TNF and keratitis: For corneal injury because of infectious keratitis, the corneal epithelium initially heals by 3 sequential processes: migration, mitosis, and differentiation.18 If something goes awry in these healing processes, injured epithelial cells secrete specific growth factors or cytokines, such as tumor necrosis factor-α (TNF-α) and transforming growth factor-β1 (TGF- β1), depending on the degree of damage.18–20 These substances can affect adjacent epithelial or stromal cells.