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Lipid droplets are fat storage organelles present in most eukaryotic cells. They consist of a neutral lipid core containing mostly triglycerides and sterol esters and covered by a monolayer of phospholipids, wherein numerous proteins are embedded. In the cell, lipid droplets have a dynamic life cycle, rapidly altering their size, location, lipid and protein composition in response to environmental stimuli and cell state. Lipid droplets are primarily involved in the coordination of lipid metabolism with cellular requirements for energy production, membrane homeostasis and cell growth. However, they are also directly or indirectly engaged in signalling pathways. On the one hand, lipid droplets sequester lipids and proteins thereby limiting their availability for participation in signalling pathways. On the other hand, the lipolytic machinery provides a highly regulated, on-demand source of signalling lipids: lipids derived from their neutral lipid core, or the phospholipid monolayer, directly act as signalling mediators or are converted into ones. In fact, emerging studies suggest that these organelles are essential for various cellular stress response mechanisms, including inflammation and immunity, acting as hubs that integrate metabolic and inflammatory processes. Here, we discuss the ways in which lipid droplets regulate the availability of fatty acids for the activation of signalling pathways and for the production of polyunsaturated fatty acid-derived lipid mediators. We focus in particular on recent discoveries in immune cells and adipose tissue that have revealed an intricate relationship between lipid droplets and inflammatory signalling and may also be relevant for other tissues and various human diseases., (Copyright © 2019 The Author(s). Published by Elsevier B.V. All rights reserved.)

Toll‑like receptor 4 (TLR4)‑mediated immune and inflammatory signaling serves a pivotal role in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). Our previous study demonstrated that celastrol treatment was able to improve hepatic steatosis and inhibit the TLR4 signaling cascade pathway in type 2 diabetic rats. The present study aimed to investigate the effects of celastrol on triglyceride accumulation and inflammation in steatotic HepG2 cells, and the possible mechanisms responsible for the regulation of cellular responses following TLR4 gene knockdown by small interfering RNA (siRNA) in vitro. A cell model of hepatic steatosis was prepared by exposing the HepG2 cells to free fatty acid (FFA) in the absence or presence of celastrol. Intracellular triglycerides were visualized by Oil red O staining, and the TLR4/myeloid differentiation primary response 88 (MyD88)/nuclear factor‑κB (NF‑κB) signaling cascade pathway were investigated. To directly elucidate whether TLR4 was the blocking target of celastrol upon FFA exposure, the cellular response to inflammation was determined upon transfection with TLR4 siRNA. The results revealed that celastrol significantly reduced triglyceride accumulation in the steatotic HepG2 cells, and downregulated the expression levels of TLR4, MyD88 and phospho‑NF‑κBp65, as well as of the downstream inflammatory cytokines interleukin‑1β and tumor necrosis factor α. Knockdown of TLR4 also alleviated FFA‑induced inflammatory response. In addition, co‑treatment with TLR4 siRNA and celastrol further attenuated the expression of inflammatory mediators. These results suggest that celastrol exerts its protective effect partly via inhibiting the TLR4‑mediated immune and inflammatory response in steatotic HepG2 cells.

Objective: Mendelian randomization studies revealed a causal role for remnant cholesterol in cardiovascular disease. Remnant particles accumulate in the arterial wall, potentially propagating local and systemic inflammation. We evaluated the impact of remnant cholesterol on arterial wall inflammation, circulating monocytes, and bone marrow in patients with familial dysbetalipoproteinemia (FD)., Approach and Results: Arterial wall inflammation and bone marrow activity were measured using 18 F-FDG PET/CT. Monocyte phenotype was assessed with flow cytometry. The correlation between remnant levels and hematopoietic activity was validated in the CGPS (Copenhagen General Population Study). We found a 1.2-fold increase of 18 F-FDG uptake in the arterial wall in patients with FD (n=17, age 60±8 years, remnant cholesterol: 3.26 [2.07-5.71]) compared with controls (n=17, age 61±8 years, remnant cholesterol 0.29 [0.27-0.40]; P <0.001). Monocytes from patients with FD showed increased lipid accumulation (lipid-positive monocytes: Patients with FD 92% [86-95], controls 76% [66-81], P =0.001, with an increase in lipid droplets per monocyte), and a higher expression of surface integrins (CD11b, CD11c, and CD18). Patients with FD also exhibited monocytosis and leukocytosis, accompanied by a 1.2-fold increase of 18 F-FDG uptake in bone marrow. In addition, we found a strong correlation between remnant levels and leukocyte counts in the CGPS (n=103 953, P for trend 5×10-276). In vitro experiments substantiated that remnant cholesterol accumulates in human hematopoietic stem and progenitor cells coinciding with myeloid skewing., Conclusions: Patients with FD have increased arterial wall and cellular inflammation. These findings imply an important inflammatory component to the atherogenicity of remnant cholesterol, contributing to the increased cardiovascular disease risk in patients with FD., (© 2017 American Heart Association, Inc.)

GPIHBP1, an endothelial cell protein, binds LPL in the interstitial spaces and shuttles it to its site of action inside blood vessels. For years, studies of human GPIHBP1 have been hampered by an absence of useful antibodies. We reasoned that monoclonal antibodies (mAbs) against human GPIHBP1 would be useful for 1) defining the functional relevance of GPIHBP1's Ly6 and acidic domains to the binding of LPL; 2) ascertaining whether human GPIHBP1 is expressed exclusively in capillary endothelial cells; and 3) testing whether GPIHBP1 is detectable in human plasma. Here, we report the development of a panel of human GPIHBP1-specific mAbs. Two mAbs against GPIHBP1's Ly6 domain, RE3 and RG3, abolished LPL binding, whereas an antibody against the acidic domain, RF4, did not. Also, mAbs RE3 and RG3 bound with reduced affinity to a mutant GPIHBP1 containing an Ly6 domain mutation (W109S) that abolishes LPL binding. Immunohistochemistry studies with the GPIHBP1 mAbs revealed that human GPIHBP1 is expressed only in capillary endothelial cells. Finally, we created an ELISA that detects GPIHBP1 in human plasma. That ELISA should make it possible for clinical lipidologists to determine whether plasma GPIHBP1 levels are a useful biomarker of metabolic or vascular disease., (Copyright © 2017 by the American Society for Biochemistry and Molecular Biology, Inc.)

Background: The prevalence of peanut allergies is increasing. Peanuts and many other allergen sources contain significant amounts of triglycerides, which affect absorption of antigens but have unknown effects on sensitization and anaphylaxis. We recently reported that dietary medium-chain triglycerides (MCTs), which bypass mesenteric lymph and directly enter portal blood, reduce intestinal antigen absorption into blood compared with long-chain triglycerides (LCTs), which stimulate mesenteric lymph flow and are absorbed in chylomicrons through mesenteric lymph., Objective: We sought to test how dietary MCTs affect food allergy., Methods: C3H/HeJ mice were fed peanut butter protein in MCT, LCT (peanut oil), or LCT plus an inhibitor of chylomicron formation (Pluronic L81). Peanut-specific antibodies in plasma, responses of the mice to antigen challenges, and intestinal epithelial cytokine expression were subsequently measured., Results: MCT suppressed antigen absorption into blood but stimulated absorption into Peyer patches. A single gavage of peanut protein with MCT, as well as prolonged feeding in MCT-based diets, caused spontaneous allergic sensitization. MCT-sensitized mice experienced IgG-dependent anaphylaxis on systemic challenge and IgE-dependent anaphylaxis on oral challenge. MCT feeding stimulated jejunal-epithelial thymic stromal lymphopoietin, Il25, and Il33 expression compared with that seen after LCT feeding and promoted T(H)2 cytokine responses in splenocytes. Moreover, oral challenges of sensitized mice with antigen in MCT significantly aggravated anaphylaxis compared with challenges with the LCT. Importantly, the effects of MCTs could be mimicked by adding Pluronic L81 to LCTs, and in vitro assays indicated that chylomicrons prevent basophil activation., Conclusion: Dietary MCTs promote allergic sensitization and anaphylaxis by affecting antigen absorption and availability and by stimulating T(H)2 responses., (Copyright © 2012 American Academy of Allergy, Asthma & Immunology. Published by Mosby, Inc. All rights reserved.)

Consistent with its central importance in lipid and energy homeostasis, lipolysis occurs in essentially all tissues and cell types, including macrophages. The hydrolytic cleavage of triacylglycerol by adipose triglyceride lipase (ATGL) generates non-esterified fatty acids, which are subsequently used as essential precursors for lipid and membrane synthesis, mediators in cell signaling processes or as energy substrate in mitochondria. This review summarizes the current knowledge concerning the consequences of ATGL deficiency in macrophages with particular emphasis on macrophage (dys)-function, apoptosis, and atherosclerosis.

Oral immunization is attractive as a delivery route because it is needle-free and useful for rapid mass vaccination programs to target pandemics or bioterrorism. This potential has not been realized for human vaccination, due to the requirement of large antigen doses and toxic (to humans) adjuvants to overcome the induction of oral tolerance and potential degradation of antigens in the stomach. To date, only oral vaccines based on live attenuated organisms have been approved for human use. In this study we describe the use of a lipid-based delivery system/adjuvant, Lipid C, for oral immunization to protect mice against genital tract chlamydial infection. Lipid C is formulated from food-grade purified and fractionated triglycerides. Bacterial shedding following vaginal challenge with Chlamydia muridarum was reduced by 50% in female mice orally immunized with the chlamydial major outer membrane protein (MOMP) formulated in Lipid C, protection equivalent to that seen in animals immunized with MOMP admixed with both cholera toxin (CT) and CpG oligodeoxynucleotides (CpG-ODN). Protection was further enhanced when MOMP, CT and CpG were all combined in the Lipid C matrix. Protection correlated with production of gamma interferon (IFN) by splenic T cells, a serum MOMP-specific IgG response and low but detectable levels of MOMP-specific IgA in vaginal lavage., (Copyright (c) 2009 Elsevier Ltd. All rights reserved.)

Mucosal adjuvants are important to overcome the state of immune tolerance normally associated with mucosal delivery and to enhance adaptive immunity to often-weakly immunogenic subunit vaccine antigens. Unfortunately, adverse side effects of many experimental adjuvants limit the number of adjuvants approved for vaccination. Lipid C is a novel, non-toxic, lipid oral vaccine-delivery formulation, developed originally for oral delivery of the live Mycobacterium bovis Bacille Calmette-Guerin (BCG) vaccine. In the present study, murine models of chlamydial respiratory and genital tract infections were used to determine whether transcutaneous immunization (TCI) with Lipid C-incorporated protein antigens could elicit protective immunity at the genital and respiratory mucosae. BALB/c mice were immunized transcutaneously with Lipid C containing the chlamydial major outer membrane protein (MOMP), with and without addition of cholera toxin and CpG-ODN 1826 (CT/CpG). Both vaccine combinations induced mixed cell-mediated and mucosal antibody immune responses. Immunization with Lipid C-incorporated MOMP (Lipid C/MOMP), either alone or with CT/CpG resulted in partial protection following live challenge with Chlamydia muridarum as evidenced by a significant reduction in recoverable Chlamydia from both the genital secretions and lung tissue. Protection induced by immunization with Lipid C/MOMP alone was not further enhanced by the addition of CT/CpG. These results highlight the potential of Lipid C as a novel mucosal adjuvant capable of targeting multiple mucosal surfaces following TCI. Protection at both the respiratory and genital mucosae was achieved without the requirement for potentially toxic adjuvants, suggesting that Lipid C may provide a safe effective mucosal adjuvant for human vaccination.

Background: It remains unclear whether immune modulation by lipids contributes to the high risk of infectious complications that is associated with the use of parenteral nutrition. Although mixed long- and medium-chain triacylglycerol (LCT-MCT)-containing emulsions, but not pure LCT emulsions, activate neutrophils and impair crucial leukocyte functions in vitro, in vivo studies have failed to corroborate these findings., Objectives: The present investigation was conducted to evaluate the effects of LCT and LCT-MCT on immune function in healthy humans and to assess whether the lack of in vivo effects results from sampling errors due to extravascular sequestration of activated neutrophils., Design: Saline, LCT-MCT, and LCT emulsions were administered intravenously for 4.5 h to 12 healthy volunteers in a randomized crossover design. Plasma triacylglycerol concentrations were clamped at a clinically relevant concentration of 3-5 mmol/L. Leukocyte population counts and neutrophil activation were assessed before and after infusion. Leukocyte sequestration was evaluated by monitoring the distribution of Technetium-99m-labeled autologous leukocytes during infusions., Results: Whereas LCT exerted no greater effects than did saline, LCT-MCT significantly decreased lymphocyte counts. However, no evidence for neutrophil activation was found with either lipid. Moreover, the clearance of radiolabeled leukocytes from the liver, spleen, and lungs was not altered by any lipid, which suggested that lipid emulsions do not induce leukocyte sequestration., Conclusions: Short-term infusion of LCT-MCT (but not LCT) to healthy humans modulates leukocyte population counts but, in clear contrast with the in vitro situation, does not induce neutrophil activation. These disparate findings cannot be explained by MCT-induced leukocyte sequestration.

Objective: This clinical trial investigates whether short-term administration of long chain triglycerides (LCT) has any influence on the immune function in children following gastrointestinal surgery., Methods: Sixty pediatric patients receiving a gastrointestinal operation were randomly divided into the experimental group (n = 36) and the control group (n = 24). After abdominal operation, the subjects received parenteral nutrition (PN) support with or without LCT for 5 days. The patients' fasting blood samples were respectively collected at 24 hours preoperative, then 24 hours and 120 hours postoperative. Blood parameters related to the patients' immune function were measured., Results: Before surgery and LCT treatment, the experimental group and control group did not differ significantly in overall state of health. Except for a small increase of serum IgM at 24 hours postsurgery (p < .05), all parameters representing the patients' immune function showed no significant difference between the LCT group and the control group with respect to peripheral blood mononuclear cell (PBMC), T lymphocyte, CD4, CD8, CD4/CD8, serum immunoglobulin A (IgA), IgG, IgM, complement C3, C4, interleukin (IL)-2, IL-4, IL-10, IL-12, tumor necrosis factor (TNF)-alpha and IFN-gamma (p > .05, respectively) before the operation, 24 hours and 120 hours after the operation., Conclusions: A short-term LCT administration at an appropriate dosage and infusion speed does not alter the pediatric patients' immune function after gastrointestinal surgery. The etiology and clinical significance of the slightly increased IgM 24 hours postsurgery need to be further investigated.

Objective: Increased low density lipoprotein (LDL) cholesterol and triglycerides, and decreased high density lipoprotein (HDL) cholesterol concentrations are associated with adverse cardiovascular risk in the general population. Patients with systemic lupus erythematosus (SLE) have an altered lipid profile characterized by increased triglycerides and decreased HDL cholesterol concentrations. We examined the relationships between lipid concentrations, cytokines, and inflammatory markers in patients with SLE., Methods: Fasting lipid concentrations, C-reactive protein (CRP), and erythrocyte sedimentation rate (ESR) were measured in 110 patients with SLE. Disease activity was quantified by the SLE Disease Activity Index (SLEDAI), and disease damage by the Systemic Lupus International Collaborating Clinics (SLICC) score. Concentrations of circulating tumor necrosis factor-alpha (TNF-alpha), interleukin 6 (IL-6), and insulin were measured and insulin sensitivity calculated., Results: Lower concentrations of HDL cholesterol were independently associated with higher ESR (p < 0.001), IL-6 (p = 0.02), SLEDAI (p = 0.04), and TNF-alpha (p = 0.04) after adjustment for age, sex, race, body mass index, insulin sensitivity, and current use of corticosteroids or hydroxychloroquine. Triglyceride concentrations were associated with higher CRP concentrations (p = 0.02) and SLICC score (p = 0.04)., Conclusion: Deleterious changes in lipid profile are independently associated with higher concentrations of markers and mediators of inflammation and disease activity and damage in patients with SLE.

Background & Aims: Reports regarding the pro- or anti-inflammatory effects of lipid emulsion used in parenteral nutrition are conflicting. Aim was to assess the effect of different intravenous lipid emulsions on immunological function in humans., Methods: We performed a computerized bibliographic search, searched reference lists in trial reports, hand-searched journals and contacted experts in the field. Randomized clinical trials evaluating the immunological effects of different parenteral lipid emulsions were included. Three authors independently performed data extraction, statistical processes were performed by two experts. Immunological parameters were classified by two immunologists as marker of improved or worsened immune function. A meta-analysis with standardized effect size estimation was performed for the comparison between long-chain triglycerides vs. glucose or other fat emulsions., Results: Of 682 assessed studies, 120 compared the immunological effects of intravenously applied lipid emulsions. Of 30 randomized trials, 14 were included in the meta-analysis. None of the lipid regimens showed any clear effect on the evolution of the immunological status or mortality in humans. Length of hospital stay and stay in the intensive care unit could not be evaluated., Conclusion: We found no evidence that lipid emulsions and in particular those containing long-chain triglycerides have an unfavorable effect on immune function.

Purpose of Review: This paper synthesizes information from recent studies on the modulation of immune responses by lipid emulsions that are applied as part of parenteral nutrition. This issue is especially relevant in light of the high rate of infectious complications and disturbed inflammatory responses in patients receiving this form of nutritional support., Recent Findings: Studies reporting on novel emulsions based on olive and fish oils, structured lipids or mixed-type emulsions in which various lipid species replace conventional long-chain triglycerides indicate that these lipids are generally well tolerated. While long-chain triglycerides may promote inflammation due to conversion of n-6 polyunsaturated fatty acids into arachidonic acid-derived eicosanoids, structured lipids and olive oil emulsions appear more immune-neutral. Leukocyte-activating effects of medium-chain triglycerides in experimental studies await further characterization in vivo. A body of evidence shows that immune modulation by fish oil emulsions is essentially anti-inflammatory in nature. This is in line with the observation that n-3 polyunsaturated fatty acids in fish oil replace arachidonic acid in cell membranes as an eicosanoid substrate, resulting in a decreased production of pro-inflammatory mediators. Importantly, recent investigations indicate beneficial effects of parenteral fish oil on relevant clinical outcome measures., Summary: The characteristics of, and mechanisms behind, the effects of various parenteral lipids on immune function are becoming increasingly well understood. The practical relevance of many of these findings is not immediately clear, however, and will have to be substantiated in adequately powered trials before we can translate these findings into a tailored approach for specific clinical situations.

This study was designed to examine the effects of dietary vitamin E (VE) on modulation of immune responses when supplied with two levels of n-3 highly unsaturated fatty acids (n-3 HUFA) in rainbow trout, Oncorhynchus mykiss. Six semipurified diets were prepared containing three levels of dietary VE (0, 100 or 1000 mg alpha-tocopheryl acetate kg(-1) diet) and n-3 HUFA either at 20 or 48% of dietary lipid provided from fish oil or docosahexaenoic acid (DHA) concentrated fish oil respectively. The diets were fed to rainbow trout (100 g initial mean weight) for 15 weeks. The VE, vitamin C (VC) content in plasma and tissues and the nonspecific immune responses, both humoral (alternative complement activity, total immunoglobulin) and cellular (phagocytosis, nonspecific cytotoxicity) were examined. VE contents in the kidney reflected the dietary input but were lower in fish fed 48% n-3 HUFA diets, and could have impaired some of immune responses compared to fish fed 20% n-3 HUFA. VC contents in kidney followed the same pattern as VE. Both humoral and cellular immune functions deteriorated in fish fed VE deficient diets whereas improvement in most of the parameters corresponded to its supplementation. However, the higher dose of dietary VE did not substantially enhance the responses assayed compared to the 100 mg dose. Besides clearly indicating the role of VE in maintaining the immune functions in fish in relation to dietary n-3 HUFA, this study has revealed that optimum health benefits could be achieved when VE is maintained slightly above the levels generally recommended for normal growth.

The immune system is involved in host defense against infectious agents, tumor cells, and environmental insults. Inflammation is an important component of the early immunologic response. Inappropriate or dysfunctional immune responses underlie acute and chronic inflammatory diseases. The n-6 PUFA arachidonic acid (AA) is the precursor of prostaglandins, leukotrienes, and related compounds that have important roles in inflammation and in the regulation of immunity. Feeding fish oil results in partial replacement of AA in cell membranes by EPA. This leads to decreased production of AA-derived mediators, through several mechanisms, including decreased availability of AA, competition for cyclooxygenase (COX) and lipoxygenase (LOX) enzymes, and decreased expression of COX-2 and 5-LOX. This alone is a potentially beneficial anti-inflammatory effect of n-3 FA. However, n-3 FA have a number of other effects that might occur downstream of altered eicosanoid production or might be independent of this effect. For example, dietary fish oil results in suppressed production of proinflammatory cytokines and can modulate adhesion molecule expression. These effects occur at the level of altered gene expression. Fish oil feeding has been shown to ameliorate the symptoms of some animal models of autoimmune disease and to protect against the effects of endotoxin. Clinical studies have reported that oral fish oil supplementation has beneficial effects in rheumatoid arthritis and among some asthmatics, supporting the idea that the n-3 FA in fish oil are anti-inflammatory. There are indications that the inclusion of fish oil in enteral and parenteral formulae is beneficial to patients.

The essentiality of n-6 polyunsaturated fatty acids (PUFA) is described in relation to a thymus/thymocyte accretion of arachidonic acid (20:4n-6, AA) in early development, and the high requirement of lymphoid and other cells of the immune system for AA and linoleic acid (1 8:2n-6, LA) for membrane phospholipids. Low n-6 PUFA intakes enhance whereas high intakes decrease certain immune functions. Evidence from in vitro and in vivo studies for a role of AA metabolites in immune cell development and functions shows that they can limit or regulate cellular immune reactions and can induce deviation toward a T helper (Th)2-like immune response. In contrast to the effects of the oxidative metabolites of AA, the longer-chain n-6 PUFA produced by gamma-linolenic acid (18:3n-6, GLA) feeding decreases the Th2 cytokine and immunoglobulin (Ig)G1 antibody response. The n-6 PUFA, GLA, dihomo-gamma-linolenic acid (20:3n-6, DHLA) and AA, and certain oxidative metabolites of AA can also induce T-regulatory cell activity, e.g., transforming growth factor (TGF)-beta-producing T cells; GLA feeding studies also demonstrate reduced proinflammatory interleukin (IL)-1 and tumor necrosis factor (TNF)-alpha production. Low intakes of long-chain n-3 fatty acids (fish oils) enhance certain immune functions, whereas high intakes are inhibitory on a wide range of functions, e.g., antigen presentation, adhesion molecule expression, Th1 and Th2 responses, proinflammatory cytokine and eicosanoid production, and they induce lymphocyte apoptosis. Vitamin E has a demonstrable critical role in long-chain n-3 PUFA interactions with immune functions, often reversing the effects of fish oil. The effect of dietary fatty acids on animal autoimmune disease models depends on both the autoimmune model and the amount and type of fatty acids fed. Diets low in fat, essential fatty acid deficient (EFAD), or high in long-chain n-3 PUFA from fish oils increase survival and reduce disease severity in spontaneous autoantibody-mediated disease, whereas high-fat LA-rich diets increase disease severity. In experimentally induced T cell-mediated autoimmune disease, EFAD diets or diets supplemented with long-chain n-3 PUFA augment disease, whereas n-6 PUFA prevent or reduce the severity. In contrast, in both T cell- and antibody-mediated autoimmune disease, the desaturated/elongated metabolites of LA are protective. PUFA of both the n-6 and n-3 families are clinically useful in human autoimmune-inflammatory disorders, but the precise mechanisms by which these fatty acids exert their clinical effects are not well understood. Finally, the view that all n-6 PUFA are proinflammatory requires revision, in part, and their essential regulatory and developmental role in the immune system warrants appreciation.

Abnormal postprandial lipoproteins are associated with an increased risk for cardiovascular disease. Postprandial remnant lipoproteins were usually analyzed indirectly using retinyl esters (RE) as a chylomicron core label during an oral fat loading test. Apo B-100 containing VLDL remnants in addition to apo B-48 containing chylomicron remnants can also be directly quantified using the RLP-Cholesterol Immunoseparation Assay. This recently available method uses monoclonal antibodies to apo A-I and apo B-100 to remove non-remnant lipoproteins and quantifies cholesterol in the remaining apo E-rich remnant fraction. In the present study we compared the analysis of retinyl ester with the immuno-based RLP-Cholesterol (RLP-C) analysis in measuring postprandial remnant lipoproteins in healthy normolipidemic subjects. Sixteen healthy normolipidemic subjects were selected for this study. Postprandial plasma retinyl esters peaked at 5.0+/-1.2 h, whereas plasma RLP-C showed a peak significantly earlier (P<0.001) at 3.5+/-0.6 h. In comparison, postprandial plasma TG and FFA peaked at 3.3+/-1.1 h (P<0.005 compared to retinyl esters). In conclusion, levels of RLP-C changed, during the postprandial phase, in parallel with plasma TG and FFA concentrations and peaked significantly earlier than retinyl esters. Postprandial measurements of RLP-C can be considered as a fast alternative method for the more laborious retinyl-ester analysis in clinical studies.

Fatty liver disease (FLD) characterised by a high plasma levels of lipoproteins and remnant-like lipoproteins (RLP) is a risk factor for impaired microvascular blood flow, endothelial cell dysfunction and atherosclerosis. Using an immunoseparation technique with a gel mixture containing human monoclonal antibodies to apo A-I and apo B-100, we separated and measured RLP cholesterol (RLP-C) levels which reflect RLP in patients with FLD (n=20). Whole blood transit time (TT) was determined by a microchannel method (MC-FAN) which allows blood flow to be viewed via a microscope connected to an image display unit. RLP-C levels were higher (P<0.01) in FLD, 15.6 +/- 1.0 mg/dl compared with 4.8 +/- 0.5 mg/dl for controls (n=20). Similarly, TT was longer (P<0.01) in FLD, 284.5 +/- 26.1 sec/100 microl compared with 82.8 +/- 1.0 sec/100 microl for controls. Since the liver is a major site for RLP formation and degradation, it is affected to a greater extent in patients with FLD. It is likely that high levels of RLP can impair microvascular perfusion in the liver tissue and contribute to the development and progression of FLD.

Bacterial endotoxin (LPS) elicits dramatic responses in the host including elevated plasma lipid levels due to the increased synthesis and secretion of triglyceride (TG)-rich lipoproteins by the liver, and the inhibition of lipoprotein lipase. This cytokine-induced hyperlipoproteinemia, clinically termed the "lipemia of sepsis", was customarily thought to represent the mobilization of lipid stores to fuel the host response to infection. However, since lipoproteins can also bind and neutralize LPS, we hypothesize that TG-rich lipoproteins (VLDL and chylomicrons) are also components of an innate, non-adaptive host immune response to infection. Herein we review data demonstrating the capacity of lipoproteins to bind LPS, protect against LPS-induced toxicity, and modulate the overall host response to this bacterial toxin. Lastly, we propose a pathway whereby lipoprotein-bound LPS may represent a novel, endogenous mechanism for regulating the hepatic acute phase response.

Consequences of alterations in the size and the lipid composition of low density lipoproteins (LDL) on apolipoprotein (apo) B immunoreactivity were analyzed using two distinct anti-apoB monoclonal antibodies (Mabs), i.e., 4G3, which recognizes an epitope closed to the binding site to the LDL receptor, and 2D8, which is directed against a distal region. Inhibition analysis revealed that the lipid transfer-mediated triglyceride enrichment of LDL isolated from 12 native human plasmas is associated with significant reductions in the expression of 2D8 and 4G3 epitopes (P < 0.05 in both cases). In contrast, triglyceride hydrolysis of triglyceride-rich LDL significantly increased apoB immunoreactivity as compared with non-lipolyzed counterparts (P < 0.05 with 2D8 and 4G3 Mabs). Among all the modified LDL fractions studied (n = 36), immunoreactivity of 2D8 and 4G3 epitopes correlated negatively and significantly with the triglyceride content (P < 0.01 in both cases), but with neither the size nor the other lipid parameters of LDL particles. Furthermore, changes in the triglyceride content of LDL correlated significantly with changes in apoB immunoreactivity after in vitro treatment with either lipid transfer activity alone (P < 0.01 with 2D8 and 4G3 Mabs) or lipid transfer activity combined with triglyceride hydrolysis (P < 0.01 with 2D8 and 4G3 Mabs). Finally, both the triglyceride content of native LDL and the total triglyceride level in 12 normolipidemic human plasmas correlated negatively and significantly with the expression of 2D8 epitope (P < 0.03 in both cases) and 4G3 epitope (P < 0.02 in both cases). It is concluded that triglycerides constitute a major determinant of the immunoreactivity of 2D8 and 4G3 apoB epitopes in LDL.

We prepared monoclonal antibody (MabB4) that selectively binds to acetylated low-density lipoprotein (LDL). Native hypertriglyceridemic LDL (HT-LDL) obtained from IIb and native normotriglyceridemic LDL (NT-LDL) from type IIa scarcely bound with MabB4. When these LDL were oxidized moderately by incubation with copper ions, the binding of MabB4 to HT-LDL was enhanced compared to that of NT-LDL, although the contents of the hydroperoxide they produced were the same. The incorporation of moderately oxidized HT-LDL into macrophages was enhanced compared to that of NT-LDL, and the rate of incorporation parallel the binding of LDL for MabB4. These results suggested that moderate oxidation of HT-LDL expressed some apolipoprotein B epitope on the surface of acetylated LDL to a much greater degree than NT-LDL, and that this expressed epitope might work as a ligand of moderately oxidized HT-LDL for the recognition by macrophages.

Tripalmitoyl-S-glycerylcysteinyl lipopeptides are B-cell and macrophage activating and may be used as low molecular weight immunogens of considerable potency and even as vaccines when conjugated with suitable epitopic structures. Selected lipopeptides carrying single Dnp haptens were found to evoke mild passive cutaneous anaphylaxis in guinea pigs sensitized against Dnp. The reactions were observed after intravenous injection whereas intradermally applied antigen was negative. The anaphylactogenicity seems unrelated to micelle or aggregate formation of the insoluble peptides which require lecithin additions as well as sonication to become solubilized. The dinitrophenylated lipopeptide tripalmitoyl-S-glyceryl-cysteinyl-seryl-lysine produced toxic reactions which were not observed with the lipopeptide devoid of Dnp. Dinitrophenylated tripalmitoyl-S-glycerylcysteiny-1,6-diaminohexane and tripalmitoyl-S-glyceryl-cysteinyl-lysine did not show these toxic reactions.

Low density lipoproteins (LDL), endogenously labelled with 3H in the triglyceride moiety, were isolated from rabbit serum and subsequently incubated in vitro at 37 degrees C with unlabelled preparations of rabbit high density lipoproteins (HDL) or very low density lipoproteins (VLDL). In incubations performed in the presence of phosphate buffer, there was no significant transfer of [3H]triglyceride from LDL to either HDL or VLDL; but when rabbit lipoprotein-free serum (the dialysed 1.21 g/ml infranatant) was added, transfer was apparent to both HDL and VLDL. The triglyceride transferring activity of the lipoprotein-free serum was abolished by heating at 85 degrees C for 10 min; all the transferring activity was found in the fraction which precipitated with ammonium sulphate at a concentration of less than 50% saturation. In direct contrast to the rabbit studies, rat serum failed to show a comparable process of triglyceride transfer. In subsequent experiments, mixtures of labelled LDL and unlabelled VLDL isolated either from rabbits or from rats were incubated with lipoprotein-free rabbit, rat or human serum. The lipoprotein-free serum of both the rabbit and man was effective in promoting transfer of 30--50% of LDL [3H]triglyceride into VLDL, regardless of the species origin of the lipoproteins. By contrast the lipoprotein-free serum of rats was only slightly more effective than buffer alone in promoting such transfers. It has been concluded that rabbit and human serum contains a triglyceride transferring factor of far greater activity than that in rat serum.