UK Food Standards Agency Workshop Report: Diet and Immune Function

The UK Food Standards Agency convened a workshop on 13 May 2009 to discuss recently completed research on diet and immune function. The objective of the workshop was to review this research and to establish priorities for future research. Several of the trials presented at the workshop showed some effect of nutritional interventions (e.g. vitamin D, Zn, Se) on immune parameters. One trial found that increased fruit and vegetable intake may improve the antibody response to pneumococcal vaccination in older people. The workshop highlighted the need to further clarify the potential public health relevance of observed nutrition-related changes in immune function, e.g. susceptibility to infections and infectious morbidity.

Selection for cuticular melanism reveals immune function and life-history trade-offs in Spodoptera littoralis

Several insect species show an increase in cuticular melanism in response to high densities. In some species, there is evidence that this melanism is correlated with an up-regulation of certain immune system components, particularly phenoloxidase (PO) activity, and with the down-regulation of lysozyme activity, suggesting a trade-off between the two traits. As melanism has a genetic component, we selected both melanic and nonmelanic lines of the phase-polyphenic lepidopteran, Spodoptera littoralis, in order to test for a causative genetic link between melanism, PO activity and lysozyme activity, and to establish if there are any life-history costs associated with the melanic response. We found that, in fact, melanic lines had lower PO activity and higher lysozyme activity than nonmelanic lines, confirming a genetic trade-off between the two immune responses, but also indicating a genetic trade-off between melanism and PO activity. In addition, we found that lines with high PO activity had slower development rates suggesting that investment in PO, rather than in melanism, is costly.

Male morph predicts investment in larval immune function in the dung beetle, Onthophagus taurus

Investment in immunity is costly, so that resource-based trade-offs between immunity and sexually selected ornaments might be expected. The amount of resources that an individual can invest in each trait will be limited by the total resources available to them. It would therefore be informative to investigate how investment in immune function changes during growth or production of the sexual trait as resources are diverted to it. Using the dung beetle, Onthophagus taurus, which displays both sexual and male dimorphism in horn size, we examined changes in one measure of immune function, phenoloxidase (PO) activity, in the hemolymph of larvae prior to and during horn growth. We found that PO levels differed between small- and large-horned males throughout the final instar prior to the point where investment in horn growth was taking place. PO levels in females were intermediate to the 2 male morphs. These differences could not be accounted for by differences in condition, measured as hemolymph protein levels and weight. We suggest that the observed differences might be associated with sex- and morph-specific variation in juvenile hormone levels.

Density-dependent prophylaxis and condition-dependent immune function in Lepidopteran larvae: a multivariate approach

1. The risk of parasitism and infectious disease is expected to increase with population density as a consequence of positive density-dependent transmission rates. Therefore, species that encounter large fluctuations in population density are predicted to exhibit plasticity in their immune system, such that investment in costly immune defences is adjusted to match the probability of exposure to parasites and pathogens (i.e. density-dependent prophylaxis).

Heritability of immune function in the caterpillar Spodoptera littoralis

Phenoloxidase (PO) is believed to be a key mediator of immune function in insects and has been implicated both in non-self recognition and in resistance to a variety of parasites and pathogens, including baculoviruses and parasitoids. Using larvae of the Egyptian cotton leafworm, Spodoptera littoralis, we found that despite its apparent importance, haemolymph PO activity varied markedly between individuals, even amongst insects reared under apparently identical conditions. Sib-analysis methods were used to determine whether individuals varied genetically in their PO activity, and hence in one aspect of immune function. The heritability estimate of haemolymph PO activity was high (h 2 = 0.690 +/- 0.069), and PO activity in the haemolymph was strongly correlated with PO activity in both the cuticle and midgut; the sites of entry for most parasites and pathogens. Haemolymph PO activity was also strongly correlated with the degree to which a synthetic parasite (a small piece of nylon monofilament) was encapsulated and melanized (r = 0.622 +/- 0.142), suggesting that the encapsulation response is also heritable. The mechanism maintaining this genetic variation has yet to be elucidated.

Macronutrient balance mediates trade-offs between immune function and life history traits

1. Diet and health are intimately linked and recent studies have found that caloric restriction can affect immune function. However, when given a choice between diets that differ in their macronutrient composition, pathogen-infected individuals can select a diet that improves their survival, suggesting that the nutritional composition of the diet, as well as its calorie content, can play a role in defence against disease. Moreover, as individuals change their diet when infected, it suggests that a diet that is optimal for growth is not optimal for immunity, leading to trade-offs.
2. Currently, our knowledge of the effects of diet on immunity is limited because previous experiments have manipulated either single nutrients or the calorie content of the diet without considering their interactive effects. By simultaneously manipulating both the diet composition (quality) and its caloric density (quantity), in both naive and immune-challenged insects, we asked how do diet quality and quantity influence an individual's ability to mount an immune response? And to what extent are allocation trade-offs driven by quantity- versus quality-based constraints?
3. We restricted individuals to 20 diets varying in their protein and carbohydrate content and used 3D response surfaces to visualize dietary effects on larval growth and immune traits. Our results show that both constitutive and induced immune responses are not limited by the total quantity of nutrients consumed, but rather different traits respond differently to variation in the ratios of macronutrients (diet quality), and peak in different regions of macronutrient space. The preferred dietary composition therefore represents a compromise between the nutritional requirements of growth and immune responses. We also show that a non-pathogenic immune challenge does not affect diet choice, rather immune-challenged insects modify their allocation of nutrients to improve their immune response.
4. Our results indicate that immune traits are affected by the macronutrient content of the diet and that no diet can simultaneously optimize all components of the immune system. To date the emphasis has been on the effects of micronutrients in improving immunity, our findings indicate that this must be widened to include the neglected impact of macronutrients on defence against disease.

Effect of fruit and vegetable consumption on immune function in older people: A randomized controlled trial

Background: Fruit and vegetable (FV) intake, which is often low in older people, is associated with reduced chronic disease risk. Objective: We determined whether increased FV intake improves measures of immune function. Design: We conducted a randomized controlled trial (The Ageing and Dietary Intervention Trial) in 83 healthy volunteers aged 65-85 y with low FV intakes (=2 portions/d); 82 subjects completed the intervention. Participants were assigned to continue their normal diets or to consume =5 FV portions/d for 16 wk. At 12 wk, tetanus toxoid (0.5 mL intramuscular) and Pneumovax II vaccine (0.5 mL intramuscular; both vaccines from Sanofi Pasteur) were administered. FV intake was monitored by using diet histories, and biomarkers of nutritional status were assessed. The primary endpoint was the antibody response to vaccination. Specific antibodies binding to tetanus toxoid (total IgG) and pneumococcal capsular polysaccharide (total IgG and IgG2) were assessed at baseline and 16 wk. Participants were recruited between October 2006 and June 2008. Results: The change in FV consumption differed significantly between groups [mean change in number of portions (95% CI): in the 2-portion/d group, 0.4 portions/d (0.2, 0.7 portions/d); in the 5-portion/d group, 4.6 portions/d (4.1, 5.0 portions/d); P < 0.001)] and also in micronutrient status. Antibody binding to pneumococcal capsular polysaccharide (total IgG) increased more in the 5-portion/d group than in the 2-portion/d group [geometric mean (95% CI) of the week 16:baseline ratio: 3.1 (2.1, 4.4) and 1.7 (1.3, 2.1), respectively; P = 0.005)]. There was no significant difference in the increases in antibody binding to tetanus toxoid. Conclusion: Increased FV intake improves the Pneumovax II vaccination antibody response in older people, which links an achievable dietary goal with improved immune function. This trial was registered at clinicaltrials.gov as NCT00858728. © 2012 American Society for Nutrition.

Costs of resistance: genetic correlations and potential trade-offs in an insect immune system

Theory predicts that natural selection will erode additive genetic variation in fitness-related traits. However, numerous studies have found considerable heritable variation in traits related to immune function, which should be closely linked to fitness. This could be due to trade-offs maintaining variation in these traits. We used the Egyptian cotton leafworm, Spodoptera littoralis, as a model system to examine the quantitative genetics of insect immune function. We estimated the heritabilities of several different measures of innate immunity and the genetic correlations between these immune traits and a number of life history traits. Our results provide the first evidence for a potential genetic trade-off within the insect immune system, with antibacterial activity (lysozyme-like) exhibiting a significant negative genetic correlation with haemocyte density, which itself is positively genetically correlated with both haemolymph phenoloxidase activity and cuticular melanization. We speculate on a potential trade-off between defence against parasites and predators, mediated by larval colour, and its role in maintaining genetic variation in traits under natural selection.

Aging in personal and social immunity: do immune traits senesce at the same rate?

How much should an individual invest in immunity as it grows older? Immunity is costly and its value is likely to change across an organism's lifespan. A limited number of studies have focused on how personal immune investment changes with age in insects, but we do not know how social immunity, immune responses that protect kin, changes across lifespan, or how resources are divided between these two arms of the immune response. In this study, both personal and social immune functions are considered in the burying beetle, Nicrophorus vespilloides. We show that personal immune function declines (phenoloxidase levels) or is maintained (defensin expression) across lifespan in nonbreeding beetles but is maintained (phenoloxidase levels) or even upregulated (defensin expression) in breeding individuals. In contrast, social immunity increases in breeding burying beetles up to middle age, before decreasing in old age. Social immunity is not affected by a wounding challenge across lifespan, whereas personal immunity, through PO, is upregulated following wounding to a similar extent across lifespan. Personal immune function may be prioritized in younger individuals in order to ensure survival until reproductive maturity. If not breeding, this may then drop off in later life as state declines. As burying beetles are ephemeral breeders, breeding opportunities in later life may be rare. When allowed to breed, beetles may therefore invest heavily in "staying alive" in order to complete what could potentially be their final reproductive opportunity. As parental care is important for the survival and growth of offspring in this genus, staying alive to provide care behaviors will clearly have fitness payoffs. This study shows that all immune traits do not senesce at the same rate. In fact, the patterns observed depend upon the immune traits measured and the breeding status of the individual.

Elafin, an Elastase-specific Inhibitor, Is Cleaved by Its Cognate Enzyme Neutrophil Elastase in Sputum from Individuals with Cystic Fibrosis

Elafin is a neutrophil serine protease inhibitor expressed in lung and displaying anti-inflammatory and anti-bacterial properties. Previous studies demonstrated that some innate host defense molecules of the cystic fibrosis (CF) and chronic obstructive pulmonary disease airways are impaired due to increased proteolytic degradation observed during lung inflammation. In light of these findings, we thus focused on the status of elafin in CF lung. We showed in the present study that elafin is cleaved in sputum from individuals with CF. Pseudomonas aeruginosa-positive CF sputum, which was found to contain lower elafin levels and higher neutrophil elastase (NE) activity compared with P. aeruginosa-negative samples, was particularly effective in cleaving recombinant elafin. NE plays a pivotal role in the process as only NE inhibitors are able to inhibit elafin degradation. Further in vitro studies demonstrated that incubation of recombinant elafin with excess of NE leads to the rapid cleavage of the inhibitor. Two cleavage sites were identified at the N-terminal extremity of elafin (Val-5—Lys-6 and Val-9—Ser-10). Interestingly, purified fragments of the inhibitor (Lys-6—Gln-57 and Ser-10—Gln-57) were shown to still be active for inhibiting NE. However, NE in excess was shown to strongly diminish the ability of elafin to bind lipopolysaccharide (LPS) and its capacity to be immobilized by transglutamination. In conclusion, this study provides evidence that elafin is cleaved by its cognate enzyme NE present at excessive concentration in CF sputum and that P. aeruginosa infection promotes this effect. Such cleavage may have repercussions on the innate immune function of elafin.

Adiponectin is produced by lymphocytes and is a negative regulator of granulopoiesis

Lymphocytes have long been established to play an important role in the regulation of hematopoiesis and produce many cytokines that act on hematopoietic progenitor cells. Previous studies by our group have shown that normal, unstimulated lymphocytes produce a protein that inhibits normal bone marrow GM colony formation. Adiponectin is an adipokine that has been demonstrated to act as a negative regulator of hematopoiesis and immune function. This study aimed to determine if the inhibitory molecule that we described previously was adiponectin. Here, we show transcription, translation, and secretion of adiponectin from lymphocytes and demonstrate that its receptors, AdipoR1 and AdipoR2, are expressed by bone marrow MNCs. We show that although the adiponectin expression is low in lymphocytes, it is sufficient to induce a significant inhibitory effect on GM precursors (CFU-GM) and activate the AMPK pathway in these cells. The regulation of adiponectin production by lymphocytes and its detailed function in suppressing GM colony formation need to be elucidated now. Our findings suggest a functional role for adiponectin as a negative regulator of granulopoiesis. J. Leukoc. Biol. 88: 807-811; 2010.

Decreased serum retinol is associated with increased mortality in renal transplant recipients

Vitamin A plays a central role in epithelial integrity and immune function. Given the risk of infection after transplantation, adequate vitamin A concentrations may be important in patients with a transplant. We assessed whether there was an association between retinol concentration and all-cause mortality in renal transplant recipients.

Aging impairs peritoneal but not bone marrow-derived macrophage phagocytosis

Aging results in deterioration of the immune system, which is associated with increased susceptibility to infection and impaired wound healing in the elderly. Phagocytosis is an essential process in both wound healing and immune defence. As such, age-related impairments in phagocytosis impact on the health of the elderly population. Phagocytic efficiency in peritoneal macrophages, bone marrow-derived macrophages and bone marrow monocytes from young and old mice was investigated. Aging significantly impaired phagocytosis by peritoneal macrophages, both in vitro and in vivo. However, bone marrow-derived macrophages and bone marrow monocytes did not exhibit age-related impairments in phagocytosis, suggesting no intrinsic defect in these cells. We sought to investigate underlying mechanisms in age-related impairments in phagocytosis by peritoneal macrophages. We hypothesized that microenvironmental factors in the peritoneum of old mice impaired macrophage phagocytosis. Indeed, macrophages from young mice injected into the peritoneum of old mice exhibited impaired phagocytosis. Proportions of peritoneal immune cells were characterized, and striking increases in numbers of T cells, B1 and B2 cells were observed in the peritoneum of old mice compared with young mice. In addition, B cell-derived IL-10 was increased in resting and LPS-activated peritoneal cell cultures from old mice. These data demonstrate that aging impairs phagocytosis by tissue-resident peritoneal macrophages, but not by bone marrow-derived macrophages/monocytes, and suggest that age-related defects in macrophage phagocytosis may be due to extrinsic factors in the tissue microenvironment. As such, defects may be reversible and macrophages could be targeted therapeutically in order to boost immune function in the elderly.

A Functional Variant of Elafin With Improved Anti-inflammatory Activity for Pulmonary Inflammation

Elafin is a serine protease inhibitor produced by epithelial and immune cells with anti-inflammatory properties. Research has shown that dysregulated protease activity may elicit proteolytic cleavage of elafin, thereby impairing the innate immune function of the protein. The aim of this study was to generate variants of elafin (GG- and QQ-elafin) that exhibit increased protease resistance while retaining the biological properties of wild-type (WT) elafin. Similar to WT-elafin, GG- and QQ-elafin variants retained antiprotease activity and susceptibility to transglutaminase-mediated fibronectin cross-linking. However, in contrast to WT-elafin, GG- and QQ-elafin displayed significantly enhanced resistance to degradation when incubated with bronchoalveolar lavage fluid from patients with cystic fibrosis. Intriguingly, both variants, particularly GG-elafin, demonstrated improved lipopolysaccharide (LPS) neutralization properties in vitro. In addition, GG-elafin showed improved anti-inflammatory activity in a mouse model of LPS-induced acute lung inflammation. Inflammatory cell infiltration into the lung was reduced in lungs of mice treated with GG-elafin, predominantly neutrophilic infiltration. A reduction in MCP-1 levels in GG-elafin treated mice compared to the LPS alone treatment group was also demonstrated. GG-elafin showed increased functionality when compared to WT-elafin and may be of future therapeutic relevance in the treatment of lung diseases characterized by a protease burden.