Epigenetics and immunology: Under-recognized aspects of suicidality

Table 1 Overview of recently published studies examining cytokines in various disease states involving or associated with suicidality

Studied biomarker	Tissue	Subjects	Number	Method	Main findings	Ref.
IL-1β, IL-2, IL-6, IL-8, IL-10, IFN-γ, TNF-α, CRP, CXCL-1, CCL2	Blood	MDD patients and healthy controls	n = 260	ELISA	Association between suicide risk and increased levels of IL-6, CRP, TNF-α, CXCL-2, and IFN-γ. Association between suicide risk and decreased levels of IL-2 and IL-8	Yang et al[84], 2024
CRP, TNF-α, IL-2, IL-6	Blood	MDD patients with severe or mild suicidal symptoms, healthy controls	n = 179	ELISA	Association between severe suicidal symptoms and increased levels of CRP and TNF-α	Chen et al[90], 2024
IL-1β, IL-2, IL-6, IL-8, IL-10, TNF-α	Blood	First-episode drug-naïve MDD patients: With suicidal ideation and without suicidal ideation	n = 88	Luminex	Association between suicidal ideation and increased levels of IL-2	Tian et al[87], 2024
IL-1β, IL-2, IL-4, IL-6, IL-10, IFN-γ, TNF-α	Blood	Schizophrenia spectrum disorder patients: Suicidality low risk and suicidality low risk	n = 141	Luminex	Association between suicidality and decreased levels of IL-2 and IL-10	Hoprekstad et al[85], 2024
TNF-α, IL-1β, IL-6	Blood	BD patients with or without suicide attempt, healthy controls	n = 64	Luminex	Association between suicidal behavior and increased levels of IL-6	Jiang et al[91], 2022
IL-1β, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12p70, IL-13, IFN-γ, TNF-α	Blood	Mood and anxiety disorders patients	n = 66	V-PLEX	Association between suicidal risk and increased levels of IL-6. Association between suicidal risk and decreased levels of IL-8	Keaton et al[92], 2019
IL-1β, IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, IL-12P70, IL-17 A, IL-17 F, IL-22, TNF-α, TNF-β, IFN-γ	Blood	Depression disorder patients with or without suicidal behavior	n = 82	Flow cytometry	Association between suicidal ideation and increased levels of TNF-α	Liu et al[89], 2024
40 chemokines (Bio-Plex Pro™ Human Chemokine 40-Plex Panel)	Brain (dorsolateral prefrontal cortex)	Suicide completers and control	n = 39	Bio-Plex	Association between completed suicide and decreased levels of CCL1, CCL8, CCL13, CCL15, CCL17, CCL19, CCL20, CXCL11, and IL-10. Association between completed suicide and increased levels of IL-16	Shinko et al[86], 2020
IL-1β, IL-2, IL-4, IL-6, IL-8, IL-10, IL-13, TNF-α VEGF	Blood, CSF	Suicide death subjects and non-suicidal death subjects	n = 65	Luminex	Association between suicide and increased levels of plasma IL-6 and IL-10. Association between suicide and decreased levels of CSF VEGF	Kaushik et al[88], 2025
IL-1β, IL-6, IL-8, TNF-α	CSF	Suicide attempters and healthy control subjects	n = 110	ELISA	Association between suicide attempt/Level of suicide violence method and increased levels of IL-6	Lindqvist et al[93], 2009

BD: Bipolar disorder; CCL: Chemokine C-C motif ligand; CRP: C-reactive protein; CSF: Cerebrospinal fluid; CXCL: Chemokine (C-X-C motif) ligand; ELISA: Enzyme-linked immunosorbent assay; IFN: Interferon gamma; IL: Interleukin; MDD: Major depressive disorder; TNF: Tumor necrosis factor; VEGF: Vascular endothelial growth factor.