Abstract
Emerging evidence indicates an association between altered immune system functioning, inflammatory response activation, and major depression (MD). This study examined the association between major depression in young people and the monocyte-to-lymphocyte (MLR) and neutrophil-to-lymphocyte ratio (NLR). Inflammation markers were estimated from DNA methylation data using an established cell-mixture deconvolution algorithm and examined in a well-characterized, antidepressant free epidemiological sample of young twins (N = 170). No statistically significant differences were observed between young persons with and without Lifetime MD for the MLR and NLR. A post-hoc analysis of time since last major depressive episode (MDE) indicated that more recent MDEs were associated with higher MLR and NLR levels compared to temporally distant MDEs. A second post-hoc analysis using the full sample determined that past year MDEs were associated with elevated MLR and NLR scores compared to persons unaffected by lifetime MD and person experiencing their last MDE over one year ago. Finally, T cell immunity was most consistently associated with recent MDEs, suggesting that levels of this adaptive immune cell were diminished. Young people experiencing a recent MDE demonstrated increased levels of inflammation with T cells exhibiting the most persistent associations with depression outcomes. Etiological and treatment implications of results are discussed.