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Biomedical subjects

J Pugin

Publications and source records attributed to J Pugin.

At least 19 recordsLinked to original sources
PubMed1999

The alveolar space is the site of intense inflammatory and profibrotic reactions in the early phase of acute respiratory distress syndrome.

OBJECTIVES: To determine the concentrations of proinflammatory mediators, collagenases, and procollagen type III peptides in undiluted pulmonary edema fluids and in plasma obtained in patients with early acute respiratory distress syndrome (ARDS) and in control patients with hydrostatic lung edema; and to assess the relationship between these inflammatory and profibrotic markers. DESIGN: A prospective, clinical study with measurements of inflammatory markers in pulmonary edema fluids and in paired plasma samples. SETTING: A medical intensive care unit. PATIENTS: Patients intubated with lung permeability (n = 23) and hydrostatic (n = 8) pulmonary edema were prospectively enrolled in the study. The severity of the disease at the time of intubation was assessed, using the Simplified Acute Physiological Score (SAPS) II and the Lung Injury Score (LIS). INTERVENTIONS: Plasma and undiluted edema fluids were obtained at the time of intubation with pulmonary edema requiring mechanical ventilation; and in some patients, a second edema fluid sample was collected a few hours later. MEASUREMENTS AND MAIN RESULTS: Proinflammatory activity, dependent on the presence of bioactive proinflammatory cytokines, interleukin (IL)-8, and neutrophil matrix metalloproteinase (MMP)-9 were significantly increased in ARDS fluids compared with plasma or control fluids from patients with congestive heart failure. In contrast, MMP-2, originating from lung cells other than phagocytes, was slightly increased in ARDS edema fluids compared with plasma, but similar to levels found in hydrostatic edema fluids. Proinflammatory activity was undetectable in plasma from ARDS patients. Levels of procollagen peptide III, a marker of collagen synthesis, were increased in permeability edema fluids compared with hydrostatic edema fluids or plasma, confirming that alveolar collagen synthesis begins very early and in parallel with acute inflammation in ARDS. Control patients with hydrostatic edema had similar SAPS II and LIS scores compared with ARDS patients. CONCLUSIONS: These results strongly support the conclusion that during the early phase of ARDS, the lung is the site of an intense inflammatory process with sequential activation of cytokines, chemokines, and secretion of proteases, as well as concomitant collagen synthesis. The inflammation is mostly limited to the lung, with low levels of inflammatory mediators in the systemic circulation. Unlike clinical scoring systems (SAPS II and LIS), inflammatory markers differentiate patients with permeability and hydrostatic pulmonary edema.

Adult↗
PubMed1999

Balance between proinflammatory cytokines and their inhibitors in bronchial lavage from patients with status asthmaticus.

Status asthmaticus (SA) is an acute respiratory failure combining an acute bronchospastic reaction with a severe airway inflammation. We previously reported an important influx of neutrophils and an increased secretion of interleukin-8 (IL-8) in patients with SA. The aim of this prospective study was to evaluate in bronchial lavage (BL) of patients with SA (n = 9) under mechanical ventilation (MV) the concentrations of cytokines and related mediators which have the ability to modulate inflammation, either proinflammatory (interleukin-1beta [IL-1beta], IL-6, tumor necrosis factor-alpha [TNF-alpha]), or anti-inflammatory mediators (IL-10, transforming growth factor-beta1 [TGF-beta1]), interleukin-1 receptor antagonist [IL-1Ra], soluble TNF receptor I and II [sTNFRI and II]). To determine the relative importance of both pro- and anti-inflammatory mediators, the net inflammatory activity was analyzed by the capacity of BL fluids (BLF) to increase intercellular adhesion molecule-1 (ICAM-1) expression in the human lung A549 epithelial cell line. These data were compared with those obtained from patients who required MV without respiratory disease (V, n = 4), controlled asthma (A, n = 11), and nonsmoking healthy volunteers (C, n = 8). Levels of IL-1, IL-6, TNF-alpha, and of the active form of TGF-beta1 were significantly higher in SA compared with the other groups. The concentrations of IL-1Ra, IL-10, the latent form of TGF-beta1, and of the sTNFRI and II were not significantly different between SA and V, albeit higher in SA than in A and C. The ratio between IL-1Ra and IL-1beta was significantly higher in patients with SA compared with the other groups, whereas there was no difference for the ratio between both types of sTNFR and TNF-alpha. Despite a marked increase of anti-inflammatory mediators in BL from patients with SA, the net inflammatory activity was found to be proinflammatory and mainly due to the presence of bioactive IL-1beta (79% inhibition of ICAM-1 expression with anti-IL-1beta antibodies) and to a lesser extent TNF-alpha (32% inhibition with anti-TNF-alpha antibodies).

Adult↗
PubMed1999

Human neutrophils secrete gelatinase B in vitro and in vivo in response to endotoxin and proinflammatory mediators.

Bacterial sepsis is characterized by a systemic inflammatory state, with activation of numerous cell types. Phagocytes participate in this phenomenon by secreting various proinflammatory cytokines and enzymes. Matrix metalloproteinases (MMPs) such as gelatinases are produced by phagocytes and are thought to play an important role in processes of cell transmigration and tissue remodeling. In this work, we show that endotoxin (lipopolysaccharide [LPS]) and other inflammatory mediators, such as tumor necrosis factor (TNF), interleukin-8, and granulocyte colony-stimulating factor, induce a rapid (within 20 min) release of gelatinase-B (MMP-9) zymogen in whole human blood, as determined by gelatin zymography. The polymorphonuclear neutrophil was identified as the cell responsible for this rapid secretion, as a result of the release of preformed enzymes stored in granules. Normal human subjects given LPS intravenously showed a similar pattern of proMMP-9 secretion, with maximum plasma levels reached 1.5 to 3 h after LPS administration (P = 0.0009). Prior administration of TNF receptor:Fc, a potent TNF antagonist, to subjects given LPS, only partially blunted the release of proMMP-9 (P = 0.033). Ibuprofen, a cyclooxygenase inhibitor, did not alter this pattern of release. Increased levels of proMMP-9 and proMMP-2, as well as activated forms of MMP-9, were found in plasma from two patients with gram-negative sepsis. The levels of MMPs paralleled the severity of clinical condition and a marker of the severity of sepsis, plasma procalcitonin. These data indicate that MMPs are released in whole blood in response to various inflammatory mediators and that they could serve as sensitive and early markers for cell activation during the course of bacterial sepsis.

Aged↗
PubMed1998

CD14-dependent endotoxin internalization via a macropinocytic pathway.

Gram-negative bacterial endotoxin (a lipopolysaccharide (LPS)) specifically binds to CD14, a glycosylphosphatidyl inositol (GPI)-anchored surface myeloid glycoprotein. This interaction leads to cell activation, but it also promotes LPS internalization and detoxification. In this work, we investigated the route of LPS and CD14 internalization and the relevance of CD14 GPI anchor in the endocytic pathway. In promonocytic THP-1 cells transfected with a GPI or a chimeric integral form of CD14, we showed by differential buoyancy in sucrose density gradients that these two forms of CD14 were sorted to different plasma membrane subdomains. However, both forms of CD14 associated preferentially with the same surface microfilament-enriched microvilli or ruffles. Electron microscopic studies indicated that CD14 internalized via macropinocytosis, a process resembling that of phagocytosis, different from "classical" receptor-mediated endocytic pathways, such as clathrin-coated pits or caveolae. With cell warming, the CD14-enriched ruffles fused and formed large vesicles. Later, these vacuoles made stacks and condensed into phago-lysosomes. CD14 was specifically associated with all of these structures. Radiolabeled LPS internalization paralleled CD14 internalization. Confocal microscopic studies confirmed the co-localization of LPS and CD14 both at the cell surface and in endosomal compartments. The microfilament-disrupting, macropinocytosis blocking agent cytochalasin D inhibited LPS and CD14 internalization but did not prevent LPS-dependent activation, indicating that these two processes are dissociated.

Cell Line↗
PubMed1998

Treponema pallidum and Borrelia burgdorferi lipoproteins and synthetic lipopeptides activate monocytic cells via a CD14-dependent pathway distinct from that used by lipopolysaccharide.

Lipoproteins of Treponema pallidum and Borrelia burgdorferi possess potent proinflammatory properties and, thus, have been implicated as major proinflammatory agonists in syphilis and Lyme disease. Here we used purified B. burgdorferi outer surface protein A (OspA) and synthetic lipopeptides corresponding to the N-termini of OspA and the 47-kDa major lipoprotein immunogen of T. pallidum to clarify the contribution of CD14 to monocytic cell activation by spirochetal lipoproteins and lipopeptides. As with LPS, mouse anti-human CD14 Abs blocked the activation of 1,25-dihydroxyvitamin D3-matured human myelomonocytic THP-1 cells by OspA and the two lipopeptides. The existence of a CD14-dependent pathway was corroborated by using undifferentiated THP-1 cells transfected with CD14 and peritoneal macrophages from CD14-deficient BALB/c mice. Unlike LPS, cell activation by lipoproteins and lipopeptides was serum independent and was not augmented by exogenous LPS-binding protein. Two observations constituted evidence that LPS and lipoprotein/lipopeptide signaling proceed via distinct transducing elements downstream of CD14: 1) CHO cells transfected with CD14 were exquisitely sensitive to LPS but were lipoprotein/lipopeptide nonresponsive; and 2) substoichiometric amounts of deacylated LPS that block LPS signaling at a site distal to CD14 failed to antagonize activation by lipoproteins and lipopeptides. The combined results demonstrate that spirochetal lipoproteins and lipopeptides use a CD14-dependent pathway that differs in at least two fundamental respects from the well-characterized LPS recognition pathway.

Acute-Phase Proteins↗
PubMed1998

Cell activation mediated by glycosylphosphatidylinositol-anchored or transmembrane forms of CD14.

CD14 is a glycosylphosphatidylinositol (GPI)-anchored membrane glycoprotein which functions as a receptor on myeloid cells for ligands derived from microbial pathogens such as lipopolysaccharide (LPS). We have studied the importance of the GPI tail of CD14 in signalling with the promonocytic cell line THP-1 expressing recombinant CD14 in a GPI-anchored form (THP1-wtCD14 cells) or in a transmembrane form (THP1-tmCD14). We found that, like other GPI-anchored molecules, GPI-anchored CD14 was recovered mainly from a Triton X-100-insoluble fraction, whereas transmembrane CD14 was fully soluble in Triton X-100. LPS induced cell activation of THP1-wtCD14 and of THP1-tmCD14 (protein tyrosine kinase phosphorylation, NF-kappaB activation, and cytokine production) in a very similar manner. However, anti-CD14 antibody-induced cross-linking caused a rapid calcium mobilization signal only in GPI-anchored CD14 cells. Studies with pharmacologic inhibitors of intracellular signalling events implicate phospholipase C and protein tyrosine kinases in the genesis of this antibody-induced calcium signal. Our results suggest that GPI anchoring and CD14 targeting to glycolipid-rich membrane microdomains are not required for LPS-mediated myeloid cell activation. GPI anchoring may however be important for other signalling functions, such as those events reflected by antibody cross-linking.

Cell Line↗
PubMed1998

Activation of human macrophages by mechanical ventilation in vitro.

Positive-pressure mechanical ventilation supports gas exchange in patients with respiratory failure but is also responsible for significant lung injury. In this study, we have developed an in vitro model in which isolated lung cells can be submitted to a prolonged cyclic pressure-stretching strain resembling that of conventional mechanical ventilation. In this model, cells cultured on a Silastic membrane were elongated up to 7% of their initial diameter, corresponding to a 12% increase in cell surface. The lung macrophage was identified as the main cellular source for critical inflammatory mediators such as tumor necrosis factor-alpha, the chemokines interleukin (IL)-8 and -6, and matrix metalloproteinase-9 in this model system of mechanical ventilation. These mediators were measured in supernatants from ventilated alveolar macrophages, monocyte-derived macrophages, and promonocytic THP-1 cells. Nuclear factor-kappaB was found to be activated in ventilated macrophages. Synergistic proinflammatory effects of mechanical stress and molecules such as bacterial endotoxin were observed, suggesting that mechanical ventilation might be particularly deleterious in preinjured or infected lungs. Dexamethasone prevented IL-8 and tumor necrosis factor-alpha secretion in ventilated macrophages. Mechanical ventilation induced low levels of IL-8 secretion by alveolar type II-like cells. Other lung cell types such as endothelial cells, bronchial cells, and fibroblasts failed to produce IL-8 in response to a prolonged cyclic pressure-stretching load. This model is of particular value for exploring physical stress-induced signaling pathways, as well as for testing the effects of novel ventilatory strategies or adjunctive substances aimed at modulating cell activation induced by mechanical ventilation.

Cytokines↗
PubMed1997

Phagocytosis of gram-negative bacteria by a unique CD14-dependent mechanism.

THP-1-derived cell lines were stably transfected with constructs encoding glycophosphatidylinositol (GPI)-anchored or transmembrane forms of human CD14. CD14 expression was associated with enhanced phagocytosis of serum (heat-inactivated)-opsonized Escherichia coli (opEc). Both the GPI-anchored and transmembrane forms of CD14 supported phagocytosis of opEc equally well. Lipopolysaccharide-binding protein (LBP) played a role in CD14-dependent phagocytosis as evidenced by inhibition of CD14-dependent phagocytosis of opEc with anti-LBP monoclonal antibody (mAb) and by enhanced phagocytosis of E. coli opsonized with purified LBP. CD14-dependent phagocytosis was inhibited by a phosphatidylinositol (PI) 3-kinase inhibitor (wortmannin) and a protein tyrosine kinase inhibitor (tyrphostin 23) but not a protein kinase C inhibitor (bisindolyl-maleimide) or a divalent cation chelator (ethylenediaminetetraacetate). Anti-LBP mAb 18G4 and anti-CD14 mAb 18E12 were used to differentiate between the pathways involved in CD14-dependent phagocytosis and CD14-dependent cell activation. F(ab')2 fragments of 18G4, a mAb to LBP that does not block cell activation, inhibited ingestion of opEc by THP1-wtCD14 cells. 18E12 (an anti-CD14 mAb that does not block LPS binding to CD14 but does inhibit CD14-dependent cell activation) did not inhibit phagocytosis of LBP-opEc by THP1-wtCD14 cells. Furthermore, CD14-dependent phagocytosis was not inhibited by anti-CD18 (CR3 and CR4 beta-chain) or anti-Fcgamma receptor mAb.

Cell Line↗
PubMed1996

Proinflammatory activity in bronchoalveolar lavage fluids from patients with ARDS, a prominent role for interleukin-1.

Proinflammatory cytokines such as tumor necrosis factor-alpha (TNF) and interleukin-1beta (IL-1) have been found to be elevated in bronchoalveolar lavage (BAL) fluid and in plasma from patients with acute respiratory distress syndrome (ARDS). In order to measure the balance of proinflammatory cytokines and their inhibitors, we quantified the upregulation of intercellular adhesion molecules (ICAM-1) induced by ARDS BAL fluids in human alveolar type II-like (A459) cells, and defined proinflammatory activity as the amount of ICAM-1 induced by the SAL fluids. Proinflammatory activity was detected in 77% of the SAL fluids sampled during the first week of ARDS, was found maximal during the 3 first days after onset of ARDS, and was significantly greater than in BAL specimens from at risk patients. Blocking experiments with specific inhibitors of TNF and IL-1 added to the BAL fluids indicated that the bioactivity measured was mainly due to IL-1. In contrast, proinflammatory activity of conditioned supernates from endotoxin-treated alveolar macrophages was mostly due to TNF. Using a bioassay that measures balance of cytokines with their inhibitors, our results indicate that the net proinflammatory activity in ARDS BAL fluids is attributable to IL-1 and not to TNF.

Adult↗
PubMed1995

Tumor necrosis factor-alpha and interleukin-1 beta mediate human endothelial cell activation in blood at low endotoxin concentrations.

Activation of endothelial cells by endotoxin (lipopolysaccharide, LPS) may occur through two different pathways. LPS can directly activate endothelial cells through its interaction with soluble CD14 or indirectly via cytokines produced in blood in response to LPS. Substitution of whole blood for plasma apparently increases the endothelial cells responses to LPS by a factor of 1,000, rendering them sensitive to subpicomolar quantities of LPS. This shift in sensitivity is dependent on the presence of monocytes or conditioned plasma from whole blood incubated with small concentrations of LPS. Herein, using agents that block the effects of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta), we demonstrate that TNF-alpha and IL-1 beta are the two LPS-induced cytokines responsible for the activation of endothelial cells, produced in blood in response to picomolar quantities of LPS. Anti-TNF-alpha monoclonal antibodies (mAbs) and IL-1 receptor antagonist separately had partial inhibitory effects. Complete and sustained inhibition of endothelial cell activation was obtained only when the two inhibitors were added together. We conclude that TNF-alpha and IL-1 beta induced in whole blood by picomolar concentrations of LPS mediate endothelial cell activation to these small quantities of LPS and that blocking of both cytokines is necessary to inhibit LPS-induced blood-dependent endothelial cell activation.

Antibodies, Monoclonal↗
PubMed1995

Activation of endothelial cells by endotoxin: direct versus indirect pathways and the role of CD14.

Optimal activation of endothelial cells by nanomolar quantities of endotoxin (lipopolysaccharide, LPS) requires the presence of plasma or serum. We and others have demonstrated that soluble CD14 (sCD14) and LPS binding protein (LBP) were the key plasma proteins mediating endothelial cell responses to LPS. The role of LBP is to transfer LPS to sCD14 and newly formed LPS-sCD14 will in turn activate endothelial cells via an as yet unknown surface receptor. This plasma-dependent pathway of endothelial cells activation is referred as to the direct pathway. However, endothelial cells are in constant contact with whole blood and not only with plasma. In experiments where whole blood was substituted for plasma, we showed that endothelial cells became sensitive to picomolar, rather than nanomolar quantities of LPS. The fact that endothelial cell responses were amplified by the presence of whole blood prompted us to search for the responsible blood cell(s) and mediator(s) for this effect. Blood cell fractionation experiments, experiments with blood from PNH patients and the use of anti-CD14 antibodies pointed to the monocyte as the blood cell responsible for the amplification effect. Moreover, the blood effect could be entirely reproduced by cells from a CD14-expressing cell line, such as calcitriol-differentiated HL-60 cells. Inhibitors to TNF and to IL-1 blocked LPS-induced activation of endothelial cells partially when added separately to whole blood, but abrogated endothelial cell responses when added together. Thus, the whole blood effect begins with LPS activation of monocytes via cell membrane CD14 and results in endothelial cell activation by the effects of TNF and IL-1. The monokine-mediated endothelial cell activation is referred as to the indirect pathway.

Cells, Cultured↗
PubMed1994

CD14 is a pattern recognition receptor.

Septic shock caused by a diverse group of bacterial pathogens is a serious human disease. Recognition of bacterial envelope constituents is one mechanism used by mammalian cells to initiate responses leading to bacterial killing or, unfortunately, responses that also cause fatal septic shock. Here we show that CD14 plays a key role in initiating cell activation by a group of bacterial envelope components from Gram-negative and Gram-positive microorganisms, as well as mycobacteria. We propose that CD14 is a receptor used by mammalian cells to recognize and signal responses to a diverse array of bacterial constituents. This finding defines the molecular basis for innate microbial immunity; implicit in these findings are new possibilities for therapeutics.

Animals↗
PubMed1994

Lipopolysaccharide (LPS)-binding protein and soluble CD14 function as accessory molecules for LPS-induced changes in endothelial barrier function, in vitro.

Bacterial LPS induces endothelial cell (EC) injury both in vivo and in vitro. We studied the effect of Escherichia coli 0111:B4 LPS on movement of 14C-BSA across bovine pulmonary artery EC monolayers. In the presence of serum, a 6-h LPS exposure augmented (P < 0.001) transendothelial 14C-BSA flux compared with the media control at concentrations > or = 0.5 ng/ml, and LPS (10 ng/ml) exposures of > or = 2-h increased (P < 0.005) the flux. In the absence of serum, LPS concentrations of up to 10 micrograms/ml failed to increase 14C-BSA flux at 6 h. The addition of 10% serum increased EC sensitivity to the LPS stimulus by > 10,000-fold. LPS (10 ng/ml, 6 h) failed to increase 14C-BSA flux at serum concentrations < 0.5%, and maximum LPS-induced increments could be generated in the presence of > or = 2.5%. LPS-binding protein (LBP) and soluble CD14 (sCD14) could each satisfy this serum requirement; either anti-LBP or anti-CD14 antibody each totally blocked (P < 0.00005) the LPS-induced changes in endothelial barrier function. LPS-LBP had a more rapid onset than did LPS-sCD14. The LPS effect in the presence of both LBP and sCD14 exceeded the effect in the presence of either protein alone. These data suggest that LBP and sCD14 each independently functions as an accessory molecule for LPS presentation to the non-CD14-bearing endothelial surface. However, in the presence of serum both molecules are required.

Acute-Phase Proteins↗
PubMed1994

Lack of correlation between tritiated deoxyglucose, thallium-201 and technetium-99m-MIBI cell incorporation under various cell stresses.

UNLABELLED: The use of fluorodeoxyglucose (FDG) and PET, recognized as an accurate tool for the specific diagnosis and staging of cancer, is currently being tested to monitor cancer therapy. Similar investigations have been performed with the nonPET markers 201Tl and 99mTc-methoxyisobutylisonitrile (MIBI), two markers of myocardial perfusion shown to concentrate in malignant cells. We have tested the hypothesis that the cellular incorporation of 201Tl and 99mTc-MIBI reflects that of FDG and correlates with treatment efficacy. METHODS: We measured the incorporation in U937 cells of tritiated deoxyglucose (3H-DG), 201Tl and 99mTc-MIBI in basal conditions after stimulation or inhibition of the glucose metabolic pathway and after exposure to toxic agents selected to mimic the effects of chemotherapy. Thallium-201 or 99mTc-MIBI cell incorporation remained at basal levels after exposure to insulin, whereas 3H-DG cell incorporation was greatly enhanced. Conversely, in the presence of 50 microM of NaF for 3 hr, only 3H-DG cell incorporation was reduced to 57.2% +/- 6.2% from control conditions. Cycloheximide (CYX), metaiodobenzylguanidine (MIBG) and bleomycin (BLM) were added to cell cultures. RESULTS: Neither 201Tl nor 99mTc-MIBI followed the changes in cell incorporation observed with 3H-DG. In addition, only 3H-DG cell incorporation was inversely correlated to the time of cell exposure or to the cell culture concentration of MIBG and BLM. CONCLUSION: In this model, cell incorporation of 201Tl or 99mTc-MIBI differed from cell incorporation of 3H-DG suggesting that it was not directly related to cell glycolysis activity and cell injury. In conclusion, these results do not support the hypothesis that 201Tl or 99mTc-MIBI could replace FDG to monitor cancer treatment.

3-Iodobenzylguanidine↗
PubMed1993

A critical role for monocytes and CD14 in endotoxin-induced endothelial cell activation.

Vascular endothelium activated by endotoxin (lipopolysaccharide [LPS]) and cytokines plays an important role in organ inflammation and blood leukocyte recruitment observed during sepsis. Endothelial cells can be activated by LPS directly, after its interaction with LPS-binding protein and soluble CD14 in plasma. LPS-LPS-binding protein complexes in blood also interact with monocytes and neutrophils bearing glycosyl-phosphatidylinositol (GPI) anchored membrane CD14 (mCD14), promoting the release of cytokines such as tumor necrosis factor and interleukin 1 (IL-1). These molecules, in turn, have the capacity to activate endothelial cells providing an indirect pathway for LPS-dependent endothelial cell activation. In this work, we address the relative importance of the direct and the indirect pathway of in vitro LPS-induced human umbilical vein endothelial cell (HUVEC) activation. Substituting whole blood for plasma resulted in a 1,000-fold enhancement of HUVEC sensitivity to LPS. Both blood- and plasma-dependent enhanced activation of HUVEC were blocked with an anti-CD14 monoclonal antibody. Blood from patients with paroxysmal nocturnal hemoglobinuria, whose cells lack mCD14 and other GPI anchored proteins, was unable to enhance LPS activation of HUVEC above the level observed with plasma alone. IL-10, an inhibitor of monocyte release of cytokines, decreased the blood-dependent enhancement of HUVEC activation by LPS. Blood adapted to small doses of LPS was also less efficient than nonadapted blood in producing this enhancement. Addition of purified mononuclear cells to HUVEC or the transfer of plasma from whole blood incubated with LPS to HUVEC, duplicated the enhancement effect observed when whole blood was incubated with HUVEC. Taken together, these data suggest that the indirect pathway of LPS activation of endothelial cell is mediated by monocytes and mCD14 through the secretion of a soluble mediator(s). The indirect pathway is far more efficient than the direct, plasma-dependent pathway.

Antigens, CD↗
PubMed1993

Lipopolysaccharide activation of human endothelial and epithelial cells is mediated by lipopolysaccharide-binding protein and soluble CD14.

Myeloid cell activation by lipopolysaccharides (LPS) involves two proteins, plasma LPS-binding protein (LBP) and cell-membrane CD14. Cell membrane CD14, anchored by a glycerophosphatidylinositol tail, is the cellular receptor for LPS-LBP complexes. Another form of CD14, without the lipid tail, circulates as a soluble plasma protein. In this work we show that soluble CD14 (sCD14) is required for activation of endothelial and epithelial cells by LPS. We propose that LPS-LBP complexes transfer LPS to sCD14, and the LPS-sCD14 complexes then bind to a cellular receptor. Support for this pathway comes from experiments in which LBP and CD14 in normal human serum are blocked by specific antibodies, experiments in which serum is replaced by purified LBP and sCD14, and experiments in which specific binding of [3H]LPS to epithelial cells is quantitated.

Acute-Phase Proteins↗