IFN λ1, 2, and 3 (also known as IL-29, IL-28A and IL-28B respectively) are distantly related to the IL-10 family and the interferons. All three IFN-lambdas use a distinct receptor system composed of an IFN-λR1 subunit (also called CRF2-12) and IL-10R2 subunit (also called CRF2-14). Signaling through this receptor system induces antiviral defenses similar to, but distinct from, that of type I interferons. Recombinant Human IFN-λ1 is a 19.8 kDa protein containing 178 amino acid residues.