Immune activity elevates energy expenditure of house sparrows: a link between direct and indirect costs?

β-Glucan enhances respiratory activity of leukocytes suppressed by stress and modulates blood glucose levels in pacu (Piaractus mesopotamicus)

We evaluated the immune response of pacu fed with a β-glucan diet (0.5%) for 10 days. After the feeding period, fish were subjected to handling and 3 h after, inoculated with Aeromonas hydrophila. Fish were sampled before handling (baseline condition), 3, 6, and 24 h and 1 week after inoculation. A higher level of blood glucose was found in fish treated with β-glucan in baseline conditions. Handling and bacterial inoculation increased the circulating levels of cortisol and glucose and promoted the acute inflammatory response (lymphopenia and neutrophilia). β-Glucan prevented the decrease in the respiratory activity of leukocytes observed in the control group at 3 h sampling. β-Glucan did not affect the complement and lysozyme, which were activated 24 h after the bacterial challenge in control fish. A reduction in the number of leukocytes was found in fish treated with β-glucan 1 week after the challenge. We suggest two plausible hypotheses for this event: (1) it could be attributed to a depletion of the immune responses or (2) it could be due to a mobilization of the leukocytes to the spleen for antigen presenting/processing. In general, β-glucan avoided the reduction of the activity of leukocytes after stress and the bacterial challenge and increased the baseline glucose levels. Our findings confirm the immunomodulatory action of glucan and add evidence showing that glucan can have a role in stress response.

Effects of Eucalypt Plant Monoterpenes on Koala (Phascolarctos Cinereus) Cytokine Expression In Vitro

Protective immunity is crucial for survival of any species, though the koala as a specialist feeder adapted to an exclusive diet of eucalypts that contain plant secondary metabolites of varying toxicity and of immunomodulatory property. Being constantly exposed to such dietary chemicals it raises the question of their immune effects in a specialist eucalypt feeder. This study demonstrates that natural levels of circulating eucalypt plant secondary metabolites have dose dependent in vitro effects on cytokine expression of koala peripheral blood mononuclear cells, suggesting a potential trade-off of reduced function in multiple arms of the immune system associated with koala's use of its specialized dietary niche.

Immune response of hibernating European bats to a fungal challenge

Immunological responses of hibernating mammals are suppressed at low body temperatures, a possible explanation for the devastating effect of the white-nose syndrome on hibernating North American bats. However, European bats seem to cope well with the fungal causative agent of the disease. To better understand the immune response of hibernating bats, especially against fungal pathogens, we challenged European greater mouse-eared bats (Myotis myotis) by inoculating the fungal antigen zymosan. We monitored torpor patterns, immune gene expressions, different aspects of the acute phase response and plasma oxidative status markers, and compared them with sham-injected control animals at 30 min, 48 h and 96 h after inoculation. Torpor patterns, body temperatures, body masses, white blood cell counts, expression of immune genes, reactive oxygen metabolites and non-enzymatic antioxidant capacity did not differ between groups during the experiment. However, zymosan injected bats had significantly higher levels of haptoglobin than the control animals. Our results indicate that hibernating greater mouse-eared bats mount an inflammatory response to a fungal challenge, with only mild to negligible consequences for the energy budget of hibernation. Our study gives a first hint that hibernating European bats may have evolved a hibernation-adjusted immune response in order to balance the trade-off between competent pathogen elimination and a prudent energy-saving regime.

Summary: Our experimental immunological study on European bats provides new information on the functionality of the immune system in hibernation. For this we challenged bats with a fungal antigen and measured different immunological parameters.

Intensity-dependent energetic costs in a reciprocal parasitic relationship

Parasitic infections elicit host defences that pose energetic trade-offs with other fitness-related traits. Bitterling fishes and unionid mussels are involved in a two-way parasitic interaction. Bitterling exploit mussels by ovipositing into their gills. In turn, mussel larvae (glochidia) develop on the epidermis and gills of fish. Hosts have evolved behavioural responses to reduce parasite load, suggesting that glochidia and bitterling parasitism are costly. We examined the energetic cost of parasitism on both sides of this relationship. We used intermittent flow-through respirometry to measure (1) standard metabolic rate (SMR) of individual duck mussels Anodonta anatina (a common bitterling host) before and during infection by embryos of the European bitterling Rhodeus amarus, and (2) SMR and maximum oxygen uptake (MO₂max) of individual R. amarus before and during infection with glochidia of the Chinese pond mussel Sinanodonta woodiana (a mussel species that successfully infects bitterling). As predicted, we observed an increase in mussel SMR when infected by bitterling embryos and an increased SMR in glochidia-infected bitterling, though this was significantly mediated by the time post-infection. Contrary to our predictions, glochidia infection did not impair MO₂max and the number of glochidia attached to gills positively (rather than negatively) correlated with MO₂max. The results suggest that tolerance is the prevailing coping mechanism for both fish and mussels when infected, while resistance mechanisms appear to be confined to the behavioural level.

Effect of temperature on antioxidant defense and innate immunity in Brandt's voles

Ambient temperature is an important factor influencing many physiological processes, including antioxidant defense and immunity. In the present study, we tested the hypothesis that antioxidant defense and immunity are suppressed by high and low temperature treatment in Brandt's voles (Lasiopodomys brandtii). Thirty male voles were randomly assigned into different temperature groups (4, 23, and 32 °C, n=10 for each group), with the treatment course lasting for 27 d. Results showed that low temperature increased gross energy intake (GEI) and liver, heart, and kidney mass, but decreased body fat mass and dry carcass mass. With the decline in temperature, hydrogen peroxide (H2O2) concentration, which is indicative of reactive oxygen species (ROS) levels, increased in the liver, decreased in the heart, and was unchanged in the kidney, testis, and small intestine. Lipid peroxidation indicated by malonaldehyde (MDA) content in the liver, heart, kidney, testis, and small intestine did not differ among groups, implying that high and low temperature did not cause oxidative damage. Similarly, superoxide dismutase (SOD) and catalase (CAT) activities and total antioxidant capacity (T-AOC) in the five tissues did not respond to low or high temperature, except for elevation of CAT activity in the testis upon cold exposure. Bacteria killing capacity, which is indicative of innate immunity, was nearly suppressed in the 4 °C group in contrast to the 23 °C group, whereas spleen mass and white blood cells were unaffected by temperature treatment. The levels of testosterone, but not corticosterone, were influenced by temperature treatment, though neither were correlated with innate immunity, H2O2 and MDA levels, or SOD, CAT, and T-AOC activity in any detected tissues. Overall, these results showed that temperature had different influences on oxidative stress, antioxidant enzymes, and immunity, which depended on the tissues and parameters tested. Up-regulation or maintenance of antioxidant defense might be an important mechanism for voles to survive highly variable environmental temperatures.

The energetic cost of parasitism in a wild population

Parasites have profound fitness effects on their hosts, yet these are often sub-lethal, making them difficult to understand and quantify. A principal sub-lethal mechanism that reduces fitness is parasite-induced increase in energetic costs of specific behaviours, potentially resulting in changes to time and energy budgets. However, quantifying the influence of parasites on these costs has not been undertaken in free-living animals. We used accelerometers to estimate energy expenditure on flying, diving and resting, in relation to a natural gradient of endo-parasite loads in a wild population of European shags Phalacrocorax aristotelis. We found that flight costs were 10% higher in adult females with higher parasite loads and these individuals spent 44% less time flying than females with lower parasite loads. There was no evidence for an effect of parasite load on daily energy expenditure, suggesting the existence of an energy ceiling, with the increase in cost of flight compensated for by a reduction in flight duration. These behaviour specific costs of parasitism will have knock-on effects on reproductive success, if constraints on foraging behaviour detrimentally affect provisioning of young. The findings emphasize the importance of natural parasite loads in shaping the ecology and life-history of their hosts, which can have significant population level consequences.

Immune challenge-induced oxidative damage may be mitigated by biliverdin

An effective immune response results in the elimination of pathogens, but this immunological benefit may be accompanied by increased levels of oxidative damage. However, organisms have evolved mechanisms to mitigate the extent of such oxidative damage, including the production and mobilization of antioxidants. One potential mechanism of mitigating immune challenge-induced changes in oxidative physiology is increasing biliverdin production. Biliverdin is chemically an antioxidant, but within-tissue correlations between biliverdin concentration and oxidative damage have never been directly examined. To test how biliverdin tissue concentrations are associated with physiological responses to an immune challenge, we exposed northern bobwhite quail (Colinus virginianus) to one of four treatments: injection of a non-pathogenic antigen - either lipopolysaccharide or phytohemagglutinin, control injection of phosphate-buffered saline or a sham procedure with no injection. Twenty-four hours later, we quantified oxidative damage and triglyceride concentration in the plasma, and biliverdin concentration in the plasma, liver and spleen. We found that both types of immune challenge increased oxidative damage relative to both non-injected and vehicle-injected controls, but treatment had no effects on any other metric. However, across all birds, oxidative damage and biliverdin concentration in the plasma were negatively correlated, which is consistent with a localized antioxidant function of biliverdin. Additionally, we uncovered multiple links between biliverdin concentration, change in mass during the immune challenges and triglyceride levels, suggesting that pathways associated with biliverdin production may also be associated with aspects of nutrient mobilization. Future experiments that manipulate biliverdin levels or oxidative damage directly could establish a systemic antioxidant function or elucidate important physiological impacts on body mass maintenance and triglyceride storage, mobilization or transport.

Early swelling response to phytohemagglutinin is lower in older toads

The effects of age on performance of life-history traits are diverse, but a common outcome is senescence, an irreversible deterioration of physical and physiological capabilities of older individuals. Immune response is potentially bound to senescence. However, little is known about immune response ageing in amphibians. In this work, we test the hypothesis that amphibian early immune response is reduced in older individuals. To this end, we captured adult natterjack toads (Epidalea calamita) and inoculated them with phytohemagglutinin, an innocuous protein that triggers a skin-swelling immune response whose magnitude is directly proportional to the ability of the individual to mount an immune response. We measured early swelling immune response (corresponding to an innate-response stage) hourly, for six hours, and we calculated the area under the curve (AUC) for each individual's time series, as a measure of immune response magnitude incorporating time. We estimated toad age by means of phalanx skeletochronology. Swelling and AUC decreased with age. Therefore, in accordance with our predictions, early immune response seems subject to senescence in these toads. Reduced ability to get over infections due to senescence of immune respose might be-together with a worse functioning of other organs and systems-among the causes of lower survival of older specimens.

The role of parasitism in the energy management of a free-ranging bird

Parasites often prompt sub-lethal costs to their hosts by eliciting immune responses. These costs can be hard to quantify but are crucial to our understanding of the host's ecology. Energy is a fundamental currency to quantify these costs, as energetic trade-offs often exist between key fitness-related processes. Daily energy expenditure (DEE) comprises of resting metabolic rate (RMR) and energy available for activity, which are linked via the energy management strategy of an organism. Parasitism may play a role in the balance between self-maintenance and activity, as immune costs can be expressed in elevated RMR. Therefore, understanding energy use in the presence of parasitism enables mechanistic elucidation of potential parasite costs. Using a gradient of natural parasite load and proxies for RMR and DEE in a wild population of breeding European shags (Phalacrocorax aristotelis), we tested the effect of parasitism on maintenance costs as well as the relationship between proxies for RMR and DEE. We found a positive relationship between parasite load and our RMR proxy in females but not males, and no relationship between proxies for RMR and DEE. This provides evidence for increased maintenance costs in individuals with higher parasite loads and suggests the use of an allocation energy management strategy, whereby an increase to RMR creates restrictions on energy allocation to other activities. This is likely to have fitness consequences as energy allocated to immunity is traded off against reproduction. Our findings demonstrate that understanding energy management strategies alongside fitness drivers is central to understanding the mechanisms by which these drivers influence individual fitness.

Seasonal variations in cellular and humoral immunity in male striped hamsters (Cricetulus barabensis)

Animals in the non-tropical zone usually demonstrate seasonal variations in immune function, which is important for their survival. In the present study, seasonal changes in immunity in striped hamsters (Cricetulus barabensis) were investigated to test the winter immunoenhancement hypothesis. Male hamsters were captured from the wild in the fall and winter of 2014 and in the spring and summer of 2015. Body mass, body fat mass and blood glucose levels of the hamsters were all highest in the summer, whereas relative fatness and thymus mass had no seasonal changes. Spleen mass was highest in the fall and white blood cells and phytohaemagglutinin (PHA) response indicative of cellular immunity were lowest in the summer among the four seasons, which supports the winter immunoenhancement hypothesis. IgG and IgM titers were lowest in the fall, which was against this hypothesis. Body fat mass had no correlations with cellular and humoral immunity, suggesting it was not the reason for seasonal changes in cellular and humoral immunity in males. Leptin titers were higher in spring and summer than in fall and winter. No correlation between leptin and cellular and humoral immunity suggested that leptin did not mediate their seasonal changes. Similarly, corticosterone levels were also higher in spring and summer than in fall and winter, which correlated negatively with cellular immunity but positively with IgG levels. This result implied that corticosterone has a suppressive effect on cellular immunity and an enhancing effect on humoral immunity. In summary, distinct components of immune systems exhibited different seasonal patterns. This article has an associated First Person interview with the first author of the paper.

Relative importance of chemical attractiveness to parasites for susceptibility to trematode infection

While the host immune system is often considered the most important physiological mechanism against parasites, precontact mechanisms determining exposure to parasites may also affect infection dynamics. For instance, chemical cues released by hosts can attract parasite transmission stages. We used the freshwater snail Lymnaea stagnalis and its trematode parasite Echinoparyphium aconiatum to examine the role of host chemical attractiveness, physiological condition, and immune function in determining its susceptibility to infection. We assessed host attractiveness through parasite chemo-orientation behavior; physiological condition through host body size, food consumption, and respiration rate; and immune function through two immune parameters (phenoloxidase-like and antibacterial activity of hemolymph) at an individual level. We found that, although snails showed high variation in chemical attractiveness to E. aconiatum cercariae, this did not determine their overall susceptibility to infection. This was because large body size increased attractiveness, but also increased metabolic activity that reduced overall susceptibility. High metabolic rate indicates fast physiological processes, including immune activity. The examined immune traits, however, showed no association with susceptibility to infection. Our results indicate that postcontact mechanisms were more likely to determine snail susceptibility to infection than variation in attractiveness to parasites. These may include localized immune responses in the target tissue of the parasite. The lack of a relationship between food consumption and attractiveness to parasites contradicts earlier findings that show food deprivation reducing snail attractiveness. This suggests that, although variation in resource level over space and time can alter infection dynamics, variation in chemical attractiveness may not contribute to parasite-induced fitness variation within populations when individuals experience similar environmental conditions.

Dietary L-glutamine supplementation improves growth performance, gut morphology, and serum biochemical indices of broiler chickens during necrotic enteritis challenge

Necrotic enteritis (NE) causes significant economic losses in the broiler chicken industry, especially in birds raised without in-feed antibiotics. L-glutamine (Gln) is an amino acid that may compensate for metabolic losses from infection and improve the intestinal development. This study investigated the effects of dietary Gln (10 g/kg) supplementation on growth performance, intestinal lesions, jejunum morphology, and serum biochemical indices of broiler chickens during NE challenge. The study employed a factorial arrangement of treatments with factors: NE challenge, no or yes; dietary Gln inclusion, 0 g/kg in starter (S), d 0 to 10, grower (G) d 10 to 24, and finisher (F) d 24 to 35; 10 g/kg in S, G, F, or 10 g/kg in S, G only. Each treatment was replicated in 6 floor pens with 17 birds per pen as the experimental unit for performance and 2 birds for other measurements. Challenge significantly reduced bird performance, increased incidence of intestinal lesions, and affected intestinal development and serum biochemical indices. Regardless of challenge, Gln supplementation increased gain (P < 0.05), feed intake (P < 0.05), and decreased FCR (P < 0.05) on d 24. On d 35, Gln improved gain (P < 0.05) and FCR (P < 0.001) whereas withdrawing Gln from finisher tended to diminish the beneficial effect on weight gain but not FCR. Dietary Gln reduced lesion scores in the jejunum (P < 0.01) and ileum (P < 0.01) in challenged birds. On d 16, Gln increased villus height to crypt depth ratio in unchallenged birds (P < 0.05) and reduced crypt depth of challenged birds on d 24 (P < 0.05). Regardless of challenge, supplementation with Gln reduced crypt depth on d 16 (P < 0.05), and increased villus height (P < 0.01) and the villus height to crypt depth ratio (P < 0.001) on d 24. Dietary Gln lowered serum uric acid level regardless of challenge (P < 0.05). The current study indicates that dietary Gln alleviates adverse effects of NE and may be useful in antibiotic-free diets.

Honey Bee (Apis mellifera) Pollen Foraging Reflects Benefits Dependent on Individual Infection Status

Parasites often modify host foraging behavior, for example, by spurring changes to nutrient intake ratios or triggering self-medication. The gut parasite, Nosema ceranae, increases energy needs of the European or Western honey bee (Apis mellifera), but little is known about how infection affects foraging behavior. We used a combination of experiments and observations of caged and free-flying individual bees and hives to determine how N. ceranae affects honey bee foraging behavior. In an experiment with caged bees, we found that infected bees with access to a high-quality pollen were more likely to survive than infected bees with access to a lower quality pollen or no pollen. Non-infected bees showed no difference in survival with pollen quality. We then tested free-flying bees in an arena of artificial flowers and found that pollen foraging bees chose pollen commensurate with their infection status; twice as many infected bees selected the higher quality pollen than the lower quality pollen, while healthy bees showed no preference between pollen types. However, healthy and infected bees visited sucrose and pollen flowers in the same proportions. Among hive-level observations, we found no significant correlations between N. ceranae infection intensity in the hive and the proportion of bees returning with pollen. Our results indicate that N. ceranae-infected bees benefit from increased pollen quality and will selectively forage for higher quality while foraging for pollen, but infection status does not lead to increased pollen foraging at either the individual or hive levels.

Pre-calving Intravaginal Administration of Lactic Acid Bacteria Reduces Metritis Prevalence and Regulates Blood Neutrophil Gene Expression After Calving in Dairy Cattle

Metritis affects up to 40% of dairy cows and it is usually treated with antibiotics. In spite of their advantages, there is an increased concern about antibiotic resistance leading to the research of alternative methods. The aim of this study was to evaluate the effects of a combination of lactic acid bacteria (LAB) on the prevalence of metritis and modulation of endometrial and neutrophil inflammatory markers in dairy cows. One hundred and thirty-five cows were enrolled 3 week before calving and randomly assigned to three treatments. Treatment groups were: (1) two intravaginal doses of LAB/wk during 3 week pre-calving (vaginal, n = 45); (2) an intra-uterine dose, once 1 d after calving (uterine, n = 44); and (3) no intervention (CTRL, n = 45). Metritis was defined as body temperature > 39.5°C and purulent vaginal discharge (> 50% pus), and diagnosed 6 d after calving. Blood samples were taken at d −14, −10, −7, −4, +1, +3, +6, and +14 relative to calving for non-esterified fatty acids (NEFA) analysis. At d −10, +1, +3, and +6 neutrophils were isolated from blood for gene expression analysis by RT-qPCR. Endometrium biopsies were taken from 30 cows, 15 from CTRL and 15 from the uterine group at d +1, +3, and +6 after calving for pro-inflammatory markers analysis by NanoString®. Vaginal treatment reduced metritis prevalence (6/45) up to 58% compared with CTRL group (14/45), but there was no difference between the uterine and CTRL group. Uterine and vaginal treatments reduced blood neutrophil gene expression. Expression of pro-inflammatory markers in the endometrium did not differ between uterine and CTRL cows. Metritic cows expressed more C-X-C motif chemokine ligand 8 (CXCL8) and interleukin 1 beta (IL1B) at d 3 than healthy cows, whereas healthy cows expressed more CXCL8 at d 1 relative to calving in the endometrium. This study shows a promising potential of LAB probiotics as a preventive treatment against metritis in dairy cows.

Antihelminthic treatment alters cellular but not humoral immune components in Magellanic Penguin (Spheniscus magellanicus) chicks

We evaluate whether helminth parasites affect both cellular and humoral components of the immune system of Magellanic Penguin (Spheniscus magellanicus (J.R. Forster, 1781)) chicks. We measured immune components after the administration of an antihelminthic drug to remove parasites. Cellular immune components included the complete white blood cell (WBC) count and the in vivo skin-swelling response to phytohemagglutinin (PHA). Humoral aspects assessed were the ability of plasma to agglutinate foreign particles and the bactericidal capacity of plasma. Antihelminthic treatment resulted in lower total WBC counts supporting the role of circulating leukocytes in fighting macroparasites. Deparasitized chicks showed a reduction in all types of leukocytes. Contrary to our expectation, deparasitized Magellanic Penguin chicks showed lower response to PHA injection than control chicks. The swelling response was positively correlated with body condition and with total WBC in circulation. We hypothesize that the specific helminth community naturally occurring in Magellanic Penguin chicks might have an overall immunostimulatory effect on the PHA response. Antihelminthic treatment did not alter the innate humoral immune parameters measured. Our results support the prediction that, given their relatively low costs of use and maintenance, innate humoral components would not be as affected by antihelminthic treatment as more costly cellular responses.

Plasmodium Infections in Natural Populations of Anolis sagrei Reflect Tolerance Rather Than Susceptibility

Parasites can represent formidable selection pressures for hosts, but the cost of infection is sometimes difficult to demonstrate in natural populations. While parasite exploitation strategies may, in some instances, actually inflict low costs on their hosts, the response of hosts to infection is also likely to determine whether or not these costs can be detected. Indeed, costs of infection may be obscured if infected individuals in the wild are those that are the most tolerant, rather than the most susceptible, to infection. Here we test this hypothesis in two natural populations of Anolis sagrei, one of the most common anole lizard of the Bahamas. Plasmodium parasites were detected in > 7% of individuals and belonged to two distinct clades: P. mexicanum and P. floriensis. Infected individuals displayed greater body condition than non-infected ones and we found no association between infection status, stamina, and survival to the end of the breeding season. Furthermore, we found no significant difference in the immuno-competence (measured as a response to phytohemagglutinin challenge) of infected versus non-infected individuals. Taken together, our results suggest that the infected individuals that are caught in the wild are those most able to withstand the cost of the infection and that susceptible, infected individuals have been removed from the population (i.e., through disease-induced mortality). This study highlights the need for caution when interpreting estimates of infection costs in natural populations, as costs may appear low either when parasites exploitation strategies truly inflict low costs on their hosts or when those costs are so high that susceptible hosts are removed from the population.

Reduced innate immunity of Cuban Treefrogs at leading edge of range expansion

During geographic range expansion, populations of non-indigenous species at the invasion front may benefit from directing resources away from immune defense. To test this hypothesis, we investigated the strength of two innate immune components in populations of invasive Cuban Treefrogs (Osteopilus septentrionalis) in a long-colonized area (core region) and at the invasion front (leading-edge region). First, we compared the region-specific metabolic response of frogs injected with an endotoxin that induces systemic inflammation (lipopolysaccharide, LPS) to sham-injected control frogs pooled from both regions. Males and females were analyzed independently because we detected a sex-related difference in mass-independent metabolism of control frogs, with males exhibiting a significantly higher metabolic rate (F_{1, 21}  = 29.02, P < 0.001) than females. We observed a significantly higher metabolic rate in LPS-injected core frogs compared with control frogs for both males (P = 0.041) and females (P = 0.007). Conversely, in leading-edge populations, there was no significant difference in the metabolic rate of LPS-injected and control frogs (males, P  = 0.195; females, P  = 0.132). Second, we directly compared bacterial killing ability of frog blood plasma between regions. Bactericidal ability of plasma was significantly greater in frogs from the core region in comparison with those at the leading edge (F_{1, 26}   = 28.67, P < 0.001). For both immune components that we examined, populations from the core exhibited stronger immune responses. Our findings support hypotheses predicting an inverse relationship between immunity and range expansion.

Anthropogenic food provisioning and immune phenotype: Association among supplemental food, body condition, and immunological parameters in urban environments

Direct or indirect supplemental feeding of free-ranging animals occurs worldwide, resulting in significant impacts on population density or altered demographic processes. Another potential impact of increased energy intake from supplemental feeding is altered immunocompetence. As immune system maintenance is energetically costly, there may be trade-offs between immune responses and other energy-demanding physiological processes in individual animals. Although increased availability of food sources through supplemental feeding is expected to increase the overall immunocompetence of animals, empirical data verifying the association between supplemental feeding and different immune parameters are lacking. Understanding the potential influence of supplemental feeding on immune phenotypes is critical, as it may also impact host-pathogen dynamics in free-ranging animals. Using urban stray cats as a study model, we tested for associations between the intensity of supplemental feeding due to cat caretaker activity (CCA); body condition; and immune phenotype (bacterial killing assay (BKA), immunoglobulin G (IgG) concentration, and leukocyte counts). Significantly higher bacterial killing ability was observed in cats from high CCA districts, whereas higher IgG concentration and eosinophil counts were observed in cats from low CCA districts. Other leukocyte counts and body condition indices showed no significant association with CCA. We observed varying patterns of different immune components in relation to supplemental feeding. Out data suggest that supplemental feeding influences immune phenotype, not only by means of energy provisioning, but also by potentially reducing exposure rates to parasite infections through stray cat behavioral changes.

Avian malaria and bird humoral immune response

Background

Plasmodium parasites are known to impose fitness costs on their vertebrate hosts. Some of these costs are due to the activation of the immune response, which may divert resources away from self-maintenance. Plasmodium parasites may also immuno-deplete their hosts. Thus, infected individuals may be less able to mount an immune response to a new pathogen than uninfected ones. However, this has been poorly investigated.

Methods

The effect of Plasmodium infection on bird humoral immune response when encountering a novel antigen was tested. A laboratory experiment was conducted on canaries (Serinus canaria) experimentally infected with Plasmodium relictum (lineage SGS1) under controlled conditions. Birds were immune challenged with an intra-pectoral injection of a novel non-pathogenic antigen (keyhole limpet haemocyanin, KLH). One week later they were challenged again. The immune responses to the primary and to the secondary contacts were quantified as anti-KLH antibody production via enzyme-linked immunosorbent assay (ELISA).

Results

There was no significant difference in antibody production between uninfected and Plasmodium infected birds at both primary and secondary contact. However, Plasmodium parasite intensity in the blood increased after the primary contact with the antigen.

Conclusions

There was no effect of Plasmodium infection on the magnitude of the humoral immune response. However, there was a cost of mounting an immune response in infected individuals as parasitaemia increased after the immune challenge, suggesting a trade-off between current control of chronic Plasmodium infection and investment against a new immune challenge.

Exploring the link between ultraviolet B radiation and immune function in amphibians: implications for emerging infectious diseases

Amphibian populations the world over are under threat of extinction, with as many as 40% of assessed species listed as threatened under IUCN Red List criteria (a significantly higher proportion than other vertebrate group). Amongst the key threats to amphibian species is the emergence of novel infectious diseases, which have been implicated in the catastrophic amphibian population declines and extinctions seen in many parts of the world. The recent emergence of these diseases coincides with increased ambient levels of ultraviolet B radiation (UVBR) due to anthropogenic thinning of the Earth's protective ozone layer, raising questions about potential interactions between UVBR exposure and disease in amphibians. While reasonably well documented in other vertebrate groups (particularly mammals), the immunosuppressive capacity of UVBR and the potential for it to influence disease outcomes has been largely overlooked in amphibians. Herein, we review the evidence for UVBR-associated immune system disruption in amphibians and identify a number of direct and indirect pathways through which UVBR may influence immune function and disease susceptibility in amphibians. By exploring the physiological mechanisms through which UVBR may affect host immune function, we demonstrate how ambient UVBR could increase amphibian susceptibility to disease. We conclude by discussing the potential implications of elevated UVBR for inter and intraspecific differences in disease dynamics and discuss how future research in this field may be directed to improve our understanding of the role that UVBR plays in amphibian immune function.

Stabilising selection on immune response in male black grouse Lyrurus tetrix

Illnesses caused by a variety of micro- and macro- organisms can negatively affect individuals’ fitness, leading to the expectation that immunity is under positive selection. However, immune responses are costly and individuals must trade-off their immune response with other fitness components (e.g. survival or reproductive success) meaning that individuals with intermediate response may have the greatest overall fitness. Such a process might be particularly acute in species with strong sexual selection because the condition-dependence of male secondary sexual-traits might lead to striking phenotypic differences amongst males of different immune response levels. We tested whether there is selection on immune response by survival and reproduction in yearling and adult male black grouse (Lyrurus tetrix) following an immune challenge with a novel antigen and tested the hypothesis that sexual signals and body mass are honest signals of the immune response. We show that yearling males with highest immune response to these challenges had higher survival, but the reverse was true for adults. Adults with higher responses had highest mass loss and adult males with intermediate immune response had highest mating success. Tail length was related to baseline response in adults and more weakly in yearlings. Our findings reveal the complex fitness consequences of mounting an immune response across age classes. Such major differences in the direction and magnitude of selection in multiple fitness components is an alternative route underpinning the stabilising selection of immune responses with an intermediate immune response being optimal.

Genes of the major histocompatibility complex highlight interactions of the innate and adaptive immune system

Background

A well-functioning immune defence is crucial for fitness, but our knowledge about the immune system and its complex interactions is still limited. Major histocompatibility complex (MHC) molecules are involved in T-cell mediated adaptive immune responses, but MHC is also highly upregulated during the initial innate immune response. The aim of our study was therefore to determine to what extent the highly polymorphic MHC is involved in interactions of the innate and adaptive immune defence and if specific functional MHC alleles (FA) or heterozygosity at the MHC are more important.

Methods

To do this we used captive house sparrows (Passer domesticus) to survey MHC diversity and immune function controlling for several environmental factors. MHC class I alleles were identified using parallel amplicon sequencing and to mirror immune function, several immunological tests that correspond to the innate and adaptive immunity were conducted.

Results

Our results reveal that MHC was linked to all immune tests, highlighting its importance for the immune defence. While all innate responses were associated with one single FA, adaptive responses (cell-mediated and humoral) were associated with several different alleles.

Discussion

We found that repeated injections of an antibody in nestlings and adults were linked to different FA and hence might affect different areas of the immune system. Also, individuals with a higher number of different FA produced a smaller secondary response, indicating a disadvantage of having numerous MHC alleles. These results demonstrate the complexity of the immune system in relation to the MHC and lay the foundation for other studies to further investigate this topic.

Perinatal exposure to 2,2',4'4' -Tetrabromodiphenyl ether induces testicular toxicity in adult rats

Since 1965, polybrominated diphenyl ethers (PBDEs) have been used internationally as flame-retardant additives. PBDEs were recently withdrawn from commerce in North America and Europe due to their environmental persistence, bioaccumulative properties and endocrine-disrupting effects. Generations exposed perinatally to the highest environmental doses of PBDE account for one-fifth of the total United States population. While, toxicity of PBDE for the male reproductive system has been demonstrated in several human and animal studies, the long-lasting effects of perinatal exposures on male reproduction are still poorly understood. In this study, pregnant Wistar rats were exposed to 0.2mg/kg 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) from gestation day 8 until postnatal day 21. Male reproductive outcomes were analyzed on postnatal day 120 in offspring. Exposed animals had significantly smaller testes, displayed decreased sperm production per testis weight, had significantly increased percentage of morphologically abnormal spermatozoa, and showed an increase in spermatozoa head size. Perinatal BDE-47 exposure led to significant changes in testes transcriptome, including suppression of genes essential for spermatogenesis and activation of immune response genes. In particular, we observed a 4-fold average decrease in expression of protamine and transition protein genes in testes, suggesting that histone-protamine exchange may be dysregulated during spermatogenesis, resulting in an aberrant sperm epigenome. The possibility of long-lasting effects of developmental PBDE exposures calls for additional studies to build a foundation for the development of preventive and protective interventions against the environmentally-induced decline in fertility.

Climatic anomaly affects the immune competence of California sea lions

The past decades have been characterized by a growing number of climatic anomalies. As these anomalies tend to occur suddenly and unexpectedly, it is often difficult to procure empirical evidence of their effects on natural populations. We analysed how the recent sea surface temperature (SST) anomaly in the northeastern Pacific Ocean affects body condition, nutritional status, and immune competence of California sea lion pups. We found that pup body condition and blood glucose levels of the pups were lower during high SST events, although other biomarkers of malnutrition remained unchanged, suggesting that pups were experiencing early stages of starvation. Glucose-dependent immune responses were affected by the SST anomaly; specifically, pups born during high SST events had lower serum concentrations of IgG and IgA, and were unable to respond to an immune challenge. This means that not only were pups that were born during the SST anomaly less able to synthesize protective antibodies; they were also limited in their ability to respond rapidly to nonspecific immune challenges. Our study provides empirical evidence that atypical climatic conditions can limit energetic reserves and compromise physiological responses that are essential for the survival of a marine top predator.

Immune responsiveness to phytohemagglutinin displays species but not sex differences in three anuran species

Phytohemagglutinin (PHA)-induced skin swelling response is widely used as a rough surrogate of integrative cell-mediated and innate immunity across multiple vertebrate taxa due to its simplification and feasibility. However, little is known whether there are sex and interspecific differences of immune responsiveness to PHA in ectotherms, especially for anurans. Therefore, we studied sex and species differences of PHA response in three anurans, Asiatic toads (Bufo gargarizans), Dark-spotted frogs (Pelophylax nigromaculatus) and Mongolian toads (Pseudepidalea raddei), captured in northern regions of Anhui Province (China). Footpad thickness was measured prior to (0 h) and after (6, 12, 24, 48 and 72 h) a PHA injection and normalized against saline injection in the opposite footpad. Body mass was recorded at the beginning (0 h) and end of each assay (72 h). Results showed effects of PHA assay, sex and taxa on body mass. Relative maximum swelling response (PHA_max) ranged from 18.58–29.75%, 9.77 to 20.56% and 21.97 to 31.78% and its occurrence over time was apparent 10.6–19.72 h , 7.74–14.01 h and 17.39–23.94 h postinjection for Asiatic toads, Dark-spotted frogs and Mongolian toads, respectively. Finally, the magnitude or timing of PHA_max in Dark-spotted frogs was significantly thinner and faster than in Mongolian toads, and Asiatic toads had an in-between value, not different from the other two species. The magnitude of PHA_max was significantly positively correlated with the timing of PHA_max considering individuals altogether, but not when analyzed within species. Our results indicate that male and female anuran species respond similarly to PHA antigen stimulation, but the magnitude and timing of PHA_max is species-specific. Briefly, we provide new evidence for the suitability of PHA assay in non-model anuran species with different body sizes, and exhort the need to further investigate the nature of PHA assay at the hematological and histological levels in order to extend its application in ecoimmunological studies of amphibians.

Effect of temperature and food restriction on immune function in striped hamsters (Cricetulus barabensis)

Small mammals in temperate areas face seasonal fluctuations of temperature and food availability, both of which may influence their immune responses, which are critical to survival. In the present study, we tested the hypothesis that low temperature and food restriction suppress immune function in striped hamsters (Cricetulus barabensis). Thirty-seven adult male hamsters were randomly assigned to warm (23±1°C) and cold (5±1°C) treatment groups, which were further divided into fed and food-restricted groups. Body mass was not affected by cold stress, food restriction or the interaction cold stress×food restriction. Cold stress decreased total body fat mass, haematological parameters including white blood cells, lymphocytes and neutrophilic granulocytes, and immunoglobin (Ig) M titres 5 days after injecting keyhole limpet haemocyanin (KLH). However, cold temperature increased bacterial killing capacity, indicative of innate immunity, and did not affect the mass of the thymus and spleen, intermediate granulocytes, the phytohaemagglutinin (PHA) response and the levels of blood glucose and serum leptin. Corticosterone concentration was affected significantly by the interaction cold stress×food restriction but not by cold stress or food restriction alone. Food restriction reduced thymus mass, but other immunological parameters including body fat mass, spleen mass, haematological parameters, innate immunity, PHA response, the titres of IgM and IgG, and the levels of blood glucose and serum leptin were all not affected by food restriction or the interaction cold stress×food restriction. Innate immunity was positively correlated with leptin levels, whereas no significant correlations were observed in the levels of blood glucose, serum leptin, corticosterone and all the detected immune parameters. Our results show that cold stress suppressed humoral immunity but enhanced innate immunity and did not affect cellular immunity in striped hamsters. Most immunological indices were not influenced by food restriction. Blood glucose, leptin and corticosterone could not explain the changes of innate, cellular and humoral immunity upon cold stress or food restriction in striped hamsters.

Experimental immune activation using a mild antigen decreases reproductive success in free-living female Dark-eyed Juncos (Junco hyemalis)

Seasonal animals time breeding so that offspring rearing coincides with favorable conditions. Offspring rearing is energetically demanding; therefore, additional energetic challenges during this life-history stage may allocate energy away from offspring care, decreasing reproductive success. Activation of the immune system may be one such energetic challenge, and may have a disproportionately higher impact on reproductive success earlier in the breeding season when resources are less abundant and thermoregulatory demands are greater. We monitored nestling growth and survival in incubating female Dark-eyed Juncos (Junco hyemalis (L., 1758)) injected with a mild antigen to stimulate antibody production and induce an energetic challenge. We found nests of treated females were more likely than controls to fail prior to 6 days post hatch, coinciding with timing of peak antibody production. No effect of season was detected. Offspring mass did not differ between treatments prior to failure, suggesting that failure was potentially due to differences in behaviour other than nestling feeding. Our findings indicate a trade-off between immunity and nest survival that is not affected by time of season. Based on the results of our study, we suggest that future research be directed toward how immune activation influences behaviours, including nest guarding and predator aggression, and mediates this trade-off.

Age, but not anthelmintic treatment, is associated with urinary neopterin levels in semi-free ranging Barbary macaques

Studying host parasite interactions and their implications for evolution and ecology recently received increasing attention, particularly with regard to host physiology and immunity. Here we assess variation of urinary neopterin (uNEO), a marker of cellular immune activation and iummunosenescence, in response to age and anthelmintic treatment in semi-free ranging Barbary macaques (Macaca sylvanus). Urinary NEO levels were measured via enzyme-immunoassay from 179 urine samples of 43 individuals between 5–29 years of age. Efficiency of treatment was assessed by Mc Master flotation on repeated faecal samples, including 18 untreated individuals as control group. We used linear mixed models with age and parasite status as main effects, controlling for sex and physical condition, assessed through urinary C-Peptide-levels, with social group and ID as random factors. Urinary NEO levels significantly increased with age, suggesting that changes in aging Barbary macaque immune responses are consistent with immunosenescence described in human and nonhuman primates and can be detected via uNEO measurements. Anthelmintic treatment, however, had no influence on uNEO levels, potentially due to quick reinfections or attenuated immune responses in repeated infections. We conclude that uNEO is a potential non-invasive marker for immune function and particularly immunosenescence in wildlife.

The Effect of Parasite Infection on Stable Isotope Turnover Rates of δ15N, δ13C and δ34S in Multiple Tissues of Eurasian Perch Perca fluviatilis

Stable isotope analysis of commercially and ecologically important fish can improve understanding of life-history and trophic ecology. However, accurate interpretation of stable isotope values requires knowledge of tissue-specific isotopic turnover that will help to describe differences in the isotopic composition of tissues and diet. We performed a diet-switch experiment using captive-reared parasite-free Eurasian perch (Perca fluviatilis) and wild caught specimens of the same species, infected with the pike tapeworm Triaenophorus nodulosus living in host liver tissue. We hypothesize that metabolic processes related to infection status play a major role in isotopic turnover and examined the influence of parasite infection on isotopic turn-over rate of carbon (δ¹³C), nitrogen (δ¹⁵N) and sulphur (δ³⁴S) in liver, blood and muscle. The δ¹⁵N and δ¹³C turnovers were fastest in liver tissues, followed by blood and muscle. In infected fish, liver and blood δ¹⁵N and δ¹³C turnover rates were similar. However, in infected fish, liver and blood δ¹³C turnover was faster than that of δ¹⁵N. Moreover, in infected subjects, liver δ¹⁵N and δ¹³C turnover rates were three to five times faster than in livers of uninfected subjects (isotopic half-life of ca.3-4 days compared to 16 and 10 days, respectively). Blood δ³⁴S turnover rate were about twice faster in non-infected individuals implying that parasite infection could retard the turnover rate of δ³⁴S and sulphur containing amino acids. Slower turnover rate of essential amino acid could probably decrease individual immune function. These indicate potential hidden costs of chronic and persistent infections that may have accumulated adverse effects and might eventually impair life-history fitness. For the first time, we were able to shift the isotope values of parasites encapsulated in the liver by changing the dietary source of the host. We also report variability in isotopic turnover rates between tissues, elements and between infected and parasite-free individuals. These results contribute to our understanding of data obtained from field and commercial hatcheries; and strongly improve the applicability of the stable isotope method in understanding life-history and trophic ecology of fish populations.

When less means more: dehydration improves innate immunity in rattlesnakes

Immune function can vary based on availability of resources, and most studies of such influences have focused on the co-investment of energy into immune and other physiological functions. When energy resources are limited, trade-offs exist, which can compromise immunity for other functions. As with energy, water limitation can also alter various physiological processes, yet water has received little consideration for its role in possibly modulating immune functions. We examined the relationship between immunocompetence and hydration state using the western diamond-backed rattlesnake (Crotalus atrox). This species is known to undergo substantial seasonal fluctuations in water availability with extreme limitations during the hot, dry season. We collected blood samples from free-ranging C. atrox to compare osmolality and innate immune function (lysis, agglutination, bacterial growth inhibition) during the milder and relatively moister early spring season, the hot-dry season, and the hot-wet season. To isolate effects of dehydration from other possible seasonal influences, we complemented this field study with a laboratory study in which we withheld food and water from individually housed adult C. atrox for up to 16 weeks. We collected blood samples from each snake as it dehydrated and collected a final sample after the snake was given ad lib water at the end of the experiment. Our results demonstrate that C. atrox experience significant dehydration during the hot-dry season, and that, in general, innate immune function is highly correlated with osmolality, whether natural or artificially manipulated.

Exercise training reveals trade-offs among endurance performance and immune function, but not growth, in juvenile lizards

Acquired energetic resources allocated to a particular trait cannot then be re-allocated to a different trait. This often results in a trade-off between survival and reproduction for the adults of many species, but such a trade-off may be manifested differently in juveniles not yet capable of reproduction. Whereas adults may allocate resources to current and/or future reproduction, juveniles can only allocate to future reproduction. Thus, juveniles should allocate resources toward traits that increase survival and their chances of future reproductive success. We manipulated allocation of resources to performance, via endurance exercise training, to examine trade-offs among endurance capacity, immune function, and growth in juvenile green anole lizards. We trained male and female captive anoles on a treadmill for eight weeks, with increasing intensity, and compared traits to those of untrained individuals. Our results show that training enhanced endurance capacity equally in both sexes, but immune function was suppressed only in females. Training had no effect on growth, but males had higher growth rates than females. Previous work showed that trained adults have enhanced growth, so juvenile growth is either insensitive to stimulation with exercise, or they are already growing at maximal rates. Our results add to a growing literature that locomotor performance is an important part of life-history trade-offs that are sex- and age-specific.

The immunomodulatory role of the hypothalamus-pituitary-gonad axis: Proximate mechanism for reproduction-immune trade offs?

The present review discusses the communication between the hypothalamic-pituitary-gonad (HPG) axis and the immune system of vertebrates, attempting to situate the HPG-immune interaction into the context of life history trade-offs between reproductive and immune functions. More specifically, (i) we review molecular and cellular interactions between hormones of the HPG axis, and, as far as known, the involved mechanisms on immune functions, (ii) we evaluate whether the HPG-immune crosstalk serves as proximate mechanism mediating reproductive-immune trade-offs, and (iii) we ask whether the nature of the HPG-immune interaction is conserved throughout vertebrate evolution, despite the changes in immune functions, reproductive modes, and life histories. In all vertebrate classes studied so far, HPG hormones have immunomodulatory functions, and indications exist that they contribute to reproduction-immunity resource trade-offs, although the very limited information available for most non-mammalian vertebrates makes it difficult to judge how comparable or different the interactions are. There is good evidence that the HPG-immune crosstalk is part of the proximate mechanisms underlying the reproductive-immune trade-offs of vertebrates, but it is only one factor in a complex network of factors and processes. The fact that the HPG-immune interaction is flexible and can adapt to the functional and physiological requirements of specific life histories. Moreover, the assumption of a relatively fixed pattern of HPG influence on immune functions, with, for example, androgens always leading to immunosuppression and estrogens always being immunoprotective, is probably oversimplified, but the HPG-immune interaction can vary depending on the physiological and envoironmental context. Finally, the HPG-immune interaction is not only driven by resource trade-offs, but additional factors such as, for instance, the evolution of viviparity shape this neuroendocrine-immune relationship.

Immune-Challenged Fish Up-Regulate Their Metabolic Scope to Support Locomotion

Energy-based trade-offs occur when investment in one fitness-related trait diverts energy away from other traits. The extent to which such trade-offs are shaped by limits on the rate of conversion of energy ingested in food (e.g. carbohydrates) into chemical energy (ATP) by oxidative metabolism rather than by the amount of food ingested in the first place is, however, unclear. Here we tested whether the ATP required for mounting an immune response will lead to a trade-off with ATP available for physical activity in mosquitofish (Gambusia holbrooki). To this end, we challenged fish either with lipopolysaccharide (LPS) from E. coli or with Sheep Red Blood Cells (SRBC), and measured oxygen consumption at rest and during swimming at maximum speed 24h, 48h and 7 days post-challenge in order to estimate metabolic rates. Relative to saline-injected controls, only LPS-injected fish showed a significantly greater resting metabolic rate two days post-challenge and significantly higher maximal metabolic rates two and seven days post-challenge. This resulted in a significantly greater metabolic scope two days post-challenge, with LPS-fish transiently overcompensating by increasing maximal ATP production more than would be required for swimming in the absence of an immune challenge. LPS-challenged fish therefore increased their production of ATP to compensate physiologically for the energetic requirements of immune functioning. This response would avoid ATP shortages and allow fish to engage in an aerobically-challenging activity (swimming) even when simultaneously mounting an immune response. Nevertheless, relative to controls, both LPS- and SRBC-fish displayed reduced body mass gain one week post-injection, and LPS-fish actually lost mass. The concomitant increase in metabolic scope and reduced body mass gain of LPS-challenged fish indicates that immune-associated trade-offs are not likely to be shaped by limited oxidative metabolic capacities, but may instead result from limitations in the acquisition, assimilation or efficient use of resources.

Plasmodium infection and oxidative status in breeding great tits, Parus major

Background

Plasmodium parasites may affect the oxidative status of their hosts, defined as the balance of pro-oxidant compounds and antioxidant defences in an organism. An increased energy requirement, the activation of immune functions or the parasite itself may lead to a higher production of pro-oxidants and/or an antioxidant depletion resulting in a higher oxidative stress and associated damage in infected individuals. Relatively little is known about the mechanisms underlying oxidative processes at play during host-Plasmodium interaction in the wild.

Methods

The effect of Plasmodium infection on host oxidative status was investigated in wild populations of breeding great tits, Parus major, naturally infected by Plasmodium spp. When chicks were 14 days old, the parents were blood-sampled to measure four complementary oxidative status markers: pro-oxidant production as mitochondrial superoxide production in red blood cells (RBC), antioxidant defences as plasma antioxidant capacity and oxidative damage as reactive oxygen metabolites in the plasma and RBC membrane resistance to oxidative attack.

Results

Plasmodium-infected individuals produced more pro-oxidants compared to uninfected ones and pro-oxidant production positively correlated to infection intensity. There was also a conditional effect of reproductive effort on oxidative damage depending on Plasmodium infection status. There was no direct effect of infection on oxidative damage and no effect on antioxidant defences.

Conclusions

The results suggest that Plasmodium parasites may impose a cost in terms of increased oxidative stress possibly mediated via a higher energy requirement in infected hosts. This further suggests that Plasmodium parasites may modify host life history traits via an induction of oxidative stress. This study highlights that measuring several complementary oxidative status markers may enable to capture oxidative processes at play during host-Plasmodium interactions.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-016-1579-9) contains supplementary material, which is available to authorized users.