Platelets as immune-sensing cells

Interactions between platelets and the cancer immune microenvironment

Cancer is a leading cause of death in both China and developed countries due to its high incidence and low cure rate. Immune function is closely linked to the development and progression of tumors. Platelets, which are primarily known for their role in hemostasis, also play a crucial part in the spread and progression of tumors through their interaction with the immune microenvironment. The impact of platelets on tumor growth and metastasis depends on the type of cancer and treatment method used. This article provides an overview of the relationship between platelets and the immune microenvironment, highlighting how platelets can either protect or harm the immune response and cancer immune escape. We also explore the potential of available platelet-targeting strategies for tumor immunotherapy, as well as the promise of new platelet-targeted tumor therapy methods through further research.

EGFR of platelet regulates macrophage activation and bacterial phagocytosis function

BACKGROUND

Beyond their crucial role in hemostasis, platelets possess the ability to regulate inflammation and combat infections through various mechanisms. Stringent control of macrophage activation is essential during innate immune responses in sepsis. Macrophages are considered crucial phagocytic cells that aid in the elimination of pathogens. Platelet interactions with monocytes-macrophages are known to be significant in the response against bacterial infections, but the primary mediator driving these interactions remains unclear. EGFR plays critical role in the regulation of inflammation and infection through various mechanisms.

RESULTS

The overexpression of platelets by thrombopoietin (TPO) leads to the sequestration of both pro-inflammatory (IL-6/IL-1) and anti-inflammatory (IL-10) cytokines in the organ tissue of septic mice. Epidermal growth factor receptor (EGFR) is critical for platelet activation in sepsis. EGFR-licensed platelets enhance macrophage immune function, including the production of reactive oxygen species (ROS) and the clearance of bacteria. Platelet EGFR also induces M1 macrophage polarization by increasing the expression of inducible nitric oxide synthase (iNOS) and CD64.

CONCLUSION

EGFR can activate platelet immune function. Moreover, activated platelets efficiently regulate bacterial phagocytosis and pro-inflammatory function of macrophages through an EGFR-dependent pathway.

Current Understanding of Immune Thrombocytopenia: A Review of Pathogenesis and Treatment Options

The management of immune thrombocytopenia (ITP) and the prediction of patient response to therapy still represent a significant and constant challenge in hematology. ITP is a heterogeneous disease with an unpredictable evolution. Although the pathogenesis of ITP is currently better known and its etiology has been extensively studied, up to 75% of adult patients with ITP may develop chronicity, which represents a significant burden on patients' quality of life. A major risk of ITP is bleeding, but knowledge on the exact relationship between the degree of thrombocytopenia and bleeding symptoms, especially at a lower platelet count, is lacking. The actual management of ITP is based on immune suppression (corticosteroids and intravenous immunoglobulins), or the use of thrombopoietin receptor agonists (TPO-RAs), rituximab, or spleen tyrosine kinase (Syk) inhibitors. A better understanding of the underlying pathology has facilitated the development of a number of new targeted therapies (Bruton's tyrosine kinase inhibitors, neonatal Fc receptors, strategies targeting B and plasma cells, strategies targeting T cells, complement inhibitors, and newer TPO-RAs for improving megakaryopoiesis), which seem to be highly effective and well tolerated and result in a significant improvement in patients' quality of life. The disadvantage is that there is a lack of knowledge of the predictive factors of response to treatments, which would help in the development of an optimized treatment algorithm for selected patients.

Platelet lifespan and mechanisms for clearance

PURPOSE OF REVIEW

Activated or aged platelets are removed from circulation under (patho)physiologic conditions, the exact mechanism of platelet clearance under such conditions remains unclear and are currently being investigated. This review focuses on recent findings and controversies regarding platelet clearance and the disruption of platelet life cycle.

RECENT FINDINGS

The platelet life span is determined by glycosylation of platelet surface receptors with sialic acid. Recently, it was shown that platelet activation and granule release leads to desialylation of glycans and accelerated clearance of platelets under pathological conditions. This phenomenon was demonstrated to be a main reason for thrombocytopenia being a complication in several infections and immune disorders.

SUMMARY

Although we have recently gained some insight into how aged platelets are cleared from circulation, we are still not seeing the full picture. Further investigations of the platelet clearance pathways under pathophysiologic conditions are needed as well as studies to unravel the connection between platelet clearance and platelet production.

Platelet transfusion in adults: An update

Many patients worldwide receive platelet components (PCs) through the transfusion of diverse types of blood components. PC transfusions are essential for the treatment of central thrombocytopenia of diverse causes, and such treatment is beneficial in patients at risk of severe bleeding. PC transfusions account for almost 10% of all the blood components supplied by blood services, but they are associated with about 3.25 times as many severe reactions (attributable to transfusion) than red blood cell transfusions after stringent in-process leukoreduction to less than 10⁶ residual cells per blood component. PCs are not homogeneous, due to the considerable differences between donors. Furthermore, the modes of PC collection and preparation, the safety precautions taken to limit either the most common (allergic-type reactions and febrile non-hemolytic reactions) or the most severe (bacterial contamination, pulmonary lesions) adverse reactions, and storage and conservation methods can all result in so-called PC "storage lesions". Some storage lesions affect PC quality, with implications for patient outcome. Good transfusion practices should result in higher levels of platelet recovery and efficacy, and lower complication rates. These practices include a matching of tissue ABH antigens whenever possible, and of platelet HLA (and, to a lesser extent, HPA) antigens in immunization situations. This review provides an overview of all the available information relating to platelet transfusion, from donor and donation to bedside transfusion, and considers the impact of the measures applied to increase transfusion efficacy while improving safety and preventing transfusion inefficacy and refractoriness. It also considers alternatives to platelet component (PC) transfusion.

Association Between Platelet Indices and Preoperative Deep Vein Thrombosis in Elderly Patients Undergoing Total Joint Arthroplasty: A Retrospective Study

To investigate the association between platelet (PLT) indices and preoperative deep vein thrombosis (DVT) in elderly patients undergoing total joint arthroplasty (TJA). A total of 1391 patients were enrolled. We created receiver operator characteristic (ROC) curve using the ratio of PLT indices to DVT before TJA, divided the enrolled patients into groups based on the cut-off value, and then analyzed risk factors for DVT before TJA in the multivariate binary logistic regression analysis. Preoperative DVT occurred in 103 cases. Based on the ROC curve, we determined that the cut-off values for PLT, mean platelet volume (MPV), platelet distribution width (PDW), platelet large cell ratio (P-LCR), and plateletcrit (PCT) were 202 × 10⁹/L, 11.4 fL, 13.2 fL, 34.6%, and 0.228%. And the areas under the curve were 0.606, 0.605, 0.617, 0.616, and 0.598. Multivariate binary regression analysis revealed that the risk of preoperative DVT in TJA patients with PLT≥202 × 10⁹/L, MPV≤11.4 fL, PDW≤13.2 fL, P-LCR≤34.6%, and PCT≥0.228% increased by 2.32 (P < .001, 95% confidence interval [CI] [1.50-3.60]), 1.86 (P < .001, 95% CI [1.22-2.83]), 2.17 (P < .001, 95% CI [1.43-3.31]), 2.27 (P < .001, 95% CI [1.50-3.45]), and 1.76 times (P = .013, 95% CI [1.13-2.76]), respectively. Age, P < .001, odds ratio (OR) = 1.08, 95% CI [1.04-1.11]; corticosteroid use, P = .011, OR = 3.66, 95% CI [1.34-9.96]. We found that increased PLT count and PCT, decreased MPV, PDW, and P-LCR, old age, and corticosteroid use were independent risk factors for preoperative DVT in elderly TJA patients.

Whole Blood Transfusion for Severe Malarial Anemia in a High Plasmodium falciparum Transmission Setting

BACKGROUND

Severe malaria resulting from Plasmodium falciparum infection is the leading parasitic cause of death in children worldwide, and severe malarial anemia (SMA) is the most common clinical presentation. The evidence in support of current blood transfusion guidelines for patients with SMA is limited.

METHODS

We conducted a retrospective cohort study of 911 hospitalized children with SMA in a holoendemic region of Zambia to examine the association of whole blood transfusion with in-hospital survival. Data were analyzed in adjusted logistic regression models using multiple imputation for missing data.

RESULTS

The median age of patients was 24 months (interquartile range, 16-30) and overall case fatality was 16%. Blood transfusion was associated with 35% reduced odds of death in children with SMA (odds ratio, 0.65; 95% confidence interval, .52-.81; P = .0002) corresponding to a number-needed-to-treat (NNT) of 14 patients. Children with SMA complicated by thrombocytopenia were more likely to benefit from transfusion than those without thrombocytopenia (NNT = 5). Longer storage time of whole blood was negatively associated with survival and with the posttransfusion rise in the platelet count but was not associated with the posttransfusion change in hemoglobin concentration.

CONCLUSIONS

Whole blood given to pediatric patients with SMA was associated with improved survival, mainly among those with thrombocytopenia who received whole blood stored for <4 weeks. These findings point to a potential use for incorporating thrombocytopenia into clinical decision making and management of severe malaria, which can be further assessed in prospective studies, and underline the importance of maintaining reliable blood donation networks in areas of high malaria transmission.

Deciphering transcriptome alterations in bone marrow hematopoiesis at single-cell resolution in immune thrombocytopenia

Immune thrombocytopenia (ITP) is an autoimmune disorder, in which megakaryocyte dysfunction caused by an autoimmune reaction can lead to thrombocytopenia, although the underlying mechanisms remain unclear. Here, we performed single-cell transcriptome profiling of bone marrow CD34⁺ hematopoietic stem and progenitor cells (HSPCs) to determine defects in megakaryopoiesis in ITP. Gene expression, cell-cell interactions, and transcriptional regulatory networks varied in HSPCs of ITP, particularly in immune cell progenitors. Differentially expressed gene (DEG) analysis indicated that there was an impaired megakaryopoiesis of ITP. Flow cytometry confirmed that the number of CD9⁺ and HES1⁺ cells from Lin⁻CD34⁺CD45RA⁻ HSPCs decreased in ITP. Liquid culture assays demonstrated that CD9⁺Lin⁻CD34⁺CD45RA⁻ HSPCs tended to differentiate into megakaryocytes; however, this tendency was not observed in ITP patients and more erythrocytes were produced. The percentage of megakaryocytes differentiated from CD9⁺Lin⁻CD34⁺CD45RA⁻ HSPCs was 3-fold higher than that of the CD9⁻ counterparts from healthy controls (HCs), whereas, in ITP patients, the percentage decreased to only 1/4th of that in the HCs and was comparable to that from the CD9⁻ HSPCs. Additionally, when co-cultured with pre-B cells from ITP patients, the differentiation of CD9⁺Lin⁻CD34⁺CD45RA⁻ HSPCs toward the megakaryopoietic lineage was impaired. Further analysis revealed that megakaryocytic progenitors (MkP) can be divided into seven subclusters with different gene expression patterns and functions. The ITP-associated DEGs were MkP subtype-specific, with most DEGs concentrated in the subcluster possessing dual functions of immunomodulation and platelet generation. This study comprehensively dissects defective hematopoiesis and provides novel insights regarding the pathogenesis of ITP.

Preoperative platelet distribution width-to-platelet ratio combined with serum thyroglobulin may be objective and popularizable indicators in predicting papillary thyroid carcinoma

Objectives

The incidence of papillary thyroid carcinoma (PTC) has increased more rapidly than that of any other cancer type in China. Early indicators with high sensitivity and specificity during diagnosis are required. To date, there has been a paucity of studies investigating the relationship between preoperative platelet distribution width‐to‐platelet count ratio (PPR) and PTC. This study thus aimed to assess the diagnostic value of PPR combined with serum thyroglobulin (Tg) in patients with PTC.

Methods

A total of 1001 participants were included in our study. 876 patients who underwent surgery for nodular goiter were divided into the PTC group or benign thyroid nodule (BTN) group according to pathology reports, and 125 healthy controls (HCs) were included. Preoperative hemogram parameters and serum Tg levels were compared among three groups. Receiver operating characteristic (ROC) curve was used to evaluate the value of PPR combined with serum Tg for diagnosing PTC.

Results

Platelet distribution width (PDW) and PPR levels were higher in the PTC group than in the BTN and HC groups (both p < 0.05) but did not significantly differ between the BTN and HC groups. PDW and PPR levels significantly differed in the presence/absence of lymph node metastasis, the presence/absence of capsule invasion (p = 0.005), and TNM stages (p < 0.001). Multivariable analyses indicated that high serum Tg levels [adjusted odds ratio (OR), 1.007; 95% confidence interval (CI), 1.004–1.009; p < 0.001], high neutrophil‐to‐lymphocyte ratio (NLR,adjusted OR, 1.928; 95% CI, 1.619–2.295; p < 0.001), and high PPR (adjusted OR, 1.378; 95% CI, 1.268–1.497; p < 0.001) were independent risk factors for PTC. In ROC analysis, the areas under the curves (AUCs) of serum Tg, PDW, PPR, and NLR for predicting PTC were 0.603, 0.610, 0.706, and 0.685, respectively. PPR combined with serum Tg (PPR + Tg) had a higher diagnostic value (AUC, 0.738; sensitivity, 60%; specificity, 74.7%) compared with PDW + Tg (AUC, 0.656; sensitivity, 64.4%; specificity, 59.9%) and NLR + Tg (AUC, 0.714; sensitivity, 61.6%; specificity, 71.1%).

Conclusions

Preoperative PPR combined with serum Tg may be objective and popularizable indicators for effective predicting PTC.

The GPIbα intracellular tail - role in transducing VWF- and collagen/GPVI-mediated signaling

The GPIbT-VWF A1 domain interaction is essential for platelet tethering under high shear. Synergy between GPIbα and GPVI signaling machineries has been suggested previously, however its molecular mechanism remains unclear. We generated a novel GPIbα transgenic mouse (GpIbαΔsig/Δsig) by CRISPR-Cas9 technology to delete the last 24 residues of the GPIbα intracellular tail that harbors the 14-3-3 and phosphoinositide-3 kinase binding sites. GPIbαΔsig/Δsig platelets bound VWF normally under flow. However, they formed fewer filopodia on VWF/botrocetin in the presence of a oIIbI3 blocker, demonstrating that despite normal ligand binding, VWF-dependent signaling is diminished. Activation of GpIbαΔsig/Δsig platelets with ADP and thrombin was normal, but GpIbαΔsig/Δsig platelets stimulated with collagen-related-peptide (CRP) exhibited markedly decreased P-selectin exposure and eIIbI3 activation, suggesting a role for the GpIbaaintracellular tail in GPVI-mediated signaling. Consistent with this, while haemostasis was normal in GPIbαΔsig/Δsig mice, diminished tyrosine-phosphorylation, (particularly pSYK) was detected in CRP-stimulated GpIbαΔsig/Δsig platelets as well as reduced platelet spreading on CRP. Platelet responses to rhodocytin were also affected in GpIbαΔsig/Δsig platelets but to a lesser extent than those with CRP. GpIbαΔsig/Δsig platelets formed smaller aggregates than wild-type platelets on collagen-coated microchannels at low, medium and high shear. In response to both VWF and collagen binding, flow assays performed with plasma-free blood or in the presence of bIIbI3- or GPVI-blockers suggested reduced bIIbI3 activation contributes to the phenotype of the GpIbαΔsig/Δsig platelets. Together, these results reveal a new role for the intracellular tail of GPIbiiin transducing both VWF-GPIbGGand collagen-GPVI signaling events in platelets.

Platelets accumulate in lung lesions of tuberculosis patients and inhibit T-cell responses and Mycobacterium tuberculosis replication in macrophages

Platelets regulate human inflammatory responses that lead to disease. However, the role of platelets in tuberculosis (TB) pathogenesis is still unclear. Here, we show that patients with active TB have a high number of platelets in peripheral blood and a low number of lymphocytes leading to a high platelets to lymphocytes ratio (PL ratio). Moreover, the serum concentration of different mediators promoting platelet differentiation or associated with platelet activation is increased in active TB.

Immunohistochemistry analysis shows that platelets localise around the lung granuloma lesions in close contact with T lymphocytes and macrophages. Transcriptomic analysis of caseous tissue of human pulmonary TB granulomas, followed by Gene Ontology analysis, shows that 53 platelet activation‐associated genes are highly expressed compared to the normal lung tissue.

In vitro activated platelets (or their supernatants) inhibit BCG‐induced T‐ lymphocyte proliferation and IFN‐γ production. Likewise, platelets inhibit the growth of intracellular macrophages of Mycobacterium (M.) tuberculosis. Soluble factors released by activated platelets mediate both immunological and M. tuberculosis replication activities. Furthermore, proteomic and neutralisation studies (by mAbs) identify TGF‐β and PF4 as the factors responsible for inhibiting T‐cell response and enhancing the mycobactericidal activity of macrophages, respectively. Altogether these results highlight the importance of platelets in TB pathogenesis.

Platelets in COVID-19 disease: friend, foe, or both?

Immuno-thrombosis of COVID-19 results in the activation of platelets and coagulopathy. Antiplatelet therapy has been widely used in COVID-19 patients to prevent thrombotic events. However, recent analysis of clinical trials does not support the major effects of antiplatelet therapy on mortality in hospitalized COVID-19 patients, despite the indisputable evidence for an increased risk of thrombotic complications in COVID-19 disease. This apparent paradox calls for an explanation. Platelets have an important role in sensing and orchestrating host response to infection, and several platelet functions related to host defense response not directly related to their well-known hemostatic function are emerging. In this paper, we aim to review the evidence supporting the notion that platelets have protective properties in maintaining endothelial barrier integrity in the course of an inflammatory response, and this role seems to be of particular importance in the lung. It might, thus, well be that the inhibition of platelet function, if affecting the protective aspect of platelet activity, might diminish clinical benefits resulting from the inhibition of the pro-thrombotic phenotype of platelets in immuno-thrombosis of COVID-19. A better understanding of the platelet-dependent mechanisms involved in the preservation of the endothelial barrier is necessary to design the antiplatelet therapeutic strategies that inhibit the pro-thrombotic activity of platelets without effects on the vaso-protective function of platelets safeguarding the pulmonary endothelial barrier during multicellular host defense in pulmonary circulation.

Study on the correlation between preoperative inflammatory indexes and adhesional perinephric fat before laparoscopic partial nephrectomy

Objective

This study was aimed to evaluate the effect of preoperative composite inflammatory index on adhesional perinephric fat (APF), providing a help for preoperative risk assessment of laparoscopic partial nephrectomy (LPN) in patients with renal cell carcinoma.

Materials and methods

A retrospective study was conducted on 231 patients with renal cell carcinoma, who underwent laparoscopic partial nephrectomy. They were divided into two groups according to whether there was APF during operation. Relevant clinical data, laboratory parameters and imaging examination were obtained before operation to calculate the composite inflammatory index and MAP score. The composite inflammatory index was divided into high value group and low value group by ROC curve method. The related predictive factors of APF were analyzed by logistic regression method.

Results

The APF was found in 105 patients (45.5%). In multivariate analysis, systemic immune inflammation index (SII) (high/low), MAP score, tumor size and perirenal fat thickness were independent predictors of APF. The operation time of patients with APF was longer, and the difference of blood loss was not statistically significant.

Conclusion

SII is an independent predictor of APF before laparoscopic partial nephrectomy.

Trial registration ChiCTR, ChiCTR2100045944. Registered 30 April 2021—Retrospectively registered, http://www.chictr.org.cn/showproj.aspx?proj=125703.

Platelets in ITP: Victims in Charge of Their Own Fate?

Immune thrombocytopenia (ITP) is an autoimmune bleeding disorder. The pathophysiological mechanisms leading to low platelet levels in ITP have not been resolved, but at least involve autoantibody-dependent and/or cytotoxic T cell mediated platelet clearance and impaired megakaryopoiesis. In addition, T cell imbalances involving T regulatory cells (Tregs) also appear to play an important role. Intriguingly, over the past years it has become evident that platelets not only mediate hemostasis, but are able to modulate inflammatory and immunological processes upon activation. Platelets, therefore, might play an immuno-modulatory role in the pathogenesis and pathophysiology of ITP. In this respect, we propose several possible pathways in which platelets themselves may participate in the immune response in ITP. First, we will elaborate on how platelets might directly promote inflammation or stimulate immune responses in ITP. Second, we will discuss two ways in which platelet microparticles (PMPs) might contribute to the disrupted immune balance and impaired thrombopoiesis by megakaryocytes in ITP. Importantly, from these insights, new starting points for further research and for the design of potential future therapies for ITP can be envisioned.

Cryopreservation alters the immune characteristics of platelets

BACKGROUND

Cryopreserved platelets are under clinical evaluation as they offer improvements in shelf-life and potentially hemostatic effectiveness. However, the effect of cryopreservation on characteristics related to the immune function of platelets has not been examined.

STUDY DESIGN AND METHODS

Buffy coat derived platelets were cryopreserved at -80°C using 5%-6% dimethylsulfoxide (DMSO, n = 8). Paired testing was conducted pre-freeze (PF), post-thaw (PT0), and after 24 h of post-thaw storage at room temperature (PT24). The concentration of biological response modifiers (BRMs) in the supernatant was measured using commercial ELISAs and surface receptor abundance was assessed by flow cytometry.

RESULTS

Cryopreservation resulted in increased RANTES, PF4, and C3a but decreased IL-1β, OX40L, IL-13, IL-27, CD40L, and C5a concentrations in the supernatant, compared to PF samples. C4a, endocan, and HMGB1 concentrations were similar between the PF and PT0 groups. The abundance of surface-expressed P-selectin, siglec-7, TLR3, TLR7, and TLR9 was increased PT0; while CD40, CLEC2, ICAM-2, and MHC-I were decreased, compared to PF. The surface abundance of CD40L, B7-2, DC-SIGN, HCAM, TLR1, TLR2, TLR4, and TLR6 was unchanged by cryopreservation. Following 24 h of post-thaw storage, all immune associated receptors and TLRs increased to levels higher than observed on PF and PT0 platelets.

CONCLUSION

Cryopreservation alters the immune phenotype of platelets. Understanding the clinical implications of the observed changes in BRM release and receptor abundance are essential, as they may influence the likelihood of adverse events.

The Toll-Like Receptor 2 Ligand Pam2CSK4 Activates Platelet Nuclear Factor-κB and Bruton's Tyrosine Kinase Signaling to Promote Platelet-Endothelial Cell Interactions

Circulating platelets establish a variety of immunological programs and orchestrate inflammatory responses at the endothelium. Platelets express the innate immunity family of Toll-like receptors (TLRs). While TLR2/TLR1 ligands are known to activate platelets, the effects of TLR2/TLR6 ligands on platelet function remain unclear. Here, we aim to determine whether the TLR2/TLR6 agonists Pam2CSK4 and FSL-1 activate human platelets. In addition, human umbilical vein endothelial cells (HUVECs) and platelets were co-cultured to analyze the role of platelet TLR2/TLR6 on inflammation and adhesion to endothelial cells. Pam2CSK4, but not FSL-1, induced platelet granule secretion and integrin α_IIbβ₃ activation in a concentration-dependent manner. Moreover, Pam2CSK4 promoted platelet aggregation and increased platelet adhesion to collagen-coated surfaces. Mechanistic studies with blocking antibodies and pharmacologic inhibitors demonstrated that the TLR2/Nuclear factor-κB axis, Bruton’s-tyrosine kinase, and a secondary ADP feedback loop are involved in Pam2CSK4-induced platelet functional responses. Interestingly, Pam2CSK4 showed cooperation with immunoreceptor tyrosine-based activation motif (ITAM)-mediated signaling to enhance platelet activation. Finally, the presence of platelets increased inflammatory responses in HUVECs treated with Pam2CSK4, and platelets challenged with Pam2CSK4 showed increased adhesion to HUVECs under static and physiologically relevant flow conditions. Herein, we define a functional role for platelet TLR2-mediated signaling, which may represent a druggable target to dampen excessive platelet activation in thrombo-inflammatory diseases.

Potential Diagnostic Approaches for Prediction of Therapeutic Responses in Immune Thrombocytopenia

Immune thrombocytopenia (ITP) is an autoimmune bleeding disorder in which, via unresolved mechanisms, platelets and megakaryocytes (MKs) are targeted by autoantibodies and/or T cells resulting in increased platelet destruction and impairment of MK function. Over the years, several therapeutic modalities have become available for ITP, however, therapeutic management has proven to be very challenging in several cases. Patients refractory to treatment can develop a clinically worsening disease course, treatment-induced toxicities and are predisposed to development of potentially life-endangering bleedings. It is therefore of critical importance to timely identify potential refractory patients, for which novel diagnostic approaches are urgently needed in order to monitor and predict specific therapeutic responses. In this paper, we propose promising diagnostic investigations into immune functions and characteristics in ITP, which may potentially be exploited to help predict platelet count responses and thereby distinguish therapeutic responders from non-responders. This importantly includes analysis of T cell homeostasis, which generally appears to be disturbed in ITP due to decreased and/or dysfunctional T regulatory cells (Tregs) leading to loss of immune tolerance and initiation/perpetuation of ITP, and this may be normalized by several therapeutic modalities. Additional avenues to explore in possible prediction of therapeutic responses include examination of platelet surface sialic acids, platelet apoptosis, monocyte surface markers, B regulatory cells and platelet microparticles. Initial studies have started evaluating these markers in relation to response to various treatments including glucocorticosteroids (GCs), intravenous immunoglobulins (IVIg) and/or thrombopoietin receptor agonists (TPO-RA), however, further studies are highly warranted. The systematic molecular analysis of a broad panel of immune functions may ultimately help guide and improve personalized therapeutic management in ITP.

Prognostic Value of Platelet-to-Lymphocyte Ratio, Neutrophil-to-Lymphocyte Ratio, and Lymphocyte-to-White Blood Cell Ratio in Colorectal Cancer Patients Who Received Neoadjuvant Chemotherapy

Background:

The objective of this study was to assess the prognostic value of pretreatment platelet-to-lymphocyte ratio (PLR), neutrophil-to-lymphocyte ratio (NLR), and lymphocyte-to-white blood cell ratio (LWR) of CRC patients who received neoadjuvant chemotherapy.

Methods:

We analyzed the peripheral blood routine parameters and other clinical data of 145 patients with colorectal cancer who had undergone neoadjuvant chemotherapy between January 2011 and February 2014. Pretreatment blood parameters of 145 patients were collected, and PLR, NLR, and LWR were calculated. The utility of PLR, NLR, and LWR in predicting treatment efficacy and patient survival was statistically evaluated using the chi-square test, log-rank test, Kaplan-Meier curves and logistic regression models, and Cox regression models.

Results:

Receiver operating characteristic curve showed that the best cutoff values of PLR, NLR, and LWR were 154.31, 3.01, and 0.22, respectively. In univariate analysis, tumor location (P = 0.044), differentiation degree (P = 0.001), lymph node metastasis (P = 0.020), and high PLR (P = 0.042) were significantly correlated with a lower overall response rate (ORR). In addition, clinical stage, lymph node metastasis, and high PLR were correlated with short OS (P < 0.01) and DFS (P < 0.01). Moreover, WBC count was correlated with a short OS. Multivariate analysis showed that tumor location (P = 0.013), differentiation degree (P = 0.001), and lymph node metastasis (P = 0.033) were independent predictors of ORR. In addition, lymph node metastasis independently predicted a shorter OS (P = 0.011). Lymph node metastasis (P = 0.013) and high PLR (P = 0.022) were independent prognostic factors for short DFS.

Conclusions:

For CRC patients who received NAC, clinical pathological stage and lymph node metastasis were correlated with lower ORR and survival, while a high PLR that may be of prognostic relevance in CRC patients receiving NAC.

Platelets instruct T reg cells and macrophages in the resolution of lung inflammation

Platelets convey important nonhemostatic immune functions; however, their potential role in resolving pulmonary inflammation remains to be determined. In this issue of JEM, Rossaint et al. (2021. J. Exp. Med. https://doi.org/10.1084/jem.20201353) reveal that platelets contribute to the resolution of pulmonary inflammation by directly recruiting T regulatory (T reg) cells to the lungs and by transcriptionally reprogramming alveolar macrophages toward an anti-inflammatory phenotype.

Protective immune response against P32 oncogenic peptide-pulsed PBMCs in mouse models of breast cancer

High expression of p32 in certain tumors makes it a potential target for immunotherapy. In the present study, the first goal was to design multi-epitope peptides from the P32 protein and the second goal was to compare the prophylactic effects of DCs- and PBMCs- based vaccines by pulsing them with designed peptides. For these purposes, 160 BALB/c mice were vaccinated in 5 different subgroups of each 4 peptides using PBS (F1-4a), F peptides alone (F1-4b), F peptides with CpG-ODN (F1-4c), F peptides with CpGODN and DCs (F1-4d), and F peptides with CpG-ODN and PBMCs (F1-4e). We found a significantly higher interferon-γ (IFN-γ) and granzyme B levels in T cells of F4d and F4e subgroups compared to control (p ≤ 0.05). The result of challenging spleen PBMCs of vaccinated mice with 4T1 cells showed significant up- and down- regulation of Fas ligand (FasL) and forkhead box P3 (Foxp3) gene expression between F4d and F4e subgroups with control, respectively. In addition, a significant change was seen in Caspase3 gene expression of F4d subgroup compared to control (p ≤ 0.05). Supernatant levels of IFN-γ and perforin were significantly increased in F4d and F4e subgroups compared to control. Consequently, significantly lower tumor sizes and prolonged survival time were detected in F4d and F4e subgroups compared to control after challenging mice with 4T1 cells. Accordingly, these results demonstrated that PBMCs pulsed F4 peptide-based vaccine could induce a protective immune response while it is a simple and less expensive vaccine.

Red blood cell alloimmunization and sickle cell disease: a narrative review on antibody induction

The high prevalence of red blood cell (RBC) alloantibodies in people with sickle cell disease (SCD) cannot be debated. Why people with SCD are so likely to form RBC alloantibodies, however, remains poorly understood. Over the past decade, a better understanding of non-ABO blood group antigen variants has emerged; RH genetic diversity and the role this diversity plays in RBC alloimmunization is discussed elsewhere. Outside of antigen variants, the immune systems of people with SCD are known to be different than those of people without SCD. Some of these differences are due to effects of free heme, whereas others are impacted by hyposplenism. Descriptive studies of differences in white blood cell (WBC) subsets, platelet counts and function, and complement activation between people with SCD and race-matched controls exist. Studies comparing the immune systems of alloimmunized people with SCD to non-alloimmunized people with SCD to race-matched controls without SCD have uncovered differences in T-cell subsets, monocytes, Fcγ receptor polymorphisms, and responses to free heme. Studies in murine models have documented the role that recipient inflammation plays in RBC alloantibody formation, with human studies reporting a similar association. Murine studies have also reported the importance of type 1 interferon (IFNα/β), known to play a pivotal role in autoimmunity, in RBC alloantibody formation. The goal of this manuscript is to review existing data on factors influencing RBC alloantibody induction in people with SCD with a focus on inflammation and other immune system considerations, from the bench to the bedside.

Evaluation of Platelet Responses in Transfusion-Related Acute Lung Injury (TRALI)

Platelets are versatile cells which are capable of eliciting nonhemostatic immune functions, especially under inflammatory conditions. Depending on the specific setting, platelets may be either protective or pathogenic in acute lung injury and acute respiratory distress syndrome (ARDS). Their role in transfusion-related acute lung injury (TRALI) is less well defined; however, it has been hypothesized that recipient platelets and transfused platelets both play a pathogenic role in TRALI. Overall, despite conflicting findings, it appears that recipient platelets may play a pathogenic role in antibody-mediated TRALI; however, their contribution appears to be limited. It is imperative to first validate the involvement of recipient platelets by standardizing the animal models, methods, reagents, and readouts for lung injury and taking the animal housing environment into consideration. For the involvement of transfused platelets in TRALI, it appears that predominantly lipids such as ceramide in stored platelets are able to induce TRALI in animal models. These studies will also need to be validated, and moreover, the platelet-derived lipid-mediated mechanisms leading to TRALI will need to be investigated.

The Immune Nature of Platelets Revisited

Platelets are the primary cellular mediators of hemostasis and this function firmly acquaints them with a variety of inflammatory processes. For example, platelets can act as circulating sentinels by expressing Toll-like receptors (TLR) that bind pathogens and this allows platelets to effectively kill them or present them to cells of the immune system. Furthermore, activated platelets secrete and express many pro- and anti-inflammatory molecules that attract and capture circulating leukocytes and direct them to inflamed tissues. In addition, platelets can directly influence adaptive immune responses via secretion of, for example, CD40 and CD40L molecules. Platelets are also the source of most of the microvesicles in the circulation and these miniscule elements further enhance the platelet’s ability to communicate with the immune system. More recently, it has been demonstrated that platelets and their parent cells, the megakaryocytes (MK), can also uptake, process and present both foreign and self-antigens to CD8+ T-cells conferring on them the ability to directly alter adaptive immune responses. This review will highlight several of the non-hemostatic attributes of platelets that clearly and rightfully place them as integral players in immune reactions.

•

Platelets can act as circulating sentinels by expressing pathogen-associated molecular pattern receptors that bind pathogens and induce their killing and elimination.

•

Activated platelets secrete and express a multitude of pro- and anti-inflammatory molecules that attract and capture circulating leukocytes and direct them to inflamed tissues.

•

Platelets express and secrete many critical immunoregulatory molecules that significantly affect both innate and adaptive immune responses.

•

Platelets are the primary source of microparticles in the circulation and these augment the platelet’s ability to communicate with the immune system.

•

Platelets and megakaryocytes can act as antigen presenting cells and present both foreign- and self-peptides to T-cells.

Platelets Promote Macrophage Polarization toward Pro-inflammatory Phenotype and Increase Survival of Septic Mice

We investigated the contribution of human platelets to macrophage effector properties in the presence of lipopolysaccharide (LPS), as well as the beneficial effects and time frame for platelet transfusion in septic animals. Our results show that platelets sequester both pro-(TNF-α/IL-6) and anti-(IL-10) inflammatory cytokines released by monocytes. Low LPS concentrations (0.01 ng/mL) induced M2 macrophage polarization by decreasing CD64 and augmenting CD206 and CD163 expression; yet, the presence of platelets skewed monocytes toward type 1 macrophage (M1) phenotype in a cell-contact-dependent manner by the glycoprotein Ib (GPIb)-CD11b axis. Accordingly, platelet-licensed macrophages showed increased TNF-α levels, bacterial phagocytic activity, and a reduced healing capability. Platelet transfusion increased inducible nitric oxide synthase (iNOS)⁺ macrophages, improving bacterial clearance and survival rates in septic mice up to 6 h post-infection, an effect that was abolished by CD11b and GPIb blockade. Our results demonstrate that platelets orchestrate macrophage effector responses, improving the clinical outcome of sepsis in a narrow but relevant time frame.

Crosstalk Between Platelets and Microbial Pathogens

Platelets, small anucleate cells circulating in the blood, are critical mediators in haemostasis and thrombosis. Interestingly, recent studies demonstrated that platelets contain both pro-inflammatory and anti-inflammatory molecules, equipping platelets with immunoregulatory function in both innate and adaptive immunity. In the context of infectious diseases, platelets are involved in early detection of invading microorganisms and are actively recruited to sites of infection. Platelets exert their effects on microbial pathogens either by direct binding to eliminate or restrict dissemination, or by shaping the subsequent host immune response. Reciprocally, many invading microbial pathogens can directly or indirectly target host platelets, altering platelet count or/and function. In addition, microbial pathogens can impact the host auto- and alloimmune responses to platelet antigens in several immune-mediated diseases, such as immune thrombocytopenia, and fetal and neonatal alloimmune thrombocytopenia. In this review, we discuss the mechanisms that contribute to the bidirectional interactions between platelets and various microbial pathogens, and how these interactions hold relevant implications in the pathogenesis of many infectious diseases. The knowledge obtained from "well-studied" microbes may also help us understand the pathogenesis of emerging microbes, such as SARS-CoV-2 coronavirus.

Influenza-induced thrombocytopenia is dependent on the subtype and sialoglycan receptor and increases with virus pathogenicity

Thrombocytopenia is a common complication of influenza virus infection, and its severity predicts the clinical outcome of critically ill patients. The underlying cause(s) remain incompletely understood. In this study, in patients with an influenza A/H1N1 virus infection, viral load and platelet count correlated inversely during the acute infection phase. We confirmed this finding in a ferret model of influenza virus infection. In these animals, platelet count decreased with the degree of virus pathogenicity varying from 0% in animals infected with the influenza A/H3N2 virus, to 22% in those with the pandemic influenza A/H1N1 virus, up to 62% in animals with a highly pathogenic A/H5N1 virus infection. This thrombocytopenia is associated with virus-containing platelets that circulate in the blood. Uptake of influenza virus particles by platelets requires binding to sialoglycans and results in the removal of sialic acids by the virus neuraminidase, a trigger for hepatic clearance of platelets. We propose the clearance of influenza virus by platelets as a paradigm. These insights clarify the pathophysiology of influenza virus infection and show how severe respiratory infections, including COVID-19, may propagate thrombocytopenia and/or thromboembolic complications.

Engineered PD-L1-Expressing Platelets Reverse New-Onset Type 1 Diabetes

The pathogenesis of Type 1 diabetes (T1D) arises from the destruction of insulin-producing β-cells by islet-specific autoreactive T cells. Inhibition of islet-specific autoreactive T cells to rescue β-cells is a promising approach to treat new-onset T1D. The immune checkpoint signal axis programmed death-1/programmed death-ligand 1 (PD-1/PD-L1) can effectively regulate the activity of T cells and prevent autoimmune attack. Here, megakaryocyte progenitor cells are genetically engineered to overexpress PD-L1 to produce immunosuppressive platelets. The PD-L1-overexpressing platelets (designated PD-L1 platelets) accumulate in the inflamed pancreas and may suppress the activity of pancreas autoreactive T cells in newly hyperglycemic non-obese diabetic (NOD) mice, protecting the insulin-producing β-cells from destruction. Moreover, PD-L1 platelet treatment also increases the percentage of the regulatory T cells (Tregs) and maintains immune tolerance in the pancreas. It is demonstrated that the rescue of β-cells by PD-L1 platelets can effectively maintain normoglycemia and reverse diabetes in newly hyperglycemic NOD mice.

Platelet depletion limits the severity but does not prevent the occurrence of experimental transfusion-related acute lung injury

BACKGROUND

Transfusion-related acute lung injury (TRALI) is a severe pulmonary reaction due to blood transfusions. The pathophysiology of this complication is still not widely elucidated by the scientific community, especially regarding the direct role of blood platelets within the cellular mechanism responsible for the development of TRALI.

STUDY DESIGN AND METHODS

In this study, a mouse model was used to induce the development of antibody-mediated acute lung injury through injections of lipopolysaccharide and an anti-major histocompatibility complex Class I antibody. BALB/c mice were pretreated with an anti-GPIbα antibody, which induces platelet depletion, or ML354, a protease receptor 4 pathway inhibitor, 30 minutes before TRALI induction.

RESULTS

Depletion of platelets before TRALI induction appeared to reduce the severity of TRALI without completely inhibiting its development. Also, inhibition of platelet activation by ML354 did not prevent the onset of TRALI. Finally, the stimuli used for TRALI induction also triggered specific platelet activation upon ex vivo stimulation.

CONCLUSIONS

This study suggests that blood platelets are not critically required for TRALI induction, although they are to some extent involved in its pathophysiology.

The effect of platelet storage temperature on haemostatic, immune, and endothelial function: potential for personalised medicine

Reports from both adult and paediatric populations indicate that approximately two-thirds of platelet transfusions are used prophylactically to prevent bleeding, while the remaining one-third are used therapeutically to manage active bleeding. These two indications, prophylactic and therapeutic, serve two very distinct purposes and therefore will have two different functional requirements. In addition, disease aetiology in a given patient may require platelets with different functional characteristics. These characteristics can be derived from the various manufacturing methods used in platelet product production, including collection methods, processing methods, and storage options. The iterative combinations of manufacturing methods can result in a number of unique platelet products with different efficacy and safety profiles, which could potentially be used to benefit patient populations by meeting diverse clinical needs. In particular, cold storage of platelet products causes many biochemical and functional changes, of which the most notable characterised to date include increased haemostatic activity and altered expression of molecules inherent to platelet:leucocyte interactions. The in vivo consequences, both short- and long-term, of these molecular and cellular cold-storage-induced changes have yet to be clearly defined. Elucidation of these mechanisms would potentially reveal unique biologies that could be harnessed to provide more targeted therapies. To this end, in this new era of personalised medicine, perhaps there is an opportunity to provide individual patients with platelet products that are tailored to their clinical condition and the specific indication for transfusion.

Platelet and immune characteristics of immune thrombocytopaenia patients non-responsive to therapy reveal severe immune dysregulation

Multifactorial mechanisms leading to diminished platelet counts in immune thrombocytopaenia (ITP) might condition the ability of patients with ITP to respond to treatments. Examining their platelet and immune features, we aimed to detect singular characteristics of patients with ITP who do not respond to any treatment. We studied patients with chronic primary ITP who had been without treatment, or untreated (UT-ITP), for at least six months; included were responders to agonists of thrombopoietin receptors (TPO-RA), patients who showed no response to first- and second-line treatments (NR-ITP), and healthy controls. Platelets from NR-ITP patients exposed a reduced amount of sialic acid residues. Increased loss of platelet surface sialic acid residues was associated with increased platelet apoptosis. NR-ITP patients had an increased fraction of naive lymphocyte (L) B cells and a reduced LTreg (Lymphocyte T-regulator) subset. They also presented an anomalous monocyte and NK (Natural Killer) cells distribution. TPO-RA-treated patients seemed to recover an immune homeostasis similar to healthy controls. In conclusion, our results indicate a severe deregulation of the immune system of NR-ITP. The inverse correlation between loss of sialic acid and LTreg count suggests a potential relationship between glycan composition on the platelet surface and immune response, positing terminal sugar moieties of the glycan chains as aetiopathogenic agents in ITP.

Mean platelet volume/platelet count ratio in colorectal cancer: a retrospective clinical study

BACKGROUND

Mean platelet volume (MPV) is a marker of platelet activation. MPV and platelet count (PC) are negatively correlated, and their ratio (MPV/PC) is informative for the diagnosis of malignant tumors. However, the relationship between MPV/PC and colorectal cancer is unclear. This retrospective clinical study aimed to evaluate the diagnostic value of MPV/PC in colorectal cancer.

METHODS

Hematological examinations were performed at initial diagnosis in patients with colorectal cancer (n = 186) or adenomatous polyp (n = 132) and healthy controls (n = 108). Hematological parameters evaluated included white blood cells, red blood cells, hemoglobin, neutrophils, lymphocytes, monocytes, PC, and MPV. Statistical analyses included Student's t-test, one-way ANOVA or Kruskal-Wallis H test, chi-square tests, Spearman's correlation test and receiver operating characteristic (ROC). ROC curve was used to evaluate the diagnostic values of MPV and MPV/PC in colorectal cancer.

RESULTS

Among these groups, MPV was significantly lower in colorectal cancer than in adenomatous polyp (p = 0.002) and healthy controls (p < 0.001) but did not significantly differ between adenomatous polyp and healthy controls (p = 0.210). MPV/PC was lower in colorectal cancer compared with adenomatous polyp and healthy controls (p < 0.001) and in adenomatous polyp compared with healthy controls (p = 0.010). MPV did not significantly differ among colorectal cancer subgroups, while MPV/PC significantly differed between TNM stages and the presence/absence of lymph node metastasis. MPV/PC was negatively correlated with the neutrophil to lymphocyte ratio(NLR) (p = 0.002) and platelet to lymphocyte ratio(PLR) concentration (p < 0.001). In the differential diagnosis between colorectal cancer and adenomatous polyp, MPV/PC produced a larger ROC curve than MPV, NLR or PLR alone. Using MPV/PC to distinguish between colorectal cancer and controls produced a larger AUC than using MPV or NLR alone.

CONCLUSIONS

MPV/PC may be useful for the diagnosis of colorectal cancer. However, further studies are warranted to include additional regions and more data, to assess the utility of MPV/PC as a novel diagnostic screening tool for colorectal cancer.

Platelet-Dense Granules Worsen Pre-Infection Thrombocytopenia during Gram-Negative Pneumonia-Derived Sepsis

Platelet-dense (δ) granules are important for platelet function. Platelets contribute to host defense and vascular integrity during pneumonia and sepsis, and δ granule products, including adenosine diphosphate (ADP), can influence inflammatory responses. We therefore aimed to study the role of platelet δ granules in the host response during sepsis. Hermansky-Pudlak syndrome (Hps)3coa mice (with reduced δ granule content), mice treated with the platelet ADP receptor inhibitor clopidogrel, and appropriate control mice were infected with the human sepsis pathogen Klebsiella pneumoniae via the airways to induce pneumonia and sepsis. In order to override potential redundancy in platelet functions, we also studied Hps3coa and control mice with moderate antibody-induced thrombocytopenia (10%) prior to infection. We found that sepsis-induced thrombocytopenia tended to be less severe in Hps3coa mice, and was significantly ameliorated in Hps3coa mice with low pre-infection platelet counts. Bacterial growth was similar in Hps3coa and control mice in the presence of normal platelet counts prior to infection, but lower in the lungs of Hps3coa mice with low pre-infection platelet counts. Hps3coa mice had unaltered lung pathology and distant organ injury during pneumosepsis, irrespective of pre-infection platelet counts; lung bleeding did not differ between Hps3coa and control mice. Clopidogrel did not influence any host response parameter. These data suggest that platelet δ granules can play a detrimental role in pneumosepsis by aggravating thrombocytopenia and impairing local antibacterial defense, but that these unfavorable effects only become apparent in the presence of low platelet counts.

Transfused platelets enhance alloimmune responses to transfused KEL-expressing red blood cells in a murine model

BACKGROUND

Factors influencing the development of alloantibodies against blood group antigens on transfused red blood cells are poorly defined. We hypothesised that transfused platelets may act as a danger signal to recipients and affect humoral immune responses to transfused red blood cells.

MATERIALS AND METHODS

Platelet-rich plasma prepared from wild-type C57BL/6 or CD40L knock-out donors was transfused into wild-type or CD40L knock-out recipients. Leucoreduced red blood cells from transgenic donors expressing high levels of the human KEL glycoprotein in an erythrocyte-specific manner (KEL^hi donors) were transfused after the platelets, and anti-KEL responses were measured longitudinally. In some experiments, recipients were treated with poly (I:C), monoclonal CD40L-blocking antibody, or CD4-depleting antibody prior to transfusion.

RESULTS

Transfusion of wild-type C57BL/6 platelets or treatment with poly (I:C) prior to KEL^hi red blood cell transfusion led to an anti-KEL alloimmune response in wild-type recipients. Transfusion of platelets from wild-type but not CD40L knock-out donors prior to KEL^hi red blood cell transfusion led to an IgG anti-KEL alloimmune response in CD40L knock-out recipients; unexpectedly, transfusion of platelets from CD40L knock-out donors prior to KEL^hi red blood cell transfusion led to a robust anti-KEL alloimmune response in wild-type recipients. Recipient treatment with MR1 CD40L-blocking antibody or CD4-depleting antibody prevented KEL alloimmunisation altogether.

DISCUSSION

Transfused platelets serve as an adjuvant in this T-dependent murine model of anti-KEL red blood cell alloimmunisation, with CD40/CD40L interactions being involved to some degree but with additional mechanisms also playing a role. These findings raise questions about the role that transfused or endogenous platelets may play in other innate/adaptive immune responses.

New perspectives on IL-33 and IL-1 family cytokines as innate environmental sensors

Interleukin (IL)-1 family cytokines are important initiators of innate immunity and host defence; however, their uncontrolled activities can cause tissue-damaging inflammation. Consequently, IL-1 family cytokines have sophisticated regulatory mechanisms to control their activities including proteolytic processing for their activation and the deployment of soluble receptors and receptor antagonists to limit their activities. IL-33 is a promoter of type 2 immunity and allergic inflammation through its alarmin activity that can rapidly initiate local immune responses by stimulating innate immune cells following exposure to environmental insults, pathogens, or sterile injury. Recent publications have provided new insights into how the range and duration of IL-33 activity is regulated by direct sensing of host-derived and exogenous proteolytic activities as well as oxidative changes during tissue damage. Here, we discuss how this impacts our understanding of the roles of IL-33 in initiating immune responses and the evidence that these sensing mechanisms might regulate the activities of other IL-1 family cytokines and their biological functions. Finally, we discuss translational challenges these discoveries pose for the accurate detection of different forms of these cytokines.

Human blood platelets and viruses: defense mechanism and role in the removal of viral pathogens

Platelets are small non-nucleated cell fragments and the second most abundant cell that play crucial role in managing vascular integrity and regulating hemostasis. Recent finding shows, beyond its hemostatic function platelets also play a main role in fighting against pathogen including viruses. With their receptors, platelet interacts with viral pathogen and this interaction between platelets and viral pathogens result in activation of platelets. Activated platelet releases different molecules that have antiviral activity including kinocidins and other platelet microbicidal peptides. In addition, activated platelet has antiviral role by different mechanism including; phagocytosis of viral pathogen, produce reactive oxygen species and interact with and activate other immune cells. In other side, antiplatelet treatments are one of defending mechanism of viral pathogen. This narrative review summarizes what is known regarding the role of human platelets in fighting viral pathogen.

Advances in chemical pharmacotherapy for the treatment of pediatric immune thrombocytopenia

INTRODUCTION

Immune thrombocytopenia (ITP) is an autoimmune bleeding disorder of heterogeneous pathophysiological mechanisms. Treatment endpoints include elevation of platelets and reduction of bleeding risk, elevation of quality of life, reduction of concomitant therapies and prevention from bleeding. Persistent and chronic ITP is more common in adults but occurs in children. Standard therapies include corticosteroids and immunoglobulins, both associated with side effects. There are new treatments, such as thrombopoietin-receptor agonists and promising investigational drugs.

AREAS COVERED

Experience from the management of adults is valuable for children with persistent and chronic symptomatic ITP. In this review first- and second-line therapies, but also investigational drugs for children with ITP are discussed.

EXPERT OPINION

Although time-consuming and based on experience, children with no or mild bleeding can be safely managed with a watch and wait strategy. Chronic symptomatic immune thrombocytopenia is an area of second-line treatments based on a highly individualized approach. Furthermore, there are investigational drugs, which may also be of benefit for children with chronic symptomatic ITP.

Platelet CLEC-2 protects against lung injury via effects of its ligand podoplanin on inflammatory alveolar macrophages in the mouse

There is no therapeutic intervention proven to prevent acute respiratory distress syndrome (ARDS). Novel mechanistic insights into the pathophysiology of ARDS are therefore required. Platelets are implicated in regulating many of the pathogenic processes that occur during ARDS; however, the mechanisms remain elusive. The platelet receptor CLEC-2 has been shown to regulate vascular integrity at sites of acute inflammation. Therefore the purpose of this study was to establish the role of CLEC-2 and its ligand podoplanin in a mouse model of ARDS. Platelet-specific CLEC-2-deficient, as well as alveolar epithelial type I cell (AECI)-specific or hematopoietic-specific podoplanin deficient, mice were established using cre-loxP strategies. Combining these with intratracheal (IT) instillations of lipopolysaccharide (LPS), we demonstrate that arterial oxygen saturation decline in response to IT-LPS in platelet-specific CLEC-2-deficient mice is significantly augmented. An increase in bronchoalveolar lavage (BAL) neutrophils and protein was also observed 48 h post-IT-LPS, with significant increases in pro-inflammatory chemokines detected in BAL of platelet-specific CLEC-2-deficient animals. Deletion of podoplanin from hematopoietic cells but not AECIs also reduces lung function and increases pro-inflammatory chemokine expression following IT-LPS. Furthermore, we demonstrate that following IT-LPS, platelets are present in BAL in aggregates with neutrophils, which allows for CLEC-2 interaction with podoplanin expressed on BAL inflammatory alveolar macrophages. Taken together, these data suggest that the platelet CLEC-2-podoplanin signaling axis regulates the severity of lung inflammation in mice and is a possible novel target for therapeutic intervention in patients at risk of developing ARDS.

Assessment of the Effects of 2'-Methoxyethyl Antisense Oligonucleotides on Platelet Count in Cynomolgus Nonhuman Primates

Decreases in platelet (PLT) counts observed in nonhuman primates (NHPs) given 2'-O-methoxyethyl modified antisense inhibitors (2'-MOE ASOs) have been reported, but the incidence and severity of the change vary considerably between sequences, studies, and animals. This article will broadly illustrate the spectrum of effects on PLT count in NHPs. From queries of an NHP safety database representing over 102 independent 2'-MOE ASOs, from 61 studies and >2200 NHPs, two patterns of PLT changes emerged. The first is a consistent and reproducible decrease in group mean values, observed with about 30% of the compounds, in which PLT count typically remains ≥150K cells/μL. The second is a sporadic decrease in PLTs to <50K cells/μL (2%-4% incidence at doses >5 mg/kg) that is often not reproducible. In both cases, the reduction in PLT count is dose dependent and reversible. The human relevance of PLT change observed in NHPs was investigated using ISIS 404173. In a chronic NHP study (20 mg/kg/wk for 26 weeks), a gradual decrease in group mean PLT count was observed at ≥10 mg/kg/wk, which plateaued by 13 weeks generally within the normal range and was maintained through 26 weeks of treatment. However, PLT counts <50K cells/μL occurred in 1 of 16 NHP at 10 mg/kg/wk and 3 of 16 NHP at 20 mg/kg/wk. In a 26-week double-blind, placebo-controlled Phase 2 trial, 62 patients were treated with 200 mg/wk ISIS 404173 (∼3.3 mg/kg/wk) there was an increased incidence of PLT count >30% decreased compared to baseline but no incidence of PLT <75K cells/μL. Based on these data, the consistent, self-limiting PLT reduction seen in NHP may translate to humans, but these changes appear to be of limited clinical significance. However, NHPs appear to overpredict the incidence of sporadic PLT <50K cells/μL compared to humans.

Management of Platelet Disorders and Platelet Transfusions in ICU Patients

Thrombocytopenia or receipt of antiplatelet drugs, with or without bleeding, is a common indication for platelet transfusions in the ICU. However, there is almost no evidence base for these practices other than expert opinion. Also common is use of platelet transfusions prior to invasive procedures or surgery in patients with thrombocytopenia. Likewise, there is no high-quality evidence that such practices are efficacious or safe. Recently, it has become clear that, whether causal or not, patients receiving prophylactic platelet transfusions experience high rates of nosocomial infection, thrombosis, organ failure, and mortality, which increase the urgency and need for randomized trials to assess these practices. Investigational methods of improving the safety and efficacy of platelet transfusions include use of alternate strategies such as antifibrinolytics; use of ABO-identical, leukoreduced, and washed platelet transfusions; and improved storage solutions.

Pathogenesis and Therapeutic Mechanisms in Immune Thrombocytopenia (ITP)

Immune thrombocytopenia (ITP) is a complex autoimmune disease characterized by low platelet counts. The pathogenesis of ITP remains unclear although both antibody-mediated and/or T cell-mediated platelet destruction are key processes. In addition, impairment of T cells, cytokine imbalances, and the contribution of the bone marrow niche have now been recognized to be important. Treatment strategies are aimed at the restoration of platelet counts compatible with adequate hemostasis rather than achieving physiological platelet counts. The first line treatments focus on the inhibition of autoantibody production and platelet degradation, whereas second-line treatments include immunosuppressive drugs, such as Rituximab, and splenectomy. Finally, third-line treatments aim to stimulate platelet production by megakaryocytes. This review discusses the pathophysiology of ITP and how the different treatment modalities affect the pathogenic mechanisms.