L-Selectin--a signalling receptor for lipopolysaccharide

Differential display profiling of the Nicotiana response to LPS reveals elements of plant basal resistance

The identification of cDNAs, representing up-regulated genes induced by lipopolysaccharides from Burkholderia cepacia, was achieved by differential display of mRNAs isolated from tobacco cells. In addition to up-regulation of superoxide dismutase, involved in the production of the signalling and defense molecule, hydrogen peroxide; differentially expressed cDNAs, indicative of the operation of an innate immune recognition system and expression of basal resistance, were identified. These include homologs to a receptor-like protein kinase; a binding protein for the type III secreted effector protein, harpin; a virus resistance N gene; an endogenous pararetrovirus and the Pto kinase. The altered gene expression may be responsible for activation of surveillance mechanisms and enhancement of the non-self recognition capacity. The putative roles of these transcripts in LPS-induced responses are discussed in relation to emerging concepts of innate immunity.

Screening for Toxoplasma gondii-regulated transcriptional responses in lipopolysaccharide-activated macrophages

Toxoplasma gondii-infected macrophages are blocked in production of the proinflammatory cytokines interleukin-12 (IL-12) and tumor necrosis factor alpha (TNF-alpha) upon activation with lipopolysaccharide (LPS). Here, we used pathway-focused cDNA arrays to identify additional T. gondii-regulated transcriptional responses. Parasite infection decreased 57 (inclusive of IL-12 and TNF-alpha) and increased expression of 7 of 77 LPS-activated cytokine and cytokine-related genes. Interestingly, we found that the LPS-induced transcriptional response of the anti-inflammatory cytokine IL-10 was synergistically increased by T. gondii, results that we validated by conventional reverse transcription-PCR and enzyme-linked immunosorbent assay. Importantly, although the parasite exerted disparate effects in LPS-signaling leading to TNF-alpha versus IL-10 production, both responses required functional Toll-like receptor 4. We suggest that these effects represent parasite defense mechanisms to avoid or delay induction of antimicrobial activity and/or T-cell-mediated immunity during Toxoplasma infection.

Recent progress in ellagitannin chemistry

Continuing studies on the total synthesis of ellagitannin plant metabolites have led to the preparation of the dimeric antitumor compound, coriariin A, as well as designed structural analogues. In related investigations, the synthesis of a 2,4-hexahydroxydiphenoyl (HHDP)-bearing glucopyranose structure has been achieved. This species is related to the geraniin family of ellagitannins, and its subsequent chemistry is suggestive of a mechanistic rationale for the observation that the HHDP units within (3,6-bridged)2,4-HHDP-containing ellagitannins invariably are oxidized further in vivo. Companion studies designed to assay the immunomodulatory properties of coriariin A and analogues have led to the thesis that tumor necrosis factor alpha (TNFalpha) serves as a mediator of this ellagitannin's tumor remissive activity. Furthermore, certain tannins and tannin analogues appear to act in an immunosuppressive capacity with peripheral blood monocytes that were exposed to the bacterially derived septic shock inducing agent lipid A.

Mutagenesis of the Ezrin-Radixin-Moesin Binding Domain of L-selectin Tail Affects Shedding, Microvillar Positioning, and Leukocyte Tethering

L-selectin is a cell adhesion molecule that mediates the initial capture (tethering) and subsequent rolling of leukocytes along ligands expressed on endothelial cells. We have previously identified ezrin and moesin as novel binding partners of the 17-amino acid L-selectin tail, but the biological role of this interaction is not known. Here we identify two basic amino acid residues within the L-selectin tail that are required for binding to ezrin-radixinmoesin (ERM) proteins: arginine 357 and lysine 362. L-selectin mutants defective for ERM binding show reduced localization to microvilli and decreased phorbol 12-myristate 13-acetate-induced shedding of the L-selectin ectodomain. Cells expressing these L-selectin mutants have reduced tethering to the L-selectin ligand P-selectin glycoprotein ligand-1, but rolling velocity on P-selectin glycoprotein ligand-1 is not affected. These results suggest that ERM proteins are required for microvillar positioning of L-selectin and that this is important both for leukocyte tethering and L-selectin shedding.

Receptors, mediators, and mechanisms involved in bacterial sepsis and septic shock

Bacterial sepsis and septic shock result from the overproduction of inflammatory mediators as a consequence of the interaction of the immune system with bacteria and bacterial wall constituents in the body. Bacterial cell wall constituents such as lipopolysaccharide, peptidoglycans, and lipoteichoic acid are particularly responsible for the deleterious effects of bacteria. These constituents interact in the body with a large number of proteins and receptors, and this interaction determines the eventual inflammatory effect of the compounds. Within the circulation bacterial constituents interact with proteins such as plasma lipoproteins and lipopolysaccharide binding protein. The interaction of the bacterial constituents with receptors on the surface of mononuclear cells is mainly responsible for the induction of proinflammatory mediators by the bacterial constituents. The role of individual receptors such as the toll-like receptors and CD14 in the induction of proinflammatory cytokines and adhesion molecules is discussed in detail. In addition, the roles of a number of other receptors that bind bacterial compounds such as scavenger receptors and their modulating role in inflammation are described. Finally, the therapies for the treatment of bacterial sepsis and septic shock are discussed in relation to the action of the aforementioned receptors and proteins.

Evaluation of antiinflammatory and antiadhesive effects of heparins in human endotoxemia

OBJECTIVE

Cytokines and adhesion molecules have a decisive role in the development of early inflammatory response as well as the late sequelae of sepsis. Because L-selectin-deficient mice are protected from lethal endotoxemia, blockade of L-selectin may provide a useful therapeutic option in human sepsis. Heparin has immunomodulatory properties and effectively inhibits L- and P-selectin binding in vitro. We therefore investigated whether clinically applied doses of unfractionated or low-molecular-weight heparin affect early inflammatory response in human endotoxemia.

DESIGN

The study was randomized, double-blinded, placebo-controlled, in three parallel groups consisting of 30 healthy male volunteers.

SETTING

University medical center.

INTERVENTIONS

All subjects received a 2-ng/kg intravenous bolus of lipopolysaccharide and 10 mins later unfractionated heparin, low-molecular-weight heparin, or placebo as bolus primed continuous infusion for 6 hrs.

MEASUREMENTS AND MAIN RESULTS

Lipopolysaccharide infusion induced similar increases of tumor necrosis factor-alpha, interleukin-6, interleukin-8, C-reactive protein, and soluble E-selectin levels in all treatment groups. CD11b expression increased by approximately 400%, but L-selectin decreased by 41% in the placebo arm 6 hrs after lipopolysaccharide infusion. Interestingly, both heparins (in particular unfractionated heparin) decreased L-selectin down-regulation as compared with placebo. Similarly, the decrease in lymphocyte counts was significantly less in the unfractionated heparin group during the first 24 hrs (p <.05 vs. placebo)

CONCLUSIONS

Heparins displayed little effects on cytokine production and endothelial cell activation in endotoxemia. Of note, however, unfractionated heparin reduced L-selectin down-regulation and lymphocytopenia. These could present novel mechanisms of action of unfractionated heparin.

Immunity and mastitis. Some new ideas for an old disease

The biggest challenge for host immune defense against mastitis-causing bacteria in dairy cows is to quickly recruit large enough numbers of opsonizing molecules and mature neutrophils into milk such that intramammary pathogens are cleared before they multiply significantly and the inflammatory response gets out of control. Currently, this challenge is best facilitated when established mastitis control procedures are practiced on the farm, including proper hygiene, milking procedures, and regular administration of approved mastitis vaccines. However, mastitis is still a significant problem. New animal functional genomics research is beginning to allow scientists to solve the puzzle of mastitis susceptibility. Results of this type of research offer the hope of giant leaps toward a clear identification of molecular genetic variation and potential gene targets for therapies and immune manipulations that could significantly reduce the risk of clinical mastitis in traditionally susceptible cows.

Outer membrane vesicles from Neisseria meningitidis

Flow cytometry was used to study the expression of leukocyte adhesion molecules CD11a, CD11b, CD11c, CD14, and CD62L (L-selectin) and production of reactive oxygen species (ROS) in an ex vivo human whole-blood system stimulated with lipopolysaccharide-containing outer membrane vesicles (LPS-OMV) from N. meningitidis. Results demonstrated a dose-dependent increase in surface expression of CD11a, CD11b, CD11c and CD14 in granulocytes and monocytes (maximal at 30-120 min) upon OMV-LPS challenge, whereas CD62L expression was heavily downregulated (maximal at 30-120 min). The OMV-associated LPS was almost as potent (on a weight basis) as purified LPS from E. coli in inducing adhesion molecule modulation but the response was delayed. Upon stimulation with OMV-LPS or E. coli-LPS, the production of intracellular ROS increased in both granulocytes and monocytes when dihydroethidium (DHE, mainly reflecting superoxide anion) was used as a probe, whereas peroxynitrite production monitored with dihydrorhodamine 123 (DHR) was not significantly changed. The OMV-mediated modulation of leukocyte adhesion molecule expression and increased ROS production may certainly lead to increased entrapment of leukocytes in the microcirculation and contribute to untoward inflammatory reactions as seen in systemic meningococcal disease.

A combination of a chemically modified doxycycline and a bisphosphonate synergistically inhibits endotoxin-induced periodontal breakdown in rats

BACKGROUND

Chemically modified non-antimicrobial tetracyclines (CMTs) have been shown to inhibit pathologically elevated collagenase (and other matrix metalloproteinase, MMP) activity and bone resorption in vivo and in vitro.

METHODS

In the current study, suboptimal doses of CMT-8 (a non-antimicrobial chemically modified doxycycline) and a bisphosphonate (clodronate, an anti-bone resorption compound) were administered daily, either as a single agent or as a combination therapy, to rats with experimental periodontitis induced by repeated injection of bacterial endotoxin (LPS) into the gingiva. At the end of the 1-week protocol, the gingival tissues were dissected, extracted, and the extracts analyzed for MMPs (collagenases and gelatinases) and for elastase, and the defleshed jaws were morphometrically analyzed for alveolar bone loss.

RESULTS

LPS injection significantly (P<0.001) increased alveolar bone loss and increased collagenase (MMP-8), gelatinase (MMP-9), and elastase activities. Treatment of the LPS-injected rats with suboptimal CMT-8 alone or suboptimal clodronate alone produced slight reductions in the tissue-destructive proteinases and no significant reductions in alveolar bone loss. However, a combination of suboptimal CMT-8 and clodronate "normalized" the pathologically elevated levels of MMPs, elastase, and alveolar bone loss, indicating synergistic inhibition of tissue breakdown in this animal model of periodontitis.

CONCLUSIONS

Combination of a CMT and a bisphosphonate may be a useful treatment to optimally suppress periodontal destruction and tooth loss and in other tissue-destructive inflammatory diseases such as arthritis.

Lactoferrin inhibits the binding of lipopolysaccharides to L-selectin and subsequent production of reactive oxygen species by neutrophils

The activation of leukocytes by lipopolysaccharides (LPS), resulting in the oxidative burst, contributes to the pathogenesis of septic shock. The binding of LPS to L-selectin, which was reported as a serum-independent LPS receptor on neutrophils, induces the production of oxygen free radicals. Human lactoferrin (hLf), an anti-inflammatory glycoprotein released from neutrophil granules during infection, binds to LPS. In this study, we investigated the capacity of hLf to inhibit the L-selectin-mediated activation of neutrophils. Our experiments revealed that hLf prevents the binding of LPS to L-selectin in a concentration-dependent manner. Inhibition was maximum (87.7+/-0.5%) at a concentration of 50 microg/ml of hLf. Furthermore, hLf inhibited up to 55.4+/-0.5% of the intracellular hydrogen peroxide production induced by LPS in neutrophils. These findings suggest that the anti-inflammatory properties of hLf are due, at least in part, to their ability to prevent the binding of LPS to neutrophil L-selectin.

Role of L-selectin in leukocyte sequestration in lung capillaries in a rabbit model of endotoxemia

After a variety of pathophysiologic stimuli, neutrophils accumulate in lung capillaries and contribute to the pathogenesis of acute lung injury. Lung neutrophil sequestration has previously been attributed to mechanical retention of stiffened neutrophils, but L-selectin-mediated leukocyte/endothelial interaction may be an essential step. We investigated the effect of the anti-L-selectin antibody HuDreg 200 on leukocyte sequestration and microhemodynamics in alveolar capillaries in a model of acute endotoxemia. We used in vivo fluorescence microscopy to analyze kinetics of fluorescently labeled red and white blood cells in alveolar capillary networks of the rabbit lung. Investigations were performed over 2 h after an intravenous infusion of 0.2 ml/kg body weight (bw) NaCl, 2 mg/kg bw HuDreg 200, 20 microg/kg bw lipopolysaccharide (LPS) of Escherichia coli 0111:B4, or the combination of HuDreg 200 and LPS, respectively. Infusion of LPS induced leukocyte sequestration in alveolar capillaries, which was accompanied by a reduction of alveolar capillary perfusion and functional capillary density. These effects could be completely blocked by pretreatment of animals with HuDreg 200. We conclude that L-selectin-mediated leukocyte/endothelial interaction is a necessary prerequisite for leukocyte sequestration in alveolar capillaries in this model. Impaired alveolar capillary perfusion appeared to result directly from capillary leukocyte sequestration.

Proteolysis of monocyte CD14 by human leukocyte elastase inhibits lipopolysaccharide-mediated cell activation

Human leukocyte elastase (HLE), a polymorphonuclear neutrophil (PMN) serine proteinase, is proteolytically active on some membrane receptors at the surface of immune cells. The present study focused on the effect of HLE on the expression of CD14, the main bacterial lipopolysaccharide (LPS) receptor at the surface of monocytes. HLE exhibited a time- and concentration-dependent downregulatory effect on CD14 surface expression. A 30-minute incubation of 3 microM HLE was required to display 95% disappearance of the receptor. This downregulation resulted from a direct proteolytic process, not from a shedding consecutive to monocyte activation as observed upon challenge with phorbol myristate acetate (PMA). To confirm that CD14 is a substrate for HLE, this enzyme was incubated with recombinant human CD14 (Mr approximately 57,000), and proteolysis was further analyzed by immunoblot analysis. Cleavage of the CD14 molecule was directly evidenced by the generation of short-lived fragments (Mr approximately 47,000 and 30,000). As a consequence of the CD14 proteolysis, a decrease in the responsiveness of monocytes to LPS was observed, as assessed by measuring tumor necrosis factor-alpha (TNF-alpha) formation. This inhibition was only observed with 1 ng/ml of LPS, i.e., when only the CD14-dependent pathway was involved. At a higher LPS concentration, such as 10 microgram/ml, when CD14-independent pathways were operative, this inhibition was overcome. The direct proteolysis by HLE of the membrane CD14 expressed on monocytes illustrates a potential anti-inflammatory effect of HLE through inhibition of LPS-mediated cell activation.

Glycoprotein-inspired materials promote the proteolytic release of cell surface L-selectin

The proteolytic release, or shedding, of a cell surface protein can serve a regulatory role; the process liberates a soluble form of the protein into circulation while downregulating its cell surface concentration. The characteristics that render a protein susceptible to proteolytic cleavage are not known. We hypothesized that the clustering of a protein at the cell surface might target it for proteolysis. To test this hypothesis, we synthesized molecules that display multiple copies of sulfated galactose residues, termed neoglycopolymers, that are designed to mimic natural ligands for the cell adhesion protein L-selectin. We found that treatment of human neutrophils with the neoglycopolymers resulted in a dose-dependent loss of L-selectin from the cell surface, while monovalent compounds and unsulfated neoglycopolymers had no effect. Because L-selectin is an important mediator in the inflammatory response, such compounds could lead to novel antiinflammatory drugs. Moreover, molecules that control receptor shedding can be used to alter cellular responsiveness to specific ligands or to promote responses at distal sites; consequently, these results have broad implications for regulating the location and presentation of important biomolecules.