ISG15 and HIV infectious disease: For example, some of the HIV restriction factors induced by interferons, such as interferon-induced transmembrane protein 1 (IFITM1) and ISG15 ubiquitin-like modifier (ISG15), were induced by HIV infection in all cells; however, bone marrow stromal cell antigen 2 (BST2, also known as tetherin) and IFITM2 were upregulated only in dividing cells, particularly cells that divided many times (Figure 4).