The Effect of Ketamine on the Immune System in Patients with Treatment-Resistant Depression

Abstract

Treatment-resistant depression (TRD) is associated with immune dysregulation. Ketamine, a rapid-acting antidepressant, may exert effects via immunomodulation. The aim was to examine ketamine's impact on immune markers in TRD, including T-cell subsets, cytokines, and in vitro T-cell responses. Eighteen TRD inpatients received 0.5 mg/kg iv ketamine. Blood was sampled at baseline, 4 h, and 24 h to analyze T-cell phenotypes (CD28, CD69, CD25, CD95, HLA-DR) and serum cytokines (IL-6, IL-8, IL-10, TNF-α, IL-1β, IL-12p70). In vitro, PBMCs from TRD patients and controls were exposed to low (185 ng/mL) and high (300 ng/mL) ketamine doses. Ketamine induced a transient increase in total T cells and CD4⁺CD25⁺ and CD4⁺CD28⁺ subsets at 4 h, followed by a reduction in CD4⁺ and an increase in CD8⁺ T cells at 24 h, decreasing the CD4⁺/CD8⁺ ratio. Activation markers (CD4⁺CD69⁺, CD4⁺HLA-DR⁺, CD8⁺CD25⁺, CD8⁺HLA-DR⁺) declined at 24 h. Serum IL-10 increased, IL-6 decreased, and IL-8 levels-initially elevated-showed a sustained reduction. In vitro, high-dose ketamine enhanced the proliferation of TRD CD4⁺ T cells and dose-dependent IL-8 and IL-6 secretion from activated cells. Ketamine induces rapid, transient immune changes in TRD, including reduced T-cell activation and cytokine modulation. A sustained IL-8 decrease suggests anti-inflammatory effects and potential as a treatment-response biomarker.

Keywords: IL-8; T cells; cytokines; inflammation; ketamine; treatment-resistant depression.

Figure 1

Comparison of percentage of CD3⁺ cells (A), CD3⁺CD4⁺ cells (B), CD3⁺CD8⁺ cells (C), CD4⁺/CD8⁺ ratio (D), CD3⁺CD4⁺CD28⁺ cells (E), CD3⁺CD4⁺CD25⁺ cells (F), CD3⁺CD4⁺CD69⁺ cells (G), CD3⁺CD4⁺CD95⁺ cells (H) CD3⁺CD4⁺HLA-DR cells (I), CD3⁺CD8⁺CD28⁺ cells (J), CD3⁺CD8⁺CD69⁺ cells (K), CD3⁺CD8⁺CD69⁺ cells (L), CD3⁺CD8⁺CD95⁺ cells (M), and CD3⁺CD8⁺HLA-DR⁺ cells (N) in TRD patients before 0 h, 4 h and 24 h after iv ketamine administration. The column bar graphs show the median value with confidence interval (CI). Wilcoxon test; * p < 0.05, ** p < 0.01.

Figure 2

Comparison of serum concentration of IL-10 (A), IL-6 (B), and IL-8 (C) in TRD patients before 0 h, 4 h and 24 h after iv ketamine administration. The column bar graphs show the median value with CI. Wilcoxon test; * p < 0.05, ** p < 0.01, *** p < 0.001.

Figure 3

Serum IL-8 concentration during ketamine treatment in 9 TRD patients. Each colored line represents one of the patients.

Figure 4

Heat map illustrating Spearman’s rank-order correlation (r) between episode length, MADRS scores at baseline and study endpoint, and IL-8 concentrations at various time points following ketamine administration. The color gradient reflects the strength and direction of correlations, with warm colors indicating positive correlations and cool colors representing negative correlations. The given r values are significant.

Figure 5

Comparison of the percentage of proliferating CD4⁺CD25⁺ cells (A), CD4⁺CD69⁺ cells (B), CD4⁺CD95⁺ cells (C), CD4⁺HLA-DR⁺ cells (D), as well as CD8⁺CD25⁺ cells (E), CD8⁺CD69⁺ cells (F), CD8⁺CD95⁺ cells (G), and CD8⁺HLA-DR⁺ cells (H). Cells of healthy individuals (HC) and TRD patients were stimulated with anti-CD3 (S) in the presence of 185 ng/mL (low doses—LD) or 350 ng/mL (HD—high dose) ketamine or without it (0) for 72 h. Non-stimulated (NS) cells were also incubated with different doses of ketamine. The column bar graphs show the median value with CI.

Figure 5

Comparison of the percentage of proliferating CD4⁺CD25⁺ cells (A), CD4⁺CD69⁺ cells (B), CD4⁺CD95⁺ cells (C), CD4⁺HLA-DR⁺ cells (D), as well as CD8⁺CD25⁺ cells (E), CD8⁺CD69⁺ cells (F), CD8⁺CD95⁺ cells (G), and CD8⁺HLA-DR⁺ cells (H). Cells of healthy individuals (HC) and TRD patients were stimulated with anti-CD3 (S) in the presence of 185 ng/mL (low doses—LD) or 350 ng/mL (HD—high dose) ketamine or without it (0) for 72 h. Non-stimulated (NS) cells were also incubated with different doses of ketamine. The column bar graphs show the median value with CI.

Figure 6

Comparison of the percentage of proliferating CD4⁺ and CD8⁺ cells from healthy controls (A,C) and TRD patients (B,D). TRD—patients, HC—healthy control, NS—non-stimulated, S—stimulated, 0—without ketamine, LD—low dose of ketamine, HD—high dose of ketamine. The column bar graphs show the median value with CI. ANOVA Friedman with Dunn’s multiple comparisons test, * p < 0.05.

Figure 7

Supernatant concentrations of IL-8 (A) and IL-6 (B) after incubation with ketamine. TRD-patients, HC—healthy control, NS—non-stimulated, S—stimulated, 0—without ketamine, LD—low dose of ketamine, HD—high dose of ketamine. The column bar graphs show the median value with CI. ANOVA Friedman with Dunn’s multiple comparisons test, * p < 0.05.

Figure 8

Timeline of the study procedure showing time points of intravenous ketamine administration, blood sample collection, and MADRS assessments.

Figure 9

Analysis of lymphocytes ex vivo. Lymphocytes were selected based on forward and side scatter characteristics (A); only single cells were included in the analysis (B). T cells were identified based on their positivity for the CD3 antigen (C). Helper T cells were identified based on the expression of CD4 antigen, and finally, activation antigens, e.g., CD25 antigen, were identified (D). The figures are presented as density plots that show cell distribution with areas of high cell concentration appearing as denser, red colored.

Figure 10

Analysis of phenotype and proliferation of lymphocytes in vitro. Non-stimulated (A,B) and stimulated (C,D) lymphocytes were identified based on the expression of CD4 antigen. Expression of activation antigens, e.g., CD25, was analyzed (A,C). VPD450 dye was used to analyze proliferating cells (B,D), which are marked with arrows (D). The figures are presented as density plots that show cell distribution with areas of high cell concentration appearing as denser, red colored.