IL-29 (alternative name IFNλ1) plays an important role in the immune response against pathogenes and especially against viruses by mechanisms similar to type I interferons, but targeting primarily cells of epithelial origin and hepatocytes.

[5] IL-29 is, with the rest of IFN-λ, structurally related to the IL-10 family, but its primary amino acid sequence (and also function) is more similar to type I interferons.

[8] IL-29 expression is dominant in virus-infected epithelial cells of the respiratory, gastrointestinal and urogenital tracts, also in other mucosal tissues and skin.

Hepatocytes infected by HCV or HBV viruses stimulate the immune response by producing IL-29 (IFN-λ in general) rather than type I interferons.

[5][6] Abnormal expression of IL-29 could be involved in the pathogenesis of the autoimmune diseases by enhancing the production of inflammatory cytokines, chemokines, and other autoimmune‐related components.