TNF and major depressive disorder: Psoriasis and depression were found to be significantly associated with each other. This association's bi-directionality was justified through the similarity of inflammatory markers involved in the pathogenesis of depression and psoriasis. The most common inflammatory markers that are elevated in this association were TNF-α, IL-1, IL-22, IL-17, IL-1β and IL-6, IL-8, raised CRP, and some genetic factors also found in this association.