By reducing the expression levels of vascular cell adhesion molecule (VCAM), macrophage chemoattractant protein 1 (MCP-1), IL-6, IL-8, and TNF-α in the ileum and colon of mice, the oral administration of Prevotella histicola ameliorated estrogen-deficiency-induced depression in an ovariectomy mouse model [109]. Here, IL6 is linked to major depressive disorder.