Influence of cell culture conditions on diet-induced changes in lymphocyte fatty acid composition

Antioxidant Status, Lipid Metabolism, Egg Fatty Acids, and Nutritional Index of White-Egg Laying Hens Fed Flaxseed Cake

Flaxseed cake contains high levels of phenolic compounds, which have numerous biological activities, as well as a considerable amount of omega-3 fatty acids, such as α-linolenic acid, which remains after oil extraction. In this study, we examined the effects of flaxseed cake meal (FSCM) on the antioxidative status, lipid metabolism, egg fatty acid profile, and egg health index of white-egg laying hens. A total of 63 Hisex White laying hens were divided into three experimental treatment groups and fed diets containing 0, 5, or 10% FSCM from 48 to 58 weeks of age. Feeding with 5 and 10% FSCM did not significantly (p>0.05) influence total lipid, triglyceride, total cholesterol, very low-density lipoprotein-cholesterol, or low-density lipoprotein-cholesterol concentrations, or the high-/low-density lipoprotein ratio in the serum and egg yolk; however, 10% FSCM significantly (P<0.05) increased serum high-density lipoprotein. Dietary FSCM also did not affect (P>0.05) antioxidant markers in the eggs and blood plasma. Notably, dietary inclusion of FSCM significantly increased (P<0.05) total n-3 polyunsaturated fatty acids (PUFAs), α-linolenic acid, docosahexaenoic acid, and eicosapentaenoic acid levels in egg yolk, whereas the n-6:n-3 PUFAs ratio was markedly (P<0.05) decreased in a dose-dependent manner. Moreover, including 5-10% FSCM improved (P<0.05) egg health indices, with 10% being the most beneficial. Together, these findings indicated that the inclusion of up to 10% FSCM in laying hen diets improved egg yolk lipid and fatty acid profiles, as well as egg quality and nutritional and metabolic indices.

Single-Cell and Subcellular Analysis Using Ultrahigh Resolution 21 T MALDI FTICR Mass Spectrometry

The mammalian brain contains ∼20,000 distinct lipid species that contribute to its structural organization and function. The lipid profiles of cells change in response to a variety of cellular signals and environmental conditions that result in modulation of cell function through alteration of phenotype. The limited sample material combined with the vast chemical diversity of lipids makes comprehensive lipid profiling of individual cells challenging. Here, we leverage the resolving power of a 21 T Fourier-transform ion cyclotron resonance (FTICR) mass spectrometer for chemical characterization of individual hippocampal cells at ultrahigh mass resolution. The accuracy of the acquired data allowed differentiation of freshly isolated and cultured hippocampal cell populations, as well as finding differences in lipids between the soma and neuronal processes of the same cell. Differences in lipids include TG 42:2 observed solely in the cell bodies and SM 34:1;O2 found only in the cellular processes. The work represents the first mammalian single cells analyzed at ultrahigh resolution and is an advance in the performance of mass spectrometry (MS) for single-cell research.

Role of EPA in Inflammation: Mechanisms, Effects, and Clinical Relevance

Many chronic inflammatory processes are linked with the continuous release of inflammatory mediators and the activation of harmful signal-transduction pathways that are able to facilitate disease progression. In this context atherosclerosis represents the most common pathological substrate of coronary heart disease, and the characterization of the disease as a chronic low-grade inflammatory condition is now validated. The biomarkers of inflammation associated with clinical cardiovascular risk support the theory that targeted anti-inflammatory treatment appears to be a promising strategy in reducing residual cardiovascular risk. Several literature data highlight cardioprotective effects of the long-chain omega-3 polyunsaturated fatty acids (PUFAs), such as eicosapentaenoic acid (EPA). This PUFA lowers plasma triglyceride levels and has potential beneficial effects on atherosclerotic plaques. Preclinical studies reported that EPA reduces both pro-inflammatory cytokines and chemokines levels. Clinical studies in patients with coronary artery disease that receive pharmacological statin therapy suggest that EPA may decrease plaque vulnerability preventing plaque progression. This review aims to provide an overview of the links between inflammation and cardiovascular risk factors, importantly focusing on the role of diet, in particular examining the proposed role of EPA as well as the success or failure of standard pharmacological therapy for cardiovascular diseases.

Insight on Polyunsaturated Fatty Acids in Endometrial Receptivity

Endometrial receptivity plays a crucial role in fertilization as well as pregnancy outcome in patients faced with fertility challenges. The optimization of endometrial receptivity may help with normal implantation of the embryo, and endometrial receptivity may be affected by numerous factors. Recently, the role of lipids in pregnancy has been increasingly recognized. Fatty acids and their metabolites may be involved in all stages of pregnancy and play a role in supporting cell proliferation and development, participating in cell signaling and regulating cell function. Polyunsaturated fatty acids, in particular, are essential fatty acids for the human body that can affect the receptivity of the endometrium through in a variety of methods, such as producing prostaglandins, estrogen and progesterone, among others. Additionally, polyunsaturated fatty acids are also involved in immunity and the regulation of endometrial decidualization. Fatty acids are essential for fetal placental growth and development. The interrelationship of polyunsaturated fatty acids with these substances and how they may affect endometrial receptivity will be reviewed in this article.

Nucleofection of Adipose Mesenchymal Stem/Stromal Cells: Improved Transfection Efficiency for GMP Grade Applications

Nucleofection (NF) is a safe, non-viral transfection method, compatible with Good Manufacturing Practice guidelines. Such a technique is useful to improve therapeutic effectiveness of adipose tissue mesenchymal stem cells (ASC) in clinical settings, but improvement of NF efficiency is mandatory. Supernatant rich in growth factors (SRGF) is a clinical-grade medium additive for ASC expansion. We showed a dramatically increased NF efficiency and post-transfection viability in ASC expanded in presence of SRGF (vs. fetal bovine serum). SRGF expanded ASC were characterized by increased vesicle endocytosis but lower phagocytosis properties. SRGF increased n-6/n-3 ratio, reduced membrane lipid raft occurrence, and lowered intracellular actin content in ASC. A statistical correlation between NF efficiency and lipid raft availability on cell membranes was shown, even though a direct relationship could not be demonstrated: attempts to selectively modulate lipid rafts levels were, in fact, limited by technical constraints. In conclusion, we reported for the first time that tuning clinical-grade compatible cell culture conditions can significantly improve ASC transfection efficiency by a non-viral and safe approach. A deep mechanistic characterization is extremely complex, but we can hypothesize that integrated changes in membrane structure and intracellular actin content could contribute to explain SRGF impact on ASC NF efficiency.

Preventive as well as therapeutic significances of linoleic acid in the containment of Leishmania donovani infection

People suffering from malnutrition show compromised levels of ω-6 fatty acid and malnutrition is frequently observed among visceral leishmaniasis (VL) patients as disease inflicts primarily the socioeconomic destitute communities. Dietary linoleic acid (LA, 18:2; ω-6 fatty acid) is the principal source of essential fatty acid and its derivatives i.e. eicosanoids possess immune-modulatory activities. However, its role in VL is not yet established. LA was measured in VL human subjects (serum) as well as in Leishmania(L.)donovani infected hamsters (serum and visceral organs). Organ-specific mRNA expressions of various enzymes of the LA metabolic pathway were measured in visceral organs of infected hamsters. Our findings showed a decrease in the concentrations of LA in the serum samples of VL patients, suggesting malnutrition among these patients. However, in L. donovani infected hamsters, its level was not altered in the early infection (15 days) and then increased at late infection (60 days). Importantly, the supplementation of LA restored the Th-1 type of immune response and significantly reduced the parasite load within infected macrophages in vitro. This protective response of LA was mediated through 5-lipoxygenase pathway not via the cyclooxygenase pathway. Preventive usage of LA to mϕ followed by L. donovani infection also showed the strengthening of Th-1 immune response and significantly fewer parasite loads. Our findings demonstrate the protective role of LA in the containment of the parasite load. Incorporating LA rich oils in daily food habits across highly inflicted regions may be a significant advancement towards the eradication of the disease.

A comparative study: In vitro effects of EPA and DHA on immune functions of head-kidney macrophages isolated from large yellow croaker (Larmichthys crocea)

Comparative effects of different concentrations of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on immune responses of head-kidney macrophages isolated from large yellow croaker were studied in vitro. After exposing to serum-free medium for 1 day, cultured cells were incubated in medium supplemented with graded levels of EPA or DHA (0, 5, 25, 100, 200 and 1000 μM, respectively) in the form of fatty acid bovine serum albumin (FA-BSA) complex for 12 h, 24 h and 36 h, respectively. Control samples were incubated in the absence of EPA or DHA (2% bovine serum albumin, BSA). Following stimulation, cell viability, lipid peroxidation, secretary phopholipase A2 (sPLA2) and prostaglandin E2 (PGE2) production as well as some immune parameters including phagocytosis, respiratory burst activity and interleukin 1β (IL-1β) production were determined. Results showed that EPA and DHA affected cell viability in dose-dependent and time-dependent manners. In particular, cell viability was significantly decreased after 24 h and 36 h incubation with 1000 μM EPA or DHA (P < 0.05). Higher levels of EPA (200 and 1000 μM) caused a significant increase in the production of malondialdehyde (MDA) (P < 0.05), while DHA did not significantly affect the MDA production. EPA significantly increased the intracellular superoxide anion synthesis which, on the contrary, was significantly reduced by DHA. Phagocytosis percentage (PP) values were significantly higher in treatments with 5 μM DHA (P < 0.05), but significantly decreased by 200 and 1000 μM EPA and DHA compared to the control group (P < 0.05). Decreased PGE2 production was produced by cells treated with relatively low doses of EPA or DHA. When high levels of stimulants (1000 μM EPA or DHA) were used, PGE2 levels were elevated and reached a significant level (P < 0.05). Both EPA and DHA significantly inhibited the production of sPLA2, where DHA exerted the more potent inhibitory effects than EPA. No pronounced effect was observed on IL-1β production among all the treatments, and IL-1β level in cell culture supernatant was fairly low (only approximately 6 pg/ml). Those findings suggested that EPA and DHA could influence the immunity and physiological conditions of macrophages from head kidney of large yellow croaker in vitro.

Activation of the mitochondrial ATP-sensitive K+ channel reduces apoptosis of spleen mononuclear cells induced by hyperlipidemia

Background

We have previously demonstrated that increased rates of superoxide generation by extra-mitochondrial enzymes induce the activation of the mitochondrial ATP-sensitive potassium channel (mitoK_ATP) in the livers of hypertriglyceridemic (HTG) mice. The resulting mild uncoupling mediated by mitoK_ATP protects mitochondria against oxidative damage. In this study, we investigate whether immune cells from HTG mice also present increased mitoK_ATP activity and evaluate the influence of this trait on cell redox state and viability.

Methods

Oxygen consumption (Clark-type electrode), reactive oxygen species production (dihydroethidium and H2-DCF-DA probes) and cell death (annexin V, cytocrome c release and Trypan blue exclusion) were determined in spleen mononuclear cells.

Results

HTG mice mononuclear cells displayed increased mitoK_ATP activity, as evidenced by higher resting respiration rates that were sensitive to mitoK_ATP antagonists. Whole cell superoxide production and apoptosis rates were increased in HTG cells. Inhibition of mitoK_ATP further increased the production of reactive oxygen species and apoptosis in these cells. Incubation with HTG serum induced apoptosis more strongly in WT cells than in HTG mononuclear cells. Cytochrome c release into the cytosol and caspase 8 activity were both increased in HTG cells, indicating that cell death signaling starts upstream of the mitochondria but does involve this organelle. Accordingly, a reduced number of blood circulating lymphocytes was found in HTG mice.

Conclusions

These results demonstrate that spleen mononuclear cells from hyperlipidemic mice have more active mitoK_ATP channels, which downregulate mitochondrial superoxide generation. The increased apoptosis rate observed in these cells is exacerbated by closing the mitoK_ATP channels. Thus, mitoK_ATP opening acts as a protective mechanism that reduces cell death induced by hyperlipidemia.

Single-cell metabolomics: changes in the metabolome of freshly isolated and cultured neurons

Metabolites are involved in a diverse range of intracellular processes, including a cell’s response to a changing extracellular environment. Using single-cell capillary electrophoresis coupled to electrospray ionization mass spectrometry, we investigated how placing individual identified neurons in culture affects their metabolic profile. First, glycerol-based cell stabilization was evaluated using metacerebral neurons from Aplysia californica; the measurement error was reduced from ∼24% relative standard deviation to ∼6% for glycerol-stabilized cells compared to those isolated without glycerol stabilization. In order to determine the changes induced by culturing, 14 freshly isolated and 11 overnight-cultured neurons of two metabolically distinct cell types from A. californica, the B1 and B2 buccal neurons, were characterized. Of the more than 300 distinctive cell-related signals detected, 35 compounds were selected for their known biological roles and compared among each measured cell. Unsupervised multivariate and statistical analysis revealed robust metabolic differences between these two identified neuron types. We then compared the changes induced by overnight culturing; metabolite concentrations were distinct for 26 compounds in the cultured B1 cells. In contrast, culturing had less influence on the metabolic profile of the B2 neurons, with only five compounds changing significantly. As a result of these culturing-induced changes, the metabolic composition of the B1 neurons became indistinguishable from the cultured B2 cells. This observation suggests that the two cell types differentially regulate their in vivo or in vitro metabolomes in response to a changing environment.

Reversal of severe methotrexate-induced intestinal damage using enteral n-3 fatty acids

Growing evidence suggests that n-3 PUFA and their specific lipid mediators can reduce the activity of inflammatory processes. In the present study, we evaluated the effects of oral n-3 PUFA supplementation on intestinal structural changes, enterocyte proliferation and apoptosis during methotrexate (MTX)-induced intestinal damage in the rat. A total of thirty-two male rats were divided into four experimental groups: control (CONTR) rats; CONTR-n-3 PUFA rats treated with oral administration of n-3 PUFA at a dose of 300 μg/kg once per d 72 h before and 72 h following vehicle injection; MTX rats treated with a single dose of MTX; MTX-n-3 PUFA rats treated with oral n-3 PUFA following the injection of MTX. Intestinal mucosal damage, mucosal structural changes, enterocyte proliferation and enterocyte apoptosis determined 72 h following MTX injection. Real-time PCR was used to determine B-cell lymphoma 2 (Bcl2)-associated X protein (Bax) and Bcl2 mRNA expression. Western blotting was used to determine phosphorylated extracellular signal-related kinase, β-catenin, Bax and Bcl2 protein levels. MTX-n-3 PUFA rats demonstrated a greater jejunal and ileal bowel weight, greater ileal mucosal weight, greater ileal mucosal DNA and protein levels, greater villus height in the jejunum and ileum and crypt depth in the ileum, compared with MTX animals. A significant decrease in enterocyte apoptosis in the ileum of MTX-n-3 PUFA rats (v. MTX) was accompanied by decreased Bax mRNA and protein expression and increased Bcl2 mRNA levels. Thus, the treatment with oral n-3 PUFA prevented mucosal injury and improved intestinal recovery following MTX-injury in rats.

Effect of n-3 fatty acids on immune function in broiler chickens

There is interest in the enrichment of poultry meat with long-chain n-3 polyunsaturated fatty acids in order to increase the consumption of these fatty acids by humans. However, there is concern that high levels of n-3 polyunsaturated fatty acids may have detrimental effects on immune function in chickens. The effect of feeding increasing levels of fish oil (FO) on immune function was investigated in broiler chickens. Three-week-old broilers were fed 1 of 4 wheat-soybean basal diets that contained 0, 30, 50, or 60 g/kg of FO until slaughter. At slaughter, samples of blood, bursa of Fabricius, spleen, and thymus were collected from each bird. A range of immune parameters, including immune tissue weight, immuno-phenotyping, phagocytosis, and cell proliferation, were assessed. The pattern of fatty acid incorporation reflected the fatty acid composition of the diet. The FO did not affect the weight of the spleen, but it did increase thymus weight when fed at 50 g/kg (P < 0.001). Fish oil also lowered bursal weights when fed at 50 or 60 g/kg (P < 0.001). There was no significant effect of FO on immune cell phenotypes in the spleen, thymus, bursa, or blood. Feeding 60 g/kg of FO significantly decreased the percentage of monocytes engaged in phagocytosis, but it increased their mean fluorescence intensity relative to that of broilers fed 50 g/kg of FO. Lymphocyte proliferation was significantly decreased after feeding broiler chickens diets rich in FO when expressed as division index or proliferation index, although there was no significant effect of FO on the percentage of divided cells. In conclusion, dietary n-3 polyunsaturated fatty acids decrease phagocytosis and lymphocyte proliferation in broiler chickens, highlighting the need for the poultry industry to consider the health status of poultry when poultry meat is being enriched with FO.

Effect of lipids on avian satellite cell proliferation, differentiation and heparan sulfate proteoglycan expression

The objective of this study was to determine the effects of fatty acids on the proliferation, differentiation, and expression of syndecan-4 and glypican-1 in avian myogenic satellite cells (SC). SC derived from the pectoralis major (PM) and biceps femoris (BF) muscles of the turkey and chicken were individually administered 8 different fatty acids in defined medium during proliferation. A parallel set of turkey SC was induced to differentiate. Highest levels of proliferation of turkey PM and BF SC occurred in cultures containing oleate. Linoleate and oleate were equipotent in supporting proliferation of chicken SC. Microscopic examination revealed that inclusion of docosahexaenoate or eicosapentaenoate was toxic towards both PM and BF SC from both species. Linolenate and arachidonate diminished levels of differentiation. Expression of glypican-1 varied between treatments to a greater extent with turkey BF than with PM SC. Expression in chicken PM and BF SC demonstrated a similar pattern in response to treatments. Turkey PM syndecan-4 expression varied between treatments, whereas expression in turkey BF SC was similar between treatments. Expression in chicken SC varied little between treatments. The results demonstrate species and muscle-specific differences in the parameters examined. It is proposed that changes in lipid raft receptor interactions may contribute to these observed differences.

Modulatory effect of fatty acids on fungicidal activity, respiratory burst and TNF-α and IL-6 production in J774 murine macrophages

The reported effects of different families of fatty acids (FA; SFA, MUFA, n-3 and n-6 PUFA) on human health and the importance of macrophage respiratory burst and cytokine release to immune defence led us to examine the influence of palmitic acid (PA), oleic acid (OA), linoleic acid, arachidonic acid, EPA and DHA on macrophage function. We determined fungicidal activity, reactive oxygen species (ROS) and cytokine production after the treatment of J774 cells with non-toxic concentrations of the FA. PA had a late and discrete stimulating effect on ROS production, which may be associated with the reduced fungicidal activity of the cells after treatment with this FA. OA presented a sustained stimulatory effect on ROS production and increased fungicidal activity of the cells, suggesting that enrichment of diets with OA may be beneficial for pathogen elimination. The effects of PUFA on ROS production were time- and dose-dependently regulated, with no evident differences between n-3 and n-6 PUFA. It was worth noting that most changes induced after stimulation of the cells with lipopolysaccharide were suppressed by the FA. The present results suggest that supplementation of the diet with specific FA, not classes of FA, might enable an improvement in host defence mechanisms or a reduction in adverse immunological reactions.

Omega-3 fatty acids and inflammatory processes

Long chain fatty acids influence inflammation through a variety of mechanisms; many of these are mediated by, or at least associated with, changes in fatty acid composition of cell membranes. Changes in these compositions can modify membrane fluidity, cell signaling leading to altered gene expression, and the pattern of lipid mediator production. Cell involved in the inflammatory response are typically rich in the n-6 fatty acid arachidonic acid, but the contents of arachidonic acid and of the n-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) can be altered through oral administration of EPA and DHA. Eicosanoids produced from arachidonic acid have roles in inflammation. EPA also gives rise to eicosanoids and these often have differing properties from those of arachidonic acid-derived eicosanoids. EPA and DHA give rise to newly discovered resolvins which are anti-inflammatory and inflammation resolving. Increased membrane content of EPA and DHA (and decreased arachidonic acid content) results in a changed pattern of production of eicosanoids and resolvins. Changing the fatty acid composition of cells involved in the inflammatory response also affects production of peptide mediators of inflammation (adhesion molecules, cytokines etc.). Thus, the fatty acid composition of cells involved in the inflammatory response influences their function; the contents of arachidonic acid, EPA and DHA appear to be especially important. The anti-inflammatory effects of marine n-3 PUFAs suggest that they may be useful as therapeutic agents in disorders with an inflammatory component.

Fatty acids and immune function: relevance to inflammatory bowel diseases

Fatty acids may influence immune function through a variety of mechanisms; many of these are associated with changes in fatty acid composition of immune cell membranes. Eicosanoids produced from arachidonic acid have roles in inflammation and immunity. Increased membrane content of n-3 fatty acids results in a changed pattern of production of eicosanoids, resolvins, and cytokines. Changing the fatty acid composition of immune cells also affects T cell reactivity and antigen presentation. Little attention has been paid to the influence of fatty acids on the gut-associated lymphoid tissue. However, there has been considerable interest in fatty acids and gut inflammation.

fat-1 transgene expression prevents cell culture-induced loss of membrane n-3 fatty acids in activated CD4+ T-cells

In order to evaluate the effects of fatty acids on immune cell membrane structure and function, it is often necessary to maintain cells in culture. However, cell culture conditions typically reverse alterations in polyunsaturated fatty acid (PUFA) composition achieved by dietary lipid manipulation. Therefore, we hypothesized that T-cells from transgenic mice expressing the Caenorhabditis elegans n-3 desaturase (fat-1) gene would be resistant to the culture-induced loss of n-3 PUFA and, therefore, obviate the need to incorporate fatty acids or homologous serum into the medium. CD4+ T-cells were isolated from (i) control wild type (WT) mice fed a safflower oil-n-6 PUFA enriched diet (SAF) devoid of n-3 PUFA, (ii) fat-1 transgenic mice (enriched with endogenous n-3 PUFA) fed a SAF diet, or (iii) WT mice fed a fish oil (FO) based diet enriched in n-3 PUFA. T-cell phospholipids isolated from WT mice fed FO diet (enriched in n-3 PUFA) and fat-1 transgenic mice fed a SAF diet (enriched in n-6 PUFA) were both enriched in n-3 PUFA. As expected, the mol% levels of both n-3 and n-6 PUFA were decreased in cultures of CD4+ T-cells from FO-fed WT mice after 3d in culture. In contrast, the expression of n-3 desaturase prevented the culture-induced decrease of n-3 PUFA in CD4+ T-cells from the transgenic mice. Carboxyfluorescein succinidyl ester (CFSE) -labeled CD4+ T-cells from fat-1/SAF vs. WT/SAF mice stimulated with anti-CD3 and anti-CD28 for 3d, exhibited a reduced (P<0.05) number of cell divisions. We conclude that fat-1-containing CD4+ T-cells express a physiologically relevant, n-3 PUFA enriched, membrane fatty acid composition which is resistant to conventional cell culture-induced depletion.

The relationship between the fatty acid composition of immune cells and their function

The immune system, including its inflammatory components, is fundamental to host defence against pathogenic invaders. It is a complex system involving interactions amongst many different cell types dispersed throughout the body. Central to its actions are phagocytosis of bacteria, processing of antigens derived from intracellular and extracellular pathogens, activation of T cells with clonal expansion (proliferation) and production of cytokines that elicit effector cell functions such as antibody production and killing cell activity. Inappropriate immunologic activity, including inflammation, is a characteristic of many common human disorders. Eicosanoids produced from arachidonic acid have roles in inflammation and regulation of T and B lymphocyte functions. Eicosapentaenoic acid (EPA) also gives rise to eicosanoids and these may have differing properties from those of arachidonic acid-derived eicosanoids. EPA and docosahexaenoic acid (DHA) give rise to newly discovered resolvins which are anti-inflammatory and inflammation resolving. Human immune cells are typically rich in arachidonic acid, but arachidonic acid, EPA and DHA contents can be altered through oral administration of EPA and DHA. This results in a changed pattern of production of eicosanoids and probably also of resolvins, although the latter are not well examined in the human context. Changing the fatty acid composition of immune cells also affects phagocytosis, T cell signaling and antigen presentation capability. These effects appear to mediated at the membrane level suggesting important roles of fatty acids in membrane order, lipid raft structure and function, and membrane trafficking. Thus, the fatty acid composition of human immune cells influences their function and the cell membrane contents of arachidonic acid, EPA and DHA are important. Fatty acids influence immune cell function through a variety of complex mechanisms and these mechanisms are now beginning to be unraveled.

N-3 polyunsaturated fatty acids modulate in-vitro T cell function in type I diabetic patients

In this work, we assessed the in-vitro effects of eicosapentaenoic acid (EPA; C20:5n-3) and docosahexaenoic acid (DHA; C22:6n-3) (final concentration, 15 microM) on T cell blastogenesis, interleukin-2 and -4 (IL-2, IL-4) secretion, fatty acid composition and intracellular oxidative status in type I diabetic patients with or without complications. Con A stimulated lymphocyte proliferation, glucose uptake, intracellular reduced glutathione levels and catalase activity were lower in diabetics as compared to controls, regardless to the presence of complications. EPA and DHA diminished T-lymphocyte proliferation and IL-2 production but enhanced IL-4 secretion in both diabetic and control groups. No changes in the levels of reduced glutathione and in the activities of catalase and SOD were observed in control T cells cultured in the presence of EPA and DHA. However, in diabetic patients, addition of n-3 PUFA to culture induced an increase in T cell levels of reduced glutathione and hydroperoxide, and in activities of catalase and SOD. Low levels of arachidonic acid (C20:4n-6) were found in plasma membrane phospholipids of lymphocytes from diabetic patients compared to controls. Incubation of lymphocytes with EPA and DHA was associated with an incorporation of these fatty acids in membrane phospholipids. In conclusion, the beneficial effects of n-3 PUFA on T cell functions in type I diabetes could be attributed to their suppressive action and modulation of cytokine secretion, and to the improvement of intracellular oxidative status.

Immunomodulation by omega-3 fatty acids

The immune system, including its inflammatory components, is fundamental to host defense against pathogenic invaders. It is a complex system involving interactions amongst many different cell types dispersed throughout the body. Central to its actions are phagocytosis, processing of antigens derived from intracellular and extracellular pathogens, activation of T cells with proliferation and production of cytokines that elicit effector cell functions such as antibody production and killing cell activity. Inappropriate immunologic activity, including inflammation, is a characteristic of many common human disorders. Eicosanoids produced from arachidonic acid have roles in inflammation and regulation of T and B lymphocyte functions. Eicosapentaenoic acid (EPA) also gives rise to eicosanoids and docosahexaenoic acid (DHA) to docosanoids; these may have differing properties to arachidonic acid-derived eicosanoids. EPA and DHA give rise to newly discovered resolvins. Human immune cells are typically rich in arachidonic acid, but arachidonic acid, EPA and DHA contents can be altered through oral administration of those fatty acids. This results in a change pattern of production of eicosanoids and probably also of docosanoids and resolvins, although the latter are not well examined in the human context. Changing the fatty acid composition of immune cells also affects phagocytosis, T-cell signaling and antigen presentation capability. These effects appear to mediated at the membrane level suggesting important roles of fatty acids in membrane order, lipid raft structure and function and membrane trafficking.

Important differences exist in the dose-response relationship between diet and immune cell fatty acids in humans and rodents

Omega-3 polyunsaturated fatty acids (n-3 PUFA) are noted for their ability to diminish inflammatory and immune responses in vitro and in a variety of animal-based models of autoimmunity and inflammation. Yet, recent systematic reviews suggest that the evidence for these fatty acids having beneficial effects on inflammation or autoimmunity in humans is equivocal. A possible explanation for these disappointing and somewhat paradoxical findings emerged from the analyses described in this review. The available data on the changes in immune cell fatty acid profiles in mice, rats and humans, fed various forms and amounts of n-3 PUFA are summarized and displayed graphically. The dose-response curves generated provide new insights into the relationship between dietary n-3 PUFA and immune cell fatty acid profiles. The author suggests that the poor predictive value of most in vitro as well as many animal trials may, in part, be a consequence of the frequent adoption of experimental conditions that create differences in immune cell fatty acid profiles that far exceed what is possible in free-living humans through dietary intervention. Recommendations for improving the preclinical value of future in vitro and animal-based studies with n-3 PUFA are provided.

Fatty acids as modulators of the immune response

Research describing fatty acids as modulators of inflammation and immune responses abounds. Many of these studies have focused on one particular group of fatty acids, omega-3. The data from animal studies have shown that these fatty acids can have powerful anti-inflammatory and immunomodulatory activities in a wide array of diseases (e.g., autoimmunity, arthritis, and infection). However, the evidence from human trials is more equivocal. In this review, a historical framework for understanding how and why fatty acids may affect the immune system is provided. Second, highlights of two recent landmark reports from the Agency for Healthcare Research and Quality are presented. These reports critically evaluate the evidence from human clinical trials of omega-3 fatty acids and rheumatoid arthritis, asthma, and a few other immune-mediated diseases. Third, the data from human clinical trials investigating the impact of various bioactive fatty acids on ex vivo and in vivo immune response are reviewed. Limitations in experimental design and immune assays commonly used are discussed. The discordance between expectation and evidence in this field has been a disappointment. Recommendations for improving both animal-based and human studies are provided.

Dietary eicosapentaenoic acid modulates CTLA-4 expression in murine CD4+ T-cells

We have demonstrated that downregulation of proliferation by CD4(+) T-cells in mice fed n-3 PUFA diets is dependent on the involvement of CD28. Therefore, we hypothesized that the balance of co-stimulatory and downregulatory properties of CD28 and CTLA-4, respectively, would be altered by diet. Mice were fed a control corn oil (CO)-enriched diet devoid of n-3 PUFA, or diets enriched with either docosahexaenoic acid (DHA) or eicosapentaenoic acid (EPA) for 14d. The proliferation of splenic CD4(+) T-cells was suppressed by DHA and EPA following stimulation with anti-CD3 and anti-CD28. Surprisingly, the number of surface CD28 molecules was not reduced in activated CD4(+) T-cells from either group of n-3 PUFA-fed mice. However, in mice fed EPA, CTLA-4 protein levels were enhanced significantly 72 h post-activation (P<0.01). Therefore, we conclude that dietary EPA may suppress CD4(+) T-cell activation by enhancing the downregulatory co-receptor CTLA-4, while not altering the levels of CD28.

Effects of dietary n-3 polyunsaturated fatty acids on T-cell membrane composition and function

Dietary n-3 PUFA have been shown to attenuate T-cell-mediated inflammation, in part, by suppressing T-cell activation and proliferation. n-3 PUFA have also been shown to promote apoptosis, another important mechanism for the prevention of chronic inflammation by maintaining T-cell homeostasis through the contraction of populations of activated T cells. Recent studies have specifically examined Fas death receptor-mediated activation-induced cell death (AICD), since it is the form of apoptosis associated with peripheral T-cell deletion involved in immunological tolerance and T-cell homeostasis. Data from our laboratory indicate that n-3 PUFA promote AICD in T helper 1 polarized cells, which are the mediators of chronic inflammation. Since Fas and components of the death-inducing signaling complex are recruited to plasma membrane microdomains (rafts), the effect of dietary n-3 PUFA on raft composition and resident protein localization has been the focus of recent investigations. Indeed, there is now compelling evidence that dietary n-3 PUFA are capable of modifying the composition of T-cell membrane microdomains (rafts). Because the lipids found in membrane microdomains actively participate in signal transduction pathways, these results support the hypothesis that dietary n-3 PUFA influence signaling complexes and modulate T-cell cytokinetics in vivo by altering T-cell raft composition.

The improved survival of experimental animals fed with fish oil is suppressed by a leukotriene inhibitor

Fish oil is believed to alter the immune response and improve survival after infections in experimental animals. This effect may be due to altered production of the leukotrienes (LT). We, therefore, performed a study in order to evaluate whether the effect of fish oil on the immune response of experimental animals is mediated through altered production of the LT. Female NMRI mice in four groups were fed with fish oil, fish oil with 5-lipoxygenase (5-LO) inhibitor (Zileuton, Abbott Laboratories, Chicago, IL, USA), corn oil or corn oil with 5-LO inhibitor. After 6 weeks, the mice were infected with Klebsiella pneumoniae and the survival was monitored. The experiment was performed twice. Analysis was performed mainly on data pooled from both experiments. The survival of the groups fed with fish oil was increased, compared to that of all the other groups and when compared to the groups fed with fish oil with 5-LO inhibitor (log-rank test) the difference was significant (P = 0.007). It has been postulated that the effect of fish oil on the immune system is mediated through altered production of LT. In our study, blocking of the production of the LT eliminated the beneficial effects of fish oil. Our results are in concord with the hypothesis that the effect of fish oil is, at least partly, mediated through altered production of LT.

Fatty acids and the immune system: from basic science to clinical applications

Over the last 25 years, the effects of fatty acids on the immune system have been characterized using in vitro, animal and human studies. Advances in fatty acid biochemistry and molecular techniques have recently suggested new mechanisms by which fatty acids could potentially modify immune responses, including modification of the organization of cellular lipids and interaction with nuclear receptors. Possibilities for the clinical applications of n-3 PUFA are now developing. The present review focuses on the hypothesis that the anti-inflammatory properties of n-3 PUFA in the arterial wall may contribute to the protective effects of n-3 PUFA in CVD, as suggested by epidemiological and secondary prevention studies. Studies are just beginning to show that dietary n-3 PUFA can be incorporated into plaque lipid in human subjects, where they may influence the morphology and stability of the atherosclerotic lesion.

Dietary n-3 polyunsaturated fatty acids promote activation-induced cell death in Th1-polarized murine CD4+ T-cells

Dietary n-3 PUFAs have been shown to attenuate T-cell-mediated inflammation. To investigate whether dietary n-3 PUFAs promote activation-induced cell death (AICD) in CD4+ T-cells induced in vitro to a polarized T-helper1 (Th1) phenotype, C57BL/6 mice were fed diets containing either 5% corn oil (CO; n-6 PUFA control) or 4% fish oil (FO) plus 1% CO (n-3 PUFA) for 2 weeks. Splenic CD4+ T-cells were cultured with alpha-interleukin-4 (alphaIL-4), IL-12, and IL-2 for 2 days and then with recombinant (r) IL-12 and rIL-2 for 3 days in the presence of diet-matched homologous mouse serum (HMS) to prevent loss of cell membrane fatty acids, or with fetal bovine serum. After polarization, Th1 cells were reactivated and analyzed for interferon-gamma and IL-4 by intracellular cytokine staining and for apoptosis by Annexin V/propidium iodide. Dietary FO enhanced Th1 polarization by 49% (P = 0.0001) and AICD by 24% (P = 0.0001) only in cells cultured in the presence of HMS. FO enhancement of Th1 polarization and AICD after culture was associated with the maintenance of eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3) in plasma membrane lipid rafts. In conclusion, n-3 PUFAs enhance the polarization and deletion of proinflammatory Th1 cells, possibly as a result of alterations in membrane microdomain fatty acid composition.

Dietary fat saturation produces lipid modifications in peritoneal macrophages of mouse

We investigated the effects of a saturated fat diet on mice lipid metabolism in resident peritoneal macrophages. Male C57BL/6 mice were weaned at 21 days of age and assigned to either the experimental diet, containing coconut oil (COCO diet), or the control diet, containing soybean oil as fat source. Fat content of each diet was 15% (w/w). Mice were fed for 6 weeks until sacrifice. In plasma of mice fed the COCO diet, the concentration of triglyceride, total cholesterol, HLD- and (LDL+VLDL)-cholesterol, and thiobarbituric acid-reactive substances (TBARS) increased, without changes in phospholipid concentration, compared with the controls. In macrophages of COCO-fed mice, the concentration of total (TC), free and esterified cholesterol, triglyceride, phospholipid (P) and TBARS increased, while the TC/P ratio did not change. The phospholipid compositions showed an increase of phosphatidylcholine and phosphatidylserine + phosphadytilinositol, a decrease of phosphatidylethanolamine, and no change in phosphatidylglycerol. (3)H(2)O incorporation into triglyceride and phospholipid fractions of macrophages increased, while its incorporation into free cholesterol decreased. Incorporation of [(3)H]cholesterol into macrophages of COCO-fed mice and the fraction of [(3)H]cholesterol ester increased. COCO diet produced an increase in myrystic, palmitic and palmitoleic acids proportion, a decrease in linoleic and arachidonic acids and no changes in stearic and oleic acids, compared with the control. Also, a higher relative percentage of saturated fatty acid and a decrease in unsaturation index (p <0.001) were observed in macrophages of COCO-fed mice. These results indicate that the COCO-diet, high in saturated fatty acids, alters the lipid metabolism and fatty acid composition of macrophages and produces a significant degree of oxidative stress.

Effects of dietary fatty acids on burn-induced immunosuppression

Previous studies from our laboratory established that low-fat diets prevent immunosuppression and reduce oxidative stress after a thermal injury. The purpose of the present study was to test the hypothesis that the type of dietary fatty acid influences splenocyte proliferation and oxidative stress following a burn injury. Female C3H/HeN mice were fed ad libitum six experimental diets (5% w/w lipids) differing in fatty acid composition for 10 days following a burn injury. Compared to the controls, burned mice fed whichever diet showed lower lymphoproliferative responses to concanavalin-A (Con-A) and lipopolysaccharide (LPS) (p<0.01), but not to an anti-T cell receptor monoclonal antibody (H-57). In burned animals, nitric oxide (NO) concentration was negatively correlated to the proliferation induced by Con-A (p<0.01) or LPS (p<0.05). These results suggest that: (1) dietary fatty acid type does not influence the splenocyte proliferation or oxidative stress and (2) NO production is involved in the immunosuppression following burn injury.

Antigen-driven murine CD4+ T lymphocyte proliferation and interleukin-2 production are diminished by dietary (n-3) polyunsaturated fatty acids

This study is the first to describe the impact of consuming a diet rich in (n-3) polyunsaturated fatty acids (PUFA) from fish oil on antigen-driven activation of naive CD4+ T lymphocytes. To accomplish this, we used lymphocytes isolated from T cell receptor (TCR) transgenic mice (i.e., DO11.10). A large portion of the T lymphocytes from these mice expresses a TCR specific for a peptide within the ovalbumin (OVA) molecule (OVA(323-339)). When this antigen is presented in the context of major histocompatibility complex I-A(d) with costimulation, these naive CD4+ T cells become activated, produce interleukin (IL)-2 and clonally expand. (n-3) PUFA enrichment was accomplished by feeding DO11.10 mice one of two nutritionally complete experimental diets that differed only in the source of fat: lard or menhaden fish oil [high in (n-3) PUFA]. After 2 wk of consuming the experimental diets, lymphocytes were isolated from the spleen of each mouse, then cultured in the presence of antigen (i.e., OVA(323-339)) or concanavalin A (Con A), a nonspecific, polyclonal T cell stimulus. IL-2 production and lymphocyte proliferation were determined after 48 and 72 h, respectively. Naive CD4+ T lymphocytes from fish oil-fed mice stimulated with antigen produced less IL-2 ( approximately 33%; P < 0.001) and proliferated to a lesser extent ( approximately 50%; P < 0.0001) than the same cells from lard-fed DO11.10 mice. When stimulated with Con A, (n-3) PUFA did not affect either proliferation or IL-2 production. In summary, we report for the first time that feeding mice a diet enriched with (n-3) PUFA reduces in vitro antigen-stimulated production of IL-2 and subsequent proliferation of naive CD4+ T lymphocytes.

Immunomodulatory effects of dietary lipids alter host natural resistance of mice to Listeria monocytogenes infection

Over the past two decades, unsaturated fatty acids have received particular attention due to their ability to suppress immune functions. Nevertheless, suppression of immune functions also involves a reduction of host natural resistance to eliminate the infectious agents. We have analyzed the role of dietary lipids on immune functions in cells cultured with Listeria monocytogenes. Bactericidal efficiency of peritoneal cells from mice fed a fish oil diet against this bacterium was reduced and the incubation of peritoneal cells with polyunsaturated fatty acids led to similar results. The levels of superoxide radicals in the presence of L. monocytogenes increased in cells from mice fed olive oil or fish oil diets. Proteasome activity, a mechanism that participates in T cell activation, was inhibited in all of the dietary groups assayed in the presence of L. monocytogenes, but this inhibition was abolished in the presence of both MG132 (a proteasome inhibitor) and L. monocytogenes. Overall, these results underline the potential role of fatty acids in the modulation of many functions of the immune system.

Effect of a moderately energy-restricted diet on obese patients with fatty liver

The effects of a moderately energy-restricted (25 kcal/kg) diet on liver-function tests, anthropometric measurements, mononuclear-cell phospholipid fatty acid, lymphocyte blastogenesis, and plasma prostaglandin E2 and alpha-tocopherol levels were observed at weeks 0, 8, and 24 in 14 obese patients with fatty liver. Serum aminotransferase levels were improved significantly, with decreases in the body mass index and waist circumference. Decreases in energy intake from carbohydrate and increases in intake of vitamin A, vitamin C, and vegetables were observed at week 24. In mononuclear-cell phospholipids, linoleic acid (18:2omega 6), which was significantly lower in patients than in controls at week 0, was increased at week 24. In contrast, arachidonic acid was decreased. Plasma prostaglandin E2 levels were significantly lower in patients than in controls at week 0 and increased at week 24. The mononuclear-cell response for phytohemagglutinin correlated with 18:2omega 6 in mononuclear-cell phospholipids (r = 0.692, P < 0.01). Improvement of the serum alanine-aminotransferase level correlated with an increase in the plasma alpha-tocopherol level (r = -0.667, P < 0.01) and increases in consumption of vitamin A, omega 3 polyunsaturated fatty acids, and vegetables. These findings suggest that a hypoenergetic diet rich in omega 3 polyunsaturated fatty acids and antioxidants might be beneficial for obese patients with fatty liver.

Extracellular release of free fatty acids by rat T lymphocytes is stimulus-dependent and is affected by dietary lipid manipulation

[(3)H]-Arachidonic acid-labelled rat T lymphocytes released radioactivity extracellularly when stimulated by the calcium ionophore A23187 or by monoclonal antibodies to some cell surface structures (CD2, CD5, CD11a, CD18, CD54, T-cell receptor) but not to others (CD49d, CD62L); release was greater with the calcium ionophore. Almost all of the radioactivity released from anti-CD2-stimulated lymphocytes was recovered in the free fatty acid fraction, whereas only about 50 per cent of that released after A23187 stimulation was recovered in this fraction. A23187 stimulation resulted in release of arachidonic acid from a variety of phospholipids (phosphatidylinositol, phosphatidylcholine and perhaps phosphatidylethanolamine), while the monoclonal antibody stimulation released arachidonic acid from phosphatidylinositol and perhaps phosphatidylcholine. Unstimulated lymphocytes released a range of fatty acids extracellularly, with palmitic acid accounting for 35-40 per cent and arachidonic acid for 5 per cent of released fatty acid. Stimulation of lymphocytes with either anti-CD2 or A23187 increased total fatty acid release 1.5- to 1.8-fold. In both cases palmitic acid remained the most predominant fatty acid released but the contribution of arachidonic acid increased. The type of lipid fed to the rats significantly influenced the amount and type of fatty acid released. Fish oil feeding significantly reduced extracellular fatty acid release by stimulated lymphocytes.

Encapsulated fish oil enriched in alpha-tocopherol alters plasma phospholipid and mononuclear cell fatty acid compositions but not mononuclear cell functions

BACKGROUND

Several studies have reported that dietary fish oil (FO) supplementation alters cytokine production and other functional activities of peripheral blood mononuclear cells (PBMC). However, few of these studies have been placebo controlled and few have related the functional changes to alterations in PBMC fatty acid composition

PATIENTS AND METHODS

Healthy subjects supplemented their diets with 9 g day-1 of encapsulated placebo oil (3 : 1 mix of coconut and soybean oils), olive oil (OO), safflower oil (SO), evening primrose oil (EPO) or FO [providing 2.1 g eicosapentaenoic acid (EPA) plus 1.1 g docosahexaenoic acid (DHA) per day] for 12 weeks; the capsules also provided 205 mg alpha-tocopherol per day. Blood was sampled at 4-weekly intervals and plasma and PBMC prepared. Plasma phospholipid and PBMC fatty acid composition, plasma alpha-tocopherol and thiobarbituric acid-reactive substance concentrations, plasma total antioxidant capacity, the proportions of different PBMC subsets, the proportions of PBMC expressing the adhesion molecules CD2, CD11b and CD54, and PBMC functions (lymphocyte proliferation, natural killer cell activity, cytokine production) were measured. All measurements were repeated after a 'washout' period of 8 weeks.

RESULTS

The placebo, OO and SO capsules had no effect on plasma phospholipid or PBMC fatty acid composition. The proportion of dihomo-gamma-linolenic acid in plasma phospholipids was elevated in subjects taking EPO and was decreased in subjects taking FO. There was no appearance of gamma-linolenic acid in the plasma phospholipids or PBMC in subjects taking EPO. There was a marked increase in the proportion of EPA in the plasma phospholipids (10-fold) and PBMC (four-fold) of subjects taking FO supplements; this increase was maximal after 4 weeks of supplementation. There was an increase in the proportion of DHA in plasma phospholipids and PBMC, and an approximately 20% decrease in the proportion of arachidonic acid in plasma phospholipids and PBMC, during FO supplementation. Plasma concentrations of alpha-tocopherol were significantly elevated during supplementation in all subjects and returned to baseline values after the washout period. There were no effects of supplementation with any of the capsules on total plasma antioxidant activity or plasma thiobarbituric acid-reactive substances or on the proportion of different PBMC subsets, on the proportion of PBMC expressing adhesion molecules, on natural killer cell activity, on the proliferation of mitogen-stimulated whole blood cultures or PBMC, or on the ex vivo production of a range of cytokines by whole blood cultures or PBMC cultures stimulated by either concanavalin A or lipopolysaccharide.

CONCLUSION

Supplementation of the diet with 3.2 g EPA plus DHA per day markedly alters plasma phospholipid and PBMC fatty acid compositions. The lack of effect of FO upon PBMC functions may relate to the level of alpha-tocopherol included in the supplements.

Modulatory effects of dietary lipids on immune system functions

Dietary lipid manipulation may affect a great number of immune parameters, such as lymphocyte proliferation, cytokine synthesis, natural killer (NK) cell activity, phagocytosis and so on. The immunomodulation induced by dietary fatty acids may be applied in the amelioration of inflammatory disorders, such as autoimmune diseases. However, the mechanisms that participate in these processes are still poorly understood. It is probable that modulation of immune system by fatty acids of the diet may occur by alteration of membrane fluidity, lipid peroxide formation, eicosanoid production or regulation of gene expression. However, recent studies have reported the effects of several free fatty acids on apoptosis induction of in vitro cultures. In fact, a possible explanation of the effects that fatty acids promote on the immune system cells could be associated with an apoptotic process performed in an irreversible way. In vivo studies have demonstrated the ability of fatty acids to alter the survival of animals fed diets containing oils and infected with a pathogenic bacterium. Experimental infection in animals fed dietary lipids produces a modification of resistance to micro-organisms. The present review analyses all of these parameters that dietary fatty acids are capable of altering in order to modify the immune response. Further studies will be needed to establish the mechanisms involved in immune system regulation, reduction of symptoms derived from autoimmune pathologies and so on.

Dietary fish oil diminishes lymphocyte adhesion to macrophage and endothelial cell monolayers

To further investigate the immunomodulatory effects of dietary lipids, rats were fed on a low-fat diet or on high-fat diets that contained hydrogenated coconut, olive, safflower, evening primrose or fish oil as the principal fat source. The fish oil diet decreased the level of expression of CD2, CD11a, CD18 and CD44 on the surface of freshly prepared lymphocytes and of CD2, CD11a, CD18, CD54 (intercellular adhesion molecule-1; ICAM-1) and CD62L (L-selectin) on the surface of concanavalin A (Con A)-stimulated lymphocytes. The olive oil diet also resulted in decreased expression of some adhesion molecules. The fish or olive oil diets, and to a lesser extent the safflower or evening primrose oil diets, decreased the adhesion of both freshly prepared and Con A-stimulated lymphocytes to macrophage monolayers. The fish oil diet, and to a lesser extent the olive or evening primrose oil diets, reduced the ability of Con A-stimulated lymphocytes to adhere to untreated endothelial cells. Furthermore, the fish oil diet resulted in a 50% reduction in Con A-stimulated lymphocyte adhesion to tumour necrosis factor-alpha (TNF-alpha)-stimulated endothelial cells. This study demonstrates that dietary lipids affect the expression of functionally important adhesion molecules on the surface of lymphocytes. Furthermore, this study suggests that such diet-induced effects on adhesion molecule expression might alter the ability of lymphocytes to bind to macrophages and to endothelial cells. Of the diets studied fish oil causes the most significant effects. The results of this study suggest that a reduction in cellular infiltration may partly explain the protective effect of a fish-oil-rich diet against the development of inflammatory and cardiovascular diseases.

Monounsaturated fats and immune function

Animal studies suggest that olive oil is capable of modulating functions of cells of the immune system in a manner similar to, albeit weaker than, fish oils. There is some evidence that the effects of olive oil on immune function in animal studies are due to oleic acid rather than to trace elements or antioxidants. Importantly, several studies have demonstrated effects of oleic acid-containing diets on in vivo immune responses. In contrast, consumption of a monounsaturated fatty acid (MUFA)-rich diet by humans does not appear to bring about a general suppression of immune cell functions. The effects of this diet in humans are limited to decreasing aspects of adhesion of peripheral blood mononuclear cells, although there are trends towards decreases in natural killer cell activity and proliferation. The lack of a clear effect of MUFA in humans may be attributable to the higher level of monounsaturated fat used in the animal studies, although it is ultimately of importance to examine the effects of intakes which are in no way extreme. The effects of MUFA on adhesion molecules are potentially important, since these molecules appear to have a role in the pathology of a number of diseases involving the immune system. This area clearly deserves further exploration.

N-3 polyunsaturated fatty acids and immune cell function

The amount and type of eicosanoids made can be affected by the type of fat consumed in the diet. It is now apparent that both eicosanoids and n-3 PUFAs are potent modulators of lymphocyte and M phi functions in vitro. Inclusion in the diet of high levels of certain lipids containing n-3 PUFAs markedly affects the functions of cells of the immune system subsequently tested in vitro. Cellular components of both natural and acquired immunity are affected. In vivo tests are perhaps the most appropriate approach for determining the effect of different dietary n-3 PUFAs upon immune function. Several studies indicate that diets rich in n-3 PUFAs are anti-inflammatory and immunosuppressive in vivo, although there have been relatively few studies in man. Although some of the effects of n-3 PUFAs may be brought about by modulation of the amount and types of eicosanoids made, it is clear that these fatty acids can also elicit their effects by eicosanoid-independent mechanisms (Fig. 12). Such n-3 PUFA-induced effects may be of use as a therapy for acute and chronic inflammation, for disorders which involve an inappropriately-activated immune response and for the enhancement of graft survival.

Level of polyunsaturated fatty acids and the n-6 to n-3 polyunsaturated fatty acid ratio in the rat diet alter serum lipid levels and lymphocyte functions

In order to further examine the effects of dietary polyunsaturated fatty acids (PUFA) upon blood lipid levels and lymphocyte functions, weanling rats were fed for 6 weeks on high fat (178 g/kg) diets which differed in the ratio of n-6:n-3 PUFA (100, 20, 10, 5, 1) and in the absolute level of PUFA (17.5 or 35 g/100 g fatty acids). The n-6:n-3 PUFA ratio of the diets was decreased by replacing linoleic acid with alpha-linolenic acid while the PUFA content of the diets was decreased by replacing PUFA with palmitic acid. Serum cholesterol concentrations decreased as the n-6:n-3 PUFA ratio of the low PUFA diet decreased. The ex vivo proliferation of spleen lymphocytes from rats fed the low PUFA diets decreased as the n-6:n-3 PUFA ratio of the diet decreased; the proliferation of spleen lymphocytes from high PUFA-fed rats was less affected by the n-6:n-3 PUFA ratio of the diet. Natural killer cell activity was lower for spleen lymphocytes from rats fed high PUFA diets with n-6:n-3 PUFA ratios of 100 or 20 than for those from rats fed low PUFA diets with these ratios. The natural killer cell activity of spleen lymphocytes decreased as the n-6:n-3 PUFA ratio of the low PUFA diet decreased. These findings indicate that dietary alpha-linolenic acid has significant blood lipid-lowering and immunomodulatory effects in rats, but that the effect is dependent upon the total PUFA content of the diet. The ratios of linoleic and alpha-linolenic acids to other fatty acids (e.g. palmitic, oleic) are important in determining the precise effect of manipulations of the fatty acid composition of the diet.