Interferon is a polypeptide hormone.

Interferons (IFNs) bind to specific high-affinity receptors on the cell surface. The human IFN-alpha receptor is a highly hydrophobic membrane protein (molecular weight about 100,000). After binding to the receptor, IFN is internalized and degraded by lysosomal proteases. The receptor is also internalized, does not recycle to the cell surface and is gradually inactivated. An unidentified mechanism transduces a signal from the interferon/receptor complex to induce the transcription of specific genes. There are striking similarities between IFN and polypeptide hormones in their interaction with cell surface receptors, internalization of polypeptide/receptor complexes and degradation of the polypeptides in lysosomes.