IFITM3 and infection: Restriction of the typically nonrestricted MLV-LP and drastically aberrant morphology with a “foamy” appearance (Fig. S1C) suggest that recombinantly overexpressed IFITMs in HUVEC, which naturally already express IFITM2 and IFITM3 at high levels, may lead to visibly distorted cellular membranes and vesicles and nonspecific effects on infection.