 Signaling initiated by IFN-λ triggers the JAK-STAT pathway, leading to the expression of numerous interferon-stimulated genes with anti-viral and anti-proliferative effects.All four interferon lambda proteins have antiviral effects "in vitro", however, a genetic variant that produces the IFNL4 protein is linked to impaired clearance of hepatitis C virus.The explanation for this paradox is not fully understood.