Several lines of evidence show immune dysfunction in the pathogenesis of depression. Approximately one-quarter of depressed patients show evidence of low-grade inflammation.
Although many isolated studies have been conducted previously in this area of research, a new study by researchers at the University of Bristol‘s MRC Integrative Epidemiology Unit is the first large-scale investigation. It reviews and statistically combines data from all studies that have reported immune cell counts, as measured by flow cytometry in adults with and without a diagnosis of depression.
The findings suggest that changes to different components of our immune system — both the innate and adaptive immune response — could play a role in causing depression.
Scientists searched PubMed and PsycINFO databases and conducted a systematic review and meta-analysis of identified studies comparing absolute count and/or relative percentage of flow cytometry-derived WBC subsets between depression cases and controls. Each study was quality-checked, and only high-quality studies were included.
Their analyses of 2,277 individuals revealed that counts of eight different types of immune cells, e.g., B cells and T cells, were increased in depression compared to counts seen in the healthy comparison group without depression.
Éimear Foley, a Ph.D. student and the study’s lead author at Bristol’s MRC Integrative Epidemiology Unit, said: “The question now is whether these changes in immune cells are a cause or consequence of depression, and we hope to examine this in future studies. It is also important to note that we are not suggesting that anyone with increases in these immune cell types will develop a depressive disorder.”
“Rather we are highlighting the differences that may exist between patients with depression and healthy individuals that were included in our sample in their counts of particular immune cell types.
“Current treatments for depression do not work for all patients, and immunotherapy could be useful for a subgroup. We aim to use these findings to guide better our selection of patients for future immunotherapy trials for depression with the hope of working towards more effective, personalized care in mental health.”
- Foley, É.M., Parkinson, J.T., Mitchell, R.E. et al. Peripheral blood cellular immunophenotype in depression: a systematic review and meta-analysis. Mol Psychiatry 28, 1004–1019 (2023). DOI: 10.1038/s41380-022-01919-7