[Immunity and inflammation in atherosclerosis]. / Immunität und Entzündung bei Arteriosklerose.

There is now overwhelming experimental and clinical evidence that arteriosclerosis is a chronic inflammatory disease. Lessons learned from genome-wide association studies, advanced in vivo imaging techniques, transgenic lineage tracing mice models and clinical interventional studies have shown that both innate and adaptive immune mechanisms can accelerate or curb arteriosclerosis. This article summarizes and discusses the pathogenesis of arteriosclerosis with a focus on the role of the adaptive immune system. Some limitations of animal models are discussed and the need for models that are tailored to better translate to human atherosclerosis and ultimately progress in prevention and treatment are emphasized.

Relevance of L-selectin shedding for leukocyte rolling in vivo.

The velocity of rolling leukocytes is thought to be determined by the expression of adhesion molecules and the prevailing wall shear stress. Here, we investigate whether rapid cleavage of L-selectin may be an additional physiologic regulatory parameter of leukocyte rolling. A unique protease in the membrane of leukocytes cleaves L-selectin after activation, resulting in L-selectin shedding. The hydroxamic acid-based metalloprotease inhibitor KD-IX-73-4 completely prevented L-selectin shedding in vitro and significantly decreased the rolling velocity of leukocytes in untreated wild-type C57BL/6 mice from 55 to 35 micrometer/seconds in vivo. When E-selectin was expressed on the endothelium (tumor necrosis factor [TNF]-alpha treatment 2.5-3 h before the experiment), rolling velocity was 4 micrometer/seconds and did not change after the application of KD-IX-73-4. However, KD-IX-73-4 decreased mean rolling velocity by 29% from 23 to 16 micrometer/seconds in E-selectin-deficient mice treated with TNF-alpha. The reduction of velocity caused by KD-IX-73-4 was immediate (<5 s) after injection of KD-IX-73-4 as shown by a novel method using a local catheter. These results establish a role for L-selectin shedding in regulating leukocyte rolling velocity in vivo.

Regulation of leukocyte rolling and adhesion to high endothelial venules through the cytoplasmic domain of L-selectin.

L-selectin (leukocyte adhesion molecule 1/MEL-14), a member of the selectin family of cell adhesion molecules, mediates leukocyte rolling and leukocyte adhesion to endothelium at sites of inflammation. In addition, L-selectin mediates the binding of lymphocytes to high endothelial venules (HEV) of peripheral lymph nodes. The strong amino acid sequence conservation of the cytoplasmic domain of L-selectin between humans and mice suggests an important role for this region. Deletion of the COOH-terminal 11 amino acids from the approximately 17 amino acid cytoplasmic domain of L-selectin eliminated binding of lymphocytes to HEV in the in vitro frozen section assay, and also abolished leukocyte rolling in vivo in exteriorized rat mesenteric venules, but did not alter the lectin activity of L-selectin. Pretreatment of cells with cytochalasin B, which disrupts actin microfilaments, also abolished adhesion without affecting carbohydrate recognition. Therefore, the cytoplasmic domain of L-selectin regulates leukocyte adhesion to endothelium independent of ligand recognition, by controlling cytoskeletal interactions and/or receptor avidity.

L-selectin shedding regulates leukocyte recruitment.

The physiologic role of L-selectin shedding is unknown. Here, we investigate the effect of L-selectin shedding on firm adhesion and transmigration. In a tumor necrosis factor alpha-induced model of inflammation, inhibition of L-selectin shedding significantly increased firm adhesion and transmigration by a lymphocyte function-associated antigen (LFA)-1 and intercellular adhesion molecule (ICAM)-1-dependent mechanism. We examined the quality of leukocyte rolling and L-selectin-mediated signaling. Blockade of L-selectin shedding significantly reduced the "jerkiness" of leukocyte rolling, defined as the variability of velocity over time. A low level of jerkiness was also observed in the rolling of microbeads conjugated with L-selectin, a model system lacking the mechanism for L-selectin shedding. Inhibition of L-selectin shedding potentiated activation of LFA-1 and Mac-1 induced by L-selectin cross-linking as shown by activation epitope expression and binding of ICAM-1-conjugated beads. We conclude that inhibition of L-selectin shedding increases leukocyte adhesion and transmigration by (a) increasing leukocyte exposure to the inflamed endothelium by decreasing jerkiness and (b) promoting leukocyte activation by outside-in signaling. These observations help to resolve the apparent discrepancy between the minor contribution of L-selectin to rolling and the significant leukocyte recruitment defect in L-selectin knockout mice.

Absence of trauma-induced leukocyte rolling in mice deficient in both P-selectin and intercellular adhesion molecule 1.

Leukocyte recruitment during inflammation is achieved through a multistep paradigm that includes margination, selectin-mediated rolling, beta 2 integrin-mediated firm adhesion, emigration, and migration into the site of inflammation. We have used the mouse cremaster muscle as a model of trauma- and cytokine-induced inflammation to study the possible role of intercellular adhesion molecule (ICAM) 1 in leukocyte rolling using gene-targeted mice deficient in ICAM-1, P-selectin, and a combination of P-selectin and ICAM-1. Rolling flux and average leukocyte rolling velocity in ICAM-1-deficient mice was not different from wild-type mice, but P-selectin/ICAM-1-deficient mice showed a total absence of rolling for at least 2 h after surgical trauma. Rolling in both wild-type and ICAM-1-deficient mice 60-120 min after trauma was significantly inhibited by a P-selectin monoclonal antibody (mAb) (RB40.34). In contrast, an mAb (KAT-1) blocking ICAM-1 binding to leukocyte function-associated antigen 1 did not block residual rolling in P-selectin-deficient mice. TNF-alpha induced leukocyte rolling in P-selectin/ICAM-1-deficient mice, but the rolling flux fraction was significantly lower than in TNF-alpha-treated ICAM-1-deficient mice. Leukocyte rolling in P-selectin/ICAM-1-deficient mice treated with TNF-alpha for 3 h was completely blocked by an E-selectin mAb (9A9E3), and partially by an L-selectin mAb (MEL-14). This clearly demonstrates E-selectin-dependent rolling in vivo. Leukocyte rolling velocities were significantly reduced after TNF-alpha treatment and were similar in wild-type and gene-targeted strains. We conclude that the residual trauma-induced leukocyte rolling seen in P-selectin-deficient mice is completely abolished by concomitant ICAM-1 deficiency. This severe defect in leukocyte rolling may explain the absence of leukocyte recruitment into the inflamed peritoneal cavity of P-selectin/ICAM-1-deficient mice at early time points (< or = 4 h).

Sequential contribution of L- and P-selectin to leukocyte rolling in vivo.

Leukocyte recruitment into inflammatory sites is initiated by a reversible transient adhesive contact with the endothelium called leukocyte rolling, which is thought to be mediated by the selectin family of adhesion molecules. Selectin-mediated rolling precedes inflammatory cell emigration, which is significantly impaired in both P- and L-selectin gene-deficient mice. We report here that approximately 13% of all leukocytes passing venules of the cremaster muscle of wild-type mice roll along the endothelium at < 20 min after surgical dissection. Rolling leukocyte flux fraction reaches a maximum of 28% at 40-60 min and returns to 13% at 80-120 min. In P-selectin-deficient mice, rolling is absent initially and reaches 5% at 80-120 min. Rolling flux fraction in L-selectin-deficient mice is similar to wild type initially and declines to 5% at 80-120 min. In both wild-type and L-selectin-deficient mice, initial leukocyte rolling (0-60 min) is completely blocked by the P-selectin monoclonal antibody (mAb) RB40.34, but unaffected by L-selectin mAb MEL-14. Conversely, rolling at later time points (60-120 min) is inhibited by mAb MEL-14 but not by mAb RB40.34. After treatment with tumor necrosis factor (TNF)-alpha for 2 h, approximately 24% of all passing leukocytes roll in cremaster venules of wild-type and P-selectin gene-deficient mice. Rolling in TNF-alpha-treated mice is unaffected by P-selectin mAb or E-selectin mAb 10E9.6. By contrast, rolling in TNF-alpha-treated P-selectin-deficient mice is completely blocked by L-selectin mAb. These data show that P-selectin is important during the initial induction of leukocyte rolling after tissue trauma. At later time points and in TNF-alpha-treated preparations, rolling is largely L-selectin dependent. Under the conditions tested, we are unable to find evidence for involvement of E-selectin in leukocyte rolling in mice.

Spontaneous skin ulceration and defective T cell function in CD18 null mice.

A null mutation was prepared in the mouse for CD18, the beta2 subunit of leukocyte integrins. Homozygous CD18 null mice develop chronic dermatitis with extensive facial and submandibular erosions. The phenotype includes elevated neutrophil counts, increased immunoglobulin levels, lymphadenopathy, splenomegaly, and abundant plasma cells in skin, lymph nodes, gut, and kidney. Very few neutrophils were found in spontaneously occurring skin lesions or with an induced toxic dermatitis. Intravital microscopy in CD18 null mice revealed a lack of firm neutrophil attachment to venules in the cremaster muscle in response to N-formyl- methionyl-leucyl-phenylalanine. A severe defect in T cell proliferation was found in the CD18 null mice when T cell receptors were stimulated either by staphylococcal enterotoxin A or by major histocompatibility complex alloantigens demonstrating a greater role of CD11/CD18 integrins in T cell responses than previously documented. The null mice are useful for delineating the functions of CD18 in vivo.

Infectious susceptibility and severe deficiency of leukocyte rolling and recruitment in E-selectin and P-selectin double mutant mice.

During the initial phase of the inflammatory response, leukocytes marginate and roll along the endothelial surface, a process mediated largely by the selectins and their ligands. Mice with mutations in individual selectins show no spontaneous disease and have mild or negligible deficiencies of inflammatory responses. In contrast, we find that mice with null mutations in both endothelial selectins (P and E) develop a phenotype of leukocyte adhesion deficiency characterized by mucocutaneous infections, plasma cell proliferation, hypergammaglobulinemia, severe deficiencies of leukocyte rolling in cremaster venules with or without addition of TNF-alpha, and an absence of neutrophil emigration at 4 h in response to intraperitoneal Streptococcus pneumoniae peritonitis. These mice provide strong evidence for the functional importance of selectins in vivo.

Phosphoinositide 3-kinase gamma required for lipopolysaccharide-induced transepithelial neutrophil trafficking in the lung.

Phosphoinositide 3-kinase gamma(PI3Kgamma) is a critical mediator of directional cell movement. Here, we sought to characterise the role of PI3Kgamma in mediating the different steps of polymorphonuclear leukocyte (PMN) trafficking in the lung. In a murine model of lipopolysaccharide (LPS)-induced lung injury, PMN migration into the different lung compartments was determined in PI3Kgamma gene-deficient (PI3Kgamma(-/-)) and wild-type mice. Bone marrow chimeras were created to characterise the role of PI3Kgamma on haematopoietic versus nonhaematopoietic cells. A small-molecule PI3Kgamma inhibitor was tested in vitro and in vivo. PMN adhesion to the pulmonary endothelium and transendothelial migration into the lung interstitium was enhanced in PI3Kgamma(-/-) mice. However, transepithelial migration into the alveolar space was reduced in these mice. When irradiated PI3Kgamma(-/-) mice were reconstituted with bone marrow from wild-type mice, migratory activity into the alveolar space was restored partially. A small-molecule PI3Kgamma inhibitor reduced chemokine-induced PMN migration in vitro when PMNs or epithelial cells, but not when endothelial cells, were treated. The inhibitor also reduced LPS-induced PMN migration in vivo. We conclude that PI3Kgamma is required for transepithelial but not for transendothelial migration in LPS-induced lung injury. Inhibition of PI3Kgamma activity may be effective at curbing excessive PMN infiltration in lung injury.

Detection of G1 proteins in Chinese hamster cells synchronized by isoleucine deprivation or mitotic selection.

Examination of labeling patterns of proteins in Chinese hamster cells(line CHO) revealed the presence of a class of protein(s) that is synthesized during G1 phase of the cell cycle. Cells arrested in G1 by isoleucine (Ile) deprivation were prelabeded with [14-C]Ile, induced to traverse G1 by addition of unlabeled Ile, and labeled with [3-H]Ile at hourly intervals. Cells were fractionated into neclear and cytoplasmic portions, and proteins were separated by sodium dodecyl sulfate-polyacrylamide get electrophoresis. Gel profiles of proteins in the 45,000-160,000 mol wt range from the cytoplasm of cells in G1 were similar to those from cells arrested in G1 except for the presence of a mojor peak of [1-H]Ile incorporated into a protein(s) of approximately 80,000 mol wt. Peaks of net [3-H]Ile incorporation were not detected in neclear preparations. Cellular fractionation by differential centrifugation showed the peak I protein was located in the soluble supernatant fraction of the cytoplasm. Time-course studies showed that synthesis of this protein began 1-2 h after initiation of G1 traverse; the protein reached maximum levels in 4-6 h and was reduced to undetectable levels by 9 h. A cytoplasmic protein with similar electrophoretic mobility was found in G1 phase of cells synchronized by mitotic selection. This class of proteins is synthesized by cells before entry into S phase and may be involved in initiation of DNA synthesis.

Regulation of initiation of DNA synthesis in Chinese hamster cells. I. Production of stable, reversible G1-arrested populations in suspension culture.

Suspension cultures of Chinese hamster cells (line CHO) were grown to stationary phase (approximately 8-9 x 10(5) cells/ml) in F-10 medium. Cells remained viable (95%) for at least 80 hr in stationary phase, and essentially all of the cells were in G(1) Upon resuspension or dilution with fresh medium, the cells were induced to resume traverse of the life cycle in in synchrony, and the patterns of DNA synthesis and division were similar to those observed in cultures prepared by mitotic selection. Immediately after dilution, the rates of synthesis of RNA and protein increased threefold. This system provides a simple technique for production of large quantities of highly synchronized cells and may ultimately provide information on the biochemical mechanisms regulating cell-cycle traverse.

REGULATION OF INITIATION OF DNA SYNTHESIS IN CHINESE HAMSTER CELLS : II. Induction of DNA Synthesis and Cell Division by Isoleucine and Glutamine in G(1)-Arrested Cells in Suspension Culture.

Suspension cultures of Chinese hamster cells (line CHO), which had stopped dividing and were arrested in G(1) following growth to high cell concentrations in F-10 medium, could be induced to reinitiate DNA synthesis and to divide in synchrony upon addition of the appropriate amounts of isoleucine and glutamine. Both amino acids were required to initiate resumption of cell-cycle traverse. Deficiencies in other amino acids contained in F-10 medium did not result in accumulation of cells in G(1), indicating a specific action produced by limiting quantities of isoleucine and glutamine. In the presence of sufficient glutamine, approximately 2 x 10(-6)M isoleucine was required for all cells to initiate DNA synthesis in a population initially containing 1.5 x 10(5) cells/ml. Under similar conditions, about 4 x 10(-6)M isoleucine was required for all G(1)-arrested cells to progress through cell division. In contrast, 1 x 10(-4)M glutamine was necessary for maximum initiation of DNA synthesis in G(1) cells, along with sufficient isoleucine. A technique for rapid production of G(1)-arrested cells is described in which cells from an exponentially growing population placed in F-10 medium deficient in both isoleucine and glutamine or isoleucine alone accumulated in G(1) after 30 hr.

Synchronization of mitochondrial DNA synthesis in Chinese hamster cells (line CHO) deprived of isoleucine.

Mitochondrial DNA (mit-DNA) synthesis was compared in suspension cultures of Chinese hamster cells (line CHO) whose cell cycle events had been synchronized by isoleucine deprivation or mitotic selection. At hourly intervals during cell cycle progression, synchronized cells were exposed to tritiated thymidine ([(3)H]TdR), homogenized, and nuclei and mitochondria isolated by differential centrifugation. Mit-DNA and nuclear DNA were isolated and incorporation of radioisotope measured as counts per minute ([(3)H]TdR) per microgram DNA. Mit-DNA synthesis in cells synchronized by mitotic selection began after 4 h and continued for approximately 9 h. This time-course pattern resembled that of nuclear DNA synthesis. In contrast, mit-DNA synthesis in cells synchronized by isoleucine deprivation did not begin until 9-12 h after addition of isoleucine and virtually all [(3)H]TdR was incorporated during a 3-h interval. We have concluded from these results that mit-DNA synthesis is inhibited in CHO cells which are arrested in G(1) because of isoleucine deprivation and that addition of isoleucine stimulates synchronous synthesis of mit-DNA. We believe this method of synchronizing mit-DNA synthesis may be of value in studies of factors which regulate synthesis of mit-DNA.

Threshold levels of fluid shear promote leukocyte adhesion through selectins (CD62L,P,E)

Leukocyte adhesion through L-selectin to peripheral node addressin (PNAd, also known as MECA-79 antigen), an L-selectin ligand expressed on high endothelial venules, has been shown to require a minimum level of fluid shear stress to sustain rolling interactions (Finger, E.B., K.D. Puri, R. Alon, M.B. Lawrence, V.H. von Andrian, and T.A. Springer. 1996. Nature (Lond.). 379:266-269). Here, we show that fluid shear above a threshold of 0.5 dyn/cm2 wall shear stress significantly enhances HL-60 myelocyte rolling on P- and E-selectin at site densities of 200/microm2 and below. In addition, gravitational force is sufficient to detach HL-60 cells from P- and E-selectin substrates in the absence, but not in the presence, of flow. It appears that fluid shear-induced torque is critical for the maintenance of leukocyte rolling. K562 cells transfected with P-selectin glycoprotein ligand-1, a ligand for P-selectin, showed a similar reduction in rolling on P-selectin as the wall shear stress was lowered below 0.5 dyn/cm2. Similarly, 300.19 cells transfected with L-selectin failed to roll on PNAd below this level of wall shear stress, indicating that the requirement for minimum levels of shear force is not cell type specific. Rolling of leukocytes mediated by the selectins could be reinitiated within seconds by increasing the level of wall shear stress, suggesting that fluid shear did not modulate receptor avidity. Intravital microscopy of cremaster muscle venules indicated that the leukocyte rolling flux fraction was reduced at blood centerline velocities less than 1 mm/s in a model in which rolling is mediated by L- and P-selectin. Similar observations were made in L-selectin-deficient mice in which leukocyte rolling is entirely P-selectin dependent. Leukocyte adhesion through all three selectins appears to be significantly enhanced by a threshold level of fluid shear stress.

A role for the epidermal growth factor-like domain of P-selectin in ligand recognition and cell adhesion.

The selectin family of adhesion molecules mediates the initial interactions of leukocytes with endothelium. The extracellular region of each selectin contains an amino-terminal C-type lectin domain, followed by an EGF-like domain and multiple short consensus repeat units (SCR). Previous studies have indirectly suggested a role for each of the extracellular domains of the selectins in cell adhesion. In this study, a panel of chimeric selectins created by exchange of domains between L- and P-selectin was used to directly examine the role of the extracellular domains in cell adhesion. Exchange of only the lectin domains between L- and P-selectin conferred the adhesive and ligand recognition functions of the lectin domain of the parent molecule. However, chimeric selectins which contained both the lectin domain of L-selectin and the EGF-like domain of P-selectin exhibited dual ligand-binding specificity. These chimeric proteins supported adhesion both to myeloid cells and to high endothelial venules (HEV) of lymph nodes and mesenteric venules in vivo. Exchange of the SCR domains had no detectable effect on receptor function or specificity. Thus, the EGF-like domain of P-selectin may play a direct role in ligand recognition and leukocyte adhesion mediated by P-selectin, with the lectin plus EGF-like domains collectively forming a functional ligand recognition unit.

Anti-inflammatory properties of cytochrome P450 epoxygenase-derived eicosanoids.

The epoxyeicosatrienoic acids (EETs) are products of cytochrome P450 epoxygenases that have vasodilatory properties similar to that of endothelium-derived hyperpolarizing factor. The cytochrome P450 isoform CYP2J2 was cloned and identified as a potential source of EETs in human endothelial cells. Physiological concentrations of EETs or overexpression of CYP2J2 decreased cytokine-induced endothelial cell adhesion molecule expression, and EETs prevented leukocyte adhesion to the vascular wall by a mechanism involving inhibition of transcription factor NF-kappaB and IkappaB kinase. The inhibitory effects of EETs were independent of their membrane-hyperpolarizing effects, suggesting that these molecules play an important nonvasodilatory role in vascular inflammation.

Therapeutic inhibition of CXCR2 by Reparixin attenuates acute lung injury in mice.

BACKGROUND AND PURPOSE: Acute lung injury (ALI) remains a major challenge in critical care medicine. Both neutrophils and chemokines have been proposed as key components in the development of ALI. The main chemokine receptor on neutrophils is CXCR2, which regulates neutrophil recruitment and vascular permeability, but no small molecule CXCR2 inhibitor has been demonstrated to be effective in ALI or animal models of ALI. To investigate the functional relevance of the CXCR2 inhibitor Reparixin in vivo, we determined its effects in two models of ALI, induced by either lipopolysaccharide (LPS) inhalation or acid instillation. EXPERIMENTAL APPROACH: In two ALI models in mice, we measured vascular permeability by Evans blue and evaluated neutrophil recruitment into the lung vasculature, interstitium and airspace by flow cytometry. KEY RESULTS: Pharmacological inhibition of CXCR2 by Reparixin reduced CXCL1-induced leukocyte arrest in the microcirculation of the cremaster muscle, but did not influence arrest in response to leukotriene B4 (LTB4) demonstrating specificity. Reparixin (15 microg g(-1)) reduced neutrophil recruitment in the lung by approximately 50% in a model of LPS-induced ALI. A higher dose did not provide additional reduction of neutrophil recruitment. This dose also reduced accumulation of neutrophils in the interstitial compartment and vascular permeability in LPS-induced ALI. Furthermore, both prophylactic and therapeutic application of Reparixin improved gas exchange, and reduced neutrophil recruitment and vascular permeability in a clinically relevant model of acid-induced ALI. CONCLUSIONS AND IMPLICATIONS: Reparixin, a non-competitive allosteric CXCR2 inhibitor attenuates ALI by reducing neutrophil recruitment and vascular permeability.

Transit time of leukocytes rolling through venules controls cytokine-induced inflammatory cell recruitment in vivo.

Leukocyte recruitment requires leukocyte rolling, activation, firm adhesion, and transmigration. Injection of the proinflammatory cytokine TNF-alpha induces expression of E-selectin, interleukin-8, and other adhesion molecules and chemoattractants on the endothelial surface. TNF-alpha- treated CD18 null mouse cremaster muscle venules show increased leukocyte rolling velocity and reduced leukocyte recruitment efficiency. Leukocyte recruitment in CD18 null but not wild-type mice is significantly blocked by an mAb to E-selectin. To understand this overlap between adhesion events previously considered separate, we introduce a quantitative analysis of the efficiency of induction of rolling, conversion of rolling to adhesion, and of adhesion to transmigration. We find that CD18 and E-selectin cooperate to control the time a leukocyte needs to roll through an inflamed area and to convert rolling to firm adhesion. Leukocyte rolling time, defined as the time it takes for a rolling leukocyte to pass through a defined length of a vessel segment, emerges as a unifying parameter determining the efficiency of inducing firm adhesion, which is a rate-limiting step controlling leukocyte recruitment in inflammation. We conclude that leukocytes integrate chemoattractant signals while rolling along the endothelial surface until they reach a critical level of activation and become firmly adherent.

Severe inflammatory defect and reduced viability in CD18 and E-selectin double-mutant mice.

CD18-deficient mice (CD18(-/-) mice) have a severe leukocyte recruitment defect in some organs, and no detectable defect in other models. Mice lacking E-selectin (CD62E(-/-) mice) have either no defect or a mild defect of neutrophil infiltration, depending on the model. CD18(-/-)CD62E(-/-), but not CD18(-/-)CD62P(-/-), mice generated by crossbreeding failed to thrive, reaching a maximum body weight of 10-15 grams. To explore the mechanisms underlying reduced viability, we investigated lethally irradiated CD62E(-/-) mice that were reconstituted with CD18(-/-) bone marrow. These mice, but not single-mutant controls, showed tenfold-increased rolling velocities in a TNF-alpha-induced model of inflammation. Leukocyte adhesion efficiency in CD18(-/-)CD62E(-/-) mice was reduced by 95%, and hematopoiesis was drastically altered, including severe bone marrow and blood neutrophilia and elevated G-CSF and GM-CSF levels. The greatly reduced viability of CD18(-/-)CD62E(-/-) mice appears to result from an inability to mount an adequate inflammatory response. Our data show that cooperation between E-selectin and CD18 integrins is necessary for neutrophil recruitment and that alternative adhesion pathways cannot compensate for the loss of these molecules.

The chemokine KC, but not monocyte chemoattractant protein-1, triggers monocyte arrest on early atherosclerotic endothelium.

In a reconstituted flow chamber system, preincubation with chemokines can trigger the arrest of rolling monocytes, suggesting that this interaction could help recruit these cells to early atherosclerotic lesions. To date, however, the contribution of endothelium-derived chemokines found in these lesion to monocyte arrests has not been investigated. The endothelium of lesion-prone carotid arteries from apolipoprotein E-deficient (ApoE(-/-)) mice, but not control mice, presents the chemokines KC (mouse GRO-alpha) and JE (mouse monocyte chemoattractant protein-1 [MCP-1]). Arrest of a monocytic cell line or mouse blood monocytes perfused through carotid arteries of ApoE(-/-) mice was reduced by treating with either pertussis toxin, an antagonist of CXCR2, or an antibody to KC, but this process was insensitive to agents that blocked CCR-2 or JE. Conversely, monocyte accumulation more than doubled upon pre-perfusion of the carotid artery with KC but not with mouse MCP-1. Blockade of alpha(4)beta(1) integrin (VLA-4) or vascular cell adhesion molecule-1, but not CD18 or intercellular adhesion molecule-1, almost completely inhibited the arrest of monocytes. We conclude that when presented by early atherosclerotic lesions, KC but not murine MCP-1 triggers VLA-4-dependent monocyte recruitment.