Interferons (IFN) are a family of cytokines with potent antiviral, anti-proliferative and immunomodulatory properties, classified based on their binding specificity to cell surface receptors. Human IFNA2 was originally cloned in the early ‘80s and now more than a dozen closely related IFN alpha subtypes have been identified in both the human and mouse genome, each sharing about 80% amino acid (aa) sequence homology . Structurally, type I IFNs belong to the class of five helical bundle cytokines, with the IFNA subtypes containing 2 conserved disulfide bonds . There is not a mouse homolog for IFNA21, but mature human IFNA21 is identical to chimpanzee IFNA21. The type I IFNs bind to the interferon alpha receptor (IFNAR), which consists of two subunits: IFNAR1 (alpha -subunit) and IFNAR2 (beta -subunit) . Individual IFNA subtypes are known to display unique efficacies to viral protection, with IFNA21 displaying intermediate activity inducing interferon stimulating genes. Further, human IFNA21 has shown weak anti-viral activity against viruses such as metapneumovirus .