Research studies were searched on PubMed using the following search strategy: (Escitalopram OR Fluoxetine OR Sertraline OR Paroxetine OR Selective Serotonin Reuptake Inhibitor OR SSRI) AND (C-Reactive Protein OR C Reactive Protein OR CRP OR IL-6 OR Interleukin 6 OR Interleukin-6 OR IL6 OR TNF-alpha OR TNF alpha OR Tumor necrosis factor α OR tumor necrosis factor alpha OR TNF-α OR TNF α) AND (Major Depressive Disorder OR Depression OR Major Depression). This evidence concerns the gene IL6 and major depressive disorder.