Although CXCL8 has not been proposed as a biomarker of MDD in previous gene expression studies, abnormalities in protein levels of pro-inflammatory cytokines, including IL-8, have been reported in MDD56–59, and alterations in the expression of genes related to cytokines other than IL-8 have also been observed in previous studies, e.g., alteration of CCL24 gene expression in peripheral blood from MDD patients was identified using targeted gene expression analysis60. The gene discussed is CCL24; the disease is major depressive disorder.