Sex differences in the impact of childhood socioeconomic status on immune function.

Early life stress increases one's risk for health problems later in life, and many studies find that these effects are sex-differentiated. Here, we examined relationships between multiple sources of early life stress and adult immune function in humans across several functional assays. Adult participants provided retrospective information about their childhood (a) socioeconomic status, (b) household unpredictability, and (c) exposure to adverse experiences. Participants' peripheral blood mononuclear cells (PBMCs) were then isolated for use in functional assays of immune performance: (a) tumor cell lysis by natural killer cells, (b) phagocytosis of Escherichia coli bioparticles, and (c) mitogen-induced leukocyte proliferation and cytokine release. In men, lower childhood socioeconomic status predicted decrements in immunological performance across functional assays, along with greater spontaneous cytokine release from PBMCs. These changes co-occurred with elevations in plasma testosterone levels. Similar effects were not observed for other sources of stress, nor were they found in women (with the exception of spontaneous cytokine release). These findings provide evidence that low childhood socioeconomic status has a lasting negative impact on multiple aspects of immune function, particularly in men.

Day length predicts investment in human immune function: Shorter days yield greater investment.

Winter is characterized by stressful conditions which compromise health and render animals more vulnerable to infection and illness than during other times of the year. Organisms are hypothesized to adapt to these seasonal stressors by increasing investment in immune function in response to diminished photoperiod duration. Here, we examined this hypothesis in a sample of healthy human participants. Using several functional immune assays in vitro, as well as by utilizing measures of in vivo proinflammatory cytokine levels, we predicted that shorter day length would be associated with greater investment in immunological function. Results revealed that shorter days predicted significant upregulation of several facets of immune function, including natural killer cell cytotoxicity, peripheral blood mononuclear cell proliferation (in response to, and in the absence of stimulation), and plasma levels of interleukin-6, as well as lower rates of Staphylococcus aureus growth in serum ex vivo. Further, consistent with the hypothesis that these trade-offs would be offset by decreased investment in mating effort, shorter day length also predicted lower levels of total testosterone in men. These results suggest that ambient photoperiod may be a powerful regulator of human immunological activity, providing some of the first evidence of seasonal changes in multiple facets of human immune function.

Inflammation Predicts Decision-Making Characterized by Impulsivity, Present Focus, and an Inability to Delay Gratification.

Here, we propose a novel theoretical model linking present-focused decision-making to the activities of the immune system. We tested our model by examining the relationship between inflammatory activity - in vivo and in vitro - and decision-making characterized by impulsivity, present focus, and an inability to delay gratification. Results support our model, revealing that inflammation predicts these outcomes even after controlling for factors that may contribute to a spurious linkage between them. Moreover, subsequent analyses revealed that our model was a better fit for the data than alternative models using present-focused decision-making and its health-harming behavioural sequelae (e.g., smoking, risky sexual behaviour) to predict inflammation, lending support for the proposed directionality of this relationship. Together, these results suggest that inflammation may contribute to decision-making patterns that can result in undesirable personal and societal outcomes.

Behavioral immune system activity predicts downregulation of chronic basal inflammation.

Here, we present a mechanistically grounded theory detailing a novel function of the behavioral immune system (BIS), the psychological system that prompts pathogen avoidance behaviors. We propose that BIS activity allows the body to downregulate basal inflammation, preventing resultant oxidative damage to DNA and promoting longevity. Study 1 investigated the relationship between a trait measure of pathogen avoidance motivation and in vitro and in vivo proinflammatory cytokine production. Study 2 examined the relationship between this same predictor and DNA damage often associated with prolonged inflammation. Results revealed that greater trait pathogen avoidance motivation predicts a) lower levels of spontaneous (but not stimulated) proinflammatory cytokine release by peripheral blood mononuclear cells (PBMCs), b) lower plasma levels of the proinflammatory cytokine interleukin-6 (IL-6), and c) lower levels of oxidative DNA damage. Thus, the BIS may promote health by protecting the body from the deleterious effects of inflammation and oxidative stress.