ISG15 and viral infectious disease: Furthermore, the production of Ifnb, Isg15, and Ccl5 was increased in Arrb2−/− mouse embryonic fibroblasts (MEFs) transfected with K171R mutant compared with WT β-arrestin 2, whereas K171Q mutant abolished the positive regulation during virus infection (Fig. 5c and Supplementary Fig. 3b, c).