ISG15 small interfering RNA (siRNA) knockdown in human cells has also suggested an antiviral role for free and/or conjugated ISG15 during infection with numerous viruses, including IAV23, human immunodeficiency virus24, 25, 26, Ebola virus21, 27, human papilloma virus28, VSV27, Japanese encephalitis virus15 and Sendai virus (SeV)29. Here, ISG15 is linked to infection.