Although the understanding of the exact pathophysiology and pathways of initiation and development of MDD is still evolving, there is strong evidence that neuroinflammation contributes to the development of depressive symptoms [4, 25, 36, 41], as indicated by the significant positive correlation between levels of MIP-1β and MCP-2 and the severity of depressive symptoms. This evidence concerns the gene CCL4 and major depressive disorder.