Platelet activation through interaction with hemodialysis membranes induces neutrophils to produce reactive oxygen species

When to start renal replacement therapy in acute kidney injury: What are we waiting for?

Acute kidney injury remains a serious condition with a high mortality risk. In the absence of any new drugs, renal replacement therapy (RRT) is the most important treatment option. Randomized controlled trials have concluded that in critically ill patients without an emergency indication for RRT, a watchful waiting strategy is safe; however, further delays in RRT did not seem to confer any benefit, rather was associated with potential harm. During this process, balancing the risks of complications due to an unnecessary intervention with the risk of not correcting a potentially life-threatening complication remains a challenge. Dynamic renal function assessment, especially dynamic assessment of renal demand-capacity matching, combined with renal biomarkers such as neutrophil gelatinase-associated lipocalin and furosemide stress test, is helpful to identify which patients and when the patients may benefit from RRT.

Current dialyzer classification in Japan and mortality risk in patients undergoing hemodialysis

Dialyzers are classified into five types based on their β2-microglobulin clearance rate and albumin sieving coefficient: Ia, Ib, IIa, and IIb. In addition, a new classification system introduced a type S dialyzer. However, limited information is available regarding the impact of dialyzer type on patient outcomes. A cohort study was conducted using data from the Japanese Society for Dialysis Therapy Renal Data Registry database. Total 181,804 patients on hemodialysis (HD) were included in the study, categorized into four groups (type Ia, IIa, IIb, and S). The associations between each group and two-year all-cause mortality were assessed using Cox proportional hazard models. Furthermore, propensity score-matching analysis was performed. By the end of 2019, 34,185 patients on dialysis had died. After adjusting for all confounders, the risk for all-cause mortality was significantly lower in the type IIa, and S groups than in the type Ia group. These significant findings were consistent after propensity score matching. In conclusion, our findings suggest that super high-flux dialyzers, with a β2-microglobulin clearance of ≥ 70 mL/min, may be beneficial for patients on HD, regardless of their albumin sieving coefficient. In addition, type S dialyzers may be beneficial for elderly and malnourished patients on dialysis.Trial registration number: UMIN000018641.

An update review on hemodynamic instability in renal replacement therapy patients

BACKGROUND

Hemodynamic instability in patients undergoing kidney replacement therapy (KRT) is one of the most common and essential factors influencing mortality, morbidity, and the quality of life in this patient population.

METHOD

Decreased cardiac preload, reduced systemic vascular resistance, redistribution of fluids, fluid overload, inflammatory factors, and changes in plasma osmolality have all been implicated in the pathophysiology of hemodynamic instability associated with KRT.

RESULT

A cascade of these detrimental mechanisms may ultimately cause intra-dialytic hypotension, reduced tissue perfusion, and impaired kidney rehabilitation. Multiple parameters, including dialysate composition, temperature, posture during dialysis sessions, physical activity, fluid administrations, dialysis timing, and specific pharmacologic agents, have been studied as possible management modalities. Nevertheless, a clear consensus is not reached.

CONCLUSION

This review includes a thorough investigation of the literature on hemodynamic instability in KRT patients, providing insight on interventions that may potentially minimize factors leading to hemodynamic instability.

Poly(ethylene-Co-vinyl Alcohol)/Titanium Dioxide Nanocomposite: Preparation and Characterization of Properties for Potential Use in Bone Tissue Engineering

A series of poly(ethylene-co-vinyl alcohol)/titanium dioxide (PEVAL/TiO2) nanocomposites containing 1, 2, 3, 4 and 5 wt% TiO2 were prepared by the solvent casting method. These prepared hybrid materials were characterized by Fourier-transform infrared (FT-IR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The pores and their interconnections inside these nanocomposites were created using naphthalene microparticles used as a porogen after having been extracted by sublimation under a high vacuum at temperatures slightly below the glass transition temperature. A cellular activity test of these hybrid materials was performed on human gingival fibroblast cells (HGFs) in accordance with ISO 10993-5 and ISO 10993-12 standards. The bioviability (cell viability) of HGFs was evaluated after 1, 4 and 7 days using Alamar Blue®. The results were increased cell activity throughout the different culture times and a significant increase in cell activity in all samples from Day 1 to Day 7, and all systems tested showed significantly higher cell viability than the control group on Day 7 (p < 0.002). The adhesion of HGFs to the scaffolds studied by SEM showed that HGFs were successfully cultured on all types of scaffolds.

Comparison of Blood Compatibility in Various Membrane Materials for Continuous Renal Replacement Therapy

Because hemofilters used for continuous renal replacement therapy contact with blood over a prolonged period during treatments, platelet activation may occur stronger. The purpose of this study is to clarify the blood compatibility in three hemofilters mostly used in Japan. We compared the blood compatibility of the two polysulfone (AEF: Asahi Kasei Medical Co., Tokyo, Japan and SHG: Toray Medical Co., Ltd., Tokyo, Japan) and one polymethylmethacrylate membranes (CH: Toray Medical Co., Ltd.). First, test blood was collected from healthy volunteers. Subsequently, the blood was circulated by a roller pump at the rate of 100 mL/min. We measured the platelet counts and platelet factor 4 (PF4). The platelet counts at 48 h in polymethylmethacrylate membrane were significantly less than that in polysulfone membranes. Levels of the PF4 after the circulation were 978.5 ± 200.0 ng/dL with AEF, 863.0 ± 233.9 ng/dL with SHG and 1780.0 ± 465.1 ng/dL with CH, respectively. Hemofilters with polysulfone membranes showed less platelet activation. It was inferred that the amount of PVP, the smoothness of the membrane surface, and the inner diameter of the hollow fiber affect the blood compatibility in the hemofilter.

A new hydrophilic polysulfone hemodialysis membrane can prevent platelet-neutrophil interactions and successive neutrophil activation

PURPOSE:

Microaggregates have often been observed during hemodialysis and are clearly associated with complications of hemodialysis therapy. In this study, we aimed to clarify the effects of two polysulfone membranes, with different abilities to activate blood cells, on the formation of these microaggregates; we also investigated their molecular mechanisms.

METHODS:

Human whole blood was circulated through a mini-module dialyzer using the membranes in vitro; platelet-neutrophil complexes in blood were determined by flow cytometry. Isolated human neutrophils were incubated with the membranes in plasma, in the presence or absence of platelets, followed by flow cytometric analysis of intracellular reactive oxygen species and cell-surface activated CD11b on neutrophils.

RESULTS:

CX-U, a conventional polysulfone membrane with remarkable cell activation, induced the formation of platelet-neutrophil complexes; however, NV-U, a new hydrophilic polysulfone membrane with slight or no cell activation, did not cause complex formation. Moreover, CX-U-induced reactive oxygen species production and the increase in activated CD11b expression on neutrophils were enhanced by platelets. On the other hand, NV-U hardly affected neutrophil activation, regardless of whether platelets were present or not. The enhancement of CX-U-induced neutrophil activations by platelets was greatly inhibited by anti-CD62P antibody.

CONCLUSION:

The ability of polysulfone membranes to activate blood cells is closely related to platelet-neutrophil interaction. Therefore, a biocompatible membrane, like NV-U, can be expected to prevent microaggregate formation during hemodialysis and avoid subsequent cell activation.

Biocompatibility of Polysulfone Hemodialysis Membranes and Its Mechanisms: Involvement of Fibrinogen and Its Integrin Receptors in Activation of Platelets and Neutrophils

Activation of blood cells during hemodialysis is considered to be a significant determinant of biocompatibility of the hemodialysis membrane because it may affect patient health adversely through microvascular inflammation and oxidative stress. This study found very different cell activation among various polysulfone (PSf) hemodialysis membranes. For example, CX-U, a conventional PSf membrane, induced marked adhesion of platelets to its surface and increased surface expression of activated CD11b and production of reactive oxygen species (ROS) by neutrophils; while NV-U, a hydrophilic polymer-immobilized PSf membrane, caused little platelet adhesion and slight CD11b expression and ROS production by neutrophils. Analysis of the molecular mechanisms of the above phenomena on CX-U and NV-U indicated that anti-integrin GPIIb/IIIa antibody blocked platelet adhesion, and that the combination of anti-CD11b (integrin α subunit of Mac-1) and anti-integrin αvβ3 antibodies blocked ROS production by neutrophils. Plasma-derived fibrinogen, a major ligand of GPIIb/IIIa, Mac-1, and αvβ3 on membranes, was thus analyzed and found to be more adsorbed to CX-U than to NV-U. Moreover, comparison between five PSf membranes showed that the number of adherent platelets and neutrophil ROS production increased with increasing fibrinogen adsorption. These results suggested that fibrinogen, adsorbed on membranes, induced GPIIb/IIIa-mediated platelet activation and Mac-1/αvβ3-mediated neutrophil activation, depending on the amount of adsorption. In conclusion, the use of biocompatible membranes like NV-U, which show lower adsorption of fibrinogen, is expected to reduce hemodialysis-induced inflammation and oxidative stress by minimizing cell activation.

Preventive Effect of α-Tocopherol and Glycyrrhizin against Platelet-Neutrophil Complex Formation Induced by Hemodialysis Membranes

Background

The intradialytic activation of leukocytes is a major cause of hemodialysis (HD)-associated complications. Contact between blood and HD membranes frequently induces the formation of microaggregates composed of activated platelets and leukocytes, causing leukocyte activation that includes the generation of reactive oxygen species (ROS). This complex formation is mediated primarily by the interaction between P-selectin on activated platelets and its counter-ligands on leukocytes.

Objective

We examined the preventive effects of α-tocopherol and glycyrrhizin in vitro against platelet-neutrophil microaggregate formation and neutrophil ROS production induced by HD membranes.

Methods and Results

Microaggregate formation induced by the incubation of heparinized whole blood with polysulfone (PS) HD membranes was effectively inhibited by α-tocopherol and glycyrrhizin. α-Tocopherol, but not glycyrrhizin, was found to inhibit PS membrane-induced P-selectin expression on the platelet surface; however, glycyrrhizin did inhibit both the formation of neutrophil-platelet microaggregates induced by adenosine diphosphate (ADP) and the adhesion of HL60 leukemic cells to P-selectin-expressing Chinese hamster ovary (CHO) cells, suggesting that glycyrrhizin acts as a competitive inhibitor of P-selectin-mediated cell adhesion. Finally, these compounds almost completely abrogated PS membrane-induced and platelet-dependent ROS production by neutrophils.

Conclusions

These results suggest that α-tocopherol and glycyrrhizin may function as preventive agents of HD-associated leukocyte activation though the modulation of platelet-leukocyte interaction.

Facile Functionalization of Electrospun Poly(ethylene-co-vinyl alcohol) Nanofibers via the Benzoxaborole-Diol Interaction

A facile functionalization method of poly(ethylene-co-vinyl alcohol) (EVOH) nanofiber meshes was demonstrated by utilizing the benzoxaborole-diol interaction between EVOH and benzoxaborole-based copolymers (BOP). EVOH and BOP were firstly mixed to prepare the quasi-gel-state solution with enough viscosity for electro-spinning. The fiber morphology was controlled via changing the mixing ratio of EVOH and BOP. The prepared EVOH/BOP nanofiber mesh showed good stability in aqueous solution. Over 97% of the nanofibers remained after the immersion test for 24 h in acid or alkali aqueous solutions without changing their morphology. Temperature and pH-responsive moieties were copolymerized with BOP, and cationic dye was easily immobilized into the nanofiber mesh via an electrostatic interaction. Therefore, the proposed functionalization technique is possible to perform on multi-functionalized molecule-incorporated nanofibers that enable the fibers to show the environmental stimuli-responsive property for the further applications of the EVOH materials.

Evaluation of the Biocompatibility of Dialysis Membranes

BACKGROUND

Improvements in the biocompatibility of dialysis membranes have reduced biological responses elicited by blood-membrane interactions. In this article, recent technological developments in dialysis membranes with regard to biocompatibility and recent progress in the evaluation of the biocompatibility of dialysis membranes are reviewed.

SUMMARY

The focus of investigation into dialysis membranes in recent years has focused on not only membrane materials, but also their surface textures, which have been changed, for example, by coating with vitamin E or by changing the amount and type of hydrophilizing agents used. Research and development is directed at altering the chemical and physical properties of membrane surfaces to suppress biological responses that are particularly elicited as a result of platelet activation. To develop membranes with excellent biocompatibility, biocompatibility should be evaluated on a like-for-like basis under conditions that are similar to those in clinical settings. Evaluation using actual dialyzers can be performed using porcine blood, platelet-rich plasma isolated from porcine blood (and platelet-rich plasma with leukocytes), or suspension of neutrophils isolated from porcine blood or cultured human monocytes.

KEY MESSAGES

Highly biocompatible dialysis membranes can be developed when the overall correlations among biological reactions are examined by integrating all data on biological responses elicited by blood-membrane interactions or mutual interactions among blood cells.

A rare case of acute respiratory distress syndrome secondary to acute lithium intoxication

Lithium carbonate is a widely administered antimanic drug used for the treatment of bipolar disorder, schizoaffective disorder, and depression. Despite the established clinical efficacy of lithium, its usage must be approached with caution due to its narrow therapeutic index. Lithium poisoning results in multisystem toxicity, and characteristic clinical manifestations are directly correlated to serum lithium concentration. We describe a rather rare but fatal side effect of lithium: acute respiratory distress syndrome (ARDS) in a 46-year-old female on lithium for the treatment of bipolar disease. She was referred for generalized weakness, found in hemodynamic compromise, and had laboratory data significant for a lithium level of 3.3 mmole/L, needing emergent hemodialysis. Subsequently, she developed hypoxic respiratory failure requiring intubation. Her chest x-rays showed new bilateral pulmonary edema, the computed tomography scan showed extensive alveolar consolidation and V/Q scan of low probability for pulmonary embolism. She underwent 3 dialysis sessions and supportive care and was able to be extubated in 5 days. To our knowledge, 4 cases of ARDS after the onset of lithium toxicity have been documented. All patients presented with altered mental status at serum lithium levels ranging from 3.8 to 4.9 mmole/L and cardiogenic etiologies in addition to other likely causes of ARDS were ruled out in each case. The patients were treated with saline hydration (50%) or hemodialysis (50%), indicating that hemodialysis may be a permissive factor in lithium-associated ARDS development rather than a required component. Taken together, we believe that lithium is a likely culprit in the initiation of ARDS and propose the addition of ARDS to the family of clinical manifestations of severe lithium toxicity.

Fabrication of zeolite-polymer composite nanofibers for removal of uremic toxins from kidney failure patients

There is a need to develop a simple, cheap, and accessible method of treating patients with kidney failure, especially in resource-limited environments such as disaster areas and the developing world due to the inaccessibility of conventional hemodialysis treatments. In this study, we develop a zeolite-polymer composite nanofiber mesh to remove uremic toxins for blood purification. The nanofiber is composed of blood compatible poly(ethylene-co-vinyl alcohol) (EVOH) as the primary matrix polymer and zeolites which are capable of selectively adsorbing uremic toxins such as creatinine. The composite fiber meshes were produced by a cost-effective electrospinning method: electrospinning composite solutions of EVOH and zeolites. Scanning electron microscope (SEM) images revealed that the 7 w/v% EVOH solution produced non-woven fibers with a continuous and smooth morphology. The SEM also showed that over 90% of zeolites in the solution were successfully incorporated into the EVOH nanofibers. Although the barrier properties of the EVOH matrix lowered the creatinine adsorption capacity of the zeolites in the fiber when compared with adsorption to free zeolites, their adsorption capacity was still 67% of the free zeolites. The proposed composite fibers have the potential to be utilized as a new approach to removing nitrogenous waste products from the bloodstream without the requirement of specialized equipment.

Activation of platelets upon contact with a vitamin E-coated/non-coated surface

The purpose of this study was to determine the effects of a vitamin E-coated surface on platelet activation, focusing on the interactions among the vitamin E-coated surface, platelets and leukocytes. Platelet-rich plasma (PRP) or PRP containing leukocytes (LPRP) was used. No difference was observed in platelet activation between PRP and LPRP for a vitamin E-coated membrane, meaning that platelet activation triggered by leukocytes was suppressed in plasma coming in contact with a vitamin E-coated membrane, while the membrane itself directly induced platelet activation. The antioxidant capacity of the vitamin E-coated membrane in contact with PRP or LPRP was partially reduced, but sufficient residual capacity remained. The in vitro experiments using an oxidized vitamin E-coated surface revealed that P-selectin expression and superoxide anion production in the platelets and platelet adhesion were induced by contact with the oxidized vitamin E-coated surface. We conclude that contact with a vitamin E-coated surface reduces platelet activation mediated by superoxide anions, probably by reducing superoxide anions, but during the process of the reduction, the vitamin E-coated surface itself becomes oxidized, which again causes platelet activation. The beneficial effects of a vitamin E-coated dialyzer in respect of platelet activation were counteracted by the formation of oxidized vitamin E.

Constitutive turnover of phosphorylation at Thr-412 of human p57/coronin-1 regulates the interaction with actin

The actin-binding protein p57/coronin-1, a member of the coronin protein family, is selectively expressed in hematopoietic cells and plays crucial roles in the immune response through reorganization of the actin cytoskeleton. We previously reported that p57/coronin-1 is phosphorylated by protein kinase C, and the phosphorylation down-regulates the association of this protein with actin. In this study we analyzed the phosphorylation sites of p57/coronin-1 derived from HL60 human leukemic cells by MALDI-TOF-MS, two-dimensional gel electrophoresis, and Phos-tag® acrylamide gel electrophoresis in combination with site-directed mutagenesis and identified Ser-2 and Thr-412 as major phosphorylation sites. A major part of p57/coronin-1 was found as an unphosphorylated form in HL60 cells, but phosphorylation at Thr-412 of p57/coronin-1 was detected after the cells were treated with calyculin A, a Ser/Thr phosphatase inhibitor, suggesting that p57/coronin-1 undergoes constitutive turnover of phosphorylation/dephosphorylation at Thr-412. A diphosphorylated form of p57/coronin-1 was detected after the cells were treated with phorbol 12-myristate 13-acetate plus calyculin A. We then assessed the effects of phosphorylation at Thr-412 on the association of p57/coronin-1 with actin. A co-immunoprecipitation experiment with anti-p57/coronin-1 antibodies and HL60 cell lysates revealed that β-actin was co-precipitated with the unphosphorylated form but not with the phosphorylated form at Thr-412 of p57/coronin-1. Furthermore, the phosphorylation mimic (T412D) of p57/coronin-1 expressed in HEK293T cells exhibited lower affinity for actin than the wild-type or the unphosphorylation mimic (T412A) did. These results indicate that the constitutive turnover of phosphorylation at Thr-412 of p57/coronin-1 regulates its interaction with actin.

Development of a device for chemiluminescence determination of superoxide generated inside a dialysis hollow-fiber membrane

Reactive oxygen species (ROS) generated during hemodialysis treatment cause dialysis complications because of the high reactivity of ROS. To prevent dialysis complications caused by oxidative stress, it is important to evaluate the generation and dismutation of ROS during hemodialysis treatment. In this study, our aim was to develop a device to determine superoxide (O(2)(-)) generated inside a dialysis hollow fiber, and also to examine whether this device could detect O(2)(-) separated from plasma using hollow fibers. Experimental apparatus was set up so that hypoxanthine (HX) solution flowed inside the hollow fibers and 2-methyl-6-p-methoxyphenylethynyl-imidazopyrazinone (MPEC) solution flowed outside the hollow fibers. Then, xanthine oxidase (XOD) solution was added to the HX solution to generate O(2)(-), and chemiluminescence resulting from the reaction of O(2)(-) with MPEC was measured with an optical fiber. Chemiluminescence intensity was measured at different HX concentrations, and the peak area of relative luminescence intensity yielded a first-order correlation with the HX concentration. Based on the relationship between HX and O(2)(-) concentrations determined by the cytochrome c reduction method, the relative luminescence intensity measured by this device was linearly dependent on the O(2)(-) concentration inside the hollow fibers. After modifications were made to the device, XOD solution injection into plasma including HX resulted in an increase in the relative luminescence intensity. We concluded that this novel device based on chemiluminescence is capable of determining aqueous O(2)(-) generated inside a hollow fiber and also of detecting O(2)(-) in plasma.

Intradialytic and postdialytic platelet activation, increased platelet phosphatidylserine exposure and ultrastructural changes in platelets in children with chronic uremia

The present research evaluated the intradialytic and postdialytic changes in platelet factor-4 and beta-thromboglobulin plasma levels by enzyme-linked immunoadsorbent assay method and platelet aggregation by ADP as well as flow cytometric percentage of annexin-V-positive platelets as a measure of phosphatidylserine externalization and ultrastructural examination of platelets in 37 uremic patients on regular hemodialysis and 25 age-matched and sex-matched controls. Platelet factor-4 plasma levels increased, remain consistently high during hemodialysis session (20.24 +/- 3.05 IU/ml after 30 min, P < 0.001 and 23.67 +/- 3.68 IU/ml after 240 min, P < 0.001) and returned to control values (6.10 +/- 1.54 IU/ml) only after 24 h following the end of the session. beta-Thromboglobulin showed a trend similar to that of platelet factor-4. Platelet aggregation by ADP showed reduced function in comparison with controls (69.32 +/- 12.37 versus 91.95 +/- 1.59%, P < 0.001). Flow cytometric percentage of annexin-V-positive platelet was significantly elevated (P < 0.001) in uremic patients when compared with normal controls. Ultrastructural studies of platelets 30 min after starting of dialysis showed degranulation of its granules and at 240 min showed complete degranulation, whereas in the postdialytic phase (12 h after the end of dialysis) refilled alpha-granules started to appear. Positive correlations were found between platelet concentration and platelet factor-4 and beta-thromboglobulin plasma levels during and after dialysis (P < 0.001) and with annexin-V-positive platelets percentage (P < 0.001). In conclusion, activated platelets were found in chronic hemodialysis patients, a finding that may explain why uremic patients often suffer from thrombotic accidents. The platelet activation is associated with exposure of phosphatidylserine on the platelet exterior. Platelet factor-4 and beta-thromboglobulin are released from platelets as a result of a defect in their granules membrane as shown by the electron microscopy, mainly as a consequence of the blood-membrane contact during dialysis, and they return only slowly to control values.

Redistribution of P-selectin ligands on neutrophil cell membranes and the formation of platelet-neutrophil complex induced by hemodialysis membranes

The formation of platelet-neutrophil microaggregates and successive activation of neutrophils are closely related to hemodialysis-associated complications. The microaggregate is mediated primarily by the interaction between P-selectin (CD62P) expressed on activated platelets and P-selectin glycoprotein ligand-1 (PSGL-1, CD162) expressed on neutrophils. We previously reported that the clustered distribution of PSGL-1 on the cell membranes of chemokine-treated neutrophils caused upregulation of the microaggregate formation. In this study, we found that neutrophils treated with human plasma that had been incubated with hemodialysis membranes greatly enhanced the microaggregate formation. The membrane-treated plasma also induced PSGL-1 to form a cap-like cluster on the neutrophil surface. Analysis of several hemodialysis membranes with different materials indicated that the inducibility for the cap-like cluster formation of PSGL-1 parallels their ability to activate the complement system. Both the enhancement of microaggregate formation and the redistribution of PSGL-1 induced by the hemodialysis membrane-treated plasma were almost completely abrogated in the presence of a specific antagonist for the complement component C5a receptor, W-54011. These results strongly suggest that the generation of anaphylatoxin C5a through complement activation induced by hemodialysis membranes is responsible for the clustered redistribution of PSGL-1 in neutrophils leading to the increase in the platelet-neutrophil microaggregate formation. The present study indicates the importance of synergistic exacerbation of complement activation and platelet-neutrophil microaggregate formation in developing hemodialysis-associated complications.

Redistribution of P-selectin glycoprotein ligand-1 (PSGL-1) in chemokine-treated neutrophils: a role of lipid microdomains

P-selectin glycoprotein ligand-1 (PSGL-1) is a mucin-like cell adhesion molecule expressed on leukocyte plasma membranes and involved in platelet-leukocyte and endothelium-leukocyte interactions. The treatment of neutrophils with a low concentration of IL-8 induced the redistribution of PSGL-1 to one end of the cell to form a cap-like structure. We investigated the role of lipid microdomains in the redistribution of PSGL-1 and its effect on the adhesive characteristics of IL-8-treated neutrophils. The redistribution of PSGL-1 induced by IL-8 was inhibited by cholesterol-perturbing agents such as methyl-beta-cyclodextrin and filipin. Sucrose density gradient centrifugation analysis revealed that PSGL-1 was enriched in a low-density fraction together with the GM1 ganglioside after solubilization of the cell membranes with a nonionic detergent, Brij 58. However, when Triton X-100 was used for the solubilization, PSGL-1 was no longer recovered in the low-density fraction, although GM1 ganglioside remained in the low-density fraction. Furthermore, immunofluorescence microscopic observation demonstrated that the localization of PSGL-1 differed from that of GM1 ganglioside, suggesting that PSGL-1 is associated with a microdomain distinct from that containing the GM1 ganglioside. Treatment of neutrophils with IL-8 increased the formation of microaggregates composed of neutrophils and activated platelets, and this treatment also enhanced reactive oxygen species production in neutrophils induced by the cross-linking of PSGL-1 with antibodies. These results suggest that the association of PSGL-1 with lipid microdomains is essential for its redistribution induced by IL-8 stimulation and that the redistribution modulates neutrophil functions mediated by interactions with P-selectin.