A type 2 immune circuit in the stomach controls mammalian adaptation to dietary chitin.

Dietary fiber improves metabolic health, but host-encoded mechanisms for digesting fibrous polysaccharides are unclear. In this work, we describe a mammalian adaptation to dietary chitin that is coordinated by gastric innate immune activation and acidic mammalian chitinase (AMCase). Chitin consumption causes gastric distension and cytokine production by stomach tuft cells and group 2 innate lymphoid cells (ILC2s) in mice, which drives the expansion of AMCase-expressing zymogenic chief cells that facilitate chitin digestion. Although chitin influences gut microbial composition, ILC2-mediated tissue adaptation and gastrointestinal responses are preserved in germ-free mice. In the absence of AMCase, sustained chitin intake leads to heightened basal type 2 immunity, reduced adiposity, and resistance to obesity. These data define an endogenous metabolic circuit that enables nutrient extraction from an insoluble dietary constituent by enhancing digestive function.

Immune and hormonal regulation of the Boa constrictor (Serpentes; Boidae) in response to feeding.

Feeding upregulates immune function and the systemic and local (gastrointestinal tract) concentrations of some immunoregulatory hormones, as corticosterone (CORT) and melatonin (MEL), in mammals and anurans. However, little is known about the immune and hormonal regulation in response to feeding in other ectothermic vertebrates, especially snakes, in which the postprandial metabolic changes are pronounced. Here, we investigated the effects feeding have on hormonal and innate immune responses in the snake, Boa constrictor. We divided juvenile males into two groups: fasting and fed with mice (30% of body mass). We measured the rates of oxygen consumption, plasma CORT levels, heterophil/lymphocyte ratio (HL ratio), plasma bacterial killing ability (BKA), and stomach and intestine MEL in fasting snakes and 48 h after meal intake. We observed increased rates of oxygen consumption, plasma CORT levels, and HL ratio, along with a tendency of decreased stomach and intestine MEL in fed snakes compared to fasting ones. BKA was not affected by feeding. Overall, we found that feeding modulates metabolic rates, CORT levels, and immune cell distribution in boas. Increased baseline CORT may be important to mobilize energy to support the metabolic increment during the postprandial period. Increased HL ratio might be an immunoregulatory effect of increased CORT, which has been shown in different physiological situations such as in response to immune challenge. Our results suggest that feeding activates the hypothalamic-pituitary-adrenal axis and modulates immune cell redistribution, possibly contributing to fighting potential injuries and infections derived from predation and from pathogens present in ingested food.

Gastric Enzyme Supplementation Inhibits Food Allergy in a BALB/c Mouse Model.

Impaired gastric digestion due to suppressed gastric acidity enhances the risk for food allergy development. In the current study, we aimed to evaluate the impact of a supported gastric digestion via application of a pharmaceutical gastric enzyme solution (GES) on food allergy development and allergic reactions in a BALB/c mouse model. The ability of the GES to restore hypoacidic conditions was tested in mice treated with gastric acid suppression medication. To evaluate the impact on allergic symptoms, mice were orally sensitized with ovalbumin (OVA) under gastric acid suppression and subjected to oral challenges with or without GES. The immune response was evaluated by measurement of antibody titers, cytokine levels, mucosal allergy effector cell influx and regulatory T-cell counts. Clinical response was objectified by core body temperature measurements after oral OVA challenge. Supplementation of GES transiently restored physiological pH levels in the stomach after pharmaceutical gastric acid suppression. During oral sensitization, supplementation of gastric enzymes significantly reduced systemic IgE, IgG1 and IgG2a levels and allergic symptoms. In food allergic mice, clinical symptoms were reduced by co-administration of the gastric enzyme solution. Support of gastric digestion efficiently prevents food allergy induction and alleviates clinical symptoms in our food allergy model.

The Effects on Immune Function and Digestive Health of Consuming the Skin and Flesh of Zespri® SunGold Kiwifruit (Actinidia Chinensis var. Chinensis 'Zesy002') in Healthy and IBS-Constipated Individuals.

Irritable bowel syndrome (IBS) is a common gastrointestinal disorder that results in constipation (IBS-C) or diarrhoea with abdominal pain, flatulence, nausea and bloating. Kiwifruit (Actinidia spp.) are nutrient-dense fruit with a number of reported health benefits that include lowering glycaemic response, improving cardiovascular and inflammatory biomarkers, and enhancing gut comfort and laxation. This study investigated the effect of consuming three whole Zespri® SunGold kiwifruit (Actinidia chinensis var. chinensis 'Zesy002') with or without skin on cytokine production and immune and gut health in healthy people and those with IBS-C symptoms. This study enrolled thirty-eight participants in a 16 week randomized cross-over study (19 healthy and 19 participants with IBS-C). Participants were randomized to consume either three kiwifruit without eating the skin or three kiwifruit including the skin for 4 weeks each, with a 4 week washout in between each intervention. There was a significant decrease in the pro-inflammatory cytokine, TNF-α, for both the healthy and the IBS-C participants when they consumed whole kiwifruit and skin, and also for the healthy participants when they ate whole kiwifruit without the skin (p < 0.001). The kiwifruit interventions increased bowel frequency and significantly reduced the gastrointestinal symptom rating scale constipation and Birmingham IBS pain scores for both participant groups. We have demonstrated that consuming the skin of SunGold kiwifruit might have beneficial effects on gastrointestinal health that are not produced by consuming the flesh alone.

Resistance of parvalbumin to gastrointestinal digestion is required for profound and long-lasting prophylactic oral tolerance.

BACKGROUND: Early introduction of food allergens into children's diet is considered as a strategy for the prevention of food allergy. The major fish allergen parvalbumin exhibits high stability against gastrointestinal digestion. We investigated whether resistance of carp parvalbumin to digestion affects oral tolerance induction. METHODS: Natural Cyp c 1, nCyp c 1, and a gastrointestinal digestion-sensitive recombinant Cyp c 1 mutant, mCyp c 1, were analyzed for their ability to induce oral tolerance in a murine model. Both antigens were compared by gel filtration, circular dichroism measurement, in vitro digestion, and splenocyte proliferation assays using synthetic Cyp c 1-derived peptides. BALB/c mice were fed once with high doses of nCyp c 1 or mCyp c 1, before sensitization to nCyp c 1. Immunological tolerance was studied by measuring Cyp c 1-specific antibodies and cellular responses by ELISA, basophil activation, splenocyte proliferations, and intragastric allergen challenge. RESULTS: Wild-type and mCyp c 1 showed the same physicochemical properties and shared the same major T-cell epitope. However, mCyp c 1 was more sensitive to enzymatic digestion in vitro than nCyp c 1. A single high-dose oral administration of nCyp c 1 but not of mCyp c 1 induced long-term oral tolerance, characterized by lack of parvalbumin-specific antibody and cellular responses. Moreover, mCyp c 1-fed mice, but not nCyp c 1-fed mice developed allergic symptoms upon challenge with nCyp c 1. CONCLUSION: Sensitivity to digestion in the gastrointestinal tract influences the capacity of an allergen to induce prophylactic oral tolerance.

Changes in the intestine microbial, digestion and immunity of Litopenaeus vannamei in response to dietary resistant starch.

Resistant starch (RS) is a constituent of dietary fibre that has beneficial effects on the intestine physiological function of animals. However, the roles of RS on shrimp intestine health is unknown. In this study, we investigated the the effects of dietary RS on the microbial composition, and digestive and immune-related indices in the intestine of Litopenaeus vannamei. The shrimp were fed with diets containing different levels of RS: 0 g/kg (Control), 10 g/kg (RS1), 30 g/kg (RS2) and 50 g/kg (RS3) for 56 days. The results showed that dietary RS improved the morphology of the intestine mucosa. RS also increased the activity of digestive enzymes (AMS, LPS, Tryp, and Pep) and immune enzymes (PO, T-AOC, T-NOS, and NO), and the expression levels of immune-related genes (proPO, ALF, Lys, HSP70, Trx, Muc-1, Muc-2, Muc-5AC, Muc-5B, and Muc-19). A microbiome analysis indicated that dietary RS increased the short-chain fatty acids (SCFAs) contents and altered the composition of the intestine microbial. Specifically, RS increased the abundances of Proteobacteria and decreased the abundance of Bacteroidetes. At the genus level, the beneficial bacteria (Lutimonas, Ruegeria, Shimia, Mesoflavibacter, and Mameliella) were enriched, which might be involved in degrading toxins and producing beneficial metabolites; while potential pathogens (Formosa and Pseudoalteromonas) were decreased in response to dietary RS. Our results revealed that dietary RS could improve the intestine health of L. vannamei, probably via modulating the intestine microbial composition and SCFAs contents, and enhancing the digestion and immunity of the shrimp.

Influence of Dietary Copper Methionine Concentrations on Growth Performance, Digestibility of Nutrients, Serum Lipid Profiles, and Immune Defenses in Broilers.

A 42-day experiment was conducted to evaluate the influence of dietary copper (Cu) concentrations on growth performance, nutrient digestibility, and serum parameters in broilers aged from 1 to 42 days. Five hundred forty 1-day-old broilers were randomly assigned into 1 of the following 6 dietary treatments: (1) control (basal diet without supplemental Cu), (2) 15 mg/kg supplemental Cu (Cu15), (3) 30 mg/kg supplemental Cu (Cu30), (4) 60 mg/kg supplemental Cu (Cu60), (5) 120 mg/kg supplemental Cu (Cu120), and (6) 240 mg/kg supplemental Cu (Cu240), Cu as copper methionine. A 4-day metabolism trial was conducted during the last week of the experiment feeding. The results showed that dietary Cu supplementation increased the average daily gain and the average daily feed intake (P < 0.01). The feed gain ratio, however, was not affected by dietary Cu (P > 0.10). Additionally, dietary Cu supplementation increased the digestibility of fat and energy (P < 0.05). The concentration of serum cholesterol, triglycerides, and high-density lipoprotein cholesterol decreased with dietary Cu supplementation (P < 0.05). The activities of serum Cu-Zn superoxide dismutase (P < 0.05), glutathione peroxidase (P < 0.05), and ceruloplasmin (P = 0.09), on the contrary, were increased by Cu addition. For immune indexes, dietary Cu supplementation increased serum IgA and IgM (P < 0.05). In addition, the activities of serum ALT increased with increasing dietary Cu supplementation (P < 0.05). In conclusion, our data suggest that Cu supplementation can increase fat digestibility and promote growth. Additionally, dietary Cu supplementation can reduce serum cholesterol and enhance antioxidant capacity in broilers.

Nutrient digestibility, organ morphometry and performance in vaccinated or non-vaccinated Lawsonia intracellularis infected piglets.

BACKGROUND: Lawsonia intracellularis is one of the world's most important infectious diseases in pork production with regard to economic losses. So far, studies are missing that describe the effects of a natural infection of piglets on the digestibility of nutrients, possible effects on performance and the morphometrics of the intestine depending on whether piglets are vaccinated, clinically healthy or clinically affected with regard to Lawsonia intracellularis induced diarrhoea. RESULTS: Digestibility studies were performed on a total of 27 eight-week-old piglets with naturally occurring Lawsonia intracellularis infection in a trial with three repetitions. Nine out of 27 animals were vaccinated as suckling pigs with a commercial Lawsonia intracellularis vaccine (vac; Enterisol®Ileitis). Half of the remaining 18 animals were without clinical signs of infection (non-vac/cs-), half showed moderate clinical signs of Lawsonia intracellularis induced diarrhoea (non-vac/cs+). All three groups were fed one identical complete diet ad libitum. Faecal shedding of Lawsonia intracellularis was found in all groups (25 out of 27 animals). Numerically, the mean excretion in the group non-vac/cs + (7.69 ± 1.65 log10 copies/ g faeces) was higher in comparison to the group non-vac/cs- (5.83 ± 2.35 log10 copies/ g faeces) and vaccinated animals (vac: 6.00 ± 2.89log10 copies/ g faeces). The average daily weight gain (ADG; Ø 8.66 day period) differed significantly (vac: 894a ± 73.3, non-vac/cs-: 857ab ± 86.3, non-vac/cs+: 785b ± 137 g/day). The apparent total tract digestibility (ATTD) of nitrogen was significantly lower in clinically affected animals (vac: 83.0a ± 1.72, non-vac/cs-: 83.9a ± 2.03, non-vac/cs+: 80.7b ± 2.57).The total length of the small intestine in clinically affected animals increased significantly (vac: 15.9ab ± 1.57, non-vac/cs-: 14.6b ± 1.12, non-vac/cs+: 16.2a ± 1.37 m). The relative body weight depending on the length of the small intestine was lower for clinically affected animals (vac: 1.72a ± 0.21, non-vac/cs-: 1.83a ± 0.17, non-vac/cs+: 1.56b ± 0.12 kg/m). CONCLUSION: These studies show that clinically moderate L. intracellularis infections lead to significantly lower ADGs in comparison to vaccinated animals. The disease is also found in altered intestinal morphometry and reduced total N digestibility if clinical signs occur.

Starvation stress affects the interplay among shrimp gut microbiota, digestion and immune activities.

Aquatic animals are frequently suffered from starvation due to restricted food availability or deprivation. It is currently known that gut microbiota assists host in nutrient acquisition. Thus, exploring the gut microbiota responses would improve our understanding on physiological adaptation to starvation. To achieve this, we investigated how the gut microbiota and shrimp digestion and immune activities were affected under starvation stress. The results showed that the measured digestion activities in starved shrimp were significantly lower than in normal cohorts; while the measured immune activities exhibited an opposite trend. A structural equation modeling (SEM) revealed that changes in the gut bacterial community were directly related to digestive and immune enzyme activities, which in turn markedly affected shrimp growth traits. Notably, several gut bacterial indicators that characterized the shrimp nutrient status were identified, with more abundant opportunistic pathogens in starved shrimp, although there were no statistical differences in the overall diversity and the structures of gut bacterial communities between starved and normal shrimp. Starved shrimp exhibited less connected and cooperative interspecies interaction as compared with normal cohorts. Additionally, the functional pathways involved in carbohydrate and protein digestion, glycan biosynthesis, lipid and enzyme metabolism remarkably decreased in starved shrimp. These attenuations could increase the susceptibility of starved shrimp to pathogens infection. In summary, this study provides novel insights into the interplay among shrimp digestion, immune activities and gut microbiota in response to starvation stress.

Dietary effects of adenosine monophosphate to enhance growth, digestibility, innate immune responses and stress resistance of juvenile red sea bream, Pagrus major.

Our study explored the dietary effects of adenosine monophosphate (AMP) to enhance growth, digestibility, innate immune responses and stress resistance of juvenile red sea bream. A semi-purified basal diet supplemented with 0% (Control), 0.1% (AMP-0.1), 0.2% (AMP-0.2), 0.4% (AMP-0.4) and 0.8% (AMP-0.8) purified AMP to formulate five experimental diets. Each diet was randomly allocated to triplicate groups of fish (mean initial weight 3.4 g) for 56 days. The results indicated that dietary AMP supplements tended to improve growth performances. One of the best ones was found in diet group AMP-0.2, followed by diet groups AMP-0.1, AMP-0.4 and AMP-0.8. The Apparent digestibility coefficients (dry matter, protein and lipid) also improved by AMP supplementation and the significantly highest dry matter digestibility was observed in diet group AMP-0.2. Fish fed diet groups AMP-0.2 and AMP-0.4 had significantly higher peroxidase and bactericidal activities than fish fed the control diet. Nitro-blue-tetrazolium (NBT) activity was found to be significantly (P < 0.05) greater in fish fed diet groups AMP-0.4 and AMP-0.8. Total serum protein, lysozyme activity and agglutination antibody titer were also increased (P > 0.05) by dietary supplementation. In contrast, catalase activity decreased with AMP supplementation. Moreover, the fish fed AMP supplemented diets had better improvement (P < 0.05) in body lipid contents, condition factor, hematocrit content and glutamyl oxaloacetic transaminase (GOT) level than the control group. Supplementation also improved both freshwater and oxidative stress resistances. Interestingly, the fish fed diet groups AMP-0.2 and AMP-0.4 showed the least oxidative stress condition. Finally it is concluded that, dietary AMP supplementation enhanced the growth, digestibility, immune response and stress resistance of red sea bream. The regression analysis revealed that a dietary AMP supplementation between 0.2 and 0.4% supported weight gain and lysozyme activity as a marker of immune functions for red sea bream, which is also inline with the most of the growth and health performance parameters of fish under present experimental conditions.

Determination of the adequate dose of garlic diallyl disulfide and diallyl trisulfide for effecting changes in growth performance, total-tract nutrient and energy digestibility, ileal characteristics, and serum immune parameters in broiler chickens.

The objective of the current experiment was to determine the adequate dose and impact of graded concentrations of garlic diallyl disulfide (DADS) and diallyl trisulfide (DATS) on growth performance, total-tract nutrient and energy digestibility, serum immune parameters, and ileal morphology in broiler chickens. At 28-d post-hatch, male broiler chickens were allotted on the basis of initial body weight (1.34 ± 0.106 kg) in a randomized complete block desing ( RCBD: ) to one of six treatments that consisted of an oral gavage of 0, 0.45, 0.90, 1.80, 3.6, or 7.2 mg of DADS + DATS per kg bodyweight (BW) with 8 replicate cages per treatment and 4 birds per cage. The DADS + DATS was administered to birds by daily oral gavage for a period of 6 d. Growth performance was recorded and excreta were collected for analysis of DM, nitrogen ( N: ), and energy ( E: ) digestibility and on the last day of the experiment, the median bird in each cage was euthanized and the mid ileum was excised for morphological and gene expression measurements and blood was collected for serum natural antibody and complement assays. Body weight gain and villus height were linearly increased (P < 0.01) with oral gavage of DADS + DATS. There was a quadratic effect (P < 0.01) of the oral gavage on digestibility of DM, N, and E that corresponded to an average broken-line regression-derived adequate dose of 1.16 mg DADS + DATS per kg BW. Supplementation of DADS + DATS by oral gavage had no impact on gene expression markers although there was a tendency for an increase (P = 0.10) in serum natural antibody activity due to treatment. Results from the current study indicate that supplementation of a gavage containing DADS + DATS improves BW gain, ileal morphology, and digestibility of DM, N, and E and may affect serum immune parameters in broiler chickens. The average broken-line regression-derived adequate dose to optimize BW gain and villus height response was 2.51 mg DADS + DATS per kg BW.

Probiotic form effects on growth performance, digestive function, and immune related biomarkers in broilers.

The aim of this work was to assess the effect of dietary viable or heat inactivated probiotic forms (PF) combined or not with avilamycin (AV) used as a growth promoter, on broiler growth performance, nutrient digestibility, digestive enzyme activities, and expression of immune response related genes.Depending on the type of PF (i.e., no addition, viable, inactivated) and AV addition (no/yes), 450 one-day-old Cobb male broilers were allocated in the following 6 treatments according to a 3 × 2 factorial arrangement with 5 replicates of 15 broilers each for 6 wk: CoN: diet without any addition; CoN+A: combination of CoN with AV; ViP: viable PF - no AV; ViP+A: combination of ViP with AV; InP: inactivated PF - no AV; InP+A: combination of InP with AV.There were no interactions (P > 0.05) for overall performance parameters. In contrast, PF or AV addition improved BW gain (PPF= 0.015; PAV < 0.001), FCR (PPF < 0.001; PAV < 0.001) and production efficiency factor (PPF= 0.001; PAV= 0.001).Significant (PPF×AV ≤ 0.05) interaction effects regarding ileal digestibility (IAD) of DM and total tract apparent digestibility (TTAD) of DM and ether extracts (EE) were noted. In addition, PF affected IAD and TTAD of CP (PPF < 0.001, PPF= 0.004, respectively). Inactivated PF increased (PPR= 0.024) lipase activity in jejunal digesta.At spleen level InP and ViP+A down-regulated TGF-ß4 (PPF × AV = 0.035) compared to CoN and ViP, whereas ViP+A up-regulated iNOS (PPF × AV = 0.022). An anti-inflammatory effect of live and inactive PF and/or AV addition at cecal tonsils was shown by iNOS down-regulation (PPF × AV= 0.015) compared to CoN. Furthermore, AV down-regulated IFN-γ (PAV= 0.002).In conclusion, viable probiotic, as well as inactivated probiotic alone or in combination with avilamycin, improved nutrient digestibility. All dietary additives affected growth performance positively and induced an anti-inflammatory response at cecal level.

In Vitro Evidence for Immune-Modulatory Properties of Non-Digestible Oligosaccharides: Direct Effect on Human Monocyte Derived Dendritic Cells.

Infant formulas containing non-digestible oligosaccharides (NDO) similar to the composition in breast milk or a combination of lactic acid bacteria (LAB) and NDO have been shown to harbor preventive effects towards immune-regulatory disorders. The aim of this study was to investigate the immune-modulatory potential of non-digestible short chain galacto- and long chain fructo-oligosaccharides (scGOS/lcFOS) mimicking the natural distribution of oligosaccharides in human breast milk in presence or absence of certain LAB strains in human monocyte derived dendritic cells (MoDC). Immature human MoDC prepared from peripheral blood of healthy non-atopic volunteers were screened in vitro after stimulation with specific scGOS/lcFOS in presence or absence of LAB. IL-10 and IL-12p70 release was analyzed after 24 hours in cell-free supernatants by enzyme-linked immunosorbent assay (ELISA). A luminex-based assay was conducted to assess further cytokine and chemokine release by MoDC. To investigate the resulting T cell response, stimulated MoDC were co-incubated with naïve T cells in allogeneic stimulation assays and intracellular Foxp3 expression, as well as immune-suppressive capacity was determined. Oligosaccharides did not induce relevant amounts of IL-12p70 production, but did promote IL-10 release by MoDC. Furthermore, scGOS/lcFOS mixtures exerted a significant enhancing effect on LAB induced IL-10 secretion by MoDC while no increase in IL-12p70 production was observed. Blocking toll like receptor (TLR)4 abrogated the increase in IL-10 in both the direct stimulation and the LAB stimulation of MoDC, suggesting that scGOS/lcFOS act via TLR4. Finally, scGOS/lcFOS-treated MoDC were shown to upregulate the number of functional suppressive Foxp3 positive T cells following allogeneic stimulation. Our results indicate anti-inflammatory and direct, microbiota independent, immune-modulatory properties of scGOS/lcFOS mixtures on human MoDC suggesting a possible induction of regulatory T cells (Tregs). The tested combinations of LAB and scGOS/lcFOS might represent a useful dietary ingredient for the maintenance of intestinal homeostasis via the induction of Tregs.

Qualitative and quantitative determination of peptides related to celiac disease in mixtures derived from different methods of simulated gastrointestinal digestion of wheat products.

During wheat digestion, gluten-derived proteolytic resistant peptides are generated, some of them involved in celiac disease. In vitro digestion models able to mimic the peptides generated in the human gastrointestinal tract are extremely useful to assess the pathogenicity of wheat-derived products. In this paper, samples belonging to three different durum wheat varieties were taken at six different steps of the pasta production chain and two different digestion models present in the literature were assessed on the different samples: a more complex one using artificial fluids simulating the exact composition of digestive juices, and a simplified method based on a peptic-tryptic/chymotryptic treatment of wheat ethanolic extract. An extensive characterization of the peptides generated using two in vitro digestion models was performed through LC-MS/MS techniques and the two methods were compared in order to evaluate qualitative and quantitative differences and their possible implications for varietal screening. Strong differences in the type of peptides produced with the two methods were detected, indicating that the simplified method can still be used for a varietal screening but is not representative of the peptides really generated after physiological human digestion. Results indicate a clear necessity of physiologically accurate models for simulating human gastrointestinal digestion of wheat products.

Cross-linking of ß-lactoglobulin enhances allergic sensitization through changes in cellular uptake and processing.

Cross-linking of proteins has been exploited by the food industry to change food texture and functionality but the effects of these manipulations on food allergenicity still remain unclear. To model the safety assessment of these food biopolymers, we created cross-linked bovine ß-lactoglobulin (CL-BLG) by laccase treatment. The purpose of the present study was to compare the immunogenicity and allergenicity of CL-BLG with native BLG in a mouse model of food allergy. First, BALB/c mice were intragastrically sensitized and orally challenged with BLG or CL-BLG and BLG-specific serum antibodies and splenic leukocyte cytokine production and cell proliferation were measured. Hereafter, epithelial protein uptake was monitored in vitro and in vivo and the effects of BLG cross-linking on interactions with dendritic cells were analyzed in vitro. Sensitization of mice with CL-BLG resulted in higher levels of IgE, IgG1, and IgG2a. In contrast, a subsequent oral challenge with CL-BLG resulted in lower mast cell degranulation. Cross-linking of BLG reduced its epithelial uptake but promoted sampling through Peyer's patches. Differences in endocytosis by dendritic cells (DCs) and in vitro endolysosomal processing were observed between BLG and CL-BLG. CL-BLG primed DCs induced higher Th2 response in vitro. Cross-linking of BLG increased its sensitizing capacity, implying that the assessment of highly polymerized food proteins is of clinical importance in food allergy. Moreover, manufacturers of foods or therapeutic proteins should pay considerate attention to the health risk of protein aggregation.

Impact of immune system stimulation on the ileal nutrient digestibility and utilisation of methionine plus cysteine intake for whole-body protein deposition in growing pigs.

The impact of immune system stimulation (ISS) on the ileal nutrient digestibility and utilisation of dietary methionine plus cysteine (SAA) intake for whole-body protein deposition (PD) was evaluated in growing pigs. For this purpose, sixty barrows were used in two experiments: thirty-six pigs in Expt I and twenty-four pigs in Expt II. Pigs were feed restricted and assigned to five levels of dietary SAA allowance (three and two levels in Expt I and II, respectively) from SAA-limiting diets. Following adaptation, pigs at each dietary SAA level were injected with either increasing amounts of Escherichia coli lipopolysaccharide (ISS+; eight and six pigs per dietary SAA level in Expt I and II, respectively) or saline (ISS - ; four and six pigs in Expt I and II, respectively) while measuring the whole-body nitrogen (N) balance. After N-balance observations, pigs were euthanised, organs were removed and ileal digesta were collected for determining nutrient digestibility. Ileal digestibility of gross energy, crude protein and amino acids was not affected by ISS (P>0·20). ISS reduced PD at all levels of dietary SAA intake (P< 0·01). The linear relationship between daily dietary SAA intake and PD observed at the three lowest dietary SAA intake levels indicated that ISS increased extrapolated maintenance SAA requirements (P< 0·05), but had no effect on the partial efficiency of the utilisation of dietary SAA intake for PD (P>0·20). Physiological and metabolic changes associated with systemic ISS had no effect on the ileal digestibility of nutrients per se, but altered SAA requirements for PD in growing pigs.

Commensal bacteria at the interface of host metabolism and the immune system.

The mammalian gastrointestinal tract, the site of digestion and nutrient absorption, harbors trillions of beneficial commensal microbes from all three domains of life. Commensal bacteria, in particular, are key participants in the digestion of food, and are responsible for the extraction and synthesis of nutrients and other metabolites that are essential for the maintenance of mammalian health. Many of these nutrients and metabolites derived from commensal bacteria have been implicated in the development, homeostasis and function of the immune system, suggesting that commensal bacteria may influence host immunity via nutrient- and metabolite-dependent mechanisms. Here we review the current knowledge of how commensal bacteria regulate the production and bioavailability of immunomodulatory, diet-dependent nutrients and metabolites and discuss how these commensal bacteria-derived products may regulate the development and function of the mammalian immune system.

Relationship between protein digestibility and allergenicity: comparisons of pepsin and cathepsin.

An association between protein allergenicity and resistance to pepsin digestion in the gastrointestinal tract has been proposed. However, although widely accepted, such an association is inconsistent with known labile allergens and resistant nonallergens. Given the central role of antigen presenting cells, and in particular dendritic cells (DC), in the development of allergic responses, the stability of allergens to intracellular processing may be more relevant than resistance to extracellular pepsin digestion. We have characterised the expression by DC of cathepsins (proteolytic enzymes), and compared the proteolytic activity of the most highly expressed cathepsin with pepsin for a range of 9 allergens and 4 putative nonallergens. Cathepsin expression in bone marrow-derived DC (BM-DC) derived from BALB/c strain mice was characterised by flow cytometry; cathepsins D, E and S were identified, with cathepsin D being the most highly expressed. Digestion studies revealed that the majority of allergens (5/9) were pepsin resistant, whereas non-allergens (3/4) were labile. If the generation of pepsin-resistant fragments was considered as a feature of allergenicity, this increased to 7/9 allergens and 4/4 nonallergens. In contrast, most of the proteins examined were resistant to cathepsin digestion, with significant digestion recorded for only 2/9 allergens and 2/4 non-allergens. Chemical reduction (to mimic intracellular reducing conditions) increased the susceptibility of proteins to digestion by cathepsins, but did not improve discrimination between allergens and nonallergens on this basis. These data confirm that there is a general relationship between resistance to digestion with pepsin and allergenicity. The relationship is not absolute, but the information gained from this characteristic does provide useful information in a weight of evidence approach for allergenicity assessment. The most abundant cathepsin detected in antigen processing BM-DC, cathepsin D, is not an appropriate substitute for pepsin. The hypothesis that pepsin stability may be a surrogate for stability to digestion within DC may still hold true, but consideration of a single enzyme in this context is possibly an oversimplification.

The sensitising capacity of intact ß-lactoglobulin is reduced by co-administration with digested ß-lactoglobulin.

BACKGROUND: It is generally believed that protein hydrolysis in the gastrointestinal tract decreases the allergenicity of food allergens. However, it remains unknown if specific properties of digestion products determine whether a sensitisation or tolerogenic immune response will develop. We sought to examine the sensitising capacity of the cow's milk allergen ß-lactoglobulin (BLG) and digestion products thereof in a Brown Norway (BN) rat model. METHODS: Intact BLG was digested in an in vitro model simulating the gastro-duodenal digestion process and subsequently fractionated by gel permeation chromatography. BN rats were dosed with either PBS, 200 µg of intact BLG, 30 µg of intact BLG, 200 µg of partially digested BLG, 200 µg of digested BLG, or with 200 µg of a fraction of large complexes or a fraction of small complexes. Sera from BN rats were analysed for specific antibodies and avidity was measured. RESULTS: BLG partly resisted the digestion process. However, the BLG molecules that did not survive the digestion process were rapidly broken down to peptides of sizes less than Mr 4,500. Specific antibody responses revealed that both 200 and 30 µg of intact BLG had immunogenic as well as sensitising capacity, while digested BLG could not induce any specific antibodies. Most importantly, while intact BLG showed a significant sensitising capacity when administered alone, this sensitising capacity was significantly reduced when co-administered with digested BLG. CONCLUSIONS: Co-immunisation of intact BLG with digested BLG reduces the sensitising capacity of intact BLG, which could result from tolerogenic mechanisms induced by the digestion products.