CCL2 and major depressive disorder: Moreover, a previous systematic review and meta-analysis reported that antidepressant treatment significantly reduced peripheral levels of monocyte chemoattractant protein 1, IL-8, TNF-α, IL-1β, and IL-6, which are elevated in depression, and granulocyte macrophage colony-stimulating factor that upgrades the activation and survival of macrophages, dendritic cells, and neutrophils [17].