Prehospital stroke mimics in the Stockholm Stroke Triage System.

Introduction: In 2017, Stockholm implemented a new prehospital stroke triage system (SSTS) directing patients with a likely indication for thrombectomy to the regional comprehensive stroke center (CSC) based on symptom severity and teleconsultation with a physician. In Stockholm, 44% of patients with prehospital code stroke have stroke mimics. Inadvertent triage of stroke mimics to the CSC could lead to inappropriate resource utilization. Aims: To compare the characteristics between (1) triage-positive stroke mimics and stroke (TP mimics and TP stroke) and (2) triage-negative stroke mimics and stroke (TN mimics and TN stroke) and to (3) compare the distribution of stroke mimic diagnoses between triage-positive and triage-negative cases. Methods: This prospective observational study collected data from October 2017 to October 2018, including 2,905 patients with suspected stroke who were transported by code-stroke ambulance to a Stockholm regional hospital. Patients directed to the CSC were defined as triage-positive. Those directed to the nearest stroke center were defined as triage-negative. Results: Compared to individuals with TP stroke (n = 268), those with TP mimics (n = 55, median 64 vs. 75 years, P < 0.001) were younger and had lower NIHSS score (median 7 vs. 15, P < 0.001). Similarly, those with TN mimics (n = 1,221) were younger than those with TN stroke (n = 1,361, median 73 vs. 78 years, P < 0.001) and had lower NIHSS scores (median 2 vs. 4, P < 0.001). Functional paresis was more common in those with TP mimics than in those with TN mimics, 18/55 (32.7%) vs. 82/1,221 (6.7%), P < 0.001. Systemic infection was less common in those with TP mimics than in those with TN mimics, 1/55 (1.8%) vs. 160/1,221 (13.1%), P < 0.011. There was a trend toward "syncope, hypotension, or other cardiovascular diagnosis" being less common in those with TP mimics than in those with TN mimics, 1/55 (1.8%) vs. 118/1,221 (9.7%), P < 0.055. Conclusions: In the SSTS, those with triage-positive and triage-negative stroke mimics were younger and had less severe symptoms than patients with stroke. All patients with TP mimics who had hemiparesis but overall exhibited less severe symptoms against true stroke but more severe symptoms than those with TN mimics were triaged to the nearest hospital. Over-triage of functional paresis to the CSC was relatively common. Meanwhile, a large majority of cases with minor symptoms caused by stroke mimics was triaged correctly by the SSTS to the nearest stroke center.

Analysis and modelling of mistriage in the Stockholm stroke triage system.

Introduction: The Stockholm Stroke Triage System (SSTS) is a prehospital triage system for detection of patients eligible for endovascular thrombectomy (EVT). Assessment of hemiparesis combined with ambulance-hospital teleconsultation is used to route patients directly to the thrombectomy centre. Some patients are not identified and require secondary transport for EVT (undertriage) while others taken to the thrombectomy centre do not undergo EVT (overtriage). The aims of this study were to characterize mistriaged patients, model for and evaluate alternative triage algorithms. Patients and methods: Patients with suspected stroke transported by priority 1 ground ambulance between October 2017 and October 2018 (n = 2905) were included. Three triage algorithms were modelled using prehospital data. Decision curve analysis was performed to calculate net benefit (correctly routing patients for EVT without increasing mistriage) of alternative models vs SSTS. Results: Undertriage for EVT occurred in n = 35/2582 (1.4%) and overtriage in n = 239/323 (74.0%). Compared to correct thrombectomy triages, undertriaged patients were younger and had lower median NIHSS (10 vs 18), despite 62.9% with an M1 occlusion. In overtriaged patients, 77.0% had a stroke diagnosis (29.7% haemorrhagic). Hemiparesis and FAST items face and speech were included in all models. Decision curve analysis showed highest net benefit for SSTS for EVT, but lower for large artery occlusion (LAO) stroke. Discussion: Undertriaged patients had lower NIHSS, likely due to better compensated proximal occlusions. SSTS was superior to other models for identifying EVT candidates, but lacked information allowing comparison to other prehospital scales. Conclusion: Using prehospital data, alternative models did not outperform the SSTS in finding EVT candidates.

The Stockholm Stroke Triage Project: Outcomes of Endovascular Thrombectomy Before and After Triage Implementation.

BACKGROUND AND PURPOSE: The Stockholm Stroke Triage System (SSTS) is a prehospital algorithm for detection of endovascular thrombectomy (EVT)-eligible patients, combining symptom severity assessment and ambulance-to-hospital teleconsultation, leading to a decision on primary stroke center bypass. In the Stockholm Region (6 primary stroke centers, 1 EVT center), SSTS implementation in October 2017 reduced onset-to-EVT time by 69 minutes. We compared clinical outcomes before and after implementation of SSTS in an observational study. METHODS: We prospectively recruited patients transported by Code Stroke ambulance within the Stockholm region under the SSTS, treated with EVT during October 2017 to October 2019, and compared to EVT patients from 2 previous years. OUTCOMES: shift in modified Rankin Scale (mRS) scores, mRS score 0 to 1, mRS score 0 to 2, and death (all 3 months), National Institutes of Health Stroke Scale (NIHSS) score change 24-hour post-EVT, recanalization (Thrombolysis in Cerebral Infarction 2b-3), and symptomatic intracranial hemorrhage. mRS outcomes were adjusted for age and baseline NIHSS. RESULTS: Patients with EVT in the SSTS group (n=244) were older and had higher baseline NIHSS versus historical controls (n=187): median age 74 (interquartile range, 63-81) versus 71 (61-78); NIHSS score 17 (11.5-21) versus 15 (10-20). During SSTS, median onset-to-puncture time was 136 versus 205 minutes (P<0.001). Adjusted common odds ratio for lower mRS in SSTS patients was 1.7 (95% CI, 1.2-2.3) versus controls. During SSTS, 83/240 (34.6%) versus 44/186 (23.7%) reached 3-month mRS score 0 to 1 (P=0.014), adjusted common odds ratio 2.3 (95% CI, 1.4-3.6). Median NIHSS change 24-hour post-EVT was 6 versus 4 (P=0.005). Differences in Thrombolysis in Cerebral Infarction, symptomatic intracranial hemorrhage, and death were nonsignificant. CONCLUSIONS: With an onset to arterial puncture time reduction by 69 minutes, outcomes in thrombectomy-treated patients improved significantly after region-wide large artery occlusion triage system implementation. These results warrant replication studies in other geographic and organizational circumstances.

Sex Equitable Prehospital Stroke Triage Using Symptom Severity and Teleconsultation.

Objectives: We aimed to determine whether there are sex differences in prehospital accuracy of the Stockholm Stroke Triage System (SSTS) to predict large artery occlusion (LAO) stroke, and endovascular thrombectomy (EVT), and whether clinical characteristics differ between men and women undergoing "code stroke" ambulance transport. Materials and Methods: This prospective observational study collected data between October 2017 and October 2018. We included 2,905 patients, transported as "code stroke," by nurse-staffed ground ambulance, to a Stockholm Region hospital. Exclusion criteria were private or helicopter transport, onset outside Stockholm, and in-hospital stroke. We compared overall accuracy, sensitivity, specificity, positive and negative predictive values, and clinical characteristics between sexes. Results: No significant sex differences in SSTS predictive performance for LAO or EVT were found, overall accuracy for LAO 87.3% in women vs. 86.7% in men. Women were median 4 years older and more frequently had stroke mimics (46.2 vs. 41.8%). Women more commonly had decreased level of consciousness (14.0 vs. 10.2%) and moderate-to-severe motor symptoms (by 2.7-3.8 percentage points), and less commonly limb ataxia (7.2 vs. 9.7%). Conclusions: The SSTS had equal predictive performance for LAO and EVT among men and women, despite minor sex differences in the clinical characteristics in patients undergoing ambulance transport for suspected stroke.

Implementation of a Prehospital Stroke Triage System Using Symptom Severity and Teleconsultation in the Stockholm Stroke Triage Study.

Importance: To our knowledge, it is unknown whether a prehospital stroke triage system combining symptom severity and teleconsultation could accurately select patients for primary stroke center bypass and hasten delivery of endovascular thrombectomy (EVT) without delaying intravenous thrombolysis (IVT). Objective: To evaluate the predictive performance of the newly implemented Stockholm Stroke Triage System (SSTS) for large-artery occlusion (LAO) stroke and EVT initiation. Secondary objectives included evaluating whether the Stockholm Stroke Triage System shortened onset-to-puncture time for EVT and onset-to-needle time (ONT) for IVT. Design, Setting, and Participants: This population-based prospective cohort study conducted from October 2017 to October 2018 across the Stockholm region (Sweden) included patients transported by first-priority ("code stroke") ambulance to the hospital for acute stroke suspected by an ambulance nurse and historical controls (October 2016-October 2017). Exclusion criteria were in-hospital stroke and helicopter or private transport. Of 2909 eligible patients, 4 (0.14%) declined participation. Exposures: Patients were assessed by ambulance nurses with positive the face-arm-speech-time test or other stroke suspicion and were evaluated for moderate-to-severe hemiparesis (≥2 National Institutes of Health stroke scale points each on the ipsilateral arm and leg [A2L2 test]). If present, the comprehensive stroke center (CSC) stroke physician was teleconsulted by phone for confirmation of stroke suspicion, assessment of EVT eligibility, and direction to CSC or the nearest primary stroke center. If absent, the nearest hospital was prenotified. Main Outcomes and Measures: Primary outcome: LAO stroke. Secondary outcomes: EVT initiation, onset-to-puncture time, and ONT. Predictive performance measures included sensitivity, specificity, positive and negative predictive values, the overall accuracy for LAO stroke, and EVT initiation. Results: We recorded 2905 patients with code-stroke transports (1420 women [49%]), and of these, 323 (11%) had A2L2+ teleconsultation positive results and were triaged for direct transport to CSC (median age, 73 years [interquartile range (IQR), 64-82 years]; 55 women [48%]). Accuracy for LAO stroke was 87% (positive predictive value, 41%; negative predictive value, 93%) and 91% for EVT initiation (positive predictive value, 26%; negative predictive value, 99%). Endovascular thrombectomy was performed for 84 of 323 patients (26%) with triage-positive results and 35 of 2582 patients (1.4%) with triage-negative results. In EVT cases with a known onset time (77 [3%]), the median OPT was 137 minutes (IQR, 118-180; previous year, 206 minutes [IQR, 160-280]; n = 75) (P < .001). The regional median ONT (337 [12%]) was unchanged at 115 minutes (IQR, 83-164; previous year, 115 minutes [IQR, 85-161]; n = 360) (P = .79). The median CSC IVT door-to-needle time was 13 minutes (IQR, 10-18; 116 [4%]) (previous year, 31 minutes [IQR, 19-38]; n = 45) (P < .001). Conclusions and Relevance: The Stockholm Stroke Triage System, which combines symptom severity and teleconsultation, results in markedly faster EVT delivery without delaying IVT.

Early Inhibition of P-Selectin/P-Selectin Glycoprotein Ligand-1 Reduces Intimal Hyperplasia in Murine Vein Grafts through Platelet Adhesion.

Inflammatory processes contribute to intimal hyperplasia (IH) and long-term failure of vein grafts used in bypass surgery. Leukocyte recruitment on endothelial cells of vessels during inflammation is regulated by P-selectin and P-selectin glycoprotein ligand-1 (PSGL-1), which also mediates the interaction between platelets and endothelial cells in vein grafts transferred to arteries. However, how this pathway causes IH in vein grafts is unclear. In this study, we used a murine model of vein grafting to investigate P-selectin-mediated platelet adhesion, followed by IH. On the luminal surface of the vein graft, leukocyte recruitment occurred mainly in areas with adhered platelets rather than on endothelial cells without adherent platelets 1 hour after vein grafting. Blockage of either P-selectin or PSGL-1 reduced platelet adhesion and leukocyte recruitment on the luminal surface of vein grafts. Inhibition of the P-selectin pathway in vein grafts significantly reduced platelet-mediated leukocyte recruitment and IH of vein grafts 28 days after surgery. The study demonstrates that functional blockage of the P-selectin/PSGL-1 pathway in the early inflammatory phase after vein grafting reduced leukocyte invasion in the vein graft wall and later IH development. The findings imply an attractive early time window for prevention of vein graft failure by manipulating platelet adhesion.

Platelet adhesion on endothelium early after vein grafting mediates leukocyte recruitment and intimal hyperplasia in a murine model.

Intimal hyperplasia (IH) is the substrate for accelerated atherosclerosis and limited patency of vein grafts. However, there is still no specific treatment targeting IH following graft surgery. In this study, we used a mouse model of vein grafting to investigate the potential for early intervention with platelet function for later development of graft IH. We transferred the inferior vena cava (IVC) from donor C57BL/6 mice to the carotid artery in recipients using a cuff technique. We found extensive endothelial injury and platelet adhesion one hour following grafting. Adhesion of leukocytes was distinct in areas of platelet adhesion. Platelet and leukocyte adhesion was strongly reduced in mice receiving a function-blocking antibody against the integrin αIIbß3. This was followed by a reduction of IH one month following grafting. Depletion of platelets using antiserum also reduced IH at later time points. These findings indicate platelets as pivotal to leukocyte recruitment to the wall of vein grafts. In conclusion, the data also highlight early intervention of platelets and inflammation as potential treatment for later formation of IH and accelerated atherosclerosis following bypass surgery.

Contribution of endothelial injury and inflammation in early phase to vein graft failure: the causal factors impact on the development of intimal hyperplasia in murine models.

OBJECTIVES: Autologous veins are preferred conduits in by-pass surgery. However, long-term results are hampered by limited patency due to intimal hyperplasia. Although mechanisms involved in development of intimal hyperplasia have been established, the role of inflammatory processes is still unclear. Here, we studied leukocyte recruitment and intimal hyperplasia in inferior vena cava grafts transferred to abdominal aorta in mice. METHODS AND RESULTS: Several microscopic techniques were used to study endothelium denudation and regeneration and leukocyte recruitment on endothelium. Scanning electron microscopy demonstrated denudation of vein graft endothelium 7 days post-transfer and complete endothelial regeneration by 28 days. Examination of vein grafts transferred to mice transgenic for green fluorescent protein under Tie2 promoter in endothelial cells showed regeneration of graft endothelium from the adjacent aorta. Intravital microscopy revealed recruitment of leukocytes in vein grafts at 7 days in wild type mice, which had tapered off by 28 days. At 28 and 63 days there was significant development of intimal hyperplasia. In contrast; no injury, leukocyte recruitment nor intimal hyperplasia occurred in arterial grafts. Leukocyte recruitment was reduced in vein grafts in mice deficient in E- and P-selectin. In parallel, intimal hyperplasia was reduced in vein grafts in mice deficient in E- and P-selectin and in wild type mice receiving P-selectin/E-selectin function-blocking antibodies. CONCLUSION: The results show that early phase endothelial injury and inflammation are crucial processes in intimal hyperplasia in murine vein grafts. The data implicate endothelial selectins as targets for intervention of vein graft disease.

Intravital microscopy on atherosclerosis in apolipoprotein e-deficient mice establishes microvessels as major entry pathways for leukocytes to advanced lesions.

BACKGROUND: There has been considerable speculation about the role of lesion microvessels in the accumulation of leukocytes in atherosclerosis. However, direct study of microvascular recruitment of leukocytes in lesions has not been performed, and the quantitative role for this route of entry is unclear. METHODS AND RESULTS: Here, microvascular recruitment of leukocytes was studied in advanced lesions in 12- to 24-month-old apolipoprotein E-deficient (ApoE(-/-)) mice. Histology and transmission electron microscopy demonstrated the presence of mainly adventitial, but also intimal, microvessels. Interactions between leukocytes and endothelium occurred in lesion venules. Leukocyte rolling was largely P-selectin dependent; however, residual rolling was mediated by L-selectin and endothelial P-selectin glycoprotein ligand 1. Leukocyte adhesion was significant and was attenuated in mice treated with antibodies against P-selectin, CD18, or both before preparation for intravital microscopy, suggesting acute activation of these 2 molecules by surgical trauma. Nonetheless, the density of firmly arrested leukocytes was 100-fold higher in lesion venules compared with the arterial lumen even in mice pretreated with antibodies against P-selectin and CD18, indicating strong recruitment of cells from venules that is unrelated to experimental manipulation. Fluorescent myelomonocytic cells in ApoE(-/-) mice carrying a knock-in mutation for enhanced green fluorescent protein (EGFP) in the lysozyme M locus (ApoE(-/-)/lysM(EGFP/EGFP) mice) were distributed specifically around lesion venules, but not around arterioles or capillaries, further indicating ongoing extravasation from venules into plaque tissue. CONCLUSIONS: These findings provide strong data for microvascular recruitment of leukocytes in atherosclerosis and indicate roles for L-selectin and P-selectin glycoprotein ligand 1 in this process.

Deletion of L-selectin increases atherosclerosis development in ApoE-/- mice.

Atherosclerosis is an inflammatory disease characterized by accumulation of leukocytes in the arterial intima. Members of the selectin family of adhesion molecules are important mediators of leukocyte extravasation. However, it is unclear whether L-selectin (L-sel) is involved in the pathogenesis of atherosclerosis. In the present study, mice deficient in L-selectin (L-sel(-/-)) animals were crossed with mice lacking Apolipoprotein E (ApoE(-/-)). The development of atherosclerosis was analyzed in double-knockout ApoE/L-sel (ApoE(-/-)L-sel(-/-)) mice and the corresponding ApoE(-/-) controls fed either a normal or a high cholesterol diet (HCD). After 6 weeks of HCD, aortic lesions were increased two-fold in ApoE(-/-)L-sel(-/-) mice as compared to ApoE(-/-) controls (2.46%±0.54% vs 1.28%±0.24% of total aortic area; p<0.05). Formation of atherosclerotic lesions was also enhanced in 6-month-old ApoE(-/-)L-sel(-/-) animals fed a normal diet (10.45%±2.58% vs 1.87%±0.37%; p<0.05). In contrast, after 12 weeks of HCD, there was no difference in atheroma formation between ApoE(-/-)L-sel(-/-) and ApoE(-/-) mice. Serum cholesterol levels remained unchanged by L-sel deletion. Atherosclerotic plaques did not exhibit any differences in cellular composition assessed by immunohistochemistry for CD68, CD3, CD4, and CD8 in ApoE(-/-)L-sel(-/-) as compared to ApoE(-/-) mice. Leukocyte rolling on lesions in the aorta was similar in ApoE(-/-)L-sel(-/-) and ApoE(-/-) animals. ApoE(-/-)L-sel(-/-) mice exhibited reduced size and cellularity of peripheral lymph nodes, increased size of spleen, and increased number of peripheral lymphocytes as compared to ApoE(-/-) controls. These data indicate that L-sel does not promote atherosclerotic lesion formation and suggest that it rather protects from early atherosclerosis.

Determining receptor-ligand interaction of human galanin receptor type 3.

Galanin is a neuropeptide found throughout the central and peripheral nervous systems of a wide range of species, ranging from human and mouse to frog and tuna. Galanin mediates its physiological roles through three receptors (GalR1-3), all members of the G-protein coupled receptor family. In mapping these roles, receptor subtype selective ligands are crucial tools. To facilitate the ligand design, data on receptor structure and interaction points are of great importance. The current study investigates the mechanism by which galanin interacts with GalR3. Mutated receptors were tested with competitive binding analysis in vitro. Our studies identify six mutagenic constructs that lost receptor affinity completely, despite being expressed at the cell surface. Mutations of the Tyr103(3.33) in transmembrane helix (TM) III, His251(6.51) in TM VI, Arg273(7.35) or His277(7.39) in TM VII, Phe263(6.63) or Tyr270(7.32) in the extracellular loop III all result in complete reduction of ligand binding. In addition, docking studies of an in silico model of GalR3 propose that four of the identified residues interact with pharmacophores situated within the galanin(2-6) sequence. This study provides novel insights into the interaction between ligands and GalR3 and highlights the requirement for correct design of targeting ligands.

Immune cell recruitment to inflammatory loci is impaired in mice deficient in basement membrane protein laminin alpha4.

For leukocytes to penetrate the vessel wall, they need to interact sequentially with the endothelial lining and the perivascular BM. The matrix protein laminin-411 is a major constituent of the vascular BM. The laminin alpha4 chain is a component of laminin-411 and has structural and signaling functions. Here, we addressed the role of BM laminin alpha4 in leukocyte recruitment to inflammatory loci. We used several recruitment models in Lam4(-/-) and WT mice to determine whether lack of laminin-411 in the perivascular BM influences extravasation of inflammatory cells. Recruitment of all major leukocyte subsets (neutrophils, monocytes, and lymphocytes) was reduced in Lam4(-/-) mice compared with WT. With the use of intravital microscopy, we concluded that this decrease was a result of impaired diapedesis through the vessel wall, as neither leukocyte adhesion to the endothelial lining nor migration in extravascular tissue was hampered in Lam4(-/-) mice. Collectively, our data suggest a reduced ability of immune cells to penetrate the vessel wall in mice deficient in laminin alpha4.

Distinct infiltration of neutrophils in lesion shoulders in ApoE-/- mice.

Inflammation and activation of immune cells are key mechanisms in the development of atherosclerosis. Previous data indicate important roles for monocytes and T-lymphocytes in lesions. However, recent data suggest that neutrophils also may be of importance in atherogenesis. Here, we use apolipoprotein E (ApoE)-deficient mice with fluorescent neutrophils and monocytes (ApoE(-/-)/Lys(EGFP/EGFP) mice) to specifically study neutrophil presence and recruitment in atherosclerotic lesions. We show by flow cytometry and confocal microscopy that neutrophils make up for 1.8% of CD45(+) leukocytes in the aortic wall of ApoE(-/-)/Lys(EGFP/EGFP) mice and that their contribution relative to monocyte/macrophages within lesions is approximately 1:3. However, neutrophils accumulate at sites of monocyte high density, preferentially in shoulder regions of lesions, and may even outnumber monocyte/macrophages in these areas. Furthermore, intravital microscopy established that a majority of leukocytes interacting with endothelium on lesion shoulders are neutrophils, suggesting a significant recruitment of these cells to plaque. These data demonstrate neutrophilic granulocytes as a major cellular component of atherosclerotic lesions in ApoE(-/-) mice and call for further study on the roles of these cells in atherogenesis.

CD44-deficiency on hematopoietic cells limits T-cell number but does not protect against atherogenesis in LDL receptor-deficient mice.

OBJECTIVE: Vascular and inflammatory cells express adhesion molecule CD44. We demonstrated previously that enhanced CD44 localizes in human atherosclerotic lesions. Apolipoprotein E/cd44 double-deficient mice and apolipoprotein E-deficient mice transplanted with CD44-deficient bone marrow (BM) exhibit reduced atherosclerosis. Since CD44 is a novel factor in atherogenesis, it is imperative that it is investigated in more than one animal model to conclusively determine its role in this particular disease pathology. To test the hypothesis that CD44 expressed by hematopoietic cells plays a critical role in atherogenesis in the low density lipoprotein (LDL) receptor-deficient mouse model, we performed BM reconstitution experiments. METHODS: Lethally irradiated LDL receptor-deficient mice were transplanted with either CD44-deficient or wild-type BM. Beginning 10 weeks after successful reconstitution, mice consumed a cholesterol-enriched atherogenic diet for 6 or 11 weeks. RESULTS: Surprisingly, CD44-deficiency on BM-derived inflammatory cells did not affect lesion size. Additionally, neither group displayed differences in smooth muscle cell, macrophage, collagen, or elastin content as well as lipoprotein levels. However, lesions in CD44-deficient BM-recipient mice contained fewer T-cells compared to wild-type BM mice. Interestingly, CD44-deficient T-cells expressed less chemokine receptor-5 mRNA. Furthermore, in vivo leukocyte adhesion decreased in CD44-deficient mice compared to wild-type mice. CONCLUSION: This study surprisingly revealed that atherogenesis does not require CD44 expression on hematopoietic cells in the LDL receptor-deficient mouse model. However, CD44 promotes T-cell recruitment, downregulates chemokine receptor-5, and participates critically in leukocyte adhesion in vivo. Consequently, the anti-atherogenic role of CD44 may require CD44-deficiency on cell types other than inflammatory cells in the LDL receptor-deficient mouse model.

ApoE(-/-)/lysozyme M(EGFP/EGFP) mice as a versatile model to study monocyte and neutrophil trafficking in atherosclerosis.

OBJECTIVES: Intravital microscopy is a useful tool for studying leukocyte trafficking in atherosclerosis. However, distinction between various subclasses of leukocytes using this technology is lacking. Therefore, we generated ApoE(-/-)/Lysozyme M(EGFP/EGFP) mice and investigated whether targeted cell types could be visualized by in vivo microscopy and whether absence of lysozyme M will influence atherosclerosis. METHODS: We crossed male ApoE(-/-) mice with mice homozygous for a knock-in mutation of enhanced green fluorescent protein (EGFP) in the lysozyme M locus (Lys(EGFP/EGFP)) creating ApoE(-/-)/Lys(EGFP/EGFP) mice. Mice were sacrificed at the age of 26 weeks. Blood was collected for serum lipid analysis, differential white blood cell count and flow cytometry. Lesion area was determined on en face mounted aortas and sections from aortic roots were stained for immunohistochemistry. Atherosclerotic lesions were also studied by confocal- and intravital microscopy. RESULTS: Basic parameters, such as white blood cell count, cholesterol profile, lesion area and plaque composition was unaltered in ApoE(-/-)/Lys(EGFP/EGFP) mice compared to ApoE(-/-) mice. Fluorescent neutrophils and monocytes were clearly visualized by intravital fluorescence and confocal microscopy. Fluorescent cells were distributed primarily in the periphery of atherosclerotic lesions indicating a preference for recruitment in these areas. CONCLUSIONS: ApoE(-/-)/Lys(EGFP/EGFP) mice will serve as a useful model to study leukocyte trafficking in atherosclerosis and how different subsets of leukocytes influence atherogenesis.

Neutrophil primary granule proteins HBP and HNP1-3 boost bacterial phagocytosis by human and murine macrophages.

In acute inflammation, infiltrating polymorphonuclear leukocytes (also known as PMNs) release preformed granule proteins having multitudinous effects on the surrounding environment. Here we present what we believe to be a novel role for PMN-derived proteins in bacterial phagocytosis by both human and murine macrophages. Exposure of macrophages to PMN secretion markedly enhanced phagocytosis of IgG-opsonized Staphylococcus aureus both in vitro and in murine models in vivo. PMN secretion activated macrophages, resulting in upregulation of the Fcgamma receptors CD32 and CD64, which then mediated the enhanced phagocytosis of IgG-opsonized bacteria. The phagocytosis-stimulating activity within the PMN secretion was found to be due to proteins released from PMN primary granules; thorough investigation revealed heparin-binding protein (HBP) and human neutrophil peptides 1-3 (HNP1-3) as the mediators of the macrophage response to PMN secretion. The use of blocking antibodies and knockout mice revealed that HBP acts via beta2 integrins, but the receptor for HNP1-3 remained unclear. Mechanistically, HBP and HNP1-3 triggered macrophage release of TNF-alpha and IFN-gamma, which acted in an autocrine loop to enhance expression of CD32 and CD64 and thereby enhance phagocytosis. Thus, we attribute what may be a novel role for PMN granule proteins in regulating the immune response to bacterial infections.

Neutrophil secretion products pave the way for inflammatory monocytes.

The leukocyte response in inflammation is characterized by an initial recruitment of polymorphonuclear leukocytes (PMN) preceding a second wave of monocytes to the site of injury or infection. In the mouse, 2 populations of monocytes have been identified, Gr1(-)CCR2(-)CX3CR1(hi) resident monocytes and Gr1(+)CCR2(+)CX3CR1(lo) inflammatory monocytes. Here, intravital microscopy of the musculus cremaster and a subcutaneous air pouch model were used to investigate a possible link between PMN extravasation and the subsequent emigration of inflammatory monocytes in response to local stimulation with PAF. In mice that were made neutropenic by injection of a PMN-depleting antibody, the extravasation of inflammatory monocytes, but not resident monocytes, was markedly reduced compared with mice with intact white blood cell count but was restored by local treatment with secretion of activated PMN. Components of the PMN secretion were found to directly activate inflammatory monocytes and further examination revealed PMN-derived LL-37 and heparin-binding protein (HBP/CAP37/azurocidin) as primary mediators of the recruitment of inflammatory monocytes via activation of formyl-peptide receptors. These data show that LL-37 and HBP specifically stimulate mobilization of inflammatory monocytes. This cellular cross-talk functionally results in enhanced cytokine levels and increased bacterial clearance, thus boosting the early immune response.

No detectable endothelial- or leukocyte-derived L-selectin ligand activity on the endothelium in inflamed cremaster muscle venules.

L-selectin is important in mediating leukocyte recruitment in inflammation. The role of L-selectin was for long believed to be influenced by an inducible endothelial ligand; however, L-selectin ligand activity was recently shown to be mediated by leukocytic P-selectin glycoprotein ligand 1 (PSGL-1). Still, it is unknown whether PSGL-1 is deposited on the endothelium or whether leukocyte fragments or leukocytic uropods are presented on the venular surface. Moreover, it is unclear whether ligands for L-selectin other than PSGL-1 are present in inflammation. Overall, this has complicated understanding of the mechanisms that guide recruitment of inflammatory cells. Here, I used intravital microscopy on mouse cremaster muscle venules to show that L-selectin influences leukocyte rolling in inflammation exclusively by mediating L-selectin/PSGL-1-dependent, secondary capture to rolling and adherent leukocytes. I show that leukocyte primary capture in inflammation is mediated almost entirely by P-selectin, whereas the capacity of E-selectin to mediate capture appears to be minimal. In parallel, primary capture remaining after function inhibition of P-selectin is not decreased by blockage or absence of L-selectin. Rolling along the endothelium in venules following a number of inflammatory treatments was abolished by simultaneous blockage of P-selectin, E-selectin, and VCAM-1, indicating that there is no additional adhesive pathway involving L-selectin or any other molecule that can mediate leukocyte rolling in inflamed cremaster muscle venules in response to the used stimuli. Moreover, in vivo staining failed to detect any L-selectin ligand activity on the endothelium. These data demonstrate that expression of L-selectin on leukocytes is insufficient for mediating rolling and efficient recruitment of leukocytes in inflammation.

A novel class of potent nonglycosidic and nonpeptidic pan-selectin inhibitors.

An early step of the inflammatory response, the rolling of leukocytes on activated endothelial cells, is mediated by selectin/carbohydrate interactions. The tetrasaccharide sialy Lewisx is a ligand for E-, P-, and L-selectin and therefore serves as a lead structure for the development of analogues. A combination of synthesis and structure-based design allowed rapid optimization. The current lead 2a was evaluated in our E-selectin cell flow chamber assay where it proved to inhibit rolling and adhesion with an IC50 of 28+/-7 microM. The assays used are predictive for the in vivo efficacy of test compounds as shown for 2a in a proteose peptone induced peritonitis model of acute inflammation in mice.