Selective inflammatory propensities in adopted adolescents institutionalized as infants

Inflammatory reactivity is unrelated to childhood adversity or provoked modulation of nociception

ABSTRACT

Adversity in childhood elevates the risk of persistent pain in adulthood. Neuroimmune interactions are a candidate mechanistic link between childhood adversity and persistent pain. We aimed to clarify whether immune reactivity is associated with provoked differences in nociceptive processing in adults with a range of childhood adversity. Pain-free adults (n = 96; 61 female; median [range] age: 23 [18-65] years old) with a history of mild to severe childhood adversity underwent psychophysical assessments before and after in vivo neural provocation (high-frequency electrical stimulation) and, separately, before and after in vivo immune provocation (influenza vaccine administration). Psychophysical assessments included the surface area of secondary hyperalgesia after neural provocation and change in conditioned pain modulation (test stimulus: pressure pain threshold; conditioning stimulus: cold water immersion) after immune provocation. Immune reactivity was operationalised as interleukin-6 and tumour necrosis factor-α expression after in vitro lipopolysaccharide provocation of whole blood. We hypothesised associations between immune reactivity and (1) childhood adversity, (2) induced secondary hyperalgesia, and (3) vaccine-associated change in conditioned pain modulation. We found that provoked expression of proinflammatory cytokines was not statistically associated with childhood adversity, induced secondary hyperalgesia, or vaccine-associated change in conditioned pain modulation. The current findings from a heterogenous sample cast doubt on 2 prominent ideas: that childhood adversity primes the inflammatory system for hyper-responsiveness in adulthood and that nociceptive reactivity is linked to inflammatory reactivity. This calls for the broader inclusion of heterogeneous samples in fundamental research to investigate the psychoneuroimmunological mechanisms underlying vulnerability to persistent pain.

Inflammatory reactivity is unrelated to childhood adversity or provoked modulation of nociception

Adversity in childhood elevates the risk of persistent pain in adulthood. Neuroimmune interactions are a candidate mechanistic link between childhood adversity and persistent pain. We aimed to clarify whether immune reactivity is associated with provoked differences in nociceptive processing in adults with a range of childhood adversity. Pain-free adults (n=96; 61 female; median (range) age: 23 (18-65) years old) with a history of mild to severe childhood adversity underwent psychophysical assessments before and after in vivo neural provocation (high-frequency electrical stimulation) and, separately, before and after in vivo immune provocation (influenza vaccine administration). Psychophysical assessments included the surface area of secondary hyperalgesia after neural provocation and change in conditioned pain modulation (test stimulus: pressure pain threshold; conditioning stimulus: cold water immersion) after immune provocation. Immune reactivity was operationalised as IL-6 and TNF-α expression after in vitro lipopolysaccharide provocation of whole blood. We hypothesised associations between immune reactivity and (1) childhood adversity, (2) induced secondary hyperalgesia, and (3) vaccine-associated change in conditioned pain modulation. We found that provoked expression of pro-inflammatory cytokines was not statistically associated with childhood adversity, induced secondary hyperalgesia, or vaccine-associated change in conditioned pain modulation. The current findings from a heterogenous sample cast doubt on two prominent ideas: that childhood adversity primes the inflammatory system for hyper-responsiveness in adulthood and that nociceptive reactivity is linked to inflammatory reactivity. This calls for the broader inclusion of heterogeneous samples in fundamental research to investigate the psychoneuroimmunological mechanisms underlying vulnerability to persistent pain.

A Brief Historic Review of Research on Early Life Stress and Inflammation across the Lifespan

BACKGROUND

Extensive evidence from animal and human studies indicates that exposure to stress during sensitive developmental periods significantly increases the risk for psychiatric and physical disorders, resulting in reduced longevity. Chronic immune activation has been suggested as one pathway through which early adverse experiences may become biologically embedded. This paper highlights selected key findings and questions that first emerged in the literature and founded the field and then examines how research methods and questions have evolved over time.

SUMMARY

During the past decades, evidence from preclinical, clinical, and epidemiological studies has accumulated suggesting consequences of early life stress (ELS) exposure for immune function, particularly increased chronic inflammation or inflammatory responses. Scientific approaches to study the effects of ELS on the immune system have changed since the first studies on this topic were published.

KEY MESSAGES

Across different study designs, species, and methods, a consistent association between childhood adversity and a pro-inflammatory phenotype has been reported. We critically discuss which topics warrant further consideration and how current findings could be used to develop targeted interventions to prevent or reverse the biological embedding of ELS and resultant disease manifestations.

Lingering Effects of Early Institutional Rearing and Cytomegalovirus Infection on the Natural Killer Cell Repertoire of Adopted Adolescents

Adversity during infancy can affect neurobehavioral development and perturb the maturation of physiological systems. Dysregulated immune and inflammatory responses contribute to many of the later effects on health. Whether normalization can occur following a transition to more nurturing, benevolent conditions is unclear. To assess the potential for recovery, blood samples were obtained from 45 adolescents adopted by supportive families after impoverished infancies in institutional settings (post-institutionalized, PI). Their immune profiles were compared to 39 age-matched controls raised by their biological parents (non-adopted, NA). Leukocytes were immunophenotyped, and this analysis focuses on natural killer (NK) cell populations in circulation. Cytomegalovirus (CMV) seropositivity was evaluated to determine if early infection contributed to the impact of an atypical rearing. Associations with tumor necrosis factor-alpha (TNF-α) and interferon-gamma (IFN-γ), two cytokines released by activated NK cells, were examined. Compared to the NA controls, PI adolescents had a lower percent of CD56bright NK cells in circulation, higher TNF-α levels, and were more likely to be infected with CMV. PI adolescents who were latent carriers of CMV expressed NKG2C and CD57 surface markers on more NK cells, including CD56dim lineages. The NK cell repertoire revealed lingering immune effects of early rearing while still maintaining an overall integrity and resilience.

Early Life Stress Is Associated with Alterations in Lymphocyte Subsets Independent of Increased Inflammation in Adolescents

Early life stress (ELS) is linked to an elevated risk of poor health and early mortality, with emerging evidence pointing to the pivotal role of the immune system in long-term health outcomes. While recent research has focused on the impact of ELS on inflammation, this study examined the impact of ELS on immune function, including CMV seropositivity, inflammatory cytokines, and lymphocyte cell subsets in an adolescent cohort. This study used data from the Early Life Stress and Cardiometabolic Health in Adolescence Study (N = 191, aged 12 to 21 years, N = 95 exposed to ELS). We employed multiple regression to investigate the association between ELS, characterized by early institutional care, cytomegalovirus (CMV) seropositivity (determined by chemiluminescent immunoassay), inflammation (CRP, IL-6, and TNF-a determined by ELISA), and twenty-one immune cell subsets characterized by flow cytometry (sixteen T cell subsets and five B cell subsets). Results reveal a significant association between ELS and lymphocytes that was independent of the association between ELS and inflammation: ELS was associated with increased effector memory helper T cells, effector memory cytotoxic T cells, senescent T cells, senescent B cells, and IgD- memory B cells compared to non-adopted youth. ELS was also associated with reduced percentages of helper T cells and naive cytotoxic T cells. Exploratory analyses found that the association between ELS and fewer helper T cells and increased cytotoxic T cells remained even in cytomegalovirus (CMV) seronegative youth. These findings suggest that ELS is associated with cell subsets that are linked to early mortality risk in older populations and markers of replicative senescence, separate from inflammation, in adolescents.

Points of divergence on a bumpy road: early development of brain and immune threat processing systems following postnatal adversity

Lifelong indices of maladaptive behavior or illness often stem from early physiological aberrations during periods of dynamic development. This is especially true when dysfunction is attributable to early life adversity (ELA), when the environment itself is unsuitable to support development of healthy behavior. Exposure to ELA is strongly associated with atypical sensitivity and responsivity to potential threats-a characteristic that could be adaptive in situations where early adversity prepares individuals for lifelong danger, but which often manifests in difficulties with emotion regulation and social relationships. By synthesizing findings from animal research, this review will consider threat sensitivity through the lenses of associated corticolimbic brain circuitry and immune mechanisms, both of which are immature early in life to maximize adaptation for protection against environmental challenges to an individual's well-being. The forces that drive differential development of corticolimbic circuits include caretaking stimuli, physiological and psychological stressors, and sex, which influences developmental trajectories. These same forces direct developmental processes of the immune system, which bidirectionally communicates with sensory systems and emotion regulation circuits within the brain. Inflammatory signals offer a further force influencing the timing and nature of corticolimbic plasticity, while also regulating sensitivity to future threats from the environment (i.e., injury or pathogens). The early development of these systems programs threat sensitivity through juvenility and adolescence, carving paths for probable function throughout adulthood. To strategize prevention or management of maladaptive threat sensitivity in ELA-exposed populations, it is necessary to fully understand these early points of divergence.

Childhood trauma and LPS-stimulated inflammation in adulthood: Results from the Netherlands Study of Depression and Anxiety

BACKGROUND

Childhood trauma (CT) is robustly associated with psychiatric disorders including major depressive and anxiety disorders across the life span. The innate immune system may play a role in the relation between CT and stress-related psychopathology. However, whether CT influences the innate production capacity of cytokine levels following ex vivo stimulation by lipopolysaccharide (LPS), is currently unknown.

METHODS

Using data from the Netherlands Study of Depression and Anxiety (NESDA, n=1237), we examined whether CT (emotional neglect, emotional, physical, and sexual abuse before the age of 16), assessed by the Childhood Trauma Interview, was associated with levels in supernatants of interferon (IFN)γ, interleukin-2 (IL-2), IL-4, IL-6, IL-8, IL-10, IL-18, monocyte chemotactic protein-1 (MCP-1), macrophage inflammatory protein (MIP)-1α, MIP-1β, matrix metalloproteinase-2 (MMP-2), TNFα and TNFβ after ex vivo stimulation with LPS. Cytokines were analysed individually and cumulatively (overall inflammation index and number of cytokines in high-risk quartile (HRQ)) using linear regression analyses.

RESULTS

After adjustment for demographic, lifestyle, and health-related covariates, total CT severity was associated with the overall inflammation index (β = 0.085, P_FDR = 0.011), the number of cytokines in HRQ (β = 0.063, P_FDR = 0.036), and individual markers of IL-2 (β = 0.067, P_FDR = 0.036), IL-6 (β = 0.091 P_FDR = 0.011), IL-8 (β = 0.085 P_FDR = 0.011), IL-10 (β = 0.094 P_FDR = 0.011), MCP-1 (β = 0.081 P_FDR = 0.011), MIP-1α (β = 0.061 P_FDR = 0.047), MIP1-β (β = 0.077 P_FDR = 0.016), MMP-2 (β = 0.070 P_FDR = 0.027), and TNFβ (β = 0.078 P_FDR = 0.016). Associations were strongest for individuals with severe CT, reporting multiple types or higher frequencies of trauma. Half of the findings persisted after adjustment for psychiatric status. The findings were consistent across different CT types.

CONCLUSION

Childhood Trauma is associated with increased LPS-stimulated cytokine levels, with evidence for a dose-response relationship. Our results highlight a dysregulated innate immune system capacity in adults with CT, which could contribute to an increased vulnerability for psychopathology and somatic disorders across the lifespan.

Psychological Stress During Childhood and Adolescence and Its Association With Inflammation Across the Lifespan: A Critical Review and Meta-Analysis

Psychological stress during childhood and adolescence increases risk of health problems across the lifecourse, and inflammation is implicated as an underlying mechanism. To evaluate the viability of this hypothesis, we used meta-analysis to quantify the association between childhood/adolescent stress and inflammation over the lifecourse. Furthermore, we addressed three unresolved conceptual questions: (a) Does the strength of this association change over the lifecourse? (b) Are different types of childhood/adolescent stressors differentially associated with inflammation? (c) And which components of the inflammatory response are involved? A systematic search identified 187 articles reporting 922 associations. Meta-analyses were conducted using a three-level multilevel approach and controlled for study quality, conversion confidence, and whether effect sizes were unadjusted or adjusted (n = 662, 72%). Results indicated a small but reliable overall adjusted association ( r ^ = .04 ) . The magnitude of the association strengthened across the lifecourse-effect sizes were smallest in studies that measured inflammation in childhoodr ^ = .02 and became progressively larger in studies of adolescencer ^ = .04 and adulthoodr ^ = .05 , suggesting the impact of early stress strengthens with time. By contrast, effect sizes did not vary by adversity type (socioeconomic disadvantage, maltreatment, other interpersonal stressors, and cumulative exposure across stressors), or component of inflammation (circulating biomarkers of low-grade inflammation vs. cytokine responses to microbial stimuli). Implications and future directions are discussed.

What was learned from studying the effects of early institutional deprivation

The effect of experiences in infancy on human development is a central question in developmental science. Children raised in orphanage-like institutions for their first year or so of life and then adopted into well-resourced and supportive families provide a lens on the long-term effects of early deprivation and the capacity of children to recover from this type of early adversity. While it is challenging to identify cause-and-effect relations in the study of previously institutionalized individuals, finding results that are consistent with animal experimental studies and the one randomized study of removal from institutional care support the conclusion that many of the outcomes for these children were induced by early institutional deprivation. This review examines the behavioral and neural evidence for altered executive function, declarative memory, affective disorders, reward processing, reactivity to threat, risk-taking and sensation-seeking. We then provide a brief overview of the neurobiological mechanisms that may transduce early institutional experiences into effects on brain and behavior. In addition, we discuss implications for policy and practice.

Adverse Life Trajectories Are a Risk Factor for SARS-CoV-2 IgA Seropositivity

Asymptomatic individuals, called “silent spreaders” spread SARS-CoV-2 efficiently and have complicated control of the ongoing COVID-19 pandemic. As seen in previous influenza pandemics, socioeconomic and life-trajectory factors are important in disease progression and outcome. The demographics of the asymptomatic SARS-CoV-2 carriers are unknown. We used the CON-VINCE cohort of healthy, asymptomatic, and oligosymptomatic individuals that is statistically representative of the overall population of Luxembourg for age, gender, and residency to characterise this population. Gender (male), not smoking, and exposure to early-life or adult traumatic experiences increased the risk of IgA seropositivity, and the risk associated with early-life exposure was a dose-dependent metric, while some other known comorbidities of active COVID-19 do not impact it. As prior exposure to adversity is associated with negative psychobiological reactions to external stressors, we recorded psychological wellbeing during the study period. Exposure to traumatic events or concurrent autoimmune or rheumatic disease were associated with a worse evolution of anxiety and depressive symptoms throughout the lockdown period. The unique demographic profile of the “silent spreaders” highlights the role that the early-life period plays in determining our lifelong health trajectory and provides evidence that the developmental origins of health and disease is applicable to infectious diseases.