Polyunsaturated fatty acids, membrane organization, T cells, and antigen presentation

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

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

Impact of PUFA on early immune and fetal development

It has recently been reported that the increased prevalence in childhood allergy may be linked to deviations in fetal immune development. One reason may be impaired nutrient supply. Hence, a well-differentiated placenta together with an optimal fetal nutrition via the mother are important prerequisites for the establishment of a functional immune system with normal immune responses. Fatty acids and their derivatives can influence both the early immune development and immune maturation by regulating numerous metabolic processes and the gene expression of important proteins such as enzymes and cytokines. The present review summarises the impact of nutritional fatty acids on the development of the immune system as well as the fetal development. It describes the mechanisms of action of PUFA, trans fatty acids and conjugated linoleic acids in programming the fetus with regard to its risk of acquiring atopic diseases in childhood.

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

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

Update on lipid membrane microdomains

PURPOSE OF REVIEW

Lipid membrane microdomains are involved in major types of disease, ranging from vascular and metabolic diseases to neurodegeneration, autoimmunity, infectious and inflammatory diseases, and cancer. This review provides an update of membrane microdomain abnormalities.

RECENT FINDINGS

Lipid membrane microdomains are dynamic assemblies of sphingolipids, cholesterol and proteins that dissociate and associate rapidly and form functional clusters. Membrane microdomain clustering is the key to how membrane microdomains can form lipid-protein platforms in cell membranes, functioning in membrane trafficking, cell polarization and signalling. Clustering of membrane microdomains can be modified, for example by dietary lipids and pharmacological agents.

SUMMARY

Metabolic overload through a cholesterol-rich and fat-rich diet can trigger metabolic learning, which is associated with membrane microdomain persistence, persistent signalling and disturbed vesicular traffic. Detailed characterization of lipid membrane microdomains and dynamics at the molecular level is necessary and will help to identify new dietary and pharmacological therapeutic targets for the treatment and prevention of lipid membrane microdomain related diseases.

Docosahexaenoic acid domains: the ultimate non-raft membrane domain

What distinguishes polyunsaturated fatty acids (PUFAs) from less unsaturated fatty acids is the presence of a repeating =CH-CH(2)-CH= unit that produces an extremely flexible structure rapidly isomerizing through conformational states. Docosahexaenoic acid (DHA) with 6 double bonds is the most extreme example. The focus of this review is the profound impact that the high disorder of DHA has on its interaction with cholesterol when the PUFA is incorporated into membrane phospholipids. Results from a battery of biophysical techniques are described. They demonstrate an aversion of DHA for the sterol that drives the lateral segregation of DHA-containing phospholipids into liquid disordered (l(d)) domains that are depleted in cholesterol. These domains are compositionally and organizationally the antithesis of lipid rafts, the much-studied liquid ordered (l(o)) domain that is enriched in predominantly saturated sphingolipids and cholesterol. We hypothesize that the introduction of DHA-rich domains into the plasma membrane where they coexist with lipid rafts is the origin, in part, of the astonishing diversity of health benefits that accrue from dietary consumption of DHA. According to our model, changes in the conformation of signaling proteins when they move between these disparate domains have the potential to modulate cell function.

Polyunsaturated fatty acids and membrane organization: elucidating mechanisms to balance immunotherapy and susceptibility to infection

Polyunsaturated fatty acids (PUFAs), notably of the n-3 series, have immunosuppressive effects which make these molecules candidates for treating inflammatory symptoms associated with cardiovascular disease, obesity, arthritis, and asthma. However, immunosuppression by PUFAs could increase susceptibility to bacterial and viral infection. A detailed molecular picture is required in order to understand the balance between the benefits and risks of utilizing PUFAs as adjuvant immunosuppressants. Here we review evidence that incorporation of PUFAs into membrane lipids of antigen presenting cells (APCs) downregulates APC function. We propose that PUFAs modulate antigen presentation by altering the organization of lipid and protein molecules of the plasma membrane and endomembranes; this alters recognition and responses by T cells. The foundation of our hypothesis is built on data from artificial bilayer experiments which provide the physical principles by which PUFA acyl chains affect membrane architecture. This review also reconciles conflicting results in the literature by discussing the advantages and disadvantages of differing methods of PUFA treatment of cells. We suggest that membrane modulation of immune cells may be an important and overlooked mechanism of immunomodulation. In addition, we propose that mechanistic studies with defined experimental protocols will speed the translation of laboratory studies on PUFAs to the clinic.

Fish consumption among pregnant women in London, Ontario: associations with socio-demographic and health and lifestyle factors

BACKGROUND

Intake of fish and omega-3 fatty acids is inversely related to adverse health outcomes; however, these relationships may be confounded by socio-economic status and health behaviours. This study's purpose was to describe the socio-demographic, health and lifestyle correlates of fish consumption among pregnant women.

METHODS

Pregnant women (n=2394) completed a telephone interview between 10-22 weeks' gestation (London, Ontario, 2002-5) containing questions on socio-demographic, health and lifestyle variables; dietary intake was measured using a 106-item validated food-frequency questionnaire. Unadjusted and adjusted risk ratios were obtained using a modified Poisson regression model.

RESULTS

Infrequent fish consumption, <1/week, was reported by 32% of women. After adjusting for age and education, infrequent fish consumption was associated with education <high school (RR=1.60; 95% CI 1.30-1.96); age (< or =21: RR=1.53; 95% CI 1.17-2.02; 22-25: RR=1.41; 95% CI 1.11-1.78; and 26-34: RR=1.39; 95% CI 1.15-1.69); current smoking status (RR=1.20; 95% CI 1.00-1.43); average exercise duration <30 minutes (never: RR=1.22; 95% CI 1.06-1.39 and 1-29 minutes: RR=1.25; 95% CI 1.08-1.45); obesity (RR=1.19; 95% CI 1.01-1.41); and not meeting Canadian dietary guidelines for consumption of vegetables and fruit (RR=1.60; 95% CI 1.42-1.79), milk products (RR=1.19; 95% CI 1.05-1.36), and meat and alternatives (RR=1.89; 95% CI 1.69-2.12). Compared to frequent fish consumers, infrequent fish consumers were less likely to be moderate drinkers prior to pregnancy (RR=0.85; 95% CI 0.75-0.96).

CONCLUSION

Infrequent fish consumption was associated with lower socio-economic status and variables indicative of a less healthy lifestyle; these variables may act as confounders in studies evaluating fish consumption and health outcomes.

Modulation of T-cell signalling by non-esterified fatty acids

Polyunsaturated fatty acids (PUFAs) have been shown to be immunosuppressive. In particular, they can decrease important T-cell functions that may have a profound impact on the acquired immune response. Several mechanisms may explain the immunosuppressive properties of PUFAs. Here we review the mechanisms by which they interfere with T-cell activation. PUFAs affect lipid rafts composition and function that play an essential role in T-cell signalling. The possible physiological and pathological significances of this immunomodulation by PUFAs are discussed. Further mechanistic studies and randomized controlled clinical trials are needed to assess more accurately their effects in healthy and pathological states.

Polyunsaturated fatty acids regulate Shiga toxin transport

Shiga toxin (Stx) is internalized by receptor-mediated endocytosis and transported retrogradely to the endoplasmic reticulum from where the enzymatically active part of the toxin is translocated to the cytosol. In this study, we have investigated the effect of polyunsaturated fatty acids (PUFA) on intoxication and retrograde transport of Stx. In HEp-2 cells, PUFA treatment inhibited Stx intoxication by a factor of 10. Moreover, both Stx internalization and endosome-to-Golgi transport were reduced by PUFA and these reductions can together explain the reduced toxicity. Also cholera toxin internalization was reduced by PUFA treatment. Finally, ricin and Pseudomonas exotoxin 1 cytotoxicity were not reduced by PUFA, demonstrating that PUFA do not cause a general block in retrograde transport to the endoplasmic reticulum. In conclusion, these results clearly demonstrate the importance of PUFA for Stx and cholera toxin trafficking.