Tissue Factor Expression on Platelet Surface during Preparation and Storage of Platelet Concentrates

The platelet storage lesion, what are we working for?

BACKGROUND

Platelet concentrate (PC) transfusions are crucial in prevention and treatment of bleeding in infection, surgery, leukemia, and thrombocytopenia patients. Although the technology for platelet preparation and storage has evolved over the decades, there are still challenges in the demand for platelets in blood banks because the platelet shelf life is limited to 5 days due to bacterial contamination and platelet storage lesions (PSLs) at 20-24°C under constant horizontal agitation. In addition, the relations between some adverse effects of platelet transfusions and PSLs have also been considered. Therefore, understanding the mechanisms of PSLs is conducive to obtaining high quality platelets and facilitating safe and effective platelet transfusions.

OBJECTIVE

This review summarizes developments in mechanistic research of PSLs and their relationship with clinical practice, providing insights for future research.

METHODS

Authors conducted a search on PubMed and Web of Science using the professional terms "PSL" and "platelet transfusion." The obtained literature was then roughly categorized based on their research content. Similar studies were grouped into the same sections, and further searches were conducted based on the keywords of each section.

RESULTS

Different studies have explored PSLs from various perspectives, including changes in platelet morphology, surface molecules, biological response modifiers (BMRs), metabolism, and proteins and RNA, in an attempt to monitor PSLs and identify intervention targets that could alleviate PSLs. Moreover, novel platelet storage conditions, including platelet additive solutions (PAS) and reconsidered cold storage methods, are explored. There are two approaches to obtaining high-quality platelets. One approach simulates the in vivo environment to maintain platelet activity, while the other keeps platelets at a low activity level in vitro under low temperatures.

CONCLUSION

Understanding PSLs helps us identify good intervention targets and assess the therapeutic effects of different PSLs stages for different patients.

Interactions of HIV and Antiretroviral Therapy With Neutrophils and Platelets

Neutrophils are important components of the innate immune system that mediate pathogen defense by multiple processes including phagocytosis, release of proteolytic enzymes, production of reactive oxygen species, and neutrophil extracellular trap formation. Abnormalities of neutrophil count and function have been described in the setting of HIV infection, with the majority of antiretroviral agents (ARVs), excluding zidovudine, having been reported to correct neutropenia. Questions still remain, however, about their impact on neutrophil function, particularly the possibility of persistent neutrophil activation, which could predispose people living with HIV to chronic inflammatory disorders, even in the presence of virally-suppressive treatment. In this context, the effects of protease inhibitors and integrase strand transfer inhibitors, in particular, on neutrophil function remain poorly understood and deserve further study. Besides mediating hemostatic functions, platelets are increasingly recognized as critical role players in the immune response against infection. In the setting of HIV, these cells have been found to harbor the virus, even in the presence of antiretroviral therapy (ART) potentially promoting viral dissemination. While HIV-infected individuals often present with thrombocytopenia, they have also been reported to have increased platelet activation, as measured by an upregulation of expression of CD62P (P-selectin), CD40 ligand, glycoprotein IV, and RANTES. Despite ART-mediated viral suppression, HIV-infected individuals reportedly have sustained platelet activation and dysfunction. This, in turn, contributes to persistent immune activation and an inflammatory vascular environment, seemingly involving neutrophil-platelet-endothelium interactions that increase the risk for development of comorbidities such as cardiovascular disease (CVD) that has become the leading cause of morbidity and mortality in HIV-infected individuals on treatment, clearly underscoring the importance of unraveling the possible etiologic roles of ARVs. In this context, abacavir and ritonavir-boosted lopinavir and darunavir have all been linked to an increased risk of CVD. This narrative review is therefore focused primarily on the role of neutrophils and platelets in HIV transmission and disease, as well as on the effect of HIV and the most common ARVs on the numbers and functions of these cells, including neutrophil-platelet-endothelial interactions.

Increased number of tissue factor protein expressing thrombocytes in canine idiopathic immune mediated hemolytic anemia

Dogs suffering from canine idiopathic immune mediated hemolytic anemia (cIIMHA) are at great risk of dying particularly in the first two weeks after the diagnosis is made. This high mortality risk may be associated with the development of thromboembolism (TE) and/or disseminated intravascular coagulation (DIC) resulting in organ failure. The exact mechanism of the development of TE and/or DIC in cIIMHA is still undetermined. Therefore, this study investigates the presence of tissue factor (TF) in thrombocytes of dogs suffering from cIIMHA, using OptiPrep™ for the isolation of blood cells and immunocytochemistry (ICC) to visualize TF on thrombocytes. The normalised TF quantity, acquired with 'colour deconvolution' (ImageJ plug in), revealed that in cIIMHA dogs the fraction TF positive thrombocytes was statistically significant higher (P < 0.001; mean 0.79; n = 7) compared to the fraction TF positive thrombocytes of the healthy dogs (mean 0.43; n = 9). We further have indications that the fraction of TF positive thrombocytes decreases with time and therapy, but that the progression rate differs individually. Since cIIMHA dogs have more thrombocytes that are TF-positive compared to healthy dogs, this may explain the increased risk to develop TE and DIC. Furthermore, it seems that the number of TF-positive thrombocytes in cIIMHA dogs remains high during the first two weeks of the disease, the time when the animals are at greatest health risk.

Flow cytometry analysis of platelet populations: usefulness for monitoringthe storage lesion in pooled buffy-coat platelet concentrates

BACKGROUND

Early detection of the platelet storage lesion is still a challenge in transfusion practice. Using flow cytometry, we evaluated the appearance of the storage lesion, based on the expression of platelet activation markers, in total platelets and platelet populations.

MATERIALS AND METHODS

Buffy-coat-derived platelet concentrates were stored under standard conditions for 5 days. The expression of activation antigens CD42b, CD36, CD62p and phosphatidylserine on total platelets and populations of small, medium-sized and large platelets was analysed by flow cytometry on storage days 1, 3 and 5.

RESULTS

The activation/lesion on total platelets and each platelet population was detected on storage day 3, by the increased expression of CD36. On the same day, increased expression of CD42b and CD62p was detected, but only on large platelets. Small and medium-sized platelets had increased CD62p expression only on day 5. Externalisation of phosphatidylserine was not detected.

DISCUSSION

Evaluation of the level of expression of various activation markers on different platelet populations could be an additional valid analysis in cell quality control of platelet concentrates, and in the assessment of novel approaches to platelet concentrate manipulation.

The vulnerable blood. Coagulation and clot structure in diabetes mellitus

Patients with diabetes are at increased risk of cardiovascular morbidity and mortality. While arteriosclerotic lesions have long been recognized as the underlying cause more recent studies suggest that alterations of the blood are also critically involved. Following plaque rupture, adherence of platelets is followed by the formation of a cross-linked fibrin clot. Patients with diabetes exhibit a prothrombotic milieu consisting of hyper reactive platelets, a tight and rigid clot structure which is due to up-regulation of coagulation factors and prolongation of clot lysis. Metabolic alterations as well as inflammatory processes, which are up-regulated in diabetes, are thought to be the main underlying causes. More recently, the complement cascade has emerged as a potential new player in this context with several complement components directly influencing both platelet function and coagulation. This review provides an overview concerning the changes that lead to alterations of platelet function and clot structure in diabetes.

Platelets do not express the oxidized or reduced forms of tissue factor

BACKGROUND

Expression of tissue factor (TF) antigen and activity in platelets is controversial and dependent upon the laboratory and reagents used. Two forms of TF were described: an oxidized functional form and a reduced nonfunctional form that is converted to the active form through the formation of an allosteric disulfide. This study tests the hypothesis that the discrepancies regarding platelet TF expression are due to differential expression of the two forms.

METHODS

Specific reagents that recognize both oxidized and reduced TF were used in flow cytometry of unactivated and activated platelets and western blotting of whole platelet lysates. TF-dependent activity measurements were used to confirm the results.

RESULTS

Western blotting analyses of placental TF demonstrated that, in contrast to anti-TF#5, which is directed against the oxidized form of TF, a sheep anti-human TF polyclonal antibody recognizes both the reduced and oxidized forms. Flow cytometric analyses demonstrated that the sheep antibody did not react with the surface of unactivated platelets or platelets activated with thrombin receptor agonist peptide, PAR-1. This observation was confirmed using biotinylated active site-blocked factor (F)VIIa: no binding was observed. Likewise, neither form of TF was detected by western blotting of whole platelet lysates with sheep anti-hTF. Consistent with these observations, no FXa or FIXa generation by FVIIa was detected at the surface of these platelets. Similarly, no TF-related activity was observed in whole blood using thromboelastography.

CONCLUSION AND SIGNIFICANCE

Platelets from healthy donors do not express either oxidized (functional) or reduced (nonfunctional) forms of TF.