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

Effect of mirasol pathogen reduction technology system on immunomodulatory molecules of apheresis platelets

Pathogen inactivation for platelets by riboflavin system (MIRASOL) efficiently reduces transfusion related pathogen transmission. However little is known about its impact on platelets' immunomodulatory biochemical profile. We aimed was to assess the effects of MIRASOL treatment on platelet quality parameters and immunomodulatory molecules CD62P, RANTES, and CD40L in Single Donor Platelets (SDPs) resuspended in plasma (SDP-P) or T-PAS and additive solution (SDP-A). Twenty nine SDPs (15 SDP-P and 14 SDP-A) were included in the study. Samples were collected before, after MIRASOL treatment and just before transfusion. P-selectin (CD62P), RANTES, and CD40L were tested by ELISA. Platelet products quality assays were also performed. Platelet count/unit decreased after Mirasol treatment by 13 %. The pH of all units decreased over the 5-day storage period but remained above expected limits and the swirling test was positive throughout storage. P-selectin levels were not different between the three different time points in both SDPs-P and SDPs-A while RANTES levels were found to differ statistically significantly at the three different time points in all units and in the SPD-A subgroup. CD40L levels in all SDP products increased slightly during storage but this was not statistically significant. CD62P, RANTES, and CD40L in all time points were elevated in SDPs-A compared to SDPs-P but not at a statistically significant level. In conclusion MIRASOL treatment apart from RANTES increase does not seem to substantially affect platelets associated other cytokines and immunomodulatory molecules namely P-selectin and sCD40L which are implicated in immune transfusion reactions.

Irradiation of platelets in Transfusion Medicine: risk and benefit judgments

Irradiation of platelet products is generally used to prevent transfusion-associated graft-versus-host disease (TA-GvHD) as well as transfusion-transmitted infections. As an essential prerequisite, gamma-irradiation of blood products prior to transfusion is required in patients who may develop TA-GVHD. Most studies suggest that gamma irradiation has no significant effect on the quality of platelet products; however, more recent studies have shown that the oxidative effects of gamma irradiation can lead to the induction of platelet storage lesion (PSL) and to some extent reduce the efficiency of transfused platelets. As the second widely used irradiation technique, UV-illumination was primarily introduced to reduce the growth of infectious agents during platelet storage, with the advantage that this method can also prevent TA-GvHD. However, the induction of oxidative conditions and platelet pre-activation that lead to PSL is more pronounced after UV-based methods of pathogen reduction. Since these lesions are large enough to clearly affect the post-transfusion platelet recovery and survival, more studies are needed to improve the safety and effectiveness of pathogen reduction technologies (PRTs). Therefore, pointing to other benefits of PRTs, such as preventing TA-GvHD or prolonging the shelf life of products by eliminating the possibility of pathogen growth during storage, does not yet seem to justify their widespread use due to above-mentioned effects. Even for gamma-irradiated platelets, some researchers have suggested that due to decreased 1-hour post-transfusion increments and increased risk of platelet refractoriness, their use should be limited to the patients who may develop TA-GVHD. It is noteworthy that due to the effect of X-rays in preventing TA-GvHD, some recent studies are underway to examine its effects on the quality and effectiveness of platelet products and determine whether X-rays can be used as a more appropriate and cost-effective alternative to gamma radiation. The review presented here provides a detailed description about irradiation-based technologies for platelet products, including their applications, mechanistic features, advantages, and disadvantages.

Effects and Side Effects of Platelet Transfusion

Aside from their canonical role in hemostasis, it is increasingly recognized that platelets have inflammatory functions and can regulate both adaptive and innate immune responses. The main topic this review aims to cover is the proinflammatory effects and side effects of platelet transfusion. Platelets prepared for transfusion are subject to stress injury upon collection, preparation, and storage. With these types of stress, they undergo morphologic, metabolic, and functional modulations which are likely to induce platelet activation and the release of biological response modifiers (BRMs). As a consequence, platelet concentrates (PCs) accumulate BRMs during processing and storage, and these BRMs are ultimately transfused alongside platelets. It has been shown that BRMs present in PCs can induce immune responses and posttransfusion reactions in the transfusion recipient. Several recent reports within the transfusion literature have investigated the concept of platelets as immune cells. Nevertheless, current and future investigations will face the challenge of encompassing the immunological role of platelets in the scope of transfusion.

Cryopreservation of buffy coat derived platelets: Paired in vitro characterization using uncontrolled versus controlled freezing rate protocols

Background

Cryopreserved platelets show a reduced recovery and viability after freezing and thawing including several ultrastructural and phenotypic deteriorations compared with liquid‐stored platelets. It is suggested that using Controlled‐Rate Freezing (CRF) can reduce variability and optimize the functionality profile for cells. The objective of the study is to compare cellular, metabolic, phenotypic and functional effects on platelets after cryopreservation using different freezing rate protocols.

Study Design and Methods

To evaluate the possible effects of different freezing rate protocols a two‐experimental study comparing diverse combinations was tested with a pool and split design. Uncontrolled freezing of platelets in materials with different thermal conductivity (metal vs cardboard) was evaluated in experiment 1. Experiment 2 evaluated uncontrolled vs a controlled‐rate freezing protocol in metal boxes. All variables were assessed pre and post cryopreservation.

Results

Directly after thawing, no major differences in platelet recovery, LDH, ATP, Δψ, CD62P, CD42b, platelet endothelial cell adhesion molecule and sCD40L were seen between units frozen with different thermal conductivity for temperature. In contrast, we observed signs of increased activation after freezing using the CRF protocol, reflected by increased cell surface expression of CD62P, PAC‐1 binding and increased concentration of LDH. Agonist induced expression of a conformational epitope on the GPIIb/IIIa complex and contribution to blood coagulation in an experimental rotational thromboelastometry setup were not statistically different between the groups.

Conclusion

The use of a uncontrolled freezing rate protocol is feasible, creating a platelet product comparable to using a controlled rate freezing equipment during cryopreservation of platelets.

The effect of gamma irradiation on platelet redox state during storage

BACKGROUND

As a method with insignificant adverse effects on in vitro quality of platelet concentrates (PCs), gamma irradiation is applied to abrogate the risk of transfusion-associated graft-vs-host disease in vulnerable recipients. However, there is some evidence of lower posttransfusion responses and proteomic alterations in gamma-irradiated platelets (PLTs), which raises some questions about their quality, safety, and efficacy. Since reactive oxygen species (ROS) are considered as markers of PLT storage lesion (PSL), the study presented here investigated oxidant state in gamma-irradiated PCs.

STUDY DESIGN AND METHODS

PLT-rich plasma PC was split into two bags, one kept as control while other was subjected to gamma irradiation. Within 7 days of storage, the levels of intra-PLT superoxide, H₂ O₂ , mitochondrial ROS, P-selectin expression, and phosphatidylserine (PS) exposure were detected by flow cytometry while intracellular reduced glutathione (GSH), glucose concentration, and lactate dehydrogenase (LDH) activity were measured by enzymocolorimetric method.

RESULTS

GSH decreased, while ROS generation and LDH activity increased, during storage. Gamma irradiation significantly attenuated GSH whereas increased ROS generation in earlier and later stages of storage associated with either P-selectin or PS exposure increments.

CONCLUSION

Gamma irradiation can significantly increase cytosolic ROS generation in two distinct phases, one upon irradiation and another later in longer-stored PCs. While earlier ROS influx seems to be governed by direct effect of irradiation, the second phase of oxidant stress is presumably due to the storage-dependent PLT activation. Intriguingly, these observations were also in line with early P-selectin increments and increased PS exposure in longer-stored PLTs. Given the mutual link between ROS generation and PLT activation, further investigation is required to explore the effect of gamma irradiation on the induction of PSL.

Effect of leukoreduction and pathogen reduction on the hemostatic function of whole blood

BACKGROUND

There is renewed interest in the use of whole blood (WB) for resuscitation of patients in hemorrhagic shock. Leukoreduction with platelet-sparing filters and pathogen reduction may be used to improve the safety profile of WB, yet the effects of leukoreduction and pathogen reduction on WB hemostatic function are not well characterized.

STUDY DESIGN AND METHODS

Blood from 32 healthy group O donors was divided into treatment groups (n = 8 for each group): untreated, pathogen reduced (PR⁺ ), leukoreduced using an in-line filter (LR⁺ ), or PR⁺ LR⁺ . Units were stored without agitation for 21 days between 1° and 6°C, with sampling on days 0 (pre- and post-treatments), 1, 3, 5, 10, 15, and 21 for hemostatic function as assessed by thromboelastometry, thrombin generation, platelet activation factors, and platelet impedance aggregometry.

RESULTS

From day 3 (D3) to D15 of storage, platelet count was reduced in PR⁺ /LR⁺ units compared to PR^- /LR^- units. From D10 to D21 of storage, maximum clot firmness (MCF) was reduced in PR⁺ /LR⁺ units compared to PR^- /LR^- units. From D3 to D21 of storage, platelet aggregation was reduced in PR⁺ /LR⁺ units compared to PR^- /LR^- units. Total thrombin generation was similar in all groups from D0 to D21.

CONCLUSIONS

The combination of LR with a platelet-sparing filter and PR significantly reduces hemostatic function compared to either treatment alone or untreated WB. The clinical consequences of LR and PR of WB in patients with severe bleeding should be examined in trials before both are used in combination in patients.

Haemostatic responsiveness and release of biological response modifiers following cryopreservation of platelets treated with amotosalen and ultraviolet A light

BACKGROUND

Due to the risk of replication of contaminating pathogens, platelets have a limited storage time of 5 days, which can be prolonged to 7 days by the use of pathogen inactivation technologies. Cryopreservation (CP) may be an alternative to permit longer storage periods and increased availability. However, the preparation of platelets can result in secretion of biological response modifiers (BRM), which can cause adverse transfusion reactions in the recipient. We investigated the impact of CP on platelet function and release of BRM in untreated (conventional) and pathogen-inactivated (PI) platelet concentrates.

MATERIALS AND METHODS

Twelve buffy coat-derived platelet units were treated with amotosalen and ultraviolet A light to inactivate pathogens. Twelve untreated units were used as controls. The 24 units were cryopreserved and in vitro variables were analysed before and after CP. The in vitro variables investigated included platelet surface receptors and activation markers by flow cytometry, and coagulation time by viscoelastography. A panel of BRM, including cytokines, was investigated.

RESULTS

CP of both conventional and PI platelets resulted in a significant increase of BRM with similar increases of most of the BRM after CP of conventional and PI platelet concentrates. The increase in some of the BRM correlated significantly with shortened coagulation time, increased P-selectin expression, reduced mitochondrial transmembrane potential, and reduced capacity to respond to stimulation with ADP and collagen.

DISCUSSION

Cryopreservation of both conventional and PI platelets results in secretion of BRM. The increase in some of the BRM correlated with changes in platelet function variables and suggests that BRM release is affected, in part, in a similar way by CP as are changes in platelet function variables. PI with amotosalen and ultraviolet A light in combination with CP did not affect the release of immunomodulatory factors more than CP alone did.

Influence of platelet preparation techniques on in vitro storage quality after psoralen-based photochemical treatment using new processing sets for triple-dose units

BACKGROUND

The INTERCEPT Blood System (IBS) for platelets (PLTs) uses a combination of psoralen and ultraviolet-A light to inactivate pathogens that may contaminate PLT concentrates (PCs). However, no data are available on the quality of IBS-treated PLTs from different apheresis and buffy-coat PC preparation platforms using the new triple storage (TS) set.

STUDY DESIGN AND METHODS

The objective of this study was to evaluate the TS set on three different preparation platforms compared with the large-volume (LV) set, as control. PLT in vitro metabolic and activation parameters were studied over 7 days.

RESULTS

Several statistical differences are observed between the two sets, particularly for pH, oxygen pressure (pO₂ ), carbonic gaz pressure (pCO₂ ), and bicarbonate. The three different preparation techniques influence PLT parameters, and the difference is statistically significant for all the studied parameters, except for pCO₂ . The TS set has the advantage of shorter compound adsorption device time, higher PLT recoveries, and less PLT activation.

CONCLUSION

Results from the measured metabolic parameters and PLT variables obtained from PCs treated by LV and TS sets indicated good PLT function preservation up to 7 days of storage. The in vitro assessment results demonstrated acceptable PLT function for transfusion.

Ultraviolet-Based Pathogen Inactivation Systems: Untangling the Molecular Targets Activated in Platelets

Transfusions of platelets are an important cornerstone of medicine; however, recipients may be subject to risk of adverse events associated with the potential transmission of pathogens, especially bacteria. Pathogen inactivation (PI) technologies based on ultraviolet illumination have been developed in the last decades to mitigate this risk. This review discusses studies of platelet concentrates treated with the current generation of PI technologies to assess their impact on quality, PI capacity, safety, and clinical efficacy. Improved safety seems to come with the cost of reduced platelet functionality, and hence transfusion efficacy. In order to understand these negative impacts in more detail, several molecular analyses have identified signaling pathways linked to platelet function that are altered by PI. Because some of these biochemical alterations are similar to those seen arising in the context of routine platelet storage lesion development occurring during blood bank storage, we lack a complete picture of the contribution of PI treatment to impaired platelet functionality. A model generated using data from currently available publications places the signaling protein kinase p38 as a central player regulating a variety of mechanisms triggered in platelets by PI systems.

Refrigeration, cryopreservation and pathogen inactivation: an updated perspective on platelet storage conditions

Conventional storage of platelet concentrates limits their shelf life to between 5 and 7 days due to the risk of bacterial proliferation and the development of the platelet storage lesion. Cold storage and cryopreservation of platelets may facilitate extension of the shelf life to weeks and years, and may also provide the benefit of being more haemostatically effective than conventionally stored platelets. Further, treatment of platelet concentrates with pathogen inactivation systems reduces bacterial contamination and provides a safeguard against the risk of emerging and re-emerging pathogens. While each of these alternative storage techniques is gaining traction individually, little work has been done to examine the effect of combining treatments in an effort to further improve product safety and minimize wastage. This review aims to discuss the benefits of alternative storage techniques and how they may be combined to alleviate the problems associated with conventional platelet storage.

Pathogen reduction technologies: The pros and cons for platelet transfusion

The transfusion of platelets is essential for diverse pathological conditions associated with thrombocytopenia or platelet disorders. To maintain optimal platelet quality and functions, platelets are stored as platelet concentrates (PCs) at room temperature under continuous agitation-conditions that are permissive for microbial proliferation. In order to reduce these contaminants, pathogen reduction technologies (PRTs) were developed by the pharmaceutical industry and subsequently implemented by blood banks. PRTs rely on chemically induced cross-linking and inactivation of nucleic acids. These technologies were initially introduced for the treatment of plasma and, more recently, for PCs given the absence of a nucleus in platelets. Several studies verified the effectiveness of PRTs to inactivate a broad array of bacteria, viruses, and parasites. However, the safety of PRT-treated platelets has been questioned in other studies, which focused on the impact of PRTs on platelet quality and functions. In this article, we review the literature regarding PRTs, and present the advantages and disadvantages related to their application in platelet transfusion medicine.

Immunomodulation Induced by Stem Cell Mobilization and Harvesting in Healthy Donors: Increased Systemic Osteopontin Levels after Treatment with Granulocyte Colony-Stimulating Factor

Peripheral blood stem cells from healthy donors mobilized by granulocyte colony-stimulating factor (G-CSF) and harvested by leukapheresis are commonly used for allogeneic stem cell transplantation. The frequency of severe graft versus host disease is similar for patients receiving peripheral blood and bone marrow allografts, even though the blood grafts contain more T cells, indicating mobilization-related immunoregulatory effects. The regulatory phosphoprotein osteopontin was quantified in plasma samples from healthy donors before G-CSF treatment, after four days of treatment immediately before and after leukapheresis, and 18–24 h after apheresis. Myeloma patients received chemotherapy, combined with G-CSF, for stem cell mobilization and plasma samples were prepared immediately before, immediately after, and 18–24 h after leukapheresis. G-CSF treatment of healthy stem cell donors increased plasma osteopontin levels, and a further increase was seen immediately after leukapheresis. The pre-apheresis levels were also increased in myeloma patients compared to healthy individuals. Finally, in vivo G-CSF exposure did not alter T cell expression of osteopontin ligand CD44, and in vitro osteopontin exposure induced only small increases in anti-CD3- and anti-CD28-stimulated T cell proliferation. G-CSF treatment, followed by leukapheresis, can increase systemic osteopontin levels, and this effect may contribute to the immunomodulatory effects of G-CSF treatment.

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

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

Tolerance of platelet concentrates treated with UVC-light only for pathogen reduction--a phase I clinical trial

BACKGROUND

The THERAFLEX UV-Platelets pathogen reduction system for platelet concentrates (PCs) operates with ultraviolet C light (UVC; 254 nm) only without addition of photosensitizers. This phase I study evaluated safety and tolerability of autologous UVC-irradiated PCs in healthy volunteers.

METHODS

Eleven volunteers underwent two single (series 1 and 2) and one double apheresis (series 3). PCs were treated with UVC, stored for 48 h and retransfused in a dose-escalation scheme: 12·5, 25% and 50% of a PC (series 1); one complete PC (series 2); two PCs (series 3). Platelet counts, fibrinogen, activated partial thromboplastin time, prothrombin time, D-dimer, standard haematology, temperature, heart rate, blood pressure and clinical chemistry parameters were measured. One- and 24-h corrected count increments were determined in series 2 and 3. Platelet-specific antibodies were assessed before and at the end of the study.

RESULTS

Neither adverse reactions related to transfusions nor antibodies against UVC-treated platelets were observed. Corrected count increments did not differ between series 2 and 3.

CONCLUSIONS

Repeated transfusions of autologous UVC-treated PCs were well tolerated and did not induce antibody responses in all volunteers studied. EudraCT No. 2010-023404-26.

Impact of intraoperatively salvaged and washed blood on stimulated cytokine release in vitro

BACKGROUND

Intraoperative blood salvage and processing it with commercially available devices is a widespread standard procedure to reduce allogeneic blood transfusion in patients undergoing major orthopedic surgery. The aim of this study was to investigate the impact of such processed blood on the immune system by measuring pro- and anti-inflammatory cytokines.

STUDY DESIGN AND METHODS

Salvaged blood from 20 patients undergoing hip arthroplasty was processed with a continuous autotransfusion system. One part of the processed blood was left without further treatment, one part was additionally leukoreduced, one part was irradiated, and one part was separated into its cellular and soluble fraction by centrifugation. Specimens from each part were mixed in vitro with venous blood from the patient in ratios of 3:1, 1:1, and 1:3 and incubated with endotoxin for 24 hours. Tumor necrosis factor (TNF)-α and interleukin (IL)-10 were measured in cell culture supernatants by enzyme-linked immunosorbent assay.

RESULTS

All parts of the salvaged blood were without a significant influence on TNF-α release. In contrast, IL-10 was significantly increased, independently of the admixtured salvaged blood being plain, additionally irradiated, or additionally leukoreduced. This IL-10 increase was also found with the cellular fraction of the plain salvaged blood, whereas the soluble fraction had no influence on IL-10 release.

CONCLUSION

Intraoperative salvaged blood is not immunologically inert. We observed a significant increase in the anti-inflammatory IL-10 response without affecting the proinflammatory TNF-α release. Neither leukofiltration nor gamma irradiation eliminated this effect that was limited only to the cellular fraction of the salvaged blood, suggesting red blood cells to be responsible for the observed immunomodulation.

Hemostatic function and transfusion efficacy of apheresis platelet concentrates treated with gamma irradiation in use for thrombocytopenic patients

BACKGROUND

During the transfusion of blood components, the transfer of allogeneic donor white blood cells (WBCs) can mediate transfusion-associated graft-versus-host disease (TA-GVHD). To minimize the reaction, exposure of blood products to gamma irradiation is currently the standard of care. The aim of our study was to evaluate and compare hemostatic function, transfusion efficacy, and safety of gamma-irradiated single-donor apheresis platelet concentrates (PCs) and of conventional non-irradiated PCs in patients with chemotherapy-induced thrombocytopenia.

METHODS

20 double-dose single-donor leukoreduced PCs were split in two identical units; one was gamma-irradiated with 25 Gy (study arm A) and the other remains non-irradiated (study arm B). Both units were stored under equal conditions. Hematologic patients were randomly assigned to receive gamma-irradiated or conventional non-irradiated PCs. Hemostatic function was evaluated by thrombelastography (TEG). TEG measurements were taken pre transfusion and 1 and 24 h post transfusion. TEG profiles were measured, noting the time to initiate clotting (R), the angle of clot formation (α), and the maximum amplitude (clot strength (MA)). Whole blood samples were collected from these thrombocytopenic patients at 1 and 24 h for PLT count increments (CIs) and corrected count increments (CCIs) with assessments of transfusion efficacy. Time to next PLT transfusion, transfusion requirement of RBCs, active bleeding, and adverse events (AEs), were analyzed.

RESULTS

No differences could be found in hemostatic function parameters (MA, R, and α) between study arms A and B (all p values > 0.096) pre transfusion as well as 1 and 24 h post transfusion. No differences between study arms A and B were observed for mean (± standard deviation (SD)) 1-hour CCI (12.83 ± 6.33 vs. 11.59 ± 5.97) and 24-hour CCI (6.56 ± 4.10 vs. 5.76 ± 4.05). Mean 1-hour CI and 24-hour CI were not significantly different in both study arms (p = 0.254 and p = 0.242 respectively). Median time to the next PC transfusion after study PC was not significantly different between groups: (2.4 vs. 2.2 days, p = 0.767). No differences could be found in transfusion requirement of red blood cells (p = 0.744) between both study arms. There were also no regarding bleeding, adverse events, and acute transfusion reaction(s).

CONCLUSIONS

This study confirms safety of gamma-irradiated PCs for treatment thrombocytopenia. Hemostatic function, transfusion efficacy, bleeding, and safety of single-donor apheresis PCs treated with gamma irradiation versus untreated control PCs are comparable.

A computerized prediction model of hazardous inflammatory platelet transfusion outcomes

Background

Platelet component (PC) transfusion leads occasionally to inflammatory hazards. Certain BRMs that are secreted by the platelets themselves during storage may have some responsibility.

Methodology/Principal Findings

First, we identified non-stochastic arrangements of platelet-secreted BRMs in platelet components that led to acute transfusion reactions (ATRs). These data provide formal clinical evidence that platelets generate secretion profiles under both sterile activation and pathological conditions. We next aimed to predict the risk of hazardous outcomes by establishing statistical models based on the associations of BRMs within the incriminated platelet components and using decision trees. We investigated a large (n = 65) series of ATRs after platelet component transfusions reported through a very homogenous system at one university hospital. Herein, we used a combination of clinical observations, ex vivo and in vitro investigations, and mathematical modeling systems. We calculated the statistical association of a large variety (n = 17) of cytokines, chemokines, and physiologically likely factors with acute inflammatory potential in patients presenting with severe hazards. We then generated an accident prediction model that proved to be dependent on the level (amount) of a given cytokine-like platelet product within the indicated component, e.g., soluble CD40-ligand (>289.5 pg/109 platelets), or the presence of another secreted factor (IL-13, >0). We further modeled the risk of the patient presenting either a febrile non-hemolytic transfusion reaction or an atypical allergic transfusion reaction, depending on the amount of the chemokine MIP-1α (<20.4 or >20.4 pg/109 platelets, respectively).

Conclusions/Significance

This allows the modeling of a policy of risk prevention for severe inflammatory outcomes in PC transfusion.

Removal of biological response modifiers associated with platelet transfusion reactions by columns containing adsorption beads

BACKGROUND

Biological response modifiers (BRMs), such as soluble CD40 ligand (sCD40L); regulated upon activation, normal T-cell expressed, and secreted (RANTES); and transforming growth factor-β1 (TGF-β1), are released from platelets (PLTs) during storage and may trigger adverse effects after PLT transfusion. Although washing PLTs is effective at reducing the level of BRMs and the incidence of transfusion reactions, the washing procedure is time-consuming and may induce PLT activation. Furthermore, some BRMs continue to accumulate during the storage of washed PLTs. A method to remove BRMs using adsorbent columns has not yet been developed.

STUDY DESIGN AND METHODS

We evaluated the ability of columns packed with Selesorb and Liposorber beads, which are both clinically used, to remove BRMs from PLT concentrates (PCs) stored for 5 days. The levels of these BRMs were determined before and after adsorption.

RESULTS

The adsorption columns significantly reduced the levels of RANTES and sCD40L and partially reduced TGF-β1. There were no significant effects on PLT activation, aggregation, morphology, and plasma lactate dehydrogenase (an indicator of PLT lysis) levels, or hypotonic shock response. Adsorption, however, reduced the PLT recovery to approximately 60% of the untreated value.

CONCLUSIONS

This study showed that the levels of BRMs were substantially reduced using columns of clinically available adsorption beads. PLT functions and the quality of PCs were maintained after adsorption. The use of adsorption columns may be useful in reducing the incidence of nonhemolytic transfusion reactions.

Update on the use of pathogen-reduced human plasma and platelet concentrates

The use of pathogen reduction technologies (PRTs) for labile blood components is slowly but steadily increasing. While pathogen-reduced plasma is already used routinely, efficacy and safety concerns impede the widespread use of pathogen-reduced platelets. The supportive and often prophylactic nature of blood component therapy in a variety of clinical situations complicates the clinical evaluation of these novel blood products. However, an increasing body of evidence on the clinical efficacy, safety, cost-benefit ratio and development of novel technologies suggests that pathogen reduction has entered a stage of maturity that could further increase the safety margin in haemotherapy. This review summarizes the clinical evidence on PRTs for plasma and platelet products that are currently licensed or under development.

Cytokine assays: an assessment of the preparation and treatment of blood and tissue samples

Cytokines are key components of the innate and adaptive immune system. As pivotal players in the progression or regression of a pathological process, these molecules provide a window through which diseases can be monitored and can thus act as biomarkers. In order to measure cytokine levels, a plethora of protocols can be applied. These methods include bioassays, protein microarrays, high-performance liquid chromatography (HPLC), sandwich enzyme-linked immunosorbent assay (ELISA), Meso Scale Discovery (MSD) electrochemiluminescence and bead based multiplex immunoassays (MIA). Due to the interaction and activity of cytokines, multiplex immunoassays are at the forefront of cytokine analysis by allowing multiple cytokines to be measured in parallel. However, even with optimized protocols, sample standardization needs to occur before these proteins can optimally act as biomarkers. This review describes various factors influencing the levels of cytokines measured in plasma, serum, dried blood spots and tissue biopsies, focusing on sample collection and handling, long term storage and the repetitive use of samples. By analyzing how each of these factors influences protein levels, it is concluded that samples should be stored at low temperatures in order to maintain cytokine stability. In addition, within a study, sample manipulations should be kept the same, with measurement protocols being chosen for their compatibility with the research in question. By having a clear understanding of what factors influence cytokine levels and how to overcome these technical issues, minimally confounded data can be obtained and cytokines can achieve optimal biomarker activity.

Bidirectional crosstalk between platelets and monocytes initiated by Toll-like receptor: an important step in the early defense against fungal infections?

Monocytes are important in the defense against fungal infections due to their phagocytic and immunoregulatory functions. Platelets also contribute in such immune responses through their release of soluble mediators, including chemokines as well as several other soluble mediators. Both monocytes and platelets express several Toll-like receptors (TLRs) that can recognize fungal molecules and thus initiate intracellular signaling events. TLR ligation on monocytes and platelets may thereby be an early immunological event and function as an initiator of a local proinflammatory crosstalk between platelets and monocytes resulting in (i) monocyte-induced increase of platelet activation and (ii) platelet-associated enhancement of the monocyte activation/function. These effects may have clinical implications both for the efficiency of antifungal treatment and for the predisposition to fungal infections, for example, increased predisposition in patients with thrombocytopenia/monocytopenia due to chemotherapy- or disease-induced bone marrow failure.

Evaluation of the tolerability and immunogenicity of ultraviolet C-irradiated autologous platelets in a dog model

BACKGROUND

The THERAFLEX ultraviolet (UV) platelets (PLTs) pathogen reduction system for PLT concentrates (PCs) operates using ultraviolet C (UVC) light at a wavelength of 254 nm. UVC treatment can potentially alter proteins, which may affect drug tolerance in humans and influence the immunogenicity of blood products. This preclinical study in beagle dogs was designed to evaluate the safety pharmacology of UVC-irradiated PCs after intravenous administration and to determine whether they are capable of eliciting humoral responses to PLTs and plasma proteins.

STUDY DESIGN AND METHODS

Six beagle dogs each were transfused once every other week for 10 weeks with UVC-irradiated or nonirradiated PCs. All PCs were autologous canine single-donor products prepared from whole blood. Safety pharmacology variables were regularly assessed. The impact of UVC irradiation on PLT and plasma proteomes was analyzed by one- and two-dimensional gel electrophoresis. Serum samples were tested for UVC-induced antibodies by Western blot and flow cytometry.

RESULTS

Dogs transfused with UVC-irradiated PCs showed no signs of local or systemic intolerance. Few but significant changes in PLT protein integrity were observed after UVC irradiation. Even after repeated administration of UVC-irradiated PCs, no antibodies against UVC-exposed plasma or PLT proteins were detected.

CONCLUSIONS

Repeated transfusions of autologous UVC-treated PCs were well tolerated in all dogs studied. UVC irradiation did not cause significant plasma or PLT protein modifications capable of inducing specific antibody responses in the dogs. High-resolution proteomics combined with antibody analysis introduces a comprehensive and sensitive method for screening of protein modifications and antibodies specific for pathogen reduction treatment.

Application of reticulated platelets to transfusion management during autologous stem cell transplantation

BACKGROUND

The immature (or reticulated) platelet fraction (IPF) is rich in nucleic acids, especially RNA, and can be used as a predictive factor for platelet recovery in platelet immunomediated consumption or in postchemotherapy myelosuppression. Our aim was to determine if transfusions with IPF-rich solutions, during autologous peripheral blood stem cell transplantation, reduce the occurrence of bleeding and hemorrhagic complications.

PATIENTS AND METHODS

Transfusions were administered to 40 children, affected with hematological pathologies, who underwent autologous peripheral hematopoietic progenitor cell transplantation. There were two groups of 20 patients, one group treated with IPF-poor and the other with IPF-rich solutions. In the two groups, the conditioning regimen was the same for the same pathology (hematological pathologies: 14 acute lymphoblastic leukemia; twelve acute myelocytic leukemia; four non-Hodgkin's lymphoma; two Hodgkin's lymphoma; eight solid tumors). A new automated analyzer was used to quantify the IPF: the XE2100 (Sysmex, Kobe, Japan) blood cell counter with upgraded software.

RESULTS

The 20 patients who received solutions with a high percentage of IPF (3%-9% of total number of infused platelets) required fewer transfusions than the 20 patients who received transfusions with a low percentage of IPF (0%-1% of total number of infused platelets): 83 versus 129 (mean of number of transfusions 4.15 versus 6.45) and a significant difference was found between the two groups by using the Mann-Whitney test (P < 0.001). The prophylactic transfusions decreased from three to two per week. There was only one case of massive hemorrhage.

CONCLUSION

The use of IPF solutions reduces the number of transfusions and bleedings after peripheral blood stem cell transplantation in pediatric patients.

Platelet derived cytokine accumulation in platelet concentrates treated for pathogen reduction

BACKGROUND

Pathogen reduction technologies (PRTs) prevent replication and proliferation of pathogens in platelet (PLT) concentrates (PCs) by modifying nucleic acids. Due to increased cell activation, PRT may also lead to increased cytokine release from α granules and promote adverse transfusion reactions in the recipient.

DESIGN

Fifteen double-dose leukoreduced apheresis PCs were collected on the Trima Accel platform (vs. 5.2.) allowing for the resuspension in PLT additive solution (PAS) immediately after collection. After a 2-h resting period (1st hour without, 2nd hour with agitation), splitting was performed: one unit remained untreated to serve as control (C), while the other was riboflavin-UVB treated using the Mirasol-PRT system according to the manufacturer's instructions (M). During 8 days of storage, PCs were analyzed for contaminating white and red blood cells, bacterial growth, PLT activation, LDH and cytokine release (MIP-1 α, RANTES, PF4, and TGF-β-1). Results obtained were opposed to a former study, where triple-dose PCs underwent Mirasol-PRT prior to resuspension or the INTERCEPT BLOOD SYSTEM (psoralen-UVA) or remained untreated.

RESULTS

Despite similar LDH release, PRT treatment was associated with significantly higher (p<0.05) cell activation but only slightly higher cytokine accumulation during storage. Differences became significant only for PF4 and RANTES at day 8 of storage. On the other hand, in the investigation on triple-dose PCs (yielding higher cytokine levels), TGF beta-1 and RANTES remained significantly (p<0.05) lower after PRT treatment compared to untreated units.

CONCLUSION

Factors, such as collection modality, onset of resuspension and additional amounts of magnesium/potassium in the PAS used may be of equal or even greater impact for cytokine accumulation in stored PCs than PRT treatment.

Platelet storage and transfusions: new concerns associated with an old therapy

Platelet transfusion has long been practiced with rudimentary knowledge about optimal storage conditions and their implications for efficacy and, particularly, safety. Recent concerns about complications such as inflammation, thrombosis and altered recipient immunity have been raised about platelet transfusion. This review will discuss recent important findings that have raised these issues about platelet transfusion associated morbidity, mortality and the possible role of platelet storage in these associations.

[Pathogen reduction for platelets: available techniques and recent developments]

The will to reach for blood components a microbiological safety comparable to that of plasma-derived drugs led to the development of numerous pathogen reduction research programs for red blood cells and\or platelets in the 1990s. A consensus conference organized in 2007 allowed to define the main steps and precautions to be taken for the implementation of these processes. In the specific case of platelet concentrates, three processes stay this day in the run, even if they are not at the same development stage. A process using ultraviolet C only is at the stage of preclinical studies. The Mirasol® process, based on the activation of riboflavin by exposure to ultraviolet A and ultraviolet B is CE marked (class IIb), and a clinical study was published in 2010. The Intercept® process, involving the activation of a psoralen molecule by exposure to ultraviolet A, is CE marked (class III) since 2002, and has been licensed in France since 2005, in Germany since 2005 and in Switzerland since 2010. At least 12 clinical studies have been published. In regard to this last pathogen reduction process, the medical and scientific documentation, from in vitro investigations to post-marketing observational studies, is much more developed than the corresponding documentation of some innovative processes at the time of their generalization, such as the SAG-mannitol solution for red cell concentrates in 1979, leukoreduction filters for platelets and red cells concentrates in the 1990s, the solvent detergent therapeutic plasma in 1992 or the methylene blue therapeutic plasma in 2006.

Current practice and future directions for optimization of platelet transfusions in patients with severe therapy-induced cytopenia

Platelet transfusions are mainly used for patients with thrombocytopenia due to bone marrow failure, especially cancer patients developing severe chemotherapy-induced thrombocytopenia (e.g. patients with acute leukemia or other hematologic malignancies). A prophylactic transfusion strategy is now generally accepted in developed countries. Some clinical data, however, support the use of a therapeutic transfusion strategy at least for certain subsets of these patients. Several methodological approaches can then be used to evaluate the outcome of platelet transfusions, including peripheral blood platelet increments and bleeding assessments. Several factors will influence the efficiency of platelet transfusions; fever and ongoing hemorrhage are among the most important patient-dependent factors, but the number and quality of the transfused platelets are also important. The quality of transfused platelets can be evaluated by analyzing platelet activation, metabolism or senescence/apoptosis. Only evaluation of metabolism is included in international guidelines, but high-throughput methods for evaluation of activation and senescence/apoptosis are available and should be incorporated into routine clinical practice if future studies demonstrate that they reflect clinically relevant platelet characteristics. Finally, platelet transfusions have additional biological effects that may cause immunomodulation or altered angioregulation; at present it is not known whether these effects will influence the long-time prognosis of cancer patients. Thus, several questions with regard to the optimal use of platelet transfusions in cancer patients still need to be answered.

Immunomodulatory mediators in platelet transfusion reactions

Our appreciation of the roles that platelets play in vascular biology is constantly expanding. One of the major roles of platelets is in initiating and accelerating immune responses. Platelet transfusion may be associated with adverse inflammatory outcomes manifested as fever, discomfort, tachycardia, and respiratory issues. This may in part be due to immune mediators either expressed by activated platelets or released into the platelet media during platelet storage. This review will highlight some more recent knowledge gained regarding the platelet storage lesion and potential mediators of platelet transfusion reactions.

Inactivation of human white blood cells in platelet products after pathogen reduction technology treatment in comparison to gamma irradiation

BACKGROUND

During the transfusion of blood products, the transfer of allogeneic donor white blood cells (WBCs) can mediate adverse reactions in recipients. To minimize reactions, blood components are leukoreduced and/or exposed to gamma irradiation. Nucleic acid-targeted pathogen reduction technologies (PRTs) processes are well suited for WBC inactivation. The Mirasol PRT system (CaridianBCT Biotechnologies) uses riboflavin and ultraviolet light to reduce the active pathogen load and inactivate residual WBCs in blood products used for transfusion. The aim of this study was to compare the effect of PRT treatment to gamma irradiation.

MATERIALS AND METHODS

WBCs were resuspended in 100% plasma or in plasma containing 65% platelet additive solution (SSP+). A single product was split into three aliquots: control, PRT treatment, or gamma irradiation. After treatment, peripheral blood mononuclear cells were isolated from products, and cell viability and functionality were assessed in limiting dilution assays (LDAs), by CD69 expression, by proliferation, and by cytokine accumulation after lipopolysaccharide addition.

RESULTS

PRT treatment and gamma irradiation reduced the ability of the T cells to proliferate by similar degrees as evidenced by a 6 log or greater reduction in the LDA and a lack of response to several stimuli. However, gamma-irradiated T cells were still capable of up regulating surface CD69, inducing a proliferative response in allogeneic responder cells, and producing levels of proinflammatory cytokines similar to those of untreated control cells, responses that PRT-treated T cells were incapable of mediating.

CONCLUSIONS

These in vitro results demonstrate that PRT treatment is more effective than gamma irradiation at abrogating selected WBC immune functions.

The Mirasol Pathogen Reduction Technology system and quality of platelets stored in platelet additive solution

BACKGROUND

The Mirasol Pathogen Reduction Technology system for platelets and plasma uses riboflavin and UV light to introduce irreparable lesions into nucleic acids thereby inhibiting pathogen and white blood cell replication and reducing the load of infectious pathogens. The aim of the present study was to evaluate low plasma buffy coat platelet concentrates obtained from the OrbiSac System and to examine the effects on the development of platelet storage lesion during storage in platelet additive solution.

MATERIAL AND METHODS

Twenty buffy coat platelet concentrates were generated by pooling five individual units using the OrbiSac System. Riboflavin was added during the final pooling step, and the units were exposed to UV light. The bag was removed after the target energy of 6.24 J/mL had been delivered and 150 mL of platelet additive solution were added prior to storage. Platelet quality was assessed by pH, swirl, CD62P expression, lactate dehydrogenase, lactate production and glucose consumption rates over 7 days of storage.

RESULTS

Buffy coat platelet concentrates generated on the OrbiSac contained an average 3.5 +/- 0.6 x 10(11) platelets at a concentration of 2976+/- 406 x 10(6)/mL. After addition of 150 mL platelet additive solution the storage concentration was 1043 +/- 148x 10(6)/mL. Values obtained for pH, lactate production and glucose consumption rates were all within the limits of previously established correlations between in vitro cell quality and in vivo performance of Pathogen Reduction Technology-treated platelets in plasma.

DISCUSSION

In vitro studies show that OrbiSac-derived platelets treated with the Mirasol Pathogen Reduction Technology system preserve adequate function, which would indicate acceptable in vitro viability.

Removal by adsorbent beads of biological response modifiers released from platelets, accumulated during storage, and potentially associated with platelet transfusion reactions

BACKGROUND

Recent studies have demonstrated that biological response modifiers (BRMs) released from platelets (PLTs) during storage may have a clinical significance in PLT transfusion reactions. Washing PLTs and partial substitution of plasma with artificial solutions reduce transfusion reactions, but the washing procedure is time-consuming, and partial plasma substitution is not sufficient to completely eliminate transfusion reactions.

STUDY DESIGN AND METHODS

This study determined the levels of three BRMs: soluble CD40 ligand (sCD40L); regulated upon activation, normal T-cell expressed, and secreted (RANTES, CCL5); and transforming growth factor-beta1 (TGF-beta1). These BRMs were released from PLTs during storage up to Day 10. To selectively remove these BRMs, four types of cellulose beads were investigated. The levels of these three BRMs in plasma derived from PLT concentrates (PCs) stored for 10 days or in PCs stored for 5 days were determined after treatment with or without each adsorbent bead for 3 hours.

RESULTS

These three BRMs accumulated in proportion to the storage duration. The 3-hour treatment with cellulose beads possessing sulfate ester groups (A) or phosphate ester groups (B) effectively removed sCD40L and RANTES and partly removed TGF-beta1. In addition, although PLT activation was minimally induced, PLT counts decreased by approximately 13% to 30%, after these treatments.

CONCLUSIONS

This study revealed that Cellulose Beads A or B are effective in removing the three BRMs that accumulate during PLT storage. Additional in vitro assays and in vivo studies are required to evaluate whether this method is effective in reducing transfusion reactions.

Impact of platelets and fresh frozen plasma in contrast to red cell concentrate on unstimulated and stimulated cytokine release in an in vitro model of transfusion

Transfusion of blood may contribute to immunomodulation. Leuco-depleted standard blood products are supposed to result in less immunomodulation compared with whole blood. To determine the influence of leuco-depleted blood products on the cytokine response, red blood cell concentrates (RBC), fresh frozen plasma (FFP) and platelet concentrates (PC) were investigated in an in vitro model of blood transfusion. Leuco-depleted standard blood bank RBC, FFP and PC were mixed in vitro with AB0 compatible venous blood from healthy volunteers in ratios of 3:1, 1:1 and 1:3. Specimens were incubated in presence or absence of lipopolysaccharide, 1 mug/ml. After 24 h of incubation cytokine release of tumour necrosis factor (TNF)-alpha and interleukin-10 (IL-10) was measured in cell culture supernatants by means of enzyme-linked immunsorbent assay. Addition of RBC, FFP and PC to venous blood from healthy volunteers led to a significant and dose-dependent increase in spontaneous TNF-alpha and IL-10 release. After endotoxin stimulation, RBC, FFP and PC significantly suppressed the TNF-alpha response, while the stimulated release of IL-10 tended to increase, reaching significance only after high doses of FFP. Addition of leuco-depleted blood products changed the spontaneous and stimulated cytokine response in an in vitro model of transfusion. These data may suggest a possible contribution of transfused FFP and PC to immunomodulation after transfusion similar to RBC.

Microarray kit analysis of cytokines in blood product units and segments

BACKGROUND

Cytokine concentrations in transfused blood components are of interest for some clinical trials. It is not always possible to process samples of transfused components quickly after their administration. Additionally, it is not practical to sample material in an acceptable manner from many bags of components before transfusion, and after transfusion, the only representative remaining fluid of the component may be that in the "segment," because the bag may have been completely transfused. Multiplex array technology allows rapid simultaneous testing of multiple analytes in small-volume samples. This technology was used to measure white blood cell (WBC) cytokine levels in blood products to determine 1) whether concentrations in segments correlate with those in the main bag and, thus, whether segments could be used for estimation of the concentrations in the transfused component and 2) whether concentrations after sample storage at 4 degrees C for 24 hours do not differ from concentrations before storage, thus allowing for processing within 24 hours, rather than immediately after transfusion.

STUDY DESIGN AND METHODS

WBC cytokines were measured in the supernatant from bags and segments of leukoreduced red blood cells (RBCs), nonleukoreduced whole blood, and leukoreduced plateletphereses using a human cytokine array kit (ProteoPlex, Novagen).

RESULTS

Cytokine concentrations in RBCs and whole blood or plateletphereses stored at 4 degrees C did not differ between bag and segment samples (all p > 0.05). There was no evidence of systematic differences between segment and bag concentrations. Cytokine concentrations in samples from plateletphereses did not change within 24 hours storage at 4 degrees C.

CONCLUSION

Samples from either bag or segment can be used to study cytokine concentrations in groups of blood products. Cytokine concentrations in plateletphereses appear to be stable for at least 24 hours of storage at 4 degrees C and, thus, samples stored with those conditions may be used to estimate the cytokine concentrations of the component at the time of transfusion.

[Platelet immunology and the immune response]

Platelets exert not only hemostatic activities, but also pro-inflammatory effects. Platelet-linked inflammation seems essentially related to their capacity of secreting cytokines, chemokines and related molecules. This activity is important in terms of concentration of secreted products. This secretory function confers to platelets a regulatory role in immunity. Besides, platelets do exhibit non-self infectious danger detection molecules on their surfaces, belonging in particular to the "Toll-like receptor family"; through this property, platelets can bind infectious agents but also deliver differential signals for the secretion of cytokines and chemokines. Platelets, which are non-nucleated cells deprived of nuclear DNA, possess however some cellular machinery which permits intracellular signalling and even the production of RNA transcripts for certain cytokines. Last, platelets express variant surface determinants of hemostatic molecules (referred to as HPA antigens) along with HLA class I variant molecules, the function of which on platelets is still unknown. An intriguing question is to reconcile those diverse properties and to understand whether the pro-inflammatory secretory process can affect the immunogenicity of transfused, allogeneic, platelet components.

Evaluation of White Blood Cell- and Platelet-Derived Cytokine Accumulation in MIRASOL-PRT-Treated Platelets

BACKGROUND: Soluble mediators in platelet concentrates (PCs) released from contaminating white blood cells (WBCs) and platelets (PLTs) themselves are supposed to promote allergic and non-hemolytic febrile transfusion reactions in the recipient. Pathogen reduction technologies (PRTs) prevent replication and proliferation of pathogens as well as of WBCs, and may reduce cytokine accumulation in PCs during storage and prevent adverse events after PLT transfusion. On the other hand, such treatments may also lead to increased cytokine production by stimulation of WBCs or PLTs due to the photochemical or photodynamical process itself. MATERIAL AND METHODS: 12 triple-dose PLT apheresis collections were leukoreduced by the process-controlled leukoreduction system of the Trima Accel machine and split into 3 units undergoing Mirasol-PRT treatment (M) or gamma irradiation (X) or remaining untreated (C). During storage for up to 7 days, PLT activation, WBC-derived Th-1/2, and inflammatory as well as PLT-derived cytokines were measured by cytometric bead array and enzymelinked immunosorbent assay, respectively. RESULTS: Independent of treatment, all PLT products exhibited low levels of WBC-associated cytokines near or below assay detection limits. WBC-associated cytokines were not elevated by Mirasol-PRT treatment. PLT-derived cytokines were detected at higher levels and increased significantly during storage in all units. Most likely due to higher PLT activation, M units showed significantly higher levels of PLT-derived cytokines compared to untreated and gamma-irradiated units on day 5 of storage. CONCLUSION: In all PCs, PLTs themselves were the main source of cytokine release. Mirasol-PRT treatment was associated with a significantly increased PLT activation and accumulation of PLT-derived cytokines during storage, without affecting WBC-derived cytokines relative to controls.

[Platelets "Toll-like receptor" engagement stimulates the release of immunomodulating molecules]

Platelets are nonnucleated cellular elements that play a role in the process of haemostasis, and also in various ways in innate immunity and in inflammation. Platelets also contain numerous secretory products and can exert critical roles in several aspects of haemostasis. In addition, they house and secrete a variety of cytokines, chemokines and associated molecules which behave as ligands for receptors/counterparts displayed by endothelial cells lining tissue vessels and most leukocyte subsets. These latter studies show that platelets have an important role in innate as well as adaptive immunity; thus platelets can take part in an immune directive response. Moreover, platelets display receptors for several types of cytokines/chemokines along with FcgammaRII receptors. Finally, platelets not only express a variety of Toll-like receptors, with recently identified functions or not as-yet fully identified, but have also been demonstrated to express the key tandem pair of inflammatory and antigen presentation molecules (CD40 and CD40-ligand/CD154), this latter function making them the major purveyors of soluble CD40L in the plasma. It appears that platelets may be regarded as one of the neglected components of immune cell regulators, and platelets contribute to some interesting aspects in bridging innate and adaptive immunity. We propose that platelets discriminate danger signals and adapt the subsequent responses, with polarized cytokine secretion. Platelets may recognize several types of infectious pathogens and limit microbial colonization by sequestering these pathogens and releasing immunomodulatory factors. This review allows us to re-explore indications that platelets exert direct anti-infection immunity and we will present experimentally-driven arguments in favour of a role of platelet TLR in regulating certain immune activities.

Donor platelets stored for at least 3 days can elicit activation marker expression by the recipient's blood mononuclear cells: an in vitro study

BACKGROUND

Recent studies have demonstrated that infused platelets (PLTs) can promote inflammation. The objective of this study was to evaluate the impact of storage of transfusion-grade PLTs on the peripheral blood mononuclear cells (PBMNCs) of the recipient.

STUDY DESIGN AND METHODS

An in vitro cell model system was established to measure the degree of activation of donor PLTs during 5 days of their storage and then to measure immune cell activation by detecting marker expression in coculture experiments.

RESULTS

The level of soluble CD62p increased significantly by Day 3, and membrane expression of CD62p increased significantly from Day 2, indicating some degree of PLT activation over time during storage (p < 0.05). Donor PLTs and PBMNC subsets (monocytes, B cells, and T cells) from recipients were cocultured for 48 hours. The number of PLT-PBMNC subset doublets detected by flow cytometry was correlated with the PLT storage time after Day 3 (p < 0.05), indicating consistent binding of PLTs to PBMNCs. The results of these experiments showed that there was a consistent and significant increase in expression of conventional activation markers of T cells, B cells, and monocytes compared with appropriate controls (p < 0.05 to <0.01).

CONCLUSION

The results of this study indicate that, from Day 3 onward, activation markers are consistently expressed on PLTs. From these results, we conclude that activated PLTs may affect PBMNC interactions in recipients.