CCL13 and major depressive disorder: Contrary to the results obtained for TNF-α, Pearson’s correlation analysis showed that serum MCP-4 levels were significantly and negatively correlated (r = -0.270, p = 0.048) (Fig 2) with Ham-D scores in MDD patients suggesting that higher MCP-4 levels are associated with lower severity of the disease and lower MCP-4 levels are linked to the higher disease severity.