The role of lipids in the regulation of the immune system

Lipid-Enriched Parenteral Nutrition and Bloodstream Infections in Hospitalized Patients: Is It a Real Concern?

Today, few clinicians are still convinced that lipids are sepsis risk factors in patients receiving parenteral nutrition. This dogma is principally based on old literature. This review deals with the most recent literature search that provided up-to-date data over the past ten years. Systematic research was performed on Pubmed, MEDLINE, and Web of Science. The recent evidence does not justify the exclusion of lipid emulsions in patients receiving parenteral nutrition for fear of bloodstream infection risk. Moreover, lipids represent a substantial proportion of the energy source providing essential fatty acids, potentially improving clinical outcomes in patients often malnourished. Understanding the actual risk factors of sepsis during parenteral nutrition is necessary to optimize patient nutritional status and care and avoid essential fatty acid deficiency. There is an urgent need to make updated nutrition training available at all levels of medical education.

Replacement of dietary fish oil with plant oils improves the immunological responses and the antioxidant status in Oreochromis niloticus exposed to suboptimal temperature

Here, we investigated the effects of total dietary fish oil (FO) substitution with plant oil (PO) on hematological indices, immune status, antioxidant activity, IL1β and TNF-α gene expression, and hypoxia stress resistance in Oreochromis niloticus at suboptimal temperatures. Fish (n = 360) were randomly divided into 12 circular fiberglass tanks (500 L; 3 replicates for each dietary group, 30 fish/replicate, 90 fish/group). The control group was fed a basal diet with FO as the lipid source. The CO, SFO, and LSO groups were fed a basal diet with complete replacement of FO with corn, sunflower, and linseed oils, respectively. After 4 weeks, no effects on hematological indices were observed in fish fed the experimental diets. The LSO and CO groups showed a significant increase in γ globulin levels. The highest levels of non-specific immune parameters, antioxidant activity, and IL-1β and TNF-α gene expressions were recorded in the LSO group. The LSO group also exhibited good resistance to hypoxia stress. Therefore, the total dietary substitution of FO with PO (especially LSO and CO) is recommended as a valuable strategy to ameliorate the immunosuppressive effects of suboptimal temperatures and enhance the resistance of O. niloticus to hypoxia stress.

Parasites of skipjack, Katsuwonus pelamis, from Madeira, Eastern Atlantic

Skipjack tuna, Katsuwonus pelamis, is a tropical species of economic importance for fisheries around the world. It occurs seasonally in subtropical waters around Madeira archipelago, in the warmer months. In this study, a parasitological analysis was carried out on a sample of 30 skipjack caught near Madeira Island. A total of 24 parasite taxa were found in this sample. The skipjack parasite community detected was characterized by a wide diversity of parasites, with a predominance of adult didymozoid trematodes, and high prevalences of Tentacularia coryphaenae cestode larvae and Anisakis sp. larvae. Microhabitat distribution of gill parasites was assessed for the most prevalent species, and correlations between parasite abundance and various host features such as size, condition, and fat content were investigated. Parasite taxa which might be useful as biological tags in future studies of skipjack migrations in the Eastern Atlantic were selected.

Altered or Impaired Immune Response to Hepatitis B Vaccine in WNIN/GR-Ob Rat: An Obese Rat Model with Impaired Glucose Tolerance

Obesity is shown to increase the incidence and severity of infectious diseases and individuals seem to exhibit poor antibody response to vaccination due to several inherent immune defects. With the increasing prevalence of impaired glucose tolerance (IGT) seen in obese individuals, the present study was aimed to investigate the basal immune response and immune response upon Hepatitis B vaccination (HBV) in an obese rat model WNIN/GR-Ob with impaired glucose tolerance (IGT). Decreased proportions of splenic CD4⁺ T helper cells and CD3⁺ T cells were observed in obese animals compared to lean animals. Upon HBV, obese animals showed reduced cell-mediated immunity and humoral immunity in terms of splenic lymphocyte proliferative response to Concanavalin A (Con A) and Hepatitis B surface antigen (HBsAg) and HBsAg-specific IgG response. Innate immunity as assessed in terms of Tumor Necrosis Factor α (TNF α) and Nitric oxide (NO) production by peritoneal macrophages upon HBV was low and unchanged, respectively, in obese animals. Thus long-term immunological memory is impaired or altered upon HBV.

Altered or impaired immune response upon vaccination in WNIN/Ob rats

The present study was aimed to study the immune response in three months old male and female naïve obese animals and upon hepatitis B vaccination in three months old female WNIN/Ob obese mutant rats, established at our institute in comparison with its lean litter mates. Altered immune profile was seen in naïve obese mutant rats in terms of percentage of splenic CD8(+) cytotoxic cells in males and percentages of splenic CD3(+) T lymphocytes and CD4(+) T helper cells in females respectively. Furthermore these obese mutant rats also exhibited impaired immune response to hepatitis B vaccine with low specific Hepatitis B surface antigen (HBsAg) specific IgG response and splenic lymphocyte proliferative response to HBsAg compared to the lean counterpart. The loss of immunological memory following vaccination could be attributed to the metabolic and hormonal changes associated with obesity. This observation has implication in public health policies related to vaccination in developed as well as developing countries.

Immunomodulatory effects of eicosapentaenoic acid through induction of regulatory T cells

Dietary intake of omega-3 polyunsaturated fatty acids (PUFAs) has been found to affect inflammation and metabolism, and many researchers have shown that omega-3 PUFAs provide benefits in immunologic and metabolic disorders. These effects were assumed to result mainly from a modification in the production of inflammatory mediators and the suppression of inflammatory leukocytes. Among PUFAs, eicosapentaenoic acid (EPA), a component of fish oil, apparently has the most potent effect. Recently, much research has focused on regulatory T cells (Tregs) as controllers of immune responses not only to self-antigens but also to non-self-antigens, including donor alloantigens. Therefore, induction of antigen-specific Tregs may be an attractive strategy for managing autoimmune diseases and transplant rejection. Peroxisome proliferator-activated receptor γ (PPARγ), a ligand-activated nuclear receptor that regulates lipid and glucose metabolism, can be activated by thiazolidinediones, fatty acids, and eicosanoids, including EPA. PPARγ was recently found to have immunoregulatory effects, and a PPARγ agonist inhibited immune responses in a rat model of autoimmune disease. Furthermore, in a murine model, one high dose of purified EPA given the day of transplantation induced marked prolongation of cardiac allograft survival in a dose-dependent manner. These findings suggest that EPA induced Tregs by means of a PPARγ-dependent mechanism. This review describes the immunomodulatory effects of PUFAs, especially EPA, and summarizes recent research that may have implications for the development of therapies for autoimmune diseases and transplant rejection that are based on induction of Tregs.

Butter feeding enhances TNF-alpha production from macrophages and lymphocyte adherence in murine small intestinal microvessels

BACKGROUND AND AIM

Dietary fat is known to modulate immune functions. Intake of an animal fat-rich diet has been linked to increased risk of inflammation; however, little is known about how animal fat ingestion directly affects intestinal immune function. The objective of this study was to assess the effect of butter feeding on lymphocyte migration in intestinal mucosa and the changes in adhesion molecules and cytokines involved in this effect.

METHODS

T-lymphocytes isolated from the spleen were fluorescence-labeled and injected into recipient mice. Butter was administered into the duodenum, and villus microvessels of the small intestinal mucosa were observed under an intravital microscope. mRNA expression of adhesion molecules and cytokines in the intestinal mucosa were determined by quantitative PCR. The effect of butter feeding on tumor necrosis factor (TNF)-alpha mRNA expression of intestinal macrophages was also determined.

RESULTS

Intraluminal butter administration significantly increased lymphocyte adherence to intestinal microvessels accompanied by increases in expression levels of adhesion molecules ICAM-1, MAdCAM-1 and VCAM-1. This accumulation was significantly attenuated by anti-MAdCAM-1 and anti-ICAM-1 antibodies. Butter administration significantly increased TNF-alpha in the lamina proprial macrophages but not interleukin-6. Anti-TNF-alpha treatment attenuated the enhanced expression of adhesion molecules induced by butter administration.

CONCLUSION

T-lymphocyte adherence to microvessels of the small intestinal mucosa was significantly enhanced after butter ingestion. This enhancement is due to increase in expression levels of adhesion molecules of the intestinal mucosa, which is mediated by TNF-alpha from macrophages in the intestinal lamina propria.

Beneficial effect of enteral feeding

The last 4 decades have seen an explosion in nutritional research investigating both clinical and laboratory issues occurring in diverse groups of patients who cannot maintain a normal oral diet. Over the past 25 years, researchers have investigated how the administration of macro- and micronutrients via the gastrointestinal tract provides additional benefit over parenteral administration of similar nutrients. The administration of enteral feeding provides effects that are far beyond those of merely administering macro- and micronutrients. Rather, the processing of nutrients via the gastrointestinal tract stimulates a complex response that has implications for body composition and for immunologic integrity. Route and type of nutrition are important aspects of successful patient recovery.

The comparative roles of polyunsaturated fatty acids in pig neonatal development

The present review focuses on the importance of polyunsaturated fatty acid (PUFA) provision for the normal development of the pig neonate. The review describes first the selected fatty acid composition of a range of porcine tissues including nervous tissues, muscle and adipose tissues, reproductive organs and immune-responsive organs and/or cells. The importance of PUFA to the functioning of the immune system of the neonate is considered briefly and is followed by an in-depth consideration of the sources of PUFA for the neonatal pig. The effects of different categories or specific types of fatty acid (i.e. non-essential, linoleic, α-linolenic, long-chain n-6 and n-3 PUFA) on various indices of pig neonatal growth are reviewed. The importance of n-3 PUFA supply to the fetal and early neonatal pig is underlined and evidence is presented for more attention to be given to the amounts available from maternal sources. Based on the material reviewed, recommendations are made on the dietary intake of PUFA in the gestating pig.

Immunonutrition in surgery and critical care

The benefits of specialty supplemented enteral diets administered to critically ill and critically injured patients and those undergoing major surgical procedures have been documented in a number of randomized prospective studies. It is unclear which nutrient or combination of nutrients causes the beneficial effects, but there are significant reductions in infectious complications depending upon the patient populations studied. It is imperative that the data be interpreted in the context of individual patient risk since specialty formulas appear most beneficial in patients at risk of subsequent complications or in those with significant pre-existing malnutrition. Although controversy exists regarding the use of specialty supplemented enteral diets in critically ill patients, they have been administered safely with minimal risk of adverse outcome in malnourished patients and in the critically ill and critically injured.

Effects on functions of ovine blood mononuclear cells for each of several fatty acids at concentrations found in plasma of healthy and ketotic ewes

OBJECTIVE

To assess effects on functions of peripheral blood mononuclear cells (PBMC) obtained from ewes for each of several fatty acids represented in ovine plasma at concentrations mimicking those of ketotic or healthy ewes.

SAMPLE POPULATION

Blood samples obtained from 6 Sardinian ewes.

PROCEDURE

The PBMC were cultured in media that contained oleic (OA), palmitic (PA), stearic (SA), linoleic (LA), or palmitoleic (POA) acid at concentrations similar to those of ketotic or healthy ewes. Synthesis of DNA was stimulated by use of concanavalin A or pokeweed mitogen (PWM). Secretion of IgM was stimulated by use of PWM.

RESULTS

High concentrations (900, 450, and 225 micromol/L) of OA significantly inhibited DNA synthesis and IgM secretion of PBMC. Conversely, low concentrations (56 or 28 micromol/L) of OA significantly enhanced DNA synthesis of PBMC. High concentrations of PA (600, 300, 150, 75, 375, or 18.7 micromol/L) and SA (300, 150, or 75 micromol/L) significantly inhibited DNA synthesis of PBMC. High concentrations of PA (600, 300, 150, 75, 375, or 18.7 micromol/L) and SA (300, 150, 75, or 38 micromol/L) also significantly inhibited IgM secretion of PBMC. None of the concentrations of LA and POA affected PBMC functions.

CONCLUSION AND CLINICAL RELEVANCE

Impaired immunoresponsiveness of ketotic ewes is likely associated with an increase of plasma concentrations of OA, PA, or SA and not with that of LA or POA. At physiologic concentrations, single fatty acids are likely to participate in modulation of immunoresponsiveness by exerting suppressive or stimulatory effects on immune cells.

Fatty acids enhance GRO/CINC-1 and interleukin-6 production in rat intestinal epithelial cells

Intestinal mucosal immunity is modulated by cytokine release from intestinal cells, but little is known about the relation between nutrient absorption and cytokine release. In this study, we examined how exposure to fatty acids affects the production of growth-regulated oncogene/cytokine-induced neutrophil chemoattractant-1 (GRO/CINC-1) and interleukin (IL)-6 in rat intestinal epithelial cells (IEC). The long-chain fatty acids, oleic, linoleic and arachidonic acids, and the middle-chain fatty acid octanoic acid were administered to subconfluent cultures of IEC-6 cells alone, or in combination with IL-1beta and transforming growth factor (TGF)-beta. The GRO/CINC-1 and IL-6 concentrations in culture media were determined by sandwich enzyme immunoassay. In epithelial cells, GRO/CINC-1 and IL-6 mRNA expression were examined by reverse transcriptase-polymerase chain reaction (RT-PCR) and mitogen-activated protein kinase (MAPK) activities determined by immunoblotting. Administration of long-chain fatty acids significantly increased the GRO/CINC-1 and IL-6 secretion into culture media, and this secretion was markedly increased (P < 0.05) in the presence of IL-1beta or TGF-beta. Octanoic acid had no effect on GRO/CINC-1 or IL-6 production. Furthermore, treatment with long-chain fatty acids significantly enhanced the GRO/CINC-1 and IL-6 expression that was induced by IL-1beta or TGF-beta. MAPK activity was significantly enhanced by treatment with long-chain fatty acids. Inhibitors of phospholipase C, protein kinase C or MAPK significantly reduced the fatty acid-induced increase in GRO/CINC-1 secretion, whereas a calcium/calmodulin inhibitor did not attenuate the secretion. These results suggest that long-chain fatty acids enhance cytokine release under conditions of inflammatory stimulation in the intestinal mucosa.

Low levels of eicosapentaenoic and docosahexaenoic acids mimic the effects of fish oil upon rat lymphocytes

Fish oil is rich in the long chain n-3 polyunsaturated fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA); typically these fatty acids constitute 20 to 25 g/100 g total fatty acids in fish oil. Feeding rodents diets rich in fish oil has been shown to decrease lymphocyte proliferation and natural killer cell activity. It is not known what level of EPA + DHA is required in the diet to exert these effects. This question was addressed in the current study. Weanling rats were fed on high fat (178 g/kg) diets which contained 4.4 g alpha-linolenic acid (control) or 4.4 g EPA + DHA (4.4 EPA + DHA) or 6.6 g EPA + DHA (6.6 EPA + DHA)/100 g total fatty acids. The n-6 to n-3 polyunsaturated fatty acid ratio was maintained at approximately 7. The fatty acid compositions of the serum and of spleen leukocytes were markedly influenced by that of the diet. Spleen lymphocyte proliferation in response to concanavalin A, spleen natural killer cell activity and PGE2 production by spleen leukocytes were reduced by feeding the EPA + DHA diets compared with feeding the control diet; the 4.4 and 6.6 EPA + DHA diets caused very similar reductions. The 4.4 EPA + DHA diet reduced popliteal lymph node weight following a localised graft versus host response; this response was not investigated in rats fed the 6.6 EPA + DHA diet. The reductions in lymphocyte functions and in the in vivo graft versus host response caused by the EPA + DHA diets were similar to those previously reported following the feeding of diets rich in fish oil. Thus, this study shows that diets containing relatively low levels of EPA + DHA (20 to 25% of the level found in fish oil) exert immunomodulatory effects. Furthermore, this study suggests that the maximal effect of EPA + DHA is exerted when these fatty acids constitute a level of less than or equal to 4.4 g/100 g total dietary fatty acids.

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.

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.

Exercise training restores decreased cellular immune functions in obese Zucker rats

This study investigated whether exercise training had a beneficial effect on the decreased mitogen response and improved a decreased expression of glucose transporter 1 (GLUT-1) in splenocytes from obese Zucker rats. Experimental groups were lean and sedentary and exercise-trained obese Zucker rats. Exercise training, running on a motor-driven treadmill for 5 days/wk for 40 wk, did not induce a significant decrease in body weight in obese Zucker rats. The plasma insulin concentration, showing a significant increase compared with lean Zucker rats, was unaffected by exercise training. However, the plasma triglyceride concentration in obese Zucker rats was significantly depressed by exercise training, whereas it was still higher than that in lean Zucker rats. In addition, natural killer cell activity and concanavalin A-induced mitogenesis of splenic lymphocytes of obese Zucker rats were significantly restored. In these splenic lymphocytes, glucose uptake was significantly lower compared with that in lean Zucker rats, which was also improved by exercise training. Although the expression of GLUT-1, the major glucose transporter in immune cells, was depressed in splenic lymphocytes of obese Zucker rats, exercise training induced a significant improvement. These results suggest that exercise training has a beneficial effect on the decreased cellular immune functions in obese Zucker rats, which is associated, in part, with the improvement in GLUT-1 expression.

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.

Effect of dietary fatty acids on humoral immune response of turkeys

1. This study examined the effect of increasing amounts of dietary polyunsaturated fatty acids on the fatty acid composition in serum and antibody production following a standard vaccination programme in growing turkeys. Turkey poults were fed on 5 diets containing 75g/kg added fat made up of different proportions of palm and soyabean oils, and were vaccinated against Newcastle disease, infectious bronchitis and necrotic enteritis according to a standard vaccination programme. Blood samples were taken before and one week after each vaccination. 2. Fatty acid composition in serum reflected the composition of the diets although arachidonic acid concentration was not changed by dietary fatty acid content. Growth, erythrocyte and leukocyte parameters were not affected by the respective diets. 3. Specific antibody production was related quadratically to serum linoleic and total n-6 polyunsaturated fatty acid concentrations. No correlation was found with linolenic or arachidonic acids. 4. It is concluded that dietary fatty acid composition can augment the specific anti-vaccine immune response in turkey poults.

Dietary unsaturated fatty acids affect antibody responses and growth of chickens divergently selected for humoral responses to sheep red blood cells

The effect of linoleic and linolenic acid on antibody (Ab) responses to SRBC and BSA and on growth performance were studied in pullets of three genetically different laying lines. Pullets were fed one of three diets: a control diet, a linoleic acid-enriched diet, or a linolenic acid enriched-diet. The linoleic and linolenic acid enriched-diets were the control diet enriched with either sunflower oil or linseed oil. Two chicken lines divergently selected for high (H) and low (L) Ab responses to SRBC, and a randombred control (C) line were used. Total Ab responses to SRBC were not affected by diet, but in the H line a tendency for higher IgG titers to SRBC after primary immunization were found when birds were fed the linoleic diet. The humoral response to BSA was significantly affected by a line by immunization by diet interaction. In the H line birds, the linoleic diet significantly enhanced Ab titers to BSA as compared to the normal diet and linolenic acid-enriched diet. The linolenic acid-enriched diet significantly decreased Ab titers to BSA in the C line birds. No dietary effects on the titer to BSA were found in the L line birds. During the first 3 wk of life, the linolenic acid-enriched diet resulted in reduced BW gain of H line birds. After that period, no effects of diet on BW gain was found. It is concluded that modulation of Ab responses of poultry to T cell-dependent antigens by essential fatty acids is affected by genotype. The relationship between magnitude of Ab responsiveness, BW, and essential fatty acids is discussed.

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.

A randomized trial of isonitrogenous enteral diets after severe trauma. An immune-enhancing diet reduces septic complications

OBJECTIVE

The authors randomized patients to an enteral diet containing glutamine, arginine, omega-3 fatty acids, and nucleotides or to an isonitrogenous, isocaloric diet to investigate the effect of septic outcome. A third group of patients, without enteral access but eligible by severity of injury, served as unfed controls and were studied prospectively to determine the risk of infection.

SUMMARY BACKGROUND DATA

Laboratory and clinical studies suggest that diets containing specialty nutrients, such as arginine, glutamine, nucleotides, and omega-3 fatty acids, reduce septic complications. Unfortunately, most clinical trials have not compared these diets versus isonitrogenous, isocaloric controls. This prospective, blinded study randomized 35 severely injured patients with an Abdominal Trauma Index > or = 25 or a Injury Severity Score > or = 21 who had early enteral access to an immune-enhancing diet ([IED] Immun-Aid, McGaw, Inc., Irvine, CA; n = 17) or an isonitrogenous, isocaloric diet (Promote [Ross Laboratories, Columbus, OH] and Casec [Mead-Johnson Nutritionals, Evansville, IN]; n = 18) diet. Patients without early enteral access but eligible by severity of injury served as contemporaneous controls (n = 19). Patients were evaluated for septic complications, antibiotic usage, hospital and intensive care unit (ICU) stay, and hospital costs.

RESULTS

Two patients died in the treatment group and were dropped from the study. Significantly fewer major infectious complications (6%) developed in patients randomized to the IED than patients in the isonitrogenous group (41%, p = 0.02) or the control group (58%, p = 0.002). Hospital stay, therapeutic antibiotics, and the development of intra-abdominal abscess was significantly lower in patients receiving the IED than the other two groups. This improved clinical outcome was reflected in reduced hospital costs.

CONCLUSIONS

An IED significantly reduces major infectious complications in severely injured patients compared with those receiving isonitrogenous diet or no early enteral nutrition. An IED is the preferred diet for early enteral feeding after severe blunt and penetrating trauma in patients at risk of subsequent septic complications. Unfed patients have the highest complication rate.

Reversal of altered intestinal mucosal immunity in rats fed elemental diet by supplementation of oleic acid

We have previously demonstrated that elemental diet (ED) induces decreased lymphocyte transport in intestinal lymph and significant changes in T cell subsets and the number of IgA-containing cells in gut-associated lymphoid tissues of rats. In order to examine whether the low fat content contributes to the induction of immunological changes in gut-associated lymphoid tissues, the effects of additional fatty acid in the ED were investigated. Rats were divided into four groups: elemental diet alone, elemental diet supplemented with 5% oleic acid (OA), elemental diet with 10% OA and conventional diet as a control. These diets were given at the same daily calorie intake for 4 weeks. The flow rate of intestinal lymph showed no significant difference between the four groups. However, lymphocyte flux as well as the percentage of CD3+ and CD4+ cells were significantly greater in the control and the 10% OA groups than in the ED and 5% OA groups. Intestinal lymph showed decreased concentrations of IgG and IgA in the ED group, whereas the addition of 10% OA significantly attenuated the decrease in these levels. In mesenteric lymph nodes, the CD4+/CD8+ ratio was significantly decreased in the ED group, but 10% OA reversed this change. Immunohistochemical analysis of the ileal mucosa showed that in the ED group the population of CD4+ cells was decreased, while the number of CD8+ cells was increased. Supplementation of OA to ED produced similar stepwise attenuation of the changes in lymphocyte subpopulations in the lamina propria, while the 10% OA group reached levels that were not statistically different from controls. In the elemental diet group, there was a significant decrease in immunoglobulin-containing cells of the IgA class in the lamina propria of the intestine. Similarly, the addition of OA induced dose-dependent recovery in the number of IgA-containing cells. These results suggest that a low dietary concentration of fat may be closely related to changes in lymphocyte transport in intestinal lymph and mucosal immunity of intestinal mucosa induced by the feeding of a long-term ED.

Nutrition and the immune system

Malnutrition frequently contributes to the immunocompromise seen in hospitalized patients. Nutritional support corrects malnutrition and can reverse the associated immunocompromise. Developing an understanding of nutritional needs and the role of nutrition in immune function is essential to prevention and treatment of nutrition-related immunocompromise. Current research is defining the role of specific nutrients in immune function. Recent evidence also suggests that the route (enteral versus parenteral) of providing nutritional support can affect immune competence. Intervention trials may show a role of key nutrients in not only maintaining normal immune competence, but also in modulating immunologic outcomes in critically ill patients.

Selective suppression of endothelial cell activation by arachidonic acid

Endothelial cell (EC) activation plays a key role in inflammation, thrombosis and organ rejection. Normally, EC are in a quiescent state in which their function is to prevent coagulation and thrombosis, and to participate in the regulation of leukocyte migration from the bloodstream into the tissue. Upon activation with cytokines or other stimuli, EC up-regulate a number of genes, including E-selectin (ELAM-1), intercellular adhesion molecule (ICAM)-1, vascular cell adhesion molecule (VCAM)-1, interleukin (IL)-1, IL-8, tissue factor (TF), plasminogen activator inhibitor-1 (PAI-1), MCP-1 (monocyte chemoattractant protein-1) and endothelial cell inducible gene (ECI-6). Arachidonic acid (AA) is produced by several cell types, including EC, and acts on various cells. We report here that AA inhibits the up-regulation of some, but not all genes that are induced with EC activation in a dose-dependent manner. AA suppresses TNF-alpha, IL-1 alpha, LPS or PMA-induced E-selectin expression, as well as mRNA accumulation of E-selectin, ICAM-1 and IL-8 stimulated by TNF-alpha. The inhibition appears to be at the level of transcription. At the same time under the same conditions AA does not, repress mRNA accumulation for PAI-1, ECI-6, MCP-1 and VCAM-1. We suggest that the induced expression of AA with EC activation may result in a negative feedback loop regulating further activation.

Effect of dietary fatty acids on antibody production and fatty acid composition of lymphoid organs in broiler chicks

This study examined the effect of increasing amounts of dietary polyunsaturated fatty acids on antibody production in vivo and fatty acid composition of plasma and lymphoid tissues in the broiler. Chicks were fed four diets containing 12% added fat made up of different proportions of palm oil and soybean oil and immunized against bovine serum albumin at 14 to 16 d of age. Blood samples were taken every 4 to 5 d for 30 d; then the chicks were killed and liver, spleen, thymus, bursa of Fabricius, and bone marrow were sampled. Fatty acid composition in serum and tissues reflected the composition of the diets, although amounts of saturated fatty acids were tissue-specific. Arachidonic acid concentration was not changed by dietary fatty acid content. Antibody production developed more rapidly, reached a higher level, and was more persistent in the chicks fed lower levels of linoleic acid. A quadratic relationship was found between tissue linoleic acid or total polyunsaturated fatty acid concentrations and antibody production at 11 and 14 d after challenge. No correlation was found with arachidonic acid. It is concluded that dietary fatty acid composition can influence immune response in broilers.

Fish oil, lipid peroxidation and mammary tumor growth

There is evidence that the level and especially the type of dietary fat can be an important determinant of mammary tumor development and growth. Diets containing high levels of fish oil have been shown to inhibit or suppress mammary tumor growth. Various mechanisms have been proposed to explain this modulatory activity of dietary fish oil or fats in general on tumor growth; of special interest is lipid peroxidation. The oxidation of long chain polyunsaturated fatty acids present in fish oil, such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) can produce an array of secondary products of lipid oxidation that may possess a cytostatic or cytolytic capacity.

Clostridium difficile infection in hamsters fed an atherogenic diet

Diarrhea and unexpected death were encountered in a group of young Syrian hamsters (Mesocricetus auratus) used for hyperlipoproteinemia and atherosclerosis research. The animals were fed an atherogenic diet containing 18% saturated fat and 0.366% cholesterol. Mortality began 45 days after hamsters were placed on this atherogenic diet. The atherogenic studies were aborted at 74 days because of high mortality. Toxigenic Clostridium difficile was isolated from animals found dead or euthanatized because of illness. Signs observed were unexpected death and acute liquid diarrhea. Characteristic pathologic changes were necrosis and hemorrhage of the intestinal mucosa with acute inflammation. Hepatic lipidosis was a consistent finding presumed to be associated with the consumption of the atherogenic diet. The study was repeated by placing 23 hamsters on the atherogenic diet and 10 hamsters on the control diet. In animals fed the atherogenic diet, the average time to mortality differed between studies, but clinical signs, gross and histologic lesions, culture findings, and toxin results in both atherogenic diet groups were similar. C. difficile was not isolated from the feeds. No antibiotics were found in the atherogenic diet. The results from these studies suggest that hamsters fed an atherogenic diet have increased susceptibility to disease caused by C. difficile as compared with hamsters fed a normal fat and cholesterol diet.

Effect of essential fatty acids on circulating T cell subsets in patients with colorectal cancer

The effect of essential fatty acids (EFA), given orally as dietary supplements, on the responsiveness in vitro of peripheral blood lymphocytes (PBL), to the mitogen concanavalin A have been studied in 10 patients with localized and 14 patients with advanced colorectal cancer. The degree of lymphocyte activation was assessed by measuring the amount of tritiated [3H]thymidine incorporated into newly synthesised lymphocyte DNA. The results were expressed as stimulation indices. T cell responses to concanavalin A stimulation showed a significant reduction of stimulation indices following EFA supplementation, in both the localized (P = 0.026) and advanced (P = 0.016) tumour groups, when compared with pretreatment activity in vitro. Mixing experiments, using EFA-supplemented and non-EFA-supplemented lymphocytes with concanavalin A, suggest no enhancement of T suppressor cell activity. Cell surface marker analysis (fluorescence-activated cell sorting for CD phenotyping) revealed a reduction of absolute numbers of CD4+ and CD8+ lymphocytes following EFA supplementation. The stimulation indices returned to pre-supplementation values 3 months following cessation of EFA intake. There was no significant change of these indices in the control (no EFA supplementation) advanced tumour group tested. This study suggests that EFA supplementation in patients with colorectal cancer selectively reduces circulating PBL, and T cell subset (including suppressor cells) numbers and/or activity. Such effects may have an important outcome in patients with malignant disease.

Cytokine production and DNA synthesis by human peripheral lymphocytes in response to palmitic, stearic, oleic, and linoleic acid

Effects of palmitic, stearic, oleic, and linoleic acid on mitogen-induced DNA synthesis, on production of IL-1 beta, IL-2, IFN-gamma, and TNF-alpha, and on IL-2R expression were determined in human peripheral lymphocytes. Free fatty acids (FFA) were added over a wide range of concentrations to cells cultured under serum free conditions with fatty acid free albumin. DNA synthesis was stimulated by low and inhibited by high FFA concentrations. Physiological concentrations were stimulatory, except for linoleic acid. Cytokine production became affected by all FFA tested. Palmitic acid enhanced the release of IFN-gamma at concentrations that diminished TNF-alpha production. Saturated fatty acids were significantly more potent than unsaturated fatty acids in affecting cytokine production. IFN-gamma secretion was significantly more stimulated or inhibited by the various FFA compared with the other cytokines. IL-2R expression correlated with the production of IL-2. When tested in combination, stimulatory as well as inhibitory effects of the individual FFA became attenuated. It is suggested that palmitic, stearic, oleic, and linoleic acid are physiological regulators of DNA synthesis and cytokine release in human peripheral lymphocytes. Modulation of FFA ratios may be an effective means for the fine tuning of the immune system. As secretory mechanisms of cytokines appear to exhibit substrate specificity for FFA, the release of individual cytokines may be selectively influenced by FFA.

Influence of dietary (n-3)-polyunsaturated fatty acids on leukotriene B4 and prostaglandin E2 synthesis and course of experimental tuberculosis in guinea pigs

In the present study eicosanoid synthesis was studied in macrophages of guinea pigs fed different amounts of (n-6)- and (n-3)-polyunsaturated fatty acids (PUFA). Three groups of weanling guinea pigs were fed by isocaloric diets differing only in their contents of PUFA: controls with 2.8 Cal% of linoleic acid (LA; 18:2(n-6)); (n-6)-rich fed animals with 15.4 Cal% of LA; and (n-3)-rich fed animals with 10.1 Cal% of LA, 1.4 Cal% of eicosapentaenoic acid (20:5(n-3)) and docosahexaenoic acid (22:6(n-3)). After 13 weeks half the number of animals from each group was infected i.m. by 180 colony forming units of Mycobacterium tuberculosis strain H37Rv. Seven weeks after infection the release of leukotriene (LT)B4 and prostaglandin (PG)E2 was quantified in calcium ionophore stimulated whole blood, peritoneal macrophage cultures and alveolar macrophages by immunoassays after high performance liquid chromatography. Synthesis of LTB4 and PGE2 was found to be reduced in (n-3)-rich fed guinea pigs (p < 0.05), and equivalent between controls and (n-6)-rich fed animals. Controls and (n-6)-rich fed animals showed the same mycobacterial counts in the spleen whereas (n-3)-rich fed guinea pigs demonstrated an increased number of mycobacteria (p < 0.05). Our results demonstrate that an increased dietary intake of (n-3)-PUFA suppress LTB4 and PGE2 synthesis. The increased number of M. tuberculosis found in the spleens of (n-3)-rich fed animals could represent persistence of the experimental infection. It may be speculated that a functional relationship exists between the two findings.

Inhibition of the thermogenic and pyrogenic responses to interleukin-1 beta in the rat by dietary N-3 fatty acid supplementation

The thermogenic (increase in oxygen consumption, VO2) and pyrogenic (Tc) responses to the cytokine interleukin-1 beta (IL-1 beta) were studied in rats fed a n-3 fatty acid supplemented diet (8.75% n-3 fatty acids/kg diet). 4-6 weeks after commencing the diets, the n-3 supplemented rats exhibited reduced pyrogenic (0.5 +/- 0.1 degrees C versus 1.1 +/- 0.2 degrees C in control animals) and thermogenic (9 +/- 3% versus 22 +/- 6% in control animals) responses to intraperitoneal (i.p.) injection of IL-1 beta (1 micrograms/rat). However, responses to centrally administered IL-1 beta (5ng intracerebroventricular (i.c.v.)) were similar in both groups at this time. After 8-9 weeks of supplementation, n-3 supplemented animals exhibited attenuated responses to both ip IL-1 beta (VO2 responses reduced by 68% and Tc by 0.8 degrees C) and also i.c.v. IL-1 beta (VO2 responses reduced by 56% and Tc by 0.7 degrees C). N-3 supplementation did not, however, influence the thermogenic capacity of these animals since responses to noradrenaline were similar in control and n-3 fed animals (50% increase in VO2). These findings demonstrate that n-3 supplementation modifies the pyrogenic and thermogenic responses to IL-1 beta, probably via changes in eicosanoid metabolism. Modification of central responses to IL-1 are delayed compared to the effects of peripheral administration indicating separate mechanisms of IL-1 on fever and thermogenesis in the brain and the periphery.

The esterified plasma fatty acid profile is altered in early HIV-1 infection

Previous studies have shown that alterations in micronutrient utilization occur in patients with Acquired Immune Deficiency Syndrome. In this study, total plasma fatty acid composition was measured in 36 homosexual men infected with the Human Immunodeficiency Virus 1 (HIV-1) and in 17 HIV-1 seronegative homosexual men in order to evaluate differences associated with early HIV-1 infection. Immunologic assessment included CD4 cell number count and lymphocyte blastogenesis in response to the mitogens phytohemagglutinin (PHA) and pokeweed (PWM). The mean total amount of omega 6 polyunsaturated fatty acids (18:2 and 20:4) was significantly lower in the HIV-1 seropositive subjects (38 +/- 8.1% SD) as compared to HIV-1 seronegative subjects (43 +/- 4.2%; P = 0.0027). This was also reflected in a higher level of total saturated fatty acids (16:0 and 18:0) in HIV-1 seropositive subjects (30 +/- 2.2% vs. 26 +/- 2.8%; P = 0.0001). The ratio of linoleic to arachidonic acid (18:2 to 20:4) was higher in the HIV-1 seropositive group (6.76 +/- 4.88) compared to the HIV-1 seronegative group (4.86 +/- 1.37; P = 0.0213). The response to PHA in seropositive subjects correlated inversely with total plasma omega 6 fatty acids (r = -0.36; P = 0.027), and directly with the 18:2 to 20:4 ratio (r = 0.33; P = 0.046). CD4 cell counts and the response to PWM did not correlate with plasma fatty acid levels in HIV-1 seropositive subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Crossfostering and early development of natural killer cytotoxic activity in various inbred mouse strains

In the present study using crossfostering among three inbred mouse strains (C57BL/6, DBA/2, and Balb/c) we compared the effects of lactation with milk of different compositions on the development of NK cells cytotoxic activity. The results show that the pups from C57BL/6 and DBA/2 mice exhibit a significant early increase of NK cells cytotoxic activity when fostered by Balb/c dams, in comparison to those fostered by natural mothers. The analysis of proteins, lactose, and lipids showed difference among the strains for all components. Strain effects for days of lactation were also observed. The naso-anal length and the body weight of young mice showed differences with the strain of fostering mothers. The results indicate that the characteristic of maternal milk composition interacts with the inbred genetic susceptibility of the pups to elicit the full expression of the level of NK activity.

Managing nutrition problems in transplant patients

Patients who undergo organ transplantation receive immunosuppressive drugs in the posttrans-plant period. All of these drugs influence host metabolic response or alter nutrient intake. One of the most prominent aspects of the posttransplant period is the occurrence of hyperlipidemia, which may require dietary or pharmacologic control. Dietary recommendations for this patient population include limiting carbohydrate intake, restricting caloric intake to maintain ideal body weight, and maintaining a low cholesterol/saturated fat diet.

Effects of dietary essential fatty acid deficiency on the development of the rat thymus and immune system

The paper describes an effect of essential fatty acid (EFA) deficiency on the development of the rat thymus and pups' immune system. From birth until being weaned (22nd day), the pups were hand-fed artificial milk diets containing a low (EFA-D) or high (EFA-R) proportion of EFA in the lipid fraction. The weight parameters of the body, thymus and spleen, the fatty acid composition of the individual thymus phospholipid subclasses, and mitogen-induced proliferation of thymus and spleen lymphocytes were studied. The results show that the total body weight of the EFA-deficient (EFA-D) fed animals was significantly decreased in comparison with the EFA-rich (EFA-R) and rat milk hand-fed animals. For the EFA-D group of young rats a high level of the (n-9) and (n-7) series fatty acids [mainly oleic 18:1(n-9) and eicosatrienoic 20:3(n-9) acids] was characteristic of the fatty acids in phosphatidylcholine and phosphatidylethanolamine in the thymus, compensating for the reduction of the content of arachidonic acid 20:4(n-6). The biochemical index of the EFA nutritional deficit in the thymus tissue was observable as early as on day 7. The mitogen-induced (Con A) proliferation of the thymus and spleen lymphocytes was decreased both on the 30th and 40th day of life. The results show that the EFA nutritional deficit in the early postnatal period caused damage to the structure of thymus in the young rats, most probably as a result of the change in the composition of the lipid fraction. These changes also affected the development of the immune system of the whole organism.