TNF and major depressive disorder: Several studies report marked hypersecretion of pro-inflammatory (Th1) cytokines, including IL-1β, IL-6 and TNF-α, among adults with depression.32, 33 However, these studies of adults,32, 33 many of which are cross-sectional, are limited in their ability to discern the role of cytokines in the ontogenesis of depression, given that the relation between immune markers and depression in adults is likely bidirectional.34 In contrast, our study linked prenatal maternal immune activity with the offspring’s risk of depression in adulthood.