Cited by 382Stress Responses and CortisolTryptophan and brain disordersTreatment of Major Depression

Why are depressed patients inflamed? A reflection on 20 years of research on depression, glucocorticoid resistance and inflammation

Open access
Pariante, Carmine M.·2017·European Neuropsychopharmacology

Abstract

Studies over the last 20 years have demonstrated that increased inflammation and hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis are two of the most consistent biological findings in major depression and are often associated: but the molecular and clinical mechanisms underlying these abnormalities are still unclear. These findings are particularly enigmatic, especially considering the accepted notion that high levels of cortisol have an anti-inflammatory action, and therefore the coexistence of inflammation and hypercortisolemia in the same diagnostic group appears counter-intuitive. To celebrate the 2015 Anna-Monika Foundation Award to our laboratory, this review will discuss our own 20 years of research on the clinical and molecular evidence underlying the increased inflammation in depression, especially in the context of a hyperactive HPA axis, and discuss its implications for the pathogenesis and treatment of this disorder.

AI snapshot

Written from the paper’s full text.

TL;DR

This narrative review reflects on 20 years of the author's laboratory research on why a subgroup of depressed patients shows both increased inflammation and HPA-axis abnormalities, proposing glucocorticoid resistance as the linking mechanism. It argues that inflammation in depression is often a "biological scar" of early-life stress and can be used to predict antidepressant non-response.

Key findings

  • Increased inflammation and HPA-axis hyperactivity coexist in depression despite cortisol's expected anti-inflammatory action; the author's in vitro work showed IL-1 induces glucocorticoid resistance (impaired GR translocation), while antidepressants reverse it.
  • In the GENDEP sample, depressed patients showed increased mRNA of pro-inflammatory cytokines (IL-1, IL-6, TNF-alpha, MIF) and reduced IL-4, together with reduced GR mRNA and increased FKBP5 — a molecular signature of GR resistance.
  • In depressed patients with coronary heart disease, higher IL-6 mRNA and CRP and reduced GR mRNA were found, but associated with HPA-axis hypoactivity rather than hyperactivity.
  • Baseline mRNA levels of IL-1, MIF and TNF-alpha predicted roughly half the variance in antidepressant response; in a replication using absolute mRNA values, cut-offs predicted non-response with positive predictive values and specificity of 100%.
  • Early-life adversity (childhood maltreatment, and prenatal maternal depression in the South London Child Development Cohort) was associated with raised inflammation markers (CRP, white cell counts, fibrinogen); a randomized controlled trial found prophylactic EPA/DHA prevented or delayed interferon-alpha-induced depression.

Methods

  • Design: narrative, self-referential review of the author's own 20 years of research (1991–2017), framed around the 2015 Anna-Monika Foundation Award.
  • Evidence base: in vitro models (mouse fibroblasts, human peripheral blood mononuclear cells, human neurons/hippocampal progenitor cells), animal studies, and clinical cohorts including GENDEP, the Dunedin study, and the South London Child Development Cohort, plus an RCT of omega-3 fatty acids.
  • Analysis: descriptive synthesis of findings across these studies; no systematic search or meta-analysis is described.

Limitations

  • Stated: the review is explicitly self-referential ("the narrative and the citations are self-referential"), and the author lists outstanding unanswered questions, including the epigenetic mechanisms linking early-life events to long-term inflammation, how anti-inflammatories help depression, and whether normalising GR function is helpful for patients.
  • Evident from the text: as a single-laboratory narrative review it is not a systematic or exhaustive synthesis, and several cited findings (e.g., the 100% predictive values, preliminary genetic and in utero evidence) are described by the author as preliminary or requiring replication.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1016/j.euroneuro.2017.04.001

Cites

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Statistics

Nothing to recompute.

Claims the paper makes

0 of 64 cited sources checked · 0 supported · 0 flagged

  • Findingcitation

    These same subjects have glucocorticoid resistance, as shown by reduced in vitro ability of their peripheral blood mononuclear cells to respond to dexamethasone and cortisol during an immune stimulus.

    “these same subjects have glucocorticoid resistance, as shown by a reduced in vitro ability of their peripheral blood mononuclear cells to respond to dexamethasone and cortisol during an immune stimulus (Carvalho et al., 2009).”
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  • Findingcitation

    Patients with the highest IL-6 levels are the least likely to respond to antidepressants.

    “Patients with the highest IL-6 levels are also the least likely to respond to antidepressants (Carvalho et al., 2013).”
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    • cites Carvalho et al., 2013 source

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  • Findingcitation

    In 2008, increased plasma cortisol levels and increased inflammation (plasma IL-6) were described in the same depressed individuals, a group of severely depressed inpatients with treatment-resistant depression.

    “In 2008 we described increased plasma cortisol levels and increased inflammation (plasma IL-6) in the same depressed individuals, a group of severely depressed inpatients with treatment-resistant depression (Carvalho et al., 2008)”
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  • Findingcitation

    In the GENDEP sample, patients have molecular evidence of GR resistance as shown by reduced expression of GR mRNA together with increased expression of the GR chaperone protein FKBP5.

    “we showed that these same patients also have molecular evidence of GR resistance as shown by a reduced expression of GR mRNA together with an increased expression of the GR chaperone protein, FKBP5 (Cattaneo et al., 2013).”
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  • Findingown data

    In the GENDEP sample, increased inflammation in depression was replicated as shown by increased mRNA expression of proinflammatory cytokines (IL-1, IL-6, TNF-alpha and MIF) together with reduced expression of anti-inflammatory cytokine IL-4.

    “we replicated the increased inflammation in depression as shown by increased mRNA expression of proinflammatory cytokines (IL-1, IL-6, TNF-alpha and macrophage inhibiting factor, MIF) together with a reduced expression of the anti-inflammatory cytokines, IL-4”
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    Findingcitation

    The effects of antidepressants potentiating GR translocation and function are mediated both directly through steroid-independent activation of the GR and indirectly by inhibition of the p-glycoprotein transporter that expels cortisol from cells.

    “we demonstrated that the effects of antidepressants potentiating GR translocation and function is not only directly mediated through steroid-independent activation of the GR, but also indirectly by inhibition of the pglycoprotein transporter that expels cortisol from cells (and, in vivo, from the brain).”
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    Findingcitation

    Antidepressants in vitro increase GR activation and function, reversing glucocorticoid resistance.

    “we also demonstrated that antidepressants in vitro increase GR activation and function, that is, reverse glucocorticoid resistance, thus confirming the crucial role of the GR as a target of both depressogenic (inflammation) and therapeutic (antidepressants) stimuli (Pariante et al., 1997).”
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    Findingcitation

    In vitro, the effects of antidepressants on GR translocation and function are common to all tested antidepressants and are present in mouse fibroblasts and rat neurons.

    “these effects are common to all tested antidepressants and are present not only in mouse fibroblasts but also in rat neurons”
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    • cites Pariante et al., 2003a

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    Findingcitation

    Incubating L929 mouse fibroblasts with the pro-inflammatory cytokine IL-1 leads to glucocorticoid resistance, i.e., impairment of GR activation and translocation from the cytoplasm to the nucleus, resulting in reduced expression of GR-stimulated genes.

    “we found that incubating L929 mouse fibroblasts cells with the pro-inflammatory cytokine interleukin (IL)-1 leads to glucocorticoid resistance, i.e., to an impairment of GR activation and translocation from the cytoplasm to the nucleus, resulting in reduced expression of GR-stimulated genes (Pariante et al., 1999).”
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    Findingcitation

    p-glycoprotein and antidepressants do not regulate cortisol levels in the brain.

    “but not, however, that pglycoprotein or indeed antidepressants regulate cortisol levels in the brain (Mason et al., 2008(Mason et al., , 2011)).”
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    Findingown data

    Depressed patients with coronary heart disease have higher inflammation (higher IL-6 mRNA and higher CRP) together with reduced expression of GR mRNA.

    “depressed patients with coronary heart disease have higher inflammation (higher IL-6 mRNA and higher levels of c-reactive protein (CRP), an acute phase response protein produced by the liver in response to IL-6) together with a reduced expression of GR mRNA”
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    • cites Nikkheslat et al., 2015

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    Findingcitation

    IL-1 and interferon-alpha reduce human neurogenesis and human neuronal survival.

    “we found that two proinflammatory cytokines, IL-1 and interferon-alpha, reduce human neurogenesis and human neuronal survival”
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    • cites Alboni et al., 2013

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    • cites Horowitz et al., 2014

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    Findingcitation

    Antidepressants increase neurogenesis via a GR-dependent mechanism that requires PKA signalling and upregulation of genes such as p11 and CDK2 inhibitors p27 and p57.

    “antidepressants increase neurogenesis via a GR-dependent mechanism that requires protein kinase A (PKA) signalling and upregulation of genes such as p11 and the cyclin-dependent kinase-2 (CDK2) inhibitors, p27and p57 (Anacker et al., 2011)”
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    Findingcitation

    Both antidepressants and cortisol require the GR to exert their effects on neurogenesis, with antidepressants activating GR to increase neurogenesis and cortisol activating GR to decrease neurogenesis.

    “both antidepressants and cortisol require the GR to exert their effects on neurogenesis: but with antidepressants activating the GR in order to increase neurogenesis, while cortisol activating the GR in order to decrease neurogenesis.”
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    • cites Anacker et al., 2013a

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    Findingcitation

    Antidepressant-induced upregulation of p11 and cortisol-induced upregulation of SGK1 were replicated in the blood (mRNA) of depressed patients, and cortisol-induced downregulation of TGFβ-SMAD2/3 and Hedgehog signalling was replicated in the hippocampus of adult rats exposed to prenatal stress.

    “we were able to replicate both the antidepressant-induced upregulation of p11 and the cortisol-induced upregulation of SGK1 in the blood (mRNA) of depressed patients, and the cortisolinduced downregulation of TGFβ-SMAD2/3 and Hedgehog signalling in the hippocampus of adult rats exposed to prenatal stress (Anacker et al., 2013a(Anacker et al., , 2013b)).”
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    Findingcitation

    Increased inflammation is present not only in subjects who are depressed and have a history of childhood maltreatment but also in those who have experienced maltreatment but are not depressed.

    “we showed that this increased inflammation is present not only in subjects who are depressed and have a history of childhood maltreatment but also in those who have experienced maltreatment but are not depressed (Danese et al., 2008)”
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    Findingcitation

    In a second independent cohort, the predictive ability of IL-1 and MIF was confirmed and extended, and cut-off values for absolute mRNA measures accurately predict response probability at an individual level, with positive predictive values and specificity for nonresponders of 100%.

    “In this second cohort, we have confirmed and extended the predictive ability of IL-1 and MIF, and have identified cut-off values for the absolute mRNA measures that accurately predict response probability at an individual level, with positive predictive values and specificity for nonresponders of 100% (Cattaneo et al., 2016).”
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    Findingcitation

    The levels of IL-1, MIF and TNF-alpha together predict approximately half of the variance in antidepressant response, with IL-1 and MIF explaining most of the variance.

    “Together, the levels of these three cytokines predict approximately half of the variance in antidepressant response, although IL-1 and MIF explain most of the variance.”
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    Premisecitation

    In depression, a dysfunction of the glucocorticoid receptor leads to impaired HPA axis negative feedback (glucocorticoid resistance), which in turn leads to HPA axis hyperactivity.

    “in depression, a dysfunction of the GR leads to an impaired HPA axis negative feedback (a phenomenon called glucocorticoid resistance), which in turn leads to the HPA axis hyperactivity (Pariante and Lightman, 2008;Pariante and Miller, 2001).”
    Quote in the paperSubstantial claim0 of 2 sources checked
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    • cites Pariante and Miller, 2001

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  • May combine two claims.

    Interpretationreasoning

    The molecular signature underlying GR resistance and increased inflammation in depression is reduced GR expression together with decreased GR responsivity (as FKBP5 binds to GR and maintains it in an unresponsive state).

    “Both these findings indicate the possible molecular signature underlying GR resistance and increased inflammation in depression: a reduced GR expression (that is, less receptor available) together with a decreased GR responsivity (as FKBP5 binds to the GR and maintains it in an unresponsive state).”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Interpretationown data

    Glucocorticoid resistance, cortisol hypersecretion and increased inflammation are coexistent and related biological abnormalities.

    “These findings confirmed the notion that glucocorticoid resistance, cortisol hypersecretion and increased inflammation are indeed coexistent and related biological abnormalities.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Interpretationcitation

    This biological picture introduces a different type of GR resistance: an ineffective GR together with lower levels of cortisol.

    “This biological picture, perhaps due to the advanced age of the subjects in questions and thus to the long chronicity of their depression, introduces a different type of GR resistance: an ineffective GR together with lower levels of cortisol (Nikkheslat et al., 2015).”
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    Interpretationcitation

    Increased inflammation is a 'biological scar' of early exposure to high levels of stress, originating in childhood and characterised by abnormalities in both mental and physical health.

    “Together, these findings indicate that the increased inflammation is a 'biological scar' of the early exposure to high levels of stress, which originates in childhood and is characterised by abnormalities in both mental and physical health (Baumeister et al., 2016).”
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  • May combine two claims.

    Premisecitation

    Genetic variants that increase immune responses are more frequent in patients with depression, or characterise a group of individuals who are at risk of developing a depressive phenotype in the context of an immune challenge.

    “There is consistent evidence from candidate gene studies that genetic variants that increase immune responses are more frequent in patients with depression, or characterise a group of individuals who are at risk of developing a depressive phenotype in the context of an immune challenge (Barnes et al., 2017).”
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  • Probably not a substantial claim: may not pass S2 (checkable), S4 (based).

    Interpretationreasoning

    The strong impact of the immune system on emotions and behaviour demonstrates that mental health is the health of the whole body.

    “The strong impact of the immune system on emotions and behaviour demonstrates that mental health is the health of the whole body.”
    Quote in the paperNot a substantial claim
20 of 20
  • The paper relies on this without support.

    The molecular and clinical mechanisms underlying the association between increased inflammation and HPA axis hyperactivity in major depression are still unclear.

    “the molecular and clinical mechanisms underlying these abnormalities are still unclear.”
  • The paper relies on this without support.

    Not all depressed patients have increased inflammation.

    “Not all depressed patients have increased inflammation: so, who are these patients that present with this biological phenotype?”
2 of 2

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

  • Abundant evidence supports the role of neuroinflammation and altered immune processes in the aetiopathogeneses of various mental conditions.

    “Abundant evidence supports the role of neuroinflammation and altered immune processes in the aetiopathogeneses of various mental conditions (Mazza, Lucchi, Rossetti, & Clerici, 2020; Pariante, 2017).”

    From Can epigenetics shine a light on the biological pathways underlying major mental disorders? (2022) · cites this paper as Pariante, 2017

    Section 5 links inflammation and altered immune responses to risk of depression, particularly in a subgroup of patients. Section 6 says an activated inflammatory system is relevant to psychotic disorders such as schizophrenia, but discusses effects on health, brain structure and outcomes rather than establishing a role in their aetiopathogenesis. The paper therefore supports the claim for depression, but not its broader implication about the origins of various mental conditions or neuroinflammation specifically. (LLM, conf=0.83)

    Experimental — accuracy not yet measured
  • Some of these biological processes participate in disease pathogenesis in parallel, such as the redox system and glutamatergic/GABAergic imbalance, or the immune system and the stress response.

    “It is important to take into account that some of these processes participate in disease pathogenesis in a parallel manner, such as via the redox system and through the glutamatergic/GABAergic imbalance (Hardingham & Do, 2016); or the immune system and the stress response (Pariante, 2017).”
  • Adverse childhood or early life experiences, such as conflict with parents, early exposure to traumatic life events, bullying, and childhood trauma, were found to increase the risk of depression.

    “A group of determinants touched upon by several studies included adverse childhood or early life experiences: ex. conflict with parents, early exposure to traumatic life events, bullying and childhood trauma were found to increase the risk of depression (ex. through pathways, such as inflammation, interaction effects, or cognitive biases) [161,182,258,358,362,380].”

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • Cited 2008 study reports the opposite direction of GR effect

    Minor

    The text presents the 2008 human-blood-cell study as showing an antidepressant-induced increase in GR function. The cited reference's title says clomipramine reduced GR function in healthy subjects and did not do so in patients with major depression.

1 of 1

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Authors
Pariante, C. M.
Affiliations
King's College London (GB)
Corresponding author
Pariante, Carmine M.
Venue
European Neuropsychopharmacology
Publisher
Elsevier BV
Published
2017-06
Volume
27
Issue
6
Pages
554-559
ISSN
0924-977X (ISSN-L)
OpenAlex
W2611710834
Cited by
382
References
50
Citations by year
2026: 29 · 2025: 31 · 2024: 56 · 2023: 32 · 2022: 40 · 2021: 44 · 2020: 59 · 2019: 43 · 2018: 39 · 2017: 9
FWCI
3.63
Type
journal article
Language
en
Open access
Locations
  • European Neuropsychopharmacology (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • Research Portal (King's College London) (publishedVersion, cc-by-nc-nd)
Funders
  • mmunopsychiatry (MR/L014815/1)
  • Medical Research Council (MR/J002739/1)
  • National Institute for Health Research Mental Health Biomedical Research Centre
  • Maudsley NHS Foundation Trust
  • King׳s College London
  • Wellcome Trust Consortium
  • NARSAD
Topics
  • Life Sciences › Neuroscience › Behavioral Neuroscience › Stress Responses and Cortisol
  • Life Sciences › Neuroscience › Biological Psychiatry › Tryptophan and brain disorders
  • Health Sciences › Medicine › Pharmacology › Treatment of Major Depression
Keywords
major depressive disorder, inflammation, glucocorticoid resistance, hypothalamic-pituitary-adrenal axis, hypercortisolism, cortisol, depression pathogenesis, depression treatment
MeSH terms
Anti-Inflammatory Agents, Depression, Glucocorticoids, Humans, Hydrocortisone, Hypothalamo-Hypophyseal System, Inflammation, Metabolism, Inborn Errors, Pituitary-Adrenal System, Receptors, Glucocorticoid, Time Factors, Inflammation Mediators, Biomedical Research

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