IFN-α is a cytokine that has an immunomodulatory function. It plays an important role not only in antiviral activity but also in several physiologic functions, such as activation of dendritic cells and accelerated expression of major histocompatibility complex I and II molecules that may cause increased antigen presentation. Many IFN-alpha subtypes differ in their sequences at only one or two positions. Among the 13 subtypes of human IFN-alpha, IFN-alpha1 subtype has 2 variants, named IFN-α 1a and IFN-α 1b, that differ from each other in only 1 amino acid, at residue 114. This cytokine, like other type I interferons, binds a plasma membrane receptor made of IFNAR1 and IFNAR2 that is ubiquitously expressed, and thus is able to act on virtually all body cells. IFN-α is upregulated in preeclamptic placentas and is thought to be a mediator of preeclampsia.