Interferon stimulates the production of two enzymes: a protein kinase and an oligoadenylate synthetase. They allow for communication between cells to trigger the protective defenses of the immune system that eradicate pathogens or tumors. They are typically divided among three IFN classes: Type I, Type II and Type III. 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 .