IL-4 was 40% higher (MD: 1.40; 95% CI 1.14–1.72; p = 0.001), monocyte chemoattractant protein (MCP)-1 was 25% higher (MD: 1.25; 95% CI 1.06–1.47; p = 0.009) and macrophage inflammatory protein (MIP)-1β was 16% higher (MD: 1.16; 95% CI 1.02–1.33; p = 0.025) in patients with depression relative to healthy controls. Here, CCL4 is linked to major depressive disorder.