TNF and infection: For example, comparison of the lethal (P. yoelii XL) and non-lethal (P. yoelii XNL) strains of P. yoelii revealed that early production of TGF-β (within 24 h) in lethal infection is associated with delayed IFN-γ and TNF-α production, leading to uncontrolled parasite growth and 100% fatality [113].