Variability in stress system regulatory control of inflammation: a critical factor mediating health effects of stress

Out of the Laboratory and Into the Field: Validation of Portable Cell Culture Protocols

OBJECTIVE

Field-based research on inflammation and health is typically limited to baseline measures of circulating cytokines or acute-phase proteins, whereas laboratory-based studies can pursue a more dynamic approach with ex vivo cell culture methods. The laboratory infrastructure required for culturing leukocytes limits application in community-based settings, which in turn limits scientific understandings of how psychosocial, behavioral, and contextual factors influence the regulation of inflammation. We aim to address this gap by validating two "field-friendly" cell culture protocols, one using a small volume of venous whole blood and another using finger-stick capillary whole blood.

METHODS

We evaluated the performance of both protocols against a standard laboratory-based protocol using matched venous and capillary blood samples collected from young adults (n = 24). Samples were incubated with lipopolysaccharide and hydrocortisone, and the production of proinflammatory cytokines interleukin 1β, interleukin 6, and tumor necrosis factor α was measured in response.

RESULTS

Comparisons indicate a high level of agreement in responses across the protocols and culture conditions. The overall correlation in results was 0.88 between the standard and small-volume protocols and 0.86 between the standard and capillary blood protocols. Repeatability for the small-volume and capillary blood protocols was high, with mean coefficients of variation across five replicates of 6.2% and 5.4%, respectively.

CONCLUSIONS

These results demonstrate the feasibility of culturing cells and quantifying the inflammatory response to challenge outside the laboratory, with a wide range of potential applications in biobehavioral research in community-based and remote field settings.

Prospective association of maternal immune pro-inflammatory responsivity and regulation in pregnancy with length of gestation

PROBLEM

The immune system represents a leading pathway of interest in the pathophysiology of preterm birth. The majority of human clinical studies interrogating this pathway have utilized circulating immune biomarkers; however, these concentrations typically reflect only basal production but not key functional properties of the immune system, particularly variation in the pro-inflammatory response to antigen challenge and the regulation of this response. Thus, in this study, we utilized an ex vivo stimulation protocol that quantifies these processes, and we examined their prospective association with the gestation length and risk of preterm birth.

METHOD OF STUDY

Immune responsiveness and regulation were assessed in 128 pregnant women in mid-gestation using an ex vivo stimulation protocol. Maternal pro-inflammatory responsivity of leukocytes was quantified by assessing the release of the pro-inflammatory cytokines IL-6, TNF-α, and IL-1β in response to antigen stimulation, and regulation of the pro-inflammatory response was quantified by assessing the suppression of stimulated cytokine response upon co-incubation with increasing dexamethasone concentrations (ie, glucocorticoid receptor resistance; GRR).

RESULTS

Higher maternal GRR, indicating impaired regulation of the pro-inflammatory response, was significantly and independently associated with shorter gestational length (β = -0.42, p = .0091) and a 3.0-fold increase in risk for preterm birth (OR = 3.01, 95% CI = 1.17-7.70, p = .0218). Basal circulating IL-6 and TNF-α were not associated with either outcome.

CONCLUSION

The association of maternal GRR with length of gestation and preterm birth risk suggests that the processes represented by this measure-maternal pro-inflammatory propensity and immune regulation-may provide further mechanistic insight into the pathophysiology of preterm birth.

The relationship between chronic stress, hair cortisol and hypertension

Inconsistencies in studies of chronic psychosocial stress and hypertension may be explained by the use of stress markers greatly influenced by circadian rhythm and transient stressors. We assessed whether hair cortisol, a marker that captures systemic cortisol over months, was independently associated with hypertension. We measured hair cortisol and blood pressure in 75 consecutive participants in the Survey of the Health of Wisconsin, using an ELISA test. Individuals with values ​≥ ​median (78.1 ​pg/mg) were considered exposed. We used approximate Bayesian logistic regression, with a prior odds ratio of 1.0–4.0, to quantify the multivariate-adjusted hair cortisol-hypertension association. Participants' average age was 46.9 years; 37.3% were male; and 25.3% were hypertensive. Hypertension prevalence was 2.23 times higher in exposed (95% CI: 1.69–3.03). This finding was unlikely explained by differential measurement errors, since we conducted blinded measurements of exposure and outcome. Sensitivity analyses showed the association was unlikely explained by an unmeasured confounder, survival bias, or reverse causality bias. Findings suggest elevated hair cortisol is a risk factor for hypertension. Although feasible, the clinical value of hair cortisol as a tool for hypertension risk stratification or for monitoring the effect of chronic psychosocial stress management interventions is still uncertain.

Effects of social support on glucocorticoid sensitivity of lymphocytes in socially deprived piglets

There is growing evidence that social support given by a conspecific attenuates stress responses of a socially deprived animal. We hypothesized that the presence of a familiar social partner modulates the effectiveness of social buffering as assessed by an altered glucocorticoid sensitivity of immune cells. The current study investigated the effects of a 4-h social deprivation procedure on stress hormone responses and immune cell functions in 7-, 21- and 35-day-old piglets (52 males and 56 females). Within each of the three age categories, nine piglets were deprived of their mother and littermates either alone or with a familiar or unfamiliar age-matched piglet. Compared to non-deprived controls, piglets that were alone displayed significant increases in plasma adrenocorticotropic hormone and cortisol concentrations, and all socially deprived piglets showed a greater in vitro proliferative response of peripheral blood mononuclear cells (PBMCs) to lipopolysaccharide (LPS)-stimulation than controls. Concanavalin A (ConA)-induced in vitro proliferation was not affected by social treatment. Additionally, both the ConA- and LPS-stimulated PBMCs from piglets that experienced any of the deprivation treatments were more resistant to the inhibitory effects of cortisol than PBMCs from the controls in each of the three age categories. Irrespective of the mitogen used, the presence of an age-matched conspecific during deprivation attenuated the dose-dependent cortisol resistance. Here, familiarity between the piglets clearly improved the effectiveness of social support in an age-dependent manner. Collectively, our findings emphasize the benefits of social partners regarding stress coping abilities, with positive implications for animal welfare and health.

Salivary cytokines as a minimally-invasive measure of immune functioning in young children: correlates of individual differences and sensitivity to laboratory stress

There is growing interest in minimally-invasive measures of environmentally-responsive biological systems in developmental science. Contributing to that endeavor, this study explores the intercorrelations, correlates, and task-sensitivity of proinflammatory salivary cytokines in childhood. Saliva was sampled from 125 healthy five-year old children (49% male) across a series of cognitive and emotional challenge laboratory tasks. Samples were assayed for cytokines (IL-1β, IL-6, IL-8, TNFα), and markers of hypothalamic-pituitary-adrenal (HPA) and autonomic nervous system (ANS) activation (salivary cortisol and alpha-amylase [sAA]). Cytokines were positively intercorrelated and task-sensitivity varied. Except IL-8, cytokines were elevated in children with oral health issues and tobacco smoke exposure. Among boys, cytokines were positively related to sAA and negatively related to cortisol. The findings suggest that in healthy children, salivary cytokine levels reflect compartmentalized oral immune activity. Associations between ANS and HPA activity and cytokines in saliva may present opportunities for minimally-invasive methods to explore neuroendocrine-immune interactions during development.

Altered salivary alpha-amylase awakening response in Bosnian War refugees with posttraumatic stress disorder

In posttraumatic stress disorder (PTSD), chronic activation of the sympathetic nervous system (SNS) has been suggested. No study so far has investigated diurnal secretion patterns of salivary alpha-amylase (sAA) in PTSD, a promising candidate for non-invasive assessment of SNS activity. We compared sAA diurnal profiles between a group of Bosnian War refugees with PTSD and a healthy control group, and further analyzed for associations with psychiatric symptoms and glucocorticoid (GC) sensitivity of inflammatory regulation. PTSD patients showed a sAA awakening response profile that was opposite to those seen in healthy controls, i.e. an increase instead of a sharp decrease. Patterns of sAA secretion were further positively associated with psychiatric symptoms of PTSD. Finally, higher sAA awakening responses were associated with higher GC sensitivity of inflammatory cytokine production. These findings are in line with altered SNS function in PTSD, and lend further support for employing assessment of diurnal sAA profiles as non-invasive biomarkers in stress-related disease.