Inflammatory Proteins Predict Change in Depressive Symptoms in Male and Female Adolescents

Inflammation has been implicated in depressive symptoms, but few studies use longitudinal designs with adolescents. Furthermore, the extant literature has yielded inconsistent results. Blood was collected from a community sample of 201 adolescents (109 female, ages 12.3-20.0) and analyzed for inflammatory proteins. Up to five follow-up assessments of depressive symptoms were conducted. Multi-level modeling indicated that high C-reactive protein (CRP) (but no other proinflammatory markers) predicted depressive symptom increases. Three-way interactions between different inflammatory biomarkers, sex, and months-to-follow-up predicted change in depressive symptoms. Higher interleukin-6 predicted increased depressive symptoms at 13-31 months after baseline assessment of depression and inflammation for females. Higher tumor necrosis factor-alpha predicted increased depressive symptoms at < 1 month after baseline for males and 13-31 months after baseline for females. Higher interleukin-8 in males predicted lower depressive symptoms at 31 months after baseline. Exploratory post-hoc analyses examined these predictive associations for specific subsets of depressive symptoms. These findings are the first to support the predictive association of elevated CRP for depressive symptoms in a community adolescent sample and serve as preliminary evidence that the relationship between cytokines and later depressive symptoms differs by sex, time-to-follow-up, and the specific biomarker.