Cytokine with immunomodulatory activity. Up-regulates MHC class I antigen expression. Displays potent antiviral activity. Also displays antitumor activity. Ligand for the heterodimeric class II cytokine receptor composed of IL10RB and IL28RA. The ligand/receptor complex seems to signal through the Jak-STAT pathway. Belongs to the IL-28/IL-29 family. Note: This description may include information from UniProtKB.