TNF and infection: Studies have demonstrated that infection of immortalized human corneal epithelial cell lines with live Staphylococcus aureus or the cell wall components lipoteichoic acid (LTA) or peptidoglycan (PGN) resulted in elevated expression of IL-6, IL-8, and TNF-α mRNA and activation of the NF-κB and MAPK signaling pathways to initiate the innate immune response [34].