To investigate the expression levels of T-cell subsets, regulatory T cells (Tregs), interleukin(IL)-6, IL-10, interferon-γ (INF-γ), and tumor necrosis factor-α (TNF-α) in peripheral blood of patients with depression, in order to explore their roles in the pathogenesis of depressive disorders.

A total of 82 patients who visited the Affiliated Hospital of Health Vocational College of West Anhui University from January 2020 to June 2022 were selected as the case group. 40 healthy volunteers from the hospital's physical examination center were selected as the control group during the same period. According to the Hamilton depression scale (HAMD) scores, the patients in the case group were divided into a severe depression group (23 cases) and a mild-to-moderate depression group (59 cases). Flow cytometry was used to detect the levels of T cells and Tregs in the peripheral blood. Enzyme-linked immunosorbent assay (ELISA) was performed to detect the levels of IL-6, IL-10, INF-γ, and TNF-α in the plasma. Changes and significance in the T-cell subsets, Tregs, and cytokine levels were compared and analyzed.

Compared with the control group, the proportion of CD8⁺ T and Tregs cells in the peripheral blood of patients with newly diagnosed depression was significantly increased, and the CD4⁺ /CD8⁺ ratio was significantly reduced [(23.13±9.24)% vs (26.72±8.12)%, (5.31±1.65)% vs(12.41±2.52)%, (1.71±0.32)vs(1.28±0.51), t=3.22, 5.94, 4.20, all P values<0.05], but there was no statistically significant difference in the proportions of CD3⁺ T and CD4⁺ T cells between groups (P>0.05). The expression levels of IL-6 and INF-γ in the peripheral blood of patients with depression were significantly higher than those in the control group[ (2.89±2.11) pg/mL vs (1.81±1.17) pg/mL, (28.12±11.02) pg/mL vs (13.18±6.41) pg/mL, t=5.10, 7.59, both P values <0.05], there was no statistical significance in the expression of IL-10 and TNF-α between groups (P >0.05). The levels of Tregs and IL-6 in patients with severe depression were significantly higher than those in patients with mild-to-moderate depression [(13.11±2.92)% vs (8.31±2.05)%, (3.21±2.37) pg/mL vs (2.59±1.91) pg/mL, t=7.43, 5.93, both P values <0.05], while no differences have been found in the levels of CD8⁺ T and INF-γ between groups (P>0.05). Compared with before treatment, the proportion of CD8⁺ T and Tregs cells, and the levels of IL-6 and INF-γ in patients with depression decreased significantly after treatment[(26.72±8.12)% vs (22.18±8.14)%, (12.41±2.52)% vs (8.11±1.95)%, (2.89±2.11) pg/mL vs (2.21±1.87) pg/mL, ( 28.12±11.02 ) pg/mL vs (17.21±9.46) pg/mL, t=21.04, 51.33, 35.38, 7.11, all P values<0.05].

CD8⁺ T cells, Tregs and IL-6 are involved in the development of immune tolerance abnormalities in patients with depression. The occurrence of depression is closely associated with abnormal changes in the immune system.

Depression; T cell subsets; Regulatory T cells; Cytokines