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Ecoimmunology conceptualizes the role of immunity in shaping life history in a natural context. Within ecoimmunology, macroimmunology is a framework that explains the effects of habitat and spatial differences on variation in immune phenotypes across populations. Within these frameworks, immune ontogeny—the development of the immune system across an individual life span—has received little attention. Here, we investigated how immune ontogeny from birth until adulthood is affected by age, sex, and developmental environment in a long-lived primate species, the bonobo.
We found a progressive, ificant decline of urinary neopterin levels, a marker for the cell-mediated immune response, from birth until 5 years of age in both sexes. The overall pattern of age-related neopterin changes was sex-specific, with males having higher urinary neopterin levels than females in the first 3 years of life, and females having higher levels than males between 6 and 8 years.
Environmental condition zoo-housed vs. Our data suggest that the post-natal development of cell-mediated immune ontogeny is sex-specific but does not show plasticity in response to environmental conditions in this long-lived primate species.
This indicates that cell-mediated immune ontogeny in the bonobo follows a stereotypic and maybe a genetically determined pattern that is not affected by environmental differences in pathogen exposure and energy availability, but that sex is an important, yet often overlooked factor shaping patterns of immune ontogeny. Investigating the causes and consequences of variation in immunity throughout life is critical for our understanding of life-history evolution and strategies, mechanisms of sexual selection, and population dynamics with respect to pathogen susceptibility.
Ecoimmunology uses an integrative approach to estimate costs, benefits, and fitness consequences of different immune defense strategies, and relates variation in immune responses to phylogeny, sociality, and ecology Martin et al.
Since the emergence of this discipline, research has focused on how immunity—the capacity to resist a particular pathogen—affects life history strategies within species Brock et al. Macroimmunology is a framework within ecoimmunology that considers habitat- and spatial-specific differences in immune phenotypes across populations Becker et al. Preliminary evidence suggests that immunity, but also exposure to immune challenges, can vary across life stages Beirne et al.
It is also reasonable to assume that sex-specific differences in development affect immune ontogeny Love et al. Additionally, developmental processes are often sensitive to environmental cues, and it is plausible that these parameters also affect immune ontogeny Martin et al. The two branches of the vertebrate immune system, innate immunity non-specific immune response and adaptive or acquired immunity specific immune responseshare two response trajectories, the cell-mediated and the humoral response Murphy and Weaver, Oviedo personal ad for sex are born with functioning immune systems, but immature and adult individuals differ in immune functionality.
These differences in immunity diminish with increasing age Dowling and Levy, ; Simon et al. After birth, infants depend mainly on innate immunity because their exposure to antigens in utero is low or absent PrabhuDas et al. During the postnatal phase, the exposure to environmental pathogens stimulates adaptive immune responses and the immune system becomes less tolerant West, ; Goenka and Kollmann, ; Simon et al.
There is evidence for ontogenetic changes in immune functioning in humans, and support for this comes from a recent study showing a peak in immune functioning between 5 and 14 years of age Glynn and Moss, Macroimmunology considers variation of environmental parameters such as resource availability, pathogen exposure and diversity on a spatial scale and relates this information to variation in immune system functioning Becker et al.
The intensity and diversity of pathogen exposure during ontogeny is hypothesized to be an important driver determining adult immunity McDade, Exposure to fewer but probably novel pathogens is expected to favor innate over adaptive immune responses. Correspondingly, populations with high but more familiar pathogen exposure, are predicted to develop adaptive immunity earlier in life McDade et al.
Contrary to these predictions, innate immunity markers were elevated in human populations with higher pathogen exposure McDade, ; Teran et al. Environmental differences affect cell-mediated responses in adult chimpanzees, where individuals from a wild population had higher activity of cell-mediated responses than those living in a zoo environment Behringer et al. Adult phenotypes that effect health can be the product of differences in developmental processes in response to environmental circumstances Bateson et al.
To consider the modulatory effect of pathogen exposure on immune ontogeny, comparative data from populations living in different pathogen environments are needed. One way to understand immune ontogeny in relation to ecological pressures and across evolutionary times, is to investigate free-living, genetically diverse, and energetically limited populations of animals using ecoimmunological and macroimmunological approaches Demas and Nelson, ; Forbes, Comparing wild and captive populations provides an ideal setting to investigate environmental drivers of immune ontogeny because of differences in dietary energy availability and pathogen exposure.
Although wild populations are probably exposed to a higher quantity of pathogens, zoo-housed animals are in close contact to humans which may increase the risk of transmission of zoonotic infections and exposure to new pathogens. This is particularly relevant for great apes because of their high susceptibility to human pathogens Calvignac-Spencer et al. In addition, zoo-housed populations usually receive intense medical care when infected, and this may also affect the strength and quality of their immunity Courtenay and Santow, Furthermore, most zoo-housed individuals enjoy a superior and more stable energy supply which permits higher investments into immune system functioning during ontogeny and adulthood without compromising e.
These Oviedo personal ad for sex in intensity and diversity of pathogen exposure and energy supply between wild and zoo environments are therefore ideal to test hypotheses about ontogenetic drivers of adult immunity. In humans and other mammals, immunity differs between the sexes. Adult females have fewer infections, stronger antibody responses, but also greater vulnerability to autoimmune diseases than males e. These differences in immunity are seen as sex-specific trade-offs in resource allocation favoring immunity or reproduction Zuk, Sex hormones with higher concentrations in females i.
For example, estradiol increases immune responses associated with pro-inflammatory processes. In contrast, testosterone biases the specific cell-mediated immune response toward anti-inflammatory processes Fischer et al. These interactions between sex steroids and cell-mediated immunity suggest that increases in estradiol and testosterone with the onset of sexual maturation in females and males, respectively, can produce similar sex-specific effects on immune system functioning during development.
While sex differences in adult immunity are well described, information about sex-specific immune ontogeny is rare Fish, ; Klein and Flanagan, For example, inflammatory processes are higher in pre-pubertal boys than girls, but after puberty this relationship is reversed Yang and Kozloski, ; Klein and Flanagan,and many vaccinations induce a greater antibody response and some a greater cell-mediated response in girls than in boys Flanagan et al.
So far, the few studies available indicate that immune ontogeny in humans is sex-specific and we can therefore expect to find similar differences in the immune ontogeny in non-human primate species. Maturation until adulthood s for one third of the total lifespan, the period between the onset of sexual maturation and first reproduction is relatively long, and there is a considerable gap between the time when adult body size is reached and the emergence of reproductive competence Lancaster and Hamburg, ; Robson and Wood, ; Walker et al.
Apes differ in their innate immune strategy from monkeys with shorter lifespans and a faster pace-of-life. The energetically costly strategy of sterilization over specificity which apes employ is thought to have evolved as a response to higher risk of pathogen exposure during their slow life history or past pathogen exposure Hawash et al. So far, studies on the influence of environment and sex on ontogenetic changes in immunity have focused on species with short lifespans and fast pace-of-life.
In long-lived species, their long developmental periods provide more time for adaptive adjustments in life history trade-offs in response to environmental factors than in short-lived species. Those adjustments can then lead to a larger variation of functional immune phenotypes Simon et al. In this regard, humans are the best studied long-lived species so far, but many aspects of human immunology have only been studied in the context of pathologies McDade, ; Martin et al.
The biotopes inhabited by African apes vary in terms of climate, forest cover, faunal composition, and in the frequency and intensity of human contact. Therefore, it is reasonable to assume that pathogen exposure varies accordingly, and that this manifests in species-specific resistance and susceptibility to pathogens.
For example, ape species seem to differ in their susceptibility to simian immunodeficiency virus SIV Gao et al. Therefore, great apes are an ideal model taxon to investigate sex-specificities and environmental impacts on the immune ontogeny of Oviedo personal ad for sex species that might explain variation in disease susceptibility and range distribution within and between populations. Within the African great apes, bonobos Pan paniscus and chimpanzees P. Given the importance of developmental changes for the reconstruction of phylogenetic trends, there is increasing interest in the postnatal development of bonobos and chimpanzees Hare and Yamamoto, ; Lee et al.
Yet, information on immune ontogeny in these species is rare. Bonobos are particularly interesting for studying immunity and its ontogeny because recent studies revealed that their major histocompatibility complex MHC class I profile has undergone selection reducing its variability compared to humans and chimpanzees, presumably due to selection for malaria protecting MHC allotypes e.
It is assumed that such a reduction in genetic diversity of the MHC influences the functioning of immunity in this species Sommer, ; de Groot et al. Additionally, the onset of sexual maturation in female bonobos occurs about three years earlier than in males Behringer et al. Therefore, sex-specific differences in immune ontogeny are predicted to occur at different ages.
In our study, we focus on cell-mediated immune ontogeny.
Cell-mediated immunity targets intra cellular pathogens such as all viruses e. Thakur et al. The activation of cell-mediated immunity can be assessed by measuring neopterin, a biomarker mainly produced by monocyte-derived macrophages and dendritic cells.
Neopterin can be readily measured in blood and urine Fuchs et al. In this study, we investigated the effects of age, environment wild vs. We measured urinary neopterin as a marker of cell-mediated immunity in individuals ranging in age between birth until 18 years of age. Using human studies as a conceptual benchmark, we considered the impact of age, environment and sex on immune ontogeny and tested the following predictions: 1 Age: If the immune system shifts from predominantly cell-mediated to more humoral responses during the first years of life, neopterin levels will be elevated in infant bonobos and decline with age.
Between June and Octoberurine samples female: ; male: were collected from two wild bonobo communities Bompusa East and Bompusa West community at the LuiKotale field site, Democratic Republic of the Congo Hohmann and Fruth, All subjects were habituated to human presence before the start of the study period and all were individually known.
Samples represent 34 individual females average: 11 samples per individual and 21 individual males average: 11 samples per individual. For wild subjects, the month and year of birth were known for 13 individuals, and for these we set the date of birth to the 15th of the respective month. For 12 individuals only the year of birth was known, and we set the birth date to June 15th of the respective year. For the remaining 30 individuals exact birthdates are known. Zoo-housed bonobos were sampled between January and Septemberand urine samples female: ; male: were collected in nine different zoos.
These samples represent 49 individual females average: three samples per individual and 26 individual males average: four samples per individual. All zoo-housed bonobos were of known age and were housed in mixed-sex groups of different sizes.
Age range was 0—18 years of age for both populations zoo average: eight years; wild average: five years. All samples were collected at a time when individuals did not show symptoms of infection or injury e. Urine samples were collected opportunistically throughout the day between and h. Samples were collected on plastic sheets or the floor for zoo-housed bonobos, and from vegetation for wild animals. Samples were protected from direct sunlight to avoid neopterin degradation Fuchs et al. In the field, urine samples were frozen in liquid nitrogen upon arrival at camp on the same day.
Zoo samples were frozen immediately after collection. Prior to analysis, urine samples were thawed, vortex-mixed for 10 seconds, and subsequently centrifuged for 5 minutes. SG population average was 1. Inter-assay variation for high- and low-value quality controls was 5.
Intra-assay variation was 6. Expecting age-related but non-linear patterns in urinary neopterin levels, we fitted a generalized additive mixed model GAM Wood, with gaussian-identity link function using R R Development Core Team, to our data. The GAM is composed of a sum of smooth functions of covariates and provides a structure for generalizing a general linear model by allowing additivity of non-linear functions of the variables Wood,; Ravindra et al.
Urinary neopterin levels were log-transformed. Sex and environmental condition zoo-housed, wild were included as ordered factors, and daytime of sample collection as a control predictor. To model changes in neopterin levels with age, we included age as a smooth term with a penalized cubic regression.
To control for time between sample collection until measurement, we included sample storage time as a smooth term. Sample storage time ranged between 6 months and nearly 12 years. Because sex and environmental condition are ordered factors, an indicator vector is generated for each level, but not for the first level of the ordered factor.
The basis dimension, k was set to 5. The choice of basis dimensions determines the maximum possible degrees of freedom allowed for each model term Wood, To control for the potential influence of time of sample collection, this parameter was included as a fixed effect in the model as a control predictor.
Concurvity, the situation where a smooth term can be approximated by some combination of the others, was not an issue.Oviedo personal ad for sex
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