Wild immunology.

Abstract

In wild populations, individuals are regularly exposed to a wide range of pathogens. In this context, organisms must elicit and regulate effective immune responses to protect their health while avoiding immunopathology. However, most of our knowledge about the function and dynamics of immune responses comes from laboratory studies performed on inbred mice in highly controlled environments with limited exposure to infection. Natural populations, on the other hand, exhibit wide genetic and environmental diversity. We argue that now is the time for immunology to be taken into the wild. The goal of 'wild immunology' is to link immune phenotype with host fitness in natural environments. To achieve this requires relevant measures of immune responsiveness that are both applicable to the host-parasite interaction under study and robustly associated with measures of host and parasite fitness. Bringing immunology to nonmodel organisms and linking that knowledge host fitness, and ultimately population dynamics, will face difficult challenges, both technical (lack of reagents and annotated genomes) and statistical (variation among individuals and populations). However, the affordability of new genomic technologies will help immunologists, ecologists and evolutionary biologists work together to translate and test our current knowledge of immune mechanisms in natural systems. From this approach, ecologists will gain new insight into mechanisms relevant to host health and fitness, while immunologists will be given a measure of the real-world health impacts of the immune factors they study. Thus, wild immunology can be the missing link between laboratory-based immunology and human, wildlife and domesticated animal health.

Full text

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OPINION
Wild immunology
AMY B. PEDERSEN and SIMON A. BABAYAN
Centre for Immunity, Infection and Evolution, Institutes of Immunology & Infection Research and Evolutionary Biology,
University of Edinburgh, Ashworth Labs, West Mains Road, Edinburgh EH9 3JT, UK
Abstract
In wild populations, individuals are regularly exposed to a wide range of pathogens. In
this context, organisms must elicit and regulate effective immune responses to protect
their health while avoiding immunopathology. However, most of our knowledge about
the function and dynamics of immune responses comes from laboratory studies
performed on inbred mice in highly controlled environments with limited exposure to
infection. Natural populations, on the other hand, exhibit wide genetic and environ-
mental diversity. We argue that now is the time for immunology to be taken into the
wild. The goal of ‘wild immunology’ is to link immune phenotype with host fitness in
natural environments. To achieve this requires relevant measures of immune respon-
siveness that are both applicable to the host–parasite interaction under study and
robustly associated with measures of host and parasite fitness. Bringing immunology to
nonmodel organisms and linking that knowledge host fitness, and ultimately population
dynamics, will face difficult challenges, both technical (lack of reagents and annotated
genomes) and statistical (variation among individuals and populations). However, the
affordability of new genomic technologies will help immunologists, ecologists and
evolutionary biologists work together to translate and test our current knowledge of
immune mechanisms in natural systems. From this approach, ecologists will gain new
insight into mechanisms relevant to host health and fitness, while immunologists will be
given a measure of the real-world health impacts of the immune factors they study. Thus,
wild immunology can be the missing link between laboratory-based immunology and
human, wildlife and domesticated animal health.
Keywords: disease ecology, eco-immunology, ecological immunology, parasitology, wild
mammals
Received 4 August 2010; revision received 15 October 2010; accepted 18 October 2010
Introduction
The advances in molecular biology of the last few years,
especially with the advent of full genome sequencing,
promised to ‘decode all life’ and in the process offer
previously unforeseen solutions to disease and human
health (Butler 2010). However, if we are to translate the
exponential growth of molecular data into real-world
benefits, much work is needed to disentangle the many
sources of variation between genes, phenotypes and the
environment (Weinberg 2010). Similarly, immunologists
are continuously enhancing our mechanistic under-
standing of immune processes, yet little has been tested
in the context of natural populations, including humans.
In the few cases in which laboratory techniques have
been applied in the wild, such natural variation has led
to unforeseen outcomes for disease spread and vaccina-
tion success (Cooper et al. 1998; Harris et al. 2009; Eze-
nwa et al. 2010; Wammes et al. 2010). We assert that
now more than ever, a two-way feedback between labo-
ratory and field studies will deliver tangible advances
in the well-being of humans, wildlife and domesticated
animals. We propose that recent progress in genomic
and postgenomic techniques and their ever-greater
affordability at last allow us to take immunology into
the wild and study how variation in genes and environ-
ment affect the key processes that maintain health.
Correspondence: Amy B. Pedersen, Fax: +44 131 650 6564;
E-mail: amy.pedersen@ed.ac.uk
? 2011 Blackwell Publishing Ltd
Molecular Ecology (2011)doi: 10.1111/j.1365-294X.2010.04938.x

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Understanding how natural populations are affected
by their interactions with pathogens (e.g. viruses, bacte-
ria, protozoans, helminths, etc.), commensal organisms
and environmental heterogeneity is crucial. However,
very little is known about how health and immunity
are shaped by co-infection when both the environment
and the host and pathogen genotypes vary. The field of
ecological immunology (‘eco-immunology’) has begun
to address the complexity of immune responses in an
ecological and evolutionary context. The primary goals
of this field have been to understand variation in
immune function across individuals, with a focus on
determining the fitness consequences of such variation
(Norris & Evans 2000; Rolff & Siva-Jothy 2003; Schmid-
Hempel 2003). This has led to some exciting discoveries
and an increase in the crosstalk between ecology and
immunology, which have previously been mostly dispa-
rate fields (Viney et al. 2005; Martin et al. 2006; Salvante
2006; Bradley & Jackson 2008; Graham et al. 2011; Haw-
ley & Altizer 2011).
This crosstalk is helpful as immunologists and ecolo-
gists often speak and think differently about infections
and the immune response. However, an important chal-
lenge remains to use state-of-the-art tools from each dis-
cipline to test and expand their respective outstanding
questions.Immunologists
immune responses of very few strains of mice, but very
little about their relevance to mammalian (human or
other) immune responses in the wild. On the other
hand, ecologists have the tools to study complex interac-
tions and variability, but typically have very little grasp
on their mechanistic underpinnings because of a lack of
relevant techniques. We need to build a bridge between
these fields within an evolutionary framework that will
allow us to test the relevance of mechanisms identified
in laboratory models to the health of individuals in nat-
ural populations and, in return, to bring variation into
the laboratory to better understand the immune system.
Here, we aim to highlight how wild immunology can
create synergistic benefits for our understanding of
immunology, ecology, evolution and health.
knowmuchabout the
Why study immunology in the wild?
Why would immunologists want to work on wild sys-
tems? Moving from highly controlled laboratory set-
tings with a constant supply of food and water, limited
genetic diversity,controlled
immune markers to the wild, with high genetic diver-
sity, multiple infections, variable nutrition and difficulty
in recapturing animals seems to be an unattractive
proposition. However, only under natural conditions is
one likely to measure the effects of immune phenotypes
on host health and fitness. Crucially, wild immunology
infectionand trusted
will help link mouse and human immunology, because
humans are a lot more like a wild mammal than a
caged laboratory mouse; we live in variable environ-
ments, are genetically diverse, and suffer multiple
simultaneous and sequential infections as do wild
mammals (Ezenwa et al. 2010, Telfer et al. 2010). In
addition, wild immunology should inform therapeutic
intervention strategies, because the range of natural
conditions that wild animals face better reflect the chal-
lenges faced by human treatment programmes. While
controlled laboratory settings are good for reproducibil-
ity of results, immunologists have long appreciated that
the genetic background has a major effect on immune
responses and susceptibility to pathogens (Reiner &
Locksley 1995). It is indeed clear for both ecologists and
immunologists that immune responses, and ultimately
health, are the result of many contributing factors: (i)
genetic variability (e.g. MHC alleles), (ii) history of
infection (immune memory, current infections), (iii)
physiological condition (e.g. sex, age, reproductive state
and history), (iv) resource availability (e.g. diet), (v) abi-
otic conditions (e.g. seasonality and temperature) and
(vi) co-evolutionary history between host and pathogen.
Life in the wild is tough. Individuals face both biotic
and abiotic pressures that will affect their survival and
reproduction. Many of these pressures may also affect
immune function and the costs associated with mount-
ing a response. Factors that will affect host fitness and
will likely affect the immune response are pathogen
interactions, resource limitation, competition, predation,
seasonality and sex differences, etc. (Martin et al. 2008;
Lazzaro & Little 2009). Recent studies on wild popula-
tions of field voles (Telfer et al. 2010) and African buf-
falo (Ezenwa et al. 2010) have shown the importance
and complexity of parasite–parasite interactions for
determining disease prevalence and the invasion of
novel infectious diseases. These studies have the poten-
tial to change our overly narrow approach to modelling
and treating infectious diseases one at a time (Fenton
et al. 2008; Lafferty 2010).
In addition, we know that wild populations are out-
bred and therefore have a high degree of genetic varia-
tion that likely affect the components that make an
immune response protective (Abolins et al. 2011). It is
also becoming clear that the gut microbiota communi-
ties of wild mammals affect both the development of
the immune system (Chung & Kasper 2010; Round &
Mazmanian 2010) and the establishment and transmis-
sion of co-infecting parasites (Hayes et al. 2010). Cur-
rently, the importance of such diversity for host health
is unknown. However, given these early findings from
laboratory systems, there is great potential for both of
these factors to structure the immune system and
its interactions with parasites and thus to affect the
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outcome of therapeutic interventions. Given this knowl-
edge and the increasing availability and affordability of
genetic tools, it is time to reevaluate the costs and bene-
fits of studying mammalian immunology in wild popu-
lations. To date, laboratory immunology has mostly
focused on a few strains of mice, and only some studies
look at comparative responses across these strains,
which often differ substantially (Butler 2010). For exam-
ple, pathogenesis of Leishmania infection differs greatly
between BALB⁄c mice, which develop a more pro-
nouncedanti-macroparasitic
infected and C57BL⁄6 mice, which develop a classically
anti-microparasitic Th1 response (Reiner & Locksley
1995). Likewise, while BALB⁄c mice allow the filarial
nematode Litomosoides sigmodontis to release transmissi-
ble offspring, C57BL⁄6 mice are resistant to this parasite,
and this protective immune phenotype requires IL-4, a
major component of the Th2 response (Le Goff et al.
2002; Babayan et al. 2003). In addition, studies from
human populations suggest that ethnicity, age and sex
can affect rates of re-infection with Schistosoma mansoni
after drug treatment (Pinot de Moira et al. 2010). Thus,
it should be clear that the mixture of genotypes in natu-
ral populations, in concert with the biotic and abiotic
pressures that affect fitness, will alter the landscape of
disease occurrence and resistance throughout the popu-
lation as well as responses to intervention. Therefore, to
truly understand how the immune system functions,
protects the host from disease or causes immunopathol-
ogy, it is crucial to bring our impressive immunologi-
cal toolbox into wild populations to measure immune
phenotypes.
Th2response when
How to study wild immunology?
Many ecological studies use the term ‘immune func-
tion’, but do not properly define it, which is problem-
atic as it can be overly general and have many different
meanings for different disciplines. Often immune func-
tion is used as a catch-all phrase to describe the com-
plete immune response, the immune system, or the
specific components of an immune response that are
elicited against a specific pathogen infection. Following
the terminology proposed by Bradley & Jackson (2008),
we define ‘immune phenotype’ as the multivariate, con-
text-dependent state of the immune system at any given
time. Thus, we could go out into a natural population
to sample an animal and measure its immune pheno-
type (antibodies, cytokines, cellular responses, etc.).
Consequently, the ‘protective immune phenotype’ is
defined as the subset of the immune phenotype that
protects an organism from disease (both pathogens and
immunopathology). A protective immune phenotype
will be defined by the commonalities across individuals
infected with a specific pathogen that either clear the
infection, or tolerate it and survive with little harm. A
protective immune phenotype can not always be mea-
sured by looking at one immune factor or by measuring
the magnitude of a specific immune response i.e. anti-
body titres, proliferative response to mitogen, T-cell
proliferation or activation), as it is most probably the
result of multiple factors acting in concert. Tradition-
ally, ecological immunology studies in wild populations
have focused on measuring a single or very few general
measures of immunocompetence i.e. phytohemaggluti-
nin (PHA) assays, leucocyte counts, L:H ratio, bacterial
killing assays, phagocytosis (Norris & Evans 2000; Lee
& Klasing 2004), but it is indeed unlikely that there is a
single measure of immune function that will predict the
outcome of infection or host health. More realistically, a
protective immune phenotype will be multi-dimen-
sional, dependent on the taxonomic class of the patho-
gen (i.e. virus, helminth, bacteria, etc.), the pathogen’s
immune evasion strategies and the history of exposure
(i.e. primary vs. secondary immune response), such that
aiming for a single immunocompetence measure is not
a realistic benchmark for wild immunology (Viney et al.
2005; Lemus et al. 2010).
The immune phenotype is thus purely descriptive
and broad, while the protective immune phenotype is
the subset of that immune phenotype that enhances
host fitness. More formally, identifying the protective
immune phenotype requires determining the direction
of the causal relationships between variation in host
health and variation in immune phenotype and can
only be measured through longitudinal sampling or
experimental manipulations. Furthermore, both are con-
text-dependant (i.e. dependent on host genotype, patho-
gen infection and co-infection, history of infection and
exposure, and the biotic and abiotic environment). For
example, a protective immune phenotype that would
likely be effective against helminth infections will
require an active Th2 response (CD4 +
eosinophils) (Anthony et al. 2007). In contrast, a protec-
tive immune phenotype of a host infected with a virus
would have an activated Th1 response (type 1 interfer-
ons, type 1 antibody, CD8+ cytotoxic T cells) (Pamer
2009; Welsh et al. 2010). Measuring and identifying a
protective immune phenotype in wild populations will
be difficult and will certainly require broad preliminary
descriptive measures (of our ‘immune phenotype’), we
would therefore suggest measuring as many factors that
have been identified from laboratory-based immunolog-
ical studies as possible.
Similar ideas are being presented in human immunol-
ogy, and there is a call to move away from a mouse
model of human health, to instead develop noninvasive
sampling‘metrics’that can
T cells, IgE,
distinguisha healthy
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immune response from an unhealthy one (Davis 2008;
Leslie 2010). Following from this, if we define a protec-
tive immune phenotype as the effective or optimal strat-
egy, we also need to understand that more, or a
stronger immune response, is not always better (Viney
et al. 2005; Graham et al. 2011). In addition, a protective
immune phenotype that responds effectively to a para-
site infection, by controlling or eliminating the parasite
and increasing host fitness, may not be correlated with
a host’s protective immune phenotype to a different
pathogen. These trade-offs in the immune response to
different pathogens have the potential to be important
for host health and pathogen transmission in cases of
co-infection (Fenton et al. 2008). For example, studies
from human populations have shown that helminth
infections, which are often associated with a strong Th2
response, may impair immune responses to concurrent
co-infections or vaccination. Specifically, helminth infec-
tion can influence immune regulation (T regulatory cells
(Treg) and IL-10), which can impair the efficacy of
immunization, by suppressing immune responses to
BCG (tuberculosis), Plasmodium falciparum-parasitized
red blood cells (Wammes et al. 2010) and to tetanus
vaccination (Cooper et al. 1998). Given that a higher
immune response (e.g. higher antibody titres, increased
inflammation) does not always maximize host fitness or
eliminate that pathogen, the definition of a protective
immune phenotype allows a nonlinear relationship
between the immune phenotype and host fitness. To
identify and measure this protective immune pheno-
type, we need to measure functional aspects of the
immune response, parasite⁄pathogen fitness and host
fitness through experimental or longitudinal studies
(Viney et al. 2005; Graham et al. 2011).
While the aim of wild immunology is to develop
tools that can be used in many wild animals, it may be
most advantageous to start with systems that are phylo-
genetically related to immunologically well-studied ani-
mals and amenable to experimentation with large
sample sizes. In particular, we suggest developing wild
rodent systems. These will allow us to adapt the vast
genetic and immunological resources that have been
developed with the laboratory mouse model of mam-
malian immunology to wild mice and voles (e.g. Jack-
son et al. 2009, 2011; Abolins et al. 2011). For example,
Abolins et al. (2011) in this issue compare wild house
mice (Mus musculus C57BL/6 strain) to laboratory mice
(M. musculus C57BL/6 strain) to assess the quantitative
and qualitative nature of immune function in wild pop-
ulations. They find that wild mice tend to have higher
and more variable immune responses (both more avid
antigen-specific responses and greater standing concen-
trations of IgG and IgE antibodies) than a relatively
immuno-responsive laboratory strain (C57BL⁄6).
Techniques and approaches for wild
immunology
There are many new and existing technologies that can
be employed for the study of wild immunology, both
by utilizing immunological tools developed for model
systems and through new molecular approaches. Using
techniques and tools from laboratory systems is a neces-
sary first step, but because a protective immune pheno-
type in a laboratory system may differ from what is
protective in a wild animal, we suggest a three-stage
programme to develop new model systems for wild
immunology. The first phase of establishing such a
model would involve deep sampling of a limited num-
ber of individuals in a wild population for immune
variables, host demography and parasitology to collect
extensive information about host–parasite interactions
and the immune phenotypes of individuals. As a first
pass, wild immunologists would test the full arsenal of
techniques and tools that have been optimized for phy-
logenetically closely related species, and where possible,
optimize them for the wild species. Second, from this
wealth of information, the goal would be to identify
representative markers that can be reliably measured
and that capture the diverse arms of the immune sys-
tem. These may be a set of individual immune factors
(i.e. quantitative PCR assays that measure cytokines,
cell identification, antibody concentrations), or a multi-
variate component of these factors (such as a principal
component analysis of several individual immune fac-
tors) that captures as much of the immune phenotype
as possible for a given host–pathogen combination. The
ultimate aim is to develop noninvasive markers to
allow longitudinal sampling, which will be crucial for
inferring causation and identifying the protective ele-
ments of an immune phenotype. Third, one would set
up a longitudinal field study or experimental manipula-
tion, to measure the immune phenotype in combination
with host demography and parasitology. From here, we
can make connections between immune phenotypes
that increase fitness for specific pathogen pressures (i.e.
the protective immune phenotype), and with this
knowledge, we can begin to address the fundamental
and interesting questions about how life in the wild
may affect the development and expression of a protec-
tive immune phenotype.
Standard laboratory immunology approaches
Unfortunately, the study of immunology in nonmodel
species suffers from a lack of reagents needed to
measure immune phenotypes (Bradley & Jackson 2008).
However, a representative subset of specific immuno-
logical reagents (such as monoclonal antibodies) could
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be developed for new species that could complement
other measures. In a few cases, it may be possible to
use laboratory reagents created for humans, laboratory
mice, poultry, or domestic animals that work effectively
in nonmodel organisms (Lee & Klasing 2004; Martin
et al. 2007; Ezenwa et al. 2010; Graham et al. 2010). For
example, Jackson et al. (2009) used reagents developed
for laboratory mice to measure splenocyte proliferation
and toll-like receptor expression in wild wood mice
(Apodemus sylvaticus) and found negative associations
with some parasite infections and innate immunity acti-
vation. In addition, Abolins et al. (2011) have used sev-
eral techniques developed for laboratory mice (e.g. in
vivo immunization and in vitro splenocyte stimulation
with keyhole limpet haemocynanin (KLH) to measure
IFNc, IgG and IgE, and FACS analysis of T helper and
regulatory cells) in wild house mouse populations, and
it is possible that some of these mouse-specific reagents
will work in related wild rodents. In addition, ELISA
for detecting IgG antibodies to KLH has been used in
laboratory populations of more than six species of Pero-
myscus mice to measure variation in standing and elic-
ited responses (Martin et al. 2007). Following on,
several bird studies have successfully used techniques
and tools developed for the poultry industry, but
adapted to work in wild birds (Lee & Klasing 2004;
Salvante 2006), for example circulating CD4 and CD8
cells were measured in wild caught kestrels using flow
cytometry and mouse antiavian monoclonal antibodies
originally designed for poultry (Lemus et al. 2010). In
addition, tools and techniques developed for livestock
have been successfully adapted to wild ungulate sys-
tems (Jolles et al. 2008; Ezenwa et al. 2010; Graham
et al. 2010). Recently, Ezenwa et al. (2010) measured
both baseline and antigen-stimulated interferon c (IFNc;
as a measure of Th1 immune function) using reagents
designed for cattle.
Many of the standard immunological assays that have
been commonly used in ecological immunology (i.e.
white blood cell counts from smears, PHA assays, bac-
teria killing assays, etc.) may, in some cases, be useful
for measuring an immune phenotype. However, to
assess parasite-specific immune
detailed measurements of immune components are
needed beyond the classical eco-immunology tool set.
Recent evidence from an experimental study that moni-
tored the immune response after parasite infection and
vaccination demonstrated that many standard measures
(WBC counts and PHA assay) did not reveal the impor-
tant changesin circulating
through flow cytometry (Lemus et al. 2010).
Classical immunological tools and techniques may be
useful in closely related species, but will probably not
have much applicability for distantly related mammals.
phenotypes,more
lymphocytesdetected
In cases where these tools cannot be readily adapted,
newly available molecular approaches should provide a
useful alternative for nonmodel organisms, and collabo-
rative efforts across research groups to develop classical
immunological reagents for new model organisms (i.e.
a zebra finch immunology consortium) could create
standard tools available for new groups of wild species.
For instance, it would be highly desirable to produce
monoclonal antibodies specific for major cytokines and
antibody isotypes, markers of cell type and activation
state as is standard for laboratory mice. However, such
standard immunological techniques used in laboratory
immunology are often invasive and may only be useful
in some aspects of wild immunological studies. We sug-
gest that developing and investigating both standard
invasive and noninvasive techniques during the first
phase of investigation will be useful for characterizing
the multi-dimensional immune phenotype. For example,
invasive (terminal) sampling of the spleen, lymphoid
organs and blood samples can be used to measure both
localand systemicimmune
strong correlations between invasive and noninvasive
data would then allow later studies (phase 3 of our sug-
gested research programme) to use only the most infor-
mative noninvasive sampling
amenable to ecological approaches and longitudinal
sampling.
responses. Identifying
methodsthat are
Genomic approaches
The progress of relatively inexpensive high-throughput
sequencing technology has opened the path for immune
studies on nonmodel animals, and it is now in principle
feasible to reach a significant coverage of the genome of
any species. In addition, the extensive knowledge of the
M. musculus genome provides the basis for accurate
identification of many genes of other rodent species,
which can then serve as a reference for comparative
transcriptomic studies of immune (or other relevant)
gene transcription profiles (Waterston et al. 2002). This
will facilitate the design of more accurate primers for
immune genes than the currently used degenerate
primers, for example to quantify the mRNA production
of known immune genes in wild mice based on knowl-
edge of the immunology of M. musculus in the labora-
tory (Jackson et al. 2011). Linking this kind of study
with experimental manipulations in the field or within
longitudinal studies that measure both co-infection and
host fitness is a goal of wild immunology. Further, deep
sequencing can be expected to allow mapping multiple
genes to complex immune phenotypes. In addition, the
recently published zebra finch genome (Warren et al.
2010), and the rapidly decreasing costs of genome
sequencing, may provide templates for developing
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immunological markers, both genomic and protein-
based, for birds.
Postgenomic approaches
Recent advances in deep sequencing technology prom-
ise unprecedented scope for the mechanistic under-
standing of health and immunity. Until now, only small
numbers of genes, usually stemming from a candidate
gene approach, could be studied. An example is the
study by Jackson et al. (2011) who use quantitative PCR
methods, developed from sequence data on laboratory
mice and other rodent sequences to measure cytokine
mRNA in natural populations of field voles. The
authors used this qPCR approach in concert with stan-
dard laboratory immunological assays (i.e. mitogen
stimulation of toll-like receptors and Th cell responsive-
ness in splenocyte culture) to measure immune expres-
sion and variation in a wild rodent population (Jackson
et al. 2009, 2011). Through the deep sequencing of tran-
scriptomes, large-scale identification of gene expression
patterns can also provide longitudinal accounts of pro-
tective immune phenotypes and immune correlates of
health. If combined with experimental manipulation in
the wild, causal links between molecular patterns and
individual infection and health status become possible.
Postgenomic tools are commonly used in human immu-
nology because of the constraints of noninvasive sam-
pling techniques, and borrowing and adapting these
tools and biomarkers to wild immunology systems will
be very important. For example, measuring the periph-
eral-blood transcriptome (Mohr & Liew 2007), quantify-
ing genome-wide expression through oligonucleotide
arrays of peripheral leucocytes (Cobb et al. 2005), and
identificationand quantification
serum (Gilad et al. 2008) could all help measure host
health, parasite infection or specific protective immune
phenotypes. Building these postgenomic tools to test
immune phenotypes across nonmodel organisms will
allow us to look at comparisons of the immune pheno-
type and the functional evolution of the immune
response across species and eventually to generalize
immune processes across taxonomic boundaries (Martin
et al. 2007).
of microRNAsin
Host demography and parasitology
Wild populations are a composite of individuals of dif-
ferent age, sex, sexual maturity, reproductive state
(e.g. gravid, lactating) and are at different population
densities and within communities of different species
compositions. This variation at the individual and pop-
ulation scale will influence host susceptibility and
exposure to parasites and therefore will affect immune
priming and maintenance of immune memory and
ultimately, host fitness (Martin et al. 2008; Lazzaro &
Little 2009). In turn, host survival and reproduction
will affect population density and future pathogen
transmission. Thus, to truly understand a protective
immune phenotype, measures of host demography
and fitness and parasite transmission must also be
included in the studies of wild immunology (Viney
et al. 2005; Graham et al. 2011). In addition, both the
history of infection and concurrent infections, both at
the individual level and over evolutionary history, will
be very important for giving context to a specific
immune phenotype. Thus, studies that identify and
measure the vast community of parasites and patho-
gens that can infect a natural population, not just a
single pathogen species, will be crucial (Pedersen &
Fenton 2007). As many methods of sampling for
pathogens use visual identification and are difficult to
scale up for large experimental studies, we suggest
incorporating diagnostic
sequence-based) to facilitate the detection of multiple
pathogens.
tests (antibody-basedor
How do we link wild and laboratory
immunology?
While it may be quite obvious how introducing immu-
nological tools can inform the study of wild population
health and dynamics, it may be less clear how wild
immunology can contribute to laboratory immunology.
We suggest that there are several reasons for immunol-
ogists to consider bringing their research questions,
tools and expertise to the wild. First, wild immunology
canhelplaboratoryimmunologists
aspects of the immune response are relevant for a pro-
tective immune phenotype in a natural setting. This is
especiallyimportant considering
dynamics can emerge from interactions between para-
site and host communities (Pedersen 2005; Telfer et al.
2010). Next, as immunologists gain an ever more
detailed understanding of immune mechanisms from
laboratory experiments, it becomes highly relevant to
weigh these advances in the context of natural popula-
tions. Wild immunology studies that incorporate immu-
nology, parasitologyand
immunologists to understand how life in the wild may
affect various aspects of an immune response, and to
define how natural variation between individuals and
over time affect the diversity of factors that contribute
to an individuals protective immune responses. In addi-
tion, the study of wild immunology may bring us closer
to understanding immunity in humans, and how best
to improve health. For example, using a wild study sys-
tem may inform strategies for how vaccines can be
identifywhich
that unexpected
demography willallow
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designed to immunize hosts under environmental stres-
sors or co-infection. It is also well documented that diet
and nutrition (e.g. protein scarcity, extreme lipid con-
tents) can affect immune responses and lead to different
immune phenotypes (Koski et al. 1999; Ing et al. 2000).
Thus, pairing the wild immunological approach with
diet manipulations may better inform immunization
and treatment strategies.
Unfortunately, there may be limits to how much
information inbred strains and controlled laboratory set-
tings can inform human, livestock and wildlife health
studies, and therefore, a wild immunology approach
that incorporates genetic variation and other ecological
noise may be necessary to broaden our knowledge. We
propose a link from laboratory studies to the wild, and
from wild immunological studies back to the labora-
tory. This two-way approach may further enlighten the
mechanisms driving the immune response, and how
they are likely to affect host health and fitness in the
wild. However, comparing results between laboratory
and wild systems will not be straight-forward. For
example, Abolins et al. (2011) in this issue attempt to
do this with wild populations of house mice, but there
are still questions about how many laboratory strains
we need to test to make sure that the variability and
degree of response is consistent with or different from
what we find in wild mice. So it seems that one of the
most important reasons to develop wild immunology
(to understand the consequences of genetic diversity for
immune response and host fitness) may also be our big-
gest hurdle.
Conclusions
To identify causal relationships between immune phe-
notypes and parasite prevalence (i.e. to define protec-
tive immune phenotypes), experimental manipulations
in wild populations will be essential. These may be
able to inform optimal treatment strategies that take
into accountthe interactions
pathogens. It may be, for instance, that the most effec-
tive strategy to reduce viral infections and increase
health and fitness of a given population is to mass
treat against helminths.
approaches can only be tested with manipulative stud-
ies on wild populations (Pedersen & Fenton 2007), at
scales that are unwieldy for livestock, and difficult in
humans for ethical reasons. We acknowledge that
bringing the tools and techniques from laboratory
immunology into wild populations will be a difficult
task. However,giventhe
human, livestock and wildlife health (e.g. emerging
pathogens, selection of drug-resistance, zoonotic dis-
eases) and the recent expansion of genomic and post-
between co-infecting
Such counter-intuitive
pressingchallenges for
genomic tools that are now available, we believe that
now is the time for wild immunology. This can be
accomplished if immunologists, ecologists, evolutionary
biologists, disease biologists, parasitologists and others
bring their expertise together to work on these com-
plex and dynamic systems. Eventually, detailed studies
across multiple wild systems may also allow phyloge-
netic comparative studies of immune strategies across
populations and species. Here, we have tried to show
why now is the time for wild immunology, what tech-
niques and approaches can be used to develop non-
model study systems and how immunologists and
ecologists can bring their unique toolboxes together to
answer shared questions about the role of the immune
system in natural populations and give greater insight
into how the host immune response, pathogens and
environment interact in the wild.
Acknowledgements
We thank Steve Paterson, Dana Hawley, Andrea Graham,
Karen Fairlie-Clarke, Tom Little, Andy Fenton, Judi Allen,
Emily Griffiths, Vincent Straszewski and one anonymous
reviewer for very helpful comments on the manuscript. ABP is
supported by a Wellcome Trust Centre for Infection, Immunity
and Evolution (CIIE) Advanced Fellowship and SAB is sup-
ported by a Wellcome Trust CIIE Junior Fellowship at the Uni-
versity of Edinburgh.
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A.B.P.’s research goal is to expand the one host – one parasite
framework that dominates the study of disease ecology and
evolution, specifically developing two major projects under this
theme: (1) to evaluate the interactions that occur between co-
infecting parasites within a host and their consequences for the
immune response and host health and (2) to expand our
knowledge of multi-host parasites, in particular to test the eco-
logical factors that facilitate persistence of a recently emerged
disease on a new host. S.B.’s research interests are to under-
stand how parasites ensure their survival and transmission in
the face of the host’s immune responses. Specifically, parasitic
nematodes employ immune-dependant phenotypic plasticity
and immune manipulation to ensure they transmit; S.A.B. is
interested in identifying the mechanisms that underlie these
strategies in order to inform vaccine design against parasitic
nematodes, and how host diversity in genetic, nutritional, and
infectious backgrounds interacts with parasite life history and
host immunity.
WILD IMMUNOLOGY 9
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