To date, the extent and variability of cytokine changes in depression are unclear.
The aim of this study was to quantify and test evidence for heterogeneity of immune markers in depression by meta-analysis of variability. Also, to investigate whether only a subset of patients with depression show evidence of inflammation.
Case-control studies reporting peripheral blood immunomarkers levels in patients with depression and healthy controls in the MEDLINE database from inception to August 29, 2018, were selected as the data source.
A total of 107 studies that included measurements from 5,166 patients with depression and 5,083 control subjects were included in the analyses. Levels of CRP, IL-3, IL-6, IL-12, IL-18, sIL-2R, and TNFα were significantly higher in patients with depression. These results were found to be robust to a number of potential confounders. Mean scaled variability, measured as CVR, was significantly lower for CRP, IL-12, and sIL-2R in patients with depression, whereas it was unchanged for IL-3, IL-6, IL-18, and TNF α.
These results suggest that depression is a pro-inflammatory state. Some of the inflammatory markers elevated in depression, including CRP and IL-12, show less variability in patients with depression, suggesting greater homogeneity of the inflammatory phenotype in depression. Some elevated inflammatory markers in depression do not appear to be due to an inflamed subgroup, but rather to a rightward shift in the distribution of immune markers.
Inflammatory markers in depression: A meta-analysis of mean differences and variability in 5,166 patients and 5,083 controls
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