A wealth of evidence has implicated inflammation in the development of depression. Yet, the heterogeneous nature of depression has impeded efforts to understand, prevent, and treat the disease. The purpose of this integrative review is to summarize the connections between inflammation and established core features of depression that exhibit more homogeneity than the syndrome itself: exaggerated reactivity to negative information, altered reward processing, decreased cognitive control, and somatic syndrome. For each core feature, we first provide a brief overview of its relevance to depression and neurobiological underpinnings, and then review evidence investigating a potential role of inflammation. We focus primarily on findings from experimental paradigms of exogenously-induced inflammation. We conclude that inflammation likely plays a role in exaggerated reactivity to negative information, altered reward reactivity, and somatic symptoms. There is less evidence supporting an effect of inflammation on cognitive control as assessed by standard neuropsychological measures. Finally, we discuss implications for future research and recommendationsfor how to test the role of inflammation in the pathogenesis of heterogeneous psychiatric disorders.

Stress research typically emphasizes the toxic effects of stress, but recent evidence has suggested that stress exposure, in moderation, can facilitate resilience. To test whether moderate stress exposure promotes psychological resilience to cancer, we examined the relationship between lifetime stress exposure prior to cancer diagnosis and postdiagnosis psychological functioning among 122 breast cancer survivors. Lifetime acute and chronic stress was assessed using an interview-based measure, and psychological functioning was assessed using measures of cancer-related intrusive thoughts and positive and negative affect. Results indicated that acute stress exposure was associated with cancer-related intrusive thoughts in a quadratic fashion (p = .016), such that participants with moderate acute stress reported fewer intrusive thoughts compared to those with low or high acute stress. Similarly, a quadratic relationship emerged between acute stress exposure and positive affect (p = .009), such that individuals with moderate acute stress reported the highest levels of positive affect. In contrast, acute and chronic stress were related to negative affect in a positive, linear fashion (ps < .05). In conclusion, moderate stress exposure was associated with indicators of psychological resilience among breast cancer survivors, supporting stress exposure as a key factor influencing adjustment to breast cancer and providing evidence for stress-induced resilience in a novel population.

Minor increases in inflammation were associated with corresponding increases in features of depression, and these associations occurred in the absence of any physical symptoms. The influenza vaccine could be used to probe causal relationships with a high degree of ecological validity, even in high-risk and vulnerable populations, to better understand the role of inflammation in the pathogenesis of depression.

Background: Alterations in reward processing are a central feature of depression and may be influenced by inflammation. Indeed, inflammation is associated with deficits in reward-related processes in animal models and with dysregulation in reward-related neural circuitry in humans. However, the downstream behavioral manifestations of such impairments are rarely examined in humans. Methods: The influenza vaccination was used to elicit a mild inflammatory response in 41 healthy young adults (age range: 18-22, 30 female). Participants provided blood samples and completed behavioral measures of three key aspects of reward-reward motivation, reward learning, and reward sensitivity-before and 1 day after receiving the influenza vaccine.

Background Early life stress (ELS) has been linked to health disparities across the human lifespan, particularly increased risk for depression and its recurrence. In this study we explore two plausible and competing pathways through which ELS may lead to depression via inflammation. Methods Participants (ages 18–22; n = 41) completed the Early Trauma Inventory as a measure of ELS. Participants then completed consecutive daily diaries of mood and other sickness behavior for the 7 days prior to and 7 days after receiving the annual influenza vaccine. Circulating concentrations of plasma interleukin‐6 (IL‐6) were measured immediately before and 24 hr after vaccination. Results ELS was not associated with the magnitude of change in IL‐6 from pre‐ to post‐vaccine, however, exposure to ELS moderated the association between change in IL‐6 from pre‐ to post‐vaccine and changes in both cognitive difficulty and depressed mood. Individuals exposed to greater ELS showed greater psychological sensitivity to increases in IL‐6. Conclusions Exposure to ELS may increase sensitivity to peripheral inflammation in the central nervous system. Future studies elaborating on the impact of ELS on the sensitivity of specific neural circuits and cells to inflammation are needed.

Background Inflammation contributes to the development of depression in a subset of individuals, but risk factors that render certain individuals vulnerable to inflammation-associated depression are undetermined. Drawing from animal studies showing that reduced neuroplasticity mediates effects of inflammation on depression, we hypothesized that individuals genetically predisposed to lower levels of neuroplasticity would be more susceptible to inflammation-associated depression. The current study examined whether the Met allele of the BDNF Val66met polymorphism, which predisposes individuals to reduced levels of brain-derived neurotrophic factor (BDNF), a protein vital for neuroplasticity, moderates the association between inflammation and depressive symptoms. Methods Our sample was 112 women with early-stage breast cancer who had recently completed cancer treatment, which can activate inflammation. Participants provided blood for genotyping and assessment of circulating inflammatory markers, and completed a questionnaire assessing depressive symptoms, including somatic, affective, and cognitive dimensions. Results There was a significant interaction between C-reactive protein (CRP) and the BDNF Val66met polymorphism in predicting cognitive depressive symptoms (p=.004), such that higher CRP was related to more cognitive depressive symptoms among Met allele carriers, but not among Val/Val homozygotes. Post-hoc longitudinal analyses suggested that, for Met carriers, higher CRP at baseline predicted higher cognitive depressive symptoms across a one-year follow-up period (p<.001). Conclusion The BDNF Met allele may be a risk factor for inflammation-associated cognitive depressive symptoms among breast cancer survivors. Women with breast cancer who carry this genotype may benefit from early identification and treatment. Limitation BDNF genotype is an indirect measure of BDNF protein levels.

Background and Objectives Chronic stress is implicated in many theories as a contributor to a wide range of physical and mental health problems. The current study presents an adaptation of a chronic stress measure based on the UCLA Life Stress Interview (LSI; Hammen et al., 1985; 1987) that was developed with community partners for use in a large community health study of low income, ethnically diverse parents of infants in the United States. We describe the instrument, its purpose and adaptations, implementation, and results of a reliability study in a subsample of the larger study cohort. Design and Methods Interviews with 272 mothers were included in the present study. Chronic stress was assessed using the CCHN LSI, an instrument designed for administration by trained community interviewers to assess four domains of chronic stress, each rated by interviewers. Results Significant correlations ranging from small to moderate in size between chronic stress scores on this measure, other measures of stress, biomarkers of allostatic load, and mental health provide initial evidence of construct and concurrent validity. Reliability data for interviewer ratings are also provided. Conclusions This relatively brief interview (15 minutes) is available for use and may be a valuable tool for researchers seeking to measure chronic stress reliably and validly in future studies with time constraints.

Purpose: Eudaimonic wellbeing (e.g., meaning, purpose in life) and hedonic wellbeing (e.g., happiness, life satisfaction) are related but conceptually-distinct facets of wellbeing. Eudaimonic wellbeing is highly underexplored in cancer research despite its relevance to important existential concerns faced by cancer survivors. Therefore, this study examined the unique associations of eudaimonic and hedonic wellbeing with adjustment in breast cancer survivors. Methods: Women diagnosed with early-stage breast cancer within two years (N=64) were recruited through the UCLA Tumor Registry and completed self-report questionnaires (Mental Health Continuum – Short Form Scale, Posttraumatic Growth Inventory, Social Provisions Scale, Quality of Life in Adult Cancer Survivors Scale, Center for Epidemiological Studies – Depression Scale, Pittsburgh Sleep Quality Index, Fatigue Symptom Inventory, Perceived Stress Scale). Findings: Controlling for their shared variance and covariates, eudaimonic wellbeing was uniquely associated with greater posttraumatic growth (β = .42, p = .026, R2 = .07), more reliable social support (β = .50, p = .010, R2 = .09), and marginally lower fear of recurrence, (β = −.40, p = .063, R2 = .06) while hedonic wellbeing was uniquely associated with lower sleep disturbance (β = −.56, p = .004, R2 = .12), fatigue (β = −.53, p = .003, R2 = .11), and depressive symptoms (β = −.59, p < .001, R2 = .14). Conclusions: Findings suggest eudaimonic wellbeing may confer quality of life benefits beyond symptom reduction in breast cancer survivors, while hedonic wellbeing is primarily associated with fewer behavioral symptoms.