Characterization of glycoprotein IIb/IIIa-specific alloantibodies induced by cross-strain platelet immunization in mice.

BACKGROUND: We previously described a mouse model in which platelet immunization between selected strains leads to production of alloantibodies and severe autoimmune thrombocytopenia and mimics the human condition posttransfusion purpura (PTP). This report describes studies defining epitopes recognized by these alloantibodies. STUDY DESIGN: Hybridomas were produced from spleen cells of immunized mice. Glycoprotein (GP) targets of resulting monoclonal antibodies were characterized by immunoprecipitation using platelets from the immunizing strains. Antigens defined by single amino acid (AA) polymorphisms recognized by monoclonal antibodies were identified by mutagenizing target glycoproteins expressed in Chinese hamster ovary cells and observing the effects on antibody binding. RESULTS: Three monoclonal antibodies (417.1, 417.3, 425.1) were produced that recognized GPIIb on immunizing platelets. Monoclonal antibodies 417.1 and 417.3 both required G111 and 425.1 required V37, located on the beta propeller domain of GPIIb, for binding to platelets from the immunizing strains C57 and PWK, respectively. Injection of 417.3 and 425.1 into mice caused platelet destruction only in mice with GPIIb containing the targeted AAs. CONCLUSIONS: Findings made provide evidence that alloantibodies produced by mice experiencing thrombocytopenia in a mouse model of PTP are specific for single AA polymorphisms that differ in GPIIb/IIIa integrin of the immunizing and immunized strains and therefore closely resemble the potent alloantibodies found in patients with PTP. The observations show that naturally occurring single AA differences in GPIIb/IIIa integrin of various mouse strains are highly immunogenic in the mouse strains studied and readily induce antibodies comparable to human platelet antigen-specific antibodies found in transfused and pregnant humans.

Vincristine-loaded platelets coated with anti-CD41 mAbs: a new macrophage targeting proposal for the treatment of immune thrombocytopenia.

Immune thrombocytopenia (ITP) is an autoimmune disorder in which platelet-reactive autoantibodies accelerate the destruction of platelets. Macrophages play an important role in ITP through Fc receptor (FcR)-mediated antigen presenting and platelet clearance. In this study, a novel drug delivery system of vincristine-loaded platelets coated with anti-CD41 mAbs (CD41-VCR-PLT, CD41-VLP) was successfully established. The therapeutic effects and safety of CD41-VLP in vitro and in vivo were evaluated, and the possible mechanism was also explored. The results showed that PLT-CD41 could load VCR with high drug loading (DL) and encapsulation efficiency (EE), which were up to 41.16 ± 1.92% and 60.73 ± 2.79%, respectively, where platelets had no obvious morphological or functional changes. CD41-VLP could facilitate vincristine accumulation in macrophages, where the intracellular VCR concentration was 30.72 ± 3.11% at 72 h, which was significantly increased compared with the other groups (P < 0.01), thus inhibiting macrophage cell viability and inducing apoptosis. The cell viability inhibition rate and total apoptosis rate were 73.06 ± 5.26% and 69.70 ± 4.26%, respectively, both much higher than those of the other groups (P < 0.05). In the ITP mouse model, CD41-VLP increased the platelet count in peripheral blood, which was 720 ± 197.98 × 109 L-1, and significantly improved the platelet count compared with that in the VCR group (P < 0.05); moreover, it reduced the systemic toxicity and peripheral neurotoxicity of vincristine. The possible mechanism was that CD41-VLP could precisely target M1 macrophages in spleen and liver tissues through FcγR, thus reducing the platelet destruction caused by M1 macrophages. Therefore, CD41-VLP provides a new targeted therapy for ITP treatment.

Novel Murine Model of Immune Thrombocytopaenia through Immunized CD41 Knockout Mice.

Immune thrombocytopaenia (ITP) is the most common autoimmune bleeding disorder, where platelets are destroyed by auto-antibodies and/or cell-mediated mechanisms. To understand the pathogenesis of ITP and explore novel therapeutics, three types of animal models have been used: passive ITP, secondary ITP and platelet-induced ITP. However, the first two are not ideal for chronic ITP pathophysiology where both T cell and B cell play important roles in platelet destruction. The most efficient model to mimic chronic ITP is developed by Chow et al through transferring splenocytes from platelet-immune CD61-knockout (KO) mice into mice with severe combined immunodeficiency (SCID). However, placental defects are evident in 25% of CD61-KO females and post-natal haemorrhage does occur, reducing the survival rate of embryos and pups. Compared with CD61-KO mice, CD41-KO ones do not present such problems. In our study, we employ CD41-KO mice as another source of immunized spleen cells. We evaluated our model with existing standards. Transferred SCID mice presented typical features of ITP, such as reduced platelet counts in the peripheral blood, increased anti-platelet antibody levels in the serum and reduced mature megakaryocytes in the bone marrow. What is more, lymphocyte-depletion experiments showed the role of CD8+ T cells in mature megakaryocyte decrease and thrombocytopaenia. And we confirmed the antibody-mediated platelet destruction by phagocytosis in the spleen. Our study develops another efficient murine ITP model through immunized CD41-KO mice.

Autoantibody against integrin αv ß3 contributes to thrombocytopenia by blocking the migration and adhesion of megakaryocytes.

Essentials The pathogenesis of immune thrombocytopenia (ITP) has not been fully clarified. We analyzed the role of anti-αvß3 autoantibody in the pathogenesis of ITP in patients. Anti-αvß3 autoantibody impeded megakaryocyte migration and adhesion to the vascular niche. Anti-αv ß3 autoantibody potentially contributes to the pathogenesis of refractory ITP. SUMMARY: Background The pathogenesis of immune thrombocytopenia (ITP) has not been fully clarified. Anti-αvß3 integrin autoantibody is detected in chronic ITP patients, but its contribution to ITP is still unclear. Objectives To clarify the potential role of anti-αvß3 integrin autoantibody in chronic ITP and the related mechanism. Methods Relationship between levels of anti-αvß3 autoantibody and platelets in chronic ITP patients was evaluated. The influence of anti-αvß3 antibody on megakaryocyte (MK) survival, differentiation, migration and adhesion was assessed, and the associated signal pathways were investigated. Platelet recovery and MKs' distribution were observed in an ITP mouse model pretreated with different antibodies. Result In this study, we showed that the anti-αvß3 autoantibody usually coexists with anti-αIIbß3 autoantibody in chronic ITP patients, and patients with both autoantibodies have lower platelets. In in vitro studies, we showed that the anti-αvß3 antibody had no significant effect on the survival and proliferation of MKs, whereas it decreased formations of proplatelet significantly. Anti-αvß3 antibody impeded stromal cell derived facor-1 alpha (SDF-1α)- mediated migration and inhibited the phosphorylation of protein kinase B. Anti-αvß3 antibody significantly inhibited MKs' adhesion to endothelial cells and Fibrogen. The phosphorylation of focal adhesion kinase and proto-oncogene tyrosine-protein kinase Src induced by adhesion was inhibited when MKs were pretreated with anti-αvß3 antibody. In in vivo studies, we showed that injection with anti-αv antibody delayed platelet recovery in a mouse model of ITP. Conclusions These findings demonstrate that the autoantibody against integrin αv ß3 may aggravate thrombocytopenia in ITP patients by impeding MK migration and adhesion to the vascular niche, which provides new insights into the pathogenesis of ITP.

Icaritin Improves Antibody-Induced Thrombocytopenia in a Mouse Model by Regulating T-cell Polarization.

Previous studies have shown that icaritin (ICT) has significant protective effects on immune thrombocytopenia (ITP), and the present study aimed to discuss the mechanism of this protective effect from the aspect of regulating T-cell polarization by an antibody-induced ITP mice model. Mice were given rat anti-mouse CD41 antibody (MWReg30) by intraperitoneal injection for 7 d to produce ITP model. At the same time, ICT was administrated at 10 mg/kg/d orally for 9 d. Peripheral blood platelets were counted by hematology analyzer. Spleen index was also tested. Spleen T-helper cell (Th), cytotoxic T-cell (CTL), Th1, Th2, Th17, regulatory T-cell (Treg), and follicular helper T-cell (Tfh) were quantified by flow cytometry. Serum Th1/Th2/Th17 cytokines were tested by mouse Th1/Th2/Th17 cytometric bead array (CBA) kit and transforming growth factor beta (TGF-ß) were analyzed by enzyme-linked immunosorbent assay (ELISA) kit. The results indicated that ICT (10 mg/kg) protected against MWReg30-induced ITP, as evidenced by increased blood platelets and decreased spleen index. In addition, the imbalance of Th/CTL in ITP mice spleen was regulated by ICT. Meanwhile, ICT inhibited Th1, Th17, and Tfh and improved Th2 and Treg in ITP mice spleen. Furthermore, the results of CBA and ELISA suggested that ICT decreased serum Th1- and Th17-related cytokines and increased Th2 cytokines, as well as promoted the release of TGF-ß. These results demonstrated that the protective effect of ICT on ITP was mediated by regulating T-cell polarization.

Mouse Models for Immune-Mediated Platelet Destruction or Immune Thrombocytopenia (ITP).

Immune thrombocytopenia (ITP) is a debilitating, life-threatening autoimmune disorder affecting more than 4 in every 100,000 adults annually, stemming from the production of antiplatelet antibody resulting in accelerated platelet destruction and thrombocytopenia. Numerous animal models of ITP have been developed that contributed to the basic understanding of the underlying mechanisms of ITP onset, progression, and maintenance. Rodent models that develop ITP spontaneously, or by passive transfer of an antiplatelet sera or antibody, play an instrumental role in the investigation of ITP mechanisms responsible for the breakdown of tolerance in human ITP, in studies of the immunopathology underlying the progression of platelet destruction, and in elucidation of the mechanisms of therapeutic amelioration of ITP by existing and new therapeutic modalities. This unit captures the protocols for the implementation and readout of passive antibody transfer mouse models of ITP, established by the infusion of a commercially-available monoclonal rat anti-mouse CD41 platelet antibody.

Integrin-Alpha IIb Identifies Murine Lymph Node Lymphatic Endothelial Cells Responsive to RANKL.

Microenvironment and activation signals likely imprint heterogeneity in the lymphatic endothelial cell (LEC) population. Particularly LECs of secondary lymphoid organs are exposed to different cell types and immune stimuli. However, our understanding of the nature of LEC activation signals and their cell source within the secondary lymphoid organ in the steady state remains incomplete. Here we show that integrin alpha 2b (ITGA2b), known to be carried by platelets, megakaryocytes and hematopoietic progenitors, is expressed by a lymph node subset of LECs, residing in medullary, cortical and subcapsular sinuses. In the subcapsular sinus, the floor but not the ceiling layer expresses the integrin, being excluded from ACKR4+ LECs but overlapping with MAdCAM-1 expression. ITGA2b expression increases in response to immunization, raising the possibility that heterogeneous ITGA2b levels reflect variation in exposure to activation signals. We show that alterations of the level of receptor activator of NF-κB ligand (RANKL), by overexpression, neutralization or deletion from stromal marginal reticular cells, affected the proportion of ITGA2b+ LECs. Lymph node LECs but not peripheral LECs express RANK. In addition, we found that lymphotoxin-ß receptor signaling likewise regulated the proportion of ITGA2b+ LECs. These findings demonstrate that stromal reticular cells activate LECs via RANKL and support the action of hematopoietic cell-derived lymphotoxin.

Alloantibody against new platelet alloantigen (Lap(a)) on glycoprotein IIb is responsible for a case of fetal and neonatal alloimmune thrombocytopenia.

BACKGROUND: Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is caused by the destruction of platelets (PLTs) in the fetus or newborn by maternal PLT antibodies that crossed the placenta during pregnancy. STUDY DESIGN AND METHODS: In this study, we aim to elucidate the properties of a new PLT alloantigen (Lap(a)) that is associated with a severe case of FNAIT. Analysis of maternal serum with phenotyped PLTs by monoclonal antibody-specific immobilization of platelet antigens showed positive reaction against PLT glycoprotein (GP)IIb/IIIa and HLA Class I expressed on paternal PLTs. RESULTS: In contrast to GPIIIa-reactive anti-HPA-1a, anti-Lap(a) alloantibodies precipitated predominantly GPIIb. Indeed, a point mutation G>C at Position 2511 located in Exon 25 of the ITGA2B gene was found in Lap(a)-positive donors. This mutation causes an amino exchange Gln>His at Position 806 located in the calf-2 domain of GPIIb. Lap(a)-positive individuals were not found in 300 random blood donors. Our expression study showed that anti-Lap(a) alloantibodies reacted with stable transfected HEK293 cells expressing the mutated GPIIb isoform (His806). CHO cells carrying this isoform, however, failed to react with anti-Lap(a) alloantibodies, indicating that Lap(a) epitopes depend on the Gln806 His mutation and the carbohydrate composition of the GPIIb. This mutation did not hamper the binding of anti-HPA-3a, which recognizes a point mutation (Ile843 Ser) located in calf-2 domain. Finally, we found that Lap(a) and some HPA-3a epitopes are sensitive to O-glycanase. CONCLUSIONS: This study not only underlines the relevance of rare HPAs on the pathomechanism of FNAIT, but also helps to understand the pitfalls of serologic assays to detect anti-GPIIb alloantibodies.

Cellular characterization of thrombocytes in Xenopus laevis with specific monoclonal antibodies.

Platelets are produced from megakaryocytes (MKs) in the bone marrow. In contrast, most nonmammalian vertebrates have nucleated and spindle-shaped thrombocytes instead of platelets in their circulatory systems, and the presence of MKs as thrombocyte progenitors has not been verified. In developing a new animal model in adult African clawed frog (Xenopus laevis), we needed to distinguish nucleated thrombocytes and their progenitors from other blood cells, because the cellular morphology of activated thrombocytes resembles lymphocytes and other cells. We initially generated two monoclonal antibodies, T5 and T12, to X. laevis thrombocytes. Whereas T5 recognized both thrombocytes and leukocytes, T12 specifically reacted to spindle-shaped thrombocytes. The T12(+) thrombocytes displayed much higher DNA ploidy than nucleated erythrocytes, and they expressed CD41 and Fli-1. In the presence of CaCl2, adenosine diphosphate, thrombin, or various collagens, T12(+) thrombocytes exhibited aggregation. These thrombocytes were located predominantly in the hepatic sinusoids and the splenic red pulp, suggesting that both organs are the sites of thrombopoiesis. Notably, circulating thrombocytes exhibited lower DNA ploidy than hepatic thrombocytes. Intraperitoneal administration of T12 produced immune thrombocytopenia in frogs, which reached a nadir 4 days postinjection, followed by recovery, suggesting that humoral regulation maintained the number of circulating thrombocytes. Although differences between MKs and thrombocytes in X. laevis remain to be defined, our results provide further insight into MK development and thrombopoiesis in vertebrates.

Identification of CDCA1-derived long peptides bearing both CD4+ and CD8+ T-cell epitopes: CDCA1-specific CD4+ T-cell immunity in cancer patients.

We recently identified a novel cancer-testis antigen, cell division cycle associated 1 (CDCA1) using genome-wide cDNA microarray analysis, and CDCA1-derived cytotoxic T lymphocyte (CTL)-epitopes. In this study, we attempted to identify CDCA1-derived long peptides (LPs) that induce both CD4+ helper T (Th) cells and CTLs. We combined information from a recently developed computer algorithm predicting HLA class II-binding peptides with CDCA1-derived CTL-epitope sequences presented by HLA-A2 (A*02:01) or HLA-A24 (A*24:02) to select candidate CDCA1-LPs encompassing both Th cell epitopes and CTL-epitopes. We studied the immunogenicity of CDCA1-LPs and the cross-priming potential of LPs bearing CTL-epitopes in both human in vitro and HLA-class I transgenic mice in vivo. Then we analyzed the Th cell response to CDCA1 in head-and-neck cancer (HNC) patients before and after vaccination with a CDCA1-derived CTL-epitope peptide using IFN-γ enzyme-linked immunospot assays. We identified two CDCA1-LPs, CDCA1(39­64)-LP and CDCA1(55­78)-LP, which encompass naturally processed epitopes recognized by Th cells and CTLs. CDCA1-specific CTLs were induced through cross-presentation of CDCA1-LPs in vitro and in vivo. In addition, CDCA1-specific Th cells enhanced induction of CDCA1-specific CTLs. Furthermore, significant frequencies of CDCA1-specific Th cell responses were detected after short-term in vitro stimulation of peripheral blood mononuclear cells (PBMCs) with CDCA1-LPs in HNC patients (CDCA1(39­64)-LP, 74%; CDCA1(55­78)-LP, 68%), but not in healthy donors. These are the first results demonstrating the presence of CDCA1-specific Th cell responses in HNC patients and underline the possible utility of CDCA1-LPs for propagation of both CDCA1-specific Th cells and CTLs.

CD41 is a reliable identification and activation marker for murine basophils in the steady state and during helminth and malarial infections.

Basophils, a rare leukocyte population in peripheral circulation, are conventionally identified as CD45(int) CD49b(+) FcεRI(+) cells. Here, we show that basophils from blood and several organs of naïve wild-type mice express CD41, the α subunit of α(IIb)ß3 integrin. CD41 expression on basophils is upregulated after in vivo IL-3 treatment and during infection with Nippostrongylus brasiliensis (Nb). Moreover, CD41 can be used as a reliable marker for basophils, circumventing technical difficulties associated with FcεRI for basophil identification in a Nb infection model. In vitro anti-IgE cross-linking and IL-3 basophil stimulation showed that CD41 upregulation positively correlates with augmented surface expression of CD200R and increased production of IL-4/IL-13, indicating that CD41 is a basophil activation marker. Furthermore, we found that infection with Plasmodium yoelii 17X (Py17x) induced a profound basophilia and using Mcpt8(DTR) reporter mice as a basophil-specific depletion model, we verified that CD41 can be used as a marker to track basophils in the steady state and during infection. During malarial infection, CD41 expression on basophils is negatively regulated by IFN-γ and positively correlates with increased basophil IL-4 production. In conclusion, we provide evidence that CD41 can be used as both an identification and activation marker for basophils during homeostasis and immune challenge.

Application of knockout mouse models to investigate the influence of FcγR on the pharmacokinetics and anti-platelet effects of MWReg30, a monoclonal anti-GPIIb antibody.

This work evaluates the influence of FcγR on the pharmacokinetics and pharmacodynamics of a rat anti-integrin-αIIb IgG1 monoclonal antibody, MWReg30, in mice. The pharmacokinetics and pharmacodynamics of MWReg30 were investigated in C57BL/6 control mice, FcγRI/RIII knockout mice, and FcγRIIb knockout mice, following intravenous doses of 0.04-0.4mg/kg. MWReg30 treatment resulted in a dose-dependent induction of thrombocytopenia in all strains, but sensitivity to MWReg30 was increased in FcγRIIb knockout mice and decreased in FcγRI/RIII knockout mice, relative to results found in control mice. Expressed as a percentage of pre-treatment platelet counts, nadir platelet counts were 28.6±5.0, 88.7±16.6 and 25.3±6.1% at 0.05mg/kg, 28.4±13.7, 56.7±5.1, and 20.6±9.5% at 0.2mg/kg, and 24.9±7.2, 38.7±7.5, and 7.4±2.2% at 0.4mg/kg in control, FcγRI/RIII(-/-) and FcγRIIb(-/-) mice. However, knocking out FcγR did not affect MWReg30 pharmacokinetics. Plasma areas under the concentration vs. time curves (AUC0-10 days) ±SD for MWReg30 were: 5.24±0.68, 5.51±0.24, and 5.39±1.05 nM×d at 0.04mg/kg, and 12.7±0.5, 13.6±1.1, and 14.5±2.0nM×d at 0.1mg/kg in control, FcγRI/RIII(-/-) and FcγRIIb(-/-) mice. The findings further emphasize the role of activating vs. inhibitory FcγR in processing immune complexes (i.e., MWReg30-platelets), while also providing an example where monoclonal antibody pharmacokinetics are not substantially influenced by FcγR expression.

Platelets support a protective immune response to LCMV by preventing splenic necrosis.

Severe arenaviral infections in humans are characterized by clinical findings common to other viral hemorrhagic fevers (VHFs), including thrombocytopenia, leukopenia, skin and internal organ hemorrhages, high viral replication, splenic necrosis, and death. Host responses, rather than direct damage by the arenaviral replication, account for most of the observed pathology, but it is not known what protective roles platelets may have in each of the manifestations. To address this issue in an animal model, we compared nondepleted (100%), partially depleted (15%), and profoundly (< 2.5%) platelet depleted mice infected with the mouse arenavirus lymphocytic choriomeningitis virus (LCMV). Here, we describe that systemic bleedings and death were seen only in those animals receiving the stronger depletion treatment. Furthermore, we showed that the nonhemorrhagic but partially platelet-depleted mice were unable to control the viral replication because of generalized splenic necrosis, affecting innate and adaptive immune cells.These data suggest that, by their supportive roles in hemostasis, platelets may be preventing the severe pathology observed in human arenaviral infections.

Recognition of highly restricted regions in the ß-propeller domain of αIIb by platelet-associated anti-αIIbß3 autoantibodies in primary immune thrombocytopenia.

Platelet-associated (PA) IgG autoantibodies play an essential role in primary immune thrombocytopenia (ITP). However, little is known about the epitopes of these Abs. This study aimed to identify critical binding regions for PA anti-αIIbß3 Abs. Because PA anti-αIIbß3 Abs bound poorly to mouse αIIbß3, we created human-mouse chimera constructs. We first examined 76 platelet eluates obtained from patients with primary ITP. Of these, 26 harbored PA anti-αIIbß3 Abs (34%). Further analysis of 15 patients who provided sufficient materials showed that the epitopes of these Abs were mainly localized in the N-terminal half of the ß-propeller domain in αIIb (L1-W235). We could identify 3 main recognition sites in the region; 2 eluates recognized a conformation formed by the W1:1-2 and W2:3-4 loops, 5 recognized W1:2-3, and 4 recognized W3:4-1. The remaining 4 eluates could not be defined by the binding sites. Within these regions, we identified residues critical for binding, including S29 and R32 in W1:1-2; G44 and P45 in W1:2-3; and P135, E136, and R139 in W2:3-4. Of 11 eluates whose recognition sites were identified, 5 clearly showed restricted κ/λ-chain usage. These results suggested that PA anti-αIIbß3 Abs in primary ITP tended to recognize highly restricted regions of αIIb with clonality.

Novel single-chain antibody-targeted microbubbles for molecular ultrasound imaging of thrombosis: validation of a unique noninvasive method for rapid and sensitive detection of thrombi and monitoring of success or failure of thrombolysis in mice.

BACKGROUND: Molecular imaging is a fast emerging technology allowing noninvasive detection of vascular pathologies. However, imaging modalities offering high resolution currently do not allow real-time imaging. We hypothesized that contrast-enhanced ultrasound with microbubbles (MBs) selectively targeted to activated platelets would offer high-resolution, real-time molecular imaging of evolving and dissolving arterial thrombi. METHODS AND RESULTS: Lipid-shell based gas-filled MBs were conjugated to either a single-chain antibody specific for activated glycoprotein IIb/IIIa via binding to a Ligand-Induced Binding Site (LIBS-MBs) or a nonspecific single-chain antibody (control MBs). Successful conjugation was assessed in flow cytometry and immunofluorescence double staining. LIBS-MBs but not control MBs strongly adhered to both immobilized activated platelets and microthrombi under flow. Thrombi induced in carotid arteries of C57Bl6 mice in vivo by ferric chloride injury were then assessed with ultrasound before and 20 minutes after MB injection through the use of gray-scale area intensity measurement. Gray-scale units converted to decibels demonstrated a significant increase after LIBS-MB but not after control MB injection (9.55±1.7 versus 1.46±1.3 dB; P<0.01). Furthermore, after thrombolysis with urokinase, LIBS-MB ultrasound imaging allows monitoring of the reduction of thrombus size (P<0.001). CONCLUSION: We demonstrate that glycoprotein IIb/IIIa-targeted MBs specifically bind to activated platelets in vitro and allow real-time molecular imaging of acute arterial thrombosis and monitoring of the success or failure of pharmacological thrombolysis in vivo.

Determination of the size distribution of blood microparticles directly in plasma using atomic force microscopy and microfluidics.

Microparticles, also known as microvesicles, found in blood plasma, urine, and most other body fluids, may serve as valuable biomarkers of diseases such as cardiovascular diseases, systemic inflammatory disease, thrombosis, and cancer. Unfortunately, the detection and quantification of microparticles are hampered by the microscopic size of these particles and their relatively low abundance in blood plasma. The use of a combination of microfluidics and atomic force microscopy to detect microparticles in blood plasma circumvents both problems. In this study, capture of a specific subset of microparticles directly from blood plasma on antibody-coated mica surface is demonstrated. The described method excludes isolation and washing steps to prepare microparticles, improves the detection sensitivity, and yields the size distribution of the captured particles. The majority of the captured particles have a size ranging from 30 to 90 nm, which is in good agreement with prior results obtained with microparticles immediately isolated from fresh plasma. Furthermore, the qualitative shape of the size distribution of microparticles is shown not to be affected by high-speed centrifugation or the use of the microfluidic circuit, demonstrating the relative stable nature of microparticles ex vivo.