Effects of fatty acids and dietary lipids on cells of the immune system

Molecular effects of Vitamin-D and PUFAs metabolism in skeletal muscle combating Type-II diabetes mellitus

Multiple post-receptor intracellular alterations such as impaired glucose transfer, glucose phosphorylation, decreased glucose oxidation, and glycogen production contribute to insulin resistance (IR) in skeletal muscle, manifested by diminished insulin-stimulated glucose uptake. Type-2 diabetes mellites (T2DM) has caused by IR, which is also seen in obese patients and those with metabolic syndrome. The Vitamin-D receptor (VDR) and poly unsaturated fatty acids (PUFAs) roles in skeletal muscle growth, shapes, and function for combating type-2 diabetes have been clarified throughout this research. VDR and PUFAs appears to show a variety of effects on skeletal muscle, in addition it shows a promising role on bone and mineral homeostasis. Individuals having T2DM are reported to suffer from severe muscular weakness and alterations in shape of the muscle. Several studies have investigated the effect on VDR on muscular strength and mass, which leads to Vitamin-D deficiency (VDD) in individuals, in which most commonly seen in elderly. VDR has been shown to affect skeletal cellular proliferation, intracellular calcium handling, as well as genomic activity in a variety of different ways such as muscle metabolism, insulin sensitivity, which is the major characteristic pathogenesis for IR in combating T2DM. The identified VDR gene polymorphisms are ApaI, TaqI, FokI, and BsmI that are associated with T2DM. This review collates informations on the mechanisms by which VDR activation takes place in skeletal muscles. Despite the significant breakthroughs made in recent decades, various studies show that IR affects VDR and PUFAs metabolism in skeletal muscle. Therefore, this review collates the data to show the role of VDR and PUFAs in the skeletal muscles to combat T2DM.

High level of dietary soybean oil depresses the growth and anti-oxidative capacity and induces inflammatory response in large yellow croaker Larimichthys crocea

Increasing demand, uncertain availability and high price of fish oil with the expansion of aquaculture made it essential to search alternative lipid sources. Vegetable oil has been proved to be the best candidate for the replacement of fish oil in aquafeeds. However, this replacement especially in high level potentially has some negative effects on fish. The present study was conducted to investigate the growth performance, anti-oxidative and inflammatory responses of large yellow croaker to replacement of dietary fish oil by soybean oil. Three isonitrogenous (46% crude protein) and isolipidic (13% crude lipids) diets were formulated to feed fish (initial body weight: 36.80 ± 0.39 g) for 12 weeks. The control diet was designed to contain 6.5% of fish oil, and named as FO. On the basis of the control diet, the fish oil was 50% and 100% replaced by soybean oil, and these two diets were named as FS and SO, respectively. Results showed that the specific growth rate significantly decreased in the SO group. Crude lipid contents in muscle and liver of fish fed SO diet were significantly higher than those in the FO group. The ratio of n-3 poly-unsaturated fatty acids (PUFAs) to identified fatty acids in liver decreased significantly, while n-6 PUFAs increased significantly with increasing dietary soybean oil inclusion. The levels of triacylglycerol, non-esterified fatty acid and tumour necrosis factor α, and the activity of aspartate aminotransferase in serum significantly increased in SO group. The total anti-oxidative capacity and expressions of the anti-oxidation-related genes (superoxide dismutase 1 and 2, catalase, glutathion peroxidase and nuclear factor erythroid 2-related factor 2) were significantly decreased by dietary soybean inclusion. Dietary soybean oil significantly decreased the gene expressions of the anti-inflammatory cytokines (arginase I and interleukin 10), and increased the pro-inflammatory cytokines (tumour necrosis factor α and interleukin 1β). The replacement of dietary fish oil by soybean oil also induced an over-expression of toll-like receptor 22 and myeloid differentiation factor 88 in liver. In conclusion, dietary soybean oil could suppress growth performance and liver anti-oxidative capacity, and induce inflammatory responses of large yellow croaker.

In vitro effects of oil's fatty acids on T cell function in gestational diabetic pregnant women and their newborns

BACKGROUND

The aim of this investigation was to determine the in vitro effects of linseed, olive and Nigel oils on T cell proliferation and function in gestational diabetes.

METHODS

Blood samples were collected from 40 control healthy and 32 gestational diabetic mothers and their newborns. Peripheral blood lymphocytes were isolated using a density gradient of Ficoll. T cell proliferation, interleukin-2 and -4 (IL-2, IL-4) secretion, fatty acid composition and intracellular oxidative status were investigated.

RESULTS

Mitogen (Concanavalin A) stimulated lymphocyte proliferation, IL-2 secretion, intracellular reduced glutathione levels, superoxide dismutase (SOD) and catalase activities were lower while intracellular malondialdehyde (MDA) and carbonyl proteins were higher in diabetic mothers and in their newborns as compared to their respective controls. Linseed oil induced a reduction in T-lymphocyte proliferation and IL-2 production, and alpha linolenic acid membrane enrichment in both diabetic and control groups. In the presence of Nigel oil, T-lymphocyte proliferation and IL-2 secretion, phospholipid linoleic and oleic acids were enhanced. Olive oil had no effect on lymphocyte proliferation in all groups. Linseed, olive and Nigel oils induced an increase in T cell levels of reduced glutathione levels and in activities of catalase and SOD with a concomitant decrease in MDA and carbonyl protein contents.

CONCLUSION

Linseed, olive and Nigel oils had beneficial effects on T cell functions in gestational diabetes.

Dietary vegetable oils: effects on the expression of immune-related genes in Senegalese sole (Solea senegalensis) intestine

The decreased availability of fish oil, traditionally used as oil source in marine aquafeeds, has lead to the search for alternatives oils. Vegetable oils (VO) are being extensively used as lipid sources in marine fish diets, inducing an imbalance on certain dietary fatty acids. Alteration on the dietary ratio of w-6/w-3 has been described to have detrimental effects on fish immunity. Senegalese sole has high susceptibility to stress and diseases, and little is known on the effects of dietary VO on its immunity. In this study, Senegalese sole juveniles were fed diets (56% crude protein, 12% crude lipid) containing linseed (100LO), soybean (100SO) or fish (100FO) oils as unique oil source. Growth, cortisol and intestinal fatty acid composition were determined after 90 days. Moreover, at the final of the experiment a stress test (5 min of net chasing) was carried out. To evaluate the effect of diets and stress on intestine immunology, expression profiles of a set of 53 immune-related genes using RT-qPCR was also performed. The use of VO did not induced changes in fish growth, but affected fatty acid profile of intestine and expression of immune-related genes. The use of SO (rich in n-6 fatty acids) induced an over-expression of those genes related to complement pathway, recognizing pathogen associated to molecular patterns, defensive response against bacteria, defensive response against viruses, antigen differentiation, cytokines and their receptors. This general over-expression could indicate an activation of inflammatory processes in fish gut. When a stress was applied, a decrease of mRNA levels of different immune-related genes with respect to the unstressed control could be observed in fish fed 100FO. However, fish fed 100LO, with a higher ALA/LA ratio, seemed to ameliorate the effects of combined effects of FO substitution plus stressful situation whereas fish fed 100SO did not show this type of response.

Type 2 diabetes, PUFAs, and vitamin D: their relation to inflammation

Chronic diseases have become one of the most important public health problems, due to their high costs for treatment and prevention. Until now, researchers have considered that the etiology of Type 2 diabetes mellitus (T2DM) is multifactorial. Recently, the study of the innate immune system has offered an explanation model of the pathogenesis of T2DM. On the other hand, there is evidence about the beneficial effect of polyunsaturated fatty acids (PUFA) n-3 and n-6 in patients with chronic inflammatory diseases including diabetes. Furthermore, high vitamin D plasmatic concentrations have been associated with the best performance of pancreatic β cells and the improving of this disease. In conclusion, certain fatty acids in the adequate proportion as well as 25-hydroxivitamin D can modulate the inflammatory response in diabetic people, modifying the evolution of this disease.

Production of TNF-α, nitric oxide and hydrogen peroxide by macrophages from mice with paracoccidioidomycosis that were fed a linseed oil-enriched diet

Omega-3 polyunsaturated fatty acids (n-3 PUFA) can modulate the immune system and their primary effect is on macrophage function. Paracoccidioidomycosis (PCM) is an endemic systemic mycosis in Latin America that is caused by the dimorphic fungus Paracoccidioides brasiliensis (Pb). Macrophages are the main defence against this pathogen and have microbicidal activity that is dependent on interferon-Γ and tumour necrosis factor (TNF)-α. These cytokines stimulate the synthesis of nitric oxide (NO) and hydrogen peroxide (H₂O₂), leading to the death of the fungus. To study the effect of n-3 PUFA on the host immune response during experimental PCM, macrophages that were obtained from animals infected with Pb18 and fed a diet enriched by linseed (LIN) oil were cultured and challenged with the fungus in vitro. The macrophage function was analysed based on the concentrations of TNF-α, NO and H₂O₂. LIN oil seems to influence the production of TNF-α during the development of disease. A diet enriched with LIN oil influences the microbicidal activity of the macrophages by inducing the production of cytokines and metabolites such as NO and H₂O₂, predominantly in the chronic phase of infection.

Efeito dos ácidos graxos essenciais sobre lipidemia e vascularização da membrana vitelina de codornas japonesas

Verificou-se o efeito de diferentes fontes de ácidos graxos essenciais ômega-3 e ômega-6 sobre o perfil lipídico de codornas japonesas e sobre o crescimento vascular na membrana vitelina dos embriões de aves suplementadas com óleo de peixe, 2% e 4%, e óleo de soja, 2% e 4%, em relação à dieta-controle, sem suplementação lipídica. Foi usado o método enzimático com reação colorimétrica para estimar o perfil lipídico sérico de colesterol total, triglicerídeos e HDL das aves. A vascularização na membrana vitelina foi quantificada por meio da dimensão fractal, utilizando-se o método de box-counting. A concentração de colesterol dos grupos controle e tratados não diferiu entre si. Para o HDL, o grupo que recebeu maior proporção de óleo de peixe, 4%, diferiu dos outros grupos. Os níveis de triglicerídeos das codornas suplementadas com óleo de peixe foram superiores aos dos demais grupos. A dimensão fractal da vascularização da membrana vitelina dos embriões de codornas dos grupos que receberam 4% de óleo de peixe e 4% de óleo de soja foi significativamente menor que a dos demais grupos, indicando efeitos antiangiogênicos no processo de formação vascular.

Perspectives on the use of marine and freshwater hydrobiont oils for development of drug delivery systems

Marine foods represent a unique source of poly-unsaturated fatty acids (PUFA) of the omega-3 (n-3) family. Today it is generally accepted that fish oil is important in a healthy and balanced omnivorous human diet. This favorable health perception of fish oil is however troubled by the high level of PUFA oxidation and low absorption in the gastro-intestinal tract. In this work we present and described various types of delivery systems which are used to improve PUFA and fish oil availability and oxidative stability.

Dietary α-linolenic acid diminishes experimental atherogenesis and restricts T cell-driven inflammation

Aims

Epidemiological studies report an inverse association between plant-derived dietary α-linolenic acid (ALA) and cardiovascular events. However, little is known about the mechanism of this protection. We assessed the cellular and molecular mechanisms of dietary ALA (flaxseed) on atherosclerosis in a mouse model.

Methods and results

Eight-week-old male apolipoprotein E knockout (ApoE^−/−) mice were fed a 0.21 % (w/w) cholesterol diet for 16 weeks containing either a high ALA [7.3 % (w/w); n = 10] or low ALA content [0.03 % (w/w); n = 10]. Bioavailability, chain elongation, and fatty acid metabolism were measured by gas chromatography of tissue lysates and urine. Plaques were assessed using immunohistochemistry. T cell proliferation was investigated in primary murine CD3-positive lymphocytes. T cell differentiation and activation was assessed by expression analyses of interferon-γ, interleukin-4, and tumour necrosis factor α (TNFα) using quantitative PCR and ELISA. Dietary ALA increased aortic tissue levels of ALA as well as of the n−3 long chain fatty acids (LC n−3 FA) eicosapentaenoic acid, docosapentaenoic acid, and docosahexaenoic acid. The high ALA diet reduced plaque area by 50% and decreased plaque T cell content as well as expression of vascular cell adhesion molecule-1 and TNFα. Both dietary ALA and direct ALA exposure restricted T cell proliferation, differentiation, and inflammatory activity. Dietary ALA shifted prostaglandin and isoprostane formation towards 3-series compounds, potentially contributing to the atheroprotective effects of ALA.

Conclusion

Dietary ALA diminishes experimental atherogenesis and restricts T cell-driven inflammation, thus providing the proof-of-principle that plant-derived ALA may provide a valuable alternative to marine LC n−3 FA.

Clinical and experimental links between diabetes and glaucoma

Glaucoma is a leading cause of blindness. It is a multifactorial condition, the risk factors for which are increasingly well defined from large-scale epidemiological studies. One risk factor that remains controversial is the presence of diabetes. It has been proposed that diabetic eyes are at greater risk of injury from external stressors, such as elevated intraocular pressure. Alternatively, diabetes may cause ganglion cell loss, which becomes additive to a glaucomatous ganglion cell injury. Several clinical trials have considered whether a link exists between diabetes and glaucoma. In this review, we outline these studies and consider the causes for their lack of concordant findings. We also review the biochemical and cellular similarities between the two conditions. Moreover, we review the available literature that attempts to answer the question of whether the presence of diabetes increases the risk of developing glaucoma. At present, laboratory studies provide robust evidence for an association between diabetes and glaucoma.

Induction and modulation of apoptosis in neonatal monocytes by polyunsaturated fatty acids

Polyunsaturated fatty acids (PUFAs), known modulators of the immune response, are the source of essential fatty acids in total parenteral nutrition-dependent patients. Critically ill infants on TPN have an increased incidence of sepsis, and lipid emulsions depress various immune functions. Recent studies have demonstrated that PUFAs induce apoptosis in various tissue cells in vitro and ex vivo. The susceptibility of neonatal monocytes, as major early effector cells in the host response to sepsis, to PUFA-mediated apoptosis and the mechanisms associated with PUFA-induced apoptosis were investigated. Both n-3 and n-6 PUFAs induced rapid, dose-dependent cell death in purified monocytes. Polyunsaturated fatty acids induced significant activation of upstream caspases 8 and 9 as well as caspase 3. The PUFA treatment resulted in a 4-fold increase in oxidative stress and a loss of monocyte mitochondrial potential compared with carrier controls (P < .05). The addition of cyclosporin, which blocks the development of mitochondrial transition pores, completely abolished the proapoptotic effects of PUFAs. Although Trolox (Sigma Aldrich) reduced PUFA-induced intracellular oxidative stress in neonatal monocytes, apoptosis was not blocked by this potent antioxidant. The data identify PUFAs as potent inducers of monocyte apoptosis, which can occur independently of the induction of oxidative stress, by using a mitochondrial dependent pathway. The TPN-dependent infant may be particularly sensitive to such PUFA effects, having a relatively poor capacity to both use and clear PUFAs.

Fatty acid-mediated inhibition of IL-12 production by murine macrophages is independent of PPARγ

Our laboratory has reported thatn-3 PUFA can reduce host resistance toListeriainfection, in part, by impairingin vivoIL-12 biosynthesis. Recently, PUFA were shown to be ligands for PPAR, a novel family of nuclear receptors with three isoforms: PPARα, PPARδ/β and PPARγ. PPARγ is expressed in immune cells, such as T cells and macrophages. Two PPARγ agonists, 15-deoxy-Δ12,14-prostaglandin (PG) J2and rosiglitazone, have been shown to have immunomodulatory activityin vitro, including inhibiting IL-12 biosynthesis. We hypothesized thatn-3 PUFA inhibit IL-12 production through activating PPARγ. We used thioglycolate-elicited mouse peritoneal macrophages to study the effect of various fatty acids and their oxidized metabolites onin vitroIL-12 production. Our present results demonstrate that bothn-3 andn-6 PUFA can reducein vitroIL-12 biosynthesis, though less potently than 15-deoxy-PGJ2and rosiglitazone. GW9662, a PPARγ antagonist, reversed the inhibitory effect of rosiglitazone, but not that of PUFA. Our present findings suggest that fatty acid-mediated inhibition of IL-12 production is independent of PPARγ.

Effect of fish or soybean oil-rich diets on bradykinin, kallikrein, nitric oxide, leptin, corticosterone and macrophages in carrageenan stimulated rats

We have previously demonstrated that both n-3 and n-6 polyunsaturated fatty acids (PUFA)-rich diets decrease the acute inflammatory response partially explained by the high corticosterone basal levels. The present study aimed to determine the effect of hyperlipidic diets (PUFA n-3 or n-6) on phagocytosis, hydrogen peroxide (H(2)O(2)) and nitric oxide (NO) release by macrophages, bradykinin (BK) and NO release in the paw inflammatory perfusate and Kallikrein (KK), corticosterone and leptin blood levels. Hyperlipidic diets decreased H(2)O(2) release from macrophages stimulated by carrageenan or phorbol-miristate-acetate (PMA), NO release from macrophage stimulated by carrageenan, BK and NO release in the edema perfusate, KK plasma levels and the increase of serum leptin after carrageenan stimulus. These data show that both fish and soybean oil-rich diets promote similar alterations on inflammatory mediators of carrageenan edema and a causal association with the anti-inflammatory effect of these diets.

Trans-10,cis-12-conjugated linoleic acid increases phagocytosis of porcine peripheral blood polymorphonuclear cellsin vitro

Trans-10,cis-12-conjugated linoleic acid (t10c12-CLA) has been shown to alter immune function. PPARγ has been shown to potentially play an important role in regulating inflammatory and immune responses by modulating the activity of monocytes and macrophages. Previous studies have indicated that the phagocytic capacity of porcine peripheral blood polymorphonuclear cells (PMN) was enhanced by the culture supernatant fraction from t10c12-CLA-stimulated porcine peripheral blood mononuclear cells (PBMC) but not by t10c12-CLA itself. In the present study, we examined the effects of t10c12-CLA on PPARγ and TNF-α expression of porcine PBMC and the phagocytic capacity of PMN. t10c12-CLA increased TNF-α mRNA expression and production by PBMC. The phagocytic capacity of porcine PMN was enhanced by either culture supernatant fraction from PBMC treated with t10c12-CLA or recombinant porcine (rp) TNF-α. Anti-rpTNF-α polyclonal antibody inhibited the enhancement of PMN phagocytic capacity. t10c12-CLA also up regulated PPARγ mRNA expression in porcine PBMC. Bisphenol A diglycidyl ether, a PPARγ antagonist, not only completely negated the t10c12-CLA-stimulating effects on TNF-α expression and production by porcine PBMC, but also decreased the enhancement of PMN phagocytic capacity by the t10c12-CLA-stimulated porcine PBMC culture supernatant fraction. These results suggest that t10c12-CLA has an immunostimulating effect on porcine PMN phagocytic capacity, which is mediated by TNF-α from PBMC via a PPARγ-dependent pathway.

Immune response and serum immunoglobulin G concentrations in beef calves suckling cows of differing body condition score at parturition and supplemented with high-linoleate or high-oleate safflower seeds

Two experiments were conducted to determine the effect of maternal lipid supplementation on the immune response to antigenic challenge in suckling calves. In Exp. 1, beginning 1 d postpartum, 18 primiparous crossbred beef cows were fed Foxtail millet hay and a low-fat (control) supplement or a supplement containing cracked, high-linoleate safflower seed in individual feeding stanchions until d 40 of lactation. The diets were formulated to provide similar quantities of N and TDN, and the linoleate diet was formulated to contain 5% of DMI as fat. Calves were injected s.c. with 15 mg of antigen (ovalbumin) at d 21 and again at d 35 of age. To measure the total serum antibody production in response to the antigen, blood samples were collected from the calves every 7 d via jugular venipuncture from d 14 to 42. Calves from linoleate-supplemented cows had a decrease (P = 0.04) in total antibody production in response to ovalbumin and appeared to have a delayed response to antigen challenge. Total antibody production increased (P < 0.001) after secondary exposure to ovalbumin. In Exp. 2, 36 Angus x Gelbvieh beef cows that were nutritionally managed to achieve a BCS of 4 or 6 at parturition were used to determine the effects of prepartum energy balance and postpartum lipid supplementation on the passive transfer of immunoglobulins and the immune response to antigenic challenge in their calves. Beginning at 3 d postpartum and continuing until d 60 of lactation, cows were fed hay and a low-fat control supplement or supplements consisting of either cracked, high-linoleate or high-oleate safflower seeds. Safflower seed supplements were formulated to provide 5% of DMI as fat. Calves were injected s.c. with 15 mg of ovalbumin at 21 d of age and again at 48 d of age. The antibody responses were determined in serum; cell-mediated immunity was assessed by intradermal antigen injection at 60 d of age. A trend was noted (P = 0.10) for calves suckling control-supplemented cows to have a greater response to antigen compared with calves from linoleate- and oleate-supplemented cows; however, no difference was observed among treatments (P = 0.86) in cell-mediated immune response. Postpartum oilseed supplementation in beef cows appears to decrease antibody production in response to antigenic challenge in suckling calves. However, BCS at parturition did not influence passive transfer of immunoglobulins in neonatal calves.

Effect of n-3 and n-6 polyunsaturated fatty acids on lymphocyte proliferation, interleukin production and phospholipid fatty acids composition in type 2 diabetic and healthy subjects in Jordan people

Dietary lipid manipulation may affect a great number of immune parameters, such as lymphocyte proliferation, cytokine synthesis. In this study, lymphocytes of diabetic type 2 were incubated with different polyunsaturated fatty acid (docosahexaenoic, eicosapentaenoic, arachidonic acid) for investigated their effect on lymphoproliferation response, the concentration of interleukin 2 produced in each essay and phospholipid fatty acid composition of lymphocyte membrane. Our results found that the concanavalin A and insulin increase significantly the proliferative response while eicosapentaenoic, arachidonic and docosahexaenoic acid inhibited that by different degrees: 47%, 37% and 19%, respectively, for healthy subjects and 39%, 29% and 13% for diabetes. However, the concentration of IL-2 produced in presence of either docosahexaenoic, eicosapentaenoic or arachidonic acid was significantly reduced by 36%, 32% and 39%, respectively, in controls while 16%, 15% and 23%, respectively, in diabetics. On the other hand, the tested fatty acids demonstrated a major impact on the fatty acid composition of different phospholipid fractions of lymphocyte membrane but these fractions were different in their response to each fatty acid examined. For instance, the addition of docosahexaenoic acid to culture media was accompanied with a predominant composition of docosahexaenoic acid in phospholipid fractions. Also, our results showed a notable increased proportion of arachidonic, eicosapentaenoic and docosahexaenoic acids in control phospholipid fractions than those of diabetic.

Modulation of immune cell function by polyunsaturated fatty acids

The n-3 and n-6 polyunsaturated fatty acids (PUFAs) are essential dietary constituents. They are important as a source of energy, as structural components of cell membranes, and as signalling molecules. They have been demonstrated to be potent modulators of the immune response, and research has endeavoured to optimise the ratio of n-3 to n-6 PUFAs in the lipid component of total parenteral nutrition (TPN) to optimise their beneficial effects in the clinical setting. Critically ill neonates on TPN have an increased incidence of sepsis, and additional studies have determined that lipid emulsions depress various elements of cellular immune responses in monocytes, lymphocytes, and neutrophils. It has been proposed that PUFAs may mediate their manifold effects through the modification of eicosanoid production and by directly or indirectly modifying intracellular signal transduction pathways, including the alteration of gene transcription, in various tissues. They are susceptible to lipid peroxidation, and there is evidence that the products of this process may result in cell death by apoptosis, a nonphlogistic homeostatic process of cell deletion. PUFAs have been shown to induce apoptosis in primary lymphocytes, colonic mucosal cells, and various cell lines. Additionally, our laboratory has shown them to be potent inducers of apoptosis in neonatal monocytes. This may represent a novel mechanism whereby PUFAs may modify the immune response.

Docosahexaenoic acid and other fatty acids induce a decrease in pHi in Jurkat T-cells

1. Docosahexaenoic acid (DHA) induced rapid (t1/2=33 s) and dose-dependent decreases in pHi in BCECF-loaded human (Jurkat) T-cells. Addition of 5-(N,N-dimethyl)-amiloride, an inhibitor of Na+/H+ exchanger, prolonged DHA-induced acidification as a function of time, indicating that the exchanger is implicated in pHi recovery. 2. Other fatty acids like oleic acid, arachidonic acid, eicosapentaenoic acid, but not palmitic acid, also induced a fall in pHi in these cells. 3. To assess the role of calcium in the DHA-induced acidification, we conducted experiments in Ca2+-free (0% Ca2+) and Ca2+-containing (100% Ca2+) buffer. We observed that there was no difference in the degree of DHA-induced transient acidification in both the experimental conditions, though pHi recovery was faster in 0% Ca2+ medium than that in 100% Ca2+ medium. 4. In the presence of BAPTA, a calcium chelator, a rapid recovery of DHA-induced acidosis was observed. Furthermore, addition of CaCl2 into 0% Ca2+ medium curtailed DHA-evoked rapid pHi recovery. In 0% Ca2+ medium, containing BAPTA, DHA did not evoke increases in [Ca2+]i, though this fatty acid still induced a rapid acidification in these cells. These observations suggest that calcium is implicated in the long-lasting DHA-induced acidosis. 5. DHA-induced rapid acidification may be due to its deprotonation in the plasma membrane (flip-flop model), as suggested by the following observations: (1) DHA with a -COOH group induced intracellular acidification, but this fatty acid with a -COOCH3 group failed to do so, and (2) DHA, but not propionic acid, -induced acidification was completely reversed by addition of fatty acid-free bovine serum albumin in these cells. 6. These results suggest that DHA induces acidosis via deprotonation and Ca2+ mobilization in human T-cells.

Thapsigargin-stimulated MAP kinase phosphorylation via CRAC channels and PLD activation: inhibitory action of docosahexaenoic acid

This study was conducted on human Jurkat T-cells to investigate the role of depletion of intracellular Ca(2+) stores in the phosphorylation of two mitogen-activated protein kinases (MAPKs), i.e. extracellular signal-regulated kinase (ERK) 1 and ERK2, and their modulation by a polyunsaturated fatty acid, docosahexaenoic acid (DHA). We observed that thapsigargin (TG) stimulated MAPK activation by store-operated calcium (SOC) influx via opening of calcium release-activated calcium (CRAC) channels as tyrphostin-A9, a CRAC channel blocker, and two SOC influx inhibitors, econazole and SKF-96365, diminished the action of the former. TG-stimulated ERK1/ERK2 phosphorylation was also diminished in buffer containing EGTA, a calcium chelator, further suggesting the implication of calcium influx in MAPK activation in these cells. Moreover, TG stimulated the production of diacylglycerol (DAG) by activating phospholipase D (PLD) as propranolol (PROP) (a PLD inhibitor), but not U73122 (a phospholipase C inhibitor), inhibited TG-evoked DAG production in these cells. DAG production and protein kinase C (PKC) activation were involved upstream of MAPK activation as PROP and GF109203X, a PKC inhibitor, abolished the action of TG on ERK1/ERK2 phosphorylation. Furthermore, DHA seems to act by inhibiting PKC activation as this fatty acid diminished TG- and phorbol 12-myristate 13-acetate-induced ERK1/ERK2 phosphorylation in these cells. Together these results suggest that Ca(2+) influx via CRAC channels is implicated in PLD/PKC/MAPK activation which may be a target of physiological agents such as DHA.

Interaction of conjugated linoleic acid, sphingomyelin, and butyrate on formation of colonic aberrant crypt foci and immune functions in rats

This study was designed to investigate possible additive or synergistic action among sphingomyelin (SPH), cis-9,trans-11-conjugated linoleic acid (CLA), and butyrate (BTY) against colon cancer and modulation of immune functions in vivo in male Sprague-Dawley rats. Each of the 5 groups of rats was fed either 35 mg SPH, 100 mg CLA, or 100 mg BTY/kg body weight, a combination of the 3 compounds at the same doses, or none of the compounds, for 7 wk. Rats were injected with azoxymethane, a colon carcinogen, to induce the formation of aberrant crypt foci, preneoplastic lesions of colon cancer. Parameters measured included number and multiplicity (number of crypts per focus) of aberrant crypts, immune functions such as innate immunity (natural killer cell cytotoxicity), humoral immunity (development of antibodies), and cell-mediated immunity (delayed-type hypersensitivity). Results show that the groups treated with SPH, CLA, and BTY individually had significantly higher natural killer cell (NK) cytotoxicity than the group treated with all compounds. The CLA group also had significantly higher NK activity than the control group. This study shows that the three compounds may not act additively or synergistically either to inhibit the development of aberrant crypts or to enhance immune functions. In fact, exposure to the combined compounds may be antagonistic to enhancement of NK function by the individual chemicals.

Participation of corticosteroids and effects of indomethacin on the acute inflammatory response of rats fed n-6 or n-3 polyunsaturated fatty acid-rich diets

We have previously shown that both n-3 (fish oil) and n-6 (soybean oil) PUFA-rich diets reduce carrageenan-induced paw edema in rats. The present study evaluated the role of corticosteroids, and the effect of indomethacin on this response. Basal (pre-carrageenan) levels of corticosterone were elevated in both lipid diets compared to the chow diet. During inflammation, corticosterone levels increased to a similar extent in the chow and lipid diets. With 2.0 mg/kg indomethacin, edema was reduced in the chow diet and the n-3 diet, while it was not changed in the n-6 diet. In contrast, the 16.6 mg/kg dose of indomethacin induced a mild increase in edema in the chow diet but a pronounced edema increase in the lipid diets. The increase in corticosterone levels induced by carrageenan was either reduced (chow) or completely abolished (lipids) by the treatment with the higher dose of indomethacin, compared to both the control (untreated) group, and the lower dose of indomethacin. These data indicate that both acute inflammation and the response to an antiinflammatory drug were attenuated by n-3 or n-6 PUFA-rich diets. They also showed that indomethacin can have anti- or proinflammatory properties reflecting the extent of the corticosterone inhibition by indomethacin.

The paradox of improved antiretroviral therapy in HIV: potential for nutritional modulation?

Chronic infection with HIV type 1 is associated with alterations in macronutrient metabolism, specifically elevated plasma lipids, glucose and reduced insulin sensitivity. These alterations are most severe in patients at the later stages of AIDS, indicating a relationship with disease progression. Recently, a metabolic syndrome, termed lipodystrophy, has been described in successfully-treated HIV patients in whom the altered macronutrient metabolism of HIV infection appears to be amplified markedly, with concurrent alterations in adipose tissue patterning. This syndrome presents a paradox, as before the development of highly-active antiretroviral therapy (HAART) the most severe perturbations in metabolism were observed in the sickest patients. Now, the patients that respond well to therapy are showing metabolic perturbations much greater than those seen before. The implications of this syndrome are that, whilst life expectancy may be increased by reducing viral load, there are concomitant increases in the risk of cardiovascular disease, diabetes and pancreatitis within this patient population. The aetiology of the syndrome remains unclear. In a collaborative trial with the Chelsea and Westminster Hospital in London we have used stable-isotope-labelled fatty acids to examine the hypothesis that treatment with HAART causes a delayed clearance of dietary lipid from the circulation, resulting in the retention of lipid within plasma and the downstream changes in insulin and glucose homeostasis. This hypothesis would indicate a role for low-fat diets, exercise and drugs that reduce plasma lipid or insulin resistance, in modulating the response to antiretroviral therapy in HIV infection.

Fatty acids and lymphocyte functions

The immune system acts to protect the host against pathogenic invaders. However, components of the immune system can become dysregulated such that their activities are directed against host tissues, so causing damage. Lymphocytes are involved in both the beneficial and detrimental effects of the immune system. Both the level of fat and the types of fatty acid present in the diet can affect lymphocyte functions. The fatty acid composition of lymphocytes, and other immune cells, is altered according to the fatty acid composition of the diet and this alters the capacity of those cells to produce eicosanoids, such as prostaglandin E2, which are involved in immunoregulation. A high fat diet can impair lymphocyte function. Cell culture and animal feeding studies indicate that oleic, linoleic, conjugated linoleic, gamma-linolenic, dihomo-gamma-linolenic, arachidonic, alpha-linolenic, eicosapentaenoic and docosahexaenoic acids can all influence lymphocyte proliferation, the production of cytokines by lymphocytes, and natural killer cell activity. High intakes of some of these fatty acids are necessary to induce these effects. Among these fatty acids the long chain n-3 fatty acids, especially eicosapentaenoic acid, appear to be the most potent when included in the human diet. Although not all studies agree, it appears that fish oil, which contains eicosapentaenoic acid, down regulates the T-helper 1-type response which is associated with chronic inflammatory disease. There is evidence for beneficial effects of fish oil in such diseases; this evidence is strongest for rheumatoid arthritis. Since n-3 fatty acids also antagonise the production of inflammatory eicosanoid mediators from arachidonic acid, there is potential for benefit in asthma and related diseases. Recent evidence indicates that fish oil may be of benefit in some asthmatics but not others.

Dietary conjugated linoleic acid modulates phenotype and effector functions of porcine CD8(+) lymphocytes

In vivo vaccination and challenge studies have demonstrated that CD8(+) lymphocytes are essential for the development of cell-mediated protection against intracellular pathogens and neoplastic cells. Depletion of peripheral blood CD8(+) cells interferes with clearance of viruses and intracellular fungi, induction of delayed type hypersensitivity responses and antitumoral activity. In contrast to humans or mice, porcine peripheral CD8(+) lymphocytes are characterized by a heterogeneous expression pattern (i.e., CD8alphabeta and CD8alphaalpha) that facilitates the study of distinctive traits among minor CD8(+) cell subsets. A factorial (2 x 2) arrangement within a split-plot design, with 16 blocks of two littermate pigs as the experimental units for immunization treatment (i.e., unvaccinated or vaccinated with a proteinase-digested Brachyspira hyodysenteriae bacterin) and pig within block as the experimental unit for dietary treatment (soybean oil or conjugated linoleic acid) were used to investigate the phenotypic and functional regulation of CD8(+) cells by dietary conjugated linoleic acid (CLA). Dietary CLA supplementation induced in vivo expansion of porcine CD8(+) cells involving T-cell receptor (TCR)gammadeltaCD8alphaalpha T lymphocytes, CD3(-)CD16(+)CD8alphaalpha (a porcine natural killer cell subset), TCRalphabetaCD8alphabeta T lymphocytes and enhanced specific CD8(+)-mediated effector functions (e.g., granzyme activity). Expansion of peripheral blood TCRalphabetaCD8alphabeta cells was positively correlated (r = 0.89, P < 0.01) with increased percentages of CD8alphabeta(+) thymocytes. Functionally, CLA enhanced the cytotoxic potential of peripheral blood lymphocytes and proliferation of TCRgammadeltaCD8alphaalpha cells. Collectively, these results indicate that dietary CLA enhances cellular immunity by modulating phenotype and effector functions of CD8(+) cells involved in both adaptive and innate immunity.

Dietary docosahexaenoic acid suppresses inflammation and immunoresponses in contact hypersensitivity reaction in mice

This study was designed to examine the immunomodulatory effects of dietary docosahexaenoic acid (DHA) in the absence of eicosapentaenoic acid (EPA). We investigated the effects of feeding dietary DHA ethyl ester (DHA-Et) (97% pure) at levels of 4.8 wt% of the total diet and of feeding EPA ethyl ester (EPA-Et) (99% pure) at 4.8 wt% on the inflammatory response in the challenge phase of the contact hypersensitivity reaction (CHR) in the ears of mice sensitized with 2,4-dinitro-1-fluorobenzene (DNFB). The effect of DHA-Et on T lymphocytes at the CHR site was examined using anti-CD4 antibodies. Furthermore, we examined the cytokines formed at the CHR site on the mRNA level. It was found that 24 h after the challenge, DHA-Et but not EPA-Et reduced the ear swelling. Infiltration of inflammatory cells, in particular, CD4-positive T lymphocytes, into the ears in the challenge phase of CHR was observed. DHA-Et reduced the infiltration of CD4-positive T lymphocytes into the ears. DHA-Et also decreased the expression of interferon-gamma, interleukin (IL)-6, IL-1beta, and IL-2 mRNA in ears. These observations suggest that DHA, but not EPA, may exert an antiinflammatory and immunosuppressive effect. The immunosuppressive effectiveness of fish oil may be attributed mainly to DHA.

Nutritional aspects of immunosuppression in athletes

The literature suggests that a heavy schedule of training and competition leads to immunosuppression in athletes, placing them at a greater risk of opportunistic infection. There are many factors which influence exercise-induced immunosuppression, and nutrition undoubtedly plays a critical role. Misinterpretation of published data and misleading media reports have lead many athletes to adopt an unbalanced dietary regimen in the belief that it holds the key to improved performance. Some sports have strict weight categories, whilst in others low body fat levels are considered to be necessary for optimal performance or seen as an aesthetic advantage. This leads some athletes to consume a diet extremely low in carbohydrate content which, whilst causing rapid weight loss, may have undesirable results which include placing the athlete at risk from several nutrient deficiencies. Complete avoidance of foods high in animal fat reduces the intake of protein and several fat-soluble vitamins. On the other hand, diets with a very high carbohydrate content are usually achieved at the expense of protein. In addition, anecdotal and media reports have often promoted the supposed performance benefits of certain vitamins and minerals, yet most athletes do not realise that micronutrient supplementation is only beneficial when correcting a deficiency, and to date there is little scientific evidence to substantiate claims that micronutrients act as an ergogenic aid. Moreover, excessive intakes of micronutrients can be toxic. Deficiencies or excesses of various dietary components can have a substantial impact on immune function and may further exacerbate the immunosuppression associated with heavy training loads. This review examines the role of nutrition in exercise-induced immunosuppression and the effect of both excessive and insufficient nutrient intake on immunocompetence. As much of the present literature concerning nutrition and immune function is based on studies with sedentary participants, the need for future research which directly investigates the relationship between exercise, training, immunity and nutrition is highlighted.

Effect of age, breed and dietary omega-6 (n-6): omega-3 (n-3) fatty acid ratio on immune function, eicosanoid production, and lipid peroxidation in young and aged dogs

The focus of this study was to examine the influence of age and diet on various parameters of immune function in young and old Fox Terriers and Labrador Retrievers. Eighteen young and old dogs were utilized for this study. Young and old dogs were fed a basal diet containing an (n-6):(n-3) ratio of 25:1 for sixty days (Phase I). Half of the dogs were then switched to a diet with an (n-6):(n-3) ratio of 5:1, and all were maintained on their respective diets for an additional sixty days (Phase II). Results from these studies revealed an age-associated decline in several immune parameters measured. Both these breeds demonstrated a reduction in sheep red blood cell titers, as well as in their ability to respond to different mitogens. Interestingly, this decline was greater in Fox Terriers, suggesting a decrease in cellular proliferative capacity in lymphocytes isolated from the larger breed. Neither cytokine production or DTH response was affected by age. Diet and breed interactions resulted in a significant increase in T- and B-cell mitogen responsiveness. In contrast, supplementation with n-3 fatty acids did not affect IL-1, IL-6 or TNF-alpha production. Supplementation with n-3 fatty acids resulted in increased PGE3 production from peritoneal macrophages but had no effect on PGE2 production from peripheral blood mononuclear cells or peritoneal macrophages. The n-3 fatty acid supplementation did not influence alpha-tocopherol status although older dogs had significantly lower serum alpha-tocopherol concentrations. Oxidative status of these dogs was assessed by serum levels of malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE). Feeding an n-3-enriched diet did not affect 4-HNE levels but significantly decreased MDA levels in old dogs. In summary, this study indicates that feeding a diet containing an (n-6):(n-3) fatty acid ratio of 5:1 had a positive, rather than a negative, effect on the immune response of young or geriatric dogs.

Effect of dietary fat on lymphocyte proliferation and metabolism

The effect of diets enriched with fat containing different fatty acids on glucose and glutamine metabolism of mesenteric lymph nodes lymphocytes, spleen, and thymus and lymphocyte proliferation was examined. The following fat-rich diets were tested: (1) standard chow (CC); (2) medium chain saturated fatty acids (MS)--coconut fat oil; (3) long chain saturated fatty acids (LS)--cocoa butter; (4) monounsaturated fatty acids (MU)--canola oil (n-9); (5) polyunsaturated fatty acids (PU)--soybean oil (n-6). Of the fat-rich diets tested, MS was the one to present the least pronounced effect. Lymphocyte proliferation was reduced by LS (64 per cent), MU (55 per cent), and PU (60 per cent). Hexokinase activity was enhanced in lymph node lymphocytes by PU (67 per cent), in the spleen by MS (42 per cent), and in the thymus by PU (30 per cent). This enzyme activity was reduced in the spleen (33 per cent) by LS and MU (35 per cent). In the thymus, this enzyme activity was reduced by LS (26 per cent) and MU (13 per cent). Maximal phosphate-dependent glutaminase activity was raised in lymphocytes by MS (70 per cent) and MU (20 per cent). This enzyme activity, however, was decreased in lymphocytes by PU (26 per cent), in the spleen by LS (15 per cent), and in the thymus by MU (44 per cent). Citrate synthase activity was increased in lymphocytes by MU (35 per cent), in the spleen by LS (56 per cent) and MU (68 per cent), and in the thymus by LS (42 per cent). This enzyme activity was decreased in lymphocytes by PU (24 per cent) only. [U-14C]-Glucose decarboxylation was raised by all fat-rich diets; MS (88 per cent). LS (39 per cent), MU (33 per cent), and PU (50 per cent), whereas [U-14C]-glutamine decarboxylation was increased by LS (53 per cent) and MU (55 per cent) and decreased by MS (17 per cent). The results presented indicate that the reduction in lymphocyte proliferation due to LS, LU and PU could well be a consequence of changes in glucose and glutamine metabolism.

The triggering signal dictates the effect of docosahexaenoic acid on lymphocyte function in vitro

Docosahexaenoic acid (DHA) is an n-3 fatty acid beneficial to several human conditions including inflammation and autoimmune disease. To better understand the effect of DHA on immunity, we monitored the rise in cytosolic free calcium, interleukin 2 receptor (IL2R) expression, and proliferation of splenic lymphocytes triggered with three different stimuli in the presence or absence of DHA. We found that 10 microg DHA/mL suppressed concanavalin A-induced mitogenesis and the mixed lymphocyte reaction while concurrently enhancing proliferation stimulated with anti-Thy-1 antibodies. Proliferation, as measured by [3H]thymidine incorporation after 2 to 5 d of culture, was affected by DHA, but earlier activation effects such as elevation of cytosolic free calcium and IL2R expression were not altered. These results imply that DHA incorporated into membrane phospholipids differentially affects the activity of distinct membrane-bound receptors and signaling molecules. This result suggests that DHA may be used to modulate immune responses selectively, e.g., to suppress undesired autoimmunity while maintaining protective immunity.

Dietary fish oil appears to prevent the activation of phospholipase C-gamma in lymphocytes

Rats were fed on a low fat diet or on high fat diets which included coconut oil, olive oil, safflower oil, evening primrose oil or fish oil as the principal fat source. The level of phosphatidylinositol-4, 5-bisphosphate in spleen lymphocytes was unaffected by diet. However, the fish oil diet significantly decreased the concentration of inositol-1,4,5-trisphosphate in stimulated lymphocytes; this concentration was also reduced following olive oil feeding. Diet did not significantly affect the level of phospholipase C-gamma1 in spleen lymphocytes but the tyrosine phosphorylation state of this enzyme in stimulated lymphocytes, as well as that of a range of other proteins, was decreased following feeding the fish oil and, to a lesser extent, the olive oil diets. It is concluded that fish oil feeding appears to result in inhibition of one or more tyrosine kinases.

Eicosapentaenoic and docosahexaenoic acids alter rat spleen leukocyte fatty acid composition and prostaglandin E2 production but have different effects on lymphocyte functions and cell-mediated immunity

Weanling rats were fed on high-fat (178 g/kg) diets which contained 4.4 g alpha-linolenic (ALA), gamma-linolenic, arachidonic (ARA), eicosapentaenoic (EPA), or docosahexaenoic acid (DHA)/100 g total fatty acids. The proportions of all other fatty acids, apart from linoleic acid, and the proportion of total polyunsaturated fatty acids (PUFA) (approximately 35 g/100 g total fatty acids) were constant, and the n-6 to n-3 PUFA ratio was maintained as close to 7 as possible. The fatty acid compositions of the serum and of spleen leukocytes were markedly influenced by that of the diet. Prostaglandin E2 production was enhanced from leukocytes from rats fed the ARA-rich diet and was decreased from leukocytes from the EPA- or DHA-fed rats. Replacing dietary ALA with EPA resulted in diminished ex vivo lymphocyte proliferation and natural killer (NK) cell activity and a reduced cell-mediated immune response in vivo. In contrast, replacing ALA with DHA reduced ex vivo lymphocyte proliferation but did not affect ex vivo NK cell activity or the cell-mediated immune response in vivo. Replacement of a proportion of linoleic acid with either gamma-linolenic acid or ARA did not affect lymphocyte proliferation, NK cell activity, or the cell-mediated immune response. Thus, this study shows that different n-3 PUFA exert different immunomodulatory actions, that EPA exerts more widespread and/or stronger immunomodulatory effects than DHA, that a low level of EPA is sufficient to influence the immune response, and that the immunomodulatory effects of fish oil may be mainly due to EPA.

Spleen cell survival and proliferation are differentially altered by docosahexaenoic acid

Omega-3 fatty acids have diverse health benefits that are not clearly understood. In this study we have examined the effects of the omega-3 fatty acid docosahexaenoic acid (DHA) on mitogen-activated and resting splenic lymphocytes. DHA inhibited lymphocyte proliferation, producing an apparent block or prolongation of S phase, without evidence for direct cytotoxicity. In contrast, DHA enhanced the survival of resting lymphocytes in culture without inducing cell cycling. When DHA was added at the start of culture, the survival advantage was apparent for 2 to 3 days, after which time typical lymphocyte attrition occurred. Using flow cytometry we observed that both T and B cell recoveries were increased by DHA, but there were DHA dose-dependent alterations of forward- and side-scatter characteristics, with some preference for B cells, perhaps indicating altered membrane properties. Our data imply that DHA may check ongoing immune response while concurrently preserving resting lymphocytes needed for subsequent immune responses.

Effects of variations in the proportions of saturated, monounsaturated and polyunsaturated fatty acids in the rat diet on spleen lymphocyte functions

To obtain further information about the immunomodulatory effects of specific dietary fatty acids, weanling male rats were fed for 6 weeks on high-fat (178 g/kg) diets which differed according to the principal fatty acids present. The nine diets used differed in their contents of palmitic, oleic, linoleic and alpha-linolenic acids; as a result the total polyunsaturated fatty acid (PUFA) content and the PUFA:saturated fatty acid ratio varied (from 17.8 to 58.5 g/100 g fatty acids and from 0.28 to 5.56 respectively). The n-6 PUFA:n-3 PUFA ratio was kept constant in all diets at approximately 7.0. The fatty acid composition of the serum and of spleen lymphocytes were significantly influenced by that of the diet fed. The ex vivo proliferation of spleen lymphocytes decreased as the level of oleic acid in the diet increased. Spleen natural killer cell activity decreased as the oleic acid content of the diet increased and increased as the palmitic acid content of the diet increased. The extent of the effects of these fatty acids on lymphocyte functions was modified by the nature of the background fatty acid composition of the diet.

Effects of varying the type of saturated fatty acid in the rat diet upon serum lipid levels and spleen lymphocyte functions

To obtain further information about the effects of specific dietary saturated fatty acids, weanling male rats were fed for 6 weeks on low fat (7.7% by weight) or high fat (17.8% by weight) diets which differed according to the principal fatty acids present. The diets were rich in caprylic and capric acids (medium chain triacylglycerols; MCT), lauric acid, palmitic acid at the sn-1(3) position, palmitic acid at the sn-2 position or stearic acid. The total proportions of saturated (42-46%), monounsaturated (36%), n-6 polyunsaturated (15%) and n-3 polyunsaturated (2.2%) fatty acids were the same in all diets. Serum cholesterol concentrations were not different among rats fed the different diets, except that the concentration in the serum of rats fed the high fat diet with palmitic acid in the sn-2 position was high. This was reflected in higher HDL and LDL cholesterol concentrations in the serum of animals fed this diet. Triacylglycerol (TAG) concentrations tended to be higher in the serum of rats fed the low fat diets compared with those fed the high fat diets. They were lowest in the serum of MCT-fed rats irrespective of the level of fat in the diet and were highest in the serum of rats fed the low fat diet rich in stearic acid. These differences were due to lower chylomicron and VLDL TAG concentrations in the serum of MCT-fed rats and higher chylomicron and VLDL TAG concentrations in the serum of low fat, stearic acid-fed animals. The fatty acid compositions of the serum and of spleen lymphocytes were influenced by that of the diet fed. The ex vivo proliferation of lymphocytes from the spleens of rats fed the high fat diet rich in palmitic acid at the sn-2 position was greater than that of lymphocytes from animals fed the other diets. Natural killer (NK) cell activity tended to be lower for spleen lymphocytes from rats fed high fat diets than for those fed low fat diets irrespective of the principal saturated fatty acid present. NK cell activity was highest for spleen lymphocytes from animals fed the diets rich in palmitic acid and was lowest for those from animals fed the high fat diet rich in stearic acid. Spleen lymphocytes from the latter animals had the lowest proportion of CD16+ cells, a marker for NK cells. Thus, this study shows that the type of saturated fatty acid present in the diet not only has subtle effects upon blood lipid and lipoprotein levels but can significantly affect lymphocyte functions. Spleen lymphocyte NK cell activity is decreased as the fat content of the diet increases. NK cell number and activity are reduced by a high fat diet rich in stearic acid. Spleen lymphocyte proliferation is enhanced by palmitic acid-rich diets, particularly if palmitic acid is in the sn-2 position of dietary TAG.