Interferon-alpha (IFN-alpha), also known as leukocyte interferon, represents a group of related but distinct proteins that share over 95% amino acid sequence homology. They are mainly involved in innate immune response against viral infection. The IFN-α family has 13 subtypes and 23 different variants. The individual proteins have molecular masses between 19-26 kDa and consist of proteins with lengths of 156-166 and 172 amino acids. All IFN-α subtypes possess a common conserved sequence region between amino acid positions 115-151 while the amino-terminal ends are variable. Interferon-alpha 4 (IFNA4) belongs to the alpha interferon family. IFNA4 is a secreted protein and produced by macrophages. Two variants of IFNA4 (IFNA4a and IFNA4b) are known, which differ from each other by changes in their coding regions at nucleotide positions 220 and 410.