P-selectin glycoprotein ligand-1 regulates chemokine-dependent leukocyte recruitment in colonic ischemia-reperfusion

Objective and design: Leukocyte recruitment is a key feature in ischemia-reperfusion (I/R) -provoked tissue injury. This study evaluated the role of P-selectin-glycoprotein ligand-1 (PSGL-1) in CXC chemokine- and ischemia-reperfusion- induced leukocyte rolling and adhesion in the colon. Materials Balb/c mice were used in an inverted intravital fluorescence microscopy study of the microvascular bed in the colon. Treatment: Mice were challenged with macrophage inflammatory protein-2 (MIP-2) intraperitonally and leukocyte-endothelium interactions were analysed 3 h later. In separate experiments, mice were exposed to I/R by clamping of the superior mesenteric artery for 30 min and leukocyte rolling and adhesion were analysed after 120 min of reperfusion. Results: MIP-2 dose-dependently increased leukocyte rolling and adhesion in the colon. Pretreatment with an anti-PSGL-1 antibody reduced MIP-2-provoked leukocyte rolling and adhesion by more than 89%. I/R increased expression of MIP-2 as well as leukocyte rolling and adhesion. Immunoneutralization of PSGL-1 decreased reperfusion-induced leukocyte rolling by 85% and adhesion by 93% in colonic venules. Conclusions: Our data demonstrates that PSGL-1 is a dominant adhesion molecule supporting MIP-2- and I/R-provoked leukocyte rolling. Inhibition of PSGL-1 abolished leukocyte rolling and abrogated I/R-induced leukocyte adhesion in colonic venules. These findings suggest that targeting PSGL-1 may be an effective strategy to prevent I/R-induced inflammation in the colon. Received 4 December 2006; returned for revision 9 January 2007; accepted by M. Parnham 6 June 2007     

咖啡酸对高同型半胱氨酸引起的小鼠软脑膜细静脉内白细胞滚动和黏附的抑制作用

目的:研究咖啡酸(CA)对同型半胱氨酸(Hcy)引起的小鼠软脑膜细静脉内滚动和黏附白细胞的抑制作用。方法:取雄性C576J/BL小鼠(体重18~22g)分成3组,每组5只,Hcy组皮下注射Hcy(0.1mg/g体重)0.2ml,Hcy+CA组皮下注射Hcy(0.1mg/g体重)0.1ml后即刻肌肉注射CA(10mg/kg体重)0.1ml,Control组皮下注射生理盐水0.2ml,4h后采用研磨法建立脑非创伤性观察窗,用动态微循环观察系统观测各组小鼠软脑膜细静脉内滚动和黏附的白细胞数量。之后取脑组织,石蜡切片,用免疫组织化学方法观察脑皮层组织中微血管内皮细胞E-选择素(E-selectin)及细胞间黏附分子-1(ICAM-1)的表达。结果:与Control组相比,Hcy组小鼠软脑膜细静脉内滚动和黏附的白细胞数量显著增加(P<0.01),且脑皮层微血管内皮E-selectin及ICAM-1的阳性区域也增加。Hcy+CA组小鼠软脑膜细静脉内白细胞的滚动和黏附数量明显少于Hcy组(P<0.05),微血管内皮的E-selectin及ICAM-1表达也明显下调。结论:CA可以抑制Hcy引起的小鼠软脑膜细静脉内白细胞的滚动和黏附,该作用与其抑制脑微血管内皮E-selectin及ICAM-1的表达有关。     

Morphologic assessment of leukocyte-endothelial cell interactions in mesenteric venules subjected to ischemia and reperfusion

Intravital microscopic studies of the mesenteric microcirculation have demonstrated that leukocyte adherence and emigration in postcapillary venules are a characteristic feature of tissues exposed to ischemia-reperfusion. The objectives of this study were to determine whether: (1) neutrophils are the predominant leukocytes that adhere and emigrate in postischemic mesenteric venules, and (2) leukocyte adherence and/or emigration are a prerequisite for reperfusion-induced increases in venular permeability. Leukocyte kinetics in cat mesenteric venules (25–35m diameter) were evaluated using both intravital microscopy and quantitative morphometry. The intestine and mesentery were exposed to 60 min of ischemia, followed by 60 min reperfusion. Some animals were pretreated with a monoclonal antibody (MoAb IB₄) against the leukocyte adhesion glycoprotein, CD11/CD18. Vessels observed by intravital microscopy and adjacent venules of similar diameter were excised and processed for light (LM) and electron microscopy (EM). Horseradish peroxidase (HRP), administered intravenously, was used to assess vascular permeability by EM. By LM, the control (nonischemic) mesentery is sparsely populated by plasma cells, mast cells, and leukocytes; 30–50% of the resident population is neutrophils. Ischemia-reperfusion led to a significant increase in the number of extravascular cells, with neutrophils accounting for >80% of the total cell population. Control and ischemic venules demonstrated no leakage of HRP into the interstitium. However, venules exposed to ischemia and reperfusion demonstrated HRP leakage between endothelial cells and into the surrounding interstitium; neutrophils were adherent to the luminal surface of the endothelium, transmigrating the vessel wall, and in the surrounding interstitium. Animals pretreated with MoAb IB₄ presented the same cell profile as nonischemic controls, with no adherent or transmigrating neutrophils. However, some HRP leakage was noted following reperfusion in venules treated with MoAb IB₄. The results of this study indicate that: (1) neutrophils are the predominate leukocytes that adhere and emigrate in postischemic venules, and (2) inhibition of leukocyte adhesion does not completely prevent the venular dysfunction associated with ischemia-reperfusion.Supported by a grant from the National Institutes of Diabetes and Digestive and Kidney Diseases (DK 33594).     

The role of selectins and integrins in adenovirus vector-induced neutrophil recruitment to the liver

Adenovirus vectors for human gene therapy induce early host inflammatory responses in transduced tissues that limit gene transfer efficiency and can result in significant morbidity. The present study aimed to elucidate the cellular mechanisms underlying the acute inflammation induced by adenovirus vectors in the liver. Leukocyte rolling and adhesion in response to an intravenously administered adenovirus vector was examined by intravital microscopy in mouse liver. Adenovirus vectors significantly increased leukocyte rolling and adhesion in the postsinusoidal venules within minutes of transduction. Unlike other inflammatory states in the liver, no leukocyte retention was seen in the sinusoids in response to adenovirus vector administration. Inhibition of P-selectin, alpha(4)-integrin, and E-selectin was necessary to completely block leukocyte rolling and subsequent adhesion. The administration of an anti-alpha(4)-integrin antibody alone significantly reduced leukocyte adhesion. In contrast, adenovirus vector-induced leukocyte adhesion was unchanged in CD18-knockout mice. Depletion of circulating neutrophils eliminated leukocyte rolling and adhesion in response to adenovirus vector transduction in the liver. In conclusion, adenovirus vectors induce rapid neutrophil-mediated inflammation in the post-sinusoidal venules by selectins and alpha(4)-integrin but surprisingly not by CD18.     

P-selectin contributes to severe experimental malaria but is not required for leukocyte adhesion to brain microvasculature

Plasmodium berghei-infected mice, a well-recognized model of experimental cerebral malaria (ECM), exhibit many of the hallmarks of a systemic inflammatory response, with organ damage in brain, lung, and kidneys. Identification of the molecules mediating pathogenesis of the inflammatory response, such as leukocyte adhesion, may lead to new therapies. Indeed, mice lacking the cell adhesion molecule P-selectin were significantly (P = 0.005) protected from death due to P. berghei malaria compared with C57BL/6 controls despite similar parasitemia (P = 0.6) being found in both groups of mice. P-selectin levels assessed by the quantitative dual radiolabeled monoclonal antibody technique increased significantly (P < 0.05) in several organs in C57BL/6 mice infected with P. berghei, supporting the concept of a systemic inflammatory response mediating malarial pathogenesis. Intravital microscopic analysis of the brain microvasculature demonstrated significant (P < 0.001) leukocyte rolling and adhesion in brain venules of P. berghei-infected mice compared with those found in uninfected controls. The maximum leukocyte adhesion occurred on day 6 of P. berghei infection, when the mice become moribund and exhibit marked vascular leakage into the brain, lung, and heart. However, P-selectin levels were significantly (P < 0.005) increased in brain, lung, and kidneys during P. berghei malaria in ECM-resistant BALB/c mice compared with those found in uninfected BALB/c controls, indicating that increased P-selectin alone is not sufficient to mediate malarial pathogenesis. Leukocyte adhesion to brain microvessels of P-selectin-deficient mice with P. berghei malaria was similar to that observed in control mice. Collectively, these results indicate that P-selectin is important for the development of malarial pathogenesis but is not required for leukocyte adhesion in brain.     

急性脑缺血白细胞与内皮细胞粘附性变化的实验研究

为探讨脑缺血再灌注损伤时局灶区白细胞的粘附变化,通过免疫荧光标记技术和显微超高速摄录像系统观察脑缺血再灌注损伤局灶区白细胞的粘附性,结果显示脑缺血再灌注损伤局灶区微动脉白细胞附壁指数升高,白细胞与内皮细胞间断裂应力降低,粘附力显著增强。上述结果表明脑缺血再灌注损伤时内皮细胞和白细胞粘附性显著增强,白细胞在脑缺血再灌注损伤中起重要作用。     

Leukocyte-endothelial cell adhesive interactions: role of xanthine oxidase-derived oxidants.

The objective of this study was to determine whether agents that either scavenge or inhibit the production of oxygen radicals can alter the adhesive interactions between leukocytes and venular endothelium elicited by ischemia-reperfusion. Cat mesenteric and intestinal blood flows were reduced to 20% of baseline for 1 hr, followed by 1 hr of reperfusion. Sixty minutes after reperfusion, red blood cell velocity (Vr), leukocyte rolling velocity (Vw), and the number of adherent leukocytes were measured in mesenteric venules. Then, either manganese-superoxide dismutase (Mn-SOD), catalase, desferrioxamine, or oxypurinol was administered intravascularly. Ten minutes later, repeat measurements were obtained and compared with pretreatment values. Catalase, Mn-SOD, and oxypurinol significantly attenuated neutrophil adherence while neither inactivated-catalase nor desferrioxamine altered the reperfusion-induced leukocyte adhesion. The ratio of Vw to erythrocyte velocity, an index of the fracture stress between rolling leukocytes and venular endothelium, was not altered by any of the agents studied. These results and data in the literature indicate that many of the agents that are commonly used to either scavenge or inhibit the production of oxygen radicals in postischemic tissues exert a significant inhibitory influence on leukocyte adhesion to microvascular endothelium in vivo. Our results are also consistent with the view that xanthine oxidase-derived oxidants contribute to the leukocyte-endothelial cell adhesive interactions associated with reperfusion of ischemic tissues.     

Inhibition of platelet adherence to brain microvasculature protects against severe Plasmodium berghei malaria

Some patients with Plasmodium falciparum infections develop cerebral malaria, acute respiratory distress, and shock and ultimately die even though drug therapy has eliminated the parasite from the blood, suggesting that a systemic inflammatory response contributes to malarial pathogenesis. Plasmodium berghei-infected mice are a well-recognized model of severe malaria (experimental severe malaria [ESM]), and infected mice exhibit a systemic inflammatory response. Because platelets are proposed to contribute to ESM and other systemic inflammatory responses, we determined whether platelet adherence contributes to experimental malarial pathogenesis. Indeed, a significant (P < 0.005) increase in the number of rolling and adherent platelets was observed by intravital microscopy in brain venules of P. berghei-infected mice compared with the number in uninfected controls. P-selectin- or ICAM-1-deficient mice exhibit increased survival after P. berghei infection. We observed a significant (P < 0.0001) reduction in the morbidity of mice injected with anti-CD41 (alpha(IIb) or gpIIb) monoclonal antibody on day 1 of P. berghei infection compared with the morbidity of infected controls injected with rat immunoglobulin G. Additionally, platelet rolling and adhesion in brain venules were reduced in P. berghei mice lacking either P-selectin or ICAM-1 or when the platelets were coated with anti-CD41 monoclonal antibody. Unlike other inflammatory conditions, we did not detect platelet-leukocyte interactions during P. berghei malaria. Because (i). leukocyte adhesion is not markedly altered in the absence of P-selectin or ICAM-1 and (ii). CD41 is not an adhesion molecule for parasitized erythrocytes, these findings support the hypothesis that inhibition of platelet adhesion to the brain microvasculature protects against development of malarial pathogenesis.     

Inhibitory effects of pentoxifylline on LPS-induced leukocyte adhesion and macromolecular extravasation in the microcirculation

Pentoxifylline (PTX) has been shown to combat effectively endotoxin induced symptoms of shock or inflammation by reducing both leukocyte activation and endogenous cytokine formation. With regard to blood perfusion, inflammation is defined as a local reaction to injury of the living microvasculature and its content. Leukocyte margination, rolling, adhesion, and emigration is mediated by adhesion molecules along the endothelium of postcapillary venules and is considered to be an important step in the inflammatory response. Changes in the vascular integrity can be estimated in terms of increased extravasation of macromolecules. Using intravital microscopy with the help of an analogous video image processing system we measured the effect of PTX on lipopolysaccharide (LPS, 15 mg/kg i.v.) induced leukocyte adhesion and extravasation of FITC-rat serum albumin (FITC-RSA) in rat mesenteric venules. The changes in vascular permeability correlates significantly (r=0.75) with a locally increased number of adherent leukocytes. PTX significantly inhibits both leukocyte adhesion and extravasation of FITC-RSA dose dependently. Our results indicate that PTX effectively preserves vascular integrity in the microcirculation by acting primarily on LPS-induced leukocyte adhesion.     

多器官衰竭早期血小板粘附与血管内皮细胞的改变

用失血再灌流加内毒素造成多器官衰竭（ＭＯＦ）的方法，在３００～１５００倍显微镜下观察血小板粘附和内皮损伤的改变，探讨血小板粘附和血管内皮损伤对微循环的影响。结果表明ＭＯＦ早期细静脉内皮上除有较多血小板贴壁或粘附在变形性差的白细胞上，细动脉内皮增厚，内皮表面出现较多血小板粘附，管腔内壁粗糙，可见到血流中的血小板迅速地粘附在损伤的内皮上，堆积、溶合形成壁栓。管腔内还有纤维蛋白形成丝网状粘附在血管腔的中间。血小板和纤维蛋白缠络在一起，形成棉絮状的团块在血管内流动。ＭＯＦ的早期细静脉内皮水肿、管壁增厚并有空泡形成，大的空泡占满整个管腔，造成血流受阻。这些改变都是造成ＭＯＦ发生的重要原因。     

Endothelial gaps and adherent leukocytes in allergen-induced early- and late-phase plasma leakage in rat airways.

Exposure of sensitized individuals to antigen can induce allergic responses in the respiratory tract, manifested by early and late phases of vasodilatation, plasma leakage, leukocyte influx, and bronchoconstriction. Similar responses can occur in the skin, eye, and gastrointestinal tract. The early-phase response involves mast cell mediators and the late-phase response is leukocyte dependent, but the mechanism of leakage is not understood. We sought to identify the leaky blood vessels, to determine whether these vessels contained endothelial gaps, and to analyze the relationship of the gaps to adherent leukocytes, using biotinylated lectins or silver nitrate to stain the cells in situ and Monastral blue as a tracer to quantify plasma leakage. Most of the leakage occurred in postcapillary venules (< 40-microns diameter), whereas most of the leukocyte migration (predominantly neutrophils) occurred in collecting venules. Capillaries and arterioles did not leak. Endothelial gaps were found in the leaky venules, both by silver nitrate staining and by scanning electron microscopy, and 94% of the gaps were distinct from sites of leukocyte adhesion or migration. We conclude that endothelial gaps contribute to both early and late phases of plasma leakage induced by antigen, but most leakage occurs upstream to sites of leukocyte adhesion.     

Direct in vivo observations of P-selectin glycoprotein ligand-1-mediated leukocyte–endothelial cell interactions in the pulmonary microvasculature in abdominal sepsis in mice

Objective

P-selectin glycoprotein ligand-1 (PSGL-1) has been shown to play a significant role in septic lung injury. However, the detailed role of PSGL-1 in the pulmonary leukocyte recruitment remains elusive. We have developed a method based on intravital fluorescence microscopy of the lung microcirculation to examine the role of PSGL-1 in the extravasation process of leukocytes in septic lung damage.

Methods

Male C57BL/6 mice were treated with a control antibody or an anti-PSGL-1 antibody prior to cecal ligation and puncture (CLP). Leukocyte–endothelium interactions and microvascular hemodynamics were studied in pulmonary arterioles, capillaries and venules 4 h after CLP.

Results

Immunoneutralization of PSGL-1 decreased CLP-induced leukocyte rolling in pulmonary arterioles and venules significantly. Inhibition of PSGL-1 had no effect on leukocyte adhesion in venules, whereas the number of adherent leukocytes in lung arterioles and the number of trapped leukocytes in capillaries were markedly decreased. Moreover, immunoneutralization of PSGL-1 improved microvascular perfusion in the lung of septic animals.

Conclusions

Taken together, these results document that PSGL-1 mediates leukocyte rolling in arterioles and venules. However, inhibition of PSGL-1 only decreases leukocyte adhesion in arterioles, suggesting that leukocyte rolling is not a prerequisite for pulmonary venular adhesion of leukocytes in sepsis. In addition, our data show that capillary trapping of leukocytes is dependent on PSGL-1 function.     

Leukocyte phosphoinositide-3 kinase {gamma} is required for chemokine-induced, sustained adhesion under flow in vivo

During inflammation, leukocytes roll along the wall of postcapillary venules scanning the surface for immobilized CXCL1, a chemokine that triggers firm adhesion by activating CXCR2 on the neutrophil. PI-3K are signaling molecules important in cellular processes, ranging from cellular differentiation to leukocyte migration. PI-3Kgamma can be activated directly by the betagamma dimer of heterotrimeric G proteins coupled to CXCR2. Here, we used in vivo and ex vivo intravital microscopy models to test the role of PI-3Kgamma in leukocyte arrest. PI-3Kgamma null mice showed an 80% decrease in CXCL1-induced leukocyte adhesion in venules of the exteriorized mouse cremaster muscle. In wild-type mice, rolling leukocytes showed rapid and sustained adhesion, but in PI-3Kgamma(-/-) mice, adhesion was not triggered at all or was transient, suggesting that absence of PI-3Kgamma interferes with integrin bond strengthening. Wild-type mice reconstituted with PI-3Kgamma null bone marrow showed a 50% decrease in CXCL1-induced leukocyte adhesion. In a blood-perfused micro-flow chamber, leukocytes from PI-3Kgamma(-/-) mice showed a defect in adhesion on a P-selectin/ICAM-1/CXCL1 substrate, indicating that leukocyte PI-3Kgamma was required for adhesion. The adhesion defect in PI-3Kgamma(-/-) mice was as severe as that in mice lacking LFA-1, the major integrin responsible for neutrophil adhesion. We conclude that the gamma isoform of PI-3K must be functional in leukocytes to allow efficient adhesion from rolling in response to chemokine stimulation.     

Overlapping roles of endothelial selectins and vascular cell adhesion molecule-1 in immune complex-induced leukocyte recruitment in the cremasteric microvasculature

Many adhesion molecule pathways have been invoked as mediating leukocyte recruitment during immune complex-induced inflammation. However the individual roles of these molecules have not been identified via direct visualization of an affected microvasculature. Therefore, to identify the specific adhesion molecules responsible for leukocyte rolling and adhesion in immune complex-dependent inflammation we used intravital microscopy to examine postcapillary venules in the mouse cremaster muscle. Wild-type mice underwent an intrascrotal reverse-passive Arthus model of immune complex-dependent inflammation and subsequently, leukocyte-endothelial cell interactions and P- and E-selectin expression were assessed in cremasteric postcapillary venules. At 4 hours, the reverse-passive Arthus response induced a significant reduction in leukocyte rolling velocity and significant increases in adhesion and emigration. P-selectin expression was increased above constitutive levels whereas E-selectin showed a transient induction of expression peaking between 2.5 to 4 hours and declining thereafter. While E-selectin was expressed, rolling could only be eliminated by combined blockade of P- and E-selectin. However, by 8 hours, all rolling was P-selectin-dependent. In contrast, inhibition of vascular cell adhesion molecule-1 had a minimal effect on leukocyte rolling, but significantly reduced both adhesion and emigration. These observations demonstrate that immune complex-mediated leukocyte recruitment in the cremaster muscle involves overlapping roles for the endothelial selectins and vascular cell adhesion molecule-1.     

Recovery of brain microcirculation during ischemia

Blood pressure in the circle of Willis in rats decreased to about 40 mmHg after ligation of both carotid arteries. Developing ischemia was accompanied by massive adhesion of leukocytes to the walls of brain venules and the smallest veins. Blood pressure in the vessels of the circle of Willis decreased to 16–20 mmHg 2 h after ligation. The number of adhesion events increased sharply. Leukocyte aggregates formed in these vessels, resulting in complete occlusion of the vessels and death of the animals. These processes were found to be reversible. Introduction of 4–4.5 ml of the plasma replacement polyglucin directly into the vessels of the circle of Willis “washed away” the leukocyte aggregates and some of the adhered leukocytes, with restoration of circulation in venules and the smallest veins by 10–15 min. __________ Translated from Rossiiskii Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 92, No. 4, pp. 420–428, April, 2006.     

Spontaneous leukocyte rolling in rat and mouse microvessels is independent of mast cell activity

OBJECTIVE AND DESIGN: The role of mast cells in spontaneous leukocyte rolling in venules of the mouse cremaster muscle and rat mesentery was investigated. MATERIALS: The experiments were carried out using mast cell-deficient rats (Ws/Ws), WBB6F1 mice (W/Wv), and their congenic littermates (wild type). Treatment: Administration of compound 48/80 intraperitoneally (50 microg) in rats and intrascrotally (5 microg) in mice, 4 h prior to the experiments. METHODS: Intravital microscopy of the terminal vascular beds in mouse cremaster muscle and rat mesentery. RESULTS: The level of spontaneous leukocyte rolling and the rolling velocity in venules of mast cell-deficient animals exactly matched that seen in wild-type animals. Challenge with compound 48/80 markedly increased leukocyte adhesion and emigration in venules of wild-type animals. In contrast, the number of adherent and extravascular leukocytes was very low in compound 48/80-challenged animals lacking mast cells and did not differ from that seen in control animals treated with phosphate-buffered saline. CONCLUSIONS: The presence or activation of mast cells has no bearing on spontaneous leukocyte rolling, at least not in rat and mouse microvessels.     

Direct leukocyte migration across pulmonary arterioles and venules into the perivascular interstitium of murine lungs during bleomycin injury and repair

During acute lung injury and repair, leukocytes are thought to enter the lung primarily across alveolar capillaries and postcapillary venules. We hypothesized that leukocytes also migrate across pulmonary arterioles and venules, which serve as alternative sites for leukocyte influx into the lung during acute lung injury and repair. Lung sections from C57BL/6J mice up to 14 days after intratracheal bleomycin (3.33 U/kg) or saline instillation were assessed by light, fluorescence, confocal, and transmission electron microscopy for evidence of inflammatory cell sequestration and transmigration at these sites. After bleomycin treatment, large numbers of leukocytes (including neutrophils, eosinophils, and monocytes) were present in the vascular lumina and in perivascular interstitia of pulmonary arterioles and venules, as well as within the vascular walls. Leukocytes were observed within well-defined pathways in arteriolar walls and much less structured pathways in venular walls, apparently in the process of transmigration. Intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) were expressed at sites of leukocyte interaction with the luminal surface, especially in arterioles. Leukocytes appeared to exit from the vessels near collagen fibers into the perivascular interstitium. Results indicate that leukocytes can directly migrate across arteriolar and venular walls into the perivascular interstitium, which may represent an important but under-recognized pathway for leukocyte influx into the lung during injury and repair.     

Differential roles of ICAM-1 and VCAM-1 in leukocyte-endothelial cell interactions in skin and brain of MRL/faslpr mice

MRL/fas(lpr) mice, which undergo a systemic autoimmune disease with similarities to systemic lupus erythematosus (SLE), display reduced pathology and prolonged survival if rendered deficient in ICAM-1. However, it remains unclear whether this is a result of the ability of ICAM-1 to promote the immune response or mediate leukocyte recruitment. Therefore, the aim of these studies was to compare the role of ICAM-1 in the elevated leukocyte-endothelial interactions, which affect MRL/fas(lpr) mice. Intravital microscopy was used to compare leukocyte rolling and adhesion in postcapillary venules in the dermal and cerebral (pial) microcirculations of wild-type (ICAM+/+) and ICAM-1-deficient (ICAM-1-/-) MRL/fas(lpr) mice. In the dermal microcirculation of 16-week MRL/fas(lpr) mice, leukocyte adhesion was increased relative to nondiseased MRL+/+ mice. However, this increase was abolished in ICAM-1-/- MRL/fas(lpr) mice. ICAM-1 deficiency was also associated with reduced dermal pathology. In contrast, in the pial microcirculation, the elevation in leukocyte adhesion observed in ICAM+/+ MRL/fas(lpr) mice also occurred in ICAM-1-/- MRL/fas(lpr) mice. VCAM-1 expression was detectable in both vascular beds, but higher levels were detected in the pial vasculature. Furthermore, VCAM-1 blockade significantly reduced leukocyte adhesion and rolling in the cerebral microcirculation of ICAM-1-/- MRL/fas(lpr) mice. Therefore, ICAM-1 was critical for leukocyte adhesion in the skin but not the brain, where VCAM-1 assumed the major function. Given the ongoing development of anti-adhesion molecule therapies and their potential in inflammatory diseases such as SLE, these data indicate that implementation of these therapies in SLE should take into account the potential for tissue-specific functions of adhesion molecules.     

Chemoattractant-induced firm adhesion of leukocytes to vascular endothelium in vivo is critically dependent on initial leukocyte rolling.

Leukocyte rolling and firm adhesion at the venular endothelium are two discrete events in the cellular inflammatory response mediated via selectin and integrin adhesion molecules, respectively. The dependency of chemoattractant-induced firm leukocyte adhesion on the preceding rolling interaction was investigated in rat mesenteric microvessels through use of intravital microscopy. Leukocyte rolling was dose-dependently inhibited by systemic treatment with the sulphated polysaccharide fucoidin. The firm leukocyte adhesion following stimulation with the chemotactic peptide fMLP was similarly inhibited when fMLP challenge was performed subsequent to inhibition of leukocyte rolling by fucoidin. Thus, based on paired observations in single venules before and after fucoidin treatment, reduced rolling leukocyte flux prior to fMLP challenge was paralleled over a wide range by a proportional decrease in fMLP-induced leukocyte adhesion. The results demonstrate quantitatively a close relationship between the extent of leukocyte rolling and the magnitude of the subsequent firm adhesion response, and, that an initial rolling interaction is a precondition for firm adhesion to occur at physiological blood flow rates in vivo.