Neutrophil adhesion and activation under flow

Inhibition of nitric oxide synthesis enhances leukocyte rolling and adhesion in human microvasculature

Background

Nitric oxide (NO) is a multifunctional signaling molecule that regulates important cellular events in inflammation including leukocyte recruitment. Previous studies have shown that pharmacological inhibition of NO synthesis induces leukocyte recruitment in various in vitro and animal models. However, it is not known whether NO modulation has similar effects on leukocyte-endothelial cell interactions within the human microvasculature. The present study explored the effect of systemic L-NAME treatment on leukocyte recruitment in the SCID-hu mouse model.

Methods

Human skin xenografts were transplanted in SCID mice to study human leukocyte dynamics in human vasculature. Early events of human leukocyte recruitment in human vasculature were studied using intravital microscopy. NO synthesis was pharmacologically inhibited using N^G-nitro-L-arginine methyl ester (L-NAME). Immunohistochemical analysis was performed to elucidate E-selectin expression in human xenograft skin. Human neutrophil-endothelial cell interactions were also studied in an in vitro flow chamber assay system. P- and E-selectin expression on cultured human umbilical vein endothelial cells (HUVECs) was measured using ELISA. Platelet-activating factor (PAF) synthesis was detected using a TLC-based assay.

Results

L-NAME treatment significantly enhanced the rolling and adhesion of human leukocytes to the human vasculature. Functional blocking of P- and E-selectins significantly inhibited rolling but not adhesion induced by inhibition of NO synthesis. Systemic L-NAME treatment enhanced E-selectin expression in human xenograft skin. L-NAME treatment significantly enhanced P- and E-selectin expression on HUVECs. L-NAME treatment did not significantly modify neutrophil rolling or adhesion to HUVECs indicating that L-NAME−induced subtle P- and E-selectin expression was insufficient to elicit dynamic neutrophil-HUVEC interactions in vitro. Moreover, synthesis of endothelial-derived PAF was not significantly modified by L-NAME treatment. These results point to the accelerated leukocyte recruitment in human vasculature following suppression of NO synthesis, effects that are mediated by P- and E-selectins. The findings are, however, not supported by the in vitro data.

Conclusion

Inhibition of endogenous NO triggers early events of human leukocyte recruitment in human vasculature, involving complex cellular or molecular mechanisms in addition to P- and E-selectin-mediated leukocyte rolling.

Statins affect the presentation of endothelial chemokines by targeting to multivesicular bodies

Background

In addition to lowering cholesterol, statins are thought to beneficially modulate inflammation. Several chemokines including CXCL1/growth-related oncogene (GRO)-α, CXCL8/interleukin (IL)-8 and CCL2/monocyte chemoattractant protein (MCP)-1 are important in the pathogenesis of atherosclerosis and can be influenced by statin-treatment. Recently, we observed that atorvastatin­treatment alters the intracellular content and subcellular distribution of GRO-α in cultured human umbilical vein endothelial cells (HUVECs). The objective of this study was to investigate the mechanisms involved in this phenomenon.

Methodology/ Principal Findings

The effect of atorvastatin on secretion levels and subcellular distribution of GRO-α, IL-8 and MCP-1 in HUVECs activated by interleukin (IL)-1β were evaluated by ELISA, confocal microscopy and immunoelectron microscopy. Atorvastatin increased the intracellular contents of GRO-α, IL-8, and MCP-1 and induced colocalization with E-selectin in multivesicular bodies. This effect was prevented by adding the isoprenylation substrate GGPP, but not the cholesterol precursor squalene, indicating that atorvastatin exerts these effects by inhibiting isoprenylation rather than depleting the cells of cholesterol.

Conclusions/ Significance

Atorvastatin targets inflammatory chemokines to the endocytic pathway and multivesicular bodies and may contribute to explain the anti-inflammatory effect of statins at the level of endothelial cell function.

Dysregulation of neutrophil CXCR2 and pulmonary endothelial icam-1 promotes age-related pulmonary inflammation

We have previously demonstrated that aging is associated with prolonged pulmonary inflammation in a murine model of thermal injury. To further investigate these observations, we examined lung congestion, markers of neutrophil chemotaxis and adhesion, and lung endothelia responses in young and aged mice following burn injury. Analysis of lung tissue and bronchoalveolar lavage fluid 24 hours after injury revealed that more neutrophils accumulated in the lungs of aged mice (p<0.05), but did not migrate into the alveoli. We then sought to determine if accumulation of neutrophils in the lungs of aged mice was due to differences in the peripheral neutrophil pool or local changes within the lung. Following burn injury, aged mice developed a pronounced peripheral blood neutrophilia (p<0.05) in comparison to their younger counterparts. In aged animals, there was a reduced frequency and mean fluorescent intensity of neutrophil CXCR2 expression (p<0.05). Interestingly, in uninjured aged mice, peripheral blood neutrophils demonstrated elevated chemokinesis, or hyperchemokinesis, (p<0.05), but showed a minimal chemotatic response to KC. To determine if age impacts neutrophil adhesion molecules, we assessed CD62L and CD11b expression on peripheral blood neutrophils. No age-dependent difference in the frequency or mean fluorescent intensity of CD62L or CD11b was observed post-burn trauma. Examination of pulmonary vasculature adhesion molecules which interact with neutrophil selectins and integrins revealed that intracellular adhesion molecule-1 (ICAM-1) was elevated in aged mice at 24 hours after burn as compared to young mice (p<0.05). Overall, our data suggests that age-associated pulmonary congestion observed following burn injury may be due to differences in lung endothelial adhesion responses that are compounded by elevated numbers of hyperchemokinetic circulating neutrophils in aged mice.

Protein kinase C-θ is required for murine neutrophil recruitment and adhesion strengthening under flow

Protein kinase C (PKC)-θ is involved in T cell activation via regulating the avidity of the β(2) integrin LFA-1 in the immunological synapse. LFA-1 also mediates leukocyte adhesion. To investigate the role of PKC-θ in neutrophil adhesion, we performed intravital microscopy in cremaster venules of mice reconstituted with bone marrow from LysM-GFP(+) (wild-type [WT]) and PKC-θ gene-deficient (Prkcq(-/-)) mice. Following stimulation with CXCL1, both WT and Prkcq(-/-) cells became adherent. Although most WT neutrophils remained adherent for at least 180 s, 50% of Prkcq(-/-) neutrophils were detached after 105 s and most by 180 s. Upon CXCL1 injection, rolling of all WT neutrophils stopped for 90 s, but rolling of Prkcq(-/-) neutrophils started 30 s after CXCL1 stimulation. A similar neutrophil adhesion defect was seen in vitro, and spreading of Prkcq(-/-) neutrophils was delayed. Prkcq(-/-) neutrophil recruitment was impaired in fMLP-induced transmigration into the cremaster muscle, thioglycollate-induced peritonitis, and LPS-induced lung injury. We conclude that PKC-θ mediates integrin-dependent neutrophil functions and is required to sustain neutrophil adhesion in postcapillary venules in vivo. These findings suggest that the role of PKC-θ in outside-in signaling following engagement of neutrophil integrins is relevant for inflammation in vivo.

Effects of different leukocyte subpopulations and flow conditions on leukocyte accumulation during reperfusion

BACKGROUND/AIMS

The study examined the interdependent effects of shear stress and different leukocyte subpopulations on endothelial cell activation and cell interactions during low flow and reperfusion.

METHODS

Human umbilical venous endothelial cells were perfused with either neutrophils or monocytes at different shear stress (2-0.25 dyn/cm(2)) and adhesion was quantified by microscopy. Effects of adherent neutrophils and monocytes on endothelial cell adhesion molecule expression were analyzed by flow cytometry after 4-hour static coincubation. After coincubation, the cocultures were reperfused with labeled neutrophils at 2 dyn/cm(2) and their adhesion was quantified selectively. For the control, endothelium monocultures with and without lipopolysaccharide activation were used.

RESULTS

At 2 dyn/cm(2), adhesion did not exceed baseline levels on nonactivated endothelium. Decreasing shear stress to 0.25 dyn/cm(2) largely increased the adhesion of both leukocyte subpopulations, similar to the effect of lipopolysaccharide at 2 dyn/cm(2). However, only adherent monocytes increased adhesion molecule expression, whereas neutrophils had no effect. As a functional consequence, adherent monocytes largely increased neutrophil adhesion during reperfusion, whereas adherent neutrophils did not.

CONCLUSION

Compromised shear stress is an autonomous trigger of leukocyte adhesion even in the absence of additional activators. Exceeding this immediate effect, adherent monocytes induce further endothelial activation and enhance further neutrophil adhesion during reperfusion.

On, around, and through: neutrophil-endothelial interactions in innate immunity

This manuscript will review our current understanding of neutrophilic polymorphonuclear leukocyte (neutrophil) interactions with the endothelium during immune and inflammatory responses, focusing on the molecular mechanisms regulating neutrophil adhesion to and migration through the endothelium in response to infection or tissue injury. This is a complex and dynamic area of research and one that has been the topic of several recent comprehensive reviews to which the interested reader is referred (64, 118, 131). By design, this review will begin with a brief review of some basic aspects of neutrophil biology and endothelial adhesion to provide a foundation. The remainder of the review will focus on selected areas of this complex field, specifically the role of the endothelial glycocalyx in regulating neutrophil adhesion and the mechanisms and consequences of migration of neutrophils between (paracellular) and through (transcellular) endothelial cells during egress from the vasculature.

Creating a pro-survival and anti-inflammatory phenotype by modulation of acetylation in models of hemorrhagic and septic shock

Shock, regardless of etiology, is characterized by decreased tissue perfusion resulting in cell death, organ dysfunction, and poor survival. Current therapies largely focus on restoring tissue perfusion through resuscitation but have failed to address the specific cellular dysfunction caused by shock. Acetylation is rapidly emerging as a key mechanism that regulates the expression of numerous genes (epigenetic modulation through activation of nuclear histone proteins), as well as functions of multiple cytoplasmic proteins involved in key cellular functions such as cell survival, repair/healing, signaling, and proliferation. Cellular acetylation can be increased immediately through the administration of histone deacetylase inhibitors (HDACI). A series of studies have been performed using: (1) cultured cells; (2) single-organ ischemia-reperfusion injury models; (3) rodent models of lethal septic and hemorrhagic shock; (4) swine models of lethal hemorrhagic shock and multi-organ trauma; and (5) tissues from severely injured trauma patients, to fully characterize the changes in acetylation that occur following lethal insults and in response to treatment with HDACI. These data demonstrate that: (1) shock causes a decrease in acetylation of nuclear and cytoplasmic proteins; (2) hypoacetylation can be rapidly reversed through the administration of HDACI; (3) normalization of acetylation prevents cell death, decreases inflammation, attenuates activation of pro-apoptotic pathways, and augments pro-survival pathways; (4) the effect of HDACI significantly improves survival in lethal models of septic shock, hemorrhagic shock, and complex poly-trauma without need for conventional fluid resuscitation or blood transfusion; and (5) improvement in survival is not due to better resuscitation but due to an enhanced ability of cells to tolerate lethal insults.As different models of hemorrhagic or septic shock have specific strengths and limitations, this chapter will summarize our attempts to create "pro-survival and anti-inflammatory phenotype" in various models of hemorrhagic shock and septic shock.

The actin-bundling protein L-plastin: a critical regulator of immune cell function

L-plastin is a leukocyte-specific protein that cross-links actin filaments into tight bundles, increasing the stability of actin-based structures such as podosomes and lamellipodia. While first identified as an abundant cytoplasmic protein in hematopoietically derived cells over 25 years ago, the requirement for L-plastin in multiple functions critical for immunity, such as antigen receptor signaling, adhesion, and motility, has only recently become clear. L-plastin has been identified as an important component in cellular processes critical for neutrophil, macrophage, osteoclast, eosinophil, and T- and B-lymphocyte biology. Following a brief description of the structure and function of L-plastin, the regulation of immune cell functions by L-plastin will be reviewed in detail.

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) preserves gut barrier function by blocking neutrophil-endothelial cell adhesion after hemorrhagic shock and resuscitation in mice

BACKGROUND

We have shown that heparin-binding epidermal growth factor-like growth factor (HB-EGF) protects the intestines from injury in several different animal models, including hemorrhagic shock and resuscitation (HS/R). The current study was designed to explore the mechanisms underlying the anti-inflammatory role of HB-EGF in preservation of gut barrier function after injury.

METHODS

In vivo, HS/R was induced in wild-type and neutropenic mice, with or without administration of HB-EGF, and intestinal permeability determined by use of the everted gut sac method. In vitro, cultured human umbilical vein endothelial cells (HUVECs) and freshly isolated human peripheral blood mononuclear cells (PMNs) were used to determine the effects of HB-EGF on HUVEC-PMN adhesion, reactive oxygen species production in PMN, adhesion molecule expression in HUVEC and PMN, and the signaling pathways involved.

RESULTS

We found that administration of HB-EGF to healthy mice led to preservation of gut barrier function after HS/R. Likewise, induction of neutropenia in mice also led to preservation of gut barrier function after HS/R. Administration of HB-EGF to neutropenic mice did not lead to further improvement in gut barrier function. In vitro studies showed that HB-EGF decreased neutrophil-endothelial cell (PMN-EC) adherence by down-regulating adhesion molecule expression in EC via the phosphoinositide 3-kinase-Akt pathway, and by inhibiting adhesion molecule surface mobilization and reactive oxygen species production in PMN.

CONCLUSION

These results indicate that HB-EGF preserves gut barrier function by inhibiting PMN and EC activation, thereby blocking PMN-EC adherence after HS/R in mice, and support the future use of HB-EGF in disease states manifested by hypoperfusion injury.

Neutrophils in innate host defense against Staphylococcus aureus infections

Staphylococcus aureus has been an important human pathogen throughout history and is currently a leading cause of bacterial infections worldwide. S. aureus has the unique ability to cause a continuum of diseases, ranging from minor skin infections to fatal necrotizing pneumonia. Moreover, the emergence of highly virulent, drug-resistant strains such as methicillin-resistant S. aureus in both healthcare and community settings is a major therapeutic concern. Neutrophils are the most prominent cellular component of the innate immune system and provide an essential primary defense against bacterial pathogens such as S. aureus. Neutrophils are rapidly recruited to sites of infection where they bind and ingest invading S. aureus, and this process triggers potent oxidative and non-oxidative antimicrobial killing mechanisms that serve to limit pathogen survival and dissemination. S. aureus has evolved numerous mechanisms to evade host defense strategies employed by neutrophils, including the ability to modulate normal neutrophil turnover, a process critical to the resolution of acute inflammation. Here we provide an overview of the role of neutrophils in host defense against bacterial pathogens and discuss strategies employed by S. aureus to circumvent neutrophil function.

Differentiation syndrome in promyelocytic leukemia: clinical presentation, pathogenesis and treatment

Differentiation syndrome (DS) represents a life-threatening complication in patients with acute promyelocytic leukemia (APL) undergoing induction therapy with all-trans retinoic acid (ATRA) or arsenic trioxide (ATO). It affected about 20–25% of all patients and so far there are no definitive diagnostic criteria. Clinically, DS is characterized by weight gain, fever not attributable to infection, respiratory distress, cardiac involvement, hypotension, and/or acute renal failure. At the histological point of view, there is an extensive interstitial and intra-alveolar pulmonary infiltration by maturing myeloid cells, endothelial cell damage, intra-alveolar edema, inter-alveolar hemorrhage, and fibrinous exsudates. DS pathogenesis is not completely understood, but it is believed that an excessive inflammatory response is the main phenomenon involved, which results in increased production of chemokines and expression of adhesion molecules on APL cells. Due to the high morbidity and mortality associated with DS, its recognition and the prompt initiation of the treatment is of utmost importance. Dexamethasone is considered the mainstay of treatment of DS, and the recommended dose is 10 mg twice daily by intravenous route until resolution of DS. In severe cases (respiratory or acute renal failure) it is recommended the discontinuation of ATRA or ATO until recovery.

The endothelial glycocalyx as a barrier to leukocyte adhesion and its mediation by extracellular proteases

The endothelial cell (EC) surface is coated with a layer of polysaccharides linked to membrane-bound and trans-membrane proteoglycans that comprise the glycocalyx, which is augmented by adsorbed proteins derived from the blood stream. This surface layer has been shown to affect hemodynamics in small blood vessels of the microcirculation, the resistance to flow, and leukocyte (WBC) to EC adhesion. Parallel studies of WBC-EC adhesion in response to chemoattractants and cytokines, and shedding of constituents of the glycocalyx, have suggested a role for activation of extracellular proteases in mediating the dynamics of WBC adhesion in response to inflammatory and ischemic stimuli. Likely candidates among the many proteases present are the matrix metalloproteases (MMPs). Inhibition of MMP activation with sub-antimicrobial doses of doxycycline, or zinc chelators, has also inhibited WBC adhesion and shedding of glycans from the EC surface in response to the chemoattractant fMLP. Taken together, these studies suggest that shedding of the EC glycocalyx exposes adhesion receptors and thus enhances WBC-EC adhesion. Future therapeutic strategies for treating pathologies such as the low flow state and inflammation may benefit by further exploration of the mechanics of the glycocalyx in light of protease activation and shear-dependent effects.

Mechanisms underlying the localisation of mast cells in tissues

Mast cells are tissue-resident cells best known for their role in allergy and host defence against helminth parasites. They are involved in responses against other pathogenic infections, wound healing and inflammatory disease. Committed mast cell progenitors are released from the bone marrow into the circulation, from where they are recruited into tissues to complete their maturation under the control of locally produced cytokines and growth factors. Directed migration occurs at distinct stages of the mast cell life-cycle and is associated with successive up- and downregulation of cell surface adhesion molecules and chemoattractant receptors as the cells mature. This article discusses some of the recent advances in our understanding of the mechanisms underlying mast cell recruitment.

Shedding of the endothelial glycocalyx in arterioles, capillaries, and venules and its effect on capillary hemodynamics during inflammation

The endothelial glycocalyx has been identified as a barrier to transvascular exchange of fluid, macromolecules, and leukocyte-endothelium [endothelial cell (EC)] adhesion during the inflammatory process. Shedding of glycans and structural changes of the glycocalyx have been shown to occur in response to several agonists. To elucidate the effects of glycan shedding on microvascular hemodynamics and capillary resistance to flow, glycan shedding in microvessels in mesentery (rat) was induced by superfusion with 10(-7) M fMLP. Shedding was quantified by reductions of fluorescently labeled lectin (BS-1) bound to the EC and reductions in thickness of the barrier to infiltration of 70-kDa dextran on the EC surface. Red cell velocities (two-slit technique), pressure drops (dual servo-null method), and capillary hematocrit (direct cell counting) were measured in parallel experiments. The results indicate that fMLP caused shedding of glycans in all microvessels with reductions in thickness of the barrier to 70-kDa dextran of 110, 80, and 123 nm, in arterioles, capillaries, and venules, respectively. Intravascular volumetric flows fell proportionately in all three divisions in response to rapid obstruction of venules by white blood cell (WBC)-EC adhesion, and capillary resistance to flow rose 18% due to diminished deformability of activated WBCs. Capillary resistance fell significantly 26% over a 30-min period, as glycans were shed from the EC surface to increase effective capillary diameter, whereas capillary hematocrit and anatomic diameter remained invariant. This decrease in capillary resistance mitigates the increase in resistance due to diminished WBC deformability, and hence these concurrent rheological events may be of equal importance in affecting capillary flow during the inflammatory process.

Introducing shear stress in the study of bacterial adhesion

During bacterial infections a sequence of interactions occur between the pathogen and its host. Bacterial adhesion to the host cell surface is often the initial and determining step of the pathogenesis. Although experimentally adhesion is mostly studied in static conditions adhesion actually takes place in the presence of flowing liquid. First encounters between bacteria and their host often occur at the mucosal level, mouth, lung, gut, eye, etc. where mucus flows along the surface of epithelial cells. Later in infection, pathogens occasionally access the blood circulation causing life-threatening illnesses such as septicemia, sepsis and meningitis. A defining feature of these infections is the ability of these pathogens to interact with endothelial cells in presence of circulating blood. The presence of flowing liquid, mucus or blood for instance, determines adhesion because it generates a mechanical force on the pathogen. To characterize the effect of flowing liquid one usually refers to the notion of shear stress, which is the tangential force exerted per unit area by a fluid moving near a stationary wall, expressed in dynes/cm(2). Intensities of shear stress vary widely according to the different vessels type, size, organ, location etc. (0-100 dynes/cm(2)). Circulation in capillaries can reach very low shear stress values and even temporarily stop during periods ranging between a few seconds to several minutes (1). On the other end of the spectrum shear stress in arterioles can reach 100 dynes/cm(2)(2). The impact of shear stress on different biological processes has been clearly demonstrated as for instance during the interaction of leukocytes with the endothelium (3). To take into account this mechanical parameter in the process of bacterial adhesion we took advantage of an experimental procedure based on the use of a disposable flow chamber (4). Host cells are grown in the flow chamber and fluorescent bacteria are introduced in the flow controlled by a syringe pump. We initially focused our investigations on the bacterial pathogen Neisseria meningitidis, a Gram-negative bacterium responsible for septicemia and meningitis. The procedure described here allowed us to study the impact of shear stress on the ability of the bacteria to: adhere to cells (1), to proliferate on the cell surface (5)and to detach to colonize new sites (6) (Figure 1). Complementary technical information can be found in reference 7. Shear stress values presented here were chosen based on our previous experience(1) and to represent values found in the literature. The protocol should be applicable to a wide range of pathogens with specific adjustments depending on the objectives of the study.

The emerging importance of α-L-fucose in human breast cancer: a review

Breast cancer cells incorporate the simple sugar alpha-L-fucose (fucose) into glycoproteins and glycolipids which, in turn, are expressed as part of the malignant phenotype. We have noted that fucose is not simply a bystander molecule, but, in fact, contributes to many of the fundamental oncologic properties of breast cancer cells. Here, we summarize the evidence from us and others that fucose is necessary for key functions of neoplastic progression including hematogenous metastasis, tumor invasion through extracellular matrices including basement membranes and up-regulation of the Notch signaling system, with implications for epithelial-to-mesenchymal transition and activation of breast cancer stem cells. Additionally, certain breast cancer biomarkers are fucose-rich while a well-known marker of breast cancer progression, soluble E-selectin, is a known counter-receptor of fucosylated selectin ligands. We provide illustrative examples and supportive evidence drawn from work with human breast cancer cell lines in vitro as well as clinical studies with human pathologic material. And finally, we discuss evidence that fucose (or its absence) is central to the mechanisms of action of several experimental targeted therapies which may prove useful in breast cancer treatment. We propose that alpha-L-fucose is essential in order to construct first, the malignant and then the metastatic phenotype of many human breast cancers. This knowledge may inform the search for novel treatment approaches in breast cancer.

Cortactin deficiency is associated with reduced neutrophil recruitment but increased vascular permeability in vivo

Cortactin is required for endothelial barrier function and leukocyte recruitment in vivo.

Neutrophil extravasation and the regulation of vascular permeability require dynamic actin rearrangements in the endothelium. In this study, we analyzed in vivo whether these processes require the function of the actin nucleation–promoting factor cortactin. Basal vascular permeability for high molecular weight substances was enhanced in cortactin-deficient mice. Despite this leakiness, neutrophil extravasation in the tumor necrosis factor–stimulated cremaster was inhibited by the loss of cortactin. The permeability defect was caused by reduced levels of activated Rap1 (Ras-related protein 1) in endothelial cells and could be rescued by activating Rap1 via the guanosine triphosphatase (GTPase) exchange factor EPAC (exchange protein directly activated by cAMP). The defect in neutrophil extravasation was caused by enhanced rolling velocity and reduced adhesion in postcapillary venules. Impaired rolling interactions were linked to contributions of β₂-integrin ligands, and firm adhesion was compromised by reduced ICAM-1 (intercellular adhesion molecule 1) clustering around neutrophils. A signaling process known to be critical for the formation of ICAM-1–enriched contact areas and for transendothelial migration, the ICAM-1–mediated activation of the GTPase RhoG was blocked in cortactin-deficient endothelial cells. Our results represent the first physiological evidence that cortactin is crucial for orchestrating the molecular events leading to proper endothelial barrier function and leukocyte recruitment in vivo.

Corticotropin-releasing hormone receptor-1 and 2 activity produces divergent resistance against stress-induced pulmonary Streptococcus pneumoniae infection

Utilizing a murine model of S. pneumoniae infection and restraint stress, we determined how corticotropin releasing hormone (CRH-R) receptors impacts disease. CRH-R1 (antalarmin) and CRH-R2 (astressin2B) antagonists were administered intraperitoneally prior to restraint stress followed by pulmonary S. pneumoniae infection. CRH-R1 inhibition is not protective against pneumococcal disease induced by stress. Conversely, CRH-R2 inhibition attenuates stress-induced bacterial growth and significantly prevented severe sepsis. Neutrophillic responses were associated with CRH receptor-specific disease outcome providing a potential cellular target for stress-induced susceptibility to the development of severe pneumococcal disease. CRH receptor-mediated effects on immune responses could prove valuable for novel therapeutics.

17(R)-Resolvin D1 differentially regulates TLR4-mediated responses of primary human macrophages to purified LPS and live E. coli

Detection and clearance of bacterial infection require balanced effector and resolution signals to avoid chronic inflammation. Detection of GNB LPS by TLR4 on m induces inflammatory responses, contributing to chronic inflammation and tissue injury. LXs and Rvs are endogenous lipid mediators that enhance resolution of inflammation, and their actions on primary human m responses toward GNB are largely uncharacterized. Here, we report that LXA(4), LXB(4), and RvD1, tested at 0.1-1 μM, inhibited LPS-induced TNF production from primary human m, with ATL and 17(R)-RvD1, demonstrating potent inhibition at 0.1 μM. In addition, 17(R)-RvD1 inhibited LPS-induced primary human m production of IL-7, IL-12p70, GM-CSF, IL-8, CCL2, and MIP-1α without reducing that of IL-6 or IL-10. Remarkably, when stimulated with live Escherichia coli, m treated with 17(R)-RvD1 demonstrated increased TNF production and enhanced internalization and killing of the bacteria. 17(R)-RvD1-enhanced TNF, internalization, and killing were not evident for an lpxM mutant of E. coli expressing hypoacylated LPS with reduced inflammatory activity. Furthermore, 17(R)-RvD1-enhanced, E. coli-induced TNF production was evident in WT but not TLR4-deficient murine m. Thus, Rvs differentially modulate primary human m responses to E. coli in an LPS- and TLR4-dependent manner, such that this Rv could promote resolution of GNB/LPS-driven inflammation by reducing m proinflammatory responses to isolated LPS and increasing m responses important for clearance of infection.

Effects of chlorogenic acid on neutrophil locomotion functions in response to inflammatory stimulus

AIM OF THE STUDY

Species of Lychnophora are used in Brazilian folk medicine as analgesic and anti-inflammatory agents. Chlorogenic acid (CGA) and their analogues are important components of polar extracts of these species, as well in several European and Asian medicinal plants. Some of these phenolic compounds display anti-inflammatory effects. In this paper we report the isolation of CGA from Lychnophora salicifolia and its effects on functions involved in neutrophils locomotion.

MATERIALS AND METHODS

LC-MS(n) data confirmed the presence of CGA in the plant. Actions of CGA were investigated on neutrophils obtained from peritoneal cavity of Wistar rats (4h after 1% oyster glycogen solution injection; 10 ml), and incubated with vehicle or with 50, 100 or 1000 μM CGA in presence of lipopolysaccharide from Escherichia coli (LPS, 5 μg/ml). Nitric oxide (NO; Griess reaction); prostaglandin E(2) (PGE(2)), interleukin-1β (IL-1β) and tumor necrosis factor-α [TNF-α; enzyme-linked immunosorbent assay (EIA)]; protein (flow cytometry) and gene (RT-PCR) expression of L-selectin, β(2)integrin and platelet-endothelial cell adhesion molecule-1 (PECAM-1) were quantified. In vitro neutrophil adhesion to primary culture of microvascular endothelial cell (PMEC) and neutrophil migration in response to formyl-methionil-leucil-phenilalanine (fMLP, 10(-8)M, Boyden chamber) was determined.

RESULTS

CGA treatment did not modify the secretion of inflammatory mediators, but inhibited L-selectin cleavage and reduced β(2) integrin, independently from its mRNA synthesis, and reduced membrane PECAM-1 expression; inhibited neutrophil adhesion and neutrophil migration induced by fMLP.

CONCLUSIONS

Based on these findings, we highlight the direct inhibitory actions of CGA on adhesive and locomotion properties of neutrophils, which may contribute to its anti-inflammatory effects and help to explain the use of Lychnophora salicifolia as an anti-inflammatory agent.

Real-time analysis of the inside-out regulation of lymphocyte function-associated antigen-1 revealed similarities to and differences from very late antigen-4

Ten years ago, we introduced a fluorescent probe that shed light on the inside-out regulation of one of the major leukocyte integrins, very late antigen-4 (VLA-4, CD49d/CD29). Here we describe the regulation of another leukocyte integrin, lymphocyte function-associated antigen-1 (LFA-1, CD11a/CD18) using a novel small fluorescent probe in real time on live cells. We found that multiple signaling mechanisms regulate LFA-1 conformation in a manner analogous to VLA-4. LFA-1 can be rapidly activated by Gα_i-coupled G protein-coupled receptors (GPCRs) and deactivated by Gα_s-coupled GPCRs. The effects of Gα_s-coupled GPCR agonists can be reversed in real time by receptor-specific antagonists. The specificity of the fluorescent probe binding has been assessed in a competition assay using the natural LFA-1 ligand ICAM-1 and the LFA-1-specific α I allosteric antagonist BIRT0377. Similar to VLA-4 integrin, modulation of the ligand dissociation rate can be observed for different LFA-1 affinity states. However, we also found a striking difference in the binding of the small fluorescent ligand. In the absence of inside-out activation ligand, binding to LFA-1 is extremely slow, at least 10 times slower than expected for diffusion-limited binding. This implies that an additional structural mechanism prevents ligand binding to inactive LFA-1. We propose that such a mechanism explains the inability of LFA-1 to support cell rolling, where the absence of its rapid engagement by a counterstructure in the inactive state leads to a requirement for a selectin-mediated rolling step.

Dysregulated neutrophil--endothelial interaction in antineutrophil cytoplasmic autoantibody (ANCA)-associated vasculitides: implications for pathogenesis and disease intervention

The interplay between neutrophils and endothelial cells allows ANCA to become pathogenic and results in uncontrolled inflammation in the vessel wall. This review presents an overall view on neutrophil-endothelial interaction during inflammation with a focus on ANCA-associated vasculitis, and summarizes the effector mechanisms which cause vascular damage in AAV. In addition, potential elements for disease intervention based on this process are discussed.

Systemic neutrophil activation in a mouse model of ischemic stroke and reperfusion

As a natural response to injury and disease, neutrophils activate, adhere to the microvasculature, migrate into brain tissue, and release toxic substances such as reactive oxygen species and proteases. This neutrophil response occurs when blood flow is returned to brain tissue (reperfusion) after ischemic stroke. Thus, the presence of activated systemic neutrophils increases the potential for tissue injury during reperfusion after ischemic stroke. Although experiments in rat models suggest that activated neutrophils play a pivotal role in cerebral ischemia reperfusion injury, little is known about systemic neutrophil activation during reperfusion following ischemic stroke in a mouse model. The purpose of this study was to characterize systemic leukocyte responses and neutrophil CD11b expression 15-min and 24-hr post-reperfusion in a mouse model of ischemic stroke. The intraluminal filament method of transient middle cerebral artery occlusion (tMCAO) with reperfusion or a sham procedure was performed in male C57Bl/6 mice. Automated leukocyte counts and manual white blood cell (WBC) differential counts were measured. Flow cytometry was used to assess systemic neutrophil surface CD11b expression. The data suggest that the damaging potential of systemic neutrophil activation begins as early as 15 min and remains evident at 24 hr after the initiation of reperfusion. In addition, because transgenic mouse models, bred on a C57Bl/6 background, are increasingly used to elucidate single mechanisms of reperfusion injury after ischemic stroke, findings from this study are foundational for future investigations examining the damaging potential of neutrophil responses post-reperfusion after ischemic stroke in genetically altered mouse models within this background strain.

The airway epithelium: more than just a structural barrier

The mammalian airway is lined by a variety of specialized epithelial cells that not only serve as a physical barrier but also respond to environment-induced damage through the release of biologically active factors and constant cellular renewal. The lung epithelium responds to environmental insults such as pathogens, cigarette smoke and pollution by secreting inflammatory mediators and antimicrobial peptides, and by recruiting immune cells to the site of infection or damage. When the epithelium is severely damaged, basal cells and Clara cells that have stem-cell-like properties are capable of self-renewal and proliferation in the affected area, to repair the damage. In order to effectively fight off infections, the epithelium requires the assistance of neutrophils recruited from the peripheral circulation through transendothelial followed by transepithelial migration events. Activated neutrophils migrate across the epithelium through a series of ligand-receptor interactions to the site of injury, where they secrete proteolytic enzymes and oxidative radicals for pathogen destruction. However, chronic activation and recruitment of neutrophils in airway diseases such as chronic obstructive pulmonary disease and asthma has been associated with tissue damage and disease severity. In this paper, we review the current understanding of the airway epithelial response to injury and its interaction with inflammatory cells, in particular the neutrophil.

Protease Activity and the Role of the Endothelial Glycocalyx in Inflammation

A new paradigm for governance of leukocyte-endothelium (WBC-EC) adhesion during the inflammatory process is presented in which shedding of the endothelial glycocalyx exposes adhesion molecules on the EC surface, which promotes WBC-EC adhesion. It is postulated that the effector of this shedding is the activation of extracellular proteases, one of which may be a member of the matrix metalloproteinase (MMP) family of zinc dependent endopetidases. This model for the role of the glycocalyx as a barrier to WBC-EC adhesion includes the additional participation of normally active extracellular proteolytic enzymes, i.e. sheddases, which may cleave proteoglycans or activate lyases that cleave GAG chains in the glycocalyx. In support of this hypothesis, studies are examined which have established the concurrent activation of MMP proenzymes on the EC surface, shedding of the glycocalyx, and enhanced WBC-EC adhesion.

Neutrophils, from marrow to microbes

Neutrophils are produced in the bone marrow from stem cells that proliferate and differentiate to mature neutrophils fully equipped with an armory of granules. These contain proteins that enable the neutrophil to deliver lethal hits against microorganisms, but also to cause great tissue damage. Neutrophils circulate in the blood as dormant cells. At sites of infection, endothelial cells capture bypassing neutrophils and guide them through the endothelial cell lining whereby the neutrophils are activated and tuned for the subsequent interaction with microbes. Once in tissues, neutrophils kill microorganisms by microbicidal agents liberated from granules or generated by metabolic activation. As a final act, neutrophils can extrude stands of DNA with bactericidal proteins attached that act as extracellular traps for microorganisms.

Mechanisms of leukocyte distribution during sepsis: an experimental study on the interdependence of cell activation, shear stress and endothelial injury

Introduction

This study was carried out to determine whether interactions of cell activation, shear stress and platelets at sites of endothelial injury explain the paradoxical maldistribution of activated leukocytes during sepsis away from local sites of infection towards disseminated leukocyte accumulation at remote sites.

Methods

Human umbilical venous endothelial cells (HUVEC) and polymorphonuclear neutrophils (PMN) were activated with lipopolysaccharide at 100 and 10 ng/ml to achieve adhesion molecule patterns as have been reported from the hyper- and hypo-inflammatory stage of sepsis. To examine effects of leukocyte activation on leukocyte-endothelial interactions, activated HUVEC were perfused with activated and non-activated neutrophils in a parallel plate flow chamber. Adhesion molecule expression and function were assessed by flow cytometry and blocking antibodies. In a subset of experiments the sub-endothelial matrix was exposed and covered with platelets to account for the effects of endothelial injury. To investigate interactions of these effects with flow, all experiments were done at various shear stress levels (3 to 0.25 dyne/cm²). Leukocyte-endothelial interactions were analyzed by videomicroscopy and analysis of covariance.

Results

Activation of neutrophils rendered adhesion increasingly dependent on shear stress reduction. At normal shear stress, shedding of L-selectin decreased adhesion by 56%. Increased rolling fractions of activated PMN at low shear stress revealed impaired integrin affinity despite numerical up-regulation of CD11b. On sub-maximally activated, intact HUVEC shear stress became the prevailing determinant of adhesion. Presence of a platelet-covered injury with high surface density of P-selectin was the strongest variable for adhesion. When compared to maximally activated HUVEC, platelets increased neutrophil adhesion by 2.7-fold. At sub-maximal activation a 10-fold increase was observed (P < 0.05 for all).

Conclusions

L-selectin shedding and integrin dysfunction render leukocyte adhesion increasingly susceptible to shear stress and alternative adhesion receptors. In combination, these effects inhibit recruitment to normally perfused sites with intact endothelium and favor maldistribution towards sites with compromised perfusion or endothelial injury.

Endothelial f-actin depolymerization enables leukocyte transmigration

A demanding task of medicine is to understand and control the immune system. Central players in the cellular immune response are the leukocytes that leave the blood stream for host defense. Endothelial cells limit the emigration rate of leukocytes. Being located between blood and tissues, they permit or deny the passage. The exact mechanism of this process called diapedesis is not solved yet. Leukocytes can principally traverse either between cells (paracellularly) or directly through an individual endothelial cell (transcellularly). The transcellular way has recently gained experimental support, but it is not clear how the endothelial cytoskeleton manages to open and close a transmigratory channel. Atomic force microscopy was used to investigate the endothelial cytoskeleton. In order to directly access the leukocyte-endothelial interaction site, we applied a special protocol ("nanosurgery"). As a result, the endothelial cell turned out to become softer in a confined region strictly underneath the leukocyte. Fluorescence microscopy confirmed a depolymerization of the f-actin strands at the invasion site. Leukocytes dramatically rearrange the endothelial cytoskeleton to form transmigratory channels.

Posttranslational modification of the NH2-terminal region of CXCL5 by proteases or peptidylarginine Deiminases (PAD) differently affects its biological activity

Posttranslational modifications, e.g. proteolysis, glycosylation, and citrullination regulate chemokine function, affecting leukocyte migration during inflammatory responses. Here, modification of CXCL5/epithelial cell-derived neutrophil-activating protein-78 (ENA-78) by proteases or peptidylarginine deiminases (PAD) was evaluated. Slow CXCL5(1-78) processing by the myeloid cell marker aminopeptidase N/CD13 into CXCL5(2-78) hardly affected its in vitro activity, but slowed down the activation of CXCL5 by the neutrophil protease cathepsin G. PAD, an enzyme with a potentially important function in autoimmune diseases, site-specifically deiminated Arg(9) in CXCL5 to citrulline, generating [Cit(9)]CXCL5(1-78). Compared with CXCL5(1-78), [Cit(9)]CXCL5(1-78) less efficiently induced intracellular calcium signaling, phosphorylation of extracellular signal-regulated kinase, internalization of CXCR2, and in vitro neutrophil chemotaxis. In contrast, conversion of CXCL5 into the previously reported natural isoform CXCL5(8-78) provided at least 3-fold enhanced biological activity in these tests. Citrullination, but not NH(2)-terminal truncation, reduced the capacity of CXCL5 to up-regulate the expression of the integrin α-chain CD11b on neutrophils. Truncation nor citrullination significantly affected the ability of CXCL5 to up-regulate CD11a expression or shedding of CD62L. In line with the in vitro results, CXCL5(8-78) and CXCL5(9-78) induced a more pronounced neutrophil influx in vivo compared with CXCL5(1-78). Administration of 300 pmol of either CXCL5(1-78) or [Cit(9)]CXCL5(1-78) failed to attract neutrophils to the peritoneal cavity. Citrullination of the more potent CXCL5(9-78) lowers its chemotactic potency in vivo and confirms the tempering effect of citrullination in vitro. The highly divergent effects of modifications of CXCL5 on neutrophil influx underline the potential importance of tissue-specific interactions between chemokines and PAD or proteases.

Crohn's disease as an immunodeficiency

The pathogenesis of Crohn's disease (CD) has widely been regarded as the consequence of a dysregulated T-cell-mediated response to intestinal microbes, and the majority of the worldwide research effort has focused on characterizing and treating the chronic inflammatory phase of the disease. However, recent molecular biological and clinical investigations indicate that CD is actually a primary immunodeficiency. At first counter-intuitive, the apparent paradox of a pathogenic innate immune defect can be linked mechanistically to the granulomatous chronic inflammation characteristic of the disease. Genome-wide association studies have corroborated the involvement of innate immune dysfunction in the pathogenesis of CD, but less than 20% of the heritable risk is accounted for. By contrast, in vitro and in vivo stimulation of the immune system has highlighted novel areas of interest that may lead to the development of targeted therapeutic and diagnostic tools.

Macrophage migration inhibitory factor increases leukocyte-endothelial interactions in human endothelial cells via promotion of expression of adhesion molecules

Macrophage migration inhibitory factor (MIF) has been shown to promote leukocyte-endothelial cell interactions, although whether this occurs via an effect on endothelial cell function remains unclear. Therefore, the aims of this study were to examine the ability of MIF expressed by endothelial cells to promote leukocyte adhesion and to investigate the effect of exogenous MIF on leukocyte-endothelial interactions. Using small interfering RNA to inhibit HUVEC MIF production, we found that MIF deficiency reduced the ability of TNF-stimulated HUVECs to support leukocyte rolling and adhesion under flow conditions. These reductions were associated with decreased expression of E-selectin, ICAM-1, VCAM-1, IL-8, and MCP-1. Inhibition of p38 MAPK had a similar effect on adhesion molecule expression, and p38 MAPK activation was reduced in MIF-deficient HUVECs, suggesting that MIF mediated these effects via promotion of p38 MAPK activation. In experiments examining the effect of exogenous MIF, application of MIF to resting HUVECs failed to induce leukocyte rolling and adhesion, whereas addition of MIF to TNF-treated HUVECs increased these interactions. This increase was independent of alterations in TNF-induced expression of E-selectin, VCAM-1, and ICAM-1. However, combined treatment with MIF and TNF induced de novo expression of P-selectin, which contributed to leukocyte rolling. In summary, these experiments reveal that endothelial cell-expressed MIF and exogenous MIF promote endothelial adhesive function via different pathways. Endogenous MIF promotes leukocyte recruitment via effects on endothelial expression of several adhesion molecules and chemokines, whereas exogenous MIF facilitates leukocyte recruitment induced by TNF by promoting endothelial P-selectin expression.

A novel mechanism for neutrophil priming in trauma: potential role of peritoneal fluid

BACKGROUND

We sought to determine the effect of peritoneal fluid from a novel animal model of abdominal compartment syndrome (ACS) on the proinflammatory status of polymorphonuclear leukocytes (PMNs) and monocytes. We hypothesize that peritoneal fluid is a potential priming and/or activating agent for PMNs/monocytes.

METHODS

ACS was induced in female Yorkshire swine, and peritoneal fluid was collected at the time of decompressive laparotomy. Naïve PMNs/monocytes were primed and/or activated with peritoneal fluid, phosphatidylcholine (PAF) plus peritoneal fluid, peritoneal fluid plus n-formyl-met-leu-phe (fMLP), and peritoneal fluid plus phorbol 12-myristate 13-acetate (PMA). Activation was determined by surface marker expression of integrins (CD11b an CD18) and selectins (CD62L). Additionally, proinflammatory cytokines in peritoneal fluid were analyzed.

RESULTS

Peritoneal fluid did not activate PMNs but increased CD11b expression on monocytes. When used as a primer for fMLP- or PMA-induced activation, peritoneal fluid significantly increased CD11b and CD18 expression on PMNs and monocytes. Peritoneal fluid collected at 6 and 12 h post decompressive laparotomy had similar effects. Interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) levels were increased in peritoneal fluid.

CONCLUSION

Peritoneal fluid represents a primer for PMNs/monocytes and seems to act through receptor-dependent and receptor-independent pathways. Strategies to reduce the amount of peritoneal fluid may decrease the locoregional and systemic inflammatory response by reducing priming and activation of neutrophils/monocytes.

Real-time imaging of trapping and urease-dependent transmigration of Cryptococcus neoformans in mouse brain

Infectious meningitis and encephalitis is caused by invasion of circulating pathogens into the brain. It is unknown how the circulating pathogens dynamically interact with brain endothelium under shear stress, leading to invasion into the brain. Here, using intravital microscopy, we have shown that Cryptococcus neoformans, a yeast pathogen that causes meningoencephalitis, stops suddenly in mouse brain capillaries of a similar or smaller diameter than the organism, in the same manner and with the same kinetics as polystyrene microspheres, without rolling and tethering to the endothelial surface. Trapping of the yeast pathogen in the mouse brain was not affected by viability or known virulence factors. After stopping in the brain, C. neoformans was seen to cross the capillary wall in real time. In contrast to trapping, viability, but not replication, was essential for the organism to cross the brain microvasculature. Using a knockout strain of C. neoformans, we demonstrated that transmigration into the mouse brain is urease dependent. To determine whether this could be amenable to therapy, we used the urease inhibitor flurofamide. Flurofamide ameliorated infection of the mouse brain by reducing transmigration into the brain. Together, these results suggest that C. neoformans is mechanically trapped in the brain capillary, which may not be amenable to pharmacotherapy, but actively transmigrates to the brain parenchyma with contributions from urease, suggesting that a therapeutic strategy aimed at inhibiting this enzyme could help prevent meningitis and encephalitis caused by C. neoformans infection.

Neutrophil microdomains: linking heterocellular interactions with vascular injury

PURPOSE OF REVIEW

Neutrophil infiltration is an important feature in inflammatory scenarios. Before these cells infiltrate tissues, however, they contribute to crucial intravascular events in which neutrophil microdomains mediate heterotypic interactions with endothelial cells, red blood cells and/or platelets. In vascular diseases, this can result in exacerbated neutrophil activation, subsequent vascular injury and obstruction of microcirculatory blood flow. This review discusses recent advances in elucidating these neutrophil domains and their associated functions in cell adhesion.

RECENT FINDINGS

Neutrophil recruitment is mediated by sequential interactions with the endothelium, termed rolling, adhesion and extravasation. Evidence points to novel signaling pathways induced during the rolling phase resulting in the transition to leukocyte adhesion, which appear to contribute to chemokine mediated activation. In addition, specific neutrophil microdomains are important for interactions with other hematopoietic cells inducing reductions in microvascular flow and injury.

SUMMARY

Neutrophils integrate signals received from the endothelium to act as linkers between the vessel wall and a variety of vascular components (i.e. endothelial cells, platelets, red blood cells) in acute and chronic inflammatory conditions to mediate interactions that can result in vascular injury and vasoocclusion.

The response of the host microcirculation to bacterial sepsis: does the pathogen matter?

Sepsis results from the interaction between a host and an invading pathogen. The microcirculatory dysfunction is now considered central in the development of the often deadly multiple organ dysfunction syndrome in septic shock patients. The microcirculatory flow shutdown and flow shunting leading to oxygen demand and supply mismatch at the cellular level and the local activation of inflammatory pathways resulting from the leukocyte–endothelium interactions are both features of the sepsis-induced microcirculatory dysfunction. Although the host response through the inflammatory and immunologic response appears to be critical, there are also evidences that Gram-positive and Gram-negative bacteria can exert different effects at the microcirculatory level. In this review we discuss available data on the potential bacterial-specific microcirculatory alterations observed during sepsis.

Immunologic messenger molecules: cytokines, interferons, and chemokines

Cytokines and chemokines are secreted proteins involved in numerous aspects of cell growth, differentiation, and activation. A prominent feature of these molecules is their effect on the immune system with regard to cell trafficking and development of immune tissue and organs. The nature of an immune response determines which cytokines are produced and ultimately whether the response is cytotoxic, humoral, cell mediated, or allergic. For this chapter, cytokines are grouped according to those that are predominantly antigen-presenting cell or T lymphocyte derived; that mediate cytotoxic, humoral, cell mediated, and allergic immunity; or that are immunosuppressive. A discussion of chemokine function and their role in cell trafficking and disease follows.

Opening the flood-gates: how neutrophil-endothelial interactions regulate permeability

Many diseases have an inflammatory component, where neutrophil interactions with the vascular endothelium lead to barrier dysfunction and increased permeability. Neutrophils increase permeability through secreted products such as the chemokines CXCL1, 2, 3, and 8, through adhesion-dependent processes involving beta(2) integrins interacting with endothelial ICAM-1, and through combinations where beta(2) integrin engagement leads to degranulation and secretion of heparin-binding protein. Some neutrophil products, such as arachidonic acid or the leukotriene LTA4, are further processed by endothelial enzymes via transcellular metabolism before the resulting products thromboxane A2 or LTC4 can activate their cognate receptors. Neutrophils also generate reactive oxygen species that induce vascular leakage. This review focuses on the mechanisms of neutrophil-mediated leakage.

Glycosylation in immune cell trafficking

Leukocyte recruitment encompasses cell adhesion and activation steps that enable circulating leukocytes to roll, arrest, and firmly adhere on the endothelial surface before they extravasate into distinct tissue locations. This complex sequence of events relies on adhesive interactions between surface structures on leukocytes and endothelial cells and also on signals generated during the cell-cell contacts. Cell surface glycans play a crucial role in leukocyte recruitment. Several glycosyltransferases such as alpha1,3 fucosyltransferases, alpha2,3 sialyltransferases, core 2 N-acetylglucosaminlytransferases, beta1,4 galactosyltransferases, and polypeptide N-acetylgalactosaminyltransferases have been implicated in the generation of functional selectin ligands that mediate leukocyte rolling via binding to selectins. Recent evidence also suggests a role of alpha2,3 sialylated carbohydrate determinants in triggering chemokine-mediated leukocyte arrest and influencing beta1 integrin function. The recent discovery of galectin- and siglec-dependent processes further emphasizes the significant role of glycans for the successful recruitment of leukocytes into tissues. Advancing the knowledge on glycan function into appropriate pathology models is likely to suggest interesting new therapeutic strategies in the treatment of immune- and inflammation-mediated diseases.

Essential hypertension: is there a role for inflammatory mechanisms?

Inflammation is a key feature in the initiation, progression, and clinical implications of cardiovascular disorders, including essential hypertension. Increasing evidence shows that activation of renin-angiotensin-aldosterone system and enhanced local production of angiotensin II have been implicated in the pathophysiology of inflammation. Besides being a potent vasoactive peptide, angiotensin II regulates the inflammatory process. Specifically, it increases vascular permeability, participates in the recruitment of inflammatory cells and their adhesion to the activated endothelium, and regulates cell growth and fibrosis. Reactive oxygen species are implicated at every stage in inflammation and activate multiple intracellular signaling molecules and transcription factors associated with inflammatory responses, such as nuclear factor-kappa B and activator protein-1. Other components of the renin-angiotensin-aldosterone system, including aldosterone and/or mineralocorticoid receptor, induce the production of reactive oxygen species and participate in vascular inflammation. Several studies suggest a role of endothelin-1 as an important mediator of chronic inflammation and there is an increasing interest in the relationship between endothelin-1 and reactive oxygen species. These data may have great impact on future therapeutic strategies.