The IFN-lambda gene family is composed of three distinct genes: IFN-lambda1 (IL29), IFN-lambda2 (IL28A), and IFN-lambda3 (IL28B). IFN-lambda proteins exhibit only weak homology to IL10, but like IL10, they also use the IL10R2 chain as a component of their receptor complex. The IFN-receptor complex consists of the unique ligand-binding chain IFN- R. The IFN-lambda-1 gene is found exclusively in primate genomes and is 81% identical to IFN-lambda-2/3. IFN-lambda-s, which are now collectively referred to as type III IFNs, exhibit several features in common with type I IFNs, such as antiviral, antiproliferative, and antitumor activities. Recombinant Human IL29 is expressed in human 293 cells as a glycoprotein with a molecular mass of 29 and 35 kDa.