Abstract
BackgroundIn an energy-limited environment, caloric investments in one characteristic should trade-off with investments in other characteristics. In high pathogen ecologies, biasing energy allocation towards immune function over growth would be predicted, given strong selective pressures against early-life mortality.MethodologyIn the present study, we use flow cytometry to examine trade-offs between adaptive immune function (T cell subsets, B cells), innate immune function (natural killer cells), adaptive to innate ratio and height-for-age z scores (HAZ) among young children (N = 344; aged 2 months–8 years) in the Bolivian Amazon, using maternal BMI and child weight-for-height z scores (WHZ) as proxies for energetic status.ResultsMarkers of adaptive immune function negatively associate with child HAZ, a pattern most significant in preadolescents (3+ years). In children under three, maternal BMI appears to buffer immune and HAZ associations, while child energetic status (WHZ) moderates relationships in an unexpected direction: HAZ and immune associations are greater in preadolescents with higher WHZ. Children with low WHZ maintain similar levels of adaptive immune function, but are shorter compared to high WHZ peers.ConclusionsReduced investment in growth in favor of immunity may be necessary for survival in high pathogen contexts, even under energetic constraints. Further, genetic and environmental factors are important considerations for understanding variation in height within this population. These findings prompt consideration of whether there may be a threshold of investment into adaptive immunity required for survival in high pathogen environments, and thus question the universal relevance of height as a marker of health.Lay SummaryAdaptive immune function is negatively associated with child height in this high pathogen environment. Further, low weight-for-height children are shorter but maintain similar immune levels. Findings question the relevance of height as a universal health marker, given that costs and benefits of height versus immunity may be calibrated to local ecology.
Highlights
In an energy-limited environment, caloric investments in one characteristic should tradeoff with investments in other characteristics
To test the prediction that having adequate energetic reserves may buffer a trade-off between immune function and growth in the child, we examine the effects of a three-way interaction between each immune marker, child or maternal energetic status and age group on child height-for-age z scores (HAZ)
We find partial support for the hypothesis that a high pathogen environment should favor early investment in adaptive immune function, and that such heavy investment may trade-off against somatic growth
Summary
In an energy-limited environment, caloric investments in one characteristic should tradeoff with investments in other characteristics. In high pathogen ecologies, biasing energy allocation towards immune function over growth would be predicted, given strong selective pressures against early-life mortality. Given the strong selective pressure against infant mortality, early investment in immune function should be prioritized despite consequences for competing energetic requirements, like growth. This may be salient in a high pathogen environment, where investment in the adaptive arm of the immune system, which confers long-lasting specific immunity, would be critical for surviving this early period [5]. The authors found that mucosal damage, which was associated with impaired growth in height, was most severe among middle-class children, leading to the conclusion that nutritional constraints may mask or confound relationships between immune function and linear growth
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