CRP and major depressive disorder: Previous studies report a bidirectional association between depression and autoimmune disease.25 Several immune biomarkers are increased in patients with depression compared with controls, including monocytes,26,27,28,29,30,31 neutrophil-lymphocyte ratio,14,32,33 and C-reactive protein.14,31,34,35 However, most immune biomarker studies of depression are limited in sample size and scope and are often unable to control for potential confounders or determine the pathway between depression and biomarkers.