ORIGINAL RESEARCH article
Front. Cell. Neurosci.
Sec. Non-Neuronal Cells
This article is part of the Research TopicThe roles of peripheral immune cells and their circulatory effector molecules in neuropsychiatric disorders: volume IIView all articles
Flow-cytometric analysis of immune cell populations in patients with depression: relationship with depression severity and electroconvulsive therapy therapeutic outcomes
Provisionally accepted
Karen M Ryan1
Aoife O'Rourke1Christopher Sheridan1Marina Balcells Quintana1Barry Moran1
Jean M Fletcher1
Declan M. McLoughlin1*
Andrew Harkin1,2*- 1The University of Dublin Trinity College, Dublin, Ireland
- 2School of Pharmacy and Pharmaceutical Sciences & Trinity College Institute of Neuroscience, Trinity College Dublin, Dublin, Ireland
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Immunological changes are implicated in the pathophysiology of depression. We aimed to assess phenotype and frequency of immune cell subtypes, including an assessment of regulatory T cells and production of cytokines by T cell subsets following stimulation, using a flow cytometric analysis, in peripheral blood samples obtained from medicated patients with depression (n = 20) compared to age-and sex-matched healthy controls (n = 21), and in patients with depression after electroconvulsive therapy (ECT) in a real-world clinical setting. Depression severity was assessed using the Hamilton Depression Rating Scale (HAM-D24). A reduction in the frequencies of CD19+ B cells and IL-17+ CD8 T cells was evident in depressed patients compared to healthy controls. For a subgroup of depressed patients assessed pre-versus post-ECT, there was no change in phenotype, frequency or function of immune cell subtypes within 72 hours of completing treatment. Further exploratory analyses found that baseline CD16-CD14+ classical monocyte frequency correlated with change in HAM-D24 score post-ECT, indicating that a higher frequency of classical monocytes at baseline is associated with greater symptom improvement after treatment. A reduced number of CCR7-CD45RO+ effector memory T cells was also found to be associated with an improvement in symptoms post-ECT. Overall, the results indicate the utility of flow cytometry in immune-profiling where classical monocytes and effector memory T cells associate with treatment response in unipolar depressed patients.
Keywords: Depression, Electroconvulsive Therapy, immune, cytokine, Flow Cytometry
Received: 27 Aug 2025; Accepted: 24 Oct 2025.
Copyright: © 2025 Ryan, O'Rourke, Sheridan, Balcells Quintana, Moran, Fletcher, McLoughlin and Harkin. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence:
Declan M. McLoughlin, d.mcloughlin@tcd.ie
Andrew Harkin, aharkin@tcd.ie
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