T cell responses in depressed mice induced by chronic unpredictable mild stress

The relationship between depression and adaptive immunity has gradually attracted increasing attentions. However, no consistent conclusions have been drawn about alterations in adaptive immunity in depression.

Eight-week-old weight-matched male C57BL/6 mice were randomly divided into a chronic unpredictable mild stress (CUMS) model group and a control group, with twelve mice in each group. After 8-week CUMS modeling duration and depressive behavioral tests, T cell responses were evaluated at the cell, cytokine, and cell-specific transcription factor levels. Lymphocytes in the spleen were detected by flow cytometry; serum cytokines were assessed by enzyme-linked immunosorbent assays; expression levels of cytokines and cell-specific transcription factors in the hippocampus were determined by quantitative PCR.

CUMS exposure induced depression-like behaviors with decreased sucrose preference and longer immobility time in the tail suspension test and forced swim test. The CUMS group had a lower proportion of CD4⁺T cells than the control group. A decreased number of T helper 17 (Th17) cells in the spleen and down regulated serum interleukin (IL)-17 and hippocampal retinoid-related orphan receptor-γt levels were detected in the CUMS group. Depressed mice in the CUMS group showed increases in serum IL-1β and IL-6 and hippocampal IL-6 and IL-4 levels.

The study was based on a mouse model. Further studies are needed to determine whether the results are applicable to patients with depression.

CUMS exposure can induce depression-like behaviors and decrease Th17 cell counts.