IFITM1 and infection: However, IFITMs can also enhance viral infection of cells: (i) both IFITM1 and IFITM3 modestly enhance human papillomavirus 16 (HPV-16) infection of a variety of cells;13 (ii) Zhao et al. have shown type I IFN-α, IFN-γ, and type II IFN-λ to significantly promote infection of human coronavirus, HCoV-OC43 by the induction of IFITM proteins.