IFITM3 and infection: Next, we showed that MARCH8 mRNA expression in 293T cells (Fig. 4A) was reduced between 2 and 24 h after (i) exposure to type I interferon (IFN) or (ii) infection with IAV, whereas IFN-regulated gene IFITM3 was strongly upregulated by both type I IFN and by IAV infection; it should be noted that previous studies reported rapid (0.5 h) induction of MARCH8 by type I IFNs in 293T cells, which returned to baseline levels within 2 to 4 h (8).