Interferon-_ (IFN-_, also known as IFN-alpha, IFN-a, IFNA and Interferon-alpha) is a type I interferon and exists as 13 subtypes: IFN-_ 1, 2, 4, 5, 6, 7, 8, 10, 13, 14, 16, 17 and 21. They are mainly produced by virus-infected cells after sensing the presence of danger signals such as viral DNA or RNA. The binding of IFN-_ to its receptor initiates an anti-viral response, but also anti-tumor effects have been shown. A key producer of type I interferons is the plasmacytoid dendritic cell.