Cytokine that may trigger an antiviral response activating the JAK-STAT pathway and up-regulating specifically some interferon-stimulated genes. Additional isoforms seem to exist. However, they may be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay. Up-regulated by polyinosinic:polycytidylic acid (polyI:C) which mimics the double-stranded hepatitis C virus. A one-base insertion, introducing a frameshift at position 22, results in inactivation of the gene in a majority of the population. That polymorphism is a good marker for predicting spontaneous hepatitis C virus (HCV) clearance and the response to treatment of chronic hepatitis C. The allele producing a functional protein able to induce an antiviral response and to prevent HCV replication in cell cultures, is less frequent in human populations and is associated with impaired spontaneous clearance of HCV. Active form which is able to induce an antiviral response and prevent hepatitis C virus (HCV) replication in cell cultures. Inactive form. Inactive form unable to elicit an antiviral response. Inactive form unable to elicit an antiviral response. Belongs to the lambda interferon family. The reference genome assembly, GRCh37, describes the non-functional copy of that gene, frameshifted at position 22, that is more frequent in human populations.