Lipopolysaccharide complexed with soluble CD14 binds to normal human monocytes

Receptor cluster formation during activation by bacterial products

The recognition of bacterial products, such as lipopolysaccharide (LPS) by the innate immune system lead to a strong pro-inflammatory response that can eventually lead to fatal sepsis syndrome in humans. Although CD14 and TLR4 have been identified as the key molecules involved in LPSinduced signal transduction, accumulating evidence indicates that multiple receptors are also involved. Our group has recently identified a cluster of receptors, involving heat-shock proteins 70 and 90, chemokine receptor 4 as well as growth differentiation factor 5, that are formed following LPS stimulation. In addition, we present data demonstrating that these molecules associate with TLR4 and accumulate in membrane microdomains following LPS ligation. Our results suggest that the entire bacterial recognition is based around the recruitment of multiple signalling molecules, in addition to CD14 and TLRs, within the lipid rafts. We propose that different combinational associations of receptors within activation clusters determine the different responses to a variety of bacterial stimuli.

Monocyte CD14 and soluble CD14 in predicting mortality of patients with severe community acquired infection

Monocyte membrane CD14 (mCD14) and soluble CD14 (sCD14) both associate with poor outcome in sepsis. Because the value of combined use of the markers is unknown we measured both in patients with severe community acquired infections. The study comprised 142 acutely ill patients with community acquired pneumonia and/or blood culture-positive sepsis. Expression of mCD14 was measured, on admission to hospital, by whole blood flow cytometry and sCD14 by ELISA. There was no significant correlation between mCD14 and sCD14. Patients in the lowest tertile of mCD14 were 9.79 times (95% CI 1.31- >50, p =0.006) more likely to die than patients in the middle/highest tertiles. Survival rates in the highest and middle/lowest tertiles of sCD14 levels were comparable. After stratification by sCD14, patients in the lowest tertile of mCD14 were 14.4 times (95% CI 1.90-39.44) more likely to die than patients in the middle/highest tertiles. A significant positive correlation was detected between C-reactive protein and sCD14 levels, providing evidence that sCD14 may serve as an acute phase reactant. In conclusion, low monocyte mCD14 level, unlike the concurrent sCD14 level, predicts 28-d mortality in patients with community acquired infections.

Cellular trafficking of lipoteichoic acid and Toll-like receptor 2 in relation to signaling: role of CD14 and CD36

Lipoteichoic acid (LTA) is a central inducer of inflammatory responses caused by Gram-positive bacteria, such as Staphylococcus aureus, via activation of TLR2. Localization of TLR2 in relation to its coreceptors may be important for function. This study explores the signaling, uptake, and trafficking pattern of LTA in relation to expression of TLR2 and its coreceptors CD36 and CD14 in human monocytes. We found TLR2 expressed in early endosomes, late endosomes/lysosomes, and in Rab-11-positive compartments but not in the Golgi apparatus or endoplasmic reticulum (ER). Rapid internalization of fluorescently labeled LTA was observed in human monocytes, colocalizing with markers for early and late endosomes, lysosomes, ER, and Golgi network. Blocking CD14 and CD36 with antibodies inhibited LTA binding and LTA-induced TNF release from monocytes, emphasizing an important role for both molecules as coreceptors for TLR2. Importantly, blocking CD36 did not affect TNF release induced by N-palmitoyl-S-[2,3-bis(palmitoyloxy)-(2R,S)-propyl]-(R)-cysteinyl-seryl-(lysyl)3-lysine or LPS. Expression of CD14 markedly enhanced LTA binding to the plasma membrane and also enhanced NF-kappaB activation. LTA internalization, but not NF-kappaB activation, was inhibited in Dynamin-I K44A dominant-negative transfectants, suggesting that LTA is internalized by receptor-mediated endocytosis but that internalization is not required for signaling. In fact, immobilizing LTA and thereby inhibiting internalization resulted in enhanced TNF release from monocytes. Our results suggest that LTA signaling preferentially occurs at the plasma membrane, is independent of internalization, and is facilitated by CD36 and CD14 as coreceptors for TLR2.

The toll-like receptor-4 (TLR-4) pathway and its possible role in the pathogenesis of Escherichia coli mastitis in dairy cattle

Mastitis is one of the most costly production diseases in the dairy industry that is caused by a wide array of microorganisms. In this review, we focus on the Gram-negative Escherichia coli infections that often occur at periods when the innate immune defence mechanisms are impaired (i.e., parturition through the first 60 days of lactation). There is substantial evidence demonstrating that at these periods, the expected influx of polymorphonuclear neutrophil leukocytes (PMN) into the mammary gland is delayed during inflammation after intramammary infection with E. coli. Here, we provide some hypotheses on the potential mechanisms of action on how the disease may develop under circumstances of immunosuppression, and describe the potential involvement of the toll-like receptor-4 signal transduction pathway in the pathogenesis of E. coli mastitis. In addition, some ideas are proposed to help prevent E. coli mastitis and potentially other diseases caused by Gram-negative infections in general.

Physicochemical and biological analysis of synthetic bacterial lipopeptides: validity of the concept of endotoxic conformation

The importance of the biological function and activity of lipoproteins from the outer or cytoplasmic membranes of Gram-positive and Gram-negative bacteria is being increasingly recognized. It is well established that they are like the endotoxins (lipopolysaccharide (LPS)), which are the main amphiphilic components of the outer membrane of Gram-negative bacteria, potent stimulants of the human innate immune system, and elicit a variety of proinflammatory immune responses. Investigations of synthetic lipopeptides corresponding to N-terminal partial structures of bacterial lipoproteins defined the chemical prerequisites for their biological activity and in particular the number and length of acyl chains and sequence of the peptide part. Here we present experimental data on the biophysical mechanisms underlying lipopeptide bioactivity. Investigation of selected synthetic diacylated and triacylated lipopeptides revealed that the geometry of these molecules (i.e. the molecular conformations and supramolecular aggregate structures) and the preference for membrane intercalation provide an explanation for the biological activities of the different lipopeptides. This refers in particular to the agonistic or antagonistic activity (i.e. their ability to induce cytokines in mononuclear cells or to block this activity, respectively). Biological activity of lipopeptides was hardly affected by the LPS-neutralizing antibiotic polymyxin B, and the biophysical interaction characteristics were found to be in sharp contrast to that of LPS with polymyxin B. The analytical data show that our concept of "endotoxic conformation," originally developed for LPS, can be applied also to the investigated lipopeptide and suggest that the molecular mechanisms of cell activation by amphiphilic molecules are governed by a general principle.

Cell activation of human macrophages by lipoteichoic acid is strongly attenuated by lipopolysaccharide-binding protein

Lipoteichoic acid (LTA) represents immunostimulatory molecules expressed by Gram-positive bacteria. They activate the innate immune system via Toll-like receptors. We have investigated the role of serum proteins in activation of human macrophages by LTA from Staphylococcus aureus and found it to be strongly attenuated by serum. In contrast, the same cells showed a sensitive response to LTA and a significantly enhanced production of tumor necrosis factor alpha under serum-free conditions. We show that LTA interacts with the serum protein lipopolysaccharide-binding protein (LBP) and inhibits the integration of LBP into phospholipid membranes, indicating the formation of complexes of LTA and soluble LBP. The addition of recombinant human LBP to serum-free medium inhibited the production of tumor necrosis factor alpha and interleukins 6 and 8 after stimulation of human macrophages with LTA in a dose-dependent manner. Using anti-LBP antibodies, this inhibitory effect could be attributed to soluble LBP, whereas LBP in its recently described transmembrane configuration did not modulate cell activation. Also, using primary alveolar macrophages from rats, we show a sensitive cytokine response to LTA under serum-free culture conditions that was strongly attenuated in the presence of serum. In summary, our data suggest that innate immune recognition of LTA is organ-specific with negative regulation by LBP in serum-containing compartments and sensitive recognition in serum-free compartments like the lung.

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.

Receptors and Counterreceptors Involved in NK-B Cell Interactions

In addition to the well-documented effect of NK cells on B cell differentiation via their ability to secrete IFN-gamma, NK cells can also induce, via direct cell-cell interactions, germline transcripts (Igamma2a) necessary for switch recombination to IgG2a. Analysis of the ligand-receptor pairs that could be involved in this induction revealed that the expression of CD48 on B cells is crucial for the induction. NK cells from mice with targeted deletions of either the CD2 or the CD244 gene, both of which encode ligands for CD48, are compromised in their ability to induce B cell Igamma2a expression. Interestingly, although CD244 can bind to CD48 with a higher affinity, the ability of NK cells from CD244(-/-) mice to stimulate Igamma2a is not as compromised as NK cells from CD2(-/-) mice. Despite the difference between cell surface receptors that are stimulated by NK cells vs those stimulated by the combination of LPS and IFN-gamma, we show in this study that the initiation of gamma2a germline transcription is regulated by similar cis-acting elements located at the 3' end of the IgH locus. However, NK cells cannot induce the final steps of switch recombination resulting in the production of mature mRNA from recombined DNA. Our findings suggest that these different signaling pathways converge on regulatory elements that are common to germline transcription; however, because NK induction does not result in the final steps of switch recombination, some signals initiated by LPS plus IFN-gamma are not induced by NK cells.

Treatment of endotoxemia

Although recognition of clinical signs of endotoxemia is not difficult, determining the underlying cause for the development of endotoxemia may be a challenging task. For this reason, importance must be placed on performance of a thorough physical examination, attention to detail, and determination of whether or not surgical intervention is required. In most instances, a definitive diagnosis may require repeated examinations and laboratory work. In the meantime, affected animals require treatment for endotoxemia, with the aim being to reduce the duration of endotoxemia, prevent the interaction of additional endotoxins with cell surface receptors, and reduce the synthesis and release of inflammatory mediators.

Heparin inhibits lipopolysaccharide (LPS) binding to leukocytes and LPS-induced cytokine production

The glycosaminoglycan heparin is known to exhibit anti-inflammatory properties unrelated to its anticoagulant activity. However, in a generalized inflammatory response with implanted or extracorporeal devices, the beneficial effect of heparin coating and/or systemic administration is still unclear as well as the precise mechanisms of action. In the present study, we have first studied the effect of heparin on lipopolysaccharide (LPS)-induced cytokine production by human blood monocytes. Our results indicated that the production of interleukin-1alpha, tumor necrosis factor-alpha, and interleukin-8 was significantly decreased when heparin was simultaneously incubated with Escherichia coli LPS. Because the modulation of heparin on monocyte activation could be mediated by its binding via CD14, the main LPS receptor on monocytes, we then studied the binding of LPS and heparin to leukocytes from human blood and to Chinese hamster ovary cells transfected with the human CD14 gene. The data by flow cytometry showed the binding of biotinylated heparin to leukocytes. Moreover, the experiments performed on leukocytes and on CD14-positive Chinese hamster ovary cells indicated that heparin inhibited LPS binding. From our results, we conclude that: 1. heparin is an effective inhibitor of LPS-induced monocyte activation, and 2. heparin inhibits the binding of LPS to cells via a CD14-independent pathway. This study suggests a potentially important therapeutic application for heparin or heparin analogs to prevent inflammation with biomaterials.

CD14 signalling in lipid rafts: new ligands and co-receptors

PURPOSE OF REVIEW

Lipid rafts on monocytes/macrophages provide a dynamic microenvironment for an integrated lipopolysaccharide receptor (CD14)-dependent clustering of a set of receptors involved in innate immunity and clearance of atherogenic lipoproteins. The purpose of this review is to summarize the recent advances in our understanding of CD14-dependent receptor clustering and its relevance in atherogenesis.

RECENT FINDINGS

Upon binding of various ligands, CD14 as a multiligand pattern recognition receptor induces specific coassembly of additional receptors present on circulating monocytes.

SUMMARY

The composition of the receptor cluster and thus the associated signalling pathways defines a ligand specific cellular response, linking endogenous and exogenous host defense to a common recognition platform in rafts.

Structural and functional analyses of bacterial lipopolysaccharides

Bacterial lipopolysaccharides (LPSs) are powerful immunomodulators in infected hosts, and may cause endotoxic shock. Most of them share a common architecture but vary considerably in structural motifs from one genus, species, and strain to another. Cells of the innate immune response recognize evolutionarily conserved LPS molecular patterns of endotoxins and structural details thereby greatly influencing their response.

Lipopolysaccharide recognition: CD14, TLRs and the LPS-activation cluster

Recognition of bacterial lipopolysaccharide (LPS) by the innate immune system elicits strong pro-inflammatory responses that can eventually cause a fatal sepsis syndrome in humans. LPS-mediated activation of mammalian cells is believed to involve the interaction of LPS with lipopolysaccharide-binding protein (LBP) in the serum and, subsequently with CD14. Although there is no doubt that CD14 binds LPS, CD14 is not capable of initiating a transmembrane activation signal because it is a glycosylphosphatidylinositol (GPI)-anchored protein. Accumulating evidence has suggested that LPS must interact with a transmembrane receptor(s) that is responsible for signal transduction. Integrins CD11c and/or CD18, Toll-like receptors (TLRs), as well as CD55, have been suggested to serve this function. Recently, we have revealed that a signalling complex of receptors is formed following LPS stimulation, which comprises heat-shock proteins (Hsps) 70 and 90, chemokine receptor 4 (CXCR4) and growth differentiation factor 5 (GDF5). Taking into account the discovery of the TLRs and the LPS-activation cluster, we propose a new model of LPS recognition.

A novel flow cytometric assay to quantify soluble CD14 concentration in human serum

BACKGROUND

CD14, the major lipopolysaccharide (LPS)-binding protein of myeloid cells, is found as a soluble molecule in human serum. Recent data describe the presence of elevated soluble CD14 (sCD14) concentration in various disorders, confirming disease activity. A novel, easy, and rapid flow cytometric assay was developed to measure sCD14 levels in serum.

METHODS

The assay is based on the competition between membrane-expressed CD14 of isolated monocytes from healthy volunteers and sCD14 in the sample sera for binding to anti-CD14 monoclonal antibodies (mAb; 26ic or 60bca). The amount of cell-associated mAb is determined with a fluorescein isothiocyanate (FITC)-labeled anti-mouse conjugate and flow cytometry. The fluorescence signal is inversely proportional with the amount of serum sCD14. Using dilutions of a standard serum, the concentration of sCD14 in the samples is calculated and compared with results obtained by a commercial sCD14 enzyme-linked immunosorbent assay (ELISA).

RESULTS

After optimization, the assay showed log-log linearity of 122.1-984.7 ng/ml sCD14 using mAb 26ic and 29.5-246.2 ng/ml sCD14 using mAb 60bca. It revealed similar results as the ELISA (mAb 26ic: r = 0.88, mAb 60bca: r = 0.92) and provided significantly elevated sCD14 levels in systemic lupus erythematosus patients compared with controls (26ic: 2,213 versus 1,676 ng/ml, P < 0.002; 60bca: 2,625 versus 1,907 ng/ml, P < 0.0002). Receiver operating characteristic curve analysis suggested a reasonable diagnostic efficacy of sCD14 quantification in this autoimmune disease.

CONCLUSIONS

The method is easy, rapid, sensitive, and can be used in the follow-up of patients suffering from sepsis or chronic inflammatory disorders.

Lipopolysaccharide (LPS) and zymosan-resistant mutant isolated from a macrophage-like cell line, WEHI-3, with a defective response to LPS under serum-free conditions

A LPS-resistant mutant, W3SF-1, was isolated from a murine macrophage-like cell line, WEHI-3. The W3SF-1 mutant did not produce a significant amount of nitric oxide (NO) or TNF-alpha even with high concentrations of LPS in the presence or absence of FCS, whereas the parental WEHI-3 cells produced them in response to LPS. The parental cells expressed a significant level of TNF-alpha mRNA after LPS stimulation, whereas the mutant cells did not. This defective response of the mutant cells to LPS was neither dependent on the concentration or chemical structure of LPS, nor on the time of LPS treatment. The mutant cells also showed a defective response to zymosan, suggesting that the defect in the mutant cells is common to LPS and zymosan in the signal transduction pathways. The parental and mutant cells showed similar levels of Mac1, F4/80 and CD14, suggesting that these surface markers of macrophages are not linked directly to the defective responses of the mutant to LPS. The treatment of mutant cells with IFN-gamma did not restore the defect of NO or TNF-alpha production on LPS treatment. Binding experiments with 125I-labelled LPS showed a similar binding affinity for LPS in the parental and the mutant cells. These results suggest that the defect in the W3SF-1 mutant cells may not reside in the LPS binding but rather in the early step of signal transduction pathways in the cells after LPS binding.

Fluorescence recovery after photobleaching reveals that LPS rapidly transfers from CD14 to hsp70 and hsp90 on the cell membrane

Although CD14 has been implicated in the immune recognition of bacterial lipopolysaccharide (LPS) from Gram-negative bacteria and also peptidoglycan (PGN) and lipoteichoic acid (LTA) from the outer cell wall of Gram-positive bacteria, accumulating evidence has suggested the possible existence of other functional receptor(s). In this study, we have used fluorescence recovery after photobleaching (FRAP) in order to get the first dynamic picture of the innate recognition of bacteria. We have found that the diffusion coefficient of CD14 remains unaffected after LPS ligation and that the diffusion coefficients of FITC-LPS and FITC-LTA bound to cells differ from that of CD14. Furthermore, FITC-LPS/LTA rapidly become immobile when bound to cells, suggesting that FITC-LPS/LTA must briefly associate with CD14 in the initial attachment process and rapidly move on to an immobile receptor or to a complex of receptors. Further FRAP experiments revealed that heat shock protein 70 (hsp70) and hsp90 are immobile in cell membranes, and antibodies against them were found to block the transfer of LPS to the immobile receptor and to inhibit interleukin 6 production upon LPS stimulation. These experiments indicated that LPS transfers from CD14 to hsp70 and hsp90, which may be part of an LPS/LTA multimeric receptor complex. Thus, hsps are implicated as mediators of the innate activation by bacteria.

A CD14-independent LPS receptor cluster

Bacterial lipopolysaccharide (LPS), the major structural component of the outer wall of Gram-negative bacteria, is a potent initiator of an inflammatory response and serves as an indicator of bacterial infection. Although CD14 has been identified as the main LPS receptor, accumulating evidence has suggested the possible existence of other functional receptor(s). In this study, using affinity chromatography, peptide mass fingerprinting and fluorescence resonance energy transfer, we have identified four new proteins that form an activation cluster after LPS ligation and are involved in LPS signal transduction. Here we present evidence that implicates heat shock proteins 70 and 90, chemokine receptor 4 and growth differentiation factor 5 as the main mediators of activation by bacterial lipopolysaccharide.

Hepatocytes contribute to soluble CD14 production, and CD14 expression is differentially regulated in hepatocytes and monocytes

CD14 presents as a glycosylphosphatidylinositol-linked membrane protein on the surface of monocytes/macrophages and as a soluble protein in the serum. Our previous studies have shown that an 80-kilobase pair (kb) genomic DNA fragment containing the human CD14 gene is sufficient to direct CD14 expression in a monocyte-specific manner in transgenic mice. In addition, we discovered that human CD14 is highly expressed in hepatocytes. Here, we report the generation of transgenic mice with either a 24- or 33-kb human CD14 genomic DNA fragment. Data from multiple transgenic lines show that neither the 24- nor the 33-kb transgenic mice express human CD14 in monocytes/macrophages. However, human CD14 is highly expressed in the liver of the 33-kb transgenic mice. These results demonstrate that human CD14 expression is regulated differently in monocytes and hepatocytes. Furthermore, we identified an upstream regulatory element beyond the 24-kb region, but within the 33-kb region of the human CD14 gene, which is critical for CD14 expression in hepatocytes, but not in monocytes/macrophages. Most importantly, the data demonstrate that the liver is one of the major organs for the production of soluble CD14. These transgenic mice provide an excellent system to further explore the functions of soluble CD14.

Important role of membrane-associated CD14 in the induction of IFN-beta and subsequent nitric oxide production by murine macrophages in response to bacterial lipopolysaccharide

The surface antigen CD14 is known to play a central role in the recognition of lipopolysaccharide by macrophages. We characterized a mutant cell line, J7.DEF.3, derived from a murine macrophage-like cell line, J774.1, to be defective in the ability to express the membrane-associated form of CD14 (mCD14) but not in the ability to release the soluble form of CD14 (sCD14), and used these parent and mutant cells to investigate the role of CD14 in lipopolysaccharide signaling. In response to lipopolysaccharide stimulation, mutant cells produced slightly less tumor necrosis factor than parent cells, and produced much less (negligible level) nitric oxide than parent cells. Production of both tumor necrosis factor and nitric oxide by parent cells upon lipopolysaccharide stimulation was suppressed by anti-CD14 serum. Expression of interferon-beta mRNA by stimulation with lipopolysaccharide, detected in parent cells, was barely detectable in mutant cells and in enzymatically mCD14-eliminated parent cells. Lipopolysaccharide-induced nitric oxide production in parent cells was suppressed by anti-(murine interferon-beta), and its production in the mutant cells appeared and increased dose dependently on exogenously supplied murine interferon-beta in the presence of lipopolysaccharide. These results provide new insight into the lipopolysaccharide signaling pathway, indicating that the lipopolysaccharide signal for interferon-beta production is transduced through a mCD14-dependent pathway and that the endogenously generated interferon-beta is an essential cofactor leading to nitric oxide production. Nuclear translocation of a transcription factor, nuclear factor kappaB, was observed in both parent and mutant cells following stimulation with a low dose of lipopolysaccharide, and mitogen-activated protein kinases were also activated in both types of cell, although a higher dose of lipopolysaccharide was required by the mutant cells than by the parent cells. These results indicate that these signaling factors may participate in the mCD14-independent lipopolysaccharide signaling pathway rather than in the mCD14-dependent interferon-beta-producing pathway.

Differential Impact of Substitution of Amino Acids 9–13 and 91–101 of Human CD14 on Soluble CD14-Dependent Activation of Cells by Lipopolysaccharide

The soluble form of the endotoxin receptor CD14 is required for the LPS-induced activation of cells lacking membrane-bound CD14. It has been shown that a deletion mutant of human CD14 consisting of the N-terminal 152 amino acids has the capacity to mediate the stimulation of different cell types by LPS. To identify the structural domains of the molecule related to this functional property, we screened a set of alanine substitution mutants using CD14-negative U373 astrocytoma cells. We show that 3 of 18 soluble mutants of human CD14 failed to mediate the LPS-induced IL-6 production in U373 cells. These mutants were located in two regions of the molecule (aa 9–13 and 91–101) that are not essential for LPS binding. In addition, the mutants had a reduced capacity to mediate LPS-stimulated IL-6 production in human vascular endothelial and SMC. In contrast, the potential of sCD14(91–94,96)A, and sCD14(97–101)A to signal LPS-induced activation of human PBMC was not significantly reduced. These results show that the regions 9–13 and 91–101 are involved in the sCD14-dependent stimulation of cells by LPS but that the mechanisms by which different cell types are activated may not be identical.

Signal transduction in leucocytes via GPI-anchored proteins: an experimental artefact or an aspect of immunoreceptor function?

Membrane proteins anchored in the membrane via a glycolipid glycosylphosphatidylinositol (GPI) as well as some glycolipids are able to transduce signals and induce diverse functional responses in cells upon their cross-linking via antibodies or natural ligands. In some cases this signaling capacity seems to be due to associations of these molecules with specific transmembrane proteins. GPI-anchored proteins are components of membrane microdomains enriched in glycosphingolipids and cholesterol and devoid of most transmembrane proteins. These membrane specializations are relatively resistant to solubilization in solutions of some mild detergents at low temperatures. These 'GPI-microdomains' contain also cytoplasmic signaling molecules such as Src-family protein tyrosine kinases and trimeric G-proteins. Thus, at least some signaling elicited upon cross-linking of GPI-anchored proteins and glycolipids may be due to perturbation of the signaling molecules associated with these microdomains. It is suggested that these specialized areas of the membrane rich in signaling molecules interact with immunoreceptors (TCR, BCR, Fc receptors) cross-linked upon their interactions with ligands and importantly contribute to initiation of proximal phases of their signaling pathways.

Differential effects of bacterial lipopolysaccharides upon neutrophil function

Lipopolysaccharide (LPS) is a potent inflammatory agent which augments neutrophil sensitivity to subsequent inflammatory stimuli. In this study, the effects of structurally different LPS types upon neutrophil effector functions were examined. Rough LPS types, which have lost the O-polysaccharide moiety, were found to act more rapidly than smooth LPS types in stimulating neutrophil beta2 integrin activity and fMLP-induced respiratory burst. These findings suggest an involvement of the O-polysaccharide region of LPS in regulating neutrophil responsiveness to different LPS chemotypes with important implications for the mechanisms underlying regulation of the inflammatory response in conditions associated with elevation of LPS in plasma, e.g. septic shock or acute respiratory distress syndrome.