized by airway inflammatory responses associated with aberrant metabolism of arachidonic acid. Lipoxins (LX) are arachidonate-derived pro-resolving mediators that are decreased in severe asthma, yet mechanisms for defective LX biosynthesis and a means to increase LXs in severe asthma remain to be established.

OBJECTIVES

To determine if oxidative stress and soluble epoxide hydrolase (sEH) activity are linked to decreased LX biosynthesis in severe asthma.

METHODS

Aliquots of blood, sputum, and bronchoalveolar lavage fluid were obtained from asthma subjects for mediator determination. Select samples were exposed to t-butyl-hydroperoxide or sEH inhibitor (sEHI) before activation. Peripheral blood leukocyte-platelet aggregates were monitored by flow cytometry, and bronchial contraction was determined with cytokine-treated human lung sections.

MEASUREMENTS AND MAIN RESULTS

8-Isoprostane levels in sputum supernatants were inversely related to LXA4 in severe asthma (r = -0.55; P = 0.03) and t-butyl-hydroperoxide decreased LXA4 and 15-epi-LXA4 biosynthesis by peripheral blood leukocytes. LXA4 and 15-epi-LXA4 levels were inversely related to sEH activity in sputum supernatants and sEHIs significantly increased 14,15-epoxy-eicosatrienoic acid and 15-epi-LXA4 generation by severe asthma whole blood and bronchoalveolar lavage fluid cells. The abundance of peripheral blood leukocyte-platelet aggregates was related to asthma severity. In a concentration-dependent manner, LXs significantly inhibited platelet-activating factor-induced increases in leukocyte-platelet aggregates (70.8% inhibition [LXA4 100 nM], 78.3% inhibition [15-epi-LXA4 100 nM]) and 15-epi-LXA4 markedly inhibited tumor necrosis factor-α-induced increases in bronchial contraction.

CONCLUSIONS

LX levels were decreased by oxidative stress and sEH activity. Inhibitors of sEH increased LXs that mediated antiphlogistic actions, suggesting a new therapeutic approach for severe asthma. Clinical trial registered with www.clinicaltrials.gov (NCT 00595114).

A decreased mean platelet volume is associated with stable and exacerbated asthma

BACKGROUND

Systemic inflammation is related to disease progression in asthma. Activated platelets play a critical role in atherogenesis, inflammation, and atherothrombosis. The mean platelet volume (MPV) is an early marker of platelet activation.

OBJECTIVES

The aim of this study is to clarify the relevance of MPV levels in patients with stable and exacerbated asthma.

METHODS

We investigated the peripheral blood cell count parameters, C-reactive protein (CRP), lung function parameters, and arterial blood gas in patients with asthma and control subjects. Eighty-five stable asthma patients and 85 asthmatics with exacerbations were investigated. Eighty-five controls matched for age, gender, body mass index (BMI), and smoking status were recruited.

RESULTS

Patients with exacerbated asthma had lower MPV and higher CRP levels and white blood cell (WBC) counts compared to patients with stable asthma and control subjects. Furthermore, the MPV was reduced in patients with stable asthma compared to control subjects. Negative correlations between MPV and CRP were present in stable and exacerbated asthma. Although there was no relationship between MPV and WBC count in stable asthma, there was an inverse relationship between MPV and WBC count in exacerbated asthma.

CONCLUSIONS

These findings show that patients with stable asthma had a lower MPV compared to controls and the MPV levels in asthmatic patients with exacerbations were lower compared to those in patients with stable asthma. Further investigations regarding the role of MPV in asthma may be beneficial in the search for therapeutic targets.

Change of mean platelet volume values in asthmatic children as an inflammatory marker

BACKGROUND

Asthma is the most common chronic disease of childhood in industrialised countries. T helper-2 (Th-2) cells, mast cells and eosinophils have a role in inflammation of asthma. Recently it was shown that platelets also play a role in asthma. Mean platelet volume shows platelet size and reflects platelet activation.

OBJECTIVE

The aim of this retrospective study is to evaluate levels of mean platelet volume in asthmatic patients during asymptomatic periods and exacerbations compared with healthy controls.

METHODS

The study consisted of 100 asthmatic patients (male/female: 55/45, mean age: 8.2±3.3) and 49 age and sex matched healthy children as a control group.

RESULTS

Mean platelet volume values of asthmatic patients during asymptomatic period were 7.7±0.8fL while mean platelet volume values in asthmatics during exacerbation were 7.8±0.9fL. Comparison of mean platelet volume values of asthmatic patients and healthy controls both in acute asthmatic attack and asymptomatic period showed no difference (p>0.05). Comparison of mean platelet volume values at asthmatic attack and asymptomatic period also had no difference (p>0.05). The presence of atopy, infection, eosinophilia, elevated immunoglobulin E, and severity of acute asthmatic attack did not influence mean platelet volume values.

CONCLUSION

The results of our study suggest that mean platelet volume values may not be used as a marker in bronchial asthma, although prospective studies with larger number of patients are needed to evaluate the role of mean platelet volume in asthma.

Asthma and coagulation

Asthma is a chronic airway disease characterized by paroxysmal airflow obstruction evoked by irritative stimuli on a background of allergic lung inflammation. Currently, there is no cure for asthma, only symptomatic treatment. In recent years, our understanding of the involvement of coagulation and anticoagulant pathways, the fibrinolytic system, and platelets in the pathophysiology of asthma has increased considerably. Asthma is associated with a procoagulant state in the bronchoalveolar space, further aggravated by impaired local activities of the anticoagulant protein C system and fibrinolysis. Protease-activated receptors have been implicated as the molecular link between coagulation and allergic inflammation in asthma. This review summarizes current knowledge of the impact of the disturbed hemostatic balance in the lungs on asthma severity and manifestations and identifies new possible targets for asthma treatment.

Writing a narrative biomedical review: considerations for authors, peer reviewers, and editors

Review articles comprehensively covering a specific topic are crucial for successful research and academic projects. Most editors consider review articles for special and regular issues of journals. Writing a review requires deep knowledge and understanding of a field. The aim of this review is to analyze the main steps in writing a narrative biomedical review and to consider points that may increase the chances of success. We performed a comprehensive search through MEDLINE, EMBASE, Scopus, and Web of Science using the following keywords: review of the literature, narrative review, title, abstract, authorship, ethics, peer review, research methods, medical writing, scientific writing, and writing standards. Opinions expressed in the review are also based on personal experience as authors, peer reviewers, and editors.

Platelet count, mean platelet volume and smoking status in stable chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD), an increasing global health problem, may be complicated by acute atherothrombotic events. Although systemic inflammation plays the leading role in atherothrombotic processes, platelet activation and increased coagulation together with oxidative stress can significantly exacerbate atherosclerosis in COPD patients. In this study we determined platelet count, mean platelet volume (MPV) and classical markers of systemic inflammation - serum C-reactive protein (CRP), white blood cell (WBC) count and the relative proportion of segmented neutrophils in COPD patients, and compared them to those from the healthy controls. The most important and novel finding of this study was that patients with COPD had a significantly increased platelet count, along with a reduced MPV when compared to healthy controls (286 vs. 260 × 10(9)/l; 9.6 vs. 8.7 fL, respectively). Cigarette smoking had no influence on these results. The presence of systemic inflammation was clearly proved by the increase in classical inflammatory markers (CRP, WBC and segmented neutrophil count).

Inflammatory markers in childhood asthma

The major characteristic of asthma is persistent airway inflammation that fails to resolve spontaneously. Dysregulation of pro- and anti-inflammatory mechanisms is responsible for the development of chronic inflammation. The inflammatory reaction is mediated by numerous cells and their mediators. Detection and quantification of airway inflammation in children are subject to many requirements, e.g., use of biologic samples obtained in a non-invasive way; use of standardized analytical methods to determine biomarkers that can identify inflammation processes (inflammation itself, oxidative stress, apoptosis and remodelling); determining the role of systemic inflammation; assessment of correlation of various biomarkers of inflammation with clinical parameters and their diagnostic efficacy; providing a tool(s) to monitor diseases, and to evaluate adequacy of therapy; and predicting the clinical course of inflammation and prognosis of asthma. Using standardized analyses, it is now possible to determine direct markers of local inflammation, i.e., fractional nitric oxide (marker of oxidative stress) in exhaled breath, pH (marker of acid stress) in breath condensate, and indirect markers in blood/serum, i.e., eosinophil granulocytes (indicating migration), eosinophil cationic protein (marker of activated eosinophil granulocytes) and C-reactive protein (marker of systemic inflammation). However, none of these biomarkers are specific for asthma. Further standardization of the known pulmonary biomarkers of local inflammation and identification of new ones will allow for longitudinal follow-up of inflammation in children with asthma.

Circulating platelet-neutrophil complexes are important for subsequent neutrophil activation and migration

Previous studies in our laboratory have shown that platelets are essential for the migration of eosinophils into the lungs of allergic mice, and that this is dependent on the functional expression of platelet P-selectin. We sought to investigate whether the same is true for nonallergic, acute inflammatory stimuli administered to distinct anatomic compartments. Neutrophil trafficking was induced in two models, namely zymosan-induced peritonitis and LPS-induced lung inflammation, and the platelet dependence of these responses investigated utilizing mice rendered thrombocytopenic. The relative contribution of selectins was also investigated. The results presented herein clearly show that platelet depletion (>90%) significantly inhibits neutrophil recruitment in both models. In addition, we show that P-selectin glycoprotein ligand-1, but not P-selectin, is essential for neutrophil recruitment in mice in vivo, thus suggesting the existence of different regulatory mechanisms for the recruitment of leukocyte subsets in response to allergic and nonallergic stimuli. Further studies in human blood demonstrate that low-dose prothrombotic and pro-inflammatory stimuli (CCL17 or CCL22) synergize to induce platelet and neutrophil activation, as well as the formation of platelet-neutrophil conjugates. We conclude that adhesion between platelets and neutrophils in vivo is an important event in acute inflammatory responses. Targeting this interaction may be a successful strategy for inflammatory conditions where current therapy fails to provide adequate treatment.

Platelet adhesion and intracellular calcium levels in antigen-challenged rats

There is considerable evidence that platelet activation occurs in allergic airways diseases. In this study we aimed to investigate platelet adhesion to immobilized fibrinogen and intracellular calcium levels in a rat model of allergic inflammation. Male Wistar rats were challenged with ovalbumin (OVA). At 30 min to 24h after OVA-challenge, assays of platelet adhesion to immobilized fibrinogen and intracellular calcium levels using fura 2-AM loaded platelets were performed. The serum levels of IgE were approximately 5-fold greater in OVA-sensitized rats. A marked eosinophil influx in bronchoalveolar lavage (BAL) fluid of OVA-challenged rats at 24h after OVA-challenge was also seen. OVA-challenge resulted in a marked thrombocytopenia, as observed within 12h after OVA-challenge. The agonists ADP (0.5-50 microM) and thrombin (30-100 mU/ml) concentration-dependently increased platelet adhesion to immobilized fibrinogen. At an early time after OVA-challenge (30 min), platelets exhibited greater platelet adhesion compared with the non-sensitized group, whereas at a late time (24h) they exhibited lower platelet adhesion to both agonists. Moreover, at 30 min after OVA-challenge, intracellular calcium levels to ADP (20 microM) and thrombin (100 mU/ml)-activated platelets were greater compared with non-challenged rats. As opposed, at 24h after OVA challenge, a lower intracellular calcium level to ADP- and thrombin-activated platelets was observed. In conclusion, OVA-challenge in rats promotes a biphasic response in platelet adhesion consisting of an increased adhesion and intracellular calcium levels at an early phase (30 min), which progress to a reduction in adhesion and intracellular calcium levels at a late time (24h) after antigen challenge.

Body mass index-percentile and diagnostic accuracy of childhood asthma

OBJECTIVE

To determine whether high BMI-percentile is associated with misdiagnosis of asthma among children referred to an asthma specialist.

METHODS

We queried the electronic records of children 8 to 18 years of age seen by a Nemours pediatric pulmonologist. All visits during a 6-year period with the chief complaint of asthma, or an asthma-like symptom such as wheeze, cough, or dyspnea, were included. We collected spirometry, blood counts, and immunoglobulin E (IgE) if available. We determined whether the child had referring physician-diagnosed asthma, specialist-diagnosed asthma, or both. Specialist-diagnosed asthmatics who met additional objective "gold-standard" criterion were labeled strict-criterion asthma.

RESULTS

Prevalence of high BMI-percentile was extremely common in all defined asthma groups, even those meeting strict criteria for diagnosis. Referring physician-diagnosed asthmatics did not have higher rates of obesity, and referring physician-diagnosed asthmatics had objective indicators of asthma that were the same as asthmatics diagnosed by a specialist. There was good diagnostic correlation between referring physicians and asthma specialists that was not affected by BMI. Among specialist-diagnosed asthmatics, increased BMI-percentile associated with significantly reduced forced expiratory volume in 1 second (FEV(1)), forced expiratory flow during the middle half of the forced vital capacity (FEF(25 - 75)), and FEV(1)/forced vital capacity (FVC); and significantly increased total blood leukocytes, neutrophils, and platelets compared to leans. For all 2,258 referrals, the estimated odds ratio of receiving a specialist-diagnosis of asthma increased by 0.4% with each increasing BMI percentile.

CONCLUSIONS

Referring physicians do not appear to erroneously diagnose children with asthma due to overweight status. Our data confirm that overweight status is extremely high in children with true asthma and likely increases the risk for true asthma. Although these data cannot discern causality, high BMI-percentile is associated with greater airflow obstruction and elevated markers of systemic inflammation that could contribute to underlying mechanisms of asthma.

Platelets stimulate airway smooth muscle cell proliferation through mechanisms involving 5-lipoxygenase and reactive oxygen species

Continuous recruitment and inappropriate activity of platelets in the airways may contribute to airway remodeling, a characteristic feature of inflammatory airway diseases that includes increased proliferation of the smooth muscle. The aim of the present investigation was to examine the effect of platelets on proliferation of airway smooth muscle cells (ASMC) in culture and to determine the possible role of 5-lipoxygenase (5-LOX) and reactive oxygen species (ROS) in this context. ASMC obtained from guinea pigs were cultured and co-incubated with washed platelets for 24 hours. Thereafter, the proliferation was measured with the MTS-assay; the results were also verified by using thymidine incorporation, DNA measurements and manual counting. The interaction between platelets and ASMC was visualized with fluorescence microscopy. We found that platelets bind to the ASMC and the presence of platelets caused a significant dose-dependent increase in ASMC proliferation. Co-incubation of ASMC with platelets also increased ROS-production, detected by the fluorescent probe DCFDA. Furthermore, the platelet-induced proliferation was reduced in the presence of the NADPH-oxidase inhibitors DPI and apocynin. A possible role of 5-LOX in platelet-induced proliferation and ROS-generation was evaluated by using the 5-LOX inhibitor AA-861 and the PLA(2)-inhibitor ATK. The results showed that inhibition of these enzymes significantly reduced the platelet-induced proliferation. Moreover, Western blot analysis revealed that the ASMC but not the platelets express 5-LOX. In addition, our experiments revealed that the presence of AA-861 and ATK significantly inhibited the ROS-production generated upon co-incubation of platelets and ASMC. In conclusion, we show that platelets have a marked capacity to induce ASMC proliferation. Furthermore, our study indicates that the interaction between platelets and ASMC leads to activation of 5-LOX in the ASMC followed by an increased ROS-production, events resulting in enhanced ASMC proliferation. The new findings are of importance in understanding possible mechanisms contributing to airway remodeling.

Dendritic cells and epithelial cells: linking innate and adaptive immunity in asthma

Dendritic cells (DCs) are generally held responsible for initiating and maintaining allergic T helper 2 (T(H)2)-cell responses to inhaled allergens in asthma. Although the epithelium was initially considered to function solely as a physical barrier, it is now seen as a central player in the T(H)2-cell sensitization process by influencing the function of DCs. Clinically relevant allergens, as well as known environmental and genetic risk factors for allergy and asthma, often interfere directly or indirectly with the innate immune functions of airway epithelial cells and DCs. A better understanding of these interactions, ascertained from human and animal studies, might lead to better prevention and treatment of asthma.