Measures of immune function of wild mice, Mus musculus

Physiological strategies in wild rodents: immune defenses of commensal rats

The importance of issues associated with urban/commensal rats and mice (property damage, management costs, and health risks) press upon research on these animals. While the demography of commensal rodents is mostly studied, the need for understanding factors influencing their natural morbidity/mortality is also stressed. In this respect, more attention is expected to be paid to immunity, the physiological mechanism of defense against host survival threats (pathogens, parasites, diseases). Commensal rats and mice carry numerous pathogens that evoke diverse immune responses. The state of immunity in commensal house mice is studied in great detail, owing to the use of laboratory strains in biomedical research. Because commensal rats are, compared to mice, carriers of more zoonotic agents, rats' immunity is studied mainly in that context. Some of these zoonotic agents cause chronic, asymptomatic infections, which justified studies of immunological mechanisms of pathogen tolerance versus clearance regulation in rats. Occurrence of some infections in specific tissues/organs pressed upon analysis of local/regional immune responses and/or immunopathology. A survey of immunological activity/responses in commensal rats is given in this review, with mention of existing data in commensal mice. It should throw some light on the factors relevant to their morbidity and lifespan, supplementing the knowledge of commensal rodent ecology.

The adaptive immune response to Trichuris in wild versus laboratory mice: An established model system in context

Laboratory model organisms have provided a window into how the immune system functions. An increasing body of evidence, however, suggests that the immune responses of naive laboratory animals may differ substantially to those of their wild counterparts. Past exposure, environmental challenges and physiological condition may all impact on immune responsiveness. Chronic infections of soil-transmitted helminths, which we define as establishment of adult, fecund worms, impose significant health burdens on humans, livestock and wildlife, with limited treatment success. In laboratory mice, Th1 versus Th2 immune polarisation is the major determinant of helminth infection outcome. Here we compared antigen-specific immune responses to the soil-transmitted whipworm Trichuris muris between controlled laboratory and wild free-ranging populations of house mice (Mus musculus domesticus). Wild mice harbouring chronic, low-level infections produced lower levels of cytokines in response to Trichuris antigen than laboratory-housed C57BL/6 mice. Wild mouse effector/memory CD4+ T cell phenotype reflected the antigen-specific cytokine response across the Th1/Th2 spectrum. Increasing egg shedding was associated with body condition loss. However, local Trichuris-specific Th1/Th2 balance was positively associated with worm burden only in older wild mice. Thus, although the fundamental relationships between the CD4+ T helper cell response and resistance to T. muris infection are similar in both laboratory and wild M. m. domesticus, there are quantitative differences and age-specific effects that are analogous to human immune responses. These context-dependent immune responses demonstrate the fundamental importance of understanding the differences between model and natural systems for translating mechanistic models to 'real world' immune function.

Mouse hygiene status-A tale of two environments for mast cells and allergy

Animal models, including those employing the use of house mice (Mus musculus), are crucial in elucidating mechanisms in human pathophysiology. However, it is evident that the impreciseness of using laboratory mice maintained in super-hygienic barrier facilities to mirror relevant aspects of human physiology and pathology exists, which is a major limitation in translating mouse findings to inferring human medicine. Interestingly, free-living wild mice are found to be substantially different from laboratory-bred, specific pathogen-free mice with respect to various immune system compartments. Wild mice have an immune system that better reflects human immunity. In this review article, we discuss recent experimental findings that address the so-called "wild immunology", which reveals the contrasting immune features between laboratory-raised mice and their wild companions as well as laboratory mice that have been exposed to a natural rodent habitat. A particular focus will be given to the development of pulmonary mast cells and its possible impact on the use of "naturalized" or "rewilded" laboratory mice as experimental asthma models.

Varying intensity of simulated infection partially affects the magnitude of the acute-phase immune response in the subterranean rodent Ctenomys talarum

The acute phase response (APR), coordinated by a complex network of components of the immune and neuroendocrine systems, plays a key role in early immune defense. This response can be elicited by a wide variety of pathogens at different intensities (frequencies and doses), hence experimental immune challenges with antigen gradients makes it possible to evaluate sickness progression with a better representation of what occurs in natural systems. However, how infection intensity could shape the APR magnitude in wild species is still poorly understood. Here, the immune response was activated in the subterranean rodent Ctenomys talarum with a gradient of lipopolysaccharide (LPS) doses (0.5, 1, 1.5, and 2 mg/kg of body mass). Changes in body temperature, body mass, and energetic costs were evaluated over time. We also assessed cortisol levels, white blood cells counts and neutrophil: lymphocyte ratios, before and after injection. Results indicated that during the APR, C. talarum shows a hyperthermic response, which is maintained for 6 h, with slight differences among antigen doses in the pattern of thermal response and body mass change. A maximum increase in body temperature of 0.83°C to 1.63°C was observed during the first hour, associated with a metabolic cost that ranged from 1.25 to 1.41 ml O₂ /gh. Although no clear effects of treatment were detected on leukocyte abundance, we found increments in neutrophil: lymphocyte ratios and gradual increases in cortisol levels corresponding to the intensity of simulated infection, which may indicate redistribution of immune cells and enhancement of immune function. An evident sickness syndrome was observed even at the lowest LPS dose that was characterized by an increase in body temperature, energy expenditure, and N: L ratio, as well as a dose-dependent increase in cortisol levels. Although in nature, other constraints and challenges could affect the magnitude and costs of immune responses, C. talarum mounts an effective APR with a low increase in their daily energy expenditure, regardless of LPS dose.

Large Mammals Have More Powerful Antibacterial Defenses Than Expected from Their Metabolic Rates

AbstractTerrestrial mammals span seven orders of magnitude in body size, ranging from the <2-g Etruscan pygmy shrew (Suncus etruscus) to the >3,900-kg African elephant (Loxodonta africana). Although body size profoundly affects the behavior, physiology, ecology, and evolution of species, how investment in functional immune defenses changes with body size across species is unknown. Here, we (1) developed a novel 12-point dilution curve approach to describe and compare antibacterial capacity against three bacterial species among >160 terrestrial species of mammals and (2) tested published predictions about the scaling of immune defenses. Our study focused on the safety factor hypothesis, which predicts that broad, early-acting immune defenses should scale hypermetrically with body mass. However, our three statistical approaches demonstrated that antibacterial activity in sera across mammals exhibits isometry; killing capacity did not change with body size across species. Intriguingly, this result indicates that the serum of a large mammal is less hospitable to bacteria than would be predicted by its metabolic rates. In other words, if metabolic rates underlie the rates of physiological reactions as postulated by the metabolic theory of ecology, large species should have disproportionately lower antibacterial capacity than small species, but they do not. These results have direct implications for effectively modeling the evolution of immune defenses and identifying potential reservoir hosts of pathogens.

Embracing the heterogeneity of natural viruses in mouse studies

Animal models are a critical tool in modern biology. To increase reproducibility and to reduce confounding variables modern animal models exclude many microbes, including key natural commensals and pathogens. Here we discuss recent strategies to incorporate a natural microbiota to laboratory mouse models and the impacts the microbiota has on immune responses, with a focus on viruses.

From germ-free to wild: modulating microbiome complexity to understand mucosal immunology

The gut microbiota influences host responses at practically every level, and as research into host-microbe interactions expands, it is not surprising that we are uncovering similar roles for the microbiota at other barrier sites, such as the lung and skin. Using standard laboratory mice to assess host-microbe interactions, or even host intrinsic responses, can be challenging, as slight variations in the microbiota can affect experimental outcomes. When it comes to designing and selecting an appropriate level of microbial diversity and community structure for colonization of our laboratory rodents, we have more choices available to us than ever before. Here we will discuss the different approaches used to modulate microbial complexity that are available to study host-microbe interactions. We will describe how different models have been used to answer distinct biological questions, covering the entire microbial spectrum, from germ-free to wild.

Potential effects of shift work on skin autoimmune diseases

Shift work is associated with systemic chronic inflammation, impaired host and tumor defense and dysregulated immune responses to harmless antigens such as allergens or auto-antigens. Thus, shift workers are at higher risk to develop a systemic autoimmune disease and circadian disruption with sleep impairment seem to be the key underlying mechanisms. Presumably, disturbances of the sleep-wake cycle also drive skin-specific autoimmune diseases, but epidemiological and experimental evidence so far is scarce. This review summarizes the effects of shift work, circadian misalignment, poor sleep, and the effect of potential hormonal mediators such as stress mediators or melatonin on skin barrier functions and on innate and adaptive skin immunity. Human studies as well as animal models were considered. We will also address advantages and potential pitfalls in animal models of shift work, and possible confounders that could drive skin autoimmune diseases in shift workers such as adverse lifestyle habits and psychosocial influences. Finally, we will outline feasible countermeasures that may reduce the risk of systemic and skin autoimmunity in shift workers, as well as treatment options and highlight outstanding questions that should be addressed in future studies.

Natural versus Laboratory World: Incorporating Wild-Derived Microbiota into Preclinical Rodent Models

Advances in data collection (high-throughput shotgun metagenomics, transcriptomics, and metabolomics) and analysis (bioinformatics and multiomics) led to the realization that all mammals are metaorganisms, shaped not only by their own genome but also by the genomes of the microbes that colonize them. To date, most studies have focused on the bacterial microbiome, whereas curated databases for viruses, fungi, and protozoa are still evolving. Studies on the interdependency of microbial kingdoms and their combined effects on host physiology are just starting. Although it is clear that past and present exposure to commensals and pathogens profoundly affect human physiology, such exposure is lacking in standard preclinical models such as laboratory mice. Laboratory mouse colonies are repeatedly rederived in germ-free status and subjected to restrictive, pathogen-free housing conditions. This review summarizes efforts to bring the wild microbiome into the laboratory setting to improve preclinical models and their translational research value.

Mast Cells Are Identified in the Lung Parenchyma of Wild Mice, Which Can Be Recapitulated in Naturalized Laboratory Mice

Background

It is well documented that laboratory mice bred and maintained in ultra-hygienic specific pathogen-free (SPF) barriers display reduced richness and complexity of microbiota compared with wild mice. The laboratory mice profoundly lack lung parenchymal mast cells. Hence, we aimed to investigate the lung distribution of mast cells in free-living wild mice.

Methods

Wild house mice were trapped in South-Eastern Norway and Hemtabad, West Bengal, India. C57BL/6 laboratory mice were bred in a purposefully built, closed environment with bedding material obtained from the natural environment in order to normalize the gut microbiota of these laboratory mice to that of the wild mice, and the offspring were collected for study at eight weeks of age.

Results

Mast cells were easily identified at a substantial density in the lung parenchymal tissues of wild mice from both Norway and India, which stands in clear contrast to the rare distribution of lung parenchymal mast cells in the conventional laboratory SPF mice. Consistently, wild mice also expressed higher pulmonary levels of stem cell factor, a critical growth factor for mast cell survival. Higher levels of histamine were recorded in the lung tissues of the wild mice. Interestingly, "naturalized" C57BL/6 laboratory mice which spent their entire life in a semi-natural environment developed lung parenchymal mast cells at an appreciable density.

Conclusion

Our observations support that environmental factors, possibly through modulation of microbiota, may impact the tissue distribution of mast cells in mouse lung parenchyma.

New insights into the microbiota of wild mice

Laboratory mice have long been an invaluable tool in biomedical science and have made significant contributions in research into life-threatening diseases. However, the translation of research results from mice to humans often proves difficult due to the incomplete nature of laboratory animal-based research. Hence, there is increasing demand for complementary methods or alternatives to laboratory mice that can better mimic human physiological traits and potentially bridge the translational research gap. Under these circumstances, the natural/naturalized mice including “wild”, “dirty”, “wildling”, and “wilded” systems have been found to better reflect some aspects of human pathophysiology. Here, we discuss the pros and cons of the laboratory mouse system and contemplate how wild mice and wild microbiota are able to help in refining such systems to better mimic the real-world situation and contribute to more productive translational research.

High-dimensional single cell mass cytometry analysis of the murine hematopoietic system reveals signatures induced by ageing and physiological pathogen challenges

BACKGROUND

Immune ageing is a result of repetitive microbial challenges along with cell intrinsic or systemic changes occurring during ageing. Mice under 'specific-pathogen-free' (SPF) conditions are frequently used to assess immune ageing in long-term experiments. However, physiological pathogenic challenges are reduced in SPF mice. The question arises to what extent murine experiments performed under SPF conditions are suited to analyze immune ageing in mice and serve as models for human immune ageing. Our previous comparisons of same aged mice with different microbial exposures, unambiguously identified distinct clusters of immune cells characteristic for numerous previous pathogen encounters in particular in pet shop mice.

RESULTS

We here performed single cell mass cytometry assessing splenic as secondary and bone marrow as primary lymphoid organ-derived leukocytes isolated from young versus aged SPF mice in order to delineate alterations of the murine hematopoietic system induced during ageing. We then compared immune clusters from young and aged SPF mice to pet shop mice in order to delineate alterations of the murine hematopoietic system induced by physiological pathogenic challenges and those caused by cell intrinsic or systemic changes during ageing. Notably, distinct immune signatures were similarly altered in both pet shop and aged SPF mice in comparison to young SPF mice, including increased frequencies of memory T lymphocytes, effector-cytokine producing T cells, plasma cells and mature NK cells. However, elevated frequencies of CD4⁺ T cells, total NK cells, granulocytes, pDCs, cDCs and decreased frequencies of naïve B cells were specifically identified only in pet shop mice. In aged SPF mice specifically the frequencies of splenic IgM⁺ plasma cells, CD8⁺ T cells and CD4⁺ CD25⁺ Treg were increased as compared to pet shop mice and young mice.

CONCLUSIONS

Our study dissects firstly how ageing impacts both innate and adaptive immune cells in primary and secondary lymphoid organs. Secondly, it partly distinguishes murine intrinsic immune ageing alterations from those induced by physiological pathogen challenges highlighting the importance of designing mouse models for their use in preclinical research including vaccines and immunotherapies.

Embracing nature's complexity: Immunoparasitology in the wild

A wealth of research is dedicated to understanding how resistance against parasites is conferred and how parasite-driven pathology is regulated. This research is in part driven by the hope to better treatments for parasitic diseases of humans and livestock, and in part by immunologists who use parasitic infections as biomedical tools to evoke physiological immune responses. Much of the current mechanistic knowledge has been discovered in laboratory studies using model organisms, especially the laboratory mouse. However, wildlife are also hosts to a range of parasites. Through the study of host-parasite interactions in these non-laboratory systems we can gain a deeper understanding of parasite immunology in a more natural, complex environment. With a focus on helminth parasites, we here explore the insights gained into parasite-induced immune responses through (for immunologists) non-conventional experimental systems, and how current core findings from laboratory studies are reflected in these more natural conditions. The quality of the immune response is undoubtedly a central player in susceptibility versus resistance, as many laboratory studies have shown. Yet, in the wild, parasite infections tend to be chronic diseases. Whilst reading our review, we encourage the reader to consider the following questions which may (only) be answered by studying naturally occurring parasites in the wild: a) what type of immune responses are mounted against parasites in different hosts in the wild, and how do they vary within an individual over time, between individuals of the same species and between species? b) can we use wild or semi-wild study systems to understand the evolutionary drivers for tolerance versus resistance towards a parasite? c) what determines the ability of the host to cope with an infection and is there a link with the type of immune response mounted? d) can we modulate environmental factors to manipulate a wild animal's immune response to parasitic infections, with translation potential for humans, wildlife, and livestock? and e) in context of this special issue, what lessons for Type 2 immunity can we glean from studying animals in their natural environments? Further, we aim to integrate some of the knowledge gained in semi-wild and wild settings with knowledge gained from traditional laboratory-based research, and to raise awareness for the opportunities (and challenges) that come with integrating a multitude of naturally-occurring variables into immunoparasitological research.

Elucidating different pattern of immunoregulation in BALB/c and C57BL/6 mice and their F1 progeny

Helminths are large multicellular parasites that infect one quarter of the human population. To prolong their survival, helminths suppress the immune responses of their hosts. Strongyloides ratti delays its expulsion from the gut by induction of regulatory circuits in a mouse strain-specific manner: depletion of Foxp3⁺ regulatory T cells (Treg) improves the anti-S. ratti immunity in BALB/c but not in C57BL/6 mice. In the current study we compare the hierarchy of immunoregulatory pathways in BALB/c, C57BL/6 mice and their F1 progeny (BALB/c × C57BL/6). Using multicolor flow cytometry, we show that S. ratti induces a distinct pattern of inhibitory checkpoint receptors by Foxp3⁺ Treg and Foxp3^- T cells. Intensity of expression was highest in C57BL/6 and lowest in BALB/c mice, while the F1 cross had an intermediate phenotype or resembled BALB/c mice. Treg subsets expanded during infection in all three mouse strains. Similar to BALB/c mice, depletion of Treg reduced intestinal parasite burden and increased mucosal mast cell activation in S. ratti-infected F1 mice. Our data indicate that Treg dominate the regulation of immune responses in BALB/c and F1 mice, while multiple regulatory layers exist in C57BL/6 mice that may compensate for the absence of Treg.

A Model System for Feralizing Laboratory Mice in Large Farmyard-Like Pens

Laboratory mice are typically housed under extremely clean laboratory conditions, far removed from the natural lifestyle of a free-living mouse. There is a risk that this isolation from real-life conditions may lead to poor translatability and misinterpretation of results. We and others have shown that feral mice as well as laboratory mice exposed to naturalistic environments harbor a more diverse gut microbiota and display an activated immunological phenotype compared to hygienic laboratory mice. We here describe a naturalistic indoors housing system for mice, representing a farmyard-type habitat typical for house mice. Large open pens were installed with soil and domestic animal feces, creating a highly diverse microbial environment and providing space and complexity allowing for natural behavior. Laboratory C57BL/6 mice were co-housed in this system together with wild-caught feral mice, included as a source of murine microbionts. We found that mice feralized in this manner displayed a gut microbiota structure similar to their feral cohabitants, such as higher relative content of Firmicutes and enrichment of Proteobacteria. Furthermore, the immunophenotype of feralized mice approached that of feral mice, with elevated levels of memory T-cells and late-stage NK cells compared to laboratory-housed control mice, indicating antigenic experience and immune training. The dietary elements presented in the mouse pens could only moderately explain changes in microbial colonization, and none of the immunological changes. In conclusion, this system enables various types of studies using genetically controlled mice on the background of adaptation to a high diversity microbial environment and a lifestyle natural for the species.

Depletion of MHC supertype during domestication can compromise immunocompetence

The major histocompatibility complex (MHC) plays an important role in infectious disease resistance. The presence of certain MHC alleles and functionally similar groups of MHC alleles (i.e., supertypes) has been associated with resistance to particular parasite species. Farmed and domesticated fish stocks are often depleted in their MHC alleles and supertype diversity, possibly as a consequence of artificial selection for desirable traits, inbreeding (loss of heterozygosity), genetic drift (loss of allelic diversity) and/or reduced parasite biodiversity. Here we quantify the effects of depletion of MHC class II genotype and supertype variation on resistance to the parasite Gyrodactylus turnbulli in guppies (Poecilia reticulata). Compared to the descendants of wild‐caught guppies, ornamental fish had a significantly reduced MHC variation (i.e., the numbers of MHC alleles and supertypes per individual, and per population). In addition, ornamental fish were significantly more susceptible to G. turnbulli infections, accumulating peak intensity 10 times higher than that of their wildtype counterparts. Four out of 13 supertypes were associated with a significantly reduced parasite load, and the presence of some supertypes had a dramatic effect on the intensity of infection. Remarkably, the ornamental and wildtype fish differed in the supertypes that were associated with parasite resistance. Analysis with a genetic algorithm showed that resistance‐conferring supertypes of the wildtype and ornamental fish shared two unique amino acids in the peptide‐binding region of the MHC that were not found in any other alleles. These data show that the supertype demarcation captures some, but not all, of the variation in the immune function of the alleles. This study highlights the importance of managing functional MHC diversity in livestock, and suggests there might be some immunological redundancy among MHC supertypes.

Relationships between immune gene expression and circulating cytokine levels in wild house mice

Quantitative PCR (qPCR) has been commonly used to measure gene expression in a number of research contexts, but the measured RNA concentrations do not always represent the concentrations of active proteins which they encode. This can be due to transcriptional regulation or post-translational modifications, or localization of immune environments, as can occur during infection. However, in studies using free-living non-model species, such as in ecoimmunological research, qPCR may be the only available option to measure a parameter of interest, and so understanding the quantitative link between gene expression and associated effector protein levels is vital.Here, we use qPCR to measure concentrations of RNA from mesenteric lymph node (MLN) and spleen tissue, and multiplex ELISA of blood serum to measure circulating cytokine concentrations in a wild population of a model species, Mus musculus domesticus.Few significant correlations were found between gene expression levels and circulating cytokines of the same immune genes or proteins, or related functional groups. Where significant correlations were observed, these were most frequently within the measured tissue (i.e., the expression levels of genes measured from spleen tissue were more likely to correlate with each other rather than with genes measured from MLN tissue, or with cytokine concentrations measured from blood).Potential reasons for discrepancies between measures including differences in decay rates and transcriptional regulation networks are discussed. We highlight the relative usefulness of different measures under different research questions and consider what might be inferred from immune assays.

Fitness outcomes in relation to individual variation in constitutive innate immune function

Although crucial for host survival when facing persistent parasite pressure, costly immune functions will inevitably compete for resources with other energetically expensive traits such as reproduction. Optimizing, but not necessarily maximizing, immune function might therefore provide net benefit to overall host fitness. Evidence for associations between fitness and immune function is relatively rare, limiting our potential to understand ultimate fitness costs of immune investment. Here, we assess how measures of constitutive immune function (haptoglobin, natural antibodies, complement activity) relate to subsequent fitness outcomes (survival, reproductive success, dominance acquisition) in a wild passerine (Malurus coronatus). Surprisingly, survival probability was not positively linearly predicted by any immune index. Instead, both low and high values of complement activity (quadratic effect) were associated with higher survival, suggesting that different immune investment strategies might reflect a dynamic disease environment. Positive linear relationships between immune indices and reproductive success suggest that individual heterogeneity overrides potential resource reallocation trade-offs within individuals. Controlling for body condition (size-adjusted body mass) and chronic stress (heterophil-lymphocyte ratio) did not alter our findings in a sample subset with available data. Overall, our results suggest that constitutive immune components have limited net costs for fitness and that variation in immune maintenance relates to individual differences more closely.

The Identity of Organisms in Scientific Practice: Integrating Historical and Relational Conceptions

We address the identity of biological organisms at play in experimental and modeling practices. We first examine the central tenets of two general conceptions, and we assess their respective strengths and weaknesses. The historical conception, on the one hand, characterizes organisms' identity by looking at their past, and specifically at their genealogical connection with a common ancestor. The relational conception, on the other hand, interprets organisms' identity by referring to a set of distinctive relations between their parts, and between the organism and its environment. While the historical and relational conceptions are understood as opposed and conflicting, we submit that they are also fundamentally complementary. Accordingly, we put forward a hybrid conception, in which historical and relational (and more specifically, organizational) aspects of organisms' identity sustain and justify each other. Moreover, we argue that organisms' identity is not only hybrid but also bounded, insofar as the compliance with specific identity criteria tends to vanish as time passes, especially across generations. We spell out the core conceptual framework of this conception, and we outline an original formal representation. We contend that the hybrid and bounded conception of organisms' identity suits the epistemological needs of biological practices, particularly with regards to the generalization and reproducibility of experimental results, and the integration of mathematical models with experiments.

Transcriptome-wide analysis reveals different categories of response to a standardised immune challenge in a wild rodent

Individuals vary in their immune response and, as a result, some are more susceptible to infectious disease than others. Little is known about the nature of this individual variation in natural populations, or which components of immune pathways are most responsible, but defining this underlying landscape of variation is an essential first step to understanding the drivers of this variation and, ultimately, predicting the outcome of infection. We describe transcriptome-wide variation in response to a standardised immune challenge in wild field voles. We find that genes (hereafter 'markers') can be categorised into a limited number of types. For the majority of markers, the response of an individual is dependent on its baseline expression level, with significant enrichment in this category for conventional immune pathways. Another, moderately sized, category contains markers for which the responses of different individuals are also variable but independent of their baseline expression levels. This category lacks any enrichment for conventional immune pathways. We further identify markers which display particularly high individual variability in response, and could be used as markers of immune response in larger studies. Our work shows how a standardised challenge performed on a natural population can reveal the patterns of natural variation in immune response.

Suppressed LPS-mediated TLR4 signaling in the plateau zokor (Eospalax baileyi) compared to the bamboo rat (Rhizomys pruinosus) and rat (Rattus norvegicus)

Ecological immunology involves the study of the immune function of wildlife, which is seldom compared with that of model animals. Here, we evaluated and compared the level of the innate immune response in the plateau zokor (Eospalax baileyi), an indigenous underground rodent from the Tibetan Plateau, with that in the bamboo rat (Rhizomys pruinosus) and Sprague-Dawley (SD) rat (Rattus norvegicus). The spleen was observed by ordinary light and transmission electron microscopy, and the spleen index was calculated. After liposaccharide (LPS) challenge, the expression of Toll-like receptor 2 (TLR2), TLR4, and hypoxia-inducible factor 1α (HIF-1α) in the spleen was detected by Western blot analysis and immunofluorescence. The expression of nuclear factor-κB1 (NF-κB1) and mitogen-activated protein kinase 14 (MAPK14) in the spleen was detected by real-time quantitative polymerase chain reaction, and the levels of interleukin 6 (IL-6), tumor necrosis factor-α (TNF-α), and interferon-β (IFN-β) in the spleen were detected by enzyme-linked immunoassay. The spleen index of the plateau zokor was lower than that of the bamboo rat and SD rat. The expression of TLR4, NF-κB1, and MAPK14 and the levels of IL-6 and TNF-α in the spleen of the plateau zokor were lower than those of the bamboo rat and SD rat, while the expression of TLR2 and HIF-1α and the level of IFN-β were higher than those of the bamboo rat and SD rat. We speculate that suppression of the TLR4 signaling pathway in the plateau zokor is an adaptation to hypoxic tunnels that decreases antigenic risk and maintains immune homeostasis. Moreover, the spleen of the plateau zokor is reduced in size, reducing the innate immunity investment in the spleen. We also noted that high levels of HIF-1α in the spleen of the plateau zokor suppressed crosstalk between HIF-1α and TLR4, promoting the innate immune response.

Immune state is associated with natural dietary variation in wild mice Mus musculus domesticus

The ability, propensity and need to mount an immune response vary both among individuals and within a single individual over time.A wide array of parameters has been found to influence immune state in carefully controlled experiments, but we understand much less about which of these parameters are important in determining immune state in wild populations.Diet can influence immune responses, for example when nutrient availability is limited. We therefore predict that natural dietary variation will play a role in modulating immune state, but this has never been tested.We measured carbon and nitrogen stable isotope ratios in an island population of house mice Mus musculus domesticus as an indication of dietary variation, and the expression of a range of immune-related genes to represent immune state.After accounting for potential confounding influences such as age, sex and helminth load, we found a significant association between carbon isotope ratio and levels of immune activity in the mesenteric lymph nodes, particularly in relation to the inflammatory response.This association demonstrates the important interplay between diet and an animal's response to immune challenges, and therefore potentially its susceptibility to disease. A plain language summary is available for this article.

Parasitic nematodes simultaneously suppress and benefit from coccidian coinfection in their natural mouse host

Within-host interactions among coinfecting parasites are common and have important consequences for host health and disease dynamics. However, these within-host interactions have traditionally been studied in laboratory mouse models, which often exclude important variation and use unnatural host-parasite combinations. Conversely, the few wild studies of within-host interactions often lack knowledge of parasite exposure and infection history. Here we exposed laboratory-reared wood mice (Apodemus sylvaticus) that were derived from wild-caught animals to two naturally-occurring parasites (nematode: Heligmosomoides polygyrus, coccidia: Eimeria hungaryensis) to investigate the impact of coinfection on parasite infection dynamics, and to determine if the host immune response mediates this interaction. Coinfection led to delayed worm expulsion and prolonged egg shedding in H. polygyrus infections and lower peak E. hungaryensis oocyst burdens. By comparing antibody levels between wild and colony-housed mice, we also found that wild mice had elevated H. polygyrus-IgG1 titres even if currently uninfected with H. polygyrus. Using this unique wild-laboratory system, we demonstrate, for the first time, clear evidence for a reciprocal interaction between these intestinal parasites, and that there is a great discrepancy between antibody levels measured in the wild vs those measured under controlled laboratory conditions in relation to parasite infection and coinfection.

Mastomys Species as Model Systems for Infectious Diseases

Replacements of animal models by advanced in vitro systems in biomedical research, despite exceptions, are currently still not satisfactory in reproducing the whole complexity of pathophysiological mechanisms that finally lead to disease. Therefore, preclinical models are additionally required to reflect analogous in vivo situations as found in humans. Despite proven limitations of both approaches, only a combined experimental arrangement guarantees generalizability of results and their transfer to the clinics. Although the laboratory mouse still stands as a paradigm for many scientific discoveries and breakthroughs, it is mandatory to broaden our view by also using nontraditional animal models. The present review will first reflect the value of experimental systems in life science and subsequently describes the preclinical rodent model Mastomys coucha that-although still not well known in the scientific community-has a long history in research of parasites, bacteria, papillomaviruses and cancer. Using Mastomys, we could recently show for the first time that cutaneous papillomaviruses-in conjunction with UV as an environmental risk factor-induce squamous cell carcinomas of the skin via a "hit-and-run" mechanism. Moreover, Mastomys coucha was also used as a proof-of-principle model for the successful vaccination against non-melanoma skin cancer even under immunosuppressive conditions.

Assessment of Trade-Offs between Simultaneous Immune Challenges in a Slow-Living Subterranean Rodent

The coexistence of two or more infectious agents in the same host is common in nature. Given this, the study of trade-offs within the immune system itself is key to understanding how immune defenses act in wild species in their natural environment. Here we assessed the possible trade-off between an inflammatory response (induced by phytohemagglutinin [PHA]; involving innate and adaptive responses in the study species) and an antibody response (induced by sheep red blood cells [SRBC]; adaptive response) in a slow-living subterranean rodent, the Talas tuco-tuco (Ctenomys talarum Thomas, 1898). According to life-history theory, slow-living species should rely more heavily on adaptive immunity, which develops more slowly than an innate response but is beneficial against repeated infections. Individual physiological condition (estimated by measuring levels of infection and immune, nutritional, and stress parameters) was analyzed during immune challenges. Contrary to what was expected, we found that the magnitude and energetic costs of both immune responses were similar when stimulated alone or simultaneously. Variation in natural antibodies, neutrophils, basophils, total leukocytes, and the ratio of neutrophils to lymphocytes in relation to the different treatments was also detected. In particular, natural antibodies were negatively affected by the induction of both immune challenges simultaneously and an increase of neutrophil counts was detected in all animals with the exception of those challenged with SRBC, while the pattern of variation of basophils, total leukocytes, and ratio of neutrophils to lymphocytes was not clearly associated with any triggered immune response. In general, our results suggest the absence of an energetic or resource-based trade-off between the immune responses triggered by PHA and SRBC in C. talarum.

A pilot study evaluating the utility of commercially available antibodies for flow cytometric analysis of Panthera species lymphocytes

Background

The immune response against tuberculosis in lions is still poorly defined and our understanding is hampered by the lack of lion specific reagents. The process for producing antibodies against a specific antigen is laborious and not available to many research laboratories. As the search for antibody cross-reactivity is an important strategy for immunological studies in veterinary medicine, we have investigated the use of commercially available antibodies to characterize T cell subsets in African lions (Panthera leo).

Results

Commercially available antibodies were screened and investigated the influence of two different sample processing methods, as well as the effect of time delay on cell surface marker expression on lion lymphocytes. Using commercially available antibodies, we were able to identify CD4⁺, CD5⁺, CD8⁺, CD14⁺, CD25⁺, CD44⁺ and CD45⁺ T lymphocytes in samples obtained by density gradient centrifugation as well as red cell lysis of lion whole blood. Two distinct lymphocyte populations, which differed in size and phenotype, were observed in the samples processed by density gradient centrifugation.

Conclusion

Commercially available antibodies are able to differentiate between T lymphocyte subsets including immune effector cells in African lion whole blood, and possibly give insight into unique specie phenotypes.

Electronic supplementary material

The online version of this article (10.1186/s12917-018-1717-4) contains supplementary material, which is available to authorized users.

The ecology of immune state in a wild mammal, Mus musculus domesticus

The immune state of wild animals is largely unknown. Knowing this and what affects it is important in understanding how infection and disease affects wild animals. The immune state of wild animals is also important in understanding the biology of their pathogens, which is directly relevant to explaining pathogen spillover among species, including to humans. The paucity of knowledge about wild animals' immune state is in stark contrast to our exquisitely detailed understanding of the immunobiology of laboratory animals. Making an immune response is costly, and many factors (such as age, sex, infection status, and body condition) have individually been shown to constrain or promote immune responses. But, whether or not these factors affect immune responses and immune state in wild animals, their relative importance, and how they interact (or do not) are unknown. Here, we have investigated the immune ecology of wild house mice-the same species as the laboratory mouse-as an example of a wild mammal, characterising their adaptive humoral, adaptive cellular, and innate immune state. Firstly, we show how immune variation is structured among mouse populations, finding that there can be extensive immune discordance among neighbouring populations. Secondly, we identify the principal factors that underlie the immunological differences among mice, showing that body condition promotes and age constrains individuals' immune state, while factors such as microparasite infection and season are comparatively unimportant. By applying a multifactorial analysis to an immune system-wide analysis, our results bring a new and unified understanding of the immunobiology of a wild mammal.

A candidate tolerance gene identified in a natural population of field voles (Microtus agrestis)

The animal immune response has hitherto been viewed primarily in the context of resistance only. However, individuals can also employ a tolerance strategy to maintain good health in the face of ongoing infection. To shed light on the genetic and physiological basis of tolerance, we use a natural population of field voles, Microtus agrestis, to search for an association between the expression of the transcription factor Gata3, previously identified as a marker of tolerance in this system, and polymorphism in 84 immune and nonimmune genes. Our results show clear evidence for an association between Gata3 expression and polymorphism in the Fcer1a gene, with the explanatory power of this polymorphism being comparable to that of other nongenetic variables previously identified as important predictors of Gata3 expression. We also uncover the possible mechanism behind this association using an existing protein-protein interaction network for the mouse model rodent, Mus musculus, which we validate using our own expression network for M. agrestis. Our results suggest that the polymorphism in question may be working at the transcriptional level, leading to changes in the expression of the Th2-related genes, Tyrosine-protein kinase BTK and Tyrosine-protein kinase TXK, and hence potentially altering the strength of the Th2 response, of which Gata3 is a mediator. We believe our work has implications for both treatment and control of infectious disease.

The Immunology of Wild Rodents: Current Status and Future Prospects

Wild animals' immune responses contribute to their evolutionary fitness. These responses are moulded by selection to be appropriate to the actual antigenic environment in which the animals live, but without imposing an excessive energetic demand which compromises other component of fitness. But, exactly what these responses are, and how they compare with those of laboratory animals, has been little studied. Here, we review the very small number of published studies of immune responses of wild rodents, finding general agreement that their humoral (antibody) responses are highly elevated when compared with those of laboratory animals, and that wild rodents' cellular immune system reveals extensive antigenic exposure. In contrast, proliferative and cytokine responses of ex vivo-stimulated immune cells of wild rodents are typically depressed compared with those of laboratory animals. Collectively, these responses are appropriate to wild animals' lives, because the elevated responses reflect the cumulative exposure to infection, while the depressed proliferative and cytokine responses are indicative of effective immune homeostasis that minimizes immunopathology. A more comprehensive understanding of the immune ecology of wild animals requires (i) understanding the antigenic load to which wild animals are exposed, and identification of any key antigens that mould the immune repertoire, (ii) identifying immunoregulatory processes of wild animals and the events that induce them, and (iii) understanding the actual resource state of wild animals, and the immunological consequences that flow from this. Together, by extending studies of wild rodents, particularly addressing these questions (while drawing on our immunological understanding of laboratory animals), we will be better able to understand how rodents' immune responses contribute to their fitness in the wild.

RNA sequencing (RNA-Seq) of lymph node, spleen, and thymus transcriptome from wild Peninsular Malaysian cynomolgus macaque (Macaca fascicularis)

The cynomolgus macaque (Macaca fascicularis) is an extensively utilised nonhuman primate model for biomedical research due to its biological, behavioural, and genetic similarities to humans. Genomic information of cynomolgus macaque is vital for research in various fields; however, there is presently a shortage of genomic information on the Malaysian cynomolgus macaque. This study aimed to sequence, assemble, annotate, and profile the Peninsular Malaysian cynomolgus macaque transcriptome derived from three tissues (lymph node, spleen, and thymus) using RNA sequencing (RNA-Seq) technology. A total of 174,208,078 paired end 70 base pair sequencing reads were obtained from the Illumina Hi-Seq 2500 sequencer. The overall mapping percentage of the sequencing reads to the M. fascicularis reference genome ranged from 53–63%. Categorisation of expressed genes to Gene Ontology (GO) and KEGG pathway categories revealed that GO terms with the highest number of associated expressed genes include Cellular process, Catalytic activity, and Cell part, while for pathway categorisation, the majority of expressed genes in lymph node, spleen, and thymus fall under the Global overview and maps pathway category, while 266, 221, and 138 genes from lymph node, spleen, and thymus were respectively enriched in the Immune system category. Enriched Immune system pathways include Platelet activation pathway, Antigen processing and presentation, B cell receptor signalling pathway, and Intestinal immune network for IgA production. Differential gene expression analysis among the three tissues revealed 574 differentially expressed genes (DEG) between lymph and spleen, 5402 DEGs between lymph and thymus, and 7008 DEGs between spleen and thymus. Venn diagram analysis of expressed genes revealed a total of 2,630, 253, and 279 tissue-specific genes respectively for lymph node, spleen, and thymus tissues. This is the first time the lymph node, spleen, and thymus transcriptome of the Peninsular Malaysian cynomolgus macaque have been sequenced via RNA-Seq. Novel transcriptomic data will further enrich the present M. fascicularis genomic database and provide future research potentials, including novel transcript discovery, comparative studies, and molecular markers development.

Simulated bacterial infection disrupts the circadian fluctuation of immune cells in wrinkle-lipped bats (Chaerephon plicatus)

Background

Leukocyte concentrations follow a circadian pattern in mammals, with elevated values at times of potential contact with pathogens and parasites. We hypothesized that this pattern is disturbed after an immune challenge.

Methods

In Thailand, we captured wrinkle-lipped bats (Chaerephon plicatus), when they returned to their colony at dawn. We challenged half of the animals (experimental group) with bacterial lipopolysaccharides and treated the others only with the carrier liquid (control group). We then compared body mass changes and differences in circulating immune cell counts at 8 h post-treatment.

Results

In experimental animals, we observed an increase in total leukocyte and neutrophil numbers of 17% and 95%, respectively. In control animals, concentrations of leukocytes decreased by 44% and those of neutrophils remained constant. Experimental treatment had no effect on lymphocytes, yet changes in eosinophil numbers were explained by sex. Eosinophils decreased by 66% in females and by 62% in males. Basophils and monocytes were rarest among all observed cell types and analysis was either impossible because of low numbers or yielded no significant effects, respectively.

Discussion

Our findings show that a simulated bacterial infection triggered a neutrophil-associated immune response in wrinkle-lipped bats, indicating a disruption of the diurnal fluctuation of immune cells. Our study suggests that bats exhibit circadian rhythms in immune cell counts. The magnitude of these fluctuations may vary across species according to specific-specific infection risks associated with colony sizes or specific roosting habits.

Resistance to RHD virus in wild Australian rabbits: Comparison of susceptible and resistant individuals using a genomewide approach

Deciphering the genes involved in disease resistance is essential if we are to understand host-pathogen coevolutionary processes. The rabbit haemorrhagic disease virus (RHDV) was imported into Australia in 1995 as a biocontrol agent to manage one of the most successful and devastating invasive species, the European rabbit (Oryctolagus cuniculus). During the first outbreaks of the disease, RHDV caused mortality rates of up to 97%. Recently, however, increased genetic resistance to RHDV has been reported. Here, we have aimed to identify genomic differences between rabbits that survived a natural infection with RHDV and those that died in the field using a genomewide next-generation sequencing (NGS) approach. We detected 72 SNPs corresponding to 133 genes associated with survival of a RHD infection. Most of the identified genes have known functions in virus infections and replication, immune responses or apoptosis, or have previously been found to be regulated during RHD. Some of the genes identified in experimental studies, however, did not seem to play a role under natural selection regimes, highlighting the importance of field studies to complement the genomic background of wildlife diseases. Our study provides a set of candidate markers as a tool for the future scanning of wild rabbits for their resistance to RHDV. This is important both for wild rabbit populations in southern Europe where RHD is regarded as a serious problem decimating the prey of endangered predator species and for assessing the success of currently planned RHDV variant biocontrol releases in Australia.

Translational Rodent Models for Research on Parasitic Protozoa-A Review of Confounders and Possibilities

Rodents, in particular Mus musculus, have a long and invaluable history as models for human diseases in biomedical research, although their translational value has been challenged in a number of cases. We provide some examples in which rodents have been suboptimal as models for human biology and discuss confounders which influence experiments and may explain some of the misleading results. Infections of rodents with protozoan parasites are no exception in requiring close consideration upon model choice. We focus on the significant differences between inbred, outbred and wild animals, and the importance of factors such as microbiota, which are gaining attention as crucial variables in infection experiments. Frequently, mouse or rat models are chosen for convenience, e.g., availability in the institution rather than on an unbiased evaluation of whether they provide the answer to a given question. Apart from a general discussion on translational success or failure, we provide examples where infections with single-celled parasites in a chosen lab rodent gave contradictory or misleading results, and when possible discuss the reason for this. We present emerging alternatives to traditional rodent models, such as humanized mice and organoid primary cell cultures. So-called recombinant inbred strains such as the Collaborative Cross collection are also a potential solution for certain challenges. In addition, we emphasize the advantages of using wild rodents for certain immunological, ecological, and/or behavioral questions. The experimental challenges (e.g., availability of species-specific reagents) that come with the use of such non-model systems are also discussed. Our intention is to foster critical judgment of both traditional and newly available translational rodent models for research on parasitic protozoa that can complement the existing mouse and rat models.

The comparative immunology of wild and laboratory mice, Mus musculus domesticus

The laboratory mouse is the workhorse of immunology, used as a model of mammalian immune function, but how well immune responses of laboratory mice reflect those of free-living animals is unknown. Here we comprehensively characterize serological, cellular and functional immune parameters of wild mice and compare them with laboratory mice, finding that wild mouse cellular immune systems are, comparatively, in a highly activated (primed) state. Associations between immune parameters and infection suggest that high level pathogen exposure drives this activation. Moreover, wild mice have a population of highly activated myeloid cells not present in laboratory mice. By contrast, in vitro cytokine responses to pathogen-associated ligands are generally lower in cells from wild mice, probably reflecting the importance of maintaining immune homeostasis in the face of intense antigenic challenge in the wild. These data provide a comprehensive basis for validating (or not) laboratory mice as a useful and relevant immunological model system.

The environment as a driver of immune and endocrine responses in dolphins (Tursiops truncatus)

Immune and endocrine responses play a critical role in allowing animals to adjust to environmental perturbations. We measured immune and endocrine related markers in multiple samples from individuals from two managed-care care dolphin groups (n = 82 samples from 17 dolphins and single samples collected from two wild dolphin populations: Indian River Lagoon, (IRL) FL (n = 26); and Charleston, (CHS) SC (n = 19). The immune systems of wild dolphins were more upregulated than those of managed-care-dolphins as shown by higher concentrations of IgG and increases in lysozyme, NK cell function, pathogen antibody titers and leukocyte cytokine transcript levels. Collectively, managed-care care dolphins had significantly lower levels of transcripts encoding pro-inflammatory cytokine TNF, anti-viral MX1 and INFα and regulatory IL-10. IL-2Rα and CD69, markers of lymphocyte activation, were both lower in managed-care care dolphins. IL-4, a cytokine associated with TH2 activity, was lower in managed-care care dolphins compared to the free-ranging dolphins. Differences in immune parameters appear to reflect the environmental conditions under which these four dolphin populations live which vary widely in temperature, nutrition, veterinary care, pathogen/contaminant exposures, etc. Many of the differences found were consistent with reduced pathogenic antigenic stimulation in managed-care care dolphins compared to wild dolphins. Managed-care care dolphins had relatively low TH2 lymphocyte activity and fewer circulating eosinophils compared to wild dolphins. Both of these immunologic parameters are associated with exposure to helminth parasites which is uncommon in managed-care care dolphins. Less consistent trends were observed in a suite of hormones but significant differences were found for cortisol, ACTH, total T4, free T3, and epinephrine. While the underlying mechanisms are likely multiple and complex, the marked differences observed in the immune and endocrine systems of wild and managed-care care dolphins appear to be shaped by their environment.

Changing expression of vertebrate immunity genes in an anthropogenic environment: a controlled experiment

Background

The effect of anthropogenic environments on the function of the vertebrate immune system is a problem of general importance. For example, it relates to the increasing rates of immunologically-based disease in modern human populations and to the desirability of identifying optimal immune function in domesticated animals. Despite this importance, our present understanding is compromised by a deficit of experimental studies that make adequately matched comparisons between wild and captive vertebrates.

Results

We transferred post-larval fishes (three-spined sticklebacks), collected in the wild, to an anthropogenic (captive) environment. We then monitored, over 11 months, how the systemic expression of immunity genes changed in comparison to cohort-matched wild individuals in the originator population (total n = 299). We found that a range of innate (lyz, defbl2, il1r-like, tbk1) and adaptive (cd8a, igmh) immunity genes were up-regulated in captivity, accompanied by an increase in expression of the antioxidant enzyme, gpx4a. For some genes previously known to show seasonality in the wild, this appeared to be reduced in captive fishes. Captive fishes tended to express immunity genes, including igzh, foxp3b, lyz, defbl2, and il1r-like, more variably. Furthermore, although gene co-expression patterns (analyzed through gene-by-gene correlations and mutual information theory based networks) shared common structure in wild and captive fishes, there was also significant divergence. For one gene in particular, defbl2, high expression was associated with adverse health outcomes in captive fishes.

Conclusion

Taken together, these results demonstrate widespread regulatory changes in the immune system in captive populations, and that the expression of immunity genes is more constrained in the wild. An increase in constitutive systemic immune activity, such as we observed here, may alter the risk of immunopathology and contribute to variance in health in vertebrate populations exposed to anthropogenic environments.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-016-0751-8) contains supplementary material, which is available to authorized users.

Caging and Uncaging Genetics

It is important for biology to understand if observations made in highly reductionist laboratory settings generalise to harsh and noisy natural environments in which genetic variation is sorted to produce adaptation. But what do we learn by studying, in the laboratory, a genetically diverse population that mirrors the wild? What is the best design for studying genetic variation? When should we consider it at all? The right experimental approach depends on what you want to know.

Experiments on a single genotype are powerful and appropriate. Experiments on multiple genotypes are powerful and appropriate. The right experimental design depends on the question being asked.

Wild immunology assessed by multidimensional mass cytometry

A great part of our knowledge on mammalian immunology has been established in laboratory settings. The use of inbred mouse strains enabled controlled studies of immune cell and molecule functions in defined settings. These studies were usually performed in specific-pathogen free (SPF) environments providing standardized conditions. In contrast, mammalians including humans living in their natural habitat are continuously facing pathogen encounters throughout their life. The influences of environmental conditions on the signatures of the immune system and on experimental outcomes are yet not well defined. Thus, the transferability of results obtained in current experimental systems to the physiological human situation has always been a matter of debate. Studies elucidating the diversity of "wild immunology" imprintings in detail and comparing it with those of "clean" lab mice are sparse. Here, we applied multidimensional mass cytometry to dissect phenotypic and functional differences between distinct groups of laboratory and pet shop mice as a source for "wild mice". For this purpose, we developed a 31-antibody panel for murine leukocyte subsets identification and a 35-antibody panel assessing various cytokines. Established murine leukocyte populations were easily identified and diverse immune signatures indicative of numerous pathogen encounters were classified particularly in pet shop mice and to a lesser extent in quarantine and non-SPF mice as compared to SPF mice. In addition, unsupervised analysis identified distinct clusters that associated strongly with the degree of pathogenic priming, including increased frequencies of activated NK cells and antigen-experienced B- and T-cell subsets. Our study unravels the complexity of immune signatures altered under physiological pathogen challenges and highlights the importance of carefully adapting laboratory settings for immunological studies in mice, including drug and therapy testing. © 2016 International Society for Advancement of Cytometry.

Global parasite and Rattus rodent invasions: The consequences for rodent-borne diseases

We summarize the current knowledge on parasitism-related invasion processes of the globally invasive Rattus lineages, originating from Asia, and how these invasions have impacted the local epidemiology of rodent-borne diseases. Parasites play an important role in the invasion processes and successes of their hosts through multiple biological mechanisms such as "parasite release," "immunocompetence advantage," "biotic resistance" and "novel weapon." Parasites may also greatly increase the impact of invasions by spillover of parasites and other pathogens, introduced with invasive hosts, into new hosts, potentially leading to novel emerging diseases. Another potential impact is the ability of the invader to amplify local parasites by spillback. In both cases, local fauna and humans may be exposed to new health risks, which may decrease biodiversity and potentially cause increases in human morbidity and mortality. Here we review the current knowledge on these processes and propose some research priorities.

Susceptibility to Ticks and Lyme Disease Spirochetes Is Not Affected in Mice Coinfected with Nematodes

Small rodents serve as reservoir hosts for tick-borne pathogens, such as the spirochetes causing Lyme disease. Whether natural coinfections with other macroparasites alter the success of tick feeding, antitick immunity, and the host's reservoir competence for tick-borne pathogens remains to be determined. In a parasitological survey of wild mice in Berlin, Germany, approximately 40% of Ixodes ricinus-infested animals simultaneously harbored a nematode of the genus Heligmosomoides. We therefore aimed to analyze the immunological impact of the nematode/tick coinfection as well as its effect on the tick-borne pathogen Borrelia afzelii. Hosts experimentally coinfected with Heligmosomoides polygyrus and larval/nymphal I. ricinus ticks developed substantially stronger systemic type 2 T helper cell (Th2) responses, on the basis of the levels of GATA-3 and interleukin-13 expression, than mice infected with a single pathogen. During repeated larval infestations, however, anti-tick Th2 reactivity and an observed partial immunity to tick feeding were unaffected by concurrent nematode infections. Importantly, the strong systemic Th2 immune response in coinfected mice did not affect susceptibility to tick-borne B. afzelii. An observed trend for decreased local and systemic Th1 reactivity against B. afzelii in coinfected mice did not result in a higher spirochete burden, nor did it facilitate bacterial dissemination or induce signs of immunopathology. Hence, this study indicates that strong systemic Th2 responses in nematode/tick-coinfected house mice do not affect the success of tick feeding and the control of the causative agent of Lyme disease.

Strongyloides ratti and S. venezuelensis - rodent models of Strongyloides infection

Strongyloides spp. are common parasites of vertebrates and two species, S. ratti and S. venezuelensis, parasitize rats; there are no known species that naturally infect mice. Strongyloides ratti and S. venezuelensis overlap in their geographical range and in these regions co-infections appear to be common. These species have been widely used as tractable laboratory systems in rats as well as mice. The core biology of these two species is similar, but there are clear differences in aspects of their within-host biology as well as in their free-living generation. Phylogenetic evidence suggests that S. ratti and S. venezuelensis are the result of two independent evolutionary transitions to parasitism of rats, which therefore presents an ideal opportunity to begin to investigate the basis of host specificity in Strongyloides spp.

Markedly Elevated Antibody Responses in Wild versus Captive Spotted Hyenas Show that Environmental and Ecological Factors Are Important Modulators of Immunity

Evolutionary processes have shaped the vertebrate immune system over time, but proximal mechanisms control the onset, duration, and intensity of immune responses. Based on testing of the hygiene hypothesis, it is now well known that microbial exposure is important for proper development and regulation of the immune system. However, few studies have examined the differences between wild animals in their natural environments, in which they are typically exposed to a wide array of potential pathogens, and their conspecifics living in captivity. Wild spotted hyenas (Crocuta crocuta) are regularly exposed to myriad pathogens, but there is little evidence of disease-induced mortality in wild hyena populations, suggesting that immune defenses are robust in this species. Here we assessed differences in immune defenses between wild spotted hyenas that inhabit their natural savanna environment and captive hyenas that inhabit a captive environment where pathogen control programs are implemented. Importantly, the captive population of spotted hyenas was derived directly from the wild population and has been in captivity for less than four generations. Our results show that wild hyenas have significantly higher serum antibody concentrations, including total IgG and IgM, natural antibodies, and autoantibodies than do captive hyenas; there was no difference in the bacterial killing capacity of sera collected from captive and wild hyenas. The striking differences in serum antibody concentrations observed here suggest that complementing traditional immunology studies, with comparative studies of wild animals in their natural environment may help to uncover links between environment and immune function, and facilitate progress towards answering immunological questions associated with the hygiene hypothesis.

The laboratory mouse and wild immunology

The laboratory mouse, Mus musculus domesticus, has been the workhorse of the very successful laboratory study of mammalian immunology. These studies--discovering how the mammalian immune system can work--have allowed the development of the field of wild immunology that is seeking to understand how the immune responses of wild animals contributes to animals' fitness. Remarkably, there have hardly been any studies of the immunology of wild M. musculus domesticus (or of rats, another common laboratory model), but the general finding is that these wild animals are more immunologically responsive, compared with their laboratory domesticated comparators. This difference probably reflects the comparatively greater previous exposure to antigens of these wild-caught animals. There are now excellent prospects for laboratory mouse immunology to make major advances in the field of wild immunology.

The Gut Microbiota of Wild Mice

The gut microbiota profoundly affects the biology of its host. The composition of the microbiota is dynamic and is affected by both host genetic and many environmental effects. The gut microbiota of laboratory mice has been studied extensively, which has uncovered many of the effects that the microbiota can have. This work has also shown that the environments of different research institutions can affect the mouse microbiota. There has been relatively limited study of the microbiota of wild mice, but this has shown that it typically differs from that of laboratory mice (and that maintaining wild caught mice in the laboratory can quite quickly alter the microbiota). There is also inter-individual variation in the microbiota of wild mice, with this principally explained by geographical location. In this study we have characterised the gut (both the caecum and rectum) microbiota of wild caught Mus musculus domesticus at three UK sites and have investigated how the microbiota varies depending on host location and host characteristics. We find that the microbiota of these mice are generally consistent with those described from other wild mice. The rectal and caecal microbiotas of individual mice are generally more similar to each other, than they are to the microbiota of other individuals. We found significant differences in the diversity of the microbiotas among mice from different sample sites. There were significant correlations of microbiota diversity and body weight, a measure of age, body-mass index, serum concentration of leptin, and virus, nematode and mite infection.

Increased biodiversity in the environment improves the humoral response of rats

Previous studies have compared the immune systems of wild and of laboratory rodents in an effort to determine how laboratory rodents differ from their naturally occurring relatives. This comparison serves as an indicator of what sorts of changes might exist between modern humans living in Western culture compared to our hunter-gatherer ancestors. However, immunological experiments on wild-caught animals are difficult and potentially confounded by increased levels of stress in the captive animals. In this study, the humoral immune responses of laboratory rats in a traditional laboratory environment and in an environment with enriched biodiversity were examined following immunization with a panel of antigens. Biodiversity enrichment included colonization of the laboratory animals with helminths and co-housing the laboratory animals with wild-caught rats. Increased biodiversity did not apparently affect the IgE response to peanut antigens following immunization with those antigens. However, animals housed in the enriched biodiversity setting demonstrated an increased mean humoral response to T-independent and T-dependent antigens and increased levels of “natural” antibodies directed at a xenogeneic protein and at an autologous tissue extract that were not used as immunogens.