TNF and major depressive disorder: Firstly, depression is characterized by a dysregulation of the pro-anti-inflammatory and Th1/Th2 cytokine balance [17] and has been positively associated with high systemic levels of inflammatory mediators (especially IL-4 (Interleukin-4), IL-6 and TNF-a (Tumor Necrosis Factor-a)) [24], which have been also implicated in asthma pathogenesis.