Changes in endotoxin-binding proteins during major elective surgery: important role for soluble CD14 in regulation of biological activity of systemic endotoxin

Postprandial lipid and vascular responses following consumption of a commercially-relevant interesterified palmitic acid-rich spread in comparison to functionally-equivalent non-interesterified spread and spreadable butter: a randomised controlled trial in healthy adults

Background: Interesterification is an industrial processing technique used widely where hard fats are essential for functionality and consumer acceptability, e.g. margarines and lower fat spreads. Objective: The aim of this study was to compare acute cardiovascular effects of functionally equivalent spreads (similar solid fat content) made with interesterified (IE) or non-IE palm-based fats, or spreadable butter. Methods: A randomised, controlled, 4-armed crossover, double-blind study (25 men, 25 women; 35-75 years; healthy; mean BMI 24.5, SD 3.8), compared effects of mixed nutrient meals containing 50 g fat from functionally equivalent products [IE spread, non-IE spread and spreadable butter (SB), with rapeseed oil (RO) as a reference treatment: with 16.7%, 27.9%, 19.3% and 4% palmitic acid, respectively] on 8 h postprandial changes in plasma triacylglycerol (TAG) and endothelial dysfunction (flow-mediated dilatation; FMD). Circulating reactive oxygen species (estimated using a neutrophil oxidative burst assay), glucose, insulin, NEFA, lipoprotein particle profiles, inflammatory markers (glycoprotein acetylation (Glyc-A) and IL-6), and biomarkers of endotoxemia were measured. Results: Postprandial plasma TAG concentrations after test meals were similar. However following RO versus the 3 spreads, there were significantly higher postprandial apolipoprotein B concentrations, and small HDL and LDL particle concentrations, and lower postprandial extra-large, large, and medium HDL particle concentrations, as well as smaller average HDL and LDL particle sizes. There were no differences following IE compared to the other spreads. Postprandial FMD% did not decrease after high-fat test meals, and there were no differences between treatments. Postprandial serum IL-6 increased similarly after test meals, but RO provoked a greater increase in postprandial concentrations of glycoprotein acetyls (GlycA), as well as 8 h sCD14, an endotoxemia marker. All other postprandial outcomes were not different between treatments. Conclusions: In healthy adults, a commercially-available IE-based spread did not evoke a different postprandial triacylglycerol, lipoprotein subclass, oxidative stress, inflammatory or endotoxemic response to functionally-equivalent, but compositionally-distinct alternative spreads. Clinical trial registry number: NCT03438084 (https://ClinicalTrials.gov).

Pathophysiological relevance of the CD14 receptor in surgical patients: biological activity of endotoxin is regulated by the CD14 receptor

Endotoxins (lipopolysaccharides, LPSs) are potent bacterial poisons, and they are always present in the intestine in considerable numbers. Stress, such that as a resulting from multiple injuries, burns, hypovolemia, hypoxia, intestinal ischemia, and surgery can lead to a breakdown of the gut barrier, allowing endotoxins to enter the systemic circulation via translocation. However, estimating the biological activity of translocated circulating endotoxins and identification of the mechanisms regulating their biological activities remain complex problems. CD14 has been found to exist as a soluble protein in the serum and as a glycosylphosphatidylinositol (GPI)-anchored protein of myeloid lineage cells. It plays key roles in both LPS-induced activation and in LPS internalization by cells. In this article, we outline: (i) the biological activity of circulating endotoxin; and (ii) the role of membrane and/or soluble CD14 regulating the bioactivity of circulating endotoxin in a human model of postoperative endotoxemia.

Modulatory effects of sCD14 and LBP on LPS-host cell interactions

LPS binding protein (LBP) and CD14 play key roles in promoting innate immunity to Gram-negative bacteria by transferring LPS to the signaling receptor complex, MD-2/Toll-like receptor 4 (TLR4). LBP and soluble CD14 (sCD14) can also inhibit responses to LPS by mechanisms that depend on their concentration and environment; during acute inflammation and infection, their concentrations increase in plasma and extravascular fluids. Whereas low concentrations of LBP enhance responses to LPS, high LBP concentrations can inhibit LPS bioactivity in vitro and in vivo. sCD14 also inhibits cell responses by diverting LPS from membrane-bound CD14 (mCD14) and by promoting LPS efflux from cell-surface mCD14 and transferring it to plasma lipoproteins. In vivo studies support the hypothesis that sCD14 has systemic anti-inflammatory effects, whereas in the tissues it may have pro-inflammatory effects that increase resistance to bacteria. Likewise, LBP increases resistance to Gram-negative bacteria by rapidly triggering pro-inflammatory responses to LPS. Thus, the dual stimulatory and inhibitory mechanisms of sCD14 and LBP may benefit the infected host by promoting inflammation in local sites, where it is needed, while at the same time preventing potentially detrimental systemic responses to LPS.

Transient Peripheral Immune Activation follows Elective Sigmoidoscopy or Circumcision in a Cohort Study of MSM at Risk of HIV Infection

BACKGROUND

Rectal and genital sampling in HIV prevention trials permits assessments at the site of HIV entry. Yet the safety and acceptability of circumcision and sigmoidoscopy (and associated abstinence recommendations) are unknown in uncircumcised men who have sex with men (MSM) at high risk of HIV infection.

METHODS

Twenty-nine HIV-seronegative high-risk Peruvian MSM agreed to elective sigmoidoscopy biopsy collections (weeks 2 and 27) and circumcision (week 4) in a 28-week cohort study designed to mimic an HIV vaccine study mucosal collection protocol. We monitored adherence to abstinence recommendations, procedure-related complications, HIV infections, peripheral immune activation, and retention.

RESULTS

Twenty-three (79.3%) underwent a first sigmoidoscopy, 21 (72.4%) were circumcised, and 16 (55.2%) completed a second sigmoidoscopy during the study period. All who underwent procedures completed the associated follow-up safety visits. Those completing the procedures reported they were well tolerated, and complication rates were similar to those reported in the literature. Immune activation was detected during the healing period (1 week post-sigmoidoscopy, 6 weeks post-circumcision), including increases in CCR5+CD4+T cells and α4β7+CD4+T cells. Most participants adhered to post-circumcision abstinence recommendations whereas reduced adherence occurred post-sigmoidoscopy.

CONCLUSION

Rectosigmoid mucosal and genital tissue collections were safe in high-risk MSM. Although the clinical implications of the post-procedure increase in peripheral immune activation markers are unknown, they reinforce the need to provide ongoing risk reduction counseling and support for post-procedure abstinence recommendations. Future HIV vaccine studies should also consider the effects of mucosal and tissue collections on peripheral blood endpoints in trial design and analysis.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02630082.

Endotoxemia-menace, marker, or mistake?

Endotoxemia is in its scientific ascendancy. Never has blood-borne, Gram-negative bacterial endotoxin (LPS) been invoked in the pathogenesis of so many diseases-not only as a trigger for septic shock, once its most cited role, but also as a contributor to atherosclerosis, obesity, chronic fatigue, metabolic syndrome, and many other conditions. Finding elevated plasma endotoxin levels has been essential supporting evidence for each of these links, yet the assays used to detect and quantitate endotoxin have important limitations. This article describes several assays for endotoxin in plasma, reviews what they do and do not measure, and discusses why LPS heterogeneity, LPS trafficking pathways, and host LPS inactivation mechanisms should be considered when interpreting endotoxin assay results.

Increased serum levels of lipopolysaccharide and antiflagellin antibodies in patients with diarrhea-predominant irritable bowel syndrome

BACKGROUND

Innate immune responses to conserved microbial products such as lipopolysaccharide (LPS) and flagellin are likely important in microbial-host interactions and intestinal homeostasis. We hypothesized that bacterial translocation and activation of mucosal immunity against common microbial antigens might be involved in the development of irritable bowel syndrome (IBS). We therefore compared serum levels of LPS, soluble CD14 (sCD14), and flagellin antibodies between patients with different subtypes of IBS and healthy controls.

METHODS

We analyzed serum obtained from 88 patients (74 females) aged 19(43)-73 years and 106 healthy volunteers (77 females) aged 19(38)-62 years. Diarrhea-predominant IBS (D-IBS) was present in 32 patients (36%), 23 patients (26%) had constipation-predominant IBS (C-IBS), and 33 patients (38%) had A-IBS. We used ELISA for sCD14 and antiflagellin immunoglobulin G and limulus amebocyte assay for LPS. Abdominal symptoms and psychiatric comorbidities were assessed using validated questionnaires.

KEY RESULTS

We found a significantly higher serum level of LPS in patients with D-IBS compared to controls (p = 0.0155). The level of antibodies to flagellin was higher in patients with IBS than in controls (mainly driven by higher levels in D-IBS, p = 0.0018). The levels of sCD14 were lower in D-IBS patients compared to controls (p = 0.0498). We found a weak, but significant correlation between the levels of antiflagellin antibodies and anxiety among IBS patients (ρ = 0.38; p = 0.0045).

CONCLUSIONS & INFERENCES

Our results support the concept that immune reactivity to luminal antigens may have a role in the development of D-IBS. The serum level of antiflagellin antibodies was found to correlate with patients' self-reported anxiety score.

Digestion and Postprandial Metabolism in the Elderly

The elderly are an increasing segment of the population. Despite the rapid gains in medical knowledge and treatments, older adults are more likely to experience chronic illnesses that decrease quality of life and accelerate mortality. Nutrition is a key modifiable lifestyle factor which greatly impacts chronic disease risk. Yet despite the importance of nutrition, relatively little is known of the impact of advancing age on the gastrointestinal function, the digestive responses, and the post-meal metabolic adaptations that occur in response to ingested food. Knowledge of the age-related differences in digestion and metabolism in the elderly is essential to the development of appropriate nutritional recommendations for the maintenance of optimal health and prevention of disease.

Oil composition of high-fat diet affects metabolic inflammation differently in connection with endotoxin receptors in mice

Low-grade inflammation observed in obesity is a risk factor for cardiovascular disease. Recent studies revealed that this would be linked to gut-derived endotoxemia during fat digestion in high-fat diets, but nothing is known about the effect of lipid composition. The study was designed to test the impact of oil composition of high-fat diets on endotoxin metabolism and inflammation in mice. C57/Bl6 mice were fed for 8 wk with chow or isocaloric isolipidic diets enriched with oils differing in fatty acid composition: milk fat, palm oil, rapeseed oil, or sunflower oil. In vitro, adipocytes (3T3-L1) were stimulated or not with lipopolysaccharide (LPS; endotoxin) and incubated with different fatty acids. In mice, the palm group presented the highest level of IL-6 in plasma (P < 0.01) together with the highest expression in adipose tissue of IL-1β and of LPS-sensing TLR4 and CD14 (P < 0.05). The higher inflammation in the palm group was correlated with a greater ratio of LPS-binding protein (LBP)/sCD14 in plasma (P < 0.05). The rapeseed group resulted in higher sCD14 than the palm group, which was associated with lower inflammation in both plasma and adipose tissue despite higher plasma endotoxemia. Taken together, our results reveal that the palm oil-based diet resulted in the most active transport of LPS toward tissues via high LBP and low sCD14 and the greatest inflammatory outcomes. In contrast, a rapeseed oil-based diet seemed to result in an endotoxin metabolism driven toward less inflammatory pathways. This shows that dietary fat composition can contribute to modulate the onset of low-grade inflammation through the quality of endotoxin receptors.

Human monocytes tolerant to LPS retain the ability to phagocytose bacteria and generate reactive oxygen species

Tolerance to lipopolysaccharide (LPS) occurs when animals or cells exposed to LPS become hyporesponsive to a subsequent challenge with LPS. This mechanism is believed to be involved in the down-regulation of cellular responses observed in septic patients. The aim of this investigation was to evaluate LPS-induced monocyte tolerance of healthy volunteers using whole blood. The detection of intracellular IL-6, bacterial phagocytosis and reactive oxygen species (ROS) was determined by flow cytometry, using anti-IL-6-PE, heat-killed Staphylococcus aureus stained with propidium iodide and 2',7'-dichlorofluorescein diacetate, respectively. Monocytes were gated in whole blood by combining FSC and SSC parameters and CD14-positive staining. The exposure to increasing LPS concentrations resulted in lower intracellular concentration of IL-6 in monocytes after challenge. A similar effect was observed with challenge with MALP-2 (a Toll-like receptor (TLR)2/6 agonist) and killed Pseudomonas aeruginosa and S. aureus, but not with flagellin (a TLR5 agonist). LPS conditioning with 15 ng/mL resulted in a 40% reduction of IL-6 in monocytes. In contrast, phagocytosis of P. aeruginosa and S. aureus and induced ROS generation were preserved or increased in tolerant cells. The phenomenon of tolerance involves a complex regulation in which the production of IL-6 was diminished, whereas the bacterial phagocytosis and production of ROS was preserved. Decreased production of proinflammatory cytokines and preserved or increased production of ROS may be an adaptation to control the deleterious effects of inflammation while preserving antimicrobial activity.

Complex links between dietary lipids, endogenous endotoxins and metabolic inflammation

Metabolic diseases such as obesity are characterized by a subclinical inflammatory state that contributes to the development of insulin resistance and atherosclerosis. Recent reports also indicate that (i) there are alterations of the intestinal microbiota in metabolic diseases and (ii) absorption of endogenous endotoxins (namely lipopolysaccharides, LPS) can occur, particularly during the digestion of lipids. The aim of the present review is to highlight recently gained knowledge regarding the links between high fat diets, lipid digestion, intestinal microbiota and metabolic endotoxemia & inflammation.

Emulsified lipids increase endotoxemia: possible role in early postprandial low-grade inflammation

Low-grade inflammation is a risk factor for the onset of atherosclerosis. Little is known about the involvement of endotoxin absorption from the gut during the digestion of lipids. In the present study, we first investigated in humans the impact of a mixed meal containing dispersed lipids on postprandial endotoxemia and inflammation. We then investigated the effect of (i) oil emulsification in vivo in rats and (ii) fatty acid amounts in vitro using Caco-2 cells on postprandial endotoxemia. In humans, postprandial endotoxemia increased early after the meal. Moreover, we evidenced that the endotoxin receptor sCD14 increased during digestion and that chylomicrons could contribute to absorbed endotoxin transport. This could explain the significant peak of inflammatory cytokine IL-6 that we observed 2 h after the mixed meal. Interestingly, in rats, the emulsion led to both higher endotoxemia and hypertriglyceridemia than oil and compared to a control saline load. In vitro, incubation of Caco-2 cells with increasing fatty acid concentrations enhanced epithelial absorption of endotoxin. To our knowledge, this is the first study evidencing in healthy humans that, following a mixed meal containing lipids, increased endotoxemia is associated with raised sCD14 and a peak of IL-6. On a repeated basis, this may thus be a triggering cascade for the onset of atherosclerosis. In this respect, optimizing both dietary fat amount and structure could be a possible strategy to limit such low-grade endotoxemia and inflammation by the control of postprandial lipemia.

Effects of acute hypervolaemic haemodilution on the expression of plasma interferon-inducible protein-10 and bactericidal/permeability-increasing protein in patients undergoing total hip replacement

This prospective, randomized controlled study evaluated the effects of acute hypervolaemic haemodilution (AHH) on the expression of plasma interferon-inducible protein-10 (IP-10) and bactericidal/permeability-increasing protein (BPI) in patients undergoing elective total hip replacement. Twenty patients were randomized to receive an infusion of either hydroxyethyl starch (HES group) or lactated Ringer's solution (LR group) immediately after anaesthesia. Plasma concentrations of IP-10 and BPI were measured before anaesthesia (baseline), at the start of surgery, 30 min after the start of surgery and at the end of surgery. Blood loss and the volume of blood transfused were significantly lower in the HES group compared with the LR group. Compared with baseline, IP-10 and BPI concentrations increased significantly in both groups 30 min after the start of surgery. The IP-10 concentrations were significantly lower and BPI concentrations significantly higher in the HES group compared with the LR group 30 min after the start of surgery and at the end of surgery. It is concluded that AHH with HES may be helpful in ameliorating immune function during total hip replacement and in reducing blood loss and the extent of blood transfusion.

A high-fat meal induces low-grade endotoxemia: evidence of a novel mechanism of postprandial inflammation

BACKGROUND

Bacterial endotoxin is a potently inflammatory antigen that is abundant in the human gut. Endotoxin circulates at low concentrations in the blood of all healthy individuals, although elevated concentrations are associated with an increased risk of atherosclerosis.

OBJECTIVE

We sought to determine whether a high-fat meal or smoking increases plasma endotoxin concentrations and whether such concentrations are of physiologic relevance.

DESIGN

Plasma endotoxin and endotoxin neutralization capacity were measured for 4 h in 12 healthy men after no meal, 3 cigarettes, a high-fat meal, or a high-fat meal with 3 cigarettes by using the limulus assay.

RESULTS

Baseline endotoxin concentrations were 8.2 pg/mL (interquartile range: 3.4-13.5 pg/mL) but increased significantly (P < 0.05) by approximately 50% after a high-fat meal or after a high-fat meal with cigarettes but not after no meal or cigarettes alone. These results were validated by the observations that a high-fat meal with or without cigarettes, but not no meal or smoking, also significantly (P < 0.05) reduced plasma endotoxin neutralization capacity, which is an indirect measure of endotoxin exposure. Human monocytes, but not aortic endothelial cells, were responsive to transient (30 s) or low-dose (10 pg/mL) exposure to endotoxin. However, plasma from whole blood treated with as little as 10 pg endotoxin/mL increased the endothelial cell expression of E-selectin, at least partly via tumor necrosis factor-alpha-induced cellular activation.

CONCLUSIONS

Low-grade endotoxemia may contribute to the postprandial inflammatory state and could represent a novel potential contributor to endothelial activation and the development of atherosclerosis.

Manipulation of the small intestine as a cause of the increased inflammatory response after open compared with laparoscopic surgery

BACKGROUND

Laparoscopic surgery of the gastrointestinal tract involves a reduced immune response compared with open surgery. The aim of this study was to assess manual handling of the gut in open procedures as the principal cause of the enhanced immune response.

METHODS

Eighteen Landrace pigs underwent gastrectomy by three different methods: conventional open wound with bowel manipulation, laparoscopically assisted gastrectomy, and gastrectomy without manipulation using a combination of open wound and laparoscopic surgical devices. Local inflammatory changes were assessed by ascites formation, intestinal adhesion development and intestinal inflammatory gene expression. Associated systemic inflammatory changes were determined by measuring portal and systemic plasma endotoxin levels, plasma inflammatory cytokine levels, liver inflammatory gene expression and transaminase levels.

RESULTS

Significantly more postoperative intra-abdominal fluid and adhesions were seen in the open group. The expression of inflammatory cytokines was significantly greater in the intestine and liver in the open group. Portal and systemic levels of endotoxin, inflammatory cytokines and transaminases were also higher.

CONCLUSION

Manual handling of organs during gastrectomy is an important contributor to the molecular and humoral inflammatory response to surgery, supporting the use of minimally invasive techniques in gastrointestinal surgery.

Association of the -159C/T polymorphism of the endotoxin receptor (CD14) with carotid artery disease and cardiovascular mortality in dialysis patients

BACKGROUND

Atherosclerosis is a major problem in end-stage renal disease (ESRD) patients treated by hemodialysis and the prevalence of carotid artery disease is much higher in this group than in the general population. Repeated exposure to cytokine-inducing material, derived from dialysate, may induce a chronic inflammatory state, that could contribute to the atherosclerotic process. Endotoxin is mainly cleared from plasma by the sCD14, the soluble form of the endotoxin receptor CD14. The levels of sCD14 are associated with a polymorphism, -159 C/T, of the CD14 gene.

METHODS AND RESULTS

We determined the genotype for the -159 C/T polymorphism in 158 haemodialysis patients and 168 healthy controls. In patients we investigated the association between the CD14 polymorphism and carotid artery disease. With a prospective follow-up study we assessed whether the CD14 polymorphism shows any relationship with cardiovascular mortality. The polymorphic frequency was comparable between patients and controls. In patients, we found a significant difference in the prevalence of carotid artery disease between groups divided by genotype: CC 87.0%, CT 71.7%, TT 48.9% (p = 0.0093). In dialysis patients with hypertension the CC polymorphism was associated with an increased cardiovascular mortality.

CONCLUSIONS

These results demonstrate an association between the -159 C/T polymorphism of the CD14 gene and carotid artery disease in dialysis patients. We hypothesize that the low plasma clearance of endotoxin associated with the CC genotype facilitates the atherogenic action of endotoxin-derived cytokines in haemodialysis patients.

Role of the gut in the course of severe acute pancreatitis

INTRODUCTION

The pathogenesis of acute pancreatitis remains elusive. Sepsis and multiple organ failure continue to cause death (overall mortality rate, approximately 10%) despite immense improvements in supportive, radiologic, and surgical therapy. The gut appears to play a key role in the development of these complications.

AIM

To critically review the evidence implicating the gut in the pathogenesis of acute pancreatitis.

METHODS

Relevant English-language literature or abstracts cited in the MEDLINE database were reviewed.

RESULTS AND CONCLUSION

Gram-negative enteric organisms account for most infections of pancreatic necrosis and subsequent sepsis, which suggests the gut as a source. Intestinal permeability is increased early in patients with severe acute pancreatitis and correlates with endotoxemia, which suggests translocation as a possible mechanism. The pathogenesis of the deranged function of the gut mucosal barrier and the possible sites of increase in intestinal permeability are discussed. The gut also plays a role in priming neutrophils and the release of inflammatory cytokines, which initiate and propagate nearly all the detrimental consequences of severe inflammation and sepsis. Future research avenues and potential therapeutic measures that may restore and preserve gut barrier function are explored.

Promoter polymorphism in the endotoxin receptor (CD14) is associated with increased carotid atherosclerosis only in smokers: the Carotid Atherosclerosis Progression Study (CAPS)

BACKGROUND AND PURPOSE

The risk of atherosclerosis from endotoxemia is increased in smokers. Endotoxin is a potent mediator of inflammation, and smokers have elevated plasma levels of endotoxin. The endotoxin receptor CD14 can enhance the endotoxin-neutralization capacity of plasma. A functional polymorphism in the promoter region of the CD14 gene (CD14 -159C/T) was studied to determine its impact on common carotid artery (CCA) intima-media thickness (IMT) and any interactions with environmental inflammatory stimuli.

METHODS

A community population (n=992; aged 50 to 65 years) underwent genotypic examination for the CD14 -159 polymorphism by restriction fragment length polymorphism analysis.

RESULTS

The CC genotype was associated with increased CCA IMT. The age- and sex-adjusted odds ratio for IMT above the 75th percentile was 1.63 (95% CI, 1.19 to 2.24; P=0.002) and 1.70 (95% CI, 1.18 to 2.44; P=0.004) after additional adjustment for conventional risk factors. This gene effect was found only in current smokers and ex-smokers. Multivariate analysis in this group (n=503) increased the odds ratio to 2.02 (95% CI, 1.23 to 3.34; P=0.006). No significant interactions were found in nonsmokers or with alcohol consumption.

CONCLUSIONS

The CD14 -159 polymorphism is associated with increased CCA IMT in smokers from a general population. CD14 may modulate the inflammatory effects of smoking in atherogenesis.

Lipopolysaccharide induced synthesis of CD14 proteins and its gene expression in hepatocytes during endotoxemia

AIM: To observe synthesis of CD14 protein and expression of CD14 mRNA in hepatic tissue and hepatocytes of rats during endotoxemia.

METHODS: The endotoxemia model of Wistar rat was established by injection of a dose of lipopolysaccharide (LPS) (5 mg·kg^-1, Escherichia coli O111:B4) via the tail vein, and then the rats were sacrificed after 3, 6, 12 and 24 h in batches. Hepatocytes were isolated from normal and LPS-injected rats by in situ collagenase perfusion technique and were collected to measure the expression of CD14 mRNA and synthesis of CD14 protein by reverse transcript-polymerase chain reaction (RT-PCR) or Western blot analysis. The binding of fluorescein isothiocyanate (FITC)-CD14 polyclonal antibody to isolated hepatocytes was also assessed by flow cytometric analysis (FCM).

RESULTS: In the rats with endotoxemia, the expressions of CD14 mRNA in hepatic tissue and isolated hepatocytes were stronger at 3, 6, and 12 h than that in control rats (3.48 ± 0.15, 5.89 ± 0.62, 4.33 ± 0.18, vs 1.35 ± 0.14 in hepatic tissue, P < 0.01; 4.12 ± 0.17, 6.24 ± 0.64, 4.35 ± 0.18, vs 1.87 ± 0.15 in hepatocytoes, P < 0.01).The synthesis of CD14 protein in hepatic tissue and isolated hepatocytes increases also obviously in 6 and 12 h when compared to that in control rats (13.27 ± 1.27, 17.32 ± 1.35, 11.42 ± 1.20,vs 7.34 ± 0.72 in hepatic tissue, P < 0.01; 14.68 ± 1.30, 17.95 ± 1.34, 11.65 ± 1.19, vs 7.91 ± 0.70 in hepatocytes, P < 0.01). FCM showed that mean fluorescence intensity (MFI) and numbers of FITC-CD14 positive cells in the rats with endotoxemia increased obviously at 3, 6, 12 and 24 h when compared with normal control group (43.4%, 70.2%, 91.4%, 32.6% vs 4.5%, P < 0.01).

CONCLUSION: LPS can markedly promote the synthesis of CD14 protein and up-regulate the expression of CD14 mRNA in isolated hepatocytes and hepatic tissue. Liver might be a main source for soluble CD14 production during endotoxemia.

Plasma CD14 decreases monocyte responses to LPS by transferring cell-bound LPS to plasma lipoproteins

CD14, a myeloid cell-surface receptor and soluble plasma protein, binds LPS and other microbial molecules and initiates the innate immune response to bacterial invasion. The blood concentration of soluble CD14 (sCD14) increases during the systemic response to infection. Although high sCD14 blood levels have correlated with increased risk of dying from severe sepsis, sCD14 can diminish cell responses to LPS. We show here that in human serum, sCD14 increases the rate at which cell-bound LPS is released from the monocyte surface and binds to plasma lipoproteins. This enhanced rate of LPS efflux is associated with a significant reduction in the ability of monocytes to produce cytokines in response to LPS. Serum from septic patients reduced the LPS-monocyte interaction by as much as tenfold, and depletion of sCD14 from the serum restored LPS-monocyte binding and release kinetics to near normal levels. In serum from septic patients, monocyte-bound LPS also moved more rapidly into lipoproteins, which completely neutralized the biologic activity of the LPS that bound to them. In human plasma, sCD14 thus diminishes monocyte responses to LPS by transferring cell-bound LPS to lipoproteins. Stress-related increases in plasma sCD14 levels may help prevent inflammatory responses within the blood.