Depressive symptoms are not associated with inflammation in younger and older adults in the Philippines

Socioeconomic status is negatively associated with immunosenescence but positively associated with inflammation among middle-aged women in Cebu, Philippines

BACKGROUND

Socioeconomic status (SES) gradients in health are well-documented, and while biological pathways are incompletely understood, chronic inflammation and accelerated immune aging (immunosenescence) among lower SES individuals have been implicated. However, previous findings have come from samples in higher income countries, and it is unclear how generalizable they are to lower- and middle-income countries (LMIC) with different infectious exposures and where adiposity-an important contributor to chronic inflammation-might show different SES patterning. To address this gap, we explored associations between SES and inflammation and immunosenescence in a sample of women in Cebu, Philippines.

METHODS

Data came from the mothers of the Cebu Longitudinal Health and Nutrition Survey birth cohort (mean age: 47.7, range: 35-69 years). SES was measured as a combination of annual household income, education level, and assets. Chronic inflammation was measured using C-reactive protein (CRP) in plasma samples from 1,834 women. Immunosenescence was measured by the abundance of exhausted CD8T (CD8 + CD28-CD45RA-) and naïve CD8T and CD4T cells, estimated from DNA methylation in whole blood in a random subsample of 1,028. Possible mediators included waist circumference and a collection of proxy measures of pathogen exposure.

RESULTS

SES was negatively associated with the measures of immunosenescence, with slight evidence for mediation by a proxy measure for pathogen exposure from the household's drinking water source. In contrast, SES was positively associated with CRP, which was explained by the positive association with waist circumference.

CONCLUSIONS

Similar to higher income populations, in Cebu there is an SES-gradient in pathogen exposures and immunosenescence. However, lifestyle changes occurring more rapidly among higher SES individuals is contributing to a positive association between SES and adiposity and inflammation. Our results suggest more studies are needed to clarify the relationship between SES and inflammation and immunosenescence across LMIC.

Three common assumptions about inflammation, aging, and health that are probably wrong

Chronic inflammation contributes to the onset and progression of cardiovascular disease and other degenerative diseases of aging. But does it have to? This article considers the associations among inflammation, aging, and health through the lens of human population biology and suggests that chronic inflammation is not a normal nor inevitable component of aging. It is commonly assumed that conclusions drawn from research in affluent, industrialized countries can be applied globally; that aging processes leading to morbidity and mortality begin in middle age; and that inflammation is pathological. These foundational assumptions have shifted focus away from inflammation as a beneficial response to infection or injury and toward an understanding of inflammation as chronic, dysregulated, and dangerous. Findings from community-based studies around the world-many conducted in areas with relatively high burdens of infectious disease-challenge these assumptions by documenting substantial variation in levels of inflammation and patterns of association with disease. They also indicate that nutritional, microbial, and psychosocial environments in infancy and childhood play important roles in shaping inflammatory phenotypes and their contributions to diseases of aging. A comparative, developmental, and ecological approach has the potential to generate novel insights into the regulation of inflammation and how it relates to human health over the life course.

Inflammation and depression in young people: a systematic review and proposed inflammatory pathways

Depression onset peaks during adolescence and young adulthood. Current treatments are only moderately effective, driving the search for novel pathophysiological mechanisms underlying youth depression. Inflammatory dysregulation has been shown in adults with depression, however, less is known about inflammation in youth depression. This systematic review identified 109 studies examining the association between inflammation and youth depression and showed subtle evidence for inflammatory dysregulation in youth depression. Longitudinal studies support the bidirectional association between inflammation and depression in youth. We hypothesise multiple inflammatory pathways contributing to depression. More research is needed on anti-inflammatory treatments, potentially tailored to individual symptom profiles.

Traumatic events and mental health: The amplifying effects of pre-trauma systemic inflammation

BACKGROUND

Traumatic experiences are strongly predictive of adverse mental health outcomes. Experimental studies have demonstrated that systemic inflammation can increase reactivity to threatening stimuli. It is not known whether naturally occurring inflammation amplifies the impact of traumatic experiences on mental health. Here we test whether incident traumatic events are more predictive of adverse mental health outcomes for individuals with greater pre-trauma systemic inflammation in a racially and ethnically diverse cohort study of youth assigned male at birth who identify as sexual or gender minorities (ages 16-29, n = 518), a group at high risk for trauma exposure.

METHODS

Measures of inflammation, depression symptom severity, and perceived stress were measured at baseline. One year later, depression symptom severity and perceived stress were measured again, and participants reported the traumatic events they had experienced in the intervening year.

RESULTS

In a model adjusted for baseline depression symptom severity and other key covariates, we found that higher baseline levels of interleukin-1β amplified the effect of incident trauma exposure on depression symptom severity at follow-up (β = 0.234, SE = 0.080, P = 0.004). In a model adjusted for baseline perceived stress and other key covariates, we found that higher baseline scores on a multi-marker inflammatory index amplified the effect of incident trauma exposure on perceived stress at follow-up (β = 0.243, SE = 0.083, P = 0.003).

CONCLUSIONS

These findings suggest that greater pre-trauma inflammation may predict poorer mental health following trauma exposure. Understanding how inflammation interacts with trauma to shape mental health may generate novel insights for preventing and treating the debilitating psychological consequences of trauma.

Challenges in researching the immune pathways between early life adversity and psychopathology

Exposure to childhood adversity is a critical risk factor for the development of psychopathology. A growing field of research examines how exposure to childhood adversity is translated into biological risk for psychopathology through alterations in immune system functioning, most notably heightened levels of inflammation biomarkers. Though our knowledge about how childhood adversity can instantiate biological risk for psychopathology is growing, there remain many challenges and gaps in the field to understand how inflammation from childhood adversity contributes to psychopathology. This paper reviews research on the inflammatory outcomes arising from childhood adversity and presents four major challenges that future research must address: (a) the measurement of childhood adversity, (b) the measurement of inflammation, (c) the identification of mediators between childhood adversity and inflammation, and (d) the identification of moderators of inflammatory outcomes following childhood adversity. We discuss synergies and inconsistencies in the literature to summarize the current understanding of the association between childhood adversity, a proinflammatory phenotype, and the biological risk for psychopathology. We discuss the clinical implications of the inflammatory links between childhood adversity and psychopathology, including possibilities for intervention. Finally, this review conclude by delineates future directions for research, including issues of how best to detect, prevent, and understand these “hidden wounds” of childhood adversity.

Elevated hs-CRP level is associated with depression in younger adults: Results from the Korean National Health and Nutrition Examination Survey (KNHANES 2016)

INTRODUCTION

Reports on the association between the level of circulating high-sensitivity C-reactive protein (hs-CRP) and depression have been inconsistent. The aim of this study was to examine the association between hs-CRP and depression in a large sample.

METHODS

This study used data obtained from a representative Korean sample of 5447 people who participated in the first (2016) year of the seventh Korean National Health and Nutrition Examination Survey (KNHNES VII-1). Depression was identified using a cutoff of 5 on the Patient Health Questionnaire-9 (PHQ-9), and high hs-CPR level was defined as ≥ 3.0 mg/L.

FINDINGS

Participants with a high CRP levels had a significantly higher rate of depression than did those with a low hs-CRP levels (25.1% vs. 19.8%, p = 0.007). Serum hs-CRP was independently associated with the PHQ-9 total score after adjusting for potentially confounding factors (B = 0.014; 95% CI = 0.008-0.020). After controlling for body mass index (BMI), smoking, alcohol use problems, hypertension, diabetes, dyslipidemia, chronic illness related hs-CRP, and metabolic syndrome. Furthermore, elevated hs-CRP level was significantly associated with an increased risk of depression (adjusted OR = 1.44; 95% CI = 1.01-2.07) in younger adults, but no significant association was observed among older adults.

CONCLUSION

These findings suggest a significant correlation between high hs-CRP levels and depression in younger adults. Further studies are necessary to investigate the age-specific association and the biological mechanism involved.

Ecological Context and Human Variation: Applying the Principles of Biological Anthropology to Psychoneuroimmunology

There is considerable research interest overlap between biological anthropology and psychoneuroimmunology (PNI), particularly given recent anthropological interest in endocrine and immune system functioning over the life span and in different environmental contexts. In this chapter, I argue that conducting research on non-WEIRD populations and applying an anthropological, evolutionary approach to PNI can greatly strengthen our understanding of immune-endocrine-behavior connections. This chapter reviews population-level variation in the human immune and endocrine systems, as well as genetic and environmental contributions to this variation. The effects of culture on shaping health outcomes and stress responses are also considered. Finally, this chapter discusses some noninvasive sampling methodologies appropriate to field research and alternatives to laboratory-based research designs. By confronting variable social and environmental contexts, PNI can greatly expand on its existing contributions to the treatment and understanding of depression, mood disorders, stress, and other aspects of health and well-being.

Perspectives on Psychological Science: Right Way/Wrong Way Symposium

In unpredictable times, it is perhaps even more important to contemplate the direction different fields of science are headed. In this article, I contemplate two directions of psychological science: the increasing integration of the study of psychology with other sciences and the concern of many sciences, including ours, with improving the reproducibility of our findings. Both of these are argued to be "right ways," but these directions also have challenges that, unless carefully addressed, could detract from our ability to move the science of psychology forward. I detail these challenges along with a consideration of how to chart our science through the unpredictable waters we face at this point in history.

Levels of C-reactive protein (CRP) in elderly patients with unipolar depression - case control analysis

AIM

C-reactive protein (CRP) is the major acute-phase plasma protein. Studies show that patients with depression have elevated levels of CRP. The aim of the study was to determine differences in CRP serum level in elderly patients with unipolar depression (DEP) compared with non-depressed elderly patients (nonDEP) using case-control analysis.

METHODS

Serum level of CRP was measured in 404 (DEP: n = 202, nonDEP: n = 202) Caucasian inpatients aged ≥60 (350 women, 86.7%; mean age = 76.7 years).

RESULTS

Mean CRP level in the study groups was: DEP 2.67 ± 2.56 mg/dL, nonDEP 2.41 ± 2.19 mg/dL, the difference was not significant (p = 0.96). The overall rate of being above the high level of CRP (set at 3.0 mg/L) was 33.2% for DEP and 29.2% for nonDEP groups (p = 0.39). It was also found that, in the whole study group, CRP level was not correlated with age (p = 0.10).

CONCLUSIONS

Elderly patients with depression have no increased CRP levels. A high percentage (∼30%) of all subjects had a CRP level >3 mg/L, which is the cut-off point for increased cardiovascular risk.

Biodiversity, the Human Microbiome and Mental Health: Moving toward a New Clinical Ecology for the 21st Century?

Advances in research concerning the brain-related influences of the microbiome have been paradigm shifting, although at an early stage, clinical research involving beneficial microbes lends credence to the notion that the microbiome may be an important target in supporting mental health (defined here along the continuum between quality of life and the criteria for specific disorders). Through metagenomics, proteomics, metabolomics, and systems biology, a new emphasis to personalized medicine is on the horizon. Humans can now be viewed as multispecies organisms operating within an ecological theatre; it is important that clinicians increasingly see their patients in this context. Historically marginalized ecological aspects of health are destined to become an important consideration in the new frontiers of practicing medicine with the microbiome in mind. Emerging evidence indicates that macrobiodiversity in the external environment can influence mental well-being. Local biodiversity may also drive differences in human-associated microbiota; microbial diversity as a product of external biodiversity may have far-reaching effects on immune function and mood. With a focus on the microbiome as it pertains to mental health, we define environmental “grey space” and emphasize a new frontier involving bio-eco-psychological medicine. Within this concept the ecological terrain can link dysbiotic lifestyles and biodiversity on the grand scale to the local human-associated microbial ecosystems that might otherwise seem far removed from one another.

Inflammatory profile in depression and associated clinical and sociodemographic features in a Middle-Eastern North-African population

BACKGROUND

Evidence of the presence of an inflammatory syndrome in depressive disorders has aroused great interest among researchers but results were heterogeneous and almost all previous studies involved patients from Europe or North America. The objectives of the current study were to determine the prevalence of biological inflammatory syndrome among patients with depression in a Middle-Eastern/North-African population and to examine the associated sociodemographic and clinical factors.

METHODS

We conducted a cross-sectional descriptive and comparative study including 65 patients and 30 healthy controls. The patients had an untreated major depressive episode and no inflammatory medical conditions; they were recruited in the psychiatry outpatient clinic in Razi hospital - Tunisia over an eight-month period ranging from May to December 2012. We examined sociodemographic and clinical characteristics and both groups had an inflammatory balance including: high sensitive C-reactive protein, interleukin 6, serum protein electrophoresis, haptoglobin and orosomucoid. A standardized inflammatory protein profile for age and sex was performed.

RESULTS

High sensitive C-reactive protein levels did not differ significantly between patients with depression and controls. The assay results of Interleukin 6 in our study showed higher values in patients with depression than in controls (p=0.024). Albumin was found to be increased in patients with depression (p<0.001). The dosage of the alpha-1-globulin including the orosomucoid and of the alpha-2-globulin including haptoglobin, showed that patients with depression had higher values than controls (p<0.001). The inflammatory protein profile (which consists of a synthesis of three inflammatory proteins: high sensitive C-reactive protein, haptoglobin and orosomucoϊd) showed a trend towards higher levels of inflammation among patients with depression than among controls.

LIMITATIONS

The relatively small number of subjects decreased the statistical power and the cross-sectional setting does not allow us to draw any conclusions about cause-to-effect relationships. Although we tried to exclude people with current infections, a small percentage of subjects may have had subclinical infections. The Body Mass Index, a parameter that might affect the levels of the investigated inflammatory markers, was not measured.

CONCLUSION

The existence of inflammation in depression has been proven by the results of four meta-analyses and over a hundred studies. However, the generalization of this finding is yet to be confirmed. It seems more likely that inflammation concerns a subgroup of patients with depression. Studies targeting this particular subgroup could provide new therapeutic approaches.

Posttraumatic Stress Disorder: Does the Gut Microbiome Hold the Key?

Gut bacteria strongly influence our metabolic, endocrine, immune, and both peripheral and central nervous systems. Microbiota do this directly and indirectly through their components, shed and secreted, ranging from fermented and digested dietary and host products to functionally active neurotransmitters including serotonin, dopamine, and γ-aminobutyric acid. Depression has been associated with enhanced levels of proinflammatory biomarkers and abnormal responses to stress. Posttraumatic stress disorder (PTSD) appears to be marked in addition by low cortisol responses, and these factors seem to predict and predispose individuals to develop PTSD after a traumatic event. Dysregulation of the immune system and of the hypothalamic-pituitary-adrenal axis observed in PTSD may reflect prior trauma exposure, especially early in life. Early life, including the prenatal period, is a critical time in rodents, and may well be for humans, for the functional and structural development of the immune and nervous systems. These, in turn, are likely shaped and programmed by gut and possibly other bacteria. Recent experimental and clinical data converge on the hypothesis that imbalanced gut microbiota in early life may have long-lasting immune and other physiologic effects that make individuals more susceptible to develop PTSD after a traumatic event and contribute to the disorder. This suggests that it may be possible to target abnormalities in these systems by manipulation of certain gut bacterial communities directly through supplementation or indirectly by dietary and other novel approaches.

Links among inflammation, sexual activity and ovulation: Evolutionary trade-offs and clinical implications

Inflammation in healthy sexually active women decreased at midcycle, around ovulation, which may have evolved to promote conception.

Background and objectives: We examined a mechanism that may coordinate trade-offs between reproduction and immune response in healthy women, namely, changes in inflammation across the ovarian cycle.

Methodology: We investigated C-reactive protein (CRP), an inflammation marker, across two consecutive ovarian cycles in 61 Bolivian women. Participants provided saliva samples every other day, and dried blood spots on 5–6 days spread across weeks 2–3 of each cycle. Cycles were characterized as ovulatory/anovulatory based on profiles of reproductive hormones. Participants also reported whether they were sexually partnered with a male or sexually abstinent during the study.

Results: High early-cycle, but not late-cycle, CRP was associated with anovulation. High inflammation at the end of one cycle was not associated with anovulation in the subsequent cycle. Among ovulatory cycles, women with sexual partners had significantly lower CRP at midcycle, and higher CRP at follicular and luteal phases; in contrast, sexually abstinent women had little cycle-related change in CRP. In anovulatory cycles, partnership had no effect on CRP. CRP varied significantly with socioeconomic status (higher in better-off than in poorer women).

Conclusions and implications: These findings suggest that the cycle-specific effect of inflammation on ovarian function may be a flexible, adaptive mechanism for managing trade-offs between reproduction and immunity. Sociosexual behavior may moderate changes in inflammation across the ovarian cycle, suggesting that these shifts represent evolved mechanisms to manage the trade-offs between reproduction and immunity. Clinically, these findings support considering both menstrual cycle phase and sexual activity in evaluations of pre-menopausal women’s CRP concentrations.

Depression as sickness behavior? A test of the host defense hypothesis in a high pathogen population

Sadness is an emotion universally recognized across cultures, suggesting it plays an important functional role in regulating human behavior. Numerous adaptive explanations of persistent sadness interfering with daily functioning (hereafter "depression") have been proposed, but most do not explain frequent bidirectional associations between depression and greater immune activation. Here we test several predictions of the host defense hypothesis, which posits that depression is part of a broader coordinated evolved response to infection or tissue injury (i.e. "sickness behavior") that promotes energy conservation and reallocation to facilitate immune activation. In a high pathogen population of lean and relatively egalitarian Bolivian forager-horticulturalists, we test whether depression and its symptoms are associated with greater baseline concentration of immune biomarkers reliably associated with depression in Western populations (i.e. tumor necrosis factor alpha [TNF-α], interleukin-1 beta [IL-1β], interleukin-6 [IL-6], and C-reactive protein [CRP]). We also test whether greater pro-inflammatory cytokine responses to ex vivo antigen stimulation are associated with depression and its symptoms, which is expected if depression facilitates immune activation. These predictions are largely supported in a sample of older adult Tsimane (mean±SD age=53.2±11.0, range=34-85, n=649) after adjusting for potential confounders. Emotional, cognitive and somatic symptoms of depression are each associated with greater immune activation, both at baseline and in response to ex vivo stimulation. The association between depression and greater immune activation is therefore not unique to Western populations. While our findings are not predicted by other adaptive hypotheses of depression, they are not incompatible with those hypotheses and future research is necessary to isolate and test competing predictions.

Serum cytokines and anxiety in adolescent depression patients: Gender effect

The present study compares the serum cytokine levels between adolescent depression patients and healthy controls and assesses correlation between depression, anxiety scores and serum levels of eight cytokines. Study also checked the variation in serum levels with medication status (medication free/naïve vs. patients on medication). Following clinical and psychometric assessment of 77 adolescent (aged 13-18 years) depression patients (49 males and 28 females; 56 medication free/naïve) and 54 healthy controls (25 males, 29 females), eight cytokines (IL-1β, IL-2, IL-6, IL-10, TNF-α, IFN-γ, TGF-β1 and IL-17A {denoted IL-17 throughout}) were measured in serum using ELISA. Depressed adolescents had significantly high levels of IL-2 (p<0.001) and IL-6 (p=0.03) as compared to controls. The female population skewed the result of one cytokine (IL-6) in patients. Anxiety scores showed positive correlation (only in female patients) with IL-1β, IL-10 and negative correlation with TGF-β1 and IL-17. The gender effect in relationship between anxiety and cytokines was not straightforward. On comparing study groups on the medication/naïve status, IL-2 and TGF-β1 showed significant difference between the groups (p<0.001, p=0.007 higher in medicated). Depression in adolescents was associated with elevation of proinflammatory serum cytokines with a gender bias for females. Anxiety scores correlated negatively with TGF-β1 and IL-17.

Influence of depression on cardiometabolic responses to a lifestyle intervention in at-risk individuals

BACKGROUND

Cardiometabolic diseases and depression are public health problems that are often related. The benefits of behavioral interventions on lifestyle are well documented. However, the influence of depression in these interventions is unclear.

OBJECTIVE

To evaluate whether depression affects the impact of a lifestyle intervention on cardiometabolic response in an at-risk sample.

METHODS

129 individuals identified by the public health system to be at risk for cardiometabolic disease were allocated to 18-month interventions on diet and physical activity. Socio-demographic and clinical data were obtained. Depressive symptoms were assessed by the Beck Depression Inventory. Changes by at least 10% in each of 6 cardiometabolic risk factors were used to define responses to intervention. Logistic regression models were employed for each gender.

RESULTS

Approximately 42% of individuals had depressive symptoms. They had higher adiposity, cholesterol, and blood pressure levels and lower quality of life and physical activity levels than non-depressed individuals. In adjusted models, only women with depression at baseline had lower chance of improving plasma glucose (OR: 0.32) and lower chance of improving mean blood pressure (OR: 0.29) after the follow-up, compared with non-depressed women.

LIMITATIONS

The small sample size may have diminished the power of the results and the instrument used to measure depression does not provide clinical diagnosis according to DSM criteria.

CONCLUSION

Depression at baseline of lifestyle interventions predicted a lower chance of improving long-term cardiometabolic risk, particularly in women, suggesting that screening and management of depression as part of lifestyle interventions can potentially improve cardiometabolic risk profile.

Microbiota, immunoregulatory old friends and psychiatric disorders

Regulation of the immune system is an important function of the gut microbiota. Increasing evidence suggests that modern living conditions cause the gut microbiota to deviate from the form it took during human evolution. Contributing factors include loss of helminth infections, encountering less microbial biodiversity, and modulation of the microbiota composition by diet and antibiotic use. Thus the gut microbiota is a major mediator of the hygiene hypothesis (or as we prefer, "Old Friends" mechanism), which describes the role of organisms with which we co-evolved, and that needed to be tolerated, as crucial inducers of immunoregulation. At least partly as a consequence of reduced exposure to immunoregulatory Old Friends, many but not all of which resided in the gut, high-income countries are undergoing large increases in a wide range of chronic inflammatory disorders including allergies, autoimmunity and inflammatory bowel diseases. Depression, anxiety and reduced stress resilience are comorbid with these conditions, or can occur in individuals with persistently raised circulating levels of biomarkers of inflammation in the absence of clinically apparent peripheral inflammatory disease. Moreover poorly regulated inflammation during pregnancy might contribute to brain developmental abnormalities that underlie some cases of autism spectrum disorders and schizophrenia. In this chapter we explain how the gut microbiota drives immunoregulation, how faulty immunoregulation and inflammation predispose to psychiatric disease, and how psychological stress drives further inflammation via pathways that involve the gut and microbiota. We also outline how this two-way relationship between the brain and inflammation implicates the microbiota, Old Friends and immunoregulation in the control of stress resilience.

Microbial 'old friends', immunoregulation and socioeconomic status

The immune system evolved to require input from at least three sources that we collectively term the ‘old friends’: (i) the commensal microbiotas transmitted by mothers and other family members; (ii) organisms from the natural environment that modulate and diversify the commensal microbiotas; and (iii) the ‘old’ infections that could persist in small isolated hunter-gatherer groups as relatively harmless subclinical infections or carrier states. These categories of organism had to be tolerated and co-evolved roles in the development and regulation of the immune system. By contrast, the ‘crowd infections’ (such as childhood virus infections) evolved later, when urbanization led to large communities. They did not evolve immunoregulatory roles because they either killed the host or induced solid immunity, and could not persist in hunter-gatherer groups. Because the western lifestyle and medical practice deplete the ‘old’ infections (for example helminths), immunoregulatory disorders have increased, and the immune system has become more dependent upon microbiotas and the natural environment. However, urbanization maintains exposure to the crowd infections that lack immunoregulatory roles, while accelerating loss of exposure to the natural environment. This effect is most pronounced in individuals of low socioeconomic status (SES) who lack rural second homes and rural holidays. Interestingly, large epidemiological studies indicate that the health benefits of living close to green spaces are most pronounced for individuals of low SES. Here we discuss the immunoregulatory role of the natural environment, and how this may interact with, and modulate, the proinflammatory effects of psychosocial stressors in low SES individuals.

Microbial 'Old Friends', immunoregulation and stress resilience

Chronic inflammatory diseases (autoimmunity, allergy and inflammatory bowel diseases) are increasing in prevalence in urban communities in high-income countries. One important factor is reduced exposure to immunoregulation-inducing macro- and microorganisms and microbiota that accompanied mammalian evolution (the hygiene hypothesis or 'Old Friends' mechanism). Reduced exposure to these organisms predisposes to poor regulation of inflammation. But inflammation is equally relevant to psychiatric disorders. Inflammatory mediators modulate brain development, cognition and mood, and accompany low socioeconomic status and some cases of depression in developed countries. The risk of all these conditions (chronic inflammatory and psychiatric) is increased in urban versus rural communities, and increased in immigrants, particularly if they move from a low- to a high-income country during infancy, and often the prevalence increases further in second generation immigrants, suggesting that critical exposures modulating disease risk occur during pregnancy and infancy. Diminished exposure to immunoregulation-inducing Old Friends in the perinatal period may enhance the consequences of psychosocial stressors, which induce increased levels of inflammatory mediators, modulate the microbiota and increase the risk for developing all known psychiatric conditions. In later life, the detrimental effects of psychosocial stressors may be exaggerated when the stress occurs against a background of reduced immunoregulation, so that more inflammation (and therefore more psychiatric symptoms) result from any given level of psychosocial stress. This interaction between immunoregulatory deficits and psychosocial stressors may lead to reduced stress resilience in modern urban communities. This concept suggests novel interpretations of recent epidemiology, and novel approaches to the increasing burden of psychiatric disease.