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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. Variants of human leukocyte interferon α 2 （IFN-α 2a, α 2b, and α 2c） differ from each other by changes in their coding regions at nucleotide positions 137 and 170. IFN-α 2a is an important cytokine and used for antiviral and anticancer treatment.