Natural Killer T cells in patients with major depressive disorder

Sex differences in depression: An immunological perspective

Depression is a heterogenous disorder with symptoms that present differently across individuals. In a subset of people depression is associated with alterations of the immune system that may contribute to disorder onset and symptomology. Women are twice as likely to develop depression and on average have a more sensitive adaptive and innate immune system when compared to men. Sex differences in pattern recognition receptors (PRRs), release of damage-associated molecular patterns (DAMPs), cell populations, and circulating cytokines play a critical role in inflammation onset. Sex differences in innate and adaptive immunity change the response of and repair to damage caused by dangerous pathogens or molecules in the body. This article reviews the evidence for sex specific immune responses that contribute to the sex differences in symptoms of depression that may account for the higher rate of depression in women.

Characterization of the signature of peripheral innate immunity in women with later-life major depressive disorder

The prevalence of depression in later life is higher in women than in men. However, the sex difference in the pathophysiology of depression in elderly patients is not fully understood. Here, we performed gene expression profiling in leukocytes of middle-aged and elderly patients with major depressive disorder, termed later-life depression (LLD) in this context, and we characterized the sex-dependent pathophysiology of LLD. A microarray dataset obtained from leukocytes of patients (aged ≥50 years) with LLD (32 males and 39 females) and age-matched healthy individuals (20 males and 24 females) was used. Differentially expressed probes were determined by comparing the expression levels between patients and healthy individuals, and then functional annotation analyses (Ingenuity Pathway Analysis, Reactome pathway analysis, and cell-type enrichment analysis) were performed. A total of 1656 probes were differentially expressed in LLD females, but only 3 genes were differentially expressed in LLD males. The differentially expressed genes in LLD females were relevant to leukocyte extravasation signaling, Tec kinase signaling and the innate immune response. The upregulated genes were relevant to myeloid lineage cells such as CD14⁺ monocytes. In contrast, the downregulated genes were relevant to CD4⁺ and CD8⁺ T cells. Remarkable innate immune signatures are present in the leukocytes of LLD females but not males. Because inflammation is involved in the pathophysiology of depression, the altered inflammatory activity may be involved in the pathophysiology of LLD in women. In contrast, abnormal inflammation may be an uncommon feature in LLD males.

White blood cell inflammatory markers are associated with depressive symptoms in a longitudinal study of urban adults

Total white blood cell count (TWBCC) and percentage (%) composition of lymphocytes (PL) or neutrophils (PN) are linked to mid- and late-life depression, though sex-specific temporal relationships between those inflammatory markers and depressive symptoms remain unclear. The association between inflammation and depressive symptoms in longitudinal data on ethnically and socioeconomically diverse urban adults was examined with two hypotheses. In hypothesis 1, we examined the relationship between TWBCC, PL and PN with change in level of depressive symptoms from baseline to follow-up, stratifying by sex. In hypothesis 2, we examined reverse causality, by testing the relationship of depressive symptoms with change in TWBCC, PL and PN. Multiple linear mixed-effects regression models were performed to examine both the hypotheses. The sample sizes of participants (n) and repeated observations (n') were: Hypothesis 1 (n=2009; n'=3501); Hypothesis 2 (n=2081; n'=3560). Among key findings (Hypothesis 1), in women, higher TWBCC was linked to a faster increase in depressive symptom total score (γ1112±s.e.: +0.81±0.28, P=0.003), with a slower increase over time in the positive affect subdomain coupled with faster increases in depressed affect and somatic complaints. Among women, baseline score on somatic complaints was positively associated with low PN (γ01a=+1.61±0.48, P<0.001) and high PL (γ01a=+1.16±0.45, P=0.011), whereas baseline score on positive affect was inversely related to higher PL (γ01a=-0.69±0.28, P=0.017). Results among men indicated that there was a positive cross-sectional relationship between low TWBCC and depressive symptoms, depressed affect and an inverse cross-sectional relationship with positive affect. However, over time, a low TWBCC in men was linked to a higher score on positive affect. There was no evidence of a bi-directional relationship between WBC parameters and depressive symptoms (Hypothesis 2). In sum, TWBCC and related markers were linked to depressive symptoms, mostly among women. Further longitudinal studies are needed to replicate this sex-specific association.

A phase-specific neuroimmune model of clinical depression

Immune dysfunction and pro-inflammatory states in particular have been implicated in the aetiology and pathogenesis of depression. Whilst the onset of an episode and certain symptoms of depression appear well explained by this inflammatory model, the underpinnings of the episodic and progressive nature, as well as relapse and remission status in depression require attention. In this review it is suggested that additional immune factors beyond pro- and anti-inflammatory cytokines may effectively contribute to the understanding of the neurobiology of clinical depression. Considering neurobiological effects of immunomodulatory factors such as T cells, macrophages, microglia and astrocytes relevant to depression, we suggest a neuroimmune model of depression underpinned by dynamic immunomodulatory processes. This perspective paper then outlines a neuroimmune model of clinical phases of depression in an attempt to more adequately explain depression-like behaviours in pre-clinical models and the dynamic nature of depression in clinical populations. Finally, the implications for immunomodulatory treatments of depression are considered.

Associations among depression, perceived self-efficacy, and immune function and health in preadolescent children

Experimental animal studies and adult research consistently show that stress exposure and/or psychological symptoms are associated with poorer health and immune functioning. The application to children is not yet clear, however, and we lack developmental models for studies in this area. The objective of this paper was to test the hypothesis that self-reported self-efficacy and depression, two markers of psychological well-being in children, would predict immunity and rate of illnesses. The data are based on a prospective study of 141 healthy, normally developing children aged 7-13 years who were recruited from an ambulatory pediatric setting. Children completed self-efficacy and depression measures and had blood obtained for IL-6 plasma levels and natural killer cell functional assays on three occasions, 6 months apart. Parents maintained weekly child illness diaries over 1 year using a thermometer to record fever. Parent psychiatric symptoms and income were used as covariates. Results indicated that, across the three occasions of measurement collected over the 1-year period, higher perceived self-efficacy was significantly associated with lower plasma interleukin 6 concentrations. There was no overall main effect of depressive symptoms on immune measures; however, for older girls, higher depression was associated with elevated natural killer cell cytotoxicity and an increased rate of total illnesses and febrile illnesses. The findings provide some of the first evidence that psychological processes are associated with immunity and health in a normally developing sample of preadolescents. Furthermore, the pattern of results suggests a modified model of a link between psychological well-being and immunological processes in children. These results build on and expand research on the notion of allostatic load and develop a groundwork for developmental studies in this area.

Psychological distress, depressive symptoms, and cellular immunity among healthy individuals: a 1-year prospective study

Cross-sectional and case-control studies have reported that psychological distress and depression are associated with reduced cellular immune competence but the directionality of the relationship remains uncertain. This study investigated whether levels of psychological distress and depressive symptoms are related to subsequent changes in counts of lymphocyte subsets (natural killer (NK), B, and T cell) and/or whether changes of immune markers predict psychological distress/depressive symptoms in a 1-year prospective study design. A total of 105 healthy employees (67 men and 38 women), aged 23-59 (mean 40) years with an average of 15years of education, underwent a blood draw for the measurement of circulating immune cells and completed the Japanese version of the 28-item General Health Questionnaire (GHQ-28) and the Center for Epidemiologic Studies Depression Scale (CES-D) in April 2002 (time 1) and 2003 (time 2). Hierarchical multiple linear regression analyses revealed that GHQ-28 and CES-D scores at time 1 were significantly (p<.05) and inversely associated with NK cells at time 2 controlling for potential confounders including time 1 NK cells (β=-.221 and -.177, respectively). In contrast, NK cells and NK cell cytotoxicity at time 1 did not predict GHQ-28 or CES-D score at time 2 controlling for GHQ-28/CES-D score at time 1. GHQ-28 and CES-D scores were not related to T or B cells at times 1 and 2. The present findings indicate that psychological distress and depressive symptoms may precede and predict suppression of NK cell immunity while NK cells did not lead to subsequent psychological distress and depressive symptoms, suggesting an absence of the bi-directional relationships.

Effects of venlafaxine and fluoxetine on lymphocyte subsets in patients with major depressive disorder: a flow cytometric analysis

BACKGROUND

Studies have yielded conflicting results concerning flow cytometric lymphocyte analyses in patients with depression. Data about the effect of antidepressants on lymphocyte subsets are also contradictory. The aim of this study was to determine effects of venlafaxine versus fluoxetine on lymphocyte subsets in depressive patients.

METHODS

Sixty-nine patients diagnosed with major depressive disorder (MDD) according to DSM-IV and 36 healthy controls are included in the study. Sixty-nine patients were randomized to take fluoxetine (FLX) (n=33) or venlafaxine (VEN) (n=36). Serum lymphocyte subsets included CD3, CD4, CD8, CD16/56, CD19, CD45, Anti-HLA-DR which were measured by flow cytometric analyses at baseline and 6 weeks after the start of treatment. The severity of depression was evaluated with Hamilton rating scale for depression.

RESULTS

At baseline, patients with MDD had significantly lower CD16/56 ratio and higher CD45 ratio compared to the controls. Although numerically higher in the VEN treated patients, treatment response rates between the FLX (53%) and the VEN (75%) groups were not different statistically. CD45 values decreased significantly in the VEN group at the end of the 6 week treatment period whereas no difference was observed in the FLX group. By the 6th week, treatment responders showed a significantly higher CD16/56 ratio than non-responders. Baseline severity of depression and anxiety was positively correlated with baseline CD45 ratio and negatively correlated with baseline CD16/56 ratio. We did not observe consistent changes in the absolute number of circulating B or T cells, nor in the helper/inducer (CD4) or suppressor/cytotoxic (CD8) subsets.

CONCLUSIONS

CD16/56 was lower in patients with MDD and increased in treatment responders at 6th week. CD45 ratio was higher in patients with MDD than healthy subjects; it decreased with antidepressant treatment and was positively correlated with the severity of depression. Antidepressant treatment contributes to immune regulation in patients with major depressive disorder.