TNF and psoriasis: Th17 cells—characterized by IL-17A, IL-17F, IL-6, tumor necrosis factor (TNF)-α, IL-21 and granulocyte–macrophage colony stimulating factor production—have been described in many inflammatory conditions, including arthritis, psoriasis, inflammatory bowel disease and eosinophilic airway inflammation as being responsible for inducing other pro-inflammatory cytokines and chemokines, such as IL-8 and IL-6 [12,13].