Assessment of interleukin-12, gamma interferon, and tumor necrosis factor alpha secretion in sera from mice fed with dietary lipids during different stages of Listeria monocytogenes infection

Dietary fatty acids and immune response to food-borne bacterial infections

Functional innate and acquired immune responses are required to protect the host from pathogenic bacterial infections. Modulation of host immune functions may have beneficial or deleterious effects on disease outcome. Different types of dietary fatty acids have been shown to have variable effects on bacterial clearance and disease outcome through suppression or activation of immune responses. Therefore, we have chosen to review research across experimental models and food sources on the effects of commonly consumed fatty acids on the most common food-borne pathogens, including Salmonella sp., Campylobacter sp., Shiga toxin-producing Escherichia coli, Shigella sp., Listeria monocytogenes, and Staphylococcus aureus. Altogether, the compilation of literature suggests that no single fatty acid is an answer for protection from all food-borne pathogens, and further research is necessary to determine the best approach to improve disease outcomes.

Acquired resistance to Listeria monocytogenes during a secondary infection in a murine model fed dietary lipids

OBJECTIVE

The ω-3 polyunsaturated fatty acids can suppress immune system functions. This property may cause adverse effects by impairing host resistance to infection. The present study focused on estimating the impact of different dietary lipids on the immune system of mice after a secondary infection with Listeria monocytogenes.

METHODS

BALB/c mice were divided into five dietary groups of olive oil, fish oil, sunflower oil, high-oleic sunflower oil, or low fat that was administered for 8 wk. The mice were immunized with 10(3) colony-forming units. Thirty-eight days later, each mouse was challenged with 10(4) colony-forming units. Mice survival and bacterial clearance from livers and spleens were determined. In addition, cytokine, chemokine, and adhesion molecule productions were quantified from the sera.

RESULTS

Survival percentage in mice fed a fish oil diet was 100% and bacterial numbers from spleen were decreased at 72 h. Interleukin-12, intercellular adhesion molecule-1, and vascular cell adhesion molecule-1 productions were decreased. Levels of tumor necrosis factor-α and interferon-γ were increased, whereas macrophage inflammatory protein-1α (MIP-1α) production was unaltered.

CONCLUSION

Immune defense in mice fed a fish oil diet was improved after secondary exposure, acquiring an adequate resistance. This result could be attributable to an increase of a T-helper type 1 response.

Dietary fish oil impairs induction of gamma-interferon and delayed-type hypersensitivity during a systemic Salmonella enteritidis infection in rats

Fish oil that is rich in n-3 polyunsaturated fatty acids markedly modulates immunological responses. Literature data indicate that the fish oil reduces cellular immunity and therefore impairs resistance to infections. We have investigated how dietary fish oil affects the immune response against a facultative intracellular pathogen, Salmonella enteritidis. Wistar rats were fed a diet containing 16% (w/w) of either fish oil or corn oil. After a 4-week adaptation period, rats were intraperitoneally challenged with 4 x 10(5) cfu of S. enteritidis. During the 14-day infection period, urine was collected on a daily basis. At days 2 and 14, eight rats per group were sacrificed. Urinary nitrate, used as a marker for NO production, was lower on a fish oil diet during days 3-8. At day 2, serum gamma-interferon was 48 +/- 7 pg/mL in the fish oil-fed rats compared with 162 +/- 52 pg/mL in the corn oil-fed rats. No effects were found on living salmonella in liver and spleen. At day 14, as markers of an impaired T-helper 1 (Th-1) response, a 38% lower delayed-type hypersensitivity responses and a lower salmonella-specific IgG2b were observed in the fish oil-fed rats. Although here dietary fish oil has affected only immune parameters, this impairment of the innate and Th-1-mediated immune response may have implications for the host resistance against other intracellular pathogens.

Enrichment of RAW264.7 macrophages with essential 18-carbon fatty acids affects both respiratory burst and production of immune modulating cytokines

Macrophages play a vital role in the innate immune system. Thereby, production of both reactive oxygen intermediates and immune modulating cytokines is crucial for successful pathogen defense. Fatty acids may interfere with immune response in several ways. In this study, we investigated the influence of essential polyunsaturated fatty acids (PUFA) on key macrophage functions. RAW264.7 macrophages were cultured in a medium supplemented with 2 or 15 micromol/L of the n-6 PUFA linoleic acid (LA) or of the n-3 PUFA alpha-linolenic acid (LNA), respectively. Cells were tested for incorporation of fatty acids as well as NADPH oxidase activity. Furthermore, supernatants were collected for detection of NO and cytokine release (TNF-alpha, IL-6, IL-10). Exposure of RAW264.7 macrophages to LA or LNA resulted in incorporation of these fatty acids and their derivatives. Thereby, supplementation with both LA and LNA caused a significant increase in NADPH oxidase activity. In contrast, synthesis of NO was not affected by PUFA supplementation. Moreover, distinct effects could be seen in the release of immune modulating cytokines. Due to enhancement of NADPH oxidase activity, PUFA presumably promote the killing of pathogens crucial in host defense. In addition, the unsaturated fatty acids tested in our study were shown to modulate cytokine release by the macrophages, thus driving immune response into an anti-inflammatory direction. Of note, distinct differences between the n-6 PUFA LA and the n-3 PUFA LNA underline the impact of PUFA family on immune response.

Multiple factors interact to produce responses resembling spectrum of human disease in Campylobacter jejuni infected C57BL/6 IL-10-/- mice

BACKGROUND

Campylobacter jejuni infection produces a spectrum of clinical presentations in humans--including asymptomatic carriage, watery diarrhea, and bloody diarrhea--and has been epidemiologically associated with subsequent autoimmune neuropathies. This microorganism is genetically variable and possesses genetic mechanisms that may contribute to variability in nature. However, relationships between genetic variation in the pathogen and variation in disease manifestation in the host are not understood. We took a comparative experimental approach to explore differences among different C. jejuni strains and studied the effect of diet on disease manifestation in an interleukin-10 deficient mouse model.

RESULTS

In the comparative study, C57BL/6 interleukin-10-/- mice were infected with seven genetically distinct C. jejuni strains. Four strains colonized the mice and caused disease; one colonized with no disease; two did not colonize. A DNA:DNA microarray comparison of the strain that colonized mice without disease to C. jejuni 11168 that caused disease revealed that putative virulence determinants, including loci encoding surface structures known to be involved in C. jejuni pathogenesis, differed from or were absent in the strain that did not cause disease. In the experimental study, the five colonizing strains were passaged four times in mice. For three strains, serial passage produced increased incidence and degree of pathology and decreased time to develop pathology; disease shifted from watery to bloody diarrhea. Mice kept on an ~6% fat diet or switched from an approximately 12% fat diet to an approximately 6% fat diet just before infection with a non-adapted strain also exhibited increased incidence and severity of disease and decreased time to develop disease, although the effects of diet were only statistically significant in one experiment.

CONCLUSION

C. jejuni strain genetic background and adaptation of the strain to the host by serial passage contribute to differences in disease manifestations of C. jejuni infection in C57BL/6 IL-10-/- mice; differences in environmental factors such as diet may also affect disease manifestation. These results in mice reflect the spectrum of clinical presentations of C. jejuni gastroenteritis in humans and contribute to usefulness of the model in studying human disease.

Diet and asthma--can you change what you or your children are by changing what you eat?

In this review we focus on dietary fat content and subsequent effects on asthma. According to the World Health Organisation over 300 million people currently have asthma. The majority of asthma cases are 'extrinsic' and result from inappropriate 'allergic' immune responses to inhaled environmental substances. Whilst some individuals are allergic to particular food components it is becoming clear that the content of the diet can more generally affect the health of the immune system. Components of maternal and early life diets have been reported to influence offspring immune function and asthma. There has been speculation that different types of dietary fat have pro- and anti-inflammatory effects but the results of various studies are contradictory. Asthma and obesity are two conditions that have almost simultaneously reached epidemic levels in some societies. There is evidence that diet-induced obesity alters immune function and there is little doubt that consumption of a high caloric diet with high fat content leads to obesity. However, there is conflicting information over whether and how obesity is linked to asthma in children and adults. Whilst obesity is to be avoided there is accumulating evidence that dietary fat per se does not necessarily predispose towards allergic symptoms.

High-fat feeding redirects cytokine responses and decreases allergic airway eosinophilia

BACKGROUND

Dietary fat intake has been associated with obesity and obesity in its turn with attenuated airway function and asthma, but it is unclear whether or how high-fat intake per se alters immune function relevant to development of allergic asthma.

OBJECTIVE

To use a non-obese mouse model of mild to moderate allergic asthma to compare effects of high-fat with isocaloric control-diet on allergic immune responses.

METHODS

C57BL/6 mice weaned and maintained on control (11% fat calories) or isocaloric high-fat diet (58% fat calories) were systemically sensitized with ovalbumin and challenged in the lungs. Allergic airway inflammation was assessed by measuring lung inflammation; serum antibodies; and, cytokines in serum, bronchoalveolar lavage (BAL) fluid and in supernatants of in vitro stimulated lung draining lymph node and spleen lymphocytes.

RESULTS

There was a significant reduction in lung eosinophilia and IL-5 in high-fat fed mice. Lung draining lymph node cells from these mice showed reduced pro-inflammatory cytokine (MCP-1 and TNF-alpha) release after ovalbumin re-stimulation and reduced release of IL-13 after concanavalin-A stimulation, indicating a general rather than just an antigen-specific change. There was no difference in IFN-gamma release. In contrast, pro-inflammatory cytokine release was increased from splenocytes. Decreased eosinophilia was not due to increased regulatory T cell or IL-10 induction in draining lymph nodes or spleen, nor to changes in antibody response to ovalbumin. However, decreased levels of serum and BAL eotaxin were found in high-fat fed animals.

CONCLUSIONS

The data indicate that high-fat dietary content redirects local immune responses to allergen in the lungs and systemic responses in the spleen and serum. These effects are not due to changes in regulatory T cell populations but may reflect a failure to mobilize eosinophils in response to allergic challenge.

Docosahexaenoic acid-enriched fish oil consumption modulates immunoglobulin responses to and clearance of enteric reovirus infection in mice

We hypothesized that consumption of the (n-3) PUFA, docosahexaenoic acid (DHA), modulates the mucosal immune response to enteric infection with respiratory enteric orphan virus (reovirus), a model intestinal pathogen. Mice were fed either AIN-93G control diet, containing 10 g/kg corn oil and 60 g/kg high oleic acid safflower oil, or AIN-93G, containing 10 g/kg corn oil and 60 g/kg DHA-enriched fish oil, for 4 wk and then orally gavaged with reovirus strain Type 1 Lang, (T1/L). Reovirus-specific IgA antibody was first detectable in the feces of mice fed a control diet at 6 d postinfection (PI) and was further elevated at 8 and 10 d PI. IgA responses in DHA-fed mice were similar at 6 and 8 d PI but greater at 10 d PI (P < 0.05). Both reovirus-specific serum IgA and IgG(2a) were comparably induced in mice fed control or DHA diets. Reovirus-specific IgA and IgG(2a) secretion by ex vivo Peyer's patch, lamina propria, and spleen cultures derived from control and DHA groups were comparable. Although both groups carried similar numbers of reovirus plaque forming units per intestine, DHA-fed mice shed nearly 10 times more viral RNA in feces than control mice at 2, 4, and 6 d PI (P < 0.05). However, viral RNA was not detectable in either group at 8 and 10 d. Taken together, these data suggest that DHA consumption did not markedly alter mucosal or systemic Ig responses to reovirus but delayed clearance of the virus from the intestinal tract.

Examination of host immune resistance against Listeria monocytogenes infection in cyclophosphamide-treated mice after dietary lipid administration

BACKGROUND & AIMS

Despite the beneficial effects in the resolution of inflammatory disorders due to their immunosuppressive properties, n-3 polyunsaturated fatty acids are associated with a reduction of immune resistance to some microorganisms. Here, we examine the influence of different dietary lipids on host immune resistance against Listeria monocytogenes in mice treated with cyclophosphamide (CPA).

METHODS

Balb/c mice were fed one of four diets, which contained either olive oil (OO), fish oil (FO), hydrogenated coconut oil (HCO) or low fat (LF) for 4 weeks. Subsequently, mice were treated with CPA or PBS, prior to L. monocytogenes infection. Splenocyte proliferation, survival analysis, counts of viable bacteria from spleens and livers, and measurement of pro-inflammatory cytokine levels were determined.

RESULTS

The FO-rich diet reduced survival, particularly in CPA-treated mice. CPA was responsible for a significant increase of viable bacteria recovery from spleens and livers within each group fed high fat diets, which was aggravated in mice fed an FO diet. In addition, a significant increase of both TNF-alpha and IL-12p70 levels was detected in this group. These results may acquire a crucial relevance in clinical nutrition, particularly when FO diets are administered to immunocompromised patients.

CONCLUSIONS

The mechanism(s) that impair(s) the elimination of L. monocytogenes could be associated with a low mitogen-stimulated splenocyte proliferation, and with an alteration of pro-inflammatory cytokine production. The application of the neutropenic agent CPA moderately aggravates the immunosuppressive state mainly in FO-fed animals.