The role of endothelium in the onset of antibody-mediated TRALI.

Transfusion Related Acute Lung Injury (TRALI) is one of the leading causes of mortality and morbidity following blood transfusion. The mechanisms behind the disease are not yet fully understood but seem to involve many different activating pathways and donor factors, in synergy with patient susceptibility. Studies have focused mostly on neutrophil activation, as aggregates of neutrophils and edema in lungs are found in post-mortem histological sections. This review aims to highlight the role of the endothelium in TRALI, as activated endothelium is the main promoter of leukocyte transmigration, and creates the barrier between blood and tissue. Since recent evidence suggests that a strong endothelial barrier prevents leukocyte transmigration and vascular leakage, we suggest that strengthening this barrier may be key to TRALI prevention.

Endothelial signalling by Ig-like cell adhesion molecules.

Leukocyte transendothelial migration is controlled by chemokine-induced signalling in leukocytes and integrin-ligand-induced bidirectional signalling in both leukocytes and endothelial cells. It is now generally accepted that endothelial signalling following leukocyte adhesion, serves to facilitate the crossing of the endothelium, be it via the paracellular or transcellular route. This brief overview discusses the main findings within this area and highlights some recent findings that shed new light on adhesion-induced signalling in the context of leukocyte transendothelial migration.

Expression and localization of NOX2 and NOX4 in primary human endothelial cells.

Reactive oxygen species (ROS) control the integrity of the vascular endothelium. Our laboratory has recently shown that transduction of human umbilical vein endothelial cells (HUVECs) with an active variant of the small GTPase Rac promotes the production of ROS, ROS-dependent activation of p38 mitogen-activated protein kinase, and loss of vascular/endothelial-cadherin-mediated cell-cell adhesion. Here we show that HUVECs express mRNAs for NOX2 as well as NOX4 mRNA, but not for NOX1 or NOX3. Interestingly, NOX4 was expressed at 100-fold higher levels compared with NOX2. NOX4-green fluorescent protein largely localizes to an intracellular compartment that costained with a marker for the endoplasmic reticulum, and its distribution did not overlap with lysosomes, Weibel-Palade bodies, or mitochondria. The NOX2-regulatory proteins p47(phox) and p67(phox) associated with the actin cytoskeleton and were found in cell protrusions and membrane ruffles, colocalizing with Rac1. This translocation to the cell periphery was promoted by tumor necrosis factor (TNF)-alpha. Finally, scavenging of ROS was found to impair TNF-alpha-induced cytoskeletal rearrangements and the formation of a confluent endothelial monolayer. Together, these data prove the differential mRNA expression of NOX family members in human endothelium and indicate that these NOX proteins and their regulators may be involved in the control of endothelial cell spreading, motility, and cell-cell adhesion.

ICAM-3 activation modulates cell-cell contacts of human bone marrow endothelial cells.

The Ig-like cell adhesion molecule ICAM-3 is mainly expressed on human leukocytes and is involved in cell-cell interactions. Its expression on endothelium is observed during disorders such as Crohn's disease and in solid tumors. We found low but detectable expression of ICAM-3 on VE-cadherin-expressing cells from primary human bone marrow aspirates, i.e. endothelial cells, and on primary human endothelial cells from cord blood. Also, immortalized human umbilical cord endothelial cells and human bone marrow endothelial cells showed ICAM-3 expression. However, its function on human endothelium is not known. Surprisingly, activation of endothelial ICAM-3 by crosslinking with specific antibodies resulted in a drop in the electrical resistance of bone marrow endothelial monolayers. In line with this, immunocytochemical analysis showed a loss of endothelial cell-cell contacts after ICAM-3 crosslinking in HBMEC. Detailed biochemical analysis showed an association of moesin and in a later stage ezrin with ICAM-3 upon crosslinking in HBMEC. Moreover, ICAM-3 crosslinking induced the production of reactive oxygen species (ROS), which are known to be involved in the control of endothelial cell-cell contacts. In conclusion, we showed that ICAM-3 is expressed on human bone marrow endothelial cells and controls endothelial integrity via ROS-dependent signaling.

Different proteolytic mechanisms involved in Fc gamma RIIIb shedding from human neutrophils.

The Fc gamma receptor type IIIb (CD16) is highly expressed on human neutrophils and is found in a soluble form in plasma and in other body fluids. Upon activation of neutrophils in vitro, Fc gamma RIIIb is shed from the cell surface by proteolytic cleavage. We have now investigated the effect of metalloproteinase inhibitors and a serine proteinase inhibitor on the shedding of Fc gamma RIIIb induced by phorbol 12-myristate 13-acetate (PMA) or cytochalasin B (cyto B) + N-formyl-methionyl-leucyl-phenylalanine (fMLP). Metalloproteinase inhibitors blocked to a large extent PMA-induced, but not cyto B + fMLP-induced shedding of Fc gamma RIIIb. Inhibition of members of the ADAM (a disintegrin and metalloproteinase) family appeared most efficient. In contrast, the serine protease inhibitor N-methoxysuccinyl-alanine-alanine-proline-valine-chloromethylketone (MeOsuc-AAPV-CMK) largely blocked cyto B + fMLP-induced, but not PMA-induced shedding of Fc gamma RIIIb. Metalloproteinase inhibitors in combination with the serine proteinase inhibitor resulted in full inhibition of Fc gamma RIIIb shedding induced by either PMA or cyto B + fMLP. The shedding of Fc gamma RIIIb that accompanied apoptosis was inhibited by 60% in the presence of inhibitors of metalloproteinases but was insensitive to inhibition of serine proteinases. These results show that distinct types of proteolytic enzyme are involved in the stimulus-induced shedding of Fc gamma RIIIb from human neutrophils and suggest that these proteinases may become differentially activated under various physiological or pathological conditions.

Measurement of cholesterol gallstone growth in vitro.

Methods to study growth of gallstones in the laboratory have not been reported. We here present such a method. Human cholesterol gallstones were harvested from patients with multiple nearly identical stones. The gallstones were washed and added to supersaturated model biles and the formation of cholesterol crystals and the increases in mass of human cholesterol gallstones were studied concurrently, over a period of weeks, using nephelometry and a microbalance, respectively. All stones incubated in model biles supersaturated with cholesterol increased in mass. Increases in the degree of supersaturation of cholesterol in the model biles resulted in increased growth of stones. The mass increases, the growth rates, and the spatial orientation of accreted crystalline cholesterol differed among various stone types. The kinetics and structures of stone growth were similar when the stones were incubated in supersaturated, native, human gallbladder biles. The structure of accreted cholesterol was the same as found on the surface of some human gallstones that were harvested during apparent active growth in situ. This simple method allows accurate measurements of stone growth in vitro, in patterns that mimic stone growth in vivo, and is useful for studies on the relationships of gallstone growth and the kinetics of cholesterol crystallization.

Actin polymerization induces shedding of FcgammaRIIIb (CD16) from human neutrophils.

FcgammaRIIIb (CD16) is a glycosyl phosphatidylinositol (GPI)-anchored low-affinity IgG receptor, exclusively expressed on human neutrophils. FcgammaRIIIb associates with complement receptor 3 (CR3, Mac-1, CD11b/CD18), which may indirectly link FcgammaRIIIb to the actin cytoskeleton. Upon neutrophil activation, apoptosis, or chemotaxis, FcgammaRIIIb is shed from the cell surface. In all of these events, actin rearrangements play an important role. To establish a role for the actin cytoskeleton in the control of FcgammaRIIIb shedding, we treated human neutrophils with jasplakinolide, an actin-polymerizing peptide. We show that enhanced actin polymerization induces time- and dose-dependent shedding of FcgammaRIIIb. This effect was not restricted to FcgammaRIIIb, because the cell surface expression of CD43, CD44, and L-selectin was also downregulated after induction of actin polymerization. This actin-dependent pathway is staurosporine sensitive but does not appear to involve activation of PKC or CR3. These data show that the actin cytoskeleton can regulate protein ectodomain shedding from human neutrophils.

Mucins and calcium phosphate precipitates additively stimulate cholesterol crystallization.

Human biliary mucin and calcium binding protein (CBP) influence formation of both calcium salt precipitates and cholesterol crystals and colocalize in the center of cholesterol gallstones. We investigated how physiological concentrations of these proteins regulate cholesterol crystallization in model biles, supersaturated with cholesterol and calcium salts, mimicking pathological human bile. Using polarizing light microscopy and nephelometry to assess cholesterol crystallization, the influence of calcium ions and calcium phosphate precipitates in the absence and presence of mucin, CBP, and human serum albumin was determined. Calcium phosphate precipitates stimulated cholesterol crystallization more strongly than soluble calcium. Mucin also stimulated, and with soluble calcium or calcium phosphate precipitates additively increased, the cholesterol crystal mass. In the absence of mucin, only human serum albumin plus CBP, not these proteins individually, decreased the stimulating effect of calcium phosphate precipitates but not of soluble calcium. However, seeding of calcium phosphate precipitates in biles with mucins resulted in near complete cholesterol crystallization within one day whether CBP and HSA were or were not also present. In conclusion, calcium salt precipitates plus human biliary mucins induce rapid and complete crystallization of cholesterol from model biles, little influenced by human biliary calcium binding proteins.