Lee H, Rhee SJ, Kim J, et al. - As per prior studies, major depressive disorder (MDD) and bipolar disorder (BD) share common pathophysiological pathways; hence, researchers sought to determine if patients with BD differ from those with MDD in terms of plasma levels of protein markers related to common depressive symptoms. They analyzed plasma samples of 71 patients with mood disorders and clinical manifestations. After adjusting for the covariates, they identified negative correlation of five proteins, viz, cholesteryl ester transfer protein (CETP), apolipoprotein D (APOD), mannan-binding lectin serine protease 2 (MASP2), Ig lambda chain V-II region BO (IGLV2-8) and Ig kappa chain V-III region NG9 (IGKV3-20), with the total scores of the Hamilton depression rating scale (HAM-D). Significant negative correlations of CETP and APOD were also identified with the anhedonia/retardation and guilt/agitation scores of the HAM-D. After adjusting for covariates, significant associations of four proteins, namely, Ig kappa chain V-II region TEW (IGKC; IGKV2D-28), Ig lambda variable 5–45 (IGLV5-45), complement factor H (CFH) and attractin (ATRN), was identified with anhedonia/retardation. Overall findings suggest predictive value of proteins that significantly correlated with the symptoms for the remission state of depression and anhedonia/retardation. Complement activation, immune response, and lipid metabolism were identified as significantly enriched pathways as per bioinformatics analysis.